Continuous measurement in a greenhouse reveals high COP of air-source heat pump in winter
Heat pumps are known to have high coefficients of performance (COPs). However, the COPs of air-source heat pumps operating in greenhouses are unknown. We developed a device for measuring COP using the air enthalpy method. The items measured were the air temperature and humidity of the outlet and inlet of the heat pump, the airflow from the outlet, and the electric power consumed. The device was tested under conditions similar to those described in JapanRSQUOs industrial standards (JIS). The COP was almost the same as that suggested in the manufacturerRSQUOs documentation, which indicates that the device was effective in measuring the COP. Next, we measured the COP of a heat pump installed in a greenhouse using the device developed in this study for heating on winter nights. The COP values obtained ranged from approximately 3 to 6, and the average COP of heating was more than 3, except during defrosting periods when the outside temperature was below 0°C. In addition, the COP was measured on two days when the average outside temperatures were similar. On Day 1, no defrosting was observed. However, on Day 2, defrosting was observed four times. The different defrosting times are thought to be associated with the differences in the outdoor relative humidity. The average relative humidities on Days 1 and 2 were 44.9 and 66.9%, respectively. The average COPs on Days 1 and 2 were 3.66 and 3.44, respectively. The electric power consumption was almost the same on the two days. The COP results obtained in this study indicate that heat pumps are effective in saving heating energy in greenhouses.
Goto, F., Shoji, K., Ito, T. and Nagatsu, T. (2015). Continuous measurement in a greenhouse reveals high COP of air-source heat pump in winter. Acta Hortic. 1107, 83-88
air-source, heat pump, COP, defrosting, heating, measurement, greenhouse