Transcript Low Energy Housing An Overview - University of Strathclyde

Low Energy Housing
An Overview
Dr Nick Kelly
Energy Systems Research Unit (ESRU)
Mechanical Engineering
University of Strathclyde
Content
• Housing and Energy Consumption
• Legislating for Better Performing Housing
– What is a Low Energy House?
– PassivHaus
• Zero Energy/Carbon Housing
– Case Studies
– Simulations
• Implications of Zero Carbon Housing
– LV Network
– Heat Networks
Housing and Energy
•
The domestic sector in the UK accounts for
almost 37% of final energy consumption
•
The majority of energy consumed is for space
and water heating, not electricity
•
The energy efficiency of the bulk of the housing
stock is poor with an average SAP rating of 52
[scale of 1-100]
•
Generally the older the building the poorer the
energy performance: ~70% of the UK housing
stock is pre-1970
•
There is significant scope for energy efficiency
improvements with savings in space heating of
up to 90% achievable
Improving Energy Efficiency
•
There have been various pieces of EU-wide legislation
to improve the energy performance of housing (and
buildings in general) in an attempt to mitigate their
GHG emissions
–
Energy Performance in Building Directive (2002)
–
Energy Efficiency Action Plan (2006)
–
End-use Efficiency and Energy Services Directive (2006)
•
These have been implemented at a sub-national level
through mechanisms such as the building regulations
(England, Scotland, Wales and Northern Ireland)
•
The UK has been active in developing its own targets
(Energy White Papers 2003, 2007), Climate Change
Act (2008); all made clear that radical improvements in
domestic energy efficiency was key to achieving deep
carbon reductions (80% by 2050)
Improving Energy Efficiency
Austria
•
•
The EPBD was a
milestone in energy
conservation legislation
and set out minimum
energy performance
targets for buildings
Many EU member
states have gone
beyond the EPBD and
set out their own criteria
for low-energy buildings
Belgium (Flanders)
Czech Republic
Denmark
Finland
France
Germany
UK (England & Wales)
UK (Scotland)
Low energy building defined as annual heating energy consumption below 60-40
KWh/m², 30 % above standard performance.
Passive building defined as 15 kWh/m²
Low Energy Class 1 for houses: 40 % lower than standard levels, 30 % lower for office
and school buildings.
Very low Energy class: 60 % reduction for houses, 45 % for schools and office buildings.
Low energy class: 51 – 97 kWh/m2 p.a. Very low energy class: below 51 kWh/m² p.a.,
also passive house standard of 15 kWh/m2 is used.
Low Energy Class 1 = calculated energy performance is 50% lower than the minimum
requirement for new buildings
Low Energy Class 2 = calculated energy performance is 25% lower than the minimum
requirement for new buildings (i.e. for residential buildings = 70 + 2200/A kWh/m² per
year where A is the heated gross floor area, and for other buildings = 95+2200/A
kWh/m² per year (includes electricity for building integrated lighting)
Low energy standard: 40 % better than standard buildings
New dwellings: the average annual requirement for heating, cooling, ventilation, hot
water and lighting must be lower than 50 kWh/m² (in primary energy). This ranges
from 40 kWh/m² to 65 kWh/m² depending on the climatic area and altitude. Other
buildings: the average annual requirement for heating, cooling, ventilation, hot water
and lighting must be 50% lower than current Building Regulation requirements for new
buildings
For renovation: 80 kWh/m² as of 2009
Residential Low Energy Building requirements defined as 60kWh/m² or maximum
energy consumption.
Passive House standard defined as 40 kWh/m² buildings with an annual heat demand
lower than 15 kWh/m² and total consumption lower than 120 kWh/m²
Graduated minimum requirements over time:
 2010 level 3 (25% better than current regulations)
 2013 level 4 (44% better than current regulations and almost similar to
PassivHaus)
 2016 level 5 zero carbon for heating and lighting.
 2016 level 6 zero carbon for all uses and appliances.
Graduated requirements over time (Sullivan, 2008):
 2010 a 30% reduction in regulated energy uses (excludes appliances);
 2013 a 60% reduction(proposed);
 2017 a 100% reduction (proposed); and
 zero lifecycle carbon buildings by 2030 (proposed).
