G : Open Loop GSHP Systems

Open Loop GSHP Systems

When is an Open Loop system the right alternative to choose?

Open loop geothermal heating systems work by extracting the heat from water pumped from a waterwell borehole, before this water is returned to the ground.

(in contrast, closed loop systems operate very much like a domestic fridge, with no substance input or exhaust, just energy)

Traditionally, open loop systems have been more often installed for larger, often commercial installations, although this may be changing, as described further down this page.

Should you be fortunate enough (and most people are!) to be located close to a good underground water source i.e. acquifer, then an open loop system might be the most cost effective answer to your heating (and cooling) problems.

Additionally, if you choose this method, you may well be able to use the water you extract for the heat pump for other purposes, e.g.

  • Grey water usage (car washing, toilet flushing etc.)
  • Drinking (this will require extra equipment, i.e. UV sterilisation, filtration)
  • Irrigation of your garden (Synergy also supplies and installs water storage and irrigation systems)

In short, you can kill several birds with one stone, save energy costs and save on your water supply bill!

A cautionary note!

As mentioned below, should the water pumping requirement of your open loop system exceed 20 000 litres per day, then an Abstraction License from the Environment Agency (EA) will be a legal requirement.

There is no guarantee that the EA will grant such a license. The application procedure is complex, time and cost consuming.

The EA may well require a pumping test on the completed borehole in order to determine whether they grant a license, or not.

This means simply that the client has to "gamble", i.e. invest in the cost of establishing the borehole without having any certainty that the Abstraction License will be granted.

In addition, the operation of an open loop system requires continued monitoring and maintainance. The water from the borehole may require sediment removal or other filtration. In this case the filters will require regular inspection and replacement of consumable filter elements.

So how do you go about it?

The first essential step is to see whether you have a good water source in close proximity as mentioned above.

Please, please, do not do anything other than commission a fully qualified hydro-geologist to ascertain this for you.

Synergy can help you with this, by either putting you in contact with an independent geologist, or commissioning a geological water survey for you.

Assuming that the survey produces a positive result, then it is time to size and choose the heat pump to best suit your property.

When doing this, it must be remembered, that for water abstraction rates of more than 20000 litres per day, an abstraction licence from the Environment Agency is a legal requirement. The risk inherent in this is described above.

The dimensioning of the heat pump is best done by an expert, Synergy can help you with this. We are not heating engineers, but we do cooperate with trusted and accredited installers of heat pumps from several manufacturers.

One of these experts will gladly help you choose the right size of heat pump for your property.

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