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How to maintain and service your ground source heat pump

Posted by John Barker-Brown on 3 August 2011 at 9:03 am

The Government's microgeneration strategy states: "More work is required on understanding the durability of microgeneration installations, including their key components. We want consumers to be aware, at least in general terms, of the minimum requirements for aftercare service and maintenance for each microgeneration technology."

So what are the requirements for a ground source heat pump?

Different manufacturers will advise you differently: varying from none to annual servicing. What is certain is the system doesn’t require the same amount of servicing as a gas or oil boiler. Think of it like this, you fridge is basically a heat pump, yet how often do you service your fridge?

However, as the heat pump contains a refrigerant, any engineer who is required to fix a fault with the refrigerant circuit needs to be certified as the refrigerant gases used can be harmful to the environment.

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.

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.

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. If the antifreeze/water mixture has to be removed from the ground arrays then this is classed as a hazardous substance and it must be disposed of correctly.

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.

If there is a problem with the unit and it is part of the refrigerant cycle, as mentioned above, a certified ‘F’ Gas engineer has to be used to repair the unit.

On larger commercial systems under the ‘F’ Gas regulations the requirements are more rigorous including written schedules and examinations. However as the amount of refrigerant is below 6kg and the compressor is  hermetically sealed (which is the limit for these more rigorous requirements) in the domestic situation these additional requirements are not usually required.

On de-commissioning if the refrigerant gas is being removed again this needs to be done by an ‘F’ Gas certified engineer who will follow set procedures to ensure that no hydrocarbons are released to the atmosphere.

There are heat pumps out there that are running after 25 years and here at Kensa we have been manufacturing ground source heat pumps for over 10 years with the majority of our early units still going strong. One thing is for certain a ground source heat pump will certainly out last a traditional fossil fuel boiler!

About the author: John Barker-Brown is special projects manager at British heat pump manufacturer Kensa Engineering.

If you have a question about anything in the above blog, please ask it in the comments section below.

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Comments

4 comments - read them below or add one

John Barker-Brown

John Barker-Brown from Kensa Engineering LtdComment left on: 5 September 2011 at 9:45 am

Thanks for the comment Andy, 

The problem here is that we still have no real details for the domestic RHI (which I presume your installation is).

The only details we have are the OFGEM guidelines which are for non-domestic situations, however it is expected that the domestic guidelines will be similar, but might not require the same level of detail.

These guidelines for non-domestic currently say:-

As an ongoing obligation, participants are required to maintain their equipment to ensure it is working effectively. Given the wide range of eligible technologies, it is not practical to specify a particular level of maintenance or frequency of servicing; what would be appropriate for a biomass boiler may not be for a solar thermal system. As a general principle Ofgem requires the equipment to be maintained in line with manufacturer instructions where available. Participants will need to keep any evidence of maintenance work carried out, for example, servicing receipts, and to provide us with this evidence on request.

Whether they will ask in domestic situations for evidence is still not known, but I believe they will refer back to the manufacturers guidelines on maintenance. Whether this is yearly, every 5 years, never etc, depends on the manufacturer. A heat pump is not like a gas or oil boiler where there is a risk of noxious gases or explosion.

I would suggest that checks above are carried out on a yