E NE RG Y MAT TER S
FACT SHEET 14:
PASSIVE SOLAR HEATING & COOLING
There are two aspects to passive solar
design for buildings: heating and cooling.
The basic principle for heating is to let the
heat from the sun warm the building in
winter, and keep the sun and hot winds
out in summer, while maintaining access
to cooling breezes.
EXERCISE 1
If you have access to the video Passive
solar energy design of buildings, watch it
and answer the following questions.
EXERCISE 1 (CONT’D)
(c) Why are eaves important?
(d) What does the term “thermal mass “
mean? Give some of examples of
material with high and low thermal
mass.
Otherwise, you can find the answers to
these questions on the Internet by
searching for the phrase “passive solar
design”.
(a) What are the key principles of passive
solar design for buildings?
(e) Why is window placement important?
(b) What is the ideal orientation and
shape of a building in Australia?
(f) Why does insulation work? What is
the R-rating in insulation?
EXERCISE 1 (CONT’D)
(g) How do gardens help in passive solar
design?
The key components that constitute a
complete passive solar design are shown in
Figure 1. Each performs a separate
function, but all five must work together
for the system to be successful.
Aperture (collector) – the large glass
(window) area through which sunlight
enters the building. Typically, the
aperture(s) should face within 30 degrees
of true north (in sthn hemisphere) and
should not be shaded by other buildings or
trees from 9 a.m. to 3 p.m. each day during
the heating season.
Absorber – the hard, darkened surface of
the storage element. This surface—which
could be that of a masonry wall, floor, or
partition (phase change material), or that
of a water container—sits in the direct path
of sunlight. Sunlight hits the surface and is
absorbed as heat.
Thermal mass – the materials that retain or
store the heat produced by sunlight. The
difference between the absorber and
thermal mass, although they often form
the same wall or floor, is that the absorber
is an exposed surface whereas storage is
the material below or behind that surface.
Distribution – the method by which solar
heat circulates from the collection and
storage points to different areas of the
house. A strictly passive design will use the
three natural heat transfer modes–
conduction, convection, and radiation–
exclusively. In some applications, however,
fans, ducts, and blowers may help with the
distribution of heat through the house.
Control – roof overhangs can be used to
shade the aperture area during summer
months. Other elements that control
under- and/or overheating include
electronic sensing devices, such as a
differential thermostat that signals a fan to
turn on; operable vents and dampers that
allow or restrict heat flow; low-emissivity
blinds; and awnings.
FIGURE 1 Elements of passive solar design (from Passive Solar Design for the Home, US Department of
Energy)
Energy Matters 14. Passive Solar Design
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10:00 am to 5:00 pm
Sunlight enters south-facing windows
and strikes the thermal mass inside
the home. The sunlight is converted
to heat energy, which heats both the
air and thermal mass materials. On
most sunny days, solar heat
maintains comfort during the midmorning to late afternoon periods.
5:00 pm to 11:00 pm
As the sun sets, it stops supplying
heat to the home. However, a
substantial amount of heat has been
stored in the thermal mass. These
materials release the heat slowly into
the passive solar rooms, keeping
them comfortable on most winter
evenings. If temperatures fall below
the comfort level, supplemental heat
is needed.
11:00 pm to 6:30 am
The home owner sets the thermostat
back at night, so only minimal backup heating is needed. Energyefficient features in the home
minimize heat losses to the outside.
6:30 am to 10:00 am
The cool early morning hours are the
toughest for passive solar heating
systems to provide comfort. The
thermal mass has usually given up
most of its heat, and the sun has not
risen enough to begin heating the
home. During this period, the home
owner may have to rely on
supplemental heat. Energy-efficient
features in the home minimize the
need for supplemental heating.
FIGURE 2 How passive solar heating works in winter (from US Dept of Energy fact sheet)
Energy Matters 14. Passive Solar Design
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Basic tips for Australian houses
Cooling
Provide an appropriate level of shade and
locate openings in the direction of cooling
breezes. Shade the entire building in hot
humid climates and hot dry climates with
warm winters.
Design narrow, elongated building forms
for best performance, with the long
elevations opening up to cooling breezes.
Elevating the house so that air can
circulate beneath it will also assist
performance.
Use landscape and building form to deflect
cooling breezes into the interior and to
exclude undesirable hot winds. Make use
of shade or windbreaks provided by
adjacent buildings or existing landscape.
Design extensions to open to cooling
breezes, particularly if they are living
areas.
Avoid large areas of exposed west facing
wall.
East and west facing openings receive the
strongest sun and are the most difficult to
shade. Keep their size to a minimum if this
does not compromise cooling by
ventilation. Alternatively, ensure they are
well shaded.
Ensure adequate north eaves overhangs,
plus south eaves overhangs above the
Tropic of Capricorn.
Design open plan interiors to facilitate
ventilation. Homes of one-room depth
with openings either side are ideal.
Design and position openings to control
air flow. Use clerestory windows, roof
ventilators, and vents in ridges, eaves and
ceilings to create convection currents to
cool the house in the absence of breezes.
Install windows that can be opened for
maximum ventilation. When renovating,
replace fixed windows with systems like
casement windows or louvres.
Add additional small windows to rooms
with only one window to improve
ventilation.
Use vents above or in internal doors to
facilitate cross ventilation.
Energy Matters 14. Passive Solar Design
Ensure outdoor living areas are shaded.
Covered balconies and verandahs can be
useful additions, providing shaded
outdoor living space. Use landscape to
provide additional shade.
Heating
Maximise the amount of daytime living
space that faces north, whether designing
a new home or configuring renovations.
Provide passive solar shading to east, west
and north facing elevations, particularly
glass areas. Correctly designed eaves are
generally all that is required to shade the
northern elevations of single storey
houses.
Place a suitable amount of glazing in north
facing walls with solar access. The glazing
area should be between 10 to 25 percent of
the floor area of the room, depending on
climate and mass.
Glazing on other facades should ideally be
less to prevent unwanted heat loss and
gain. South facing glass facilitates winter
heat loss, while east and particularly west
facing glass encourages summer heat gain
if not properly shaded. Smaller, well
shaded windows are desirable for cross
ventilation.
Avoid west facing bedrooms where
possible. East facing bedrooms are
acceptable as they capture morning sun
but remain cool on summer evenings.
Locate utility areas such as laundries,
bathrooms, garages and sheds to the
south, west and east to protect living areas
from summer sun and winter winds.
Maximise the distance between the house
and any building development to the
north. Avoid placing obstructions such as
carports or sheds to the north.
Building on the south boundary (if
permitted by your local council) can be
useful to increase the amount of north
facing outdoor space. Avoid compromising
the solar access of neighbours by
overshadowing.
Plant shade trees in the appropriate
locations. Landscaping can also be used to
block or filter harsh winds.
Prune vegetation that blocks winter sun.
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