Field experiments of cooling operation were conducted using a ground source heat pump (GSHP) system installed at greenhouse in Itoshima city, Fukuoka, Japan. There are water loss zones in the lower part of heat exchange wells which were completed without grouting. Groundwater was injected into the wells by varying the flow rate for evaluating the effects of its flow rate on enhancement of heat exchange capacity of ground heat exchangers. The results showed that significant enhancement of heat exchange capacity was achieved by injected water at the flow rate about 9 L/min in the field. Then, a numerical model was developed to simulate heat transport with injected water in the wells. Sensitivity studies were carried out with the model changing the flow rate and temperature of injected water. The results showed that injecting water at 1 L/min/well of 18oC could improve heat exchange rate by 1.7 times compared to that without injection case.

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