Effects of weather parameters on vertical ground heat exchanger design.
Ground-source heat pump (GSHP) systems use the ground as a heat source or heat sink to provide space heating and cooling as well as domestic hot water. The GSHP system can offer higher energy efficiency for air conditioning compared to conventional air-conditioning systems because the underground environment provides lower temperatures for cooling and higher temperatures for heating with less temperature fluctuation than ambient air.
The ground heat exchanger (GHE) is a major component of the GSHP system and a way by which the thermal energy is extracted from and injected into the ground. The GHE operation induces a simultaneous heat and moisture flow in its surrounding soil. The transfer of heat between the GHE and adjoining soil is primarily by heat conduction and to a certain degree by moisture migration. The entire process of heat injection and extraction is transient in nature due to the weather-dependent ground surface boundary conditions and heating/ cooling load. The soil thermal conductivity varies greatly with the soil type (texture, mineralogical composition), moisture content, dry bulk density, and temperature. The soil moisture content in close vicinity to the GHE can be influenced by numerous factors such as soil structure, temperature gradient, moisture gradient, irrigation, and gravity effects. In particular, the temperature gradient in the soil surrounding the GHE plays an important role in the combined heat and moisture flow. When the soil temperature near the GHE is well above 40[degrees]C (104[degrees]F), the effect of the moisture gradient is limited as compared to the temperature gradient, which may lead to a dry-soil belt around the GHE behaving like an annular zone of insulation (Leong et al. 1998; Wang et al. 2012). Moreover, depending on the moisture content and temperature, structural and textural properties of the same soil sample can vary considerably with seasonal climatic conditions. Therefore, thorough understanding of the intricate nature of soils and transport phenomena related to coupled heat and moisture flow in the ground is essential to both the design and the operation of GSHP systems. Due to the very complex characteristics of the ground, the actual design of the GHE should be based on a detailed mathematical model of simultaneous heat and moisture flow in soils, plus an integrated heat pump model and reliable ground hydrogeological data.
A number of design tools for vertical ground heat exchangers (VGHE) based on some typical heat transfer models have been developed in the last two decades. A good design program for VGHE should have high computational efficiency, which allows for a quick simulation of the transient effects over a long period of time. There are numerous factors that affect to some extent the final sizing of a VGHE and should be considered in the mathematical methodology or heat transfer model as a crucial part of a design program (Leong and Tarnawski 2010).
HOUSE LOAD AND SYSTEM CONFIGURATION House Load
The house selected for this study is located in the town of Milton, Ontario. The house was one of two energy efficient demonstration houses built by a local builder in 2005. It is a detached two-storey building having 498 [m.sup.2] (5360 [ft.sup.2]) of heated area, including the basement.
As per builder specifications, the house temperature is set at 21[degrees]C (70[degrees]F) and 24[degrees]C (75[degrees]F) in the heating and cooling periods, respectively. Air leakage at 50 Pa (0.007 psi) is 1.41 ach (518 l/s). A continuous ventilation of 0.16 ach through heat recovery ventilation (HRV) system is also considered. The sensible internal heat gain from occupants is set to be 2.4 kWh/day (8.2 kBtu/day). The occupancy of the house is two adults and two children for 50% of the time with a hot water consumption of 225 L/day (59.44 gal/day). The base loads are considered to be 22 kWh/day, including interior lighting, appliances use, and others. TRNBuild, a component of the TRNSYS simulation software, was used to generate the house load profile (Rad et al. 2013).
TRNBuild (TRNBuild 2004), a component of the TRNSYS simulation software, was used to generate the house load profile. TRNBuild was developed as a part of TRNSYS for simulating multizone buildings. It works under Type 56 (house model) in the TRNSYS studio (system generating module). This component models the thermal behavior of a building divided into different thermal zones. In order to use it, a separate preprocessing program must be first executed. The TRNBuild program reads in and processes a file containing the building description and then generates two files used by the TYPE 56 component during TRNSYS simulation. TRNBuild generates an information file describing the outputs and required inputs of TYPE 56.
In TRNBuild, the house was modeled in three zones: (1) basement, (2) first floor, and (3) second floor. The maximum heating and cooling demand is 11.5 kW (39 MBH) and 9.5 kW (32.4 MBH), respectively. The annual space-heating consumption for the house was estimated to be 95 GJ (89 MMBtu) with an annual space cooling consumption of 19 GJ (18 MMBtu).
