The performance of a heat pump degrades (i.e., its COP decreases) as the temperature of the heat source decreases. This makes using heat pumps at locations with severe weather conditions unattractive. Consider a house that is heated and maintained at 20∘∘C by a heat pump during the winter.
What is the maximum COP for this heat pump if heat is extracted from the outdoor air at
b) -5∘∘C, and