Under CERT (The Carbon Emissions Reduction Target) the design life for a ground source heat pump is 25 years. There is no equivalent figure for air source heat pumps although life span is expected to be 20-25 years. In comparison between the two, given that an air source heat pump requires an outdoor unit that will be exposed to the elements, where as a ground source heat pump only requires an indoor unit; one would expect the ground source to outlive the air source.

Maintenance

Service and annual maintenance is an important consideration when considering any large purchase for the home.

A heat pump system is an investment for your home and it can significantly increase the value of a property in exactly the same way that other types of home improvement will. However it is important to maintain and look after your heat pump in order to protect your investment and safeguard its future service.

Luckily heat pumps require very little in the way of maintenance. They are often referred to as fit and forget technology. A heat pump is very similar in operation and components to your fridge.

How often do you service your fridge?

A heat pump is a lot less onerous to service on an annual basis than other conventional types such as boiler based heating systems

Heat pumps do not contain a burner

Concerns over the risk of carbon monoxide are completely removed with a heat pump installation

Considering that a Heat Pump has the same refrigeration components as a domestic refrigerator but on a larger scale it is clear that heat pumps have a lower maintenance requirement than a gas or oil boiler with no risk of carbon monoxide fumes or smells etc.

Heat pumps are easy to live with as long as the basic service requirements are met and the initial selection of the heat pump is correct and matched to the needs of the client. Like all machines, heat pumps perform at their best when they are in tip-top condition. Recommended procedures for maintaining ground source and air source heat pumps are listed below

Recommended ground source heat pump maintenance

Looking at the main components of a ground source heat pump,

1) The compressor is hermetically sealed, (this is the heart of the unit and the item which has a design life of 20-25 years). Hermetically sealed means it’s basically air tight and is a non-maintainable device. Highly unlikely, but if this was to go wrong it’s a replacement compressor.

2) Water pumps are the only other moving parts within the ground source heat pump and it is a good idea that pre-heating season these are checked and the internals spun.

3) Electronics – ideally these should be checked before the heating season starts to make sure that they are operational.

4) External pipes and fittings – it is always a good idea that these are checked to ensure that there are no leaks.

5) The ground arrays for a heat pump are generally manufactured from MDPE and have an expected life of around 70 years. It is the same material as is used for your mains water supply, only water pipe is blue indicating potable water. Once buried the ground array can generally be forgotten.

6) The anti-freeze that circulates around the ground arrays doesn’t need any maintenance, as long as it is correct with the right biocides in it, as the system is sealed. It might be a good idea to take a sample at the same time as the pre-season checks just to confirm everything is okay.

7) As with any heating systems, a good corrosion inhibitor should be used on the heating distribution side, and the heating fluid should be checked to ensure that the inhibitor is working and the fluid is not corrosive.

These checks are generally combined into a pre-heating system check where the heat pump is turned on and its operation checked prior to the heating season so any issues can be solved, before the unit is required for full load

The ground source heat pump itself has a design life of around 20-25 years and a number of Government funding streams, such as the RHI reflect this. However to achieve this design life, the system does need to be maintained.

Recommended air source heat pump source maintenance

Air source heat pumps require little maintenance. However, regular cleaning will ensure optimum performance from your heat pump unit. It is essential that the heat pump filters are kept free of debris and cleaned on a regular basis – (at least every 6-8 weeks.)

The outdoor unit can be regularly hosed down especially if you are in a high salt area. Treat it as you would your car. Keeping it free of debris, especially at the rear of the unit, will help it perform better.

The following six tips will help to make sure your heat pump stays in best form:

1. Replace air filters monthly - especially during winter and summer seasons. Dirty clogged up filters will reduce the airflow and make your heat pump less effective.

2. Check the thermostat - how often does the unit run? Constant operation of your heat pump is often due to its thermostat being set far too high, low refrigerant levels, leaves and other rubble jamming the outside unit or cool drafts next to the thermostat. You can fix this by lowering the thermostat setting.

3. Test the air handler - ensure that the air handler is receiving power; this can be done quite simply by switching from ‘auto’ to ‘on’. To check that it is in running order, see if the blower runs properly.

4. Check the breakers - in the unit breaker cabinet and also in the main breaker cabinet, reset any tripped breakers. However be careful, if the breakers trip again, do not attempt to reset as it is tripping for a reason and there is a fault.

5. Set the temperature - check that your thermostat settings are correct. To heat a room, you must set the temperature higher than the room’s real temperature and to cool the room, set it lower. It is also worth changing the batteries quite often on such thermostats, to make sure they are performing at optimum level.

Heat pump servicing gives peace of mind and assurance that your heat pump system is running efficiently.


Which heat pump is cheaper?

While there is only one type of air source heat pump, there are several types of ground loop associated with ground source heat pumps, each with different costs associated. Bore holes are renowned for being particularly expensive, although demand and competition are bringing cost down. Due to the extra work associated with a ground array (whichever type) you can expect to pay considerably more for a ground source heat pump than an air source heat pump. VAT is only chargeable at 5% on any renewable energy installation.

