Rising energy costs, increasing requirements in terms of home energy efficiency and greater environmental awareness have brought about great interest in gas absorption heat pumps (GAHP). These systems provide high thermal comfort combined with high energy efficiency and CO2 reductions when compared to state of the art condensing boilers. The gas absorption heat pump uses primary energy (natural gas) directly, which means that it does not require highly exergetic electricity as driving energy for the heat pump process. The gas absorption heat pump subject of this paper uses outside air as renewable heat source. Modeling and simulation is applied in order to gain insight into the main characteristics of the GAHP thermodynamic cycle. The paper presents a modular, steady-state model for the simulation of an air sourced gas absorption heat pump operating with an ammonia-water mixture. The GAHP refrigerant circuit is designed as a GAX cycle (Generator Absorber heat eXchanger) which boosts the efficiency of the unit by recovering the heat that is released from the absorption process. Modeling is based on heat and mass balances for each component. Investigation the cycle performance requires calculation of the thermodynamic properties of the ammonia-water solution. The model uses the equations presented by Ziegler and Trepp (1984), based on the equations of state provided by Schultz (1971). The bubble point temperature and the dew point temperature are computed from the explicit relationship developed by El-Sayed and Tribus (1985). The model was implemented in MODELICA/DYMOLA. It calculates the heat pump heating power as a function of the water temperature at the inlet and outlet at different outdoor air temperatures. The results are compared with some manufacturer data reported in the open literature. In general a very good agreement between the simulation results and the experimental data is found. The model is then used to investigate the influence of important design and operating parameters on the performance of the gas absorption heat pump.
Modeling and simulation of a gas absorption heat pump
STARACE, Giuseppe;
2014-01-01
Abstract
Rising energy costs, increasing requirements in terms of home energy efficiency and greater environmental awareness have brought about great interest in gas absorption heat pumps (GAHP). These systems provide high thermal comfort combined with high energy efficiency and CO2 reductions when compared to state of the art condensing boilers. The gas absorption heat pump uses primary energy (natural gas) directly, which means that it does not require highly exergetic electricity as driving energy for the heat pump process. The gas absorption heat pump subject of this paper uses outside air as renewable heat source. Modeling and simulation is applied in order to gain insight into the main characteristics of the GAHP thermodynamic cycle. The paper presents a modular, steady-state model for the simulation of an air sourced gas absorption heat pump operating with an ammonia-water mixture. The GAHP refrigerant circuit is designed as a GAX cycle (Generator Absorber heat eXchanger) which boosts the efficiency of the unit by recovering the heat that is released from the absorption process. Modeling is based on heat and mass balances for each component. Investigation the cycle performance requires calculation of the thermodynamic properties of the ammonia-water solution. The model uses the equations presented by Ziegler and Trepp (1984), based on the equations of state provided by Schultz (1971). The bubble point temperature and the dew point temperature are computed from the explicit relationship developed by El-Sayed and Tribus (1985). The model was implemented in MODELICA/DYMOLA. It calculates the heat pump heating power as a function of the water temperature at the inlet and outlet at different outdoor air temperatures. The results are compared with some manufacturer data reported in the open literature. In general a very good agreement between the simulation results and the experimental data is found. The model is then used to investigate the influence of important design and operating parameters on the performance of the gas absorption heat pump.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
