Paper Title (Use Style: Paper Title) s48

International Journal of Enhanced Research Publications, ISSN: XXXX-XXXX Vol. 2 Issue 4, April-2014, pp: (1-4), Available online at: www.erpublications.com Integrated Inbuilt Roof Cooling System (IIRCS): Thermal Design Optimization and Techno- Economic Analysis Author Name: Vanita Thakkar1 Associate Professor, Mechanical Engineering Department, Babaria Institute of Technology, BITS Edu Campus, Vadodra-Mumbai N H # 8, Varnama, Vadodara – 391 240. Address (for correspondence) : “Devashish”, 317, Sahakarnagar, New Sama Road, Vadodara – 390 024

Abstract: There is increasing awareness the world round regarding energy-efficient, environment-friendly space cooling systems. Such systems become more important in developing countries like India, having acute power shortage problems, especially if they are cost-effective. Integrated Inbuilt Roof Cooling System (IIRCS) is a low cost, energy efficient, easy-to-maintain and non-polluting Active Solar Architecture System having promising prospects of use in rural and urban areas for residential/commercial buildings, cattle sheds, etc. in hot, dry regions. In an IIRCS, heat, from solar radiant energy and internal heat-load from occupants, appliances, etc. is carried away by coolant, water circulated through piping system laid in the roof called Roof Piping System (RPS) and hot coolant is cooled in a heat exchanger. The coolant is re-circulated in RPS. The paper presents Thermal Design Optimization of an IIRCS using a java-based Simulation Program for modeling a BPHE-based IIRCS for a building, 10mx10m with horizontal roof, followed by Costing.

Keywords: Active Solar Architecture, Inbuilt Roof Cooling System, BPHE, ETHE, Thermal Design Optimization.

Introduction

A substantial share of world energy resources are being spent on heating, cooling and lighting buildings, which are designed to squeeze in as much as possible per sq. m. area due to rapid urbanization. Ensuring means of enhancing and maintaining thermal comfort in buildings has thus become an important requirement. The emerging Energy-conscious Architectural style, SOLAR ARCHITECTURE, aims at comfortable, energy efficient buildings. “Passive Solar Architecture” relies on design of buildings based on natural thermal conduction, convection and radiation to ensure climate control. Vaastu Shaastra – the ancient Indian guide to building a structure, according to specific principles, all of which are based on strong scientific fundamentals, actually advocates what we call – Passive Solar Architecture. “Active Solar Architecture” involves the use of solar collectors, which require an external source of energy. “Active features” are incorporated to ensure finer control on the internal climate heat distribution. Active Solar Systems use means like solar panels and solar photovoltaics for heat collection and electrically-driven pumps or fans to transport heat / cold to the space to be conditioned. In the present scenario, with lots of space and planning constraints, a proper combination of Passive and Active Solar Architecture – which gives “Hybrid Systems” – needs to be applied to ensure a comfortable, energy-efficient residence / working place [1]. The paper introduces Integrated In-built Roof Cooling System (IIRCS). An IIRCS is a low cost, energy efficient, easy-to-maintain and non-polluting Active Solar Architecture System [2]. It has promising prospects of use in rural and urban areas for residential / commercial buildings, cattle sheds, etc. in hot, dry regions. In an IIRCS, heat – due to solar radiant energy and internal heat load due to occupants, appliances, etc. – is carried away by coolant – water – circulated through a piping system laid in the roof – either in slab or in water-proofing – and the hot coolant is cooled in a heat exchanger – either Buried Pipe Heat Exchanger (BPHE) or any other simple heat exchanger. The cooled coolant from heat exchanger is re-circulated in the Roof Piping System (RPS). The paper presents Thermal Design www.erpublications.com Optimization [3] of an IIRCS using a java-based Simulation Program for modeling a BPHE-based IIRCS for a building – 10m x 10m area, having a horizontal roof – followed by Costing [4], which involves : 1. Roof Piping Analysis – Using an electrical analogy network to do Heat Transfer Analysis. A parametric study is done for designing RPS laid in roof slab, which includes selection of pipe material and specifications and computation of various parameters of the RPS. 2. BPHE Analysis – to select best suited configuration and compute various parameters of the BPHE. 3. Pumping Power Computations.

