College of Engineering and Computer Science Mechanical Engineering Department Mechanical Engineering 370
A heat pump is used to maintain a house at a constant temperature of 23
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4 A heat pump is used to maintain a house at a constant temperature of 23oC. The house is losing heat to the outside air through the walls and windows at a rate of 60,000 kJ/h while the energy generated within the house from people, lights and appliances amounts to 4,000 kJ/h. For a COP of 2.5, determine the required power input to the heat pump. The COP definition for a heat pump is different from the definition for the refrigerator. Here we are interested in the amount of heat added to the house which is the high temperature heat rejection from the refrigeration cycle. The COP for a heat pump is defined as follows:  . We can solve this equation for the power input and plug in the given data to compute the power required. Here we note that the heat supplied by the heat pump to keep the room temperature constant is just the difference between the heat loss and the heat generation. Thus, QH = 60,000 kJ/h – 4000 kJ/h = 56,000 kJ/h. The power consumption is then found to be
 = 6.22 kW
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