Transcript Figure 1.1 - University of Toronto

Energy and the New Reality, Volume 1:
Energy Efficiency and the
Demand for Energy Services
Chapter 4: Energy Use in Buildings
L. D. Danny Harvey
[email protected]
Publisher: Earthscan, UK
Homepage: www.earthscan.co.uk/?tabid=101807
This material is intended for use in lectures, presentations and as
handouts to students, and is provided in Powerpoint format so as to allow
customization for the individual needs of course instructors. Permission
of the author and publisher is required for any other usage. Please see
www.earthscan.co.uk for contact details.
Overview
• Kinds of buildings, breakdown of energy use in
different kinds of buildings in different climates
• Role of building shape, orientation, size and
clustering (multi-unit vs single unit, multi-story vs
single story, self shading)
• Building thermal envelope (insulation, windows,
doors and air tightness)
• Heating
• Cooling
• HVAC systems
Overview (continued)
• Hot Water
• Lighting
• Appliances, consumer electronics, office
equipment
• Embodied energy
• Building design process
• Examples of exemplary new buildings from
around the world
• Examples from around the world of “deep”
retrofits of existing buildings
This Chapter covers all forms of passive solar
energy (for heating, cooling, ventilation, and
daylighting), but does not cover active forms of
solar energy, namely:
• Photovoltaic (PV) systems mounted on
buildings, and building-integrated photovoltaic
(BiPV) systems (covered in Volume 2, Chapter
2)
• Solar thermal collectors for heating, hot water,
and cooling (covered in Volume 2, Chapter 2)
• Seasonal storage of solar thermal energy as
part of district heating and cooling systems
(covered in Volume 2, Chapter 11)
OVERVIEW OF ENERGY USE IN
BUILDINGS
Figure 4.1a Residential Energy Use in the US in 2001
Figure 4.1b Residential Energy Use in the EU-15 in 1998
Cooking
Lighting and
7%
Appliances
11%
Water Heating
25%
Space
Heating
57%
Figure 4.1c Residential Energy Use in China in 2005
Other
5%
Air Conditioning
4%
Appliances
15%
Space Heating
36%
Cooking
6%
Lighting
9%
Water Heating
25%
Figure 4.2a Commercial Building Energy Use
in the US in 2003
Computers
Other
2%
9%
Office Equipment 1%
Refrigeration 6%
Space Heating
35%
Cooking
3%
Lighting
21%
Ventilation
7%
Water Heating
8%
Cooling
8%
Figure 4.2b Commercial Building Energy Use in the
EU-15 in 1998
Other
16%
Cooling
4%
Cooking
5%
Space
heating
52%
Lighting
14%
Water
heating
9%
Figure 4.2c Commercial Building Energy Use in China
in 2005
Cooling
15%
Space Heating
38%
Lighting & Other
29%
Water Heating
18%
Supplemental figure: Average energy intensity of
commercial buildings in different countries in 1990
Energy Intensity (kWh/m2/yr)
600
District Heat
Other Fuels
Oil
Gas
Electric Heating
Cooling (HVAC)
Lighting
Other Electricity
500
400
300
200
100
0
U.S.
Sweden
Japan
France Denmark Canada
Source: Harvey (2006, A Handbook on Low-energy Buildings and District-Energy Systems,
Earthscan, London)
BACKGROUND PHYSICS
Processes of Heat Transfer
• Conduction (transfer of molecular energy)
• Convection (movement of air parcels)
• Exchange of air between inside and
outside
• Radiative energy transfer
Conduction and Convection
• Rate of heat flow (W/m2) is given by
Qc = (Temperature Difference) x U-value
or
Qc = (Temperature Difference)/ Resistance (R-value)
U-value has units of W/m2/K (smaller is better)
R-value is the reciprocal of the U-value (larger is
better)
Warning to North American readers:
• Insulation and window manufacturers in Canada and the
US use non-metric R-values and U-values
• To distinguish between metric and non-metric R-values,
the term “RSI-value” is used in Canada (where the “SI”
means “système international”)
• Both R-values and RSI-values are printed on insulation
packages in Canada
• In Europe, the term RSI is not used, and R-value means
the metric value
• US and Canadian window manufacturers (and sales
agents!) invariably quote U-values without giving the
units, but the non-metric U-values are 5.7 times smaller
than the metric U-values and so would appear to be
incredibly good if one thought that they were metric Uvalues
Computing heat flow through wall
and window systems
• In computing heat flow through multiple layers in an
envelope component (such as the portion of a wall with a
particular amount of insulation), add the resistances of
the layers to get the total resistance, then take the
reciprocal to get the U-value for that component
• The U-value (W/m2/K) times the area of the component
(m2) times DT (K) gives the rate of heat flow (watts)
• Rate of heat flow times time (in seconds) gives the heat
loss (joules)
• To get the average U-value for the various adjacent
components, just compute the area-weighted average of
the individual U-values
Heat flow through walls:
For layers: add resistances
For adjacent components: add U values (with area weighting)
0.5
K2
3.5
K3
K4
1
U3
K5
T out
T in
R 1 =1/h1
R2
R5
R 6 = 1/h 6
U4
U3=k3/D, U4=k4/D, U34=f3U3+f4U4,
where f3 and f4 are cross-sectional area
fractions
R34=1/U34
Rtotal = R1 + R2 + R34 + R5 + R6
U-value = 1/Rtotal
Source of figures: Sherman and Jump (1997, CRC Handbook of Energy Efficiency, CRC Press, Boca Raton)
Heat flow through a double-glazed window
T1 T2
T3 T4
T out
T in
h oc
R2
h c23
R4
h ic
h or
h r23
h o=h oc +h or
h 23=h o23+h r23
h i=h ic+h ir
R 3=1/h 23
R 5=1/h i
R 1=1/h o
h ir
R total=R 1+R 2+R 3+R 4+R 5
U-value=1/R total
Here, hr23 and hc23 are added together because both processes act over
the entire surface area – no need for weighting by an areal fraction
(as in U3 and U4 in the previous slide)
Exchange of air between inside and
outside
• The sensible heat content per unit volume (J/m3)
of a parcel of density ρ, specific heat cpa
(J/kg/K), and temperature T (K) is ρcpaT
• The net rate of heat flow (W) due to a rate of
exchange Q (m3/s) of inside and outside air is
Qe=ρcpaQ (Tindoor-Toutdoor)=ρcpaQDT
Emission of radiant energy
• All matter above absolute zero in temperature
(0 K) emits electromagnetic radiation
• The maximum possible rate of emission of
radiant energy is given by the Stefan-Boltzman
law,
F = σT4, where σ=Stefan Boltzman constant
=5.67 x 10-8 W/m2/K4
• This rate of emission is called blackbody
emission
Notes on temperatures and
temperature differences
• Temperatures on the Celsius scale are “degrees Celsius’
• However, temperature differences are Celsius degrees
or kelvin
• ‘kelvin’ also refers to absolute temperatures on the kelvin
scale, but a difference of 1 on the Celsius scale is the
same as a difference of 1 on the kelvin scale – so a
difference of one Celsius degree is the same as 1 K
• You should write, for example: 26ºC – 22ºC = 4 K
• Thus, the U-value has units of W/m2/K – you are
supposed to know from your physical understanding that
the K refers to temperature differences, not absolute
temperatures
• However, the Stefan-Boltzman constant has units of
W/m2/K4 – here K refers to absolute temperature,
because emission of radiation depends on absolute
temperature
Notes on temperatures and
temperature differences
(continued)
• The proper convention is to write ‘kelvin’ with lower-case
letters (just like for ‘watts’ and ‘joules’) and to use upper
case for the shorthand (oC, K, J, W). The exception is
‘Celsius’, where upper case C is used. Note that it is
incorrect to say or write ‘degrees kelvin’.
• The term ‘centigrade’ has long since been abolished
Figure 4.3 Blackbody Radiation
2000
100
1800
90
80
Solar Radiation (left scale)
Extraterrestrial
Surface (1.5 atm)
1400
70
1200
60
1000
Relative
Sensitivity
of Human
Eye
800
600
Blackbody
Radiation
(right scale):
50
50oC
30
o
20
400
0C
200
40
10
o
-50 C
0
0.1
1.0
10.0
Wavelength (mm)
0
100.0
Intensity (W/m2/mm)
Intensity (MW/m2/mm)
1600
Emission of radiant energy (continued)
• The sun emits radiation almost exclusively at
wavelengths < 4 μm (1 μm=10-6 m)
• Objects at typical Earth-atmosphere temperatures
emit radiation almost exclusively at wavelengths >
4 μm
• Actual total emission (W/m2) is given by the
blackbody emission times the emissivity ε:
E =εσT4
• The absorption of infrared radiation is equal to the
incident infrared flux times the absorptivity, but
because absorptivity=emissivity (Kirchoff’s Law),
absorption equals incident flux times emissivity
Supplying heat to a room
• Heat is supplied to a room if air entering the room (from a
heating vent) is warmer than air leaving the room, or if hot
water entering a radiator is warmer than the water leaving
the radiator
• The rate at which heat is supplied to the room is equal to
the rate at which heat is lost from the ventilation airflow or
from the water circulating through a radiator. This is given
by
QH=ρcpQ (Tsupply-Treturn)=ρcpQDT
where Q is the volumetric rate of flow (m3/s) of air or water
• For a given flow rate and temperature drop, 3333 times
more heat is delivered by circulating warm water through a
radiator than by circulating warm air
Energy Required to Move Air or Water
• Rate at which energy must be imparted (power) to the
moving fluid is:
Pfluid= DP Q, but DP varies with Q2 for turbulent flow, so
Pfluid α Q3
• Electrical power requirement for fixed-speed motors
Pelec= Pfluid/(ηmηp) α Q3/(ηmηp)
• Electrical power requirement for variable-speed motors
Pelec= Pfluid/(ηVSDηmηp)
Based on the cubic law (whereby the power
that must be supplied to a fluid varies with Q3):
• Cutting the flow rate in half would seem to cut
the required power by a factor of 8
• However, the efficiencies of motors and pumps
decrease at lower flows, so the reduction is
more like a factor of 6-7
• This assumes that what the system is trying to
do decreases in proportion to the required power
input to the fluid (Pfluid)
• However, a common procedure is for a pump or
fan system to operate at full power irrespective
of the actual requirements, and to throttle
(restrict) the flow if less flow is actually needed
Figure 4.6 Variation of fan or pump power with flow, using
various methods to reduce the rate of flow
110
Fans
Throttle Valve
Pumps
Inlet Vane
100
90
%Peak Power
80
70
60
Outlet Damper
50
40
30
VSDs
20
Cubic Law
10
0
0
10
20
30
40
50
60
%Peak Flow
70
80
90 100
So, if the required air (or water) flow rate can
be reduced, there are potentially huge fan or
pump energy savings. However,
• for these savings to be achieved, it is necessary that the
fan motor or pump be able to operate at slower speeds
when full-speed operation is not needed
• this in turn requires a variable-speed drive – which
converts the AC electricity to DC electricity and back to
AC electricity but at a slower frequency, entailing some
small energy loss even when the fan operates at full
speed
• many pumps and motors can operate only at full speed,
so throttling is required to reduce the air or water flow.
The ratio of energy used circulating air or water
to heat energy released (to a room) by the
circulating air or water is
R = ∆P/ρcp∆T
For the given ρ and cp of air and water, and for
typical ∆P and ∆T values of air vs hydronic
(water-based) systems, it takes about 25 times
less energy to deliver a given amount of heat by
circulating warm water than by circulating warm
air
In many buildings, heat is provided by
circulating air. This air circulation also
provides fresh air. However,
• if fresh air were all we wanted, the required air flow (and
fan energy use) would be much less
• Since the ratio of fan or pump energy use to heat
delivered is 25 times less when heat is delivered with
water rather than air, it saves energy to separate the
heating and ventilation functions – using water to deliver
heat (or coldness) and much reduced airflow for
ventilation
Note: I am talking here about energy used to deliver heat or
coldness, not in generating it (with a boiler or chiller)
Definitions
• Sensible heat – heat that can be felt as warmth
• Latent heat – heat that is released when water
vapour condenses (or that is absorbed when liquid
water evaporates)
• Absolute vapour pressure (ea) – the partial pressure
of the water vapour in the air
• Saturation vapour pressure (es) – the partial
pressure of water vapour in the air when the air is
saturated (unable to hold any more water vapour)
• Relative humidity – ratio of actual to saturation
vapour pressures (multiplied by 100 to give as a
percent). RH(%) = ea/es x 100%
• Mixing ratio – the ratio of mass of water vapour in an
air parcel to mass of dry air
Saturation vapour pressure increases sharply
with increasing temperature:
Saturation Vapour Pressure (mb)
80
70
60
50
40
30
20
10
0
0
10
20
Temperature (oC)
30
40
The mixing ratio (mass of water vapour over mass
of dry air) is proportional to the ratio of the
pressures of water vapour and dry air,
r = 0.622 ea/(Pa-ea)
(Pa = total atmospheric pressure, Pa-ea is the
pressure of the dry air alone) but it is more
convenient to use graphs with r rather than ea on
the vertical axis, because r is unchanged when an
air parcel cools whereas ea decreases slightly as T
decreases
Supplemental Figure: plot of saturation mixing ratio and mixing
ratio at various relative humidities on a T-mixing ratio graph
100%RH
Humdity Mixing Ratio (gm moisture per kg dry air)
30
60% RH
40%RH
28
26
24
22
20
20%RH
18
16
14
12
10
8
6
4
2
0
0
10
20
30
Temperature (oC)
40
50
The sensible and latent heat contents (J/kg) of a
parcel of air are given by
H=cpaT+rcpwvT
and
L=rLc
respectively, where cpa and cpwv are the specific
heats (J/kg/K) of dry air and water vapour,
respectively, r is the water vapour mixing ratio (in
terms of kg/kg, so that its dimensions cancel out),
and Le is the latent heat of condensation (J/kg). The
latent plus sensible heat is called the enthalpy.
