Ground source heat pumps / air source heat pumps and under-floor heating systems.
Heat pump technology
Ground source and air source heat pumps act by extracting energy from our surroundings and using a compressor to add to this heat gain. The output is a low temperature (up to 40 degrees) heating supply that can be used to drive low temperature radiators or towel rails, pre-heat your domestic hot water, or most effectively, in new build situations, fuel a wet under-floor heating system. Appropriately sized, the heat pumps can provide any, or all, of the above services, and provide a constant output with only small seasonal effects.
Most heat pumps use the same ‘vapour compression’ technology that is used in a domestic refrigerator. Systems use a compressor, an evaporator and a condenser. In general, an electric heat pump covering 100 % of the requirements of a dwelling will only need 20 % to 40 % of the electricity requirement compared to an electric heating system. This ratio of heat output to the electricity input is termed the coefficient of performance (COP).
Types of heat pump
Heat pumps are characterised depending on the source of the heat from which they draw. In the heating mode, energy can be extracted from the air, water or from the ground and delivered to the building via a ducted air circuit or a water circuit (such as under-floor heating or normal radiators).
Air source heat pumps use the air as the energy source in heating and the energy sink in cooling. Air source heat pumps have the disadvantage of extremely variable temperature conditions throughout the year. However, air source heat pumps still have COP’s of around 2.5 to 3.5 and avoid the disturbance and cost of extensive ground works. The heat pump is usually situated on an external wall with one of the heat exchange units inside the building.
Ground source heat pumps have the advantage that the ground remains at a relatively constant temperature throughout the year and this gives good conditions for a slightly higher performance. The heat pump can be coupled to the ground in a number of configurations including horizontal (straight and spiral) trenched ground loops and vertical borehole ground loops. Due to the more ideal temperature conditions, ground source heat pumps perform better than air source heat pumps. Typical COP’s for ground source heat pumps are between 3 and 4.5, however, they are installed at greater cost.
Three types of ground coupling for heat pumps: Horizontal Coil, Vertical Coil and Slinky Coil
Type of heat pump |
Operating COP |
Energy Input |
Applications |
Air source |
2.5 to 3.5 |
Electricity |
Space heating, hot water heating, cooling, and dehumidification |
Ground source |
3 to 4.5 |
Electricity |
Space heating, hot water heating, and cooling |
Grants
Grants available to private businesses, public sector organisations, community and charitable organisations, range from 35% to 50% up to a maximum depending on the project and status. Please see http://www.lowcarbonbuildings.org.uk/about/ for further information.
Our engineers are fully trained and approved. Additionally, every aspect of all our installations will be certified.
What is required?
For the majority of projects, either a ground source or an air source heat pump is an effective solution. For small extensions or small heating loads, an air source heat pump may well be more appropriate. For very large projects with sufficient space, a ground source heat pump may well be preferential, especially if ground-working plant is already on site.
If you are considering a ground source heat pump, then a minimum accessible and clear land area (that you do not mind disturbing) of 15m by 15m is required (this is enough space to accommodate a heat pump capable of fuelling the under-floor heating for a standard three bed domestic house with a 250m length of ground collector). This provides for a trenched ground loop, where trenches are generally 1m wide by 1m or 2m deep. If such an area is not available, then a drilled bore-hole ground loop may be appropriate, however, although this approach slightly improves operating efficiency, it does increase costs. For any scheme where there is insufficient land area, or in retrofit situations, where large scale ground disturbance is not wanted, an air-source heat pump is likely to be more appropriate, and is very often the most cost effective option. These units are still highly efficient and sit on the floor against an outer wall of the building. We will advise on the best approach case by case when we come and survey your project.
Heat pumps are very quiet in operation and range in size from that of a small fridge to that of a larger fridge/freezer. This allows them to be positioned wherever appropriate and commonly they will be located in the utility room or garage or even under a kitchen unit.
An air source heat pump, small and then large ground source heat pump units.
Planning issues
Generally, there will be few planning issues involved. please consult your local planning authority to check.
Under-floor heating
Whether or not you are considering a renewable energy source we are happy to assist in any under-floor heating, standard heating or general plumbing projects you may have. Under floor warm water heating systems are generally best suited to new build or extension projects and provide highly efficient space heating. A screed floor with a stone, slate or tiled surface is most effective, timber floors (engineered board is preferable) generally result in a 20% reduction in heat transfer efficiency, and carpets (only certain types are acceptable) further insulate the heat source causing a further 20% reduction in efficiency. On the ground floor a heating loop under the screed is the ideal solution, and on the first floor or above, a floating floor or between joist system provides the best performance. Again, there are options available and these can be discussed with you case by case.
Warranty
Generally under-floor heating pipe is covered by a manufacturer’s 25 year warranty and the overall system by a manufacturer’s 10 year warranty. The heat pump itself is covered by a 2 year manufacturer warranty. A 25 yr lifetime can be expected from a typical heat pump installation. Hendra Renewable Energy provides a further one year warranty on all workmanship.
If your hot water usage is large then perhaps a solar hot water heating system can be a cost effective addition. The use of a thermal store cylinder means that under-floor heating systems, if not fuelled by a ground source heat pump or your existing boiler direct, can be part loaded by solar heating with the addition of a solar coil in the thermal store.
We believe that sustainable heating systems incorporating a renewable energy source will become a valuable investment to any home or premises, and could be of further financial benefit when the new energy efficiency ratings are introduced.
For more information on grants and how heat pumps work, please see:
http://www.lowcarbonbuildings.org.uk/micro/ground/ and
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