Use of Heat Pumps for Heating and Night Cooling of Greenhouses

Abstract

The use of heat pumps for heating and night cooling of greenhouses was investigated using a computer simulation program and weather data from Typical Meteorological Year (TMY2) datasets for Raleigh, NC, and Wilmington, NC. A greenhouse computer model taken from the literature, along with the heat pump subroutines (HPHEAT and HPCOOL) developed in this study, were used for the simulations. The use of heat pumps for heating only, and for heating plus night cooling, were examined separately using both standard and time-of-use electricity rates for two North Carolina utility providers. When heat pumps were used only for heating, standard electricity rates were predicted to provide greater savings in utility costs compared to time-of-use rates. When heat pumps were used for both heating and night cooling, the predicted savings in utility costs was greater for time-of-use electricity rates. Night cooling was predicted to decrease the average daily temperature (0.10C to 1.10C) and average nighttime temperature (0.10C to 2.00C) inside the greenhouse providing the potential for increased yield. Although a heat pump of capacity 36.5 W/m2 of floor area provided less savings in total costs compared to a capacity of 76 W/m2, the heat pump with the smaller capacity (36.5 W/m2) may be a better proposition because of the lower purchase cost.