The heating season was set from 1st of October (6553 h) to 30th of April (2880 h) and the cooling season from 1st of May (2881 h) to 31st of September (6552 h).
The system selected for this study is from a previously studied system by Rad et al. (2009,2013). It is a solar-assisted ground-source heat pump (SAGSHP) system. The VGHE system consists of four vertical U-tube closed-loop circuits joined in parallel. Each borehole has 0.25 m (10 in.) diameter and 55 m (180 ft) length. They are located 3.6 m (12 ft) apart from each other in the backyard and merged at 1.8 m (6 ft) below grade. Figure 1 shows this arrangement.
The VGHE is connected in parallel to the solar thermal collectors. The solar collectors receive a percentage of the total flow from the VGHE. Two circulation pumps are located upstream and downstream of the VGHE flow. A solenoid valve and a control valve control the flow rate to the solar collectors.
The heat pump is selected to suit the space-heating requirements of the house for both radiant-floor heating for the basement and forced-air heating for the first and second floors. The same heat pump provides cooling via forced air in the summer. The heat pump has a dedicated domestic hot-water generation through its desuperheater with an internally mounted loop and pump. The hot water from the desuperheater loop flows into a hot-water tank. Both the hot-water tank and heat pump are equipped with auxiliary electric heaters.
Cold main water is directed to gray-water heat recovery equipment and then sent to the hot-water tank and/or desuperheater. Basement in-floor radiant heating is directly fed from the hot-water tank by a dedicated pump.
Figure 2 shows the system equipment configuration modeled in TRNSYS 16. The main system's components are as follows:
* House model: Type 56
* Heat pump model: Type 505
* Ground loop heat exchanger model: Type 557
* Solar collector model: Type 1
* Water tank model: Type 4
* In-floor radiant heating model: Type 653
* Gray-water heat recovery model: Type 91
* Ventilation model: Type 667b
* Pump component and flow-control model: Type 114
* Control flow mixer: Type 11h and 11d
* Control model for heat pump: Type 698, 14e, and 14k
* Cold main water and domestic hot-water draw model: Type 14b
* Weather model: Type 109
In this study, three main systems' components of (1) heat pump, (2) weather data, and (3) VGHE are more focused on. Solar collectors are bypassed as they are not part of this study. This also helps to reduce the simulation time.
This component models a single-stage liquid source heat pump with desuperheater for hot-water heating. The heat pump conditions a moist airstream by rejecting energy to (cooling mode) or absorbing energy from (heating mode) a liquid stream. The desuperheater is attached to a secondary fluid stream. In cooling mode, the desuperheater relieves the liquid stream from some of the burden of rejecting energy. However, in heating mode, the desuperheater requires the liquid stream to absorb more energy than would be required for space heating only. This heat pump model is intended for residential GSHP application (Klein et al. 2004)
This model is based on user-supplied data files containing catalogue data for the capacity (total in heating mode and both total and sensible in cooling mode) and power based on the water temperature entering the heat pump, the entering water flow rate, and the airflow rate. The model is also equipped with a two-stage auxiliary heater. A selected, residential heat pump model with a desuperheater (EIT, 2005) is a good match with Type 505. Table 1 shows the parameters from the technical manual of the chosen heat pump needed for simulation.
Vertical Ground Heat Exchanger
TRNSYS 16 Default Component, Type 557. Type 557 models the VGHE that interacts thermally with the ground. GSHP applications commonly use this VGHE model. This component models vertical U-tube or vertical tube-in-tube heat exchangers. A heat carrier fluid is circulated through the VGHE and either rejects heat to or absorbs heat from the ground, depending on the temperatures of the heat carrier fluid and the ground. In typical U-tube or tube-in-tube applications, a vertical borehole is drilled into the ground. A U-tube or tubein-tube heat exchanger is then pushed into the borehole. The top of the VGHE is typically several feet below the ground surface. Finally, the borehole is filled with a backfill material, either virgin soil or a grout of some type. The model assumes that the boreholes are placed uniformly within a cylindrical storage volume of ground. There is convective heat transfer within the pipes and conductive heat transfer to the groundstorage volume. The temperature of the surrounding ground is calculated from three parts: a global temperature, a local solution, and a steady-flux solution. The global and local problems are solved with the use of an explicit finite-difference method. The steady-flux solution is obtained analytically. The resulting temperature is then calculated using superposition methods. This component was developed by the Department of Mathematical Physics at the University of Lund, Sweden (Hellstrom 1989).
