A water source heat pump can use a river, small stream or a spring as its source of heat. In the past systems using copper coils in the water have been used, containing an anti-freeze solution. However, rules and regulations (to prevent water pollution) and the lack of available manufactured equipment have made this type of system less attractive.
You can pump the river water itself through a heat pump and this can give very good results, but heat pump units require water at temperatures above 5 to 8°C (varying depending on type) so this system may fail to operate in the middle of winter during lower temperatures – just when you need the most heat. Therefore 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. However water-source heat pumps 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 required for pumping 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 will need to be sought from the relevant authorities as an abstraction license may be needed.