The document discusses Earth Air Tunnels (EAT), a passive cooling system that uses the constant underground temperature to cool buildings. EAT works by pumping air through underground pipes/tunnels 4 meters deep, where the temperature remains stable year-round. Key factors that affect EAT performance include pipe design parameters, soil properties, air velocity, and system operation as open or closed loop. EAT provides both cooling and heating, is low cost to operate, and can be used for various building types from homes to hospitals. However, EAT requires significant space and has a high initial installation cost.

1. Submitted by
Amandeep Singh
Vikas Mahala
Ashok Dhayal

2. Introduction
Passive cooling
Earth Air Tunnel
Principle
Factors affecting thermal conductivity
Applications of EAT
Design guidelines
Classification
Advantage and limitations
Potential issues
Conclusion
References

3. Energy Saving:
One of the most important global
challenges
Energy Efficiency:
Supply Side: Higher
Efficiency power plants,
renewable sources of energy, Smart Grids, etc.
Demand Side: Energy efficient,
Building Envelopes (direct systems),
Earth Air Tunnels(indirect systems), etc.

4. • Passive cooling systems are least expensive means of cooling a
home which maximizes the efficiency of the building envelope
without any use of mechanical devices.
• It rely on natural heat-sinks to remove heat from the building. They
derive cooling directly from evaporation, convection, and radiation
without using any intermediate electrical devices.
• All passive cooling strategies rely on daily changes in temperature
and relative humidity.
• The applicability of each system depends on the climatic conditions.
• These design strategies reduce heat gains to internal spaces.
- Natural Ventilation
- Shading
-Wind Towers
- Courtyard Effect
- Earth Air Tunnels
- Evaporative Cooling
- Passive Down Draught Cooling
- Roof Sprays
[1]

5. • The Earth Air Tunnel (EAT) systems utilizes the heat-storing capacity of earth.
• The fact that the year round temperature four meter below the surface remains almost constant
throughout the year. That makes it potentially useful in providing buildings with air-conditioning.
• It depends on the ambient temperature of the location, the EAT system can be used to provide
both cooling during the summer and heating during winter.
• The tunnels would be especially useful for large buildings with ample surrounding ground.
• The EAT system can not be cost effective for small individual residential buildings.
• The ground temperature remains constant and air if pumped in appropriate amount that allows
sufficient contact time for the heat transfer to the medium attains the same temperature as the
ground temperature.

6. Underground heat exchanger
Also called:
Earth-Air Heat Exchangers
Air-to-soil Heat Exchangers
Earth Canals

8. Earth acts a source or sink
High thermal Inertia of
soil results in air
temperature fluctuations
being dampened deeper
in the ground
Utilizes Solar Energy
accumulated in the soil
Cooling/Heating takes
place due to a temperature
difference between
the soil and the air

9. SOIL:
Moisture content
Most not able impact on thermal conductivity
Thermal conductivity increases with moisture to a certain point
(critical moisture content)
Dry density of soil
As dry density increase thermal conductivity increase
Mineral Composition
Soils with higher mineral content have higher conductivity
Soils with higher organic content have lower conductivity
Soil Texture
Coarse textured, angular grained soil has higher thermal
conductivity
Vegetation
Vegetation acts as an insulating agent moderating the affect of
temperature
[2]

10. EAT’s can be used in a vast variety of buildings:
Commercial Buildings: Offices, showrooms, cinema halls etc.
Residential buildings
University Campuses
Hospitals
Greenhouses
Livestock houses

12. The design parameters that impact the performance of the
EAT are:
• Tube Depth
• Tube Length
• Tube Diameter
• Air velocity
• Air Flow rate
• Tube Material
• Tube arrangement
 Open-loop system
 Closed-loop system
• Efficiency
• Coefficient of Performance (COP)
[3]

13. Ground temperature defined by:
External Climate
Soil Composition
Thermal Properties of soil
Water Content
Ground temperature
fluctuates in time,
but amplitude of
fluctuation diminishes with depth.
Burying pipes/tubes as
deep as possible would be ideal.
A balance between going
deeper and reduction in
temperature needs to be drawn.
Generally ~4m below
the earth’s surface dampens
the oscillations significantly.

14. Heat Transfer depends on surface area.
Surface area of a pipe:
Diameter
Length
So increased length would
mean increased heat
transfer and hence
higher efficiency.
After a certain length,
no significant heat transfer
occurs, hence optimize length.
Increased length also results
in increased pressure drop and
hence increases fan energy.
So economic and design
factors need to be balanced to
find best performance at lowest cost.

15. Heat Transfer depends on surface area.
Surface area of a pipe:
Diameter
Length
Smaller diameter gives better thermal performance.
Smaller diameter results in larger pressure drop increasing fan
energy requirement.
Increased diameter results in reduction in air speed and heat
transfer.
So economic and design factors need to be balanced to find best
performance at lowest cost.
Optimum determined by actual cost of tube and excavation cost.
[4]

16. As the velocity of air increases the exit temp
decreases
[6]

17. For a given tube diameter, increase in airflow rate results in:
Increase in total heat transfer
Increase in outlet temperature
High flow rates desirable for closed systems
For open systems airflow rate must be selected by considering:
Outlet temperature
Total cooling or heating capacity

18. The main considerations in selecting tube material are:
Cost
Strength
Corrosion
Resistance
Durability
Tube material has little influence on performance.
Selection would be determined by other factors like ease of
installation, corrosion resistance etc.
Spacing between tubes should enough so that tubes are thermally
independent to maximize benefits.