Literature Review

Three main categories of Non-Conventional Space Conditioning Systems can be identified – 1. Solar-assisted air conditioning systems, 2. Earth Tube Heat Exchanger (ETHE) / Buried Tube Heat Exchanger (BPHE) based Space Conditioning Systems and 3. Other non-conventional space conditioning systems. There can be varieties in each type depending upon the geographic and climatic conditions for which they are developed, the specific requirements of the system – like, residential building, work-place, greenhouse, auditorium, etc. as well as the principle on which they are based and the technology they make use of [5]. The current paper focuses on the use of the second type of systems, the details regarding which are discussed in the succeeding review. It is a well-known fact that while ambient temperatures are subjected to diurnal, seasonal and annual fluctuations, temperatures of the soil beyond a certain depth remain virtually constant. Though these variations do occur, amplitudes of fluctuations in the deep soil temperatures remain much smaller than those at the surface. So, deeper layer of the soil can be used as both – heat sink (during summer) and heat source (during winter) [2]. BPHE / ETHE Systems are low cost, reliable and easy-to-maintain systems based on this concept. The coolant / heating fluid may be air or water or any other suitable fluid and it is circulated with the help of a blower – when air is used – or a centrifugal pump – when water / liquids are used – through an underground piping system – to reject the heat gained from the thermal load on the structure being cooled, or – to gain heat from the ground to heat the structure [5]. Figure 1 shows outline of various ETHE / BPHE based space conditioning systems [5].

www.erpublications.com International Journal of Enhanced Research Publications, ISSN: XXXX-XXXX Vol. 2 Issue 4, April-2014, pp: (1-4), Available online at: www.erpublications.com

Figure 1 : Outline of various Earth Tube Heat Exchanger (ETHE) / Buried Pipe Heat Exchanger (BPHE) based space conditioning systems. Figure 2 shows a typical Earth-Air Heat Exchanger (EAHE) system, in which air is circulated through piping laid in the ground and after being heated or cooled, as per the requirement / season, the air is circulated in the space to be conditioned [6]. Figure 3 shows the working of Heat Pumps – commonly known as Geo-exchange or Geothermal systems, which are double circuit systems and work on the principle of Vapour Compression refrigeration systems and are widely used in the USA, Canada and European countries like Germany, Denmark, Finland, Sweden, etc. [7].

www.erpublications.com Figure 2: Typical Earth-Air Heat Exchanger (EAHE) System [6]

Figure 3 : Heat Pumps [7]

The other type of ETHE / BPHE based space conditioning system – Integrated Inbuilt Roof Cooling System (IIRCS) is described in the succeeding discussions. A combination of EAHE and IIRCS is being used in the office building of a company named Universal Medicap Ltd. (UML), Vadodara. The design of the Roof Piping System in the IIRCS at UML is based on thumb rules and logic. A systematic study and analysis and implementation of its conclusions can help in optimizing performance of the system [8].

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Integrated Inbuilt Roof Cooling System (IIRCS) : System description

An Integrated Inbuilt Roof Cooling System (IIRCS) – an Active Solar Architecture System – consists of : 1. Roof Piping System (RPS) – the thermal circuit on which it is based is shown in fig. 1. 2. Heat Exchanger. 3. Pump. Figure 4 shows a schematic diagram of BPHE-based IIRCS. Figure 5 shows the thermal circuit diagram of the system under consideration. Here, heat – due to solar radiant energy as well as internal heat load due to occupants, appliances, etc. – is carried away by coolant – water – circulated through a piping system laid in the roof – either in slab or in water-proofing – and the hot coolant is cooled in a heat exchanger – either Buried Pipe Heat Exchanger (BPHE) or any other simple heat exchanger. The cooled coolant from the heat exchanger is re-circulated in the Roof Piping System (RPS).

Figure 4 : Schematic Diagram of BPHE-based Integrated Inbuilt Roof Cooling System (IIRCS) [2]

Figure 5 : Thermal Circuit Diagram of Roof Piping System (RPS) [2] Thermal Analysis of IIRCS

The thermal analysis of IIRCS involves the use of various theoretical and experimental models – predicting correlations, based on investigations carried out by earlier investigators over the years. A model – based on Electrical analogy, shown in figure 5 – is developed, using appropriate correlations for computing and estimating relevant parameters. A simple Java-based Simulation Program is developed for computation and analysis. The thermal design of IIRCS can be divided into 3 important stages: Roof Piping Analysis : It involves: 1. Estimation of Total Heat Load, which consists of : a. Load from Solar Radiant Energy. [2] b. Internal Load due to various sources like occupants, appliances, etc. 2. Assessment of various modes of heat transfer taking place on the Roof-Top as well as in the RPS, embedded in it – with the help of Electrical Network Analogy. 3. Computing : a. Optimum Pipe Center Distance from the Roof Surface. b. Optimum Horizontal Distance between the pipes to obtain the required room temperature for the given pipe specifications (d). c. Outlet temperature of water (tfoc) – for given pipe length, which depends on the Roof Geometry. d. The Room Temperature (ti,cal). e. Number of pipes required in the RPS (Np) and the total mass flow rate of water (mtotal).

