An environmentally friendly model house is heated by solar panels on the roof and a ground source heat pump. The heat pump relies on the ground beneath the surface retaining heat from the sun and is able to keep the house at an unfluctuating temperature, independent of the weather outside. (a) Explain the difference between a heat pump and refrigerator. If the heat pump is reversed, state the name of the device due to this action. (b) Explain why it is not usual to describe the performance of a heat pump in terms of its efficiency. In domestic accommodation where the desired living space temperature is 22C and the minimum temperature difference required for the (condenser) heat exchanger is 8 K. The heat is absorbed from a groundwater source at 8C and there is a minimum temperature difference required for the (evaporator) heat exchanger of 4 K, and R134a as its working fluid. There are no pressure losses in the components nor is there superheating or subcooling of the refrigerant in the evaporator or condenser respectively. (c) Sketch the ideal cycle on the p-h chart and determine the maximum and minimum pressures in the circuit required by this ideal heat pump to provide heating to the environment in living space. (d) Explain the problems may occur in the evaporator heat exchanger if the pressure in the evaporator was less than 3 bar. (e) Calculate the mass flow rate of the refrigerant R134a required to ensure the heating capacity of the heat pump of 15 kW. (f) Calculate the COP of the heat pump and comment on its value. (g) Comment on the effect on the Coefficient of Performance of a heat pump as the difference between the condenser pressure and the evaporator pressure decreases.