Chiller Efficiency: Cold to Hot 

As we learned in part 1, hot to cold temperature transfers involve the absorption of indoor heat, which is dumped outdoors. Because the chiller is working against the usual way of heat transfer (to produce cooling), its energy output is lower than the electrical input.  

This gives us a simple output to input ratio of less than 100%, which is used to describe efficiency. This is measured under different operating conditions, leading to specific metrics such as EER and SEER. 

However, for heat pumps that process – heat from low temperature ambient air, machines are using the heat energy from low temperatures to in turn produce more heating energy. Even air that is ‘cold’ by standards of human comfort has heat in it....