www.erpublications.com Initially, a segment of roof is considered, in which length of roof is equal to 1m – corresponding to 1m length of Coolant Flow Pipe (CFP) laid length-wise in the roof. Width of roof is equal to the sum of twice the outer diameter of CFP and horizontal distance between the edges of the two pipes under consideration (d). For given pipe specifications, a value of d is assumed. After computing the values of various thermal resistances, as shown in figure 5, the heat gained by water (qw) and the outlet temperature of water can be computed with the help of Efficiency Factor (F’) – actual heat gain rate per pipe per unit length to the gain, which would occur if the roof were at inlet temperature of water in the CFP (tfi) – and Heat Removal Factor (Fr) – the ratio of actual useful heat gain rate to the gain, which would occur if the roof were at temperature, tfi everywhere [2]. These values will be for 1m length of CFP. Considering the outlet temperature at the end of first segment as the inlet temperature for the next segment and adding up the heat gained by water in each segment, tfoc and total heat gained by water across the length of the pipe, qw,total can be computed. The temperature of room (ti,cal) for the assumed value of d can be thus found and it should match the value of required room temperature. If it is more, then the assumed value of d should be reduced and calculations for the optimum horizontal spacing between the pipes (dopti) have to be repeated till the desired value of room temperature (ti) is obtained and vice versa. Having known the dopti, Number of pipes required for the RPS, Np and mass flow rate of coolant – water – mtotal required to be circulated through the RPS can be known. The heated water at temperature tfoc goes through a header to the BPHE under gravity flow. BPHE Analyasis : It involves: 1. Computing Buried Depth – the depth below ground level, where a stable thermal environment is available and where the BPHE has to be laid. 2. Computing the Length and Number of pipes required in BPHE and the distance between them – considering only radial heat flow in one direction for buried pipe, there will be three resistances in series across the heat flow path : a. Resistance to Convective Heat Transfer to water flowing through Buried Pipe (Rf’). b. Conduction Resistance of the Pipe Material (Rp’). c. Conduction Resistance offered by Soil (Rs’). For a given velocity of water and mass flow rate required in RPS, there is a maximum possible number of pipes which can be laid in the BPHE. A further increase in the number would cause the Reynold’s Number in the BPHE pipes to go below 1800, which makes the flow laminar and thus heat transfer performance will be lowered. Also, for a given velocity, the length of pipe cannot be reduced beyond a certain limit. Knowing these two, a proper combination of length and number of pipes can be obtained.

Total Thermal Resistance of the circuit (Rtotal) is the sum of above three resistances. Assuming LMTD temperature variation across the buried pipe, the radius of cylindrical soil layer surrounding the buried pipe is the only unknown parameter, which can be found from the value of Rs’ – which can be computed by trial and error method. For an assumed length and number of pipes of pipe specifications considered, if the value of Rs’ turns out to be negative, changes in pipe length and number can be made such that Rs’ becomes positive and a proper combination of both parameters is obtained.

The cooled water – at temperature tfi – gets collected in an underground tank and it needs to be pumped to the RPS. An underground tank of appropriate size is constructed at buried depth and water from the BPHE pipes is considered to get directly collected in the tank. Pumping Computations : It involves calculating, using usual hydraulics formulae: 1. Suction Head. 2. Delivery Head. 3. Head losses due to friction, bends, valves, contractions and enlargements in the piping system, etc. www.erpublications.com International Journal of Enhanced Research Publications, ISSN: XXXX-XXXX Vol. 2 Issue 4, April-2014, pp: (1-4), Available online at: www.erpublications.com

Thermal Design of IIRCS

In Thermal Design of IIRCS, attempt is made to one by one reach an optimum value of various parameters and further design / analysis is carried out with values decided upon, in the succeeding sub- sections. Effects of variations in the parameter under consideration in logically decided range, on various important system parameters are tabulated and checked graphically and conclusions are drawn. Thermal Design of IIRCS is based on the cooling load estimated on a Design Day – “A day when the dry bulb temperature (DBT) and wet bulb temperature (WBT) peak simultaneously.” However, this does not normally happen. So, the maximum DBT is considered. For Vadodara, maximum DBT is observed in the month of May and solar load on 15th of May at 12 noon is considered maximum solar load during summer. The procedure of Thermal Design of IIRCS is divided into two stages: 1. Thermal Design of RPS:

