Passive Cooling and Heating of Rooms
‘Passive design’ is
the design that does not require mechanical heating or cooling.
Homes that are
take advantage of natural energy flows to maintain thermal comfort.
Passive design in your home:
or eliminates heating and cooling bills.
greenhouse gas emissions from heating, cooling, mechanical ventilation
'Building envelope’ is
a term used to describe the roof, walls, windows, floors and internal
walls of a home. The envelope controls heat
gain in summer and heat loss in winter. Its performance in modifying
or altering climatic extremes is greatly improved by passive design.
Well-designed envelopes maximize cooling air movement and exclude sun
in summer. In winter, they trap and store heat from the sun and minimize
heat loss to the external environment. Buildings, as they are designed
and used today, contribute to serious environmental problems because
of excessive consumption of energy and other natural resources. Demands
of energy use in buildings and environmental damage arise because of
energy-intensive solutions sought to meet the requirements of heating,
cooling, ventilation and lighting.
However, buildings can be designed to meet the occupant’s need
for thermal and visual comfort at reduced levels of energy and resources
consumption. Energy consumption in new constructions can be controlled
by way of adopting an integrated approach to building design.
steps in this approach are as below:
solar passive techniques in a building design to minimize load
on conventional systems
cooling, ventilation, and lighting)
energy-efficient lighting and HVAC (heating, ventilation, and air-conditioning)
renewable energy systems (solar photovoltaic systems/solar water
heating systems) to meet a part of building load.
low energy materials and methods of construction and reduce transportation
Climate and architecture
India is divided into six climatic zones based on different climatic
conditions. Knowledge of climate at a given location can help in the
design of solar passive buildings that eliminate the adverse effects
of climate, yet simultaneously take advantage of effects that are beneficial.
For instance, in a place like Mumbai (Indian coastal mega city), a
building can be designed in such a way that appropriate shading prevents
solar radiation and adequate ventilation reduces humidity. In a place
like Shimla (Indian hill station), where the climate is cold and cloudy,
a building can be designed to make maximum use of sunlight, and thereby
keep its interiors as warm as possible.
The various climatic factors
that affect the solar passive design are listed below:
- Wind velocity
- Relative humidity
126.96.36.199 Solar Passive Techniques
Various concepts and techniques are used to design energy-efficient buildings.
Some of these are as described below:
Direct heat gain
The direct heat gain technique is generally used in cold climates. The
basic principle is that sunlight is admitted into the living spaces directly
through openings or glazed windows to heat walls, floors, and inside
air. The glazed windows are generally located facing south to receive
maximum sunlight during winter. They are usually double-glazed with insulated
curtains to reduce heat loss during the night. During the day the heat
is stored in walls and floors.
Thermal storage walls
In this approach, a thermal storage wall is placed between the living
space and the glazing. It prevents solar radiation to enter the living
space. Radiation is absorbed by the storage wall, and then transferred
into the living space. Thermal storage walls include brick, cement and
clay walls, water walls, transwalls.
Evaporative cooling is a passive cooling technique generally employed
in hot and dry climates. It works on the principle that when warm air
is used to evaporate water the air itself becomes cool.
Passive desiccant cooling
Passive desiccant cooling method is effective in a warm and humid climate.
Natural cooling of the human body through sweating does not occur in
highly humid conditions. To decrease the humidity level of the surroundings,
desiccant salts or mechanical de-humidifiers are used.
Passive cooling by induced ventilation can be most effective in hot and
humid climates as well as in hot and dry climates. This method involves
the heating of air in a restricted area through solar radiation; thus,
creating a temperature difference and causing air movements or drafts.
The drafts cause hot air to rise and escape from the interior causing
Earth-berming technique is used for both passive cooling and heating
of buildings. It is based on the fact that the earth acts like a massive
heat sink. Thus, underground or partially sunk buildings remain cool
in summer and warm in winter.
In addition to above concepts, there are many other solar passive techniques
such as wind towers, earth air tunnels, curved roofs and air vents, which
can be incorporated according to the requirements of the buildings.
Advantages of solar passive buildings
With the incorporation of solar passive concepts into a building
a large quantity of energy can be saved. Furthermore, these concepts
comfortable living conditions to the inhabitants in an eco-friendly
manner. However, they cannot totally eliminate the use of conventional
for modern facilities such as air-conditioning.
Cost and payback period
The cost of a building may increase by about 5-15% because of incorporation
of solar passive concepts. However, the investment may be recovered
within a period of 1-7 years due to energy savings.
