MENG11202 THERMODYNAMICS 1

The Heat Pump

Kaviraj Singh Khurana

kk14194@my.bristol.ac.uk

Personal Tutor: Richard Martin

Aerospace Engineering

Date of Laboratory: 27th November 2014

Date Submitted:

700 Words

Abstract

The task was to understand the performance of the heat pump, by finding the Coefficient of Performance

(COP). This can be calculated by dividing the rejected heat by the heat input. Several readings of different

variables were needed to obtain this. Few assumptions had to be taken for this experiment.

Air pressure was needed to calculate the air velocity and the air mass flow rate. The manometer was used

to calculate the air pressure. Water mass flow rate was measured using the rotameter. The inlet and outlet

temperatures of water and air were measured in order to calculate the heat input and the rejected. The

highest and lowest temperatures in the cycle were also measured to about the Carnot COP. Finally the

power of the compressor was also measured, which was used to find the Discrepancy in energy balance.

Using all of the above readings and calculations, we obtained the COP and the ‘Ideal’ Carnot COP. This

gave us the performance of the heat pump and it was within the range of an average heat pump.

Introduction

The objectives of this experiment were to understand the performance of the heat pump by calculating the

Coefficient of Performance, the Carnot Coefficient of Performance and the Discrepancy in energy

balance.

COP = QH

W

Carnot COP = T H−T L

T H

Results

Table 1 - Raw Data

Entity Value

Atmosphere pressure, 1.007 mbar

Manometer reading,H

43 mmH20

Rotameter reading 3 l/min

Compressor Power,W

0.815 kW

Inlet temperature of air,T1

23.9°C

Outlet temperature of air,T2

40.3°C

Inlet temperature of water,T3

22.3°C

Outlet temperature of water,T4

16.1°C

Temperature of compressed refrigerant,T5

72.7°C

Temperature before compression,T6

15.4°C

Temperature after evaporation,T7

15°C

Temp during evaporation,T8

16.1°C

Temperature during condensation,T9

72.7°C

Temperature after condensation,T10

44.1°C

Table 2 – Results from calculations

Entity Results from calculations

Air Velocity,vcl

27.5 ms−1

Air mass flow rate,mair

0.122 kgs−1

Water mass flow rate,mwater

0.05 kgs−1

Heat input,QL

1.2958kW

Rejected heat,QH

2.01 kW

COP 2.466

Carnot COP 5.991

Discrepancy in energy balance 0.1008

Discussion

Few assumptions had to be taken before starting the experiment like, the process was in a steady state, no

instrumentation error taken into account and 100% water transfer was taken into account.

The discrepancy in energy balance of the heat pump was 0.1008 kW which is 7.77 percent of the heat

input, which is a small considered quite a small figure. Moreover, the ‘Ideal’ Carnot COP was calculated

to show the value of 5.991 while the actual COP showed 2.466. The difference between them is not too

much which shows that this heat pump is quite an efficient one. An average heat pump has an average

COP of about 2-3.5 depending whether it is cooling or heating. The calculated COP is quite good

compared to this one, which again shows that the heat pump is rather a good one.

Few errors could have occurred during the experiment which may have reduced the accuracy of the

results. The instruments could have been calibrated better, as the greater accuracy in them could give us

more accurate results.

The fan provides cooling in the system while the compressor increases the pressure of the air. It was

needed to be switched off for 10 seconds in order to find out the exact work done by the compressor.

Doing this causes a slight error in the whole system causing temperatures in other reservoirs to fluctuate.

Conditions in the experiment need to be steadier. While taking other readings as well, caused fluctuations

in other variables which results in less accurate results.

Conclusion

The experimental results matched well with the simulated results of the heat compressor. The difference

between the ‘Ideal’ Carnot COP and the actual COP was quite less, which shows that the heat pump has a

good performance.

References

ROGERS, G. & MAYHEW, Y. (1992) Engineering Thermodynamics: Work and Heat Transfer 4th

edition. Longman Scientific.

WU, C. (2007) Thermodynamics and Heat Powered Cycles: A Cognitive Engineering Approach. Nova

Publishers.

RAJPUT, R.K. (2010) A Textbook of Engineering Thermodynamics. Firewall Media.

Appendix 1

Table 3 – Formulas used

Entity Formula used for calculations

Air Velocity,vcl

4.2√ h

Air mass flow rate,mair

0.96ρairAvcl

Water mass flow rate,mwater

v60

Heat input,QL

mwater.Cp,water.(T3-T4)

Rejected heat,QH

mair.Cp,air.(T2-T1)

COP QH

W

Carnot COP T H

T H−T L

= T 5

T5−T7

Discrepancy in energy balance

(QL+W ) -QH