By comparison with air and ground heat pumps, the water sourced version is the poor cousin, in terms of sales of units when viewed on a residential basis. The reason is that most homeowners do not have a site suitable to obtain the volumes of water for use with such a system. Oddly enough, when we compare the water source pump to the other two, usually it wins hands down on the coefficient of performance (CoP). So the most efficient source of heat pump is the least used version in the market. How odd!  

Water Source Heat Pump Benefits And Drawbacks

The reason for the better efficiency lies in the consistency of the source. Most of the time the water at depth has a consistent temperature and hardly varies at all throughout the year. Unlike the GSHP and ASHP, while can fluctuate in efficiency with seasonal variations, the WSHP can deliver a consistent flow at the temperature required. In theory the components of the pump should also last longer, as they are not exposed to the variances in temperature either. And with less moving parts than the ASHP, that augers well for reduced maintenance issues.

The big drawback is that few people have access to a suitable source to provide the water. If you are lucky enough to have a river or lake on your property then a WSHP can be an ideal heating source. However, care needs to to taken with placement of the collector, so that it is firmly established in place and cannot be moved by water current or other objects.  Also, if you have a well source, then that too is a possible candidate for a heat pump; however the caveat is that you need 2 boreholes - one which delivers the water from the well and another to discharge the spent water back. This is usually what prohibits many from implementing it, as they usually have only one borehole.

Further complications could arise when using the well for both the heat pump and for mains water to the house, and what would happen if the well were to run dry? Perhaps now I can understand why so few of these are sold....

WSHP Space Requirements:

Most WSHP units are usually the same size as the GSHP versions; in fact many companies sell models which look identical from the outside, and units generally are less than 900x900mm. These can usually fit in small boiler rooms, but of course the more important requirement is to site the pump as close as possible to the circulation coils, to reduce any heat loss in the water being fed to the pump. The ideal spot for this is if you live right beside a river, an option not available to most of us.

WSHP Heating Options:

Most WSHP system will heat to the same temperatures as the GSHP, i.e. in the 30-45°C range. So to be able to use this heat effectively would require replacing the radiators with an under floor system or else over sizing the radiators to accommodate the lower heat range. In terms of price range, refer to the prices for the GSHP systems I listed previously, as the WSHP options appear to be broadly similar in both cost and system components. The cost of installation will be less if you are laying in a lake or river close by, but will be greater if you opt for the well borehole route and require a second borehole to be dug.

Now lets look at the final option, space heating using solar panels...