GHEADS Component, Type 201a. Vertical ground heat-exchanger analysis, design, and simulation (VGHEADS) is based on computer simulation of the performance of an entire GSHP system (Leong and Tarnawski 2010). A detailed numerical solution incorporates the following:
1. Equations describing simultaneous heat and moisture transfer in ground heat storage solved by the finite element method.
2. A steady-state model of heat pump units
3. The heating and cooling loads of the house
4. Average daily climatological data
5. An initial soil temperature and moisture content profile
Temperature variation of circulating fluid along the closed-loop VGHE is calculated upon the energy balance and heat transfer between the circulating fluid and surrounding soil. It is assumed that the ground heat storage around the borehole has axisymmetric conditions; thus, soil temperature and moisture profiles in ground heat storage are calculated only in the axial and radial directions, reducing the problem to a two-dimensional one (Leong andTarnawski 2010). The developed computer program takes into account a large number of obstacles which are normally disregarded for a simpler analysis. Major processes that have been addressed in this program could be highlighted as follow:
1. Coupled heat and moisture flow in ground heat storage
2. Soil freezing/thawing and drying/rewetting due to heat extraction and heat deposition
3. Different soil types and layers, as well as the presence of the ground water table
4. Dynamic ground-surface effects (radiation, convection, advection, evapotranspiration, snow cover, etc.)
The soil moisture transport properties are obtained from the Philip-de Vries model (1957) and field experimental data provided by Clapp and Hornberger (1978) and Campbell (1985). The site topography and comprehensive climatological data, such as ambient temperature, solar radiation, wind speed, rainfall, snow cover, snow density, and water vapor pressure, are used to simulate the boundary conditions at the ground surface.
The program can simulate a multiple full-year operation of a GSHP system in the heating and cooling mode. The entire computer program is written in FORTRAN 77 software and can be run on a wide range of computers.
The program was modified and imported into TRNSYS 16 as component Type 201a in 2009.
The default weather data, used for the North American cities in the TRNSYS 16, is a typical meteorological year 2 (TMY2) data set derived from 1961 to 1990. Data are from National Solar Radiation Data Base (NSRDB), which was completed in March 1994 by the National Renewable Energy Laboratory (NREL) (Marion and Urban 1995). TRNSYS 16 database does not contain all the weather data components by default. The output parameters of the Type 109-TMY2 are used as an input for the house simulation module (Type 56) and GHE (Type 557). This TMY2 data has enough information required for the Type 557.
In order to run VGHEADS's module (Type 201a) in TRNSYS, a more detailed weather file is required. Table 2 shows the output parameters required in addition to the default parameters in Type 109-TMY2 for using the Type 201a module. These parameters are extracted from Environment Canada (n.d) and defined in a supplementary data file read by Type 300b. Figures 3, 4, 5, and 6 show the yearly mentioned parameters for the city of Toronto. It can be seen that these parameter values are relatively large. Therefore, they should be taken into the consideration for accurate heat transfer calculations, particularly for the shallower borehole arrangements.
SENSITIVITY ANALYSIS--DIFFERENT BOREHOLE LENGTHS, TYPE 201A
Based on the input data explained in the previous section, the system simulations were performed with each of the following vertical ground loop heat exchanger (VGHE) modules:
1. Type 557, TRNSYS default VGHE module
2. Type 201a, GHEADS VGHE module in conduction-only mode (mode 0)
Using the Type 201a module, a sensitivity analysis was carried out to find the effect of the borehole depth in the system performance. The borehole arrangements and depths were selected as follows (the total borehole lengths are 220 m [721.6 ft] and the borehole separations are 3.6m [12 ft] for all the cases):
1. 4 boreholes at 55 m (180 ft) depth, each as shown in Figure 1 (55 x 4 m [180 x 4 ft), which is considered as the base case
2. 8 boreholes in one row at 27.5 m (89 ft) depth each, 27 x 8 m (89 x 8 ft)
3. 12 boreholes in one row at 18.33 m (62 ft) depth each, 19 x 12 m (62 x 12 ft)
4. 16 boreholes in one row at 13.75 m (46 ft) depth each, 14 x 16 m (46 x 16 ft)
Figures 7 and 8 show the result of the simulation for entering fluid temperatures (EFTs) in Cases 2 and 4, as mentioned above, compared to the base case.
For the system with Type 201a module, Figure 9 shows the difference between IN and OUT temperatures of the heat pump ([DELTA]IOT) for a whole year. In shoulder seasons (late March to late May and early September to mid November), the results show that the [DELTA]IOT are lesser in the shallower borehole arrangements than the base case. The average [DELTA]IOTs in shallower boreholes are 0.34% lesser than the base case for the whole year.
