A small heat pump unit is used to heat water for a hot-water supply. Assume that

Question

A small heat pump unit is used to heat water for a hot-water supply. Assume that the unit uses R-22 and operates on the ideal refrigeration cycle. The evaporator temperature is 15°C and the condenser temperature is 60°C. If the amount of hot water needed is 0.1 kg/s, determine the amount of energy saved by using the heat pump instead of directly heating the water from 15 to 60°C.

Explanation / Answer

T1 = 15oC, T3 = 60oC From Table B.4.1 h1 = 255.02 kJ/kg, s2 = s1 = 0.9062 kJ/kg K P2 = P3 = 2.427 MPa, h3 = 122.18 kJ/kg Entropy compressor: s2 = s1 => T2 = 78.4oC, h2 = 282.86 kJ/kg Energy eq. compressor: wC = h2 - h1 = 27.84 kJ/kg Energy condenser: qH = h2 - h3 = 160.68 kJ/kg To heat 0.1 kg/s of water from 15oC to 60oC, Q.H2O = m.(?h) = 0.1(251.11 - 62.98) = 18.81 kW Using the heat pump W.IN = Q.H2O(wC/qH) = 18.81(27.84/160.68) = 3.26 kW a saving of 15.55 kW

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