More definitions:
• Drybulb temperature – the temperature of the air
(measured with a dry thermometer)
• Wetbulb temperature – the temperature that the
air acquires when liquid water is allowed to
evaporate into the air until the air is saturated
and the remaining liquid and air have adjusted
(equilibrated) to have the same temperature (it is
the same as the temperature measured with a
wet thermometer with air flowing past it)
• Dewpoint temperature – the temperature at
which condensation begins when an air parcel is
cooled with fixed water vapour mixing ratio
Figure 4.7 Psychrometric chart
100%RH
60%RH
40%RH
28
26
24
Wetbulb
Temperature
Dewpoint
Temperature
Lines of
constant
enthalpy
•
22
•
20
18
••
16
Drybulb (actual)
temperature
20%RH
14
12
10
8
6
4
2
0
0
5
10
15
20
25
30
Dry Bulb Temperature (oC)
35
40
45
50
Humdity Mixing Ratio (gm moisture per kg dry air)
30
Conventional dehumidification process
100%RH
60%RH
40%RH
28
26
24
22
20
18
Cooling to the dewpoint temperature
•
Condensation
from over
cooling
16
20%RH
14
12
10
8
Reheating
6
4
2
0
0
5
10
15
20
25
30
Dry Bulb Temperature (oC)
35
40
45
50
Humdity Mixing Ratio (gm moisture per kg dry air)
30
Adaptive Thermal Comfort
• The temperature that appears to be comfortable
depends on how hot or cold it is outside (which
conditions our expectations)
• Thus, the temperature down to which a building
is air conditioned can be increased on hotter
days
Figure 4.8 Proposed Range of Thermostat Temperature
Settings – varying with the outdoor temperature
41
50
59
68
77
86
95
o
( F)
30
85
28
82
26
79
24
75
22
72
90% acceptability limits
20
68
18
64
80% acceptability limits
16
61
14
0
5
10
15
20
25
30
Mean Monthly Outdoor Air Temperature ( oC)
Source: Brager and de Dear (2000, ASHRAE Journal 42, 10, 21–28)
35
40
Indoor Comfort Temperature ( o F)
o
Indoor Comfort Temperature ( C)
32
REDUCING HEATING ENERGY USE
• Reduce the heat load (the amount of heat
that needs to be provided)
• Provide the required heat as efficiently as
possible
Thermal Envelope
•
•
•
•
•
Insulation
Windows and doors
Curtainwalls in commercial buildings
Air leakage
Double skin façades
As noted above,
• Heat flow across a window or wall varies with
ΔT/R
• R (or RSI) in turn varies with the thickness D of
the insulation: R = D/k, where k is the thermal
conductivity (W/m/K) of the insulation
• The total R (or RSI) value of a wall is just the
sum of the R’s of each layer
• Uoverall=1/Rtotal (has units W/m2/K)
Figure 4.9 Wall and Ceiling Heat Loss
1.0
Walls at R12
(RSI 2.1, U=0.47 W/m2/K)
0.9
Relative Heat Loss
0.8
0.7
Walls at R20
(RSI 3.52,U=0.28 W/m2/K)
0.6
Roof at R32 (RSI 5.6,
U=0.18 W/m2/K)
0.5
0.4
0.3
0.2
Walls (R40, RSI 7.0)
Advanced House: Roof (R60, RSI 10.6)
0.1
0.0
0
10
20
30
40
50
60
R-Value
0
2
4
6
RSI-Value
8
10
The heating requirement is the residual (or
difference) between heat loss, useful passive heat
gain, and useful internal heat gain – so a given
percentage reduction in heat loss has a
disproportionately larger effect in reducing the
heating requirement
Greater sensitivity of heating requirement than of
heat loss to changes in the amount of insulation
120
100 units
heat loss
100
80 units
heating
requirement
80
50 units
heat loss
60
40
20
0
Source: Danny Harvey
Internal Heat Gain
Passive Heat
Gain
30 units
heating
requirement
Types of insulation
•
•
•
•
•
•
Glass fibre (fibreglass) batts
Mineral fibre batts (roxul)
Cellulose – blown in or spray-on
Foam – solid panels or spray-on
Wood fibre (e.g., hemp)
Vacuum insulation panels
Issues with regard to insulation
•
•
•
•
Thickness
Cost
Thermal bridges, gaps
Embodied energy (the energy required to make
it – not negligible for all except cellulose and
wood-fibre insulation)
• Leakage of halocarbon blowing agents for foam
insulation (HFCs vs CO2, H2O, or pentane as
blowing agents)
• Degradation over time (for HFC-blown foam
insulation)
Figure 4.10 Engineered Wood –
reduces thermal bridges, has strength equal to a rectangular
joist with the same outside dimensions
Source: The Engineered Wood Association (www.apawood.com)
Vacuum insulation panels
• Thermal conductivity is ~ 1/10 that of plastic foam,
fibreglass, or cellulose insulation (all of which have a
similar thermal conductivity)
• Thus, a 1-cm thick panel gives the same resistance to
heat flow as 10 cm of regular insulation
• Ideal where space is tight
• Large market in Switzerland for insulating roof-top
decks without requiring a step between the inside and
outside
• Also used in doors and super-low energy refrigerators
and freezers
• Also about 10x the cost of regular insulation
Figure 4.11: Niche application of vacuum-insulation
panels in Europe
Normal insulation
thickness
Interior
wallboard
Vacuum
insulation
panel
Triple-glazed
window
Solid foam
insulation
Cavity for
retracted
external
blind
Retracted
external
blind
Grundschule am Reidburg, Frankfurt (illustrating
external blinds, not necessarily with VIP)
Source: Danny Harvey
Figure 4.12 Prefabricated VIP Wall
Source: Binz and Steinke (2005, 7th International Vacuum Insulation Symposium, EMPA, Duebendorf,
Switzerland, www.empa/ch/VIP-Symposium)
VIPs in prefabricated roof units
Reducing the heat loss through
windows
•
•
•
•
•
•
Extra glazing (glass) layers
Low-emissivity (low-e) coatings
Inert gas between glazings (Ar, Kr, Xe)
Vacuum between glazing layers
Highly insulating frame
Airtight
Benchmark
• A single-glazed, non-coated window has a Uvalue of about 5 W/m2/K – so the rate of heat
loss is 200 W/m2 when the outdoor temperature
is -20ºC and the indoor temperature is +20ºC
• The best commercially-available highperformance window will have a centre-ofglazing U-value of 0.5 W/m2/K – so the heat loss
will be a factor of 10 smaller!
• Windows with 2-3 times lower U-value are under
development
The normal practice in building design is to place the
heaters or warm-air vents below the window. This is
because normally there is large heat loss from the
window, so heating at the base of the window
• Keeps the window warm, thereby avoiding
radiant asymmetry
• Prevents drafts
• Prevents condensation on the window
With high performance windows, the heat loss is
so low that the heaters can be placed on the side
of the room near the core of the building, thereby
reducing costs (and reducing heat loss even
further) by allowing for shorter heating ducts or hotwater pipes
Figure 4.13 Required window U-value at which
perimeter heating can be eliminated as a function
of the coldest designed-for temperature
2
Window U-value (W/m /K)
4
3
Perimeter Heating
Needed
2
Perimeter Heating
Not Needed
1
0
-30
-20
-10
0
Design Temperature (oC)
10
Window Frames and
Window Installation
• Window frames (which can be 10-20% of the total
window area) can be a weak point – with U-values of 1.5
W/m2/K in windows with glazing U-values as low as 0.5
U/m2/K
• The best frames are insulated fibreglass frames, with Uvalues of ~ 0.5 W/m2/K (now available in Canada)
• One approach is to wrap the insulation partly over the
frame
• The way that the window is installed (how it is aligned
relative to the wall insulation, and whether or not gaps
outside the frame are caulked) can have a big effect on
overall performance
Common but
poor choice
Good choice
– window aligned
with and centred
over the insulation
Penetration of solar energy through a window
• Direct transmission of solar radiation
• Partial absorption of solar radiation by the glazing layers,
warming up the layer and
- causing re-emission (by the inner glazing surface,
toward the inside) of some of the absorbed solar
radiation as infrared radiation
- reducing the conduction heat flow from the room to the
glazing surface, by reducing the temperature difference
the room air temperature and the window glazing
temperature (in fact, if the window glazing becomes
warmer than the inside air, heat will flow into the room)
Solar heat gain coefficient (SHGC)
or g-value (in Europe)
• accounts for both the direct effect (reduced
transmission) and indirect effect (re-emission of IR
radiation into the room and reduced conductive heat
loss) of extra glazing layers or added coatings
• For uncoated double-glazed windows, SHGC = 0.7
and U-value = 2.5 W/m2/K
• Windows can be engineered to have
-a SHGC of 0.23 with a U-value of 0.4 W/m2/K, or
-a SHGC of 0.60 and a U-value of 0.7 W/m2/K
Solar radiation
• Divided into three parts
- Ultraviolet (minor)
- Visible (0.4-0.7 μm wavelength)
- Near infrared (NIR) (0.7-4.0 μm)
• Roughly half of the solar energy reaching the
ground is in the visible and half in the NIR
• Windows having a SHGC of ~ 0.25 have roughly
50% transmittance in the visible and zero
transmittance in the NIR, so there is still plenty
of light for daylighting while greatly reducing
heat gain and the resulting air conditioning
requirements in the summer
Impact of Increasing Glazing Fraction
• Increasing conductive heat loss in winter – the very best
windows have a U-value of 0.5 W/m2/K, while so-called
“energy efficient” windows (double glazed windows, lowe, argon fill) have U ~ 1.5 W/m2/K, compared to 0.25
W/m2/K for typical insulation levels in cold climates and
0.1 W/m2/K or less in super-insulated buildings
• Increasing passive solar heat gain – but useful only up to
a point, and more useful if there is thermal mass to
absorb the heat by day and slowly release it at night
• Increasing daylight, but useful only up to a point and only
if the electric lighting can automatically dim down if there
is more daylight
• Increasing problem of heat gains in summer
(exacerbated by the usual absence of thermal mass and
external shading)
• The negative impacts can only be partly compensated by
specifying high-performance glazing
Figure 4.15 Impact of increasing the glazing fraction (shown
as the % below each bar) and choice of windows (either
“base” or “upgraded”) an energy use in Swedish Offices
Energy Intensity (kWh/m2/yr)
200
180
160
140
120
100
80
60
40
20
0
30% Base
Heating
Equipment
60% Base
60%
Upgraded
Cooling
Pumps & fans
100% Base
100%
Upgraded
Lighting
Server rooms
Summary on Windows:
• The two key parameters are the U-value (ranging from
0.5-5 W/m2/K) and the SHGC (ranging from 0.25-0.875)
• In hot climates, a low U-value is desirable
• Even in cold climates, on south or west-facing windows,
you might want a SHGC to limit summer cooling
requirements, with only a minimal increase in U-value
compared to a window with a larger SHGC.
• Frames and installation details should not be neglected.
• Very low energy buildings require both high-performance
windows and a limitation on the window fraction (to ~
40% in cold climates)
Impact of larger houses and
role of building form
Figure 4.16 Impact of house size on heating requirement in
Boston in comparison to thermal envelope characteristics
Annual Energy Use (GJ/year)
120
100
Poor: R13 walls, R19 attic, R2.1 doors, SG windows,
uninsulated ducts
Moderate: R19 walls, R30 attic, R4.4 doors, R6 ducts,
DG low-e windows
Cooling
Heating
80
60
40
20
0
Small, Poor
Small,
Moderate
Large,
Moderate
Figure 4.17 Annual heat loss (kWh per m2 of floor area per year) for a
detached house or apartment building in Stockholm, and the associated
U-values for different thermal envelope elements
U-value (W/m2/K)
2.0
1.8
Reference house,
70 kWh/m2/yr
1.6
Single-family house at
20 kWh/m2/yr
1.4
Apartment building at
20 kWh/m2/yr
1.2
Apartment building at
6.5 kWh/m2/yr
1.0
0.8
0.6
0.4
0.2
0.0
Walls
Roof
Floor
Window
frame
Window
glass
Envelope
average
As illustrated in the preceding slides,
• The impact of about 50% more insulation in US
houses since the 1950s has been more than offset
by the effect of larger houses (at least in Boston)
• Decreasing the heating energy requirement from the
typical value of 70 kWh/m2/yr for new detached
houses in Stockholm to 20 kWh/m2/yr (a factor of
3.5 times less) can be achieved either by decreasing
the overall window and wall U-values by about 40%,
or by building apartments instead with slightly less
stringent U-values than for the original house
• Conversely, if we apply in an apartment the Uvalues needed to get the detached house down to
20 kWh/m2/yr, the result is a heating energy
requirement of 6.5 kWh/m2/yr – about a factor of 10
smaller than for the typical detached house in
Stockholm
However, building form has many competing
effects on overall energy use. Smaller, narrow
buildings in place of one large building would have
• Greater heating requirements in cold climates,
but
• Smaller ventilation energy requirements if
designed to take advantage of passive
ventilation
• Smaller lighting energy requirements if designed
to have daylighting with dimmable electric
lighting and photo- and occupancy sensors.
Heating Systems
•
•
•
•
•
•
•
•
Passive solar
Furnaces
Boilers
Wood-burning stoves
District heating
Electric resistance heating
Heat pumps
On-site cogeneration
Passive Solar Heating
• Direct gain
• Solar collectors
• Air-flow windows
Not all solar gain is usable – some leads to
overheating, requiring the windows to be opened
To maximize the useful solar gain, thermal mass (such
as concrete or stone) is needed and should be
exposed to the indoor air (so minimize interior
finishings) (this is the new look anyway in many
buildings now)
With thermal mass, absorbed solar energy goes into
storing heat with minimal temperature rise (apart from
being uncomfortable, high temperatures result in
greater radiant and convective heat loss, and thus less
heat available for later)
At night, the heat is slowly released if there is high
thermal mass. This is adequate if the building is
highly insulated with high-performance windows.
