Passive design

Objectives

After completing this unit, the student should be able to

1 Discuss the procedure in passive design

2. Design a house using passive design techniques

Key Words

Direct Gain Thermal Mass Solarium Solar Orientation

Overhung Building Envelope Sunshade Solar Control

Introduction

In the hostile territory of the dessert many animals reverse their life

rhythm, live by night, and tuck away underground at dawn. This is how

nature smoothly operates without mechanical ventilation and heater. On

the other hand, mankind’s physical flexibility and capacity for adaptation

are relatively feeble compared to those of many animals. But man has

learned through the ages how to harness the afternoon solar radiation

for heating purpose at night.

The primary source of energy for such efficient system is solar energy.

Solar energy is a

radiant heat source that causes natural processes upon which all life

depends. The free energy source sun can be easily managed to have a

comfortable climate in a building. The basic natural processes that are

used in passive solar energy are the thermal energy flows associated

with radiation, conduction, and natural convection

Considering all behaviors of the relationship between the

sun and the building materials like reflection, transmission,

and absorption an economical and comfortable building will

be achieved.

Description

Passive solar energy systems involve designing the structures themselves

in ways that use solar energy for heating and cooling. As in

active solar design, the sun energy is not used with trapping materials

directly exposed to the sun.

Passive solar design uses nothing but the arrangements of structural

elements, windows, walls, and floors to store and distribute the sun's heat

in the winter and reject solar heat in the summer.

In addition to the thermal comfort of the room, passive design has

big role in the room lightings and other comfort aspects

of a room. For passive heating and cooling, the plan of the house,

careful site selection and planning, construction materials, building

features and other aspects of the home are designed to collect,

store and distribute the sun's heat in winter; and to block the sun's

rays in summer. Passive solar houses can be built in any

architectural style and in anywhere else. A "passive" solar house

provides cooling and heating to keep the home comfortable without

the use of mechanical equipment.

This style of construction results in homes that respond

to the environment. They typically incorporate natural

ventilation and roof overhangs to block the sun's

strongest rays during that season. Passive solar systems

make use of natural energy flows as the primary means of

harvesting solar energy. Passive solar systems can

provide space heating,/ cooling load avoidance, natural

ventilation, water heating, and day lighting.

Passive solar design can be applied in different ways such as

1. Building Envelope - The roof, walls, windows, floors and

internal walls of a home. The envelope controls heat gain in summer

and heat loss in winter. This process is done with the selection of

the building materials exposed to the sun directly. 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. Thick

concrete walls modulate wide

swings in temperature by

absorbing heat in winter and

insulating in summer. Water

compartments provide a

thermal mass for storing heat

during the day and releasing

heat at night

2. Sun space - uses a separate

solar room (solarium) to store

solar heat. A sunspace can be

built as part of a new building or as

an addition to an existing one.

Sunspaces also require a

thermal mass to store heat. “

Sun space” serves as a collector in

winter when the solar shades are open

and as a cooler

in summer when the solar shades are

closed. This method is used for both

cooling and

heating purposes.

3. Direct Gain - simplest technique. Sunlight enters

a building through an opening — usually south-facing

windows. It then strikes the building's thermal mass —

usually dark colored masonry floors and/or walls in the

interior space that absorb and store the solar heat.

4. Thermal Mass - any material in the home that

absorbs and stores heat. Concrete, brick, tile and

other masonry materials are the most common choices

for thermal mass in a passive solar home, these

materials absorb and release heat slowly and are easily

5. Properly placed trees and vine-covered trellises

can stop summer sun on the south, east

and west sides of your home. Landscaping is one of

the best methods to keep the house

cool. The temperature inside can increase as much

as 20 degrees or more if east and west

Windows and walls are not shaded.

6. Roof pond systems - six to twelve inches of water are

contained on a flat roof. This system is best for cooling in low

humidity climates but can be modified to work in high humidity

climates. Water is usually stored in large plastic or fiberglass

containers covered by glazing and the space below is warmed by

radiant heat from the warm water above

7. Orientation - the need for auxiliary

heating and cooling is reduced, resulting in

lower energy bills and reduced greenhouse

emissions..

Elements of passive design:

1. aperture or collector — the large glass area through which

sunlight enters the building

2. absorber — the dark surface of the storage element that

absorbs the solar heat.

3. thermal mass — the material that stores the absorbed heat.

This can be masonry materials such as concrete, stone, and brick;

or a water tank.

4. distribution method — the natural tendency of heat to move

from warmer materials to cooler ones (through conduction,

convection, and radiation) until there is no longer a temperature

difference between the two.

5. control mechanism — to regulate the amount of sunlight

entering the aperture. This can be roof overhang to allow more

sunlight to enter in the winter, less in the summer.

Pop quiz

1.What is stack effect ? Demonstrate with sketch

2.What are the limitations of natural ventilation design ?

3.Give three examples of natural ventilation design application

4. List the different ways passive design can be applied in ?