Page 142 - Low Temperature Energy Systems with Applications of Renewable Energy

Effective use of heat pumps for various heating applications 131

Fig. 3.E1 Heat pump cycle in the psychrometric chart.

Part C. The heating load (kJ/kg) would be nearest: (a) 355; (b) 305.5; (c) 308.7; (d) 330.9.
Part D. If the compressor is 80% adiabatic efficient, the enthalpy (kJ/kg) of the R152a at
the compressor outlet is nearest: (a) 601.5; (b) 590.2; (c) 595.5; (d) 588.7.
Part E. If the average logarithmic temperature of the coolant is T e ¼ 273 K, the ambient

temperature is t 0 ¼ 10 C, and the heat load of the evaporator is q e ¼ 210 kJ/kg, the
exergy (kJ/kg) given to the low-temperature R152a in the evaporator is: (a) 6.75; (b)
8.41; (c) 7.69; (d) 7.32.
Part F. If the average logarithmic temperature of the high-temperature refrigerant is
T k ¼ 313 K, the ambient temperature is t 0 ¼ 10 C, and the thermal load in the

condenser is q c ¼ 335 kJ/kg, then the exergy (kJ/kg) obtained by the coolant in the
condenser is: (a) 53.6; (b) 48.8; (c) 48.0; (d) 49.8.
Part G. If the efficiency of the electrical network is h el ¼ 0.95 and the efficiency of the
compressor motor h el.c. ¼ 0.80, then the specific energy (kJ/kg) consumed by the
compressor motor is: (a) 119.5; (b) 164.5; (c) 120.1; (d) 128.8.
Part H. For the conditions of Parts E and F, if the efficiency of the electrical network is
h el ¼ 0.95 and the efficiency of the compressor motor h el.c. ¼ 0.80, then the exergic ef-
ficiency of the heat pump is: (a) 0.311; (b) 0.350; (c) 0.382; (d) 0.348.

References

[1] European Environmental Agency. Part 1. Overall progress towards the European Union’s
‘20-20-20’ climate and energy targets. 2017. https://www.eea.europa.eu/themes/climate/
trends-and-projections-in-europe/trends-and-projections-in-europe-2016/1-overall-
progress-towards-the.