Passive cooling is a building design approach aimed at controlling heat gain and promoting natural cooling for improved indoor thermal comfort without significant energy use. Techniques like ground cooling utilize the earth as a heat sink, employing buried pipes to regulate air temperature through conductive heat transfer. Various systems, including vertical and horizontal ground loops and lake/pond loops, are used to harness the earth's stable temperatures, impacting energy efficiency in heating and cooling.

2. 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).

3. 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.

4. •Pipes are laid in the earth at least 4 to 5metre deep in the ground
through which air is passed.
•The air passing through a tunnel or a buried pipe at a depth of few meters
gets 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 the
earth, humidity of inlet air velocity, affect the exchange of heat between air
and the surrounding soil.

5. PROCESS:
•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.
< ÉARTH DUCT

6. 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.

8. 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.

9. HORIZONTAL GROUND LOOP SYSTEMS.

10. 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.

11. LAKE/POND SYSTEM
POSSIBLE WHEN THERE IS A WATER BODY
IN THE VICINITY.

12. 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 building
above the ground on posts.

13. •www.greenbuildings.com
•Wikipedia
•www.sciencedirect.com