3472 -- Simulation of Vertical U-Tube Ground-Coupled Heat Pump Systems Using the Cylindrical Heat Source Solution PDF

Air-source heat pumps are currently the most popular heat pump used in residential applications. However, ground-coupled heat pump systems are now becoming the choice of many homeowners. Associated with this increased interest in using the earth as a heat source is the desire to predict the thermal performance of the ground-coupled heat exchanger. The heat pump entering water temperature is needed to compute capacity and operating costs. However, this temperature is often difficult to determine accurately because of the many transient variables combined with the cyclic operation of the heat pump. Describes the use of the unsteady conduction equation (cylindrical source solution) to model the thermal response of vertical closed-loop U-tube ground couplings. The cylindrical source was chosen, rather than the simpler line source solution, for greater accuracy in predicting heat pump entering water temperatures at critical periods during daily operation. A computer program was developed to predict heat pump entering water temperatures for both daily and hourly increments. Simulation results are compared with actual test data obtained from two installations. Although the cylindrical source solution has previously been applied to ground couplings, this paper presents two variations on the application of this solution. These methods yield improved results when simulating the intermittent operation normally encountered in residential systems. In addition, a method of estimating effective soil properties from a continuous six-hour heat pump test is also presented.

KEYWORDS: heat pumps, soil heat pumps, vertical, cylindrical, energy sources, heat flow, calculating, soil heat exchangers, temperature, closed cycle heat pumps, computer programs, domestic