A heat pump (working in a thermodynamic cycle mode) is to be used to heat a hous
ID: 939691 • Letter: A
Question
A heat pump (working in a thermodynamic cycle mode) is to be used to heat a house during the winter. The house is to be maintained at 294 K at all times. The house is estimated to be losing heat at a rate of 135,000 kJ/h when the outside temperature drops to 268 K. If the heat pump under these conditions has a coefficient of performance of 4, (a) Determine the power required to drive this heat pump (b) Determine the rate at which heat is absorbed from the cold outdoor air Repeat the questions assuming the heat pump works in a reversible mode. You need to calculate the coefficient of performance under these conditions.Explanation / Answer
given COP =4, QC= heat is absorved and QH= Heat rejected at the condenser= 135000 Kj/h
QC/ W= 4 and QH= 135000 Kj/hr, TC= 268 K and TH= 294K
QC= 4W, QC/QH= TC/TH. QC/135000 = 268/294, QC= 123061.2 Kj/hr
W= QH- QC= 135000-123061.2= 11938.8 Kj/h
b) when it works reversibly, it becomes a refrigenration system
W/QC= TC/(TH-TC)= 268/(294-268)=10.3
given QC= 135000 kj/hr
W= 10.3*135000 kg/hr=1390500
W= QH- QC
QH= W+QC= 135000+1390500=1525500 Kj/Hr