Table 1 shows the Thermal Design Input Data required for the design of RPS. A Horizontal Roof having dimensions – 10m x 10m – is considered for study. Initially, the values of parameters are taken as shown in the table. The first parameter to get optimized is vertical distance between Pipe Center and Roof Surface. Also, initially, it is assumed that the pipe is laid at the center of the slab. Table 1 – Thermal Design Input Data for Inbuilt Roof Piping System.

S. Input Parameter Value No. 1. Location Vadodara 2. Nature of Roof Horizontal 3. Slope of Roof 0 4. Orientation of Roof Due South 5. Ambient Air Temperature (oC) 42 6. Roof Surface Temperature (oC) 60 7. Emissivity of Roof Surface 0.92 8. Pipe outer diameter – do (mm) 29 9. Pipe Thickness (mm) 2 10. Thermal Conductivity of Pipe (W/m K) 40 11. Horizontal Distance between the pipes – d (mm) To be found. 12. Pipe embedded in (Water-Proofing / Slab) Slab 13. Thickness of Roof Water-Proofing (mm) 100 14. Thermal Conductivity of Roof Water-Proofing (W/m K) 0.7 15. Thickness of Roof Slab (mm) 150 16. Thermal Conductivity of Concrete (W/m K) 1.4 17. Pipe Centre Distance from Roof Surface (mm) 175 18. Velocity of water in Coolant Flow Pipe (m/s) 1 19. Total Internal Load (W/m2) 600 20. Required Room Temperature – ti (oC) 29 21. Roof length (m) 10 22. Roof width (m) 10

Table 2 shows the sequence of steps involved in the Thermal Design of RPS, along with the observations and conclusions – in brief :

www.erpublications.com Table 2 – Steps, Observations and Conclusions of Thermal Design of Roof Piping System (RPS).

S. No. Step Observation Conclusion Optimizing Pipe RPS should be laid as close x = (thickness of water-proofing) + Center Distance from to the Roof Surface as 10 + [(pipe outer diameter) / 2]. 1. Roof Surface (x in possible. mm). Deciding Pipe Thermal Conductivity of Pipe Material Chosen – HDPE Material. Pipe material does not (thermal conductivity varies 2. contribute significantly to between 0.4-0.51). system performance. 3. Deciding Pipe Specification : Deciding Pipe Pipe Thickness should be as Min. possible thickness to be a) Thickness. less as possible. considered for the pipe outer diameters considered. Deciding Pipe Outer Pipe Outer Diameter should 16mm outer diameter, 1.5mm thk. b) Diameter - dopti. be as less as possible. HDPE pipe selected.

Effect of velocity of dopti does not vary Values of tfoc and mtotal influence water (vw) in RPS. considerably, tfoc decreases BPHE design and pumping power till a certain point and m requirements. So, v can be decided 4. total w increases with increase in on the basis of length and no. of vw. pipes in BPHE and pumping power requirements.

2. Thermal Design of BPHE and Estimating Pumping Requirements:

Water from RPS comes to BPHE (it is a set of pipes arranged parallel to each other at buried depth) for cooling, gets collected in the Underground Tank and is pumped back to the RPS from there. The temperature of water at the inlet of BPHE is the temperature of water at the outlet of RPS and the mass flow rate through the BPHE is the same as that calculated for RPS. The temperature of water at outlet of BPHE would be the same as that required at the inlet of RPS or a degree less than that.

Table 2 shows the input data for BPHE and Pump Calculations. vw is taken as 2 m/s, as the rate of variations in dopti, tfoc and mtotal become negligible after this value of vw. Table 3 – Input Data for BPHE and Pump Calculations.

