River
water can be utilised to heat a boat and in the past systems using
copper coils in the water have been used in conjunction with heat
pumps. However, rules and regulations and the lack of available
manufactured equipment have made this type of system less attractive.
Pumping river water through a heat pump can give very good results,
but heat pump units require water at temperatures above 5 to 8°C
(varying depending on type). Whilst delivering very
high-efficiencies for much of the time, this system may fail to
operate in the middle of winter during lower temperatures- just when
you need the most heat, so a back-up heat source is usually
advisable.
Oxygen and contaminants in the river water may also be a concern in
some circumstances, causing pump failure and possibly a system
refrigerant leak. But don't let me put you off; this system can give
excellent results if installed correctly.
For those lucky enough to have a spring, this is a much more stable and better heat source. Its an opportunity not to be overlooked, offering excellent efficiencies. Again, acidity and impurities in the water can sometimes make its use prohibitive, but some heat pump units will tolerate ‘corrosive’ water (some Dimplex models etc). A possible alternative is to use an intermediate heat exchanger in such circumstances. However, the added temperature drop and necessary extra pump can reduce the performance considerably.
The water source should ideally be fairly close to the property, and should not require pumping up any significant height or the power for pumping it may detract from the energy savings. Having said that, water could be taken over considerable distances if the pipe diameter is big enough, especially in a downward direction. It is a relatively simple exercise to calculate the pump power required (if any) to get the water to and through the heat pump unit.
Permission should be sought from the relevant authorities as an abstraction licence may be needed.