COMPUTER SIMULATION OF A HEAT PUMP WATER HEATER AND EXPERIMENTAL EVALUATION OF A DUAL-FUEL WATER HEATER SYSTEM.

摘要

A mathematical simulation of a heat pump water heater is developed and verified through comparison with the performance data from laboratory experiments. Similarly, the performance of a gas-fired water heater is simulated, and the combined system of a heat pump water heater and a gas-fired water heater is investigated. For the heat pump, four major components (compressor, evaporator, condenser and expansion device) are modelled separately and then coupled by mass and pressure balance experiments. The model used to simulate the hermetic compressor is divided into three submodels: cylinder and valve processes; induction motor characteristics and motor-compressor interactions; and oil circulation effect on compressor performance. This model approximates the valve dynamics, manifold pressure pulsations and cylinder-manifold interactions. It uses real gas properties and includes the effect of motor cooling on compressor performance. It also approximates mechanical friction and includes submodels for all four processes in each complete compressor stroke.; The model for simulation of the condenser is divided into three major sections: simulation of the condenser; calculation of heat transfer coefficients and pressure drop; and calculation of effectiveness. This model provides the outlet state of the refrigerant. It uses the E-NTU method of heat exchanger analysis and calculates the pressure drop and heat transfer coefficients for the laminar, transition and turbulent regions.; The model used in simulation of the evaporator is adopted from a different source with minor changes. This model determines whether moisture removal occurs, and uses the E-NTU method, receiving heat transfer coefficients and pressure drops from corresponding submodels.; The capillary tube as an expansion device is modelled by curvefitting the available data. The model for the gas-fired water heater is developed using the laboratory results. A commercially available heat pump and gas-fired water heater are used for the experiments. These two heaters were coupled and instrumented. The performance of each heater and of the coupled system was then investigated under several different conditions.; The maximum deviation between the experimental results and the mathematical simulation was within the estimated uncertainty.