Avapour compression cycle using r134a refrigerant operated with an evaporator absolute pressure of 2 bar and a condenser saturation absolute pressure of 8 bar. the vapour entering the compressor is saturated at 2 bar and the liquid leaving the condenser is saturated at 8 bar. assuming the compression process is isentropic i. sketch the process on a p-h diagram. ii. identify the pressure and enthalpy at each of the four points on the refrigeration cycle. iii. calculate the coefficient of performance of the cycle.

To save energy, the air supply to a 2000 ft office has been shut off overnight and the room temperature has dropped to 40°f. in the morning, the thermostat is reset to 70°f and warm air at 120 f begins to flov in at 200ft'/min. the air is well mixed within the room, and an equal mass flow of air at room temperature (changing with time) is withdrawn through a return duct. the air pressure is nearly 1 atm everywhere. ignoring heat transfer with the surroundings and kinetic and potential energy effects, estimate how long it takes for the room temperature to reach 70°f. plot the room temperature as a function of time.