S. No. Input Parameter Value 1. Temperature at buried depth (oC). 25 2. Surface Temperature (oC). 42 3. Initial Soil Temperature (oC). 22 4. Pipe Outer Diameter (mm). 16 5. Pipe Thickness (mm). 1.5 Thermal Conductivity of the Pipe material 6. 0.51 (initially – same as that of roof piping). (W/m K). 7. Pipe Length (m) To be found. 8. Pipe Number. To be found. 9. Roof Height (m) 4.5 10 Tank Depth (m) 2 . 11 Pump Efficiency (%). 85 . Same as the Roof Piping Outlet Header 12 Roof Piping Inlet Header Inner Diameter Diameter – computed in Roof Piping . (mm) Analysis. 13 Number of bends in roof piping. 6 . 14 R/D ratio of bends in the roof piping. 1 www.erpublications.com International Journal of Enhanced Research Publications, ISSN: XXXX-XXXX Vol. 2 Issue 4, April-2014, pp: (1-4), Available online at: www.erpublications.com

The Table 4 shows the steps followed in this stage of design, along with the observations and conclusions – in brief :

www.erpublications.com Table 4 – Steps, Observations and Conclusions in the Thermal Design of BPHE.

S. No. Step Observation Conclusion Deciding No. of pipes required in Pipe Material for BPHE – GI (easily BPHE Pipe BPHE decreases with available, less costly and higher 1. Material. increase in Thermal thermal conductivity than HDPE and Conductivity of Pipe SS.) Material. 2. Deciding Pipe Specification : Deciding BPHE Pipes should be as Max. possible thickness to be a) BPHE Pipe thick as possible. considered for the pipe outer Thickness. diameters considered. Deciding Pipe OD should be as less as 16mm outer diameter, 3mm thk. GI BPHE Pipe possible (i.e. smallest pipe selected. b) Outer possible size of pipe with Diameter. maximum thickness should be selected). Deciding Pumping Power Requirement The decision regarding selection of

Pump increases, min. length of vw should be taken after taking in Capacity and BPHE pipe decreases and consideration the space available for Velocity of max. permissible no. of pipes laying BPHE and the cost factor. If 3. water in RPS increases with increase in vw. more space is available, longer pipes (vw). can be laid, lesser vw and hence lesser mtotal and pumping power will be required, which would reduce the operating cost of the system.

Result, Discussion and Costing

Based on the Thermal Analysis and Design procedure for IIRCS, developed above, attempt was made to design an IIRCS using specifications of pipes and pumps available in the market. For RPS, ½” dia. HDPE pipe was chosen, which has 20mm outer diameter and 2.8mm maximum thickness for 10kg/cm2 rating. For BPHE, 10mm NB, Heavy IS 1239 pipe was selected, which has 16.7mm outer diameter and 2.9mm thickness.

Applying the procedure discussed in the preceding sections, it was found that when value of vw = 0.9m/s, mtotal = 2kg/s and total head required for pumping is about 8.8m. The inlet and outlet header appropriate for these conditions would be – DN 63, PN 6 HDPE pipe – i.e., 63mm outer diameter HDPE pipe for 6 kg/cm2 rating. For these requirements, a centrifugal mono-block pump (high discharge, single phase) with following specifications can be chosen, which is available in the market – Total Head : 9m, Discharge : 120 lpm, Delivery pipe : 25mm (1”), Power : 0.75 kW (1 HP). The estimated Installation Cost IIRCS is Rs.100000/- (Rs.45000/- : Material + Labour + Installation Cost, Rs.25000/- : Cost of Intangible Assets). A 3 TR Split A.C. Unit, required for the same operating conditions, costs Rs.60000/-. Table 5 shows the cost comparison of the two systems. Table 5 – Pay-back Period for Integrated Inbuilt Roof Cooling System

Integrated Inbuilt Roof Cooling S. No. Comparison Factor System (IIRCS) 3.0 TR Split A.C. Unit 1 Power Input. 750 W 3900 W . 2 Capital Cost. Rs.100000/- Rs.60000/- . 3 Hours of operation. 6 hours operation / day for 6 At least 9 hours operation / day for 3 . months / year (total 1080 hours). months and 6 hours operation / day for 3 months (total 1350 hours). 4 Units / day. (750 x 6) / 1000 = 4.5 kWh (3900 x 6) / 1000 = 23.4 kWh www.erpublications.com International Journal of Enhanced Research Publications, ISSN: XXXX-XXXX Vol. 2 Issue 4, April-2014, pp: (1-4), Available online at: www.erpublications.com

. 5 Units / month. 135 units. 702 units. . 6 Power Cost / month. Rs.688.50 (say, Rs.689/-) Rs.3580/- . (Considering Rs.6.00 Saving in cost of power / month = Rs.2891/- per unit for Saving in cost of power / year = Rs.2891/- x 6 = Rs.17346/- per year. After 6 residential building.) years, saving in cost of power = 6 x Rs.17346/- = Rs.104076/-

The operation of IIRCS is assumed to be 6 hours / day for 6 months / year, i.e. total 1080 hours. Here, steady state conditions are assumed, whereas in practice transient conditions prevail. When the inlet and outlet temperature of the fluid become same after certain duration of operation, the system can be switched off till the temperature of the ceiling calls for restarting of cooling. A simple auto-control system can be employed for this. Table 6 shows the prospects of various types of ETHE / BPHE based space conditioning systems [5]. Table 6 – Prospects of various types of ETHE /BPHE based space conditioning systems [5].