Figure 10 shows the heat-pump coefficient of performance (COP) for the base case and shallower borehole arrangements. The average COPs in the cooling season for 14 x 16 m (46 x 16 ft) cases are 2.2% higher than the base case and the COPs in the heating season are showing a 1.47% increase.
SENSITIVITY ANALYSIS DIFFERENT BOREHOLE LENGTHS, TYPE 201A
VERSUS TYPE 557
The effect of the different borehole arrangements and depths for the default TRNSYS VGHE (Type 557) versus VGHEADS VGHE (Type 201a) are investigated.
The performance of the systems for the two different modules, Type 201a and Type 557, were investigated. Figures 11a and 11b, show the averages of differences in temperatures in and out of the heat pump ([DELTA]IOT) for Types 201a and 557 in the heating and cooling modes, respectively. The average [DELTA]IOTs are shown for different borehole arrangements and depths.
In heating mode, the average [DELTA]IOT for the Type 201a is higher than for the Type 557 by 21.6% for the base case and by 23% for the 14 x 16 m (46 x 16 ft) case. In cooling mode the average [DELTA]IOT for the Type 201a is higher than for the Type 557 by 19% for the base case and by 18% for the 14 x 16 m case. Figures 12a and 12b show the average annual coefficient of performance (COP) of heat pumps for Types 201a and Type 557 in the heating and cooling modes, respectively. The average COPs are also shown for different borehole arrangements and depths.
In the heating mode, the average heat pump COP for the Type 201a is almost the same as for the Type 557. For the base case, the average heat pump COP forType 557 is 2% higher-than for the Type 201a. In the cooling mode the average heat pump COP for Type 201a is higher than for the Type 557 by 3.9% for the base case and by 3.8% for the 14 x 16 m (46 x 16 ft) case.
RESULT DISCUSSIONS AND CONCLUSIONS
Sensitivity analysis for the Type 201a (VGHEADS) for heat pump EFTs and the different borehole arrangements and depths gives the following results:
1. Heat pump EFT increases with the decrease of the borehole depths in the heating mode.
2. Heat pump EFT decreases with the decrease of the borehole depths in the cooling mode.
The above results show that by decreasing the borehole depth, the heat pump EFTs are in favor of the system performance in both heating and cooling modes. The increases of the performance are quantified by the heat pump COPs in the heating and cooling modes by 1.5% and 2.2%, respectively. The performance increases correspond to 75% borehole depth reduction from 55 m to 14 m (180 to 46 ft).
The results for the effect of borehole depth reduction on the heat pump EFTs for Type 557 are as follows:
1. The heat pump EFT decreases with decreasing of borehole depths in the heating mode.
2. The heat pump EFT decreases with decreasing of borehole depths in the cooling mode.
In the cooling mode, the two simulation results for Type 557 and Type 201a are in agreement with each other, whereas in heating mode the effect of borehole depth reduction in two systems are opposite.
For Type 201a, which considers the effects of all climatic data such as rainfall and snow cover, it can be concluded that, in the heating mode, the shallower boreholes perform better than the deeper boreholes comparing to the Type 557. In the cooling mode, both Type 201a and 557 have almost the same trend in efficiency results as the borehole depths decrease. This could be due to considering only rainfall parameter that Type 201a has in addition to the Type 557.
Table 3 shows the summary of the sensitivity analysis results for the system performance with different borehole arrangements and depths.
From Table 3 and Figures 11a, 11b, 12a, and 12b the following conclusions can be made from the results:
1. In the heating and cooling modes, the average heat pump in and out fluid temperature differences ([DELTA]IOT) in the system with Type 201a (VGHEADS) are higher than in the system with Type 557 (TRNSYS default). It can be concluded that the Type 201a module calculates more heat transfer to/from the ground. The average heat pump [DELTA]IOTs for the Type 201a in the cooling mode are higher than in the heating mode. In the heating mode the average heat pump [DELTA]IOTs of Type 201a are 21.6% and 23% higher than those of Type 557 for the base case and the 14 x 16 m case, respectively. In the cooling mode the average heat pump [DELTA]IOTs of Type 201a are 19% and 18% higher than those of Type 557 for the base case and the 14 x16 m (46 x 16 ft) case, respectively.
