Seasonal Performance Simulation of an Air Sourced Gas Absorption Heat Pump

摘要

Gas driven heat pumps are currently considered a next generation heating technology following up on state-of-the-art condensing boilers. Subject of this paper is the seasonal performance evaluation of a novel gas absorption heat pump (GAHP) operating with an ammonia-water mixture in a GAX (Generator Absorber Heat EXchange) thermodynamic cycle. The air-sourced GAHP currently under development within the European Project HEAT4U is designed for the application in the retrofit of existing residential buildings. Nominal capacity is 18 kW at an outdoor temperature of 7°C and a supply temperature of 50°C. For good performance under part load conditions modulation of the thermodynamic cycle is implemented. Based on a first experimental characterization of a prototype of the GAHP a performance map model is implemented in TRNSYS which includes both full load and part load behavior of the appliance. This appliance model is used in a system simulation of monovalent operation of the GAHP. To this purpose, building simulations were performed in order to generate typical building load profiles. By means of system simulations system performance is evaluated for different climatic conditions and supply temperatures of the heat distribution system. As an outcome of these simulations the strong dependency of the seasonal performance on the supply temperature of the heat distribution system is highlighted. In order to assess the gas utilization savings which can be expected by using the novel type of GAHP, a benchmark system was also implemented in the simulation. A system with a stand-alone gas condensing boiler is chosen for reference. Preliminary results of this ongoing simulation comparison clearly indicate that significant savings in gas utilization in the order of 25 % when compared to state-of-the-art condensing boilers may be expected for the average climate. Savings against standard non-condensing boilers may even be higher. Therefore, it is concluded that GAHP technology may be a very efficient future option to supply heat to retrofitted existing residential buildings.