If there is too large a glazing fraction (which
typically means > 60%), there will be more solar
gain than can be used, and greater heat loss at
night
Figure 4.18 Example of fan-assisted passive
solar heating in a Japanese school
Source: Yoshikawa (1997, CADDET Energy Efficiency Newsletter June, 8–10)
Figure 4.19 Air-flow windows to preheat incoming
ventilation air
Figure 4.20: Triple-glazed air flow window serving as a
counterflow heat exchanger
Source: Gosselin and Chen (2008, Energy and Buildings 40, 452-458,
http://www.sciencedirect.com/science/journal/03787788)
Figure 4.21 Finnish supply-air window
Source: www.domus.fi
Boilers, Furnaces
• Non-condensing, 75-85% full-load
efficiency, lower efficiency at part load
(which is achieved through on/off
cycling)
• Condensing, 88-95% full-load
efficiency, greater at part load (which is
achieved through modulation of the fuel
and air flow) and with lower return
temperatures (because more water
vapour can be condensed and used to
preheat the return water flow)
Figure 4.22 Efficiency of a condensing boiler vs temperature of the water
returning to the boiler from the heating loop, and vs load
100
98
Thermal efficiency (%)
96
94
92
90
88
86
25% input
84
50% input
82
100% input
80
20
25
30
35
40
45
50
55
60
65
70
Return water temperature (oC)
Source: Durkin (2006, ASHRAE Journal 48, 7, 51–57)
75
80
85
In houses a good thermal envelope, the heating
requirement is small enough that a small boiler
than can be mounted on the wall in a closet can
supply both the heating and hot water
requirements – at efficiencies > 95%. These are
called wall-hung boilers. See
http://www.wallhungboilers.com/prod_baxi_conden
sing_145.html
Pellet-burning boilers
• 86-94% efficiency
• Have a maximum output as low as 10 kW and
can operate between 30-100% of maximum
output (we want the capability for minimal output
in super-insulated houses)
• Largest units have 40 kW peak output
• Pneumatic delivery of pellets from trucks to
storage bins in houses
• Automatic transfer of pellets to the burner and
removal of ash
• Common in Austria
Electric Resistance Heating
• 100% efficiency at the point of use
• Easily controlled – can supply just the amount of
heat required and no more
• In super-insulated houses, about 1/3 of the total
heat required comes from waste heat from lighting,
appliances and electronic equipment, so a
significant fraction of the heating is already electric
• Overall efficiency – including loss at the electric
powerplant (which is typically coal fired) and
transmission - can be quite low (30-40%)
• However, if electricity is supplied on the margin by
renewable electricity at certain times then, in a
superinsulated house, one could use electricity for
heating only or mostly at those times and let the
temperature drift in between
Heat Pumps
• This is an alternative electric heating system
• Electricity is used to transfer heat against its
‘will’, from cold to warm
• Typically, 1 unit of electricity can provide 3 units
of heat – so this nullifies the losses associated
with the roughly 33% overall efficiency in
supplying electricity from coal plants at the
typical 35-40% generation efficiency
Heat Pump, Operating Principles
• Heat pumps transfer of heat from cold to warm
(against the macro temperature gradient)
• At each point in the system, heat flow is from
warm to cold
• Heat pumps rely on the fact that a gas cools
when it expands, and is heated when it is
compressed, creating local temperature
gradients contrary to the macro-gradient
Components of a heat pump
• Compressor
• Evaporator
• Condenser
Figure 4.23a Heat pump in heating mode
Reject air
O
(-5 C)
Reversing valve
High-pressure
refrigerant (60 C)
O
Outdoor coil as
evaporator
Heated air
(30 C)
O
Fan
Outdoor air
O
(0 C)
Compressor
Indoor coil as
condenser
Blower
Low-pressure
refrigerant (-10O C)
Expansion device
Indoor air
(20OC)
Figure 4.23b. Heat pump in cooling mode
Reject air
O
(35 C)
High-pressure
refrigerant
(60 C)
Reversing valve
O
Outdoor coil as
condenser
Cooled air
(15 C)
O
Fan
Outdoor air
O
(30 C)
Compressor
Indoor coil as
evaporator
Blower
Expansion device
Low-pressure
refrigerant (-10O C)
Indoor air
(25 C)
O
Heat Pump, Efficiency Principles
• The ratio of heat delivered to energy input is called
the coefficient of performance (COP)
• The maximum possible COP (called the Carnot cycle
COP) is related to the temperature lift, TH-TL, where
TH=condenser temp and TL=evaporator temp
COPcooling,Carnot = TL/(TH-TL)
COPheating,Carnot = TL/(TH-TL)+1.0
• The actual COP (in the case of cooling) is given by
COPcooling, real = ηc (TL/(TH-TL))
where ηc is the Carnot efficiency
Figure 4.24a: Heat Pump COP in heating mode
10
nc=0.65
Heating COP
8
6
Condenser
Temperature:
30oC
50oC
4
70oC
90oC
2
0
-20
-15
-10
-5
0
5
Evaporator Temperature (oC)
10
15
Figure 4.24b: Heat Pump COP in Cooling Mode (or
chiller COP)
12
Cooling COP
nc=0.65
Evaporator
Temperature:
8
o
o
-10oC
4
0 C
5o C
10oC
-5 C
0
30
35
40
45
Condenser Temperature (oC)
50
Figure 4.25: Heat flow, temperature lifts, and COPs of a
heat pump in cooling mode
Thus, to reduce heat pump energy use,
• Distribute heat at the lowest possible
temperature (e.g., at 30ºC instead of 60ºC –
using radiant floor or ceiling heating)
• Distribute coldness at the warmest possible
temperature (e.g., at 20ºC instead of 6ºC – using
chilled ceiling or chilled floor slab)
• Minimize ΔTH and ΔTL by
- minimizing the required heat flows (which must
balance heat loss or heat gain, so this means a
super-insulated building with high-performance
windows)
- using as large a radiator surface as possible
Underfloor heating pipes
Sources of heat for a heat pump:
• The outside air (gives an Air-Source Heat Pump)
• The ground (gives a Ground-Source Heat Pump,
now quite incorrectly called “geothermal heating”
by vendors of this equipment)
• The exhaust air (gives an Exhaust-Air Heat
Pump – now standard practice for new houses in
Sweden) (extracts more heat from the outgoing
exhaust air than a simple heat exchanger)
Figure 4.26a Ground Source Heat Pump, horizontal pipes
(a)
Fo u
n da t
io n
Wa ll
S upply
R unouts
30 m
R eturn
R unouts
84
m
30 m x 84 m
available s urface area
Source: Caneta Research Inc (1995, Commercial/Institutional Ground-Source Heat Pump Engineering Manual,
American Society of Heating, Refrigerating and Air-Conditioning Engineers, Atlanta)
Figure 4.26b Ground Source Heat Pump, vertical pipes
(b)
15 m
46
m
Foundation Wall
Supply Return
Runouts Runouts
15 m x 46 m
available
surface area
Source: Caneta Research Inc (1995, Commercial/Institutional Ground-Source Heat Pump Engineering Manual,
American Society of Heating, Refrigerating and Air-Conditioning Engineers, Atlanta)
The ground is a better source of heat than the air
because, during the winter, the ground might be at
8-10ºC while the outside air is at -20ºC.
Conversely, during the summer the ground will be
cooler than the air and so it is a good heat sink
However, if a ground-source heat pump is mostly
used for winter heating, the ground will get
progressively colder from one year to the next,
while if a ground-source heat pump is used mostly
for air conditioning, the ground will get
progressively warmer over time, in both cases
reducing the COP of the heat pump.
Solutions:
• Try to balance winter heating and summer air
conditioning loads (by shifting the priorities in the
design of the building)
• Circulate hot water from solar thermal collectors
to restore ground temperatures during the
summer
• Cool the ground down during the winter by
circulating some fluid (with antifreeze) between
the ground and some sort of heat exchanger in
the outside air
The downside of heat pumps is that they have a
high upfront cost, although they often pay for
themselves over their lifespan (see the RETScreen
heat pump module)
A key economic issue will be the ratio of peak
heating requirement to average heating
requirement (a lower ratio will be more favourable).
This will be affected by the character of the
envelope, building thermal mass, and the building
surface/volume ratio (which is smaller in multi-unit
than in single unit residential buildings)
If a building has a high-performance envelope (so that heat is
lost or gained slowly) and a high thermal mass (so that the
temperature change for a given heat loss is small), then the
heating or cooling system can be turned off for some period of
time without an important effect on the building temperature.
Thus, if the heating and cooling are provided by electric heat
pumps, then we have an electric load that can be ramped up
or down to match variations in the supply of C-free electricity.
If we are running a heat pump when, example, there is excess
wind-derived electricity supplied to the grid, and not running it
at other times, we are in effect using the building thermal
mass to store wind energy in the form of useful heat (or
coldness during the summer season when the heat pump is
used as an air conditioner).
In summary, a high-performance envelope
saves fossil fuel energy in 3 ways
• By reducing the heating load (the amount of
heat that needs to be provided)
• By increasing the efficiency of a furnace, boiler
or (especially) of a heat pump in providing the
required heat
• By providing flexibility as to when heat is
provided (this flexibility is amplified if the building
has a high thermal mass)
Heat Pump Energy Savings Summary:
• The energy required for heating is given by the heating load
divided by the efficiency (as a fraction) of the heating device.
• For heat pumps, the fractional efficiency is the same as the
COP
• So, if we go from a furnace with an efficiency of 80% to a heat
pump with a seasonal average COP for heating of 4.0 (which
could be achieved with a ground-source heat pump and a low
heat-distribution temperature, which is possible in a building
with a high-performance thermal envelope), the energy
required to supply a given heat load is reduced by a factor of
5
• If we’ve also reduce the heat load by a factor of 10, the overall
savings in on-site (secondary) energy is a factor of 50
REDUCING COOLING
ENERGY USE
• Reduce the amount of heat that a building
receives, thereby reducing the cooling load (the
amount of the heat that needs to be removed)
• Use passive and low-energy techniques to meet
as much of the cooling load as possible
• Use efficient equipment and systems to meet the
remaining cooling load
Figure 4.27a Cooling load in a Los Angeles office
building
Fresh Air
10%
Lighting
28%
Roof
8%
Walls
3%
Windows
21%
Office
Equipment
5%
Fans
13%
People
12%
Figure 4.27b Cooling load in a typical Hong Kong
building
Fresh Air
20%
Lighting
18%
Roof
0%
Fans
10%
Walls
4%
Windows
8%
Office
Equipment
13%
People
27%
Reducing Cooling Loads
•
•
•
•
•
•
•
Building orientation and clustering
High-reflectivity building materials
External insulation
External shading devices
Windows with low SHGC
Thermal mass
Vegetation (provides shading and evaporative
cooling)
• Efficient equipment and lighting to reduce
internal heat gains
Thermal Mass
• By itself, does not reduce the cooling load
• High thermal mass means that it takes longer for
the building to warm up, but with a prolonged
heat wave, a building with high thermal mass
eventually heats up (and then will take a long
time to cool down)
• However, thermal mass will greatly reduce the
temperature increase from morning to late
afternoon, so if the night becomes cool enough,
night air can be used to remove heat from the
thermal mass – so that it does not build up from
day to day (or at least not as much)
To most effective, thermal mass
needs to be combined with
• External insulation
• Night-time ventilation with cool outside air flowing
into the core of the thermal mass (such as hollow
concrete slab ceilings or walls)
• In effect, the coldness of the night air is stored and
used to keep the building cool during the day
• This of course reduces total energy use but also
reduces required peak rates of mechanical cooling –
saving on purchase costs for cooling equipment and
electrical transformers, and reducing utility charges
to meet peak electricity demand
The traditional materials used to add thermal mass
are concrete and stone
However, phase change materials can also be used
– either as small spheres in regular plaster or in the
ventilation air flow. These are waxes that can be
designed to melt at, say, 26ºC, absorbing heat in the
process and resisting any further increase in air
temperature. If the air temperature drops below 26ºC
at night, they will refreeze (releasing heat that is
taken away with the night-time air flow), ready to
absorb heat again the next day. These would be
ideal in arid parts of the world (where nights get cold
and days are hot)
Figure 4.28 Micro-encapsulated phase-change
material (left) and spheres containing phase
change materials in an air flow pipe (right)
Source: Schossig et al (2005, Solar Energy Materials and Solar Cells 89, 297–306, http://www.sciencedirect.com/science/journal/09270248) &
Arkar and Medved (2007, Solar Energy 81, 1078-1087, http://www.sciencedirect.com/science/journal/0038092X)
Double-skin façades
• Consist of an outer glass façade and an inner
façade (which could also be largely glass) separated
by an air layer that is not actively heated or cooled
• Contain adjustable shading devices in the gap
between the two façades
• Permit passive ventilation (through operable
windows) even in very high buildings
• Solve the problem of overheating in highly glazed
buildings, especially for west-facing facades
• Do not eliminate the need to limit the glazing
(window) fraction (generally to no more than 0.4-0.6)
in order to optimize the overall design from an
energy point of view
DSF example from Berlin
Source: Danny Harvey
Corridor DSF,
Genzyme
Headquarters,
Boston
Source: Danny Harvey
Corridor DSF, Centre for Cellular and
Molecular Biology, University of Toronto
Source: Sandy Kiang,Toronto
Figure 4.29a Comparison of double-skin façades (DSF) and single-skin
façades (SSF) with moderate or high levels of insulation and normal or
optimal ventilation strategies with regard to heating load in a
5-story office building in Belgium
100000
90000
Heating Load (kWh/yr)
80000
70000
60000
50000
40000
30000
20000
10000
0
Moderate,
SSF Base
Moderate,
SSF Opt
Moderate,
DSF Opt
High, SSF
Base
High, SSF
Opt
High, DSF
Opt
Figure 4.29b: Comparison of double-skin façades (DSF) and single-skin
façades(SSF) with moderate or high levels of insulation and normal
or optimal ventilation strategies with regard to cooling load in a
5-story office building in Belgium
100000
90000
Cooling Load (kWh/yr)
80000
70000
60000
50000
40000
30000
20000
10000
0
Moderate,
SSF Base
Moderate,
SSF Opt
Moderate,
DSF Opt
High, SSF
Base
High, SSF
Opt
High, DSF
Opt
Lessons on DSFs from the previous slides
• The insulation level is far more important than adding a
second skin for the heating load
• The building operating strategy (opening windows when
appropriate, and appropriate use of day and night-time
ventilation) is far more important than adding a DSF for
the cooling load
• If there is already a sensible operating strategy, adding a
second facade can increase the cooling load
• However, the second facade may be necessary to permit
a sensible operating strategy in the first place (by
protecting against wind, noise, dust and intruders
(human or animal) with open windows)
• Based on simulations for a 5-story office building in
Belgium, the combination of modestly higher insulation
levels and modestly better glazing with addition of a
second facade and the use of the natural ventilation that
it permits reduces heating energy use by ~50% and
cooling energy use by ~80%
Double skin facades Summary
• Permit adjustable external shading on tall
buildings
• Permit day and night ventilation when it
would not otherwise be possible
• In so-doing, they can greatly reduce
cooling loads
• Design details are important, however
Low-energy Cooling Techniques
• Natural (passive) ventilation
• Hybrid (passive-mechanical) ventilation
• Mechanical ventilation at night (combined with
thermal mass and external insulation)
• Evaporative cooling
• Earth-pipe cooling
Natural driving forces for air flow:
• Wind forcing
• Temperature differences (which create
pressure differences)
Wind forcing:
•
•
•
•
Cross ventilation
Wing walls
Wind catchers
Wind cowls
Cross-ventilation
Source: Givoni (1998), Passive and Low Energy Cooling of Buildings,
von Nostrand Reinhold, New York
Wing walls:
