What kit is required for a system?
The heat pump collects thermal energy from the ground by a “ground collector” which consists of pipework filled with water and anti-freeze. The pipes can either be laid horizontally at a depth of 1,2 meters or placed in a vertical boreholes which can be as deep as 200 meters.
The heat pump, which is usually the size of a fridge, is located internally. The other main components of the system are a how water cylinder, a buffer thank and three expansion vessels.
Ground-source Vs Air-Source Heat Pumps
What are the differences?
A ground source system is considerably more expensive than an air source one, but a ground source is usually a better investment in the long term for the following reasons:
Ground source is more efficient than air source, as the ground is warmer than the air in the winter when most space heating is required. Both types of heat pumps use electricity, but an air-source heat pump will use around 18% more electricity than a ground source to produce the same heat.
The expected life of a ground source unit is 20 years, while the expected life of an air source heat pump is 15 years. A significant part of the cost for a ground source system is the ground collector. The ground collector will support many generations of heat pumps. It is an energy well that is likely to last for a very long time.
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Frequently Asked Questions about Ground Source Heat Pumps
- What size heat pump do I need?
In order to determine the right size of the heat pump (in kW) and in the case of the ground source, the right size ground collector, we do a room-by-room heat loss calculation. For newly built properties, this is also required for the design of the underfloor heating system and/or radiators.
- How does a ground source heat pump work?
The physics of heat pumps is the same as that of a fridge or a freezer. In all refrigeration processes, heat is produced as a bi-product. In a heat pump system, the ground (in case of ground source) or outside air (in the case of air source) and the heat produced are used for space heating and hot water in a property.
- Do I need a backup boiler?
In most cases, the heat pump is sized to cover the whole heating load of the property and then no backup is required. This is called a monovalent system. A heat pump can also work in tandem with a boiler. This is called a bivalent system. In this case, the boiler is controlled by the heat pump in such a way that the heat pump is the master and the boiler is the slave.
- What is the best option for my house – boreholes or horizontal loops?
Boreholes are always the more expensive option. Horizontal loops require quite a lot more space. For a newly built property, around twice the total floor area, and for older properties up to five times the total floor area. In a garden with trees, the available space for collector pipes is reduced as roots have to be avoided. If a paddock or a field is available, it is usually the best option. The efficiency of a borehole system is the same as that of a horizontal loop system, provided that the size of the collector is correct. If passive cooling is required, boreholes are a better option, as the temperature in the borehole is more constant over the year.
- For horizontal loops, what is the difference between slinkies (coils) and straight pipes?
Horizontal loops can be either in the form of slinkies; 1 meter-wide coils, typically consisting of 350 m of 32 mm pipes stretched over 50 m, or straight loops (laid in a similar pattern as underfloor pipes). Sized correctly, both systems can provide enough thermal energy to the heat pump. Straight loops extract heat in a more uniform way, and it is therefore usually Better Planet’s recommendation. Sometimes slinkies can be the best option when trenching is complicated.
- For horizontal loops, how deep are the pipes laid and what is the pipe separation?
We always recommend laying the pipes at a depth of 1.2 meters. For straight loops, the minimum pipe separation is 1 meter, and for slinkies 5 meters.
- For boreholes, how deep are they and what is the distance between them?
For our projects, boreholes are drilled between 80 and 150 meters. The depth is related to the local geology and the type of drilling rig. For heat pumps sized over 6kW, several boreholes are required and they need to be separated by at least 6 meters.
- What are the planning requirements?
The installation of a ground source heat pump or a water source heat pump on domestic premises is usually considered to be permitted development, not needing an application for planning permission. If you live in a listed building or a conservation area you should contact your council to check on local requirements.