Investigating the Effect of Soil Type and Moisture on the Performance of a Ground Source Heat Pump System Used for a Greenhouse in Iran

We investigate the effect of soil type and moisture on the operation of a ground source heat pump (GSHP) system in supplying the energy needs of a greenhouse in Karaj, Alborz province, Iran, in terms of the required length of ground heat exchanger, the working hours, the electricity consumption, as well as the coefficient of performance (COP) of heat pumps. In order to predict the capacity of heat pumps, we use the numerical heat transfer model of Noorollahi et al. (2016, "Numerical Modeling and Economic Analysis of a Ground Source Heat Pump for Supplying Energy for a Greenhouse in Alborz Province, Iran," J. Cleaner Prod., 131, pp. 145-154) in which the governing equations of heat transfer in the ground heat exchanger are numerically solved through a novel finite difference method. Thermal properties of various soil types, namely sandy soil, sand, silty loam, and silty clay, with three different levels of moisture content referred to as dry, damp, and saturated, are considered as the main inputs for the computer code. The simulations indicate that when moisture is increased from dampness to saturation, the annual working hours of heat pumps decrease by 1.1%, 5.1%, 6.1%, and 4.6%, and their annual electricity consumption is reduced by 2.2%, 10.6%, 12.6%, and 9.7% for sandy soil, sand, silty loam, and silty clay, respectively. Moreover, the average COP of heat pumps increase by 0.9%, 4.0%, 5.2%, and 3.7% in heating mode and 2.4%, 13.0%, 16.5%, and 11.7% in cooling mode for the mentioned soils, respectively.