PassivHaus
•
The PassivHaus standard is gaining popularity
around Europe as a benchmark for energy
efficient buildings
•
The requirements for a Northern European
PassivHaus are:
–
very high levels of insulation (wall U-values less than 0.15
W/m2K);
–
high-quality building construction (thermal bridge free, airtightness of construction better than 0.6 air changes per
hour [ACH] measured at 50 Pa with ventilation openings
closed, equivalent to 0.03 ACH under normal conditions);
–
high-performance glazing (U-value less than 0.85 W/m2K
including installation, frame and glazing edge losses, solar
transmittance greater than 50%);
–
a high efficiency ventilation system with heat recovery
(MVHR);
–
construction mass, ventilation openings, thermal capacity
and shading designed for comfortable summer
temperatures; high efficiency appliances and lighting.
Zero Carbon Housing
• The PassivHaus standard focuses
on reducing energy demand
• Whilst microgeneration can be
integrated with a PassivHaus their
contribution is not counted
• A step beyond PassivHaus is to
offset the energy demand of the
building using local zero-carbon
generation
Zero Energy/Carbon Housing
• What does zero energy or zero carbon mean? There are multiple
definitions:
– Autonomous Zero Energy Buildings – all demand are met by on-site
generation, no external network connections
– Net-zero site energy – local generation completely offsets on-site demand,
demand and supply are not temporally matched but balance over a year
– Net-zero source energy - local generation completely offsets primary energy
demands, demand and supply are not temporally matched but balance over a
year
– Lifecycle net-zero energy buildings - local generation completely offsets
primary energy demands AND embodied energy, demand and supply are not
temporally matched but balance over the lifetime of the building
– NB For a building to be zero carbon (as opposed to just zero energy) then the
local generation needs to be carbon free: e.g. PV, solar thermal, biomass,
SWEC
Zero Carbon Housing
Standards
• England and Wales have been one of the first areas in Europe to develop
specific zero carbon standards for new homes
• Code for Sustainable Homes (CSH) (DCLG, 2008a) defined voluntary
levels of performance (Codes 1 to 6)
• Two of these levels are described as zero-carbon buildings:
– Code 5 equates to a 100% reduction in regulated energy use, with these
being offset by renewable heat and power generation. Energy use from
appliances is not offset (so-called unregulated energy use).
– Code 6 proposed zero-carbon for all energy use including appliances by
2016. This equates to a 140% reduction in calculated regulated energy uses
such as heating and cooling (i.e. 100% reduction in regulated energy use plus
40% from local electrical generation technologies such as PV to offset the
unregulated energy use by appliances)
Zero Carbon Housing
Standards
•
To encourage the development of a zerocarbon housing market, the UK Government
has announced a tax incentive for new zerocarbon buildings to become effective in 2016
•
There is also a feed-in tariff (FIT) for smallscale renewable electricity generation and a
proposed renewable heat incentive (RHI) to
replace the defunct low-carbon building
programme
•
Technologies covered under the FIT include
PV, CHP and SWECs
•
Note there is growing doubt as to whether the
RHI will actually appear
Supply Technologies
Electrical
Thermal
Despatchable
Microhydro
CHP
Biomass
boiler
storage +
storage +
storage +
Non despatchable
SWECS
PV
Heat
Pump
Solar
thermal
Supply Technologies
Supply Technologies
Supply Technologies
Supply Technologies
Supply Technologies
Supply Technologies
ZCH: Examples
BedZED, UK (2002)
•
The Beddington Zero Energy Development
(BedZED) project in Hackbridge, London was an
attempt to create a zero-energy community
•
Consisted of 99 super-insulated dwellings of
various sizes, workspaces and community facilities.
•
on-site zero-carbon generation provided by a
prototype 120kWe wood-waste fuelled combined
heat and power (CHP) system with 777m2 of
photovoltaic panels
•
designed to meet all of the energy demands of the
residents along with providing the potential to
power up to 40 electric vehicles at some future
date.
ZCH: Examples
•
Monitoring indicated:
– that space heating demand was 90% lower than the UK average
– electrical power consumption for appliances and lighting was 33%
lower than average, however this was still higher than anticipated due
to residents using back-up electrical water heating
•
The development did not achieve zero-carbon operation, primarily due to
the fact that the prototype biomass CHP system was unreliable and never
operated effectively (it was shut down in 2005)
•
The remaining PV system only offset around 20% of the total energy
demands of the community with the remainder being drawn from external
supplies
ZCH: Examples
Portland House, Australia (2009)
•
Demonstration family dwelling in Portland Victoria
with a super-insulated and tightly sealed fabric,
thermal mass and a cooling tower (promoting
stack ventilation) for summer cooling
•
All appliances in the dwelling were low-energy
•
Energy was provided by a 1.4kW PV installation
and 3 solar thermal panels augmented with an
electric back-up heater were used to meet the
dwellings’ hot water demands
•
A reversible heat pump met the dwelling’s small
space heating and cooling requirements.
