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Chapter 19: Problem 9

Why do refrigerators and heat pumps have different definitions of COP?

Short Answer

Expert verified
The definitions of Coefficient of Performance (COP) differ for refrigerators and heat pumps because their operations have different objectives. Refrigerators aim to remove heat and therefore the COP focuses on the heat removed, whereas heat pumps aim to add heat and their COP focuses on the heat delivered.

Step by step solution

01

Understand Coefficient of Performance (COP)

The COP is a measure of efficiency that is widely utilized in heating and cooling systems. It basically puts forth the ratio of the useful heat movement per work input.
02

Define COP for a refrigerator

For a refrigerator, the COP (COP_R) is defined as the ratio of the heat removed from the refrigerator's interior to the amount of work done to remove that heat. In other words, COP_R = \(\frac{Q_{in}}{W}\) where \(Q_{in}\) is the heat extracted from the interior, and W is the work done by the refrigerator.
03

Define COP for a heat pump

For a heat pump, the COP (COP_HP) is the ratio of the heat delivered to the reservoir to the work done to deliver that heat. That is, COP_HP = \(\frac{Q_{out}}{W}\) where \(Q_{out}\) is the heat delivered to the destination, and W is the work done by the heat pump.
04

Explain the difference

The main difference lies in where the focus of the system is. For refrigerators, the main aim is to maintain a cold interior, hence we focus on the heat that is removed. For heat pumps, the focus is on heating a space, hence we focus on the heat that is delivered. Due to these differing goals, the definitions of COP are different.

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