n Refrigeration
Slow at reaching mass adoption, heat pump water heaters can save homeowners on energy consumption by 60 per cent. By Greg Scrivener In the last issue, we discussed some of the fundamentals of heat pumps and how they are being applied in many applications, like clothes dryers, to increase the efficiency of heating systems and decarbonize our energy use. One of the obvious areas where heat pump technology can be applied is in hot water heating. For residential applications, hot water heat pumps have been available for quite a while (see Bruce Nagy’s article in Plumbing & HVAC magazine from January/February 2019). The uptake for heat pump water heaters has not happened quickly even though they can save approximately 60 per cent in energy consumption compared to standard electric water heaters. There are two reasons for this. First, the lower price of conventional equipment and the availability of inexpensive natural gas, are both really just about cost. Compared to a typical electric or natural gas water heater, heat pump water
heaters cost two to three times as much depending on specifics. They can, however, be less expensive to install because they don’t require the same size electrical service that comparable capacity electric water heaters do and there is no gas line or venting required. The second reason relates to the fact that context is needed to know whether the energy efficiency can be realized, which is discussed below.
Figure 1 shows a diagrammat ic representation of how a heat pump water heater works. Heat is absorbed from the air in the mechanical room or wherever the water heater is located, and a refrigeration system moves that energy into the water at a higher temperature. If you are wondering – wouldn’t this air condition my mechanical room? You are right, it would. The average Canadian household uses 75L of hot water per day. This means that for a four-person household, the water heater will need to move about 56 megajoules (53 MBH) of energy per day, not counting parasitic heat loss.
Real-life application Recall the following from the first article in this series:
For this example, this means:
Figure 1: Diagrammatic representation of a heat pump water heater.
If we assume some typical operating conditions for an R404A heat pump water heater, this means that about 75 per cent of the energy we put into our water is going to come out of the mechanical room air and 25
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