188.8.131.52 Passive Solar Heating
Passive solar heating is one strategy of ‘solar design’.
When combined properly, this strategy can contribute to heating, cooling,
and day lighting of any building. Passive solar heating in particular
uses building components to collect, store and distribute solar heat
gains to reduce the demand for space heating. It does not use mechanical
equipments because the heat flow is by natural means (radiation, convection & conductance)
and thermal storage is in the structure itself.
It is best to incorporate passive solar heating into a building during
the initial design. Window design, especially glazing choices, is a
critical factor for determining the effectiveness of passive solar
solar systems do not have a high initial cost or long-term payback
period, both of which are common with many active solar heating systems.
climates, large south-facing windows are used, as these have the most
exposure to the sun in all seasons. Although passive solar heating
systems do not require mechanical equipments for operation, yet fans
should be used to assist the natural flow of thermal energy. Thus,
the passive systems assisted by mechanical devices are referred to
as ‘hybrid’ heating
Architectural design of the building usually consists of: buildings
with rectangular floor plans, elongated on an east-west axis; a glazed
wall; a thermal storage media exposed to the solar radiation which
penetrates the south-facing glazing; overhangs or other shading devices
shade the south-facing glazing from the summer sun; and windows on
the east and west walls, and preferably none on the north walls.
The following are general recommendations that should be followed in
the design of passive solar heated buildings:
Five Elements of Passive Solar Home Design
Following five elements constitute a complete
passive solar home design. Each performs
a separate function,
work together for
the design to be successful.
Aperture (Collector): It
is the large glass (window) area through
Typically, the aperture(s)
within 30° of true south and should
not be shaded by other buildings or
trees from 9 a.m. to 3 p.m. each day
during the winter season.
Absorber: It is the hard, dark surface
of the storage element. This surface,
be that of a
masonry wall, floor,
partition (phase change
material), or water container, sits in
direct path of sunlight. Sunlight hits
the surface that
Thermal Mass: The
materials that retain or store the
heat produced by sunlight are ‘thermal mass’.
Difference between the absorber and
thermal mass, although they often form
same wall or floor, is
that the absorber is an exposed surface whereas thermal mass is the material
below or behind that surface.
is the method by which solar heat circulates from the collection and
to different areas of the house.
A strictly passive design will use 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 electron sensing devices e.g. differential thermostat that
signals a fan to turn on, operable vents and dampers that allow or
flow, low-emissive blinds, and awnings.
- Passive solar design is highly energy
efficient that reduces building's energy demands for lighting,
winter heating and summer cooling.
Energy from the sun is free. Strictly passive designs capture
it without additional
investments in mechanical and electrical "active solar" devices
such as pumps, fans and electrical controls.
- Passive solar design
also helps conserve valuable fossil fuel resources so that
they can be directed toward other uses. Incorporating passive
solar design elements into buildings and homes can reduce heating
bills by 50%. Day lighting, a component of many passive solar
one of the most cost-effective means of reducing energy usage in buildings.
well-designed and built passive solar building does not have to
sacrifice aesthetics either. It can be as attractive as conventionally
buildings and still save energy and money.
- Passive solar
design also reduces greenhouse gases that contribute to global
- In areas where experienced solar architects
and builders are not available, construction costs can run higher
than for conventional
homes, and mistakes can be made in the choice of building materials
especially window glass.
Passive solar homes are often built using
glass that, unfortunately, rejects solar energy. Such a mistake can
be costly. Choosing
passive solar designs isn't easy. The right
glass choice depends on
which side of the building (east, west, north or south)
the glass is installed and the climate.
- In addition, room and furniture
layouts need to be planned carefully
to avoid glare on equipment such as computers
- During the summer or in consistently
warm climates, day lighting could actually increase energy
use in a building by
to its air-conditioning load.
Trombé Wall is a passive solar heating system. Trombé wall
is a sun-facing wall built from material
that can act as a thermal mass (such as adobe, stone, concrete
water tank), combined with
space, insulated glazing and vents
to form a large solar thermal collector. By attaching a translucent
board or glass) on the
vault, the sun heating effect is
created. The absorbing vault face should be painted black in order
as much heat as possible.
During the day, sunlight shines through
the glazing and heats the surface
of the thermal mass.
primarily to the outside.
of the insulating glazing the average
temperature of thermal mass can significantly
average outdoor temperature. If the
glazing insulates well enough
temperatures are not
too low, the average temperature
thermal mass will be significantly
flow into the house
interior. Indirect gain is that the
Trombé wall stores heat during the day.