Source: Givoni (1998), Passive and Low Energy Cooling of Buildings,
von Nostrand Reinhold, New York
Winds catchers in Iran and Doha
Source: Koch-Nielsen (2002), Stay Cool: A Design Guide for the Built Environment
in Hot Climates, James and James, London
Wind catcher at Sir Sanfred Fleming
College, Peterborough, Canada
Source: Loghman Azar, Line Architects, Toronto
Airflow at Sir Sanfred Fleming College,
Peterborough, Canada
Source: Loghman Azar, Line Architects, Toronto
Wind cowl
Source: www.arup.com
Thermally-driven ventilation
• Atria
• Solar chimneys
• Cool towers
Figure 4.30 Solar chimneys on the Building Research
Establishment (BRE) building in Garston, UK
Source: Copyright by Dennis Gilbert, View Pictures (London)
Figure 4.31 Torrent Centre, Ahmedabad, India
Exhaust
Exhaust
Inlet
Micrionizers
Offices
Laboratories
Exhaust
Source: George Baird (2001, The Architectural Expression of
Environmental Control Systems, Spon Press, London)
Exhaust
0
5m
Figure 4.32 Torrent Centre, Ahmedabad, India
Source: George Baird (2001, The Architectural Expression of
Environmental Control Systems, Spon Press, London)
Evaporative Cooling
• Direct – water evaporates into the airstream
being cooled, increasing its relative humidity
• Indirect – water evaporates into a secondary
airstream (such as exhaust air heading to the
outside) but cools the primary airstream (which
enters the building) through a heat exchanger
without adding moisture to the primary airstream
Figure 4.33: Combined direct-indirect evaporative cooler
Dry Outside Air
Recirculation of a portion
of the pre-cooled outside air,
mixed with exhaust air
Falling films
of water
26
100%RH
80%RH
60%RH
24
22
Original T wb
20
Direct evaporative
cooling of
secondary
Final T wb
Direct evaporative
cooling of primary
airstream
18
40%RH
airstream
16
Indirect evaporative
cooling of primary
airstream
14
12
10
20
25
30
Dry Bulb Temperature (oC)
35
40
Humdity Mixing Ratio (gm moisture per kg dry
air)
Figure 4.34: Indirect+direct evaporative cooling
Figure 4.35: Rooftop (left) and window-mounted (right)
direct evaporative coolers from Adobe Air
Source: www.adobeair.com
Earth-pipe cooling
• Ventilation air is first drawn through underground
pipes so as to be cooled by the ground
• COP (cooling over fan energy) of 7-50 obtained
(depending on ground and air temperatures)
• Airflow can also be driven with solar chimneys
Figure 4.36: Jaer School, Norway – combining
solar chimneys and earth-pipe cooling
Source: Schild and Blom (2002, Pilot Study Report: Jaer School, Nesodden
Municipality, Norway, International Energy Agency, Energy Conservation in
Buildings and Community Systems, Annex 35, hybvent.civil.auc.dk)
Atria and stair wells can also serve
as solar chimneys, driving a natural
ventilation if so-designed
Figure 4.37 Panasonic building in Tokyo – hybrid
mechanical/passive ventilation
Source: Nikken Sekkei, Japan
Mechanical cooling equipment
• Air conditioners – directly cool the air, and the
condenser is cooled with outside air
• Electric chillers (normally just called “chillers”) –
produce cold water, which is circulated through the
building, with small chillers having an air-cooled
condenser and large chillers having a condenser
cooled with water from a cooling tower
• Absorption chillers – use heat to drive a
thermodynamic cycle that produces chilled water,
with the condenser invariably cooled with water from
a cooling tower
The efficiency of air conditioners and chillers is represented by
the coefficient of performance (COP), the ratio of cooling
provided to energy used by the unit
• Wall-mounted air conditioners, COP = 2.5-3.5 except in
Japan, where COP=3.5-6.5
• Electric chillers, COP = 4.0-7.5 (larger units have a higher
COP)
• Absorption chillers, COP = 0.6-1.2
Energy required for cooling = cooling load divided by chiller COP
Note: for electric chillers, we should multiply the COP times the efficiency
in generating electricity to get the COP in terms of primary energy. So, if
COP=3.0 and the powerplant efficiency is 0.33, the COP in terms of
primary energy is only 1.0 – that is, one unit of primary energy gives one unit
of cooling
Desiccant cooling systems
• Use a solid or liquid desiccant to remove moisture
from the outdoor air supplied to a building
• Then use evaporative cooling to cool the air without
making the final relative humidity too large
• Use heat (ideally, from solar thermal panels) to
regenerate the desiccant
• In effect, extends evaporative cooling to the hothumid regions of the world where it otherwise
cannot be used because the air is already too humid
Key difference between desiccant and
electric (or absorption) chillers:
• In electric or absorption chillers, humidity is
reduced by overcooling the air (forcing some
water vapour to condense out), then reheating
the air
• In a desiccant system, we go directly to the
desired final T-humidity combination
• Apart from tending to save energy, it is healthier
to avoiding over chilling and reheating – as there
are no wet surfaces where moulds and fungi can
grow
Impact of desiccant systems
on primary energy use
• If the desiccant is regenerated using heat from a boiler –
primary energy use can increase or decrease slightly
compared to over chilling with large electric chillers and
reheating (the COP of desiccant systems today is only
about 0.8-1.0, compared 5-7.5 for electric chillers)
• If the desiccant is regenerated using waste heat from
micro-turbine cogeneration, there may or may not be a
net savings in primary energy use, depending on the
overall (electric + thermal) efficiency of cogeneration and
the efficiency of the powerplant that would otherwise
supply electricity to an electric chiller
• If the desiccant is regenerated using solar heat, then
there is a large energy savings (up to 90%)
Figure 4.41
Idealized
soliddesiccant
cooling
system
Desiccant wheel.
Rotation rate: 2 rpm if passive (is dried only by the unheated outgoing air)
60 rpm if active (outgoing air is heated before passing through)
Source: Danny Harvey, photo taken at GreenBuild 2011 in Toronto
Figure 4.42 Desiccant Chiller Performance
Source: IEA (1999, District Cooling, Balancing the Production and Demand in CHP, Netherlands Agency for Energy and Environment, Sittard)
Summary so far on chillers
• Major kinds: electric (vapour-compression),
absorption (by-passed here) and desiccant
• The COP of an electric chiller in terms of primary
energy is equal to the chiller COP x efficiency in
generating electricity ~ 5.0-7.5 x 0.35-0.6 = 1.8-4.5
• Desiccant chiller COP is based on the heat input
and is much smaller than the COP of an electric
chillier, namely, ~ 0.6-1.2
• Because of the low COP, desiccant chillers are not
very interesting unless either waste heat or solar
heat is used to regenerate the desiccant
• The energy required for cooling equals the cooling
load (the amount of heat that needs to be removed
from the building) divided by the chiller COP
Cooling Towers
• These are usually found on the roof of big buildings
• Water is cooled evaporatively and then used to cool
the condenser of the chiller
• As evaporation produces temperatures cooler than
the air temperature (approaching the wetbulb
temperature, rather than the drybulb temperature), a
condenser that is cooled with water from the cooling
tower rather than with air will be cooler.
• This in turn means a smaller temperature lift (from
the evaporator to the condenser temperatures) (see
Figure 4.25), and so a larger COP for the chiller.
Reminder: Figure 4.25: Heat flow, temperature lifts, and
COPs of a heat pump in cooling mode
Figure 4.43: Schematic diagram of a cooling tower
Source: ASHRAE (2001, 2001 ASHRAE Handbook, Fundamentals, SI Edition, American Society of
Heating, Refrigeration and Air-Conditioning Engineers, Atlanta)
Cooling Tower on Top of Medical Sciences Building
Water is cooled through partial evaporation, to below the air
temperature, then goes to the condenser of the “chiller” to
remove heat, with the result that the chiller does not need
to work as hard (and does not require as much energy) as it
would if it had to make the condenser hot enough to dump
heat directly to the hot outside air
Source: Photo by Danny Harvey
Fans on a Cooling Tower
Fans are used to force a greater flow of air next to the evaporating water,
thereby forcing faster evaporation and greater cooling. Electricity energy use
for fans and pumps can be 15% or more of the electricity needed to operate
the chiller itself
Source: Photo by Danny Harvey
Using the cooling tower as an
evaporative cooler
• The cooling tower can often produce water at a
temperature of 16-18ºC or colder
• For displacement-ventilation/chilled ceiling HVAC
systems (described later), this is plenty cold enough
for cooling purposes
• Thus, the cooling tower water can bypass the chiller
condensers (and the chillers can be turned off) and
be used directly for cooling the building
• The cooling tower thus becomes another type of
evaporative cooling system
Figure 4.44a Cooling tower during normal operation. There is a
cooling water loop between the cooling tower and the condenser of
the chiller, and a chilled water loop from the evaporator through the
building and back to the evaporator
Cooling
Load
Evaporator
Compressor
Condenser
Cooling Tower
Figure 4.44b Cooling tower as an evaporative cooler with direct
connection of the cooling water loop and the chilled water loop
Cooling
Load
Evaporator
Compressor
Condenser
Cooling Tower
Correct Sizing of Cooling Equipment
• The amount of cooling required in a building is
usually vastly over-estimated, due to the use of
simple but inaccurate estimation techniques with
a desire to “play it safe”
• As a result, the air conditioning equipment
installed in buildings is usually way too big,
causing it to operate at a small fraction of its
peak capacity
• This in turn increases the energy requirements
by up to 20% or so compared to properly sized
equipment (and increases first costs)
Off-peak air conditioning
• Cool down water in a large storage tank at night,
when electricity rates are often lower, and use
the chilled water for cooling purposes during the
day when it is needed
• The amount of coldness stored depends on:
volume of water x temperature drop
• If the water is cooled twice as much, only half
the volume would be needed to store the same
amount of coldness
• If ice is made, even less volume is required
Energy implications of off-peak chilling:
• The colder the stored water, the lower the required
evaporator temperature, reducing the COP of the
chiller (and hence increasing its energy use)
• To make ice, the evaporator T has to be at around
-10ºC, whereas in a system with chilled ceiling cooling
and displacement ventilation (which requires chilled
water and air cooled only to about 18-20ºC), the
evaporator could be at around 10ºC – so there would
be a substantial energy penalty with an evaporator
cold enough to make ice
• On the other hand, the condenser would be a little
cooler at night (which would improve the chiller COP),
fossil fuel powerplants are more efficient at night (up to
40% less primary energy is required to make one kWh
of electricity at night), and transmission losses are up
to 5% less at night than during the day
Reminder: Figure 4.25: Heat flow, temperature lifts, and
COPs of a heat pump in cooling mode
Solution (if you really want to reduce the need for
running cooling equipment during the day):
Store coldness in something that freezes at a
temperature warmer than 0ºC
Eutectic salts (which have been used for this
purpose) fit the bill – they have a freezing point in
the 8-10ºC range and a latent heat of freezing
about half that of water (which is not bad – they
store about half the coldness of water when they
freeze)
Heating Ventilation Air
Conditioning (HVAC) systems
HVAC Energy-Efficiency
Principles
• Circulate only the amount of air needed for
ventilation, and only when needed, while
circulating hot or cold water for most of the
heating and cooling (recall: energy required to
move air or water varies with flow rate cubed,
and ~ 25-100 times less energy is required to
deliver heat via water than via air)
• In other words, separate the heating/cooling and
ventilation functions
• Separate cooling from dehumidification functions
using solid or liquid desiccants, with the
desiccant regenerated using either waste heat
from cogeneration (entailing ~ 0 sacrificed
electricity because temperatures of only 50-65ºC
are needed) or using solar thermal energy
• Distribute heat at the coolest possible
temperature and coldness at the warmest
possible temperature – in both cases by using
large radiators (such as radiant ceiling or floors)
• Allow the temperature maintained by the HVAC
system to vary seasonally (allowing
temperatures of up to 28-30ºC on the hottest
days)
HVAC systems in residential
buildings
• If super-insulated, heat from the airflow at the
rates required for ventilation only is often
sufficient (with perhaps supplemental radiant
heating of floors or towel racks in bathrooms)
• Otherwise, use radiant floor heating or large wall
radiators (water at 30ºC will be plenty warm
enough in super-insulated buildings)
• Mechanical ventilation with heat recovery via a
heat exchanger when windows need to be
closed
• Variable-speed drives on ventilation fans
Large wall-mounted radiator in a daycare centre in Frankfurt
– an inexpensive alternative to radiant floor heating
Source: Danny Harvey
Heat Exchangers
• Transfer heat from a warm air or water flow to a
cold air or water flow
• Do so by maximizing the surface area between
the two fluid flows
• This can be done either with one tube inside
another, or through a series of plates
Figure 4.45a Counterflow flat plate heat exchanger
Source: Bower (1995, Understanding Ventilation: How to design, select, and install residential
ventilation systems, Healthy House Institute, Bloomington, Indiana)
Figure 4.45b Crossflow flat plate heat exchanger
Source: Bower (1995, Understanding Ventilation: How to design, select, and install residential
ventilation systems, Healthy House Institute, Bloomington, Indiana)
Figure 4.46 Residential heat exchanger (as part of a
mechanical (fan-driven) ventilation system)
Source: Danny Harvey
Apartment heat exchanger (top)
and heating or cooling coil (bottom)
Damper
Heat exchanger
Fan
Heating or cooling coil (depending on
if hot or cold water is sent through it)
Source: Danny Harvey, photo taken at GreenBuild 2011 in Toronto
The performance of a heat exchanger is measured by its
“effectiveness”, which is defined as
(Tsupply-Tincoming)/(Toutgoing-Tincoming)
Heat exchangers for commercial buildings have an effectiveness
of 60-80%, meaning that 60-80% of the temperature difference
and hence heat content difference between the incoming and
outgoing air can be added to the incoming air rather than sent
outside.
Residential heat exchangers have an effectiveness as high as
95%
However, adding a heat exchanger increases the fan energy
required to move air (since it adds resistance to air motion) – so
it should be bypassed when there is little difference in the
temperature of inside and outside air
Fans
• Do not cool the air, they only make the air feel
cooler
• They in fact add heat to the air
• Thus, they should be turned off when not in use
• They only save energy if people set the
thermostat on the air conditioner to a higher
temperature (or dispense with the AC
altogether)
• Most are incredibly inefficient (only 4-12% of
electrical power input ends up moving air)
Figure 4.47 An aerodynamic ceiling fan (36% efficiency at
high speed vs 12% for typical fans, where efficiency = power
imparted to air flow divided by electrical power)
Source: Florida Solar Energy Center
Recent conventional
HVAC heating systems
• The fans operate at a fixed speed, tending to
circulate a fixed quantity of air all the time
• The air is either overcooled centrally, then
reheated electrically by the required amount just
before entering a room, or
• The air flow is throttled to prevent overcooling
(but usually some rooms end up too warm and
others too cold)
Recall: Figure 4.6 Variation of fan or pump power with flow, using
various methods to reduce the rate of flow
110
Fans
Throttle Valve
Pumps
Inlet Vane
100
90
%Peak Power
80
70
60
Outlet Damper
50
40
30
VSDs
20
Cubic Law
10
0
0
10
20
30
40
50
60
%Peak Flow
70
80
90 100
New HVAC systems
• Will use variable speed fans – with the airflow
rate varying according to a fixed schedule.
