Papers by Keyword: Ground Heat Exchanger

Abstract: Combined the problems during the promotion of ground-coupled heat pump technology with the growing of power peak load, and considering the advantages of underground storage, this paper proposes a multi-source building air conditioning system based on heat storage capacity of the soil.On the basis of energy balance, established a mathematical model of the ground heat exchanger storaging, releasing cold and stopping running. Through simulation, analysis the effects of different types of backfill material to system operation.

Abstract: Ground source heat pumps (GSHP) have been widely used in recent years. The heat transfer between borehole heat exchanger (BHE) and earth is the key factor impacting on the performance of GSHP. However, in order to setup BHE, a large amount of area of land is necessary, since the heat capacity of earth is limited. In this paper, phase change materials (PCMs) are used as grout instead of common materials. Thus, the heat capacity of soil has been improved, but the heat transfer characteristic of BHE has also changed. To prove its feasibility, the 3-dimensional numerical heat transfer simulation has been carried for three models which grout are respectively soil, PCMs, and PCMs with heat transfer enhancement measures. The characteristics of heat transfer and the land areas used of the three models are compared. The results show that the land area can be reduced effectively with PCMs as backfilling, while heat transfer enhancements must be adopted because the conductivity of PCM is small.

Abstract: In order to improve EER of the ground source heat pump system and reduce heat transfer area of the ground heat exchanger, the authors had developed a series connection ground source heat pump water chiller-heater unit, after theoretical analyses, proved that placing the water chilled in front of the hot water unit could acquire a higher EER comparing to the opposite. In the meantime, this unit had a higher EER than a common water chiller-heater unit or a water chiller-heater unit with condensing heat recovery device. In an air conditioning system of ground source heat pump, employing the above mentioned unit can also reduce heat transfer area of the ground heat exchanger. It suggested that series connection ground source heat pump water chiller-heater unit is a kind of technology with a great development potential.

Abstract: In the paper, by studying the underground heat exchanger heat transfer mode, the computing platform for ground source heat pump system was established. Through a engineering case, the influence character of the fluid temperature at the outlet of ground heat exchange on the length of system, the fluid temperature in ground heat exchange, and the heat pump power consumption were analyzed, which provide an approach for engineering design and operation prediction, and for the thermodynamic analysis of performance of system year by year and prospective study to guide the engineering practice.

Abstract: Ground has been proven that it is able to supply cooling and heating resulting in significant reduction of electricity consumption. This paper discusses potential of ground towards implementation of ground thermal storage by using ground heat exchanger (GHE) to supply passive cooling for any application. Analysis has been conducted based on empirical equation from conduction heat transfer for depth up to 6 m and thermal diffusivity from 0.04 to 0.1 m²/day. The main input parameters were obtained from local weather station for three consecutive years. The results showed that significant reduction of temperature occur at depth below than 2.0 m in which cooling can be supplied constantly throughout the year. Temperature amplitude also gets attenuated relatively with depth in which amplitude less than 1°C occur at depth more than 4 m for thermal diffusivity 0.04 m²/day. In addition, thermal diffusivity plays important role in determining ground temperature variation. It has been obtained that the temperature amplitude significantly increase when the thermal diffusivity increase. Therefore, this paper had suggested that the application of GHE should be placed in condition of thermal diffusivity 0.06 m²/day and below.

Abstract: This paper presents experimental study on the evaluation of thermal performance of U and W type ground heat exchangers (GHEs). These GHEs were installed in a partially saturated landfill ground which was composed of silt and clay in the runway area of Incheon International airport. Thermal performance tests (TPTs) were conducted for 100 hours under the continuous operation condition. Heat exchange rate of individual GHE was evaluated from the TPT results, and construction cost was also estimated. The required Borehole length of U and W type GHEs was calculated considering real construction condition from GLD (ground loop design) program.

Abstract: Focus on the unfavorable effects of initial operation to the performance of ground heat exchangers, a three-dimensional CFD simulation of full-scale ground heat exchanger under dynamic load was established to investigate the heat transfer performance of a 120-meter vertical U-Tube ground heat exchanger under different initial operating time. The results show that initial operation has influence on the performance of ground heat exchangers.

Abstract: This paper does the simulation analysis of the annual energy consumption of an office building and the simulation of the whole GSHP(Ground Source Heat Pump) air conditioning system operation for two years. With the dynamic load, The simulation of the temperature field is done about the ground heat exchanger soil area with the radius of 2.5m during the heating period and the downtime. The result shows that soil temperature variation decreases gradually from the center to the distal end, in the first five days after shutdown, the soil temperature recovers faster, and then gradually becomes slowlier.

Abstract: This paper dynamically simulates the soil source heat pump air conditioning system of a library in Nanning with the eQUEST software combined with the geology and climate characteristics, unit parameters. Comparing the simulated values with the measured values to verify the correctness of the model. Then simulate and analyze the variation of ground temperature rise at well bore with long-term intermittent operation for the system and the influence of different well spacingground and backfill materials thermal conductivitywell depth on the outlet temperature and the ground temperature rise at well bore. The simulation results show that the reasonable selection of relevant parameters has important significance to improve the operating performance and economy of the system.

Abstract: 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.