Which is easier to install?

Quite obviously an air source heat pump is easier to install. It comprises of an outdoor unit and an indoor unit. These ideally, are mounted back to back with the wall in the middle. The outdoor unit comes in a box and simply requires a hard standing to take its weight eg. a couple of paving slabs. It will require an electrical supply and pipe work to link it to the indoor unit. The indoor unit is coupled to the heating and hot water system and this too will require an electrical supply.

A ground source heat pump has only an indoor unit which the pipe work from the ground loop will be attached to. The ground loop will need a fair deal of installation, a bore hole drill rig or a digger will be needed to bury the pipe work and install the loop. This is a lot more work than is associated with an air source heat pump installation but at present greater efficiencies can be achieved with a ground source heat pump due to the all round stable 8-12°C temperature in the ground. It is therefore left for you to decide between the extra cost and upheaval verses the extra efficiencies on offer.

Efficiency - COP – SPF

Currently ground source offer the highest COPs and SPFs due to the year round stable ground temperature. They are a sure fire bet, tried and tested, proven form of technology. Air source heat pumps are an all together newer technology. They have been in the mainstream for less time and are less tried and tested.

Their COP and SPF are only slightly lower and the gap has been diminishing year on year. Technology is moving at a rapid rate in heat pumps and manufactures are developing new methods of extracting more energy and making their products more efficient. Ground source is currently in the lead with efficiency but nothing is to say that it will always be.

If you want the higher efficiencies of the ground source but have no room for the ground array, why not combine your air source heat pump with solar thermal or a wood burning stove or both!
Government incentive RHI payment tariffs

To be launched in the summer of 2013 and without a doubt, the most influential factor of decision making, firstly when deciding whether to have a heat pump and if so; air source or ground source. Exact tariff levels have yet to be confirmed although what is certain is that the ground source tariff will be slightly higher to offset the initial extra capital investment. One great thing about the RHI is that tariffs will be set at a period of 20 years, however, payments will be condensed into 7 years, meaning you will receive all 20 years worth of payments over the first seven!

Another idea being ‘bounced around’ is to reward better performing systems with higher tariffs in order to encourage good workmanship and higher efficiencies from installers and manufacturers. We think this is a good idea.

Noise levels

Air source heat pumps have an outdoor fan unit that makes a low level noise varying from model and manufacturer. Fitting them under a bungalow bedroom window for example would not be advised. Ground source heat pumps on the other hand are silent apart from the pumps which you won’t hear.

Planning Permission

Ground source or water source heat pump?
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.

Air source heat pump

From 1 December 2011 the installation of an air source heat pump on domestic premises is considered to be permitted development, not needing an application for planning permission, provided ALL the limits and conditions listed below are met.

These permitted development rights apply to the installation, alteration or replacement of an air source heat pump on a house or block of flats, or within the curtilage (garden or grounds) of a house or block of flats, including on a building within that curtilage. A block of flats must consist wholly of flats (e.g. should not also contain commercial premises).

Limits to be met:

Development is permitted only if the air source heat pump installation complies with the Microgeneration Certification Scheme Planning Standards or equivalent standards.

The volume of the air source heat pump’s outdoor compressor unit (including housing) must not exceed 0.6 cubic metres.

Only the first installation of an air source heat pump would be permitted development, and only if there is no existing wind turbine on a building or within the curtilage of that property. Additional wind turbines or air source heat pumps at the same property requires an application for planning permission.

All parts of the air source heat pump must be at least one metre from the property boundary.

Installations on pitched roofs are not permitted development. If installed on a flat roof all parts of the air source heat pump must be at least one metre from the external edge of that roof.

Permitted development rights do not apply for installations within the curtilage of a Listed Building or within a site designated as a Scheduled Monument.

On land within a Conservation Area or World Heritage Site the air source heat pump must not be installed on a wall or roof which fronts a highway or be nearer to any highway which bounds the property than any part of the building.

On land that is not within a Conservation Area or World Heritage Site, the air source heat pump must not be installed on a wall if that wall fronts a highway and any part of that wall is above the level of the ground storey.

In addition, the following conditions must also be met. The air source heat pump must be:

Used solely for heating purposes.

Removed as soon as reasonably practicable when it is no longer needed for microgeneration.

Sited, so far as is practicable, to minimise its effect on the external appearance of the building and its effect on the amenity of the area.

Aesthetics

Again the air source unit will be on show outside your home and although they are not particularly ugly, in comparison to a ground array that is buried, they are seen. In terms of indoor units there is a lot of variance between models and it simply personal preference.

Conclusion

RHI will have its part to play as will the selection of the heat pump for your premises and its set up, however, it appears that at present a ground source heat pump will achieve higher efficiencies, is likely to require less maintenance over its life and therefore have a longer life span; where as an air source heat pump proves the cheaper more convenient option.