J. Składzień

Thermal Analysis of Vertical Ground Exchangers of Heat Pumps

The heat rate absorbed from the ground by a vertical ground exchanger of a heat pump unit is considered. The aim is to investigate the time variation of this energy rate for a set of parameters. The analyzed set of alternatives encompasses arrangements of the exchanger tubes, values of the temperature of the heat carrier, thermal parameters of the ground, periodic operation of the compressor, and, when appropriate, different values of seepage velocity. To achieve this goal, the transient temperature distributions in the soil surrounding the ground exchanger are evaluated. The calculations are carried out using both PATRAN-THERMAL, a commercial finite volume code, and FEMCONV, an in-home FEM package. Characteristic features of the latter are discussed briefly along with some results of simulations for a ground exchanger with tube-in-tube (Field-type) elements. It is shown that in every case, the heat rate absorbed from the ground depends on the season and reaches the minimum value in the second part of winter. As expected, a strong influence of the arrangement of the exchanger tubes and the motion of moisture is observed. It is shown that if the prices of the electric energy are variable during a day, it may be profitable to operate an HP unit compressor in a periodic regime. The approximate values of the heat pump unit coefficient of performance, defined as the ratio of heat output of HP and compressor driving power, are evaluated. It is pointed out that this coefficient depends on the heat carrier temperature, and therefore this temperature may also be a subject of optimization calculations.

Operation Characteristics of Heat Pump Systems With Ground Heat Exchangers

This article examines the merits of heating systems with a vapor compressor heat pump unit for small residential homes. In this case, the ground is assumed to serve as the low heat source, and the ground heat exchanger may be horizontal or vertical in form. A mathematical model for all vapor compressor heat pump (VCHP)–ground heat exchanger (GHE) systems is briefly presented. The model consists of two elements. The first contains the calculation model of the ground heat exchanger with the adjoining area of the ground. The equations for the elements of the VCHP, supplemented by the state equations for the working medium, form the second element of the general model. This model was used to perform thermal calculations for typical ground and VCHP parameters. The cumulative energy and ecological results of the application of VCHP–GHE systems were also estimated.

3D Numerical Analysis Of The Temperature Fields In Cold Store Foundations

The subject of analysis is the temperature field in cold store foundations protected from freezing by a system of heating pipes. The pipes can include an electric heater or a hot liquid medium. The foundations consist of several layers. Freezing of the water in the foundation can cause heaving of its layers and, in an extreme case, can destroy the building structure. The considered heat transfer problem in the cold store foundations is described by a typical transient initial-boundary heat conduction value problem with Stefans boundary condition on the phase change interface. The problem has been solved using FEM and the spatial averaging technique has been employed to take into account phase change effect. Results of 3D calculations of the temperature field in the cold store foundation are presented and discussed, particularly the influence on the temperature field of the heat transfer from surroundings of the cold store and of the heat transfer through bearing piles.