Passive cooling:

•It is a building design approach that focuses on heat gain control

and heat dissipation in a building in order to improve the indoor

thermal comfort with low or nil energy consumption.

• This approach works either by preventing heat from entering the

interior (heat gain prevention) or by removing heat from the

building (natural cooling).

•Natural cooling utilizes on-site energy, available from the natural

environment, combined with the architectural design of building

components (e.g. building envelope), rather than mechanical

systems to dissipate heat.

• Therefore, natural cooling depends not only on the architectural

design of the building but how it uses the local site natural

resources as heat sinks (i.e. everything that absorbs or dissipates

heat).

WHAT IS GROUND COOLING/COUPLING?

This technique is used for passive cooling as well as heating of buildings,

which is made possible by the earth acting as a massive heat sink.

PRINCIPLE:

At depths beyond 4 to 5m below the surface of the earth, both daily and

seasonal fluctuations die out and the soil temperature remains almost

constant throughout the year.

Thus, this constant temperature of the earth is used to cool the air

entering in a building.

The Earth acts like a heat sink, as it absorbs the heat from the air thus

cooling the air efficiently.

•The air passing through a tunnel or a buried pipe at a depth of few metersgets cooled in summers and heated in

winters.

•The air in these pipes(which is now cooled by the earth) is made to enter buildings, Sometimes using a fan to draw air from the pipes.

• Parameters like surface area of pipe, length and depth of the tunnel below ground, dampness of theearth, humidity of inlet air velocity, affect the exchange of heat between airand the surrounding soil.

•Pipes are laid in the earth at least 4 to 5metre deep in the ground through which air is passed.

•A building can be indirectly coupled with the earth by means of earth ducts.

• An earth duct is a buried tube that acts as avenue for supply air to travel through before entering the building.

•Supply air is cooled by way of conductive heat transfer between the concrete tubes and soil.

•Therefore, earth ducts will not perform well as a source of cooling unless the soil temperature is lower than the desired room air temperature.

•Earth ducts typically require long tubes to cool the supply air to an appropriate temperature before entering the building•. A fan is required to draw the cool air from the earth duct into the building.

PROCESS:

< ÉARTH DUCT

TYPES OF EARTH COUPLING:

Vertical ground loop system:

•Used mainly in commercial buildings or where space is limited.•Vertical holes 100 to 400 feet deep are drilled in the ground, and a

single loop of pipe with a U-tube at the bottom is installed.• The borehole is then sealed with grout to ensure good contact with

the soil.•The earth's temperature is more stable farther below the surface

which is an advantage for the system. •Vertical ground loop fields may be located under buildings or parking

lots. •The life expectancy is in excess of 50 years.

Horizontal ground loop system:•This type of design is cost effective on smaller projects or where there is

sufficient space for the loop.

•Trenches, 3 to 6 ft deep, are created and a series of parallel plastic pipes

are laid inside them.

• These pipes can also be laid in loops.

• The fluid/air is then circulated, absorbing or rejecting heat to the earth

depending on the mode of operation.

•A typical horizontal loop will be 400 to 600 feet long for each ton of

heating and cooling but will vary according to the soil type and the layout

of the piping.

HORIZONTAL GROUND LOOP SYSTEMS.

Lake/ pond loop system:•This type of design is economical when a project is located near a body

of water.

•Fluid circulates through polyethylene piping in a closed system, just as

it does through ground loops but in this case underwater.

•The pipes may be coiled in a slinky to fit more surfaces into a given

amount of space.

•The lake needs to be a minimum size and depth depending on the

load.

• Lake loops have no adverse impact on the aquatic system.

LAKE/POND SYSTEM

POSSIBLE WHEN THERE IS A WATER BODY

IN THE VICINITY.

Some of the factors that affect the performance of an earth duct are:duct length, number of bends, thickness of duct, depth of duct, diameter of the duct,and air velocity.

The temperature of the earth ten feet or more deep is slightly above the average annual air temperature. This temperature can be further lowered by these techniques:

•mulching with pea stone or wood chips to a depth of at least four inches, and irrigating if necessary to provide moisture for evaporation. The mulch must be vapor permeable.

•Shading the earth's surface of which one way is to raise the buildingabove the ground on posts.

•www.greenbuildings.com

•Wikipedia

•www.sciencedirect.com