2. In the heating mode, the average heat pump COPs for the system with Type 201a and Type 557 for the shallower borehole arrangements (14 x 16 m [46 x 16 ft]) are the same (2.04). In the base case borehole arrangements (55 x 4 m [180 x 4 ft]), the average heat pump COP for the system with Type 557 is slightly (2%) higher than the system with Type 201a. This is not what was expected based on the above [DELTA]IOT conclusions. This could be due to the average taking approach for data comparison for the heat pump COPs, which might not be an appropriate approach for this case. A further detailed investigation for this part is required.
3. In the cooling mode, the average COP for the Type 201a is higher than the Type 557 by 3.9% for the base case and by 3.8% for the 14 x 16 m (46 x 16 ft) case.
Clapp, R.B. and G.M. Hornberger.1978. Empirical equations for some soil hydraulic properties. Water Resources Research 14:601-04.
Campbell, G.S. 1985. Soil physics with BASIC. New York, Elsevier.
EIT. 2005. EI Geo-Exchange System. Surrey, BC, Canada, Essential Innovation Technology Corporation, Surrey, BC, Canada.
Environment Canada. n.d. Weather. www.weather.gc.ca.
Hellstrom, G. 1989. Duct ground heat storage model: Manual for computer code. Department of Mathematical Physics, University of Lund, Sweden.
Klein, S.A., B. Beckmann, and J. Duffie. 2004. TRNSYS, a Transient System Simulation Program, Version 2. Solar Energy Laboratory, University of Wisconsin-Madison, TRNSYS 16 Manual, TESS Library.
Leong, W.H., V.R. Tarnawski, and A. Aittomaki. 1998. Effect of Soil Type and Moisture Content on Ground Heat Pump Performance. International Journal of Refrigeration 21(8):595-606.
Leong, W.H., and V.R. Tarnawski. 2010. Effects of Simultaneous Heat and Moisture Transfer in Soils on the Performance of a Ground Source Heat Pump System. ASMEATI-UIT 2010 Conference on Thermal and Environmental Issues in Energy Systems, May, Sorrento, Italy.
Marion, W. and K. Urban. 1995. User's manual for TMY2s typical meteorological years: Derived from the 19611990 National Solar Radiation Data Base, National Renewable Energy Laboratory (NREL), Golden, CO.
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TRNBuild and Multi-zone Building Modeling. 2004. TRNSYS, a Transient System Simulation Program 16 Manual, 6. Solar Energy Laboratory, University of Wisconsin-Madison, Madison, WI.
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Farzin M. Rad, PEng
Alan S. Fung, PhD, PEng
Wey H. Leong, PhD, PEng
Farzin M. Rad is a doctoral candidate, Alan S. Fung is an associate professor, and Wey H. Leong is an assistant professor in the Department of Mechanical and Industrial Engineering, Ryerson University, Toronto, ON, Canada.
Table 1. GSHP Parameters Density of liquid stream 1036 kg/[m.sup.3] (64.67 lb/[ft.sup.3]) Specific heat of the liquid stream 3.6 kJ/kg x K (0.86 Btu/lb x [degrees]F) Specific heat of domestic hot 4.18 kJ/kg x K water (DHW) fluid (0.99 Btu/lb x [degrees]F) Blower power 0.19 kW Controller power 0.01 kW Capacity of Stage 1 auxiliary heater 5 kW Capacity of Stage 2 auxiliary heater 5 kW Total airflow rate 944 l/s (2000 cfm) Total cooling capacity 17 kW (57,800 Btu/h) Energy efficiency ratio (EER) 14.8 Heating capacity 14.5 kW (49,500 Btu/h) COP heating 3.3 Table 2. Supplementary Weather Data File, Output Parameters Output of Units Supplementary Weather Data File Ground surface albedo -- Cloudiness -- Rainfall mm (in.) Snow cover depth m (ft) Snow cover density kg/[m.sup.3](lb/[ft.sup.3]) Table 3. Summary of Sensitivity Analysis Results