Savings of 50-60% in overall HVAC energy use
have been achieved from this alone
• As the airflow is still much more than required for
ventilation purposes, 80% or so of the air will be
recirculated on each circuit and blended with
20% outside air,
• This saves energy compared to venting 100% of
the air to the outside and completely replacing it
with fresh air that needs to be cooled and
dehumidified or heated and humidified
However, we can still do much better
• If heating and cooling are largely provided through
radiant floor or ceiling panels, then the airflow can be
reduced to just that needed for ventilation (fresh-air
purposes)
• Having reduced the airflow to that level, it can be
entirely vented to the outside and replaced with 100%
fresh air on each circuit (this is called a Dedicated
outdoor air supply, or DOAS, system) without wasting
energy
• This gives better indoor air quality and saves energy
- reduced fan energy use
- heat picked up from lights at the ceilings is directly
vented to the outside rather than having to be
removed by the chillers before 80% of the air is sent
through the building again
We can also do much better in the way that the
ventilation enters in and passes through a room.
The ventilation air typically enters a room from
some outlet in the ceiling or in a wall and mixes
turbulently with the room air, relying on dilution to
remove air contaminants. This requires greater air
flow (and recall, required fan power increases with
air flow rate almost to the third power) but is not
very effective in providing good air quality. A better
alternative is outlined next.
Two essential elements of highly-efficient
HVAC systems in commercial buildings
are:
• Displacement ventilation
• Chilled ceiling cooling
Chilled ceiling cooling
• Our perception of temperature depends roughly
50:50 on the air temperature and on the radiant
temperature (the temperature of the
surroundings, which are a source of infrared
radiation on our bodies)
• A nice sensation of coolness is achieved if the
ceiling is cooled to 16-20ºC by circulating water
at this temperature through panels attached to
the ceiling
• The result is a much higher chiller COP than
conventional cooling systems (which use water
at 6-8ºC) and warmer permitted air temperature
Figure 4.48 Chilled Ceiling cooling panels
Source: www.advancedbuildings.org
Energy Savings
• Compared to an all-air cooling system, simulations
indicate that chilled ceiling cooling save about 5-40%
cooling energy use, with the smallest relative savings in
hot-humid climates and the largest relative savings in
hot-dry climates.
• This does not include savings from direct use of the
cooling tower (as noted earlier, because the ceiling
panels need water cooled down to only 16-20ºC, and the
cooling tower almost always produces water at this
temperature, the cooling tower water can be directly
used in a chilled ceiling cooling system most of the time)
Displacement ventilation
• Ventilation air is introduced from vents in the
floor or at the base of walls at a temperature
slightly below the desired room temperature
• The air is heated from internal heat sources and
rises in a laminar manner, displacing the preexisting air, and exiting through vents in the
ceiling
• 40-60% less airflow is required than in a
conventional ventilation system (which we
assume to be already reduced to the flow
required for air quality purposes only)
Figure 4.49 Displacement ventilation floor diffuser
Source: Danny Harvey
Because the airflow has been reduced to that
needed for ventilation purposes only (with most of
the cooling done with chilled ceilings), 100% of the
(much reduced) airflow must be vented to the
outside and replaced with fresh outside air on each
circuit. As previously noted, this forms a dedicated
outdoor air supply (DOAS) system. It is healthier
because air is not recirculated from one part of the
building to another, and saves energy because
internal heat that is transferred to the air is directly
vented to the outside, rather than passing having
to be removed by the chiller before the air is
recirculated
Energy savings
• The overall impact of energy use of
displacement ventilation/chilled ceiling system
compared to mixed ventilation/chilled ceiling or a
VAV all-air cooling system depends on many
competing factors, and if the system is not fully
optimized (through computer simulation tests),
there can be little net savings
• If overcooling and subsequent reheating for
dehumidification are avoided, then
cooling+ventilation energy use can be reduced
by 30-60%
Demand-Controlled Ventilation
A further efficiency measure is to vary the airflow
based on human occupancy (as determined by
CO2 sensors). This gives a demand-controlled
ventilation (DCV) system (this is now required by
the California building code for high-density
buildings). DCV alone can save 20-30% of total
HVAC energy use.
Hierarchy of Progressively More
Energy-Efficient HVAC Systems
• All-air heating and cooling, fixed air flow rate, once-through
and 100% vented to the outside
• Hydronic heating and cooling fan coils to handle some
portion of the heating and cooling requirements, and
- Fixed air flow ventilation, 100% vented to the outside
- Variable air flow ventilation, 100% vented to the outside
- Variable air flow with recirculation of ~ 80% of airflow,
___20% vented to the outside on each circuit
• Radiant ceiling cooling, radiant ceiling or floor heating (if
heating is needed), and
- Variable air flow now reduced to the purely ventilation
___requirement – so back to once-through flow (DOAS)
- Variable Displacement Ventilation air flow, preferable
___Demand-Controlled
To summarize, the most energy-efficient building will have
• Optimal orientation and form
• A high performance envelope
• Capacity to use passive ventilation and cooling
whenever outdoor conditions permit
• Demand-controlled, displacement ventilation that, of
necessity, will be a DOAS system
• Chilled ceiling cooling
• Desiccant dehumidification using either waste heat from
cogeneration (ideally supplied by a district heating
system) or using solar thermal energy
• Heat exchangers to transfer heat or coldness from the
outgoing to the incoming air
• High efficiency equipment, correctly sized and
commissioned
Supplemental figures, EnergyBase building,
Vienna
Source: Danny Harvey
Adjustable external shading
Source: Danny Harvey
Windows on south facade are slightly overhanging
Source: Ursula Schneider, Pos Architekten, Vienna
Exhaust air is overheated by passing through a
sort of solarium, then passes through a heat
exchanger to heat the incoming fresh air to a
greater extent than would be possible with a
conventional heat exchanger system. And unlike
systems for passive solar preheating of ventilation
air, we still get the benefit of heat recovery on the
exhaust air at night
Air temperatures during flow through solarium
and heat exchanger
Source: Ursula Schneider, Pos Architekten, Vienna
Storage tank
for solar hot
water – used
in a
desiccant
cooling
system
Source: Danny Harvey
Solar-desiccant cooling unit
Source: Danny Harvey
Recap: Fig. 4.41(top)
Heat
Exchanger
Evaporative
Cooler
D
E
Desiccant
Wheel
F
G
H
Heat
Input
C
B
A
DOMESTIC HOT WATER
Figure 4.50 Breakdown of DHW energy use in the US
Bath
16%
Showers
35%
Dishwasher
7%
Clothes Washer
11%
Standby and
Distribution
Losses
31%
Reducing DHW Energy Use
• More efficient production and supply
• Reduced demand
• Heat recovery after use
More efficient DHW supply
• Efficient, condensing boilers are normally not
available as stand-alone heaters for DHW (typical
efficiency ~ 65%)
• For single-family housing – use a combined space
and hot and water heating system (90-95%
efficiency)
• Reduce storage and distribution losses through a
wall-hung boiler – this is a small, tankless,
modulating and condensing boiler that can be located
in a closet close to the DHW load (see
http://www.wallhungboilers.com/prod_baxi_condensi
ng_145.html)
• In multi-unit housing – use a separate, small boiler for
DHW in the summer (otherwise, the boiler used for
space heating and DHW in the winter will be running
at ~ 10% of peak load on average during the
summer, and hence very inefficiently)
Recirculation-loop systems in
hotels, office buildings, schools
• Hot water is continuously circulated through a pipe
loop that returns to the boiler
• Branches provide water to faucets
• The result is that hot water is instantly available (so
water is not wasted running the tap until warm water
is received)
• Insulating the pipes well allows ‘priming’ the pipes
with hot water only once every hour for 5 minutes
• This combined with replacing one central boiler with
separate boilers in different zones resulted in a 91%
savings in total energy use for hot water (including
pump energy use) in a school in Tennessee
More efficient use of DHW
• Low-flow showerheads and faucets
• Cold-water clothes washing
• Personal behaviour:
- showers instead of baths (this is an issue
_especially in Japan)
- shorter showers, water not running all the time
- water-efficient hand washing of dishes instead of
_using a dishwasher
• The fractional savings is diluted by the fact that, in
most systems, a large part of the energy used to
heat water is used to overcome standby losses
Recovery of heat from wastewater
• Applicable only when there are simultaneous hot
and cold water flows
• Thus, applicable to showering but not to using a
bathtub
• 45-65% of the available heat can be recovered
from that portion of the hot water use related to
simultaneous flows
Figure 4.51 Heat exchanger for wastewater
Hot
Drain water from showers & sinks
Preheated or cold
Water to fixtures & water heater
Model F-601
Falling film
heat exchanger
Incoming
Cold water
60% cooler
Waste water to sewer
Source: Left: Vasile (1997, CADDET Energy Efficiency Newsletter December, 15–17) ,
Right: Danny Harvey, NSEA 2004 Conference exhibits
Finally – solar energy can provide 50-80% of
DHW requirements in most countries (this is
C-free energy supply, not energy efficiency,
and so is discussed in Volume 2)
REDUCING LIGHTING ENERGY
USE
• Daylighting
• Efficient lighting systems (including controls and
sensors)
• Efficient lighting devices (ballasts, lamps and
luminaires)
Daylighting
• Simple passive daylighting – window size,
orientation, shape, building floor plan
• Complex passive daylighting – devices to collect
and reflect daylight deep into a building
• Complex active daylighting – devices to actively
track the sun so to collect more daylight
• All kinds of daylighting require photosensors and
dimmable electric lighting
• Efficient design of electric lighting systems
• Efficient lighting fixtures (ballasts, lamps,)
Daylighting – Clerestory Windows and
other architectural features
Figure 4.52 Daylighting Roof Configurations
Source: Hastings (1994, Passive Solar Commercial and Institutional Buildings: A Sourcebook of
Examples and Design Insights, John Wiley, Chichester)
Clerestory, Oberlin College, Ohio
Clerestory
Source: Torcellini et al (2006)
Clerestory Window, Cambria Office
Clerestory
Source: Torcellini et al (2006)
Daylighting – Interior and Exterior
Light Shelves
Figure 4.53a Interior Light Shelf
Source: Danny Harvey
Source: Donald Yen, BCIT
Light shelves, Cambria Office, Pennsylvania
Source: Torcellini, P., S. Pless, M. Deru, B. Griffith, N. Long, and R. Judkoff, 2006: Lessons Learned from Case
Studies of Six High-Performance Buildings, National Renewable Energy Laboratory, Technical Report
NREL/TP-550-37542.
Figure 4.54a Fixed exterior and interior light shelves
Increased uniformity of daylight level
Shading from high summer sun
Source: Hastings (1994, Passive Solar Commercial and Institutional Buildings: A Sourcebook of
Examples and Design Insights, John Wiley, Chichester)
Daylighting – Reflective Blinds
Passive Daylighting
(light louver)
View from inside
View from outside
Source: Danny Harvey, photo taken at GreenBuild2011 in Toronto
Source: Donald Yen, BCIT
Daylighting effects
Source: Donald Yen, BCIT
Daylighting – Light Pipes with Passive
and Active Sun Tracking
Figure 4.57 Passive Light Pipe
(a)
(b)
Source: Zhang and Muneer (2002, Lighting Research and Technology 34, 149–169)
Daylight central chamber, Barnim Service and
Administration Centre, Brandenburg, Germany
Source: EnOB website (www.enob.info/en), new buildings case studies
Active Light Tracking Skylight
Source: Danny Harvey, photo taken at GreenBuild 2011 in Toronto
Figure 4.56 Light Pipe
Source: International Association of Lighting Designers
Figure 4.54b Adjustable light Shelf
Ra y s
low from
a
wint ltitude
er su
n
Ref lec
rays
Protective
glazing
m
fro de
y s itu
Ra h alt r sun
hig mme
su
Reflective pla stic film
ted
Roller
Path of roller
Tilted
glazing
View glazing
d
Reflecte
rays
Pla
stic
film
Roller
Source: Hastings (1994, Passive Solar Commercial and Institutional Buildings: A Sourcebook of
Examples and Design Insights, John Wiley, Chichester)
Figure 4.55 Sun-tracking light pipe
Tracking
Reflector
Heliostat
Drive
Converging Rays
Re
flec
te
S o la
R ay r
s
dR
ay
s
Converging
Reflector
L ight
End Mirror
Ray
Prism Light Guide
Pipe Solar Input Housing
Reflector
Prism Light Guide
Light
Diffuser
Source: Hastings (1994, Passive Solar Commercial and Institutional Buildings: A Sourcebook of
Examples and Design Insights, John Wiley, Chichester)
Electric Lighting - Systems
• Zonation and controls
• Task vs Ambient Lighting
• Occupancy Sensors
Electric Lighting - Lamps
• Incandescent – requires heating a tungsten filament
to 2100-2800ºC
• Halogen – like an incandescent lamp, but has some
halogen gas and a quartz rather than a glass
envelope, permitting higher temperatures (with more
of the emitted radiation in the visible part of the
spectrum)
• Fluorescent tube and compact fluorescent lamp
(CFL) – an electric arc travels between electrodes,
vapourizing mercury and producing UV radiation
that in turn is absorbed by phosphors lining the inner
tube, which in turn emit light of various colours as
they drop down in energy level
• Light emitting diode (LED) – like a photovoltaic cell
but running in reverse
Technical notes:
• Energy is transmitted from the sun in the form of
electromagnetic (EM) radiation
• Light is simply EM radiation of the wavelengths that we
can see
• When EM is absorbed (whether visible or not), it warms
the object that is absorbing the radiation. Thus, the light
emitted from a lamp (as well as daylight) has a heating
effect (and the distinction sometimes made between
“heat” and “light” from the sun is artificial)
• To maximize the amount of light from a lamp while
minimizing the amount of heat that it also produces, the
lamp should emit only at wavelengths that we see and
not at other wavelengths.