ZCH: Examples
•
Monitoring over the period September 09 to June 10 indicated that the PV
installation provided 93% of the dwelling’s electrical energy consumption
•
Note that this period did not cover all of the winter months and it is likely that
the quantity of imported electricity will be slightly greater over the course of
a full year.
•
The developers have since indicated that the PV installation is due to be
doubled in size to a capacity 2.8kW. Given the current performance, this is
likely to turn the building into a net electricity exporter.
ZCH: Examples
Wheat Ridge, Colorado (2005)
•
The Habitat for Humanity home in Wheat Ridge,
Colorado is a 119m2 super insulated dwelling e.g.
the building features low-e solar glass with argon
fill and a U-value of 1.14W/m2K
•
Renewable heat provided by a 9m2 solar collector
with a 760 l thermal store, backed up by a gas-fired
water heater
•
Renewable electricity provided by a 4 kWp roof-top
PV system
•
The building also features a mechanical ventilation
system with heat recovery.
ZCH: Examples
•
Monitoring indicated that during the period April 2005 to the end of March
2007, the PV system produced an excess of 1542 kWh
•
Gas consumption for the water heater amounted to some 1670 kWh.
•
The net site energy requirement for all fuels of the home was approximately
0.6 kWh/m2/year.
ZCH:Lessons?
•
From the evidence of the case studies achieving
zero-carbon operation is not straightforward!
•
A building designed to be zero-carbon does not
necessarily perform as zero carbon
•
Most fail to achieve this due to 1) under-prediction
of demands at the design stage 2) over-prediction
of energy yields from renewables or 3) poorly
performing equipment in-situ
•
PV seems to be the ubiquitous option for electricity
generation
•
Most achieve significant reductions in thermal
demand … less success with curbing electrical and
demands
ZCH: Simulating Performance
•
In addition to data emerging from the limited
number of demonstration “zero-carbon”
buildings simulation can provide useful
performance information
•
This study investigated a typical detached
dwelling with a floor area of 136m2. The building
was assumed to be occupied by a family of 4 in
which the parents work;
•
Occupancy was therefore intermittent;
•
The building performance was assessed for a
Scottish West-coast climate.
•
NB The mechanics of building simulation will be
covered in more detail in the next presentation
ZCH: Simulating Performance
•
modelling indicated that for the detached
house to achieve the 140% reduction target as
set out in the Code for Sustainable Homes
required the following measures:
– 46m2 PV electrical generation (approx 6 kWp)
– passive house building envelope
– high efficiency mechanical ventilation heat
recovery (MVHR)
– 4m2 Solar thermal panels
– 2kW Biomass heating
– high A+ rating efficiency appliances
– high efficiency lighting
ZCH: Simulating Performance
•
To illustrate the change in energy performance of housing, a comparative
simulation was undertaken with the proposed zero-carbon house and a more
conventional dwelling (built in UK post 1997)
2
External walls W/m K
2
Floor W/m K
2
Ceiling W/m K
2
Glazing W/m K
Average
uncontrolled
infiltration ACH
Heating
Base Case Dwelling
0.45
0.6
0.25
2.10
0.5
Zero Carbon Dwelling
0.11
0.10
0.13
0.70
1
0.03
Gas boiler + radiators
Biomass boiler + heating coil
in MVHR
•
Dynamic simulation of the building energy flows over a 1-year period @ 10
minute time intervals, west coast climate (solar radiation, temperature, wind
speed, wind direction), pre-defined occupant and equipment heat gains,
control settings (on/off times, set point temperatures), etc.
•
Produces large volumes of time series data: temperatures; heat fluxes,
electrical production (PV), etc.