19. EAT can be used in either:
Closed loop system
Open loop system
Open Loop system:
Outdoor air is drawn into tubes
and delivered to AHUs or
directly to the inside of the building
Provides ventilation while
hopefully cooling or heating
the building interior
Improves IAQ
Closed Loop system:
Interior air circulates through EATs
Increases efficiency
Reduces problem with humidity
condensing inside tubes.
Hybrid System:
EATHE system is coupled to another heating/cooling system, which
may be an air conditioner , evaporative cooling system or solar air
heater

20. EAT can be used in either:
One-tube system
Parallel tubes system
One tube system may
not be appropriate to meet
air conditioning requirements
of a building, resulting
in the tube being too large
Parallel tubes system
More pragmatic design option
Reduce pressure drop
Raise thermal performance

21. Classification of EATHE system
According to layout of pipe in ground
According to mode of arrangement
There are four different types according to layout of pipe in the
ground
Horizontal/ straight Loop
Vertical Looped
Slinky/ spiral Looped
Pond/Helical Looped

23. Calculating benefits from EAT is difficult due to:
Soil Temperatures
Conductivity
Performance of EAT can be calculated as:
where;
To = Inlet Air Temperature
To (L) = Outlet Air Temperature
Ts = Undisturbed ground temperature

24. COP based on:
Amount of heating or cooling done by EAT (Heat Flux)
Amount of power required to move the air through the EAT
Q= Heat Flux
W= Power
COP decreases as system is operated
COP can be integrated into system control strategies
When COP down to a certain point, EAT should be shut down and
conventional system should take over

25. [8]

26. ETHE based systems cause no toxic emission and therefore, are
not detrimental to environment.
Ground Source Heat Pumps (GSHPs) do use some refrigerant but
much less than the conventional systems.
ETHE based systems for cooling do not need water - a feature
valuable in arid areas like Kutch. It is this feature that motivated
our work on ETHE development.
ETHEs have long life and require only low maintenance
Low operating cost.

27. Require large space to make setup.
Give a limited cooling effect.
Initial cost high.

29. ISSUE
• Condensation inside the tubes
has been observed
• Condensation occurs if temp. in
the tube is lower that dew point
temp.
• Condensation occurs in systems
with low airflow and high
ambient dew point temperature
• Removal of moisture from the
cooled air is always an issue and
system may be used with a
regular air conditioner or a
desiccant
• Water in tubes also results in
growth of mould or mildew
leading to IAQ issues
SOLUTIONS
• Good construction and
drainage
• Tubes are tilted to prevent
water from standing in the
tubes
• In the service pit at the lowest
point water can be captured
and pumped
• Water tight tubes can be used
to prevent ground water from
entering into the system

31. EATs are based on the following principles
Using earth as a source or sink
Uses Soil Thermal inertia
Depends on the Thermal Conductivity of Soil
Various Factors affect the performance of EAT which need to be
optimized to maximize performance.
Integrate the EAT into the building systems to maximize
performance and maximize energy savings.

32. 1. A passive solar system for thermal comfort conditioning of buildings in composite climates†,1
p. RAMAN, SANJAY MANDE and V. V. N. KISHORE received 19 august 1998; revised
version accepted 13 october 2000
2. Earth air heat exchanger in parallel connection manojkumardubey1, dr. J.L.Bhagoria2, dr.
Atullanjewar M.Tech student1 MANIT bhopal professor mech deptt. , MANIT bhopal asst.
Professor mech deptt, MANIT bhopal(figures)
3. Jalaluddin, Miyara A, Thermal performance investigation of several types of vertical
ground heat exchangers with different operation mode, Applied Thermal
Engineering 33-34 (2012) 167–74.
4. Performance analysis of earth–pipe–air heat exchanger for winter heating vikas bansal *, rohit
misra, ghanshyam das agrawal, jyotirmay mathur
5. Performance analysis of earth–pipe–air heat exchanger for summer cooling vikas bansal *,
rohit misra, ghanshyam das agrawal, jyotirmay mathur
6. Performance evaluation and economic analysis of integrated earth–air–tunnel heat exchanger–
evaporative cooling system vikas bansal∗, rohit misra, ghanshyam das agrawal, jyotirmay
mathur
7. Thermal performance investigation of hybrid earth air tunnel heat exchanger rohit misraa,
vikas bansala, ghanshyam das agarwala, jyotirmay mathura,∗, tarun aserib
8. ANALYTICAL MODEL FOR HEAT TRANSFER IN ANUNDERGROUND AIR TUNNEL
MONCEF KRARTI and JAN F. KREIDER (received 27 october 1994; received for
publication 11 july 1995)