Excess heat is vented to the interior space. At night, Trombé wall
vents are closed and the storage
wall radiates heat into the interior
Common Modifications to the Trombé wall:
vent near the top is opened to vent during the summer. Such venting
makes the Trombé wall pump in the fresh air during
the day even if there is no breeze.
in the Trombé wall
though lower the efficiency, but they may be fitted for natural
lighting or aesthetic reasons. If the outer
glazing has high ultraviolet transmittance and the window in
is of normal glass, this uses ultraviolet light efficiently
for heating purpose while protecting people from its harmful effects.
blowers controlled by thermostats are used to improve air and heat
Fixed or movable shades,
which can reduce nighttime heat losses, might be fitted in the wall.
may be trellises to shade the solar collector during summer months.
Insulating cover can
be used at night on the glazing surface.
Tubes, pipes or water
tanks make part of a solar hot water system, and fish tanks as thermal
Selective surface can
be increased for more absorption of solar radiation by the thermal
The specific Lak’a Uta Trombé wall, built in Bolivia, is
mounted to the roof after plastering. It is simple frame of prefabricated
concrete elements (or small adobes). For glazing (translucent cover)
flat fiber plastic boards (calamina plástica) are used. Black
paint or black colored earth-mud-plaster is used to make absorbing
of Trombé Wall
- Low or zero energy consumption for heating
- Non-toxic; and low cost
of Trombé Wall
Trombé wall are an effective alternative to heating from stoves
or heaters. However the design is neither simple nor easily comprehensible.
A number of pre-conditions must be considered, especially, the design
application, thermal conditions (well insulated, accumulation of heat,
etc.) and maintenance. Before opting Trombé as low cost housing
in cold climate, it is recommended to do a thorough preliminary study
and appropriate detailed design. A number of web pages can help the specific
design process. See the Laka Uta Trombé manual.
184.108.40.206 Passive Solar Cooling
Reducing Internal Heat Gain
- Turn lights off when
not in use, and remove light bulbs in areas where they are not required;
water heater temperature down to 120°F;
- Take shorter showers,
open window when showering, and run exhaust fan when showering;
- Install water heater
insulation blanket, and insulate hot water pipes;
- Open window to
utility room when the clothes dryer is in use during summer;
cold meals in the summer, and cook outside;
microwave in the summer, and bake at night;
- Run exhaust fan when
- Use cold or warm water
settings on washing machine;
- Wash clothes at night,
and hang clothes outside;
- Dry larger loads; close
off utility room;
- Turn computers and other
electronic devices off when not in use;
- Unplug TV and stereo
when not in use;
- Turn off furnace pilot
light during the cooling season;
- Spend more time outdoor
on porches and patios; and
- Switch off drying option
Reducing External Heat Gain
- Plant shade trees, and
build artificial shade structures such as arbors and trellises;
awnings, and install and use window shades;
- Seal cracks in building
- Replace energy-inefficient
- Repaint with a lighter
- Replace roof shingles
with lighter ones or metal roofing or Spanish tiles; and
- Use natural ventilation
early and late in cooling season;
- Purge heat at night
in dry climates;
- Install and use window
fans, install attic fan, and install whole house fan;
- Improve efficiency
of air conditioning system (seal ducts, replace dirty filters,
shade air conditioner, etc.);
- Replace inefficient
air conditioners with more efficient models;
- Install an air-source
Insulation is an essential component of passive design. It improves
building envelope performance by minimizing
heat loss and heat gain through walls, roof and floors.
Externally insulated, dense materials like concrete, bricks and
other masonry are used in passive
design to absorb, store and re-release thermal
energy. This moderates internal
temperatures by averaging day/night (diurnal) extremes, therefore, increasing
comfort and reducing
Windows and glazing are a very
important component of passive
heat loss and gain in a
occurs mostly through
Shading of glass is a critical
consideration in passive design.
is the single greatest
source of heat gain
in a well insulated
home. Shading requirements vary
according to climate and house
In climates where winter heating
required, shading devices should
exclude summer sun but allow
full winter sun to penetrate.
achieved on north facing walls.
facing windows require
different shading solutions to
north facing windows. In climates
no heating is
of the whole
will improve comfort and save
Well-positioned and high quality
skylights can improve the energy
of home and bring welcome