Experimental investigation of a heat pipe heat exchanger for heat recovery

An air-to-air heat pipe heat exchanger has been designed, constructed and tested. Gravity-assisted wickless heat pipes (thermosiphons) were used to transfer heat from one air stream to another air stream, with a low temperature difference. A thermosiphon heat exchanger has its evaporation zone below the condensation zone. Heat pipes allow keeping a more uniform temperature in the heat transfer area. The heat exchanger consists of 20 copper tubes with circular copper fins on their outer surface. The tubes were arranged in a row and the air passed across the pipes. R245fa was used as a working fluid in the thermosiphons. Each heat pipe had a 40 cm evaporation section, a 20 cm adiabatic section and a 40 cm condensation section. The thermosiphon heat exchanger has been tested in different conditions of air stream parameters (flows, temperatures and humidity). The air face velocity ranged from 1,0 m/s to 4,0 m/s. The maximum thermal efficiency of the thermosiphon heat exchanger was between 26÷40%, depending on the air velocity. The freezing of moisture from indoor air was observed when the cold air temperature was below - 13°C

The analysis of the differences between the results of the thermal response test and the data from the operation of the brine-to-water heat pump’s vertical exchanger

The article discusses the principles and the problems of obtaining an accurate data input for the design of brine-to-water heat pump’s vertical exchangers. Currently, the most accurate method is the thermal response test (TRT). Unfortunately, the test procedure has its limitations and the quality of the results depends on many factors that cannot be fully controlled during the test. As an illustration of the problems, the results of the TRT were presented. The test was executed on the vertical boreholes (one actively regenerated and one not actively regenerated during the summer) which are parts of the operating heat pump system. The test results were compared to the data from the device’s operation, in particular with the measurements of the undisturbed ground temperature profiles and the actual unit energy gains from the boreholes. The level of difference between the results of the test and the data from the operation of the boreholes under the real load and the threats concerning the boreholes overload were shown. Additionally the performance differences between the actively regenerated and not actively regenerated boreholes have been emphasised