Reminder: Figure 4.3, Blackbody Radiation
2000
100
1800
90
Solar Radiation
Extraterrestrial
Surface (1.5 atm)
1400
1200
800
70
Blackbody
Radiation:
Relative
Sensitivity
of Human
Eye
1000
80
50oC
0oC
600
400
-50oC
200
60
50
40
30
20
10
0
0.1
1.0
10.0
Wavelength (um)
0
100.0
Intensity (W/m2/um)
Intensity (MW/m2/um)
1600
Emission from incandescent lamps (T = 2100-2800ºC)
2000
400
Intensity (MW/m2/um)
1600
Relative
Sensitivity of
Human
Eye
1400
1200
Solar Radiation
Extraterrestrial
Surface (1.5 atm)
360
320
280
Blackbody
Radiation:
1000
2800oC
800
200
160
2100oC
600
240
120
400
80
200
40
0
0.1
1.0
Wavelength (um)
0
10.0
Intensity (10000s of W/m2/um)
1800
The “efficiency” of a lamp is measured in
terms of its efficacy, which is the ratio of
lumens of light to watts of power
• A lumen is the electromagnetic radiation output (W)
weighted by the sensitivity of the human eye (times a
factor of 683)
• Efficacies range from:
10-17 for incandescent lamps
50-70 for compact fluorescent lamps
105 for T5 fluorescent tubes
50-60 now and 200 projected for LEDs
105-130 for natural sunlight
Appliances and Consumer
Electronics
5000
5
4000
4
3000
3
2000
2
1000
1
0
0
OECD North
America
OECD Europe
OECD Pacific
Non-OECD
Growth Rate (%/yr)
Electricity Consumption (kWh/yr/person)
Figure 4.60 Residential per capita electricity use in 2005
(bars) and average growth rate (squares) from 1995 to 2005
Figure 4.61a US non-space or water heating residential
electricity use in 2001
Stereo system, 0.6%
Other
11.7%
Water bed, 0.6%
Refrigerators &
Freezers
21.2%
Coffee maker, 0.7%
Pool/hot tub/spa, 0.8%
Ceiling fan, 1.0%
Pool filter/pump, 1.1%
Clothers washer, 1.1%
Computers, 2.5%
Dishwasher, 3.2%
Electric range, 3.5%
Air conditioning
19.9%
Furnace fan, 4.2%
Ovens, 4.6%
TV and related, 5.3%
Clothes dryers
7.2%
Lighting
10.9%
Figure 4.61b EU-27 non-space or water heating
residential electricity use in 2007
External power
supplies 2.6%
Other
7.3%
Computers 3.7%
Refrigerators and
freezers
21.0%
Ventilation 3.7%
Dishwashers 3.7%
Air conditioners
6.1%
Lighting
14.5%
Standby
7.5%
Clothes washers
8.6%
TVs 9.3%
Electric ovens
10.4%
Set top boxes 1.7%
Figure 4.61c Indian residential electricity Use in
2007
TVs
4%
Other
10%
Evaporative
coolers
4%
Fans
34%
Air conditioners
7%
Refrigerators
13%
Lighting
28%
Figure 4.62a. Annual electricity use by
refrigerator/freezer units available in North America
800
Annual Electricity Use (kWh)
700
600
500
400
300
200
100
0
2.5
4.5
6.5
8.5 10.5 12.5 14.5 16.5 18.5 20.5 22.5 24.5 26.5 28.5 30.5 32.5
Volume (ft3)
Figure 4.62b Annual electricity use by freezers
available in North America
800
Annual Electricity Use (kWh)
700
600
Upright
500
400
300
Chest
200
100
0
3.5
5.5
7.5
9.5
11.5
13.5
15.5
Volume (ft3)
17.5
19.5
21.5
23.5
25.5
2500
25
Energy Use
20
Adjusted Volume
3
2000
Adjusted Volume (ft )
Average Energy Use Per Unit (kWh/yr)
Figure 4.65 Energy use by new refrigerators sold in the US
1978 California
Standard
1500
1980 California
Standard
1000
15
10
1987 California Standard
1993 US Standard
500
5
2001 US Standard
0
1940
1950
1960
1970
1980
1990
Year
Source: Rosenfeld (1999, Annual Review of Energy and the Environment 24, 33–82)
0
2000
Figure 4.66 Average energy use by the
refrigerator stock in different countries
1500
USA
Energy Use (kWh/yr)
Canada
1000
Australia
Japan
Finland
500
Sweden
Norway
Denmark
UK
Netherlands
Germany
Italy
France
0
1973
1980
1990
Year
1998
Further opportunities for energy savings
in refrigerator/freezer units
• Use of vacuum insulation panels
• Separate chilling of the fridge and freezer
compartments (at present, the fridge is cooled
indirectly by cooling down to the temperature
required by the freezer, which means a greaterthan-necessary temperature lift and lower COP)
• Variable speed compressor
• 200 kWh/year for a standard size unit is a
reasonable target
• Get rid of the beer fridge!
Clothes washers
• Vertical axis (top opening) – lots of water
required
• Horizontal axis (side opening) – uses less water,
has higher spin speed, so the clothes come out
dryer
• Energy use should take into account direct
energy use, hot water requirements, detergent
embodied energy (horizontal axis machines
require less detergent) and the energy required
to dry the clothes after washing (greater
electricity used to spin the clothes is more than
compensated by reduced clothes dryer energy
use)
Figure 4.67 Energy used to wash 200 3.2kg loads per
year, with heating of 1/3 of the water used by 50 K
700
Water heating
600
Annual Energy Use (kWh)
Motor
500
400
300
200
100
0
US pre2000
US 2007
EU Worst
Category
EU Best
Category
Chinese
impellor
Chinese
drum
Note: the impact of 100% hot-water vs 100% coldwater washing is 3 times greater than shown in the
preceding figure
Clothes Dryers
• Vented (almost all there is in North America)
• Condensing (common in Europe)
• Heat pump (becoming common in some
European countries)
Alternatives
• Clothes line outside (perhaps the simplest and
cheapest form of solar energy!)
• Air drying indoors in winter (common practice in
most European countries)
- as evaporation of water cools the surrounding
air, the heat for drying the clothes comes from
the building space-heating system, but the air is
also humidified
Dishwashers
• An energy-intensive way of washing dishes
compared to water-efficient washing by hand
• Air-drying option minimizes electricity use
Televisions and related equipment
• Energy use depends on
- technology
- size
- hours of use
- standby energy use (when turned off)
- auxiliaries (set-top boxes, DVD players and
_DVRs)
• Annual energy use by auxiliaries alone can
equal the total average per capita residential
electricity use for all purposes in the non-OECD
group of countries (300 kWh/yr)!
Figure 4.68a Power draw by TVs when turned on
Average On Mode Power (Watts)
500
400
LCD
CRT
300
Plasma
200
100
0
0
2000
4000
6000
8000
10000
Screen Area (square cm)
Source: Digital CEnergy (2007, www.energyrating.gov.au/library/pubs/200710-tv-meps-labelling.pdf)
Figure 4.68b Power draw by TVs when turned off
100
LCD
Standby Power (w)
CRT
10
Plasma
1
0.1
0
2000
4000
6000
8000
10000
Screen Size (Square cm)
Source: Digital CEnergy (2007, www.energyrating.gov.au/library/pubs/200710-tv-meps-labelling.pdf)
Figure 4.69 Number of TVs per household
3.0
USA
Japan
2.5
TVs per household
Australia
Canada
2.0
Europe (EU25)
1.5
Brazil
Mexico
1.0
China (urban)
China (rural)
0.5
India (urban)
India (rural)
0.0
1990
1992
1994
1996
1998
2000
2002
2004
2006
Year
Source: IEA (2009, Gadgets and Gigawatts: Policies for Energy Efficiency Electronics, International Energy Agency, Paris)
Figure 4.70 Household TV viewing
Average Daily Household TV Viewing (hours)
0
1
2
3
4
5
6
7
8
United States
Turkey
Italy
Belgium
Japan
Spain
Portugal
Australia**
South Korea***
Canada*
Britain**
Denmark
Finland
Austria
New Zealand
Ireland**
Switzerland
Sweden
Source: OECD (2007, OECD Communications Outlook 2007, OECD, Paris,
www.economist.com/research/articlesBySubject/displaystory.cfm?subjectid=7933596&story_id=9527126)
9
Figure 4.71 Power draw by set top boxes
70
Power Draw (Watts)
60
50
40
30
20
10
0
No Disc
Cable
Disc
No Disc
Satellite
Disc
No Disc
Aerial
Disc
The big opportunities for reducing TV
energy use are
• Improved technology – 40-50% savings possible
• Setting upper absolute limits to the allowed
electricity use (rather than limits in energy use
per cm2 screen area) – which would come close
to setting an upper limit on size – an approach
now adopted in California
• Reductions in standby energy use by TVs and
set-top boxes
• Improving the quality of public space, making
more recreational facilities available (or making
them free) to encourage alternative forms of
entertainment and a healthier lifestyle
Embodied Energy vs
Operating Energy
• Embodied energy is the energy required to
make the materials used in the building, and the
energy used during the construction process.
Include both original construction and ongoing
maintenance and repair
• Operating energy refers to the recurring, annual
energy use for operating the building – heating,
cooling, lighting, and so on
Embodied energy and non-energy
GHG emissions
•
•
•
•
•
Concrete vs wood vs steel construction
Advanced windows
Embodied energy in insulation
Blowing agents used for foam insulation
Demolish and rebuild vs retrofit
Figure 4.74 Building Embodied Energy
Lifecycle Energy Use (German Case) or
2 x Lifecycle Energy Use (Norwegian case)
(kWh/m2)
25000
Operating Energy
Recurring Embodied Energy
20000
Initial Embodied Energy
15000
10000
5000
0
German, 1984 Passive House
code
Norwegian,
1987 code
Low energy
Concrete vs Wood
• Much higher embodied energy and CO2 emissions than
wood
• However, it provides thermal mass – which can be used
to greatly reduce air conditioning requirements if
combined with night ventilation and external insulation
• The analyses of wood vs concrete that I have seen do
not take this into account
• It also absorbs sound, making multi-unit residential
buildings (with their large energy savings potential) more
acceptable
• As there are other ways to get thermal mass (such as
through phase-change materials in drywall) and reduce
sound transmission, wood deserves serious
consideration (the Ontario Building Code now permits
wood buildings of up to 6 stories, from 4, but some argue
that 30-story all-wood buildings would now be safe,
given advances in wood technology)
Advanced windows
• Extra layers of glass, low-e coatings, and argon
between the layers of glass can all be justified from
an energy point of view in regions with cold winters
– the savings in heating energy is many times
(1000s of times in the case of low-e coatings) the
extra energy needed to add these features
• A lot of energy is required to separate krypton from
air, so windows with krypton between the layers of
glass can only be strongly justified if the krypton
makes the windows good enough that perimeter
radiators (which have lots of aluminum in them) can
be eliminated (if they could not otherwise be
eliminated)
Insulation
• Each extra cm of added thickness of insulation
has a diminishing benefit (see Fig. 4.9), but the
energy required to make the insulation increases
in direct proportion to the thickness of insulation
• Thus, at some point (as the thickness of
insulation is increased) the savings in heating
energy due to extra insulation (over its 50-100
year lifespan) will be less than the extra energy
required to make the insulation, and this point
will come sooner the milder the winters
Insulation (continued)
• Fibreglass and foam insulation require a lot of
energy to make (fibreglass is melted sand, foam
insulation is made from petroleum), so this is an
important consideration for these kinds of
insulation
• Cellulose is just recycled newsprint, so the
embodied energy is essentially zero. However,
newsprint and other biomass materials have
energy value as a fuel for heating or
cogeneration, so this energy value should be
included in doing the accounting
The savings in heating energy with successive equal sized
increments is smaller with each successive increment, so
the energy benefit-energy cost ratio decreases
1.0
Walls at R12
(RSI 2.1, U=0.47 W/m2/K)
0.9
Relative Heat Loss
0.8
0.7
Walls at R20
(RSI 3.52,U=0.28 W/m2/K)
0.6
Roof at R32 (RSI 5.6,
U=0.18 W/m2/K)
0.5
0.4
0.3
0.2
Walls (R40, RSI 7.0)
Advanced House: Roof (R60, RSI 10.6)
0.1
0.0
0
10
20
30
40
50
60
R-Value
0
2
4
6
RSI-Value
8
10
Another consideration, for foam insulation, is
the blowing agent used to make the bubbles
in the insulation: these have tended to be
halocarbon gases that are strong
greenhouse gases, and leak from the
insulation over time. The latest (2012) foam
insulation products available use (or could
be using) a new generation of blowing
agents (including some made in part from
soy oil) that have substantially less global
warming effect.
Applications of Foam Insulation
• Structural Insulation Panels
• External Framing and Insulation Systems
(EIFSs)
• Solid Insulation Forms
• Spray-on Foam Insulation
Various Insulation Levels with Structural Insulation Panels
(SIPs), consisting of solid foam insulation, oriented strand
board (OSB) for strength on one or both sides, or some
other finish on one side
Different facings on the insulation
are illustrated here
Different thicknesses (R-values)
Illustrated here (divide by 5.678 to
get RSI value)
Source: Danny Harvey, Green Build 2011 exhibits, Toronto
Example of EIFS (External Insulation Finishing System)
Almost any finish is
Available to go over
the insulation, including
those looking like bricks
Expanded polystyrene
foam insulation
Behind the insulation
is an undulating plate
to permit drainage of
any water that gets
Into the system and
behind the insulation. Thus,
there is an air gap that is
open at the bottom only. If there are any openings at the top,
air will flow behind the insulation, short circuiting the
insulation and rendering it next to useless. Other systems (which
I prefer) have a gap between a separate rain barrier and the
insulation on the outside of the insulation.
Source: Danny Harvey, Green Build 2011 exhibits, Toronto
Solid insulation forms – concrete is poured into the gap.
The white is solid foam insulation that serves as the forms
for the concrete, and remains after the concrete sets
Source: Danny Harvey, 2004 Construct Canada exhibits, Toronto
Use of spray-on foam in difficult-to-reach, irregular
spaces during a renovation
Before
After (not quite finished, wraps around a chimney)
Source: Danny Harvey, Toronto, 2010
Before (left) and after (right). Note the hollow column (which formerly
held acounter-weight) to the left of the triple-glazed window in the
before photo – a horrendous thermal bridge! A gap (not visible) between
the door joist and outside wall is also filled with foam insulation.
