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1. Earth Air Tunnel Heat Exchanger (EATHE) Submitted by Amandeep Singh Vikas Mahala Ashok Dhayal

2. contents 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. introduction 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 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. Earth Air Tunnel 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. EARTH-AIR TUNNEL: PRINCIPLE Underground heat exchanger Also called: Earth-Air Heat Exchangers Air-to-soil Heat Exchangers Earth Canals

7. Principle Diagram

8. EARTH-AIR TUNNEL: 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

9. FACTORS AFFECTING THERMAL CONDUCTIVITY 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. 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

11. DESIGN GUIDELINES

12. IMPORTANT DESIGN PARAMETERS : 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. 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.

14. 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.

15. 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]

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

17. 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

18. 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.

19. 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

20. 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

21. 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

22. Contd ….

23. 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

24. 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

25. Advantage AND LIMITATIONS [8]

26. 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.

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

28. POTENTIAL ISSUES

29. MOISTURE ACCUMULATION AND IAQ PROBLEM

30. CONCLUSIONs

31. 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.

32. REFRENCES 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 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) 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. Performance analysis of earth–pipe–air heat exchanger for winter heating vikas bansal *, rohit misra , ghanshyam das agrawal , jyotirmay mathur Performance analysis of earth–pipe–air heat exchanger for summer cooling vikas bansal *, rohit misra , ghanshyam das agrawal , jyotirmay mathur Performance evaluation and economic analysis of integrated earth–air–tunnel heat exchanger–evaporative cooling system vikas bansal ∗, rohit misra , ghanshyam das agrawal , jyotirmay mathur Thermal performance investigation of hybrid earth air tunnel heat exchanger rohit misraa , vikas bansala , ghanshyam das agarwala , jyotirmay mathura ,∗, tarun aserib 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)

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