Heat pumps in district heating and district cooling systems

摘要

This thesis presents an analysis of heat pump operation in a District Heating and District Cooling system. Two heat pumps with supersonic centrifugal compressors use untreated sewage as their heat source/sink for the simultaneous production of heating and cooling. The heat pumps operate in one of three different modes, according to the momentary demand for heating and cooling. The performance of the heat pumps in each mode is analysed, and the feasibility of the installed control system is discussed. The analysed performance is based on momentary measurements of the process variables, while the heat pump plant was in normal operation during the measuring period of two years. It was not possible to manipulate the operation as would be possible in a laboratory. This limited the available operational conditions. To evaluate the performance of the supersonic centrifugal compressors their part load efficiencies in the different modes are calculated and presented. The limitation of the operation of the heat pump due to the risk of surging is discussed. When the District Heating and Cooling plant was designed, the possible energy source were raw sewage and sea water. The evaluation of the most suitable energy source is discussed, and the operational experiences with the use of untreated sewage are presented. No alternative system design for the distribution of heating and cooling was discussed prior to the design of the heat pump plant in Sandvika, Norway. For future plants the distribution of energy at intermediate temperature with distributed heat pumps may be an alternative. Some aspects of this concept is discussed, based on the experiences from the District Heating and Cooling plant in Sandvika. The cost of an intermediate temperature system is compared to the resulting cost for the conventional District Heating and Cooling plant. 60 refs., 93 figs., 15 tabs. (ERA citation 19:024929)