Filterclean are professional installers for Geothermal International and Danfoss UK, two well-established UK based specialist in ground source heat pump (GSHP) systems with  extensive portfolios of successful installations nationwide. In-house expertise ranges from the small domestic systems to the largest commercial installations, and perhaps uniquely in the industry.

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Heat Loss and System Sizing

To achieve optimum long-term efficiency, we match the systems we install as closely as possible to the target heat load, i.e. the heat pump has to be capable of providing more heat (but not too much more) than the property will lose on the coldest of days, plus some extra capacity to take care of hot water generation. Many people feel happier with an amount of overcapacity in their heating system, however, this is seldom the best policy with Ground Source Heat Pumps and should only be considered if an extension to the area to be heated is a real and immediate possibility. Therefore, identifying the likely heat loss of a property is an important step in sizing a suitable heat pump system. The main factors involved in calculating heat loss are the materials and techniques used in the building of the property. Initially we use best-fit models to identify a suitable heat pump, but where detailed plans are available or a site survey has been carried out, we can derive a more accurate picture of likely heat loss. The Standard Assessment Procedure (SAP) report will be required to confirm the bespoke design for the system.

Example

The average pre 1980’s  4-5 bedroom home that has good loft insulation and double glazing is likely to have an average heat loss in the order of 75W/m² (average heat loss per square metre of floor space). Such a property would be adequately served by a 17kW heat pump system. However, the same home constructed using the latest techniques and materials, may have an average heat loss as low as 40W/m², and therefore would be adequately served by an 8kW heat pump system.  

Ground Loop and trench sizes

The various forms of ground loop for residential applications are mentioned on the previous page. Where space allows, we recommend the installation of Horizontal loops; they are the most cost effective and give shorter payback periods in most cases. Vertical loops, although potentially more efficient and compact in terms of surface area requirements are, more often than not, a more expensive alternative due to the drilling expense.  

A desktop survey can be carried out to obtain the exact soil makeup in your area, this makeup can then be used in conjunction with your heat loss calculation in our design process to calculate the exact size of heat pump and ground loop needed.

• Trench dimensions (Depth and width)

• Horizontal loop: up to 1metre wide x 1.5metres deep

• Slinky loop: 1metre wide x 1metre deep

• Vertical loop: A number of boreholes to be drilled, on average around 100metres deep

Example

To implement a GSHP system to suit an average pre 1980’s  4-5 bedroom home that has good loft insulation and double glazing would require a 17kW heat pump. To support this arrangement, a horizontal ground loop would be installed in adjacent ground, the overall size of which would depend upon the type of soil found in the local area. Generally, heavier soils and clays are more favorable to ground loop installations, sands and light loams less so. In the case of clayey sub-soil, a 17kW heat pump would require 2 x 85m (or 4 x 43m) trenches.  

Generally, for a horizontal system the installation process would proceed as follows:

•  We meet with yourselves and the other contractors involved in the project to agree timings and share information on requirements for the system to be installed, culminating in a Project Agreement: a clear statement of what is expected from ourselves and what measures are required regarding other works in order to successfully accommodate the Heat Pump system.  

• Excavation of trenches (as specified) will be carried out, and the laying and thermal welding of ground loop polyethylene pipes.  

• Connecting trenches will be excavated by our ground workers, header pipes run to boiler room/utility area via an external flushing chamber and the whole system pressure tested prior to back filling of trenches.  

• Flushing of the system will be carried out to remove any thermal welding swarf or other contaminants and the system charged with a specialist non-toxic antifreeze/water mixture.  

• Ground Source Heat Pump(s) will be installed by our engineers and connected to the ground loop system, the domestic distribution system (domestic hot water and central heating etc.) and mains electricity supply.  

• Pre-commissioning checks will be carried out by our engineers - this process will concentrate on completeness and suitability of the domestic distribution system, heating controls and electrical supply.  The system will then be commissioned.

This collects solar energy stored in the ground or body of water into which it is installed. A water/antifreeze mix is circulated through the ground loop (whichever form this takes), transferring heat from the ground or body of water to the heat pump and hence, your home or building.  

Usually located outside (ground loops can hold typically 1000 - 2000 litres of heat exchange fluid; handling such a quantity is easier with a little elbow room); allows charging and purging of ground loop.  

Heart of the system; converts bulk low-grade heat from ground loop to sufficiently high-grade heat for heating purposes using similar technology to that of a domestic refrigerator or freezer.  

Optional but strongly recommended system element. Heat pumps do not like frequent starts and stops (short cycling). A suitably sized buffer vessel gives the heat pump(s) a load to drive regardless of demand from heating zones. This allows the heat pump to work at its own pace and prevents problems arising from short cycling, such as ‘lock-out’ due to high return water temperatures.

Unit

Supply

Full Load Current (A)

Breaker Size/Type

Dimensions (mm)

Weight (kg)

L

W

H

EKW06

1 Phase

16.7

32/D

648

457

668

91.7

3 Phase

4.5

10/D

EKW08

1 Phase

22.6

32/D

826

559

668

120.3

3 Phase

5.1

10/D

EKW12

1 Phase

28.3

45/D

826

559

668

147.6

3 Phase

7.7

15/D

EKW17

1 Phase

32.2

45/D

826

559

668

163.4

3 Phase

10.6

20/D

Domestic Hot Water Cylinders

The type of hot water cylinder required to work most efficiently with the proposed heat source would be an indirect type cylinder featuring 2 or possibly 3 separate heat exchange coils (themselves being optimised for surface area and flow rate), and be extremely well insulated.

Projected Savings

A 17kW geothermal heating system as per our example could save in the region of  £2000 per annum over equivalent oil fired systems, based on current maintenance and energy prices, and the expectation that the heat pump unit will outlast at least one boiler during normal service.  
Based on July 2009 prices