A Study on Improving the Coefficient of Performance by Comparing Balancing Well and Standing Column Well Heat Exchange Systems
Abstract
:1. Introduction
2. Experimental Methodology
- where is the total cooling capacity of the heat pump (W),
- is the total heating capacity of the heat pump (W),
- is the heat pump inlet temperature (°C) of circulating water on the source side,
- is the heat pump outlet temperature (°C) of circulating water on the source side,
- is the specific heat of heat source circulation water J/(kg·K)],
- is the mss flow rate of circulating water on the heat source side (kg/s),
- is the total power consumption (W).
3. Results and Investigations
3.1. Initial Ground-Water Temperature
3.2. Effective Thermal Conductivity
3.3. Coefficient of Performance
3.4. Thermal Environment of the Groundwater Temperature
4. Conclusions
- Using the SCW and cross-mixing balancing well underground heat exchanger, the effective thermal conductivity characteristics and COP characteristics during heating and cooling modes were compared and analyzed. Thus, the cross-mixing balancing well underground heat exchanger exhibited more effective thermal conductivity than the SCW underground heat exchanger with a high COP. Therefore, we assumed that the performance was improved because it utilized the groundwater flow in contrast to the SCW.
- The effective heat transfer value of the cross-mixing balancing well underground heat exchanger was 9.22 (W/m·K). The thermal performance of the ground was measured using two types of underground heat exchangers; the results showed that the thermal performance of the cross-mixing balancing well underground heat exchanger was more than three times higher than that of the SCW underground heat exchanger.
- In the case of SCW geothermal heat exchanger, the average effective thermal conductivity values of the heating and cooling modes were 5.86 and 3.19 W/mK, respectively. In case of balancing well cross-mixing geothermal heat exchanger, the effective thermal conductivity values using the line-source expression were 11.3 and 16.2 W/mK, respectively, during the heating and cooling modes. A comparison of the SCW and cross mixing balancing well geothermal heat exchanger showed that the balancing well system has much better performance than SCW.
- The result of comparing and analyzing the characteristics of the effective heat map using the results of SCW and balancing well system showed that the heating operation for the SCW underground heat exchanger had better thermal conductivity characteristics than the cooling operation. In addition, in the case of a balancing well underground heat exchanger, the cooling operation showed suitable thermal conductivity characteristics. As such, it is considered that the improvement in performance was caused by the flow of activated groundwater in the ground and rapid heat transfer without heat accumulation.
- The COP of two types of geothermal heat exchangers indicates a better performance of cross-mixed balancing well underground heat exchangers as compared with the SCW type. It is believed that reflecting these systems in the design would reduce the construction costs and improve the overall performance.
- The results of analysis of the thermal environment characteristics of the ground water through the cross mixing of the SCW and balancing well methods showed that, when driving the balancing well, the thermal efficiency of cross-mixing balancing well system increases more than that of the SCW, optimizing the thermal environmental conditions of the ground water, which can be a condition for long-term operation.
Author Contributions
Funding
Conflicts of Interest
References
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Location | Transducer Reading (W) | Average q (W) | Difference (W) | % of Average Power |
---|---|---|---|---|
A | 2506.6 | 2657.8 | 101.2 | 3.88 |
B | 3207.2 | 3302.5 | 93.3 | 2.82 |
Actual Flow (LPM) | Calibration Flow (LPM) | Error (%) |
---|---|---|
3.316 | 3.292 | 0.73 |
15.87 | 16.032 | 1.01 |
100.90 | 102.99 | 2.03 |
350.62 | 355.41 | 1.35 |
SCW Type | Initial Temperature | Ave. Diff. of Temperature between Inlet and Out Water | Heat Injection | Slope (K) | Effective Thermal Conductivity | Ratio of Bleeding to No Bleeding |
---|---|---|---|---|---|---|
°C | °C | W | - | W/m·K | % | |
SCW | 16.51 | 4.01 | 81,000 | 7.66 | 3.075 | - |
Balancing well | 17.71 | 3.67 | 76,000 | 2.41 | 9.22 | 300% |
Parameters | Initial Temperature | Ave. Diff. of Temp. between Inlet and Out Water | Heat Injection | Slope (K) | Effective Thermal Conductivity | Ratio of Bleeding to No Bleeding | |
