| The technology of Ground source heat pump (GSHP) is a green and clean energytechnology for shallow geothermal resources, and has been applied more widely inEurope and the United States and other Western developed countries. In recent yearsin China ground source heat pump system has also get widespread attention. Thecore technology of ground source heat pump system is the design of heat exchangersin the hole, so thermal parameters of rock and soil is very important. In the earlystages of development of ground source heat pump system, commonly usedempirical data or make laboratory test to determine the thermal parameters. With thedeepening study on heat transfer model of ground source heat pump system, thermalresponse test has been used widely to determine rock and soil thermal parameters.The early thermal response test equipment usually use electric heater as the heatsource, and it can only test in refrigeration condition and calculate thermo physicalproperties in heating condition through software simulation. Subsequently, sometest equipment which used heap pump as the heat source and can test in refrigerationand heating condition were developed. But during the testing of the heatingconditions, heat pump was used as cold source. For the operation mechanism of heatpump, heat pump had to extract heat from the circulating water through thecondenser and fan discharge to the ambient air, the temperature of circulating waterwill inevitably be subject to the influence of environmental temperature. Change ofthe ambient temperature could influence of the cooling efficiency of the heat pumpwill not control the temperature by auxiliary heat source, the output power of testequipment and circulating water temperature will be fluctuated by environmentaltemperature.Thermoelectric refrigeration is a new artificial refrigeration technology based onPeltier effect. Thermoelectric refrigeration unit has the advantages of small size, no noise, high cooling rate and easy to control. However, because of the high cost andlow conversion efficiency, thermoelectric refrigeration unit has not been acceptwidely, and only used in chemical industry, electronics, biotechnology, medical,military, and other special areas.Aiming at the problem of current thermal response test equipment, thermoelectricrefrigeration unit and thermal response test were combined to develop a new kind oftest equipment. It use thermoelectric refrigeration unit as refrigeration/heating source,has two circulation loops which connect to two side of thermoelectric refrigerationunit. So it can output heat and refrigeration at the same time, and can do thermalresponse test in two conditions.In thermal response test, the average temperature of circulating water usually biswithin 20 30°C in cooling condition, and 3 8°C in heating condition, so whenthe average temperature of cold side and heat side of thermoelectric coolingequipment is considered at 20°C (at 293 K), the figure of merit Z of commonthermoelectric cooling element in general ( 2 3 )×10-3K-1,ΔTmax up to 60 80°C. The actual temperature difference between hot and cold side is nearly to0.5ΔTmax. Therefore, choose the best cooling efficiency thermoelectric coolingdevice as test equipment design conditions.According to the measured data, the cold output power of developed thermoelectriccooling device is within -1802 -1744 W, average output power is -1778 W, powerfluctuation range is only 3.28%; the heat output power of developed thermoelectriccooling device is within 8235 8528 W, average output power is 8387 W, powerfluctuation range is only 3.49%. Stable output can reduce the error of data processingin thermal response testing, guarantee the accuracy of test results. In addition thethermoelectric cooling device can output stable cold and heat without external heatexchange with environment, to avoid environmental impact of temperature on thetemperature of circulating water.In order to reduce the harmful effect such as voltage fluctuations, change of environment temperature and so on, some research on variable heat flux model werestudied on the base of constant heat flux line source model and constant heat fluxcolumn source model. The corresponding data processing program were developedto improve the accuracy of the calculation results.
|
PDF Full Text Request