The document discusses Earth Tube Heat Exchangers (ETHE). It describes ETHE as a system that uses underground pipes to exchange heat between the air and the more constant temperature of the earth. It explains the basic principles of how ETHE works to provide heating in the winter and cooling in the summer by using the earth as a heat source or sink. It also outlines several key factors to consider in the design of ETHE systems, such as tube depth, length, diameter, air velocity, and arrangement (open vs closed loop).

1. S U B M I T T E D B Y
S A G A R K E L K A R ( 0 2 0 6 M E 1 3 11 2 5 )
S A N D E E P C H O U D H A RY ( 0 2 0 6 M E 1 3 11 2 8 )
S H I K H A R S K U S H WA H A ( 0 2 0 6 M E 1 3 11 4 0 )
S H U B H A M K U M A R ( 0 2 0 6 M E 1 3 11 5 0 )
S U S H A N T S I D D H E Y ( 0 2 0 6 M E 1 3 11 6 7 )
S WA P N I L V I S H WA K A R M A ( 0 2 0 6 M E 1 3 11 6 9 )
Earth Tube Heat Exchanger
(ETHE)

2. Contents
 Aim
 Introduction
 Earth Tube Heat Exchanger
 Classification
 Passive Heat Exchange
 Principle
 Factors affecting thermal conductivity
 Applications of EAT
 Design guidelines
 Advantage and limitations
 Potential issues
 Conclusion
 References

3. Heating and Cooling of given space
Using Earth Tube Heat Exchanger System
Challenges
 Energy Saving:
One of the most important global challenges.
 Energy Efficiency:
 Renewable sources of energy
 Demand Side: Energy efficient
Aim

4. Introduction
 If building air is blown through the heat exchanger for heat
recovery ventilation, they are called Earth Tubes.
 These systems are known by several other names,
including: air-to-soil heat exchanger, earth channels, earth
canals, earth-air tunnel systems, ground tube heat
exchanger, hypocausts, subsoil heat exchangers, thermal
labyrinths, underground air pipes, and others.

5. ETHE
• The Earth Air Tunnel (EAT) systems utilizes the heat-storing capacity of earth.
• The fact that the year round temperature approx. 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. Classification
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

7. Contd….

8. Passive Heat Exchange
• Passive HE systems are least expensive means of cooling a
home which maximizes the efficiency of the building.
• 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 HE strategies rely on daily changes in temperature and
relative humidity.
• The applicability of each system depends on the climatic conditions.
• These design strategies helps heat exchange to internal space.

9. Principle

10. EARTH-AIR TUBE: PRINCIPLE
 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

11. FACTORS AFFECTING THERMAL
CONDUCTIVITY
SOIL:
 Moisture content
Most notable 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

12. No. Type of ground qE [W/m2]
1 Dry sandy 10-15
2 Moist sandy 15-20
3 Dry clay 20-25
4 Moist clay 25-30
Heat exchange rate for different soil types

13. APPLICATIONS OF EAT’S
 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

14. DESIGN GUIDELINES

15. IMPORTANT DESIGN
PARAMETERS:
 The design parameters that impact the performance of the EAT are:
• Time-Temperature-Depth
• Tube Depth
• Tube Length
• Tube Diameter
• Air velocity
• Air Flow rate
• Tube Material
• Tube arrangement
 Open-loop system
 Closed-loop system
• Pit Area
• Slope
• Efficiency
• Coefficient of Performance (COP)
[3]

16. Time-Temperature-Depth

17. Contd…
No Season Ambient air
temperature
Soil
temperature
Space
temperature
1 Winter 12oC-20oC 25oC-30oC 24oC-26oC
2 Summer 40oC-45oC 22oC-28oC 25oC-28oC
Temperature profile

18. TUBE DEPTH
 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.

19. TUBE LENGTH
 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.

20. TUBE DIAMETER
 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]

21. AIR VELOCITY
 As the velocity of air increases the exit temp decreases.
[6]

22. AIR FLOW RATE
 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

23. TUBE MATERIAL
 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.

24. TUBE ARRANGEMENT
 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

25. TUBE ARRANGEMENT
 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

26. EAT EFFICIENCY
 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

27. CO-EFFICIENT OF PERFORMANCE(COP)
 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

28. Advantage
 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.

29. LIMITATIONS
 Require large space to make setup.
 Give a limited cooling effect.
 Initial cost high.

30. POTENTIAL ISSUES

31. Moisture Accumulation And IAQ Problems
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

32. CONCLUSIONS
 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.

33. REFRENCES
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)

34. THANK YOU