You are allowed to abstract up to 20,000 litres per day without the need for a licence. Therefore in most domestic installations a licence will not be required.
When drilling boreholes for water abtraction over 20,000 litres per day the Environmental Agency will need to be consulted for an abstraction licence. As the water will be discharged back into the ground this should be a formality, but the licence is required none the less.
In open loop systems, water is abstracted directly from (and discharged to), boreholes, rivers, lakes, ponds or even the sea and used as the heat source for a heat pump.
Open loop systems (depending on the type) can be cheaper to install than other types of heat pumps as there is no requirement for digging trenches. Also due to the higher constant temperature of the water source efficiencies are slightly higher.
However there are a number of points which need to be taken into consideration and these include permissions from the Environmental Agency and include but are not limited to:-
In order to drill or test pump a water supply borehole, you will require a consent to
investigate a groundwater source under section 32 of the Water Resources Act. This will be carried out by the company that drills the boreholes for your system.
To operate an open loop scheme you will need an abstraction licence (if the abstraction is greater than 20m3/d) and an environmental permit to discharge water.
In addition to permission requirements you should consider the design of any scheme to ensure its longevity and efficient performance. Such design considerations are the responsibility of the operator, designer and installer of the scheme. Consideration should be given to the following points:
Employ the services of a professional hydrogeologist and/or groundwater engineer to ensure you have a well-designed open-loop GSHC scheme;
Ensure that, in a twin borehole system there is adequate separation of the abstraction and discharge boreholes to ensure that large quantities of discharged water do not feed back into the abstraction borehole affecting the temperature of the abstracted water and hence performance of the system.
Ensure the discharge borehole is well designed so that it does not clog within a short period of operation. Careful control of the gas content, water chemistry and the particulate content of the water is required as small bubbles of gas and particulates can result in rapid clogging of the borehole or aquifer.
Biofouling with bacterial growth can also become problematic.
The hydraulic efficiency of the scheme will reduce over time, even with a good design, due to the clogging of the face of discharge as detailed above and especially if thermal breakthrough occurs between the abstraction and discharge boreholes. Background temperature of the groundwater may also change over time if more schemes are constructed in the area.
To avoid possible freezing and corrosion of the heat pump it is advised that the heat pump and water source are separated by an intermediate plate heat exchanger as shown below. It is also important that the water is filtered and bacterial growth minimised to avoid fouling. This does mean that a regular
maintenance schedule is required.
The signal for them extraction pump can be taken (via a relay) from the 24V supply between the controller and compressor contactor, contact Kensa Engineering for further details.
A check valve is also required on the water source side to ensure that the system does not drain down when the extraction pump is turned off.
As an alternative to open loop it is possible to place the ground loops directly in the water sourcemounted on mats, called pond mats. This removes the need for an intermediate heat exchanger, removes the filtration issues and allows the use of antifreeze within the system to avoid problems with freezing.
With pond mats there are issues which need to addressed and these include:-
A good place to install pond mats is mounting them to the underside of a floating pontoon.