between Type 201a (VGHEADS) and Type 557 (TRNSYS Default Geo-Exchange Modules) Type 201a: VGHEADS, Borehole Layouts Geo-exchange Module 55 x 4 m 27 x 8 m (180 x 4 ft) (89 x 8 ft) Average HP, [DELTA]IOT (in and out 5.84 (10.5) 5.84 (10.5) [DELTA]T): Heating [degrees]C ([degrees]F) Average HP, [DELTA]IOT (in and out -9.07 (-16.3) -9.08 (-16.3) [DELTA]T): Cooling [degrees]C ([degrees]F) Average HP COP: Heating 2.01 2.01 Average HP COP: Cooling 7.24 7.23 Type 557: TRNSYS, -- -- Geo-exchange Module Average HP [DELTA]IOT (in and out 4.80 (8.6) 4.77 (8.6) [DELTA]T): Heating [degrees]C ([degrees]F) Average HP [DELTA]IOT (in and out -7.62 (-13.7) -7.67 (-13.8) [DELTA]T): Cooling [degrees]C ([degrees]F) Average HP COP: Heating 2.05 2.04 Average HP COP: Cooling 6.97 7.01 Type 201a: VGHEADS, Borehole Layouts Geo-exchange Module 19 x 12 m 14 x 16 m (62 x 12 ft) (46 x 16 ft) Average HP, [DELTA]IOT (in and out 5.82 (10.4) 5.82 (10.4) [DELTA]T): Heating [degrees]C ([degrees]F) Average HP, [DELTA]IOT (in and out -9.19 (-16.5) -9.19 (-16.5) [DELTA]T): Cooling [degrees]C ([degrees]F) Average HP COP: Heating 2.04 2.04 Average HP COP: Cooling 7.40 7.40 Type 557: TRNSYS, -- -- Geo-exchange Module Average HP [DELTA]IOT (in and out 4.81 (8.7) 4.73 (8.5) [DELTA]T): Heating [degrees]C ([degrees]F) Average HP [DELTA]IOT (in and out -7.76 (-14) -7.78 (-14) [DELTA]T): Cooling [degrees]C ([degrees]F) Average HP COP: Heating 2.05 2.04 Average HP COP: Cooling 7.11 7.13 Note: HP = heat pump, [DELTA]IOT (IN and OUT [DELTA]T) = the average heat pump IN and OUT fluid temperature differences ([DELTA]IOT), COP = coefficient of performance of the heat pump. Figure 11 (a) Average heat pump differential in and out fluid temperature (HP MOT) for different borehole layout arrange ments in heating mode. (b) Average heat pump differential in and out fluid temperature (HP MOT) for different borehole layout arrangements in cooling mode. Average HP [DELTA]IOT for Diffrent Borehole Layout Arrangements- Heating Type 201a Type 557 55mx4 5.84[degrees]C 4.80[degrees]C (180ftx4) (10.5[degrees]F) (8.6[degrees]F) 27mx8 5.84[degrees]C 4.77[degrees]C (89ftx8) (10.5[degrees]F) (8.6[degrees]F) 19mxl2 5.82[degrees]C 4.81[degrees]C (62ftxl2) (10.4[degrees]F) (8.7[degrees]F) 14mxl6 5.82[degrees]C 4.73[degrees]C (46ftxl6) (10.4[degrees]F) (8.5[degrees]F) Borehole Ai rangments (a) Average HP [DELTA]IOT for Diffrent Borehole Layout Airangments- Cooling Type 201a Type 557 55mx4 9.07[degrees]C 7.62[degrees]C (180ftx4) 16.3[degrees]F) 13.8[degrees]F 27mx8 9.08[degrees]C 7.67[degrees]C (89ftx8) (16.3[degrees]F) 14.[degrees]F 19mxl2 9.19[degrees]C 7.76[degrees]C (62ftxl2) (16.5[degrees]F] 14[degrees]F 14mxl6 9.19[degrees] 7.78[degrees]C (46ftxl6) 16.5[degrees]F) 14.8[degrees]F Borehole Air augments (b) Note: Table made from Bar graph. Figure 12 (a) Average heatpump coefficients of performance (COPs) for different borehole layout arrangements in heating mode. (b) Average heat pump coefficients of performance (COPs) for different borehole layout arrangements in cooling mode. Type 201a Type 557 55mx4 2.01 2.05 (180ftx4) 27mx8 2.01 2.04 (89ftx8) 19mxl2 2.01 2.05 (62ftxl2) 14mx16 2.04 2.04 (46ftxl6) Borehole Ai rangments (a) Average HP COP-Heating Type 201a Type 557 55mx4 7.24 6.97 (180ftx4) 27mx8 7.23 7.01 (89ftx8) 19mxl2 7.40 7.11 (62ftxl2) 14mxl6 7.40 7.11 (46ftxl6) (b) Note: Table made from Bar graph.
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|Author:||Rad, Farzin M.; Fung, Alan S.; Leong, Wey H.|
|Date:||Jul 1, 2014|
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