It is proposed to use a heat pump working on the ideal vapor-compression cycle for the purpose of heating the air supply to a building. The supply of heat is taken from a river at 5°C. A temperature difference of 20 K is necessary for the transfer of heat from the river to the refrigerant in the evaporator. The air is heated at constant pressure from 8°C as it passes over the condenser coils of the heat pump. The refrigerant is R134a which is dry saturated leaving the evaporator; there is no undercooling in the condenser. The delivery pressure of the compressor is 14.837 bar.

(i) Sketch the system diagram and show the cycle on T-s and p-h diagrams

(ii) List the enthalpies

(iii) the overall COPHP

(iv) The COPHP for a reverse Carnot cycle operating at these conditions

(v) The mass flow of refrigerant, when the air is required to be delivered into the building at 1.013 bar and 30 °C at a rate of 0.5 m3 /s

Comprehension Questions:

1. Comment on the difference between the COPHP calculated in (iii) and (iv).

2. Comment on the effect the dryness fraction after the throttle valve might have on the system performance.

3. How could you improve the system performance?

4. Define ODP and GWP and discuss both with respect to R134a.