Source: Danny Harvey, Toronto, 2010
Before
Source: Danny Harvey, Toronto, 2010
After
Solid-foam insulation example
Source: Danny Harvey, Toronto, 2011
Low-Embodied Energy Insulation
• Cellulose (recycled newsprint, can be
blown in)
• Hemp
• Wood-fibre products
• Recycled blue jeans
Hemp Insulation
Source: Danny Harvey, 2009 Passive House Conference exhibits, Frankfurt
Passive House Levels of insulation on display at the
2009 Passive House Conference in Frankfurt
Full thickness of
insulation under the
entire roof area
(including edges)
Rain barrier
with a gap
behind it
Wood fibre insulation
Cellulose insulation
Source: Danny Harvey, 2009 Passive House Conference exhibits, Frankfurt
Insulation made from recycled blue jeans
Source: Danny Harvey, Green Build 2011 exhibits, Toronto
Demolition and replacement of existing
buildings
• What matters from an energy point of view is how
much energy would be required to make the
materials that would go into the building that would
replace the existing building, not how much energy
was used in the past to make the materials in the
existing building
• If the replacement building is designed to be highly
energy efficient, the energy required to make a new
building will usually be paid back through reduced
annual operating energy use in only a few years
• Thus, from an energy point of view, demolishing old,
energy-guzzling buildings and replacing them with
new, efficient buildings is generally highly favourable
Demolition (continued)
• However, the energy savings through renovation
can often be almost as large as in replacing an
energy-guzzling building with a new building
• For example, with regard to heating, we might go
from 100 units to 20 units through renovation, and
from 100 units to 10 units with replacement. The
renovated building requires twice as much heating
energy as the new building, but the savings is 80/90
= ~ 90% as large
• There are of course other considerations in the
choice of renovation vs replacement, such as
preserving the architectural heritage and reducing
the generation of waste materials
EXEMPLARY BUILDINGS
FROM AROUND THE WORLD
Residential Buildings
The German Passive Standard:
• A heating load of no more than 15 kWh/m2/yr,
irrespective of the climate, and
• A total on-site energy consumption of no more
than 42 kWh/m2/yr
• For cooling-dominated climates, the standard is
a cooling load of no more than 15 kWh/m2/yr
Current average residential
heating energy use:
• 60-100 kWh/m2/yr for new residential buildings
in Switzerland and Germany
• 220 kWh/m2/yr average of existing buildings in
Germany
• 250-750 kWh/m2/yr for existing buildings in
central and eastern Europe
• 150 kWh/m2/yr average of all existing (singlefamily and multi-unit) residential buildings in
Canada
Estimated fuel energy use (largely for heating) in
Canadian multi-unit residential buildings
150
2
Fuel Use (kWh/m /yr)
200
Passive
House
Standard
100
50
)
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To
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o
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ifa
x
0
Climate Comparisons, Heating Season
Heating Degree Days (K-days)
6000
5000
4000
3000
2000
1000
Source: Danny Harvey
i
H
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si
nk
a
Vi
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B
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r
Va
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0
Heating energy requirements of residential buildings built at different
times in the past in various countries, in comparison with the Passive
House standard
Heating Energy Intensity (kWh/m2/yr)
500
Sweden
UK
Germany
Bulgaria
Slovenia
Portugal
Italy
Canada
Australia
400
300
200
100
Passive House Standard
0
1905
1915
1925
1935
1945
1955
1965
Mid-Decade Year
Source: Harvey (2013a)
1975
1985
1995
2005
2015
Saskatchewan House, 1977 – inspiration for
the first Passive House in 1991
Source: The Encyclopedia of Saskatchewan, http://esask.uregina.ca/entry/energy-efficient_houses.html
The first Passive House, Darmstadt, Germany, 1991
Source: Steinmüller (2008), Reducing Energy by a Factor of 10 – Promoting Energy Efficient Housing in the Western
World, http://www.bsmc.de/BSMC-Factor10-WesternWorld.pdf
The first Passive House community,
Weisbaden Lummerlund, 1997
Source: Steinmüller (2008), Reducing Energy by a Factor of 10 – Promoting Energy Efficient Housing in the Western
World, http://www.bsmc.de/BSMC-Factor10-WesternWorld.pdf
Number of dwelling units meeting the
Passive House standard in Austria
12000
New during current year
10000
Number of Dwelling Units
Finished at start of year
8000
6000
4000
2000
0
2000
2001
2002
2003
2004
2005
Year
2006
2007
2008
2009
2010
Occurrence of buildings meeting the
Passive House Standard:
• Several thousand houses have now been built to
and certified (based on measurements after
construction) to have achieved the PH standard
in Germany, Austria and many other countries in
Europe
• The standard has also been successfully
achieved in schools, daycare centres, nursing
homes, gymnasia, a savings bank and a highrise office tower (in Vienna) (so it does not apply
just to houses)
The PH standard is now the legally
required building standard in many cities
and towns in Germany and Austria
• City of Frankfurt: since 2007, all municipal buildings
must meet the standard
• City of Wels, Austria: same thing since 2008
• Vorarlberg, Austria: Passive Standard is mandatory
for all new social housing
• Freiberg, Germany: all municipal buildings must
meet close to the PH standard
• City of Hanover: since 2005, all new daycare
centres to meet the Passive House standard
(resolution only – legal status not clear)
Modern Examples of
Passive House Buildings
The Biotop office building in Austria, with a combined heating+cooling
energy demand of 19.4 kWh/m2/yr.
Two views of the new wing of the Aarhus Municipal building, Denmark, which
is intended to meet the Passive Building standard.
Source: www.buildup.eu/cases/12312
Best Ontario Building (to my knowledge):
EnerModal Engineering headquarters building, Waterloo, Ontario.
Measured heating+DHW: 23 kWh/m2/yr
Measured total onsite energy: 70 kWm/m2/yr
Cost premium: 10%, payback time: 20 years
s
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2
Thermal Energy Intensity (kWh/m /yr)
Thermal energy requirement for U of T student residences
300
250
200
150
100
Passive
Building
Standard
for space
heating
load
50
0
To achieve the Passive House standard on the
heating side requires
• High levels of insulation (U-values of 0.10-0.15
W/m2/K, R35-R60)
• High performance windows (usually TG, double
low-e, argon-filled)
• Meticulous attention to avoidance of thermal
bridges
• Meticulous attention to air-tightness
• Mechanical ventilation with heat recovery
• Attention to building form (achieving the
standard is much easier in multi-unit than single
family housing)
Rule-of-thumb insulation levels required in southern
Canada (in non-metric units) (assuming windows,
thermal bridges, and air sealing are up to the
Passive House standard)
• R10 – below the basement slab and wall footings
• R20 – below-grade basement walls
• R40 – above grade walls (the Ontario Building code
currently requires R32)
• R60 – roof (higher insulation levels are recommended for
the roof not because of hot air next to the ceiling – which
is not an issue in well-insulated houses, which would
have uniform interior temperatures), but because
insulating the roof is cheaper, so higher roof insulation is
part of an optimization that allows less wall insulation)
Passive House level of insulation on display at the 2009
Passive House Conference in Frankfurt
Insulation strips
here reduce the
thermal bridge
around the
window
frame
Insulation
layers
Cross section of the frame of window (imported from
Germany) used in a renovation project in Toronto
Insulated spacer,
low psi-value
Insulation attached
to both parts of
window frame,
reducing the
frame U-value
Outside
From this line
and below
would be excluded
in Canadian
applications
Inside
Two ways of installing a window- which one is a poor way?
(answer is on the next slide)
Insulation
Bricks
Answer:
The installation on the left is poor, because
there is no insulation below the window
frame, so heat can flow from inside to
outside underneath the frame. The
installation psi-value would be large, as
there is a large thermal bridge.
The window should be aligned with the
insulation, as in the figure on the right.
A Zero Net Energy project in 2010 – correction of the errors in this design
(windows not centred over the insulation, thereby creating a huge thermal
bridge) throughout the project would have allowed elimination of several
$1000 in PV panels while still giving net zero energy, at much less cost
Source: Malcolm Isaacs, Canadian Passive House Institute
Complicated roof structures
• Are more expensive to build
• Create a large surface-to-volume ratio,
which will leads to greater heat loss for a
given house volume and roof and wall Uvalues
• Add lots of potential and actual thermal
bridges, which are other sources of heat
loss
Potential thermal bridges
Source: Danny Harvey, Toronto
This slide shows that buildings with a simpler shape cost a lot less to build than
buildings with more complex shapes. The simpler shape also makes it easier to
achieve the Passive House standard. So, if in striving to meet the Passive
Standard we adopt a simpler building shape, the net result can be that building
to the Passive House standard can cost no more than regular construction.
(The shape factor is just the surface: volume ratio (m2/m3))
Source: Smutny et al. (2011)
Recall: buildings with a simpler shape
save energy by
• Reducing the surface area for a given building
volume
• Reducing the number of thermal bridges
• Making it easier to make the building air tight (by
having fewer joints that need to be sealed)
Thermallyseparated
balconies in
Frankfurt
Source: Danny Harvey
Supplemental figures: High school
example: Grandschule in Riedberg,
Frankfurt
South facade
Source: Danny Harvey
Triple-glazing throughout, maximized passive solar heat gain
Source: Danny Harvey
Retractable external shading
Source: Danny Harvey
Passive ventilation and night-time cooling; mechanical
system shut off from ~ early May to end of September
Source: Danny Harvey
Heating required during the winter for only a couple of
hours Monday mornings, using two small biomass-pellet
boilers
Source: Danny Harvey
High Performance New
Commercial Buildings
Trends in energy use of new commercial buildings in California, complying with
various versions of the ASHRAE-90.1 building code
1.2
75% reduction:
Representative of
the improvement
needed everywhere
for a global zeroCO2 emission
scenario
Relative Energy Use
1.0
0.8
0.6
?
0.4
0.2
0.0
Stock
average
1999
2004
2007
Year of Construction
2010
2014
2020
Some illustrative factoids
• The average energy intensity of Canadian and
northern US hospitals is about 850 kWh/m2yr; that of
the most efficient new hospital in Sweden is 150
kWh/m2yr
• Under current regulations, the heating energy
requirement for an office building in Atlanta is 80%
that of the same building in Chicago
• In Chicago, the heating energy requirement in winter
of a high-performance office building is ¾ that of the
summer heating requirement of the worst legal
design and 1/6 that of the winter heating
requirement of the worst design
Simulated heating Energy Use in a Chicago office building
Source: Lin and Hong (2013, Applied Energy 111:515-528)
Modern commercial buildings (such as office
buildings) in most parts of the world have an
energy use of 200-500 kWh/m2/yr. I have
been advocating a standard (maximum
allowed used) of 100 kWh/m2/yr for most
types of new buildings. Case studies
showing that this can be achieved, and an
explanation of how, are contained in the
following slides.
Hot Dry
Mild
Seattle, WA
Kirkland, WA
Baraboo, WI
Provincetown, MA
Cold
Weston, MA
St Paul, MN
100
Golden, CO
Harrisburg, VT
Ferry, PA
Cambria, PA
Chicago, IL
Seaside, CA
San Diego, CA
120
New Haven, CT
Hot Humid
Overland, MO
Arlington, VA
Houston, TX
Atlanta, GA
Energy Intensity (kWh/m2/yr)
Case studies of low-energy new buildings in the
US (from the New Buildings Institute web site)
140
Other
DHW
Pumps & Fans
Lighting
Cooling
Heating
80
60
40
20
0
Iowa Association of Municipal Utilities Office Building –
energy use according to standard design (“Reference”),
estimated energy use (“Design”) and measured energy use
250
Equipment
Lighting
Fan/Pump
Cooling
Heating
HVAC
Energy Intensity (kWh/m2/yr)
200
150
100
50
0
Reference
Design
Measured
2002-07
Measured
2008-09
LEO (Low Energy Office) Building, Malaysia
(computer simulation study)
Reference
Add daylighitng
Add Insulation
Add EE lighting
Add EE equipment
Cooling
Lighting
Pumps, fans, equipment
Total
Add energy
management
Increase room temp 1 K
Reduce leakage
0
50
100
150
200
250
Energy Intensity (kWh/m2/yr)
This figure is an enhancement of Fig 4.81
300
Shanghai Eco-Building (simulation study)
Reference
Add window
shading
Cooling
Heating
Add advanced
glazing
Add more insulation
Add natural
ventilation
0
This figure is an enhancement of Fig 4.82
50
100
150
Energy Intensity (kWh/m2/yr)
200
Centre for Environmental Sciences and
Engineering, Kanpur, India (simulation study)
Reference
Orientation,
envelope
Lighting
improvements
HVAC equipment
HVAC controls
Earth pipe
0
50
100
150
200
Energy Intensity (kWh/m2/yr)
250
300
Energy intensity for baseline and low-energy designs
of two office buildings (GEO and JKR) in Malaysia
Reduction in cooling loads (the amount of heat that needs
to be removed by the chiller) in the JKR office building
2000
Reference building
Case study building
Average Heat Gain (kW)
1500
1000
500
0
To achieve ultra-low-energy office
buildings requires
• Attention to building form, glazing fraction,
thermal mass (all four facades will not be
identical!)
• Attention to insulation levels and glazing
properties
• Provision for passive ventilation (even in 50story office towers), daylighting, heat recovery
• Almost mandatory use of demand-controlled
displacement ventilation with radiant slab
heating and cooling
• Lots of attention to control systems
In complex buildings, the usual largely
linear design process needs to be
replaced with the Integrated Design
Process (IDP), in which
• The building is treated as a system
• Architects, engineers of various sorts, and
specialists get together at the very beginning of
the design process
• Multiple options for achieving deep energy
savings are considered, then tested with building
computer simulation specialists in order to find
the optimal solution
Figure 4.79a Conventional design process when
client will not occupy the building
Level 1:
Building design proc ess
Client
Architect
Engineers
Contractors
Government
Source: Hien et al (2000, Building and Environment 35, 709-736, http://www.sciencedirect.com/science/journal/03601323)
Figure 4.79b Conventional design process when
the client will occupy the building
Level 2:
Building design proce ss
Client
Architect
Engineers
Contractors
Government
Source: Hien et al (2000, Building and Environment 35, 709-736, http://www.sciencedirect.com/science/journal/03601323)
Figure 4.79c Integrated Design Process
Level 3:
Dy namic inte gration in design proce ss
Client
Architect
Engineers
Contractors
Simulation team
De sign Te am
Government
Source: Hien et al (2000, Building and Environment 35, 709-736, http://www.sciencedirect.com/science/journal/03601323)
Source: Montanya et al (ASHRAE Journal,
July 2009, p30-40)
Core team assembled at the beginning of a
project
Source: Pope and Tardiff (2011, ASHRAE Transactions 117, pp433-440)
Participants in the integrated design process
Source: Pope and Tardiff (2011, ASHRAE Transactions 117, pp433-440)
Integrated Design Process: Principles
• Consider building orientation, form, shape,
thermal mass and glazing fraction
• Specify a high-performance thermal envelope
• Maximize passive heating, cooling, ventilation
and day-lighting
• Install efficient systems to meet remaining loads
• Ensure that individual energy-using devices are
as efficient as possible and properly sized
• Ensure that systems and devices are properly
commissioned
Sample Work Load in the IDP
Source: Pope and Tardiff (2011, ASHRAE Transactions 117, pp433-440)
CASE STUDIES OF NEW
BUILDINGS WITH NATURAL
VENTILATION AND EARTHPIPE COOLING
Deutches Post Headquarters
• 45 stories high with double skin façade to
permit natural ventilation
• Big savings in air conditioning and
ventilation energy use
• Heating load is large compared to the
Passive House standard, but small
compared to typical buildings in spite of a
largely all-glass facade
Wind Catchers in Israel
Source: MED-ENEC (Energy Efficiency in the Construction Sector in the Mediterranean) website,
www.med-enec.com, under pilot projects, Israel
Source: MED-ENEC (Energy Efficiency in the Construction Sector in the Mediterranean) website,
www.med-enec.com, under pilot projects, Israel
Wagner KfW Bank
Airflow
Declining energy use during the 1st few years as
the systems are adjusted
Case study buildings from the German Research
for Energy-Optimized Construction (EnOB)
program. Web site: www.enob.info/en
Energon Passive Office, Ulm, 21.7 kWh/m2/yr measured heating +
DHW demand, 67 kWh/m2/yr total onsite demand (a typical German
office building is around 280 kWh/m2/yr and a typical Canadian office
building is around 350 kWh/m2/yr total energy demand)
Intakes for
ground
conditioning
of ventilation
air
Lamparter Passive Office (17.9 kWh/m2/yr measured heating
+ DHW energy use, 125 kWh/m2/yr primary energy use)
Earth-pipe
intakes
Wagner Passive Office with hot water storage of summer solar heat for
use in the winter, 23.1 kWh/m2/yr measured heating+DHW energy use
and 66 kWh/m2/yr primary energy use
Clerestory windows
for daylighting
Hot water tank
Solar
thermal
collectors
Hot water tanks, earth-pipe for
ventilation air,
solar thermal collectors
Centre for Interactive Research in Sustainability (CIRS)
building, UBC, Vancouver – Net Energy Positive
Extra Cost of Ultra-Low Energy Buildings
• Residential – aiming for the Passive House standard can
increase cost by 5-10% if an otherwise identical building
is built
• Residential – with simplifications to the design,
residential buildings have now (in Europe) been built to
the Passive House standard at no extra cost
• Commercial – due to savings in costs of greatly
downsized mechanical systems, low-energy buildings
can cost no more than conventional buildings, or have
such small additional costs (1-2%) that the extra cost I
paid back within a few years.