---|---|---|---|---|---|---|---|
SCW Type | |||||||
°C | °C | W | - | W/m·K | % | ||
SCW | Single well | 16.51 | 4.01 | 81,000 | 7.66 | 3.075 | - |
Heating mode (two well) | 16.99 | 5.0 | 131,000 | −2.292 | 5.86 | 190% | |
Cooling mode (two well) | 17.72 | 6.9 | 119,000 | 1.256 | 3.19 | 103% | |
Balancing well | Single well | 17.71 | 3.67 | 76,000 | 2.41 | 9.22 | 300% |
Heating mode (two well) | 16.98 | 5.23 | 137,000 | −1.283 | 11.3 | 367% | |
Cooling mode (two well) | 17.75 | 7.22 | 132,000 | 1.209 | 16.2 | 527% |
Initial Ground Water Temp. | Temperature of Geothermal Side | Temperature of Load Side | Total Power | Power Consumption | COP | |||||
---|---|---|---|---|---|---|---|---|---|---|
Inlet | Outlet | Flow Rate | Inlet | Outlet | Flow Rate | |||||
NO/Units | °C | °C | °C | LPM | °C | °C | LPM | kW | kW | (-) |
SCW geothermal heat exchanger at cooling mode | ||||||||||
1 | 17.72 | 28.37 | 35.08 | 305.69 | 15.60 | 10.63 | 346.39 | 120.11 | 38.35 | 3.13 |
2 | 19.94 | 29.90 | 36.62 | 304.75 | 15.60 | 11.10 | 346.68 | 119.10 | 39.03 | 3.05 |
3 | 19.98 | 30.45 | 37.14 | 306.05 | 16.28 | 11.35 | 346.58 | 119.06 | 39.29 | 3.03 |
4 | 20.09 | 30.61 | 37.31 | 306.03 | 16.34 | 11.43 | 347.47 | 119.22 | 39.52 | 3.02 |
5 | 20.54 | 31.01 | 37.71 | 304.36 | 16.46 | 11.53 | 348.26 | 119.83 | 39.74 | 3.02 |
Average | 19.65 | 30.07 | 36.77 | 305.38 | 16.06 | 11.21 | 347.08 | 119.46 | 39.19 | 3.05 |
SCW geothermal heat exchanger at heating mode | ||||||||||
1 | 16.99 | 12.30 | 7.77 | 324.62 | 41.64 | 47.03 | 349.12 | 131.26 | 44.89 | 2.92 |
2 | 16.15 | 12.40 | 7.87 | 324.31 | 41.85 | 47.25 | 349.12 | 131.65 | 45.01 | 2.92 |
3 | 15.84 | 12.12 | 7.62 | 324.55 | 41.99 | 47.37 | 349.29 | 131.01 | 45.01 | 2.92 |
Average | 16.94 | 12.27 | 7.75 | 324.49 | 41.83 | 47.22 | 349.20 | 131.31 | 45.00 | 2.92 |
Initial Ground Water Temp. | Temperature of Geothermal Side | Temperature of Load Side | Total Power | Power Consumption | COP | |||||
---|---|---|---|---|---|---|---|---|---|---|
Inlet | Outlet | Flow Rate | Inlet | Outlet | Flow Rate | |||||
NO/Units | °C | °C | °C | LPM | °C | °C | LPM | kW | kW | (-) |
Balancing well geothermal heat exchanger in cooling mode | ||||||||||
1 | 17.75 | 20.61 | 27.56 | 317.81 | 17.61 | 12.14 | 349.69 | 133.55 | 35.26 | 3.79 |
2 | 17.63 | 20.44 | 27.33 | 318.14 | 17.22 | 11.79 | 349.47 | 132.58 | 35.13 | 3.77 |
3 | 17.91 | 20.44 | 27.21 | 318.76 | 16.49 | 11.13 | 349.14 | 130.54 | 35.00 | 3.73 |
4 | 17.64 | 20.46 | 27.32 | 318.73 | 17.05 | 11.63 | 349.64 | 132.37 | 35.18 | 3.76 |
5 | 17.84 | 20.48 | 27.33 | 318.90 | 16.99 | 11.58 | 349.63 | 132.06 | 35.19 | 3.75 |
Average | 17.75 | 20.49 | 27.35 | 318.47 | 17.07 | 11.65 | 349.51 | 132.22 | 35.15 | 3.76 |
Balancing well geothermal heat exchanger in heating mode | ||||||||||
1 | 16.98 | 14.28 | 9.36 | 319.20 | 40.53 | 46.19 | 348.31 | 137.48 | 41.91 | 3.28 |
2 | 16.85 | 14.26 | 9.33 | 318.75 | 40.47 | 46.14 | 348.60 | 137.95 | 41.91 | 3.27 |
3 | 16.85 | 14.29 | 9.36 | 319.32 | 40.36 | 46.03 | 348.32 | 137.80 | 41.91 | 3.27 |
Average | 16.89 | 14.28 | 9.35 | 319.09 | 40.45 | 46.12 | 348.41 | 137.74 | 42.06 | 3.27 |
Initial Ground-Water Temperature | Cooling Operation | Heating Operation | ||
---|---|---|---|---|
SCW | Balancing Well | SCW | Balancing Well | |
1 | 17.72 | 17.75 | 16.99 | 16.98 |
2 | 19.94 | 17.63 | 16.15 | 16.85 |
3 | 19.98 | 17.91 | 15.84 | 16.85 |
4 | 20.09 | 17.63 | ||
5 | 20.54 | 17.84 | ||
Standard deviation | 1.11 | 0.12 | 0.6 | 0.08 |
COP Performance Coefficient | Cooling Operation | Heating Operation | ||||
---|---|---|---|---|---|---|
SCW | Balancing Well | Remarks | SCW | Balancing Well | Remarks | |
minimum | 2.58 | 3.45 | 2.08 | 2.21 | ||
maximum | 3.96 | 4.29 | 3.44 | 3.66 | ||
Average | 3.05 | 3.76 | 23% ↑ | 2.92 | 3.27 | 12% ↑ |
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Lim, M.; Lim, K.; Lee, C. A Study on Improving the Coefficient of Performance by Comparing Balancing Well and Standing Column Well Heat Exchange Systems. Sustainability 2020, 12, 10445. https://doi.org/10.3390/su122410445
Lim M, Lim K, Lee C. A Study on Improving the Coefficient of Performance by Comparing Balancing Well and Standing Column Well Heat Exchange Systems. Sustainability. 2020; 12(24):10445. https://doi.org/10.3390/su122410445
Chicago/Turabian StyleLim, Myungkwan, Kyoungbin Lim, and Changhee Lee. 2020. "A Study on Improving the Coefficient of Performance by Comparing Balancing Well and Standing Column Well Heat Exchange Systems" Sustainability 12, no. 24: 10445. https://doi.org/10.3390/su122410445