Criteria for Earth-Air Heat Heat Pumps [7] Pond or Lake Loop Systems [7,9] Integrated Inbuilt Roof Comparison Exchanger (EAHE) Cooling System [2, 3, 4, System [6] 5, 8] Simplicity of Simple More complex in construction, since More complex in construction, Simple construction. construction. construction. they work on the principle of Vapour since they work on the principle of Compression Refrigeration System Vapour Compression Refrigeration and hence they have Compressor, System and hence they have Expansion Device and Evaporator. Compressor, Expansion Device Also, these are double circuit, and Evaporator. Also, these are closed loop systems and they double circuit, closed loop systems require refrigerant for their and they require refrigerant for their operation. operation. Ease in Installation. Easy to install. Comparatively, more difficult to Comparatively, more difficult to Easy to install, but have install. install. to be installed in newly constructed buildings only, not in existing ones.

Capital Cost. Less than or almost Higher capital cost. Higher capital cost. Less than or almost equal to that of equal to that of Convention Space Convention Space Conditioning Conditioning Systems. Systems. Maintenance Cost. Much less Maintenance cost similar to those of Maintenance cost similar to those Much less maintenance maintenance cost conventional systems, since of conventional systems, since cost compared to compared to components like compressor are components like compressor are conventional systems. conventional there and refrigerant is also there and refrigerant is also systems. required. required. Operating Cost. Less compared to Less compared to conventional Less compared to conventional Much less compared to conventional systems. systems. those of conventional systems. systems, lesser than EAHE, Heat Pumps and Pond or Lake Loop Systems. Are they Yes. No – refrigerant used. No – refrigerant used. Yes. Environment Friendly ?

References

[1]. Urja Bharati – Solar Architecture : Sustainable Designs for Comfortable Space (April 2003), Ministry of Non-Conventional Energy Sources, New Delhi. [2]. Vanita N. Thakkar, “Thermal Design Optimization of Integrated Inbuilt Roof Cooling System”, A thesis submitted in partial fulfilment of the requirements for the degree of Master of Engineering (Thermal Science) at the M. S. University of Baroda, Vadodara, 2003. [3]. Vanita N. Thakkar, “Thermal Design Optimization of Integrated Inbuilt Roof Cooling System”, National Conference on Global Technologies in Manufacturing and Thermal Sciences (GTMTS-2004), Sethu Institute of Technology, July, 2004, Virudhunagar (Tamil Nadu), India.

www.erpublications.com [4]. Vanita N. Thakkar, “Techno-economic Analysis of Integrated In-built Roof Cooling System”, Proceedings of Renewable Energy Asia – 2008, International conference, IIT, 11-13 December, 2008, New Delhi, p – 1065-1072. [5]. Vanita N. Thakkar, “Recent Trends In Non-Conventional Space-Conditioning Systems”, International Journal of Engineering Research & Technology (IJERT), Vol. 2 Issue 3, March – 2013, ISSN: 2278-0181. [6]. Prof. Girija Sharan and Ratan Jadhav, “Performance of Single Pass earth-Tube Heat Exchanger : An Experimental Study”, Journal of Agricultural Engineering, Vol. 40, Issue 1, January-March, 1-8. [7]. Steven P. Rottmayer, “Simulation of Ground Coupled Vertical U-Tube Heat Exchangers”, A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science (Mechanical Engineering) at the University of Wisconsin-Madison, 1997. [8]. Vanita N. Thakkar, “Study and Analysis of Non-conventional Space Conditioning Systems installed at Universal Medicap, Vadodara”, Proceedings of International Conference on Advances in Mechanical Engineering, SVNIT, Surat, 3-5 August, 2009, p – 450-455. [9]. John W. Bartok, Feasibility Study of a Geothermal Heating System within a Commercial Greenhouse, … grantreport_pioneergardens.htm (Massachusetts Department of Agricultural Resources).

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