Transcript Chapter 5: Designing for Heating and Cooling

Chapter 5: Designing for Heating and Cooling
5.1 Organizing the problem
a) Fenestration
How much is optimum for the building?
What should the form of the building be?
internal load dominated
skin load dominated
Daylighting issues
side lighting vs top lighting
role of direct sunlight, solar gain vs. glare
seasonal adjustments to daylight openings
daily daylight control
daylight distribution
Chapter 5: Designing for Heating and Cooling cont’d
5.1 Heating issues
can the sun be used to heat spaces? South wall design.
openings to other orientations? U-value
relationship to daylighting
how to minimize cooling effects of large glass surfaces?
how can incoming fresh air be warmed?
is there surplus heat in the building that can be used at perimeter?
Cooling issues
Which strategy…
Open the building to breezes or close it to retain coolth?
How to keep out direct sunlight?
How to allow daylighting in winter without overheating in summer?
When can cooling be provided by outside air rather than refrigeration?
Can use of refrigeration be confined to off peak times?
How can incoming fresh air be cooled?
Can the structure of the building be used to absorb daytime heat and
flush it out at night?
Chapter 5: Designing for Heating and Cooling
5.2 Zoning your building
based on function, schedule, orientation fig. 5.3
5.3 Daylighting guidelines (calculations optional)
daylight factor def’n: indoor illumination from daylight x 100%
outdoor illumination
Fig. 5.4 Design diagrams - one way structure → high windows
Table 5.2 Recommended daylight factors
Fig. 5.7 EPUD building
Chapter 5: Designing for Heating and Cooling
5.4 Passive Solar Heating Guidelines
Incorporates sun collection and storage as part of a building’s
wall, floors or ceilings.
“Insulate before you isolate”
Principle of whole building heat loss.
Relative to conventional buildings, passively solar-heated
buildings usually conserve purchased energy, yet buildings
that aim at very high percentages of solar heating can use
more total heating energy than is used by buildings with
smaller window areas. Designers interested primarily in
saving purchased energy may aim at lower solar percentages
and more insulation; designers interested in buildings that
closely relate to climate and climatic changes may aim at
higher solar percentages (and more daylighting) along with
higher thermal masses and probably greater ranges of indoor
temperature.
Chapter 5: Designing for Heating and Cooling
5.4 b) Solar Savings Fraction
a measure of the solar building’s conservation advantage
(not the percentage of solar energy used)
c) Thermal mass (calculations optional)
phase change materials
d) Orientation
best within 30˚ of south.
figures 5.12 and 5.13
e) Roof ponds
not recommended for climates with snow since they require
moving insulating panels
f) Active Solar Heating
Uses mechanical equipment to collect and store solar energy
Chapter 5: Designing for Heating and Cooling
5.6 Passive Cooling Guidelines
a) Cross ventilation
provides air movement and fresh air
indoor temperature will be slightly above outdoor temperature
difficult to quantify
b) Stack ventilation
also maintains slightly above outdoor air temperature
c) Night Ventilation of Thermal Mass
Maintains a building at temperatures lower than outside by day
and flushes the building with plentiful fresh air by night.
Example 5.3 describes how to calculate appropriateness of
system with respect to climate
Chapter 5: Designing for Heating and Cooling
5.6 Passive Cooling Guidelines
d) Evaporative cooling
calculations optional
e) Cool towers
passive approach to evaporative cooling
Figure 21
f) Roof Ponds
calculations optional
g) Earth Tubes
feasible if trenches already required.
Chapter 5: Designing for Heating and Cooling
5.9 b) Degree Days def’n
5.10 Passive Solar Heating Performance
figure 5.13 Passive Solar Heating Systems compared
a) glazing performance
the issue of nighttime insulation
Chapter 5: Designing for Heating and Cooling
b) Direct Gain Systems
Problems:
possible overheating on sunny winter days
inadequate area of thermal mass
Thermal mass should be widely distributed around the room so that
direct sun can strike the mass surface or be reflected onto it as soon as
possible upon entering the window.
Figure 3.6
Chapter 5: Designing for Heating and Cooling
c) Sunspaces
Problem:
Expectation that the sunspace will be a greenhouse.
Comfortable temperatures in the main spaces are achieved at the
expense of very wide temperature swings in the sunspace.
Wall between sunspace and main space should be vented masonry or
contain water containers.
All sunspace systems are assumed to have a thermally massive
perimeter insulated floor slab on grade.
Figure 5.26
Chapter 5: Designing for Heating and Cooling
d) Trombe Walls
The main advantages of the Trombe wall systems:
Thermal stability.
The diurnal temperature swings are less than with most other passive systems.
They deliver a large portion of their heat by radiation to the space.
The main disadvantages:
The loss of view and daylight
Keeping the air space clean between the Trombe wall mass wall and the glass.
Vented walls use the stack effect to circulate warm air to the main space.
Deliver warm air sooner, but introduce dust into the space behind the glass.
Unvented spaces deliver heat quite late and are somewhat less efficient than
vented spaces.
Figure 5.27
Chapter 5: Designing for Heating and Cooling
e) Water Walls
Water phobia?
A real water wall is not transparent but opaque. Black selective paint
(excellent absorber of short-wave solar radiation, poor emitter of longwave radiation from the heated black surface) behind double glazed
unit.
Leave airspace for water expansion due to temperature, also rust
inhibitor.
Figure 5.28
Chapter 5: Designing for Heating and Cooling
5.11 Calculating heat gain (cooling load)
Be aware of the factors involved in heat gain; calculations optional.
roof and walls q = U x A x DEDT
glass
outdoor air (infiltration, mechanical ventilation)
people
lights
equipment
latent heat gain (varies with occupancy)
Chapter 5: Designing for Heating and Cooling
5.14 Passive cooling calculation procedures
Read through the UK pavilion at the Seville Expo 1992.
Look at figures 5.48 5.59