Cost of conserved energy (CCS) for low-energy
residential buildings in Europe
0.15
Individual case studies
Audenaert, SFH, Belgium
CCE (2010US$/kWh)
Morrisey, SFH, Australia
Georges, SFH, Belgium
0.10
Aste MFH. Italy
Kurnitski, SFH, Estonia
0.05
0.00
0
50
100
150
2
Energy Savings (kWh/m yr)
200
Figure 4.78 Progressive decrease in cost with learning.
Extra costs are about 5% of the construction cost in Europe,
and about 10% of the construction cost in Canada.
Additional Investment (€/m2) of Passive Row Houses
350
1991 Prototype: experimental house,
4 dwellings in Kranichstein using
handicraft batch production
300
PH in Groß-Umstadt:
Reduced costs by
simplification
250
200
Row houses in Darmstadt,
80 €/m2
150
Settlement in Wiesbaden:
Serially produced windows
& structural elements
100
Settlements in Wuppertal,
Stuttgart, Hanover
50
Profitability with
contemporary
interest rates & energy prices
2010
2009
2008
2007
2006
2005
2004
2003
2002
2001
2000
1999
1998
1997
1996
1995
1994
1993
1992
1991
1990
0
Source: Feist (2007, Conference Proceedings, 11th International Passive House Conference
2007, Bregenz, Passive House Institute, Darmstadt, Germany, 383-392)
This slide shows that buildings with a simpler shape cost a lot less to build than
buildings with more complex shapes. The simpler shape also makes it easier to
achieve the Passive House standard. So, if in striving to meet the Passive
Standard we adopt a simpler building shape, the net result can be that building
to the Passive House standard can cost no more than regular construction.
(The shape factor is just the surface: volume ratio (m2/m3))
Source: Smutny et al. (2011)
Table 4. 20 Comparison of component costs for a building with a conventional VAV mechanical
system and conventional (double-glazed, low-e) windows with those for a building with radiant
slab heating and cooling and high-performance (triple-glazed, low-e, argon-filled) windows,
assuming a 50% glazing area/wall area ratio. Costs are in 2001 Canadian dollars for the
Vancouver market in 2001, are given per m 2 of floor area, and are based on fully costed and built
examples over a 3-year period. Source: Geoff McDonell (Omicron Consulting, Vancouver),
personal communication, December 2004, and McDonell (2003).
Building Component
Conventional Building
High-performance Building
2
Glazing
$140/m
$190/m2
Mechanical System
$220/m 2
$140/m2
Electrical System
$160/m 2
$150/m2
Tenant finishings
$100/m 2
$70/m2
Floor-to-floor height
4.0 m
3.5 m
2
Total
$620/m
$550/m 2
Energy Use
180 kWh/m2/yr
100 kWh/m2/yr
Table 4. 22 Energy savings relative to ASHRAE 90.1 -1999 and cost
premium for buildings meeting various levels of the LEED standard in the
USA. Source: Kats et al. (2003).
LEED
Sample
% Energy Savings, Based on
Cost
Level
Size
Premium
Gross Energy Use
Net Energy Use
Certified
8
18
28
0.66 %
Silver
18
30
30
2.11 %
Gold
6
37
48
1.82 %
Table 4.23 Economics of the new Oregon Health and Science
University building. Source: Interface Engineering (2005).
Item
Total project cost
$145.4 million
Energy efficiency features
$975,000
PV system
$500,000
Solar thermal system
$386,000
Commissioning
$150,000
Total
$2,011,000
Savings in mechanical systems
$3,500,000
Value of saved space
$2,000,000
Net cost
-$3,489,000
Estimated annual operating cost savings
$600,000
Extra Cost of New Ultra-Low Energy Buildings
• Residential – aiming for the Passive House standard can
increase cost by 5-10% if an otherwise identical building
is built
• Residential – with simplifications to the design,
residential buildings have now (in Europe) been built to
the Passive House standard at no extra cost
• Commercial – due to savings in costs of greatly
downsized mechanical buildings, low-energy buildings
frequently cost no more than conventional buildings, or
have such small additional costs (1-2%) that the extra
cost is paid back within a few years.
DEEP RETROFITS OF
EXISTING BUILDINGS
Terminology
• The term “retrofit” refers to the deliberate
upgrading of the building envelope or systems
some time after the building has been built
• The term “renovation” refers to the renewal of
building components in response to deterioration
over time, and may or may not be accompanied
by an improvement in the performance levels
• The ideal will be to perform a significant retrofit
when routine renovations are required anyway,
as this will greatly reduce the cost of the energy
efficiency upgrade
Retrofits of existing buildings
•
•
•
•
•
•
Insulation
Windows
Air sealing
Mechanical systems
Lighting
Solar measures
Renovations to the Passive House
Standard (15 kWh/m2/yr heating load)
• Dozens carried out in old (1950s, 1960s) multiunit residential buildings in Europe, resulting in
80-90% reduction in heating energy use
• Two examples will be shown here:
-BASF buildings in Ludwigshafen, Germany
- apartment block in Dunaújváros, Hungary
Figure 4.83 BASF retrofit, before and after
Source: Wolfgang Greifenhagen, BASF
Figure 4.84 BASF retrofit (a) installation of external insulation, (b)
installation of plaster with micro-encapsulated phase change materials
Source: Wolfgang Greifenhagen, BASF
Figure 4.85 Renovation to the Passive House
Standard in Dunaújváros, Hungary. Before:
Source: Andreas Hermelink, Centre for Environmental Systems Research,
Kassel, Germany
After:
Source: Andreas Hermelink, Centre for Environmental Systems Research,
Kassel, Germany
Net result:
• 90% reduction in heating energy use – this
saves natural gas that can be used to generate
electricity at 60% efficiency (or even higher
effective efficiency in cogeneration), thereby
serving as an alternative to new nuclear power
plants
• Problems of summer overheating were greatly
reduced
• A grungy, deteriorating building was turned into
something attractive and with another 50 years
at least of use
In Toronto and some other North
American cities
• There are opportunities for similarly large
reductions through retrofitted old 1960s and
1970s apartment towers
• Single-family houses will be harder and more
expensive, but are doable
• But what will we do with all the glass
condominiums and office towers being built
now?
Table 4.34 Current and projected energy use (kWh/m2/yr) after various
upgrades of a typical pre-1970 high-rise apartment building in Toronto.
Measure
Current building
Roof insulation
Cladding upgrade
Window upgrade
Balcony enclosure
All of the above
Boiler upgrade
HRV
Water conservation
Parkade lighting
All of the above
Above with 50% less
tenant electricity
Natural Gas
Heating
DHW
203
36
184
36
167
36
122
36
122
36
47
36
118
36
136
36
203
25
203
36
9.4
25
24.1
25
Electricity
71
70
69
64
68
64
70
68
70
70
59
Primary
Energy
443
420
398
336
345
252
347
362
430
440
185
29
128
Cost
($/m2)
Payback
(years)
IRR
(%/yr)
13
44
73
121
199
23
17
5
0
257
11.4
18.1
13.5
21
18.6
5.5
7.8
3.4
4.4
16.9
11.3
3.4
9.2
4.3
5.6
23
25.8
35.1
28
6.7
DHW=domestic hot water, IRR=internal rate of return,
HRV=heat recovery ventilator.
Karlsruhe High rise, before and after renovation
(measured energy requirement for heating+DHW dropped
from 115 kWh/m2/yr to 61 kWh/m2/yr)
Source: http://www.enob.info/en/refurbishment/
Figure 4.86 Prefabricated replacement roof for a residential
building in Zurich, Switzerland
Source: Zimmermann (2004, ECBCS News October 2004, 11–14, www.ecbcs.org)
Figure 4.87 VIP
Dormer Retrofit
Source: Binz and Steinke (2005,
7th International Vacuum Insulation
Symposium, EMPA, Duebendorf,
Switzerland, 28–29 September, p43–48,
www.empa/ch/VIP-Symposium )
Examples of installation of
external insulation in retrofit projects as part of
the EnOB (Energy Optimized Building)
program in Germany
Construction
of pre-fabricated
window-wall units
in a factory – allows
for quality
assurance
Source: http://www.enob.info/en/refurbishment/
Installation of external pre-fabricated unit
over the pre-existing wall (Hofheim pilot project)
Source: http://www.enob.info/en/refurbishment/
External vacuum-insulation
panels are shown here
Source: http://www.enob.info/en/refurbishment/
Before and after photos of the previous project (each of the
three buildings was insulated to a different
standard, so as to provide a basis for comparing
costs and benefits)
Source: http://www.enob.info/en/refurbishment/
Energy savings from building retrofits
Source: Harvey (2013a)
From the Retrofit For the Future database in the UK: Comparison of projected
energy intensity after a retrofit vs measured energy intensity before (ongoing
monitoring to verify or refute the projected savings is occurring). About half the
buildings are expected to achieve a factor of 2-4 reduction in energy use, and
half are expected to achieve a factor of 4-10 reduction. This is what we need
for “sustainability”!
No
Savings
2
Final Primary Energy Intensity (kWh/m /yr)
500
400
Factor of 2
reduction
300
Factor of 4
reduction
200
Factor of 10
reduction
100
0
0
500
1000
1500
2
Initial Primary Energy Intensity (KWh/m/yr)
2000
ur
si
ng
ho
m
e
Sc
h
en
oo
tr
l
Se
es
co
id
en
nd
ce
ar
P
y
rin
sc
tin
ho
g
ol
H
co
*
ig
hm
ri
pa
se
ny
D
ou
re
*
si
bl
de
enc
fa
m
e*
ily
ho
us
Ro
e*
w
ho
us
in
Sp
g
or
ts
ha
ll*
Li
br
ar
y
S
ch
D
ay
oo
ca
l*
re
C
en
tr
e
S
tu
d
N
Heating+DHW Energy Intensity (kWh/m2 /yr)
Comparison of before and after heating+DHW for buildings
retrofitted in Germany under the EnOB Program
300
250
Before renovation
After renovation
200
150
100
50
0
Retrofit Costs
Cost of conserved energy for residential retrofits
0.25
Canada
0.20
China
CCE (2010US$/kWh)
Europe, case studies
Europe, simulated
architypes
Europe, Voralberg case
studies
Ireland, average of 318
projects
US cases
0.15
0.10
0.05
0.00
0
50
100
150
200
Energy Savings (kWh/m2yr)
250
300
Cost of conserved energy of commercial building retrofits
CCE (2010US$/kWh)
0.12
Canada
China
Europe
US
0.08
0.04
0.00
0
50
100
150
Energy Savings (kWh/m2yr)
200
250
Recall: Table 4.34 Current and projected energy use (kWh/m2/yr) after
various upgrades of a typical pre-1970 high-rise apartment building in
Toronto.
Measure
Current building
Roof insulation
Cladding upgrade
Window upgrade
Balcony enclosure
All of the above
Boiler upgrade
HRV
Water conservation
Parkade lighting
All of the above
Above with 50% less
tenant electricity
Natural Gas
Heating
DHW
203
36
184
36
167
36
122
36
122
36
47
36
118
36
136
36
203
25
203
36
9.4
25
24.1
25
Electricity
71
70
69
64
68
64
70
68
70
70
59
Primary
Energy
443
420
398
336
345
252
347
362
430
440
185
29
128
Cost
($/m2)
Payback
(years)
IRR
(%/yr)
13
44
73
121
199
23
17
5
0
257
11.4
18.1
13.5
21
18.6
5.5
7.8
3.4
4.4
16.9
11.3
3.4
9.2
4.3
5.6
23
25.8
35.1
28
6.7
DHW=domestic hot water, IRR=internal rate of return,
HRV=heat recovery ventilator.
Comments on Retrofit Costs
• Generally lower CCE for commercial buildings
than for residential buildings
• For residential buildings in Europe, costs are
fairly modest up to about 75% savings, but
increase sharply after that.
• Refrofitting 1960s and 1970s apartment
buildings in Toronto to 90% heating energy
savings is profitable (at least according to one
analysis)
• In these buildings, putting heat recovery on the
ventilation exhaust air is highly profitable
Solar Retrofits
• Double-skin facades (protects deteriorating
original facade from further deterioration)
• Enclosure of balconies (so that they no longer
serve as radiator fins)
• Transpired solar collectors
Figure 4.88 Telus Retrofit, Vancouver
Source: Terri Meyer-Boake, School of Architecture, University of Waterloo, Canada
Figure 4.89 Solar renovation in Zurich
Source: Zimmermann (2004, ECBCS News October 2004, 11–14, www.ecbcs.org)
Figure 4.90 Transpired solar collector (“Solarwall”) on
an apartment building in Windsor, Canada
Source: www.solarwall.com