Fei Lei

Evaluation of the Performance of a Ground-Water Heat Pump System in Hot-Summer and Cold-Winter Region

This study presented the energy performance evaluation of a ground-water heat pump (GWHP) system based on actual operational data. The GWHP system was installed for apartment buildings in Wuhan, China. During one year, various operating parameters of the GWHP system were monitored and the coefficient of performance (COP) of system was determined based on the measurement. The energy consumption of the GWHP system is more than twice the average value of split air conditioner on residential application, because of continuously operating of the GWHP system and frugally intermittence operating of split air conditioner. The GWHP system is more economical than other central system. The energy savings rate of the GWHP system was 41.5% for the heating season comparing with boiler and 42% for the cooling season comparing with air source heat pump.

Performance Evaluation of a Vertical U-Tube Ground Heat Exchanger Using a Numerical Simulation Approach

A vertical U-tube ground heat exchanger can be utilized to exchange heat with the soil in ground source heat pump systems. The outlet temperature of the working fluid through the U-tube not only accounts for heat transfer capacity of a ground heat exchanger, but also greatly affects the operational efficiency of heat pump units, which is an important characteristic parameter of heat transfer process. It is quantified by defining a thermal effectiveness coefficient. The performance evaluation is performed with a three dimensional numerical model using a finite volume technique. A dynamic simulation was conducted to analyze the thermal effectiveness as a function of soil thermal properties, backfill material properties, separation distance between the two tube legs, borehole depth and flow velocity of the working fluid. The influence of important characteristic parameters on the heat transfer performance of vertical U-tube ground heat exchangers is investigated, which may provide the references for the design of ground source heat pump systems in practice.

The Influencing Factor on Test of Parameter of the Rock-Soil Thermal Properties

In this paper, the principle of a measuring device on thermal response test is introduced and a three-dimensional numerical model is developed. What¡¯s more, the effect of testing time, starting time point, ending time point and volumetric specific heat on the calculation results of the thermal response test by two variable parameter fitting method and three-dimensional numerical model are also discussed. It is validated that the volumetric specific heat is not sensitive to the thermal conductivity of the soil and has a little effect on borehole thermal resistance. The initial soil temperature, the end data point and start data point all affect the thermal conductivity and borehole thermal resistance to some extent. An enough length of testing time should be remained.