ZCH: Simulating Performance
ZCH: Simulation Results
•
Aggregating the data from the simulation gives the following annual
performance characteristics
Heating demand kWh
Hot water heating demand kWh
Electrical Demand kWh
Total Demand kWh
PV Output kWh
Solar Thermal Output kWh
Biomass boiler Output kWh
Total Production kWh
Base Case Dwelling
3083
2342
5776
11201
-
Zero Carbon Dwelling
372
1850
3240
5462
5023
1709
1172
7904
ZCH: Simulating Performance
ZCH: Analysis
•
•
•
•
•
•
•
Dramatic reduction in demand for space heating, dropping from 3083 to 372 kWh
The heat-to-power ratio of the simulated dwelling shifts from 1:1 in the base case dwelling to
0.7:1 in the zero carbon dwelling
The calculated electrical demand reduces from 5776 to 3240 kWh (due to the adoption of
high efficiency appliances)
The modelled electrical demand for the zero carbon dwelling also indicated a drop in peak
demand of around 10%
The addition of 6kWp of PV generation to the simulated dwelling gives rise to striking
seasonal variations in electrical energy flows: in winter 768 kWh of electrical energy is
imported, whilst in summer a total of 1,756 kWh if exported to the network
There are also significant daily variations. For example, on an average summer day, a peak
electrical demand of 4 kW occurs in the morning. By mid-day this has changed to a peak
electrical output of 5 kW
The variability in solar hot water production is as pronounced with 40kWh produced by the
solar collectors in January, offsetting around 18% of the total thermal demand compared to
219kWh in June, which exceeds the total thermal demand in the zero carbon dwelling.
ZCH: Analysis
Implications?
•
The dramatic reduction in demand for space heating
raises questions as to how space heating could be
provided in future dwellings.
– Often in current UK dwellings, low space heating
demands in premises such as flats have tempted
developers to install low-cost technologies such as
electric resistance heating or storage heating.
– Any move to electrically-based heating technologies will
further change the energy demand patterns of zero
carbon dwellings as heating energy loads are displaced
from the gas grid to the electrical grid
•
Thermal energy demands for the zero carbon dwelling
shift from space heating to hot water
– This offers an opportunity for load shifting with regards
to when heating is provided – a particularly useful
feature if those thermal loads were met by
cogeneration, heat pumps or direct electric heaters enables a high degree of control over heating-related
electrical loads and/or generation.
Implications?
•
•
•
•
The low overall heating demand seen in the zerocarbon house also raises some serious questions
regarding the development of heat networks (e.g.
zero-carbon district heating schemes).
The very low heat requirements make the prospect of
heat distribution unlikely in all but the highest density
housing developments such as flats: elsewhere the
small revenue from heat sales per dwelling would be
unlikely to offset the capital costs associated with the
installation of metering, piping, heat sources, thermal
storage and other balance of plant.
The heat-to-power ratio of the simulated dwelling
shift from 1:1 in the base case dwelling to 0.7:1 in the
zero carbon dwelling.
This seems to favour lower heat-to-power ratio
equipment such as bio-fuelled internal combustion
engines or (in future) fuel cells
Implications?
• Electrical
energy
becomes
the
predominant demand in the dwelling currently over 80% of demand is thermal
energy
• The reduction in electrical demand in
zero-carbon houses is less dramatic than
is seen for thermal demands, with in the
case examined here.
• The modelled electrical demand for the
zero carbon dwelling also indicated a
drop in peak demand of around 10%
• Using a large areas of roof-mounted PV
could lead to power management
problems in climates with the highly
variable daily and seasonal solar
insolation levels such as those seen in the
UK.
Conclusions
• To curb carbon emissions from dwellings building standards are being
tightened leading to the development of a raft of low-energy building
definitions
• In Europe, the Passive House standard is seen as a reference for lowenergy buildings and has been demonstrated to reduce space heating
demands by up to 90% (compared to conventional dwellings)
• Zero-carbon and zero-energy building standards are beginning to emerge
such as those defined in the UK’s Code for Sustainable Homes
• There are different definitions as to what constitutes a zero-carbon or
zero-energy building; the most common definition appears to be net-zerosource-energy where on-site renewable sources are used to offset a
building’s primary energy demands.
• There are numerous examples of zero-carbon demonstrations throughout
Europe and North America.
• Monitoring of actual performance indicates that most do not actually
achieve zero-carbon operation.
Conclusions
• Zero-carbon buildings will have radically different energy demand
characteristics compared to existing housing.
– space heating demand is minimal
– electricity for appliances and lighting becomes the major energy demand
• In Northern latitudes there are very significant seasonal variations in PV
electrical production the high levels of export to the network in summer
could result in significant power management problems in areas with high
levels of PV penetration.
• Significant swings from export to import were also evident throughout the
course of a day.
• The change in the primary thermal demand from space heating to hot
water provision affords opportunities for significant demand/supply
control opportunities if adequate hot water storage is provided and if
some of the heat demand is met by heat pumps or micro-cogeneneration
devices.