The highly efficient heat pump concept discussed in the previous post can also be used to heat water. Pros and cons of heat pumps for water heating are a little different from those for space heating though. We will take a brief look at those here.
Similarly to a heat pump for space heating, a heat pump for water heating is only applicable to relatively moderate climates. If the temperature in your area regularly drops below freezing, a heat pump is not the best idea. For all the places where temperatures usually stay above this threshold, however, heat pumps can reliably deliver hot water for half the usual electricity cost and environmental impact of a standard electrical resistance water heater.
That being said, however, if you have access to natural gas in your area, a natural gas water heater will still be cheaper (in terms of upfront investment) while delivering similar running costs and environmental impact. Natural gas is an especially attractive option in cold areas where heat pumps and solar water heating are not effective.
In mild to hot climates, however, both heat pumps and solar heaters can be very attractive solutions for hot water. The competition between solar water heaters and heat pumps is actually fairly equal, but the factor that can swing the balance to either side is the ratio between sunshine and ambient temperature. Heat pumps draw heat from the surrounding air and work better if this air is warmer, while solar water heaters capture direct radiation from the sun and work better in full sunshine.
Thus, if you live in a place where with a fairly mild climate, but regular cloudy spells, a heat pump water heater may well be the best choice for you. For places with mostly clear skies and lots of direct solar radiation, a solar water heater should be the better option.
So, have a little think about your local climate and do the right thing. Water heating consumes a surprisingly large portion of society’s overall energy usage and still has lots of room for efficiency improvements. Heat pumps can make a significant contribution in this area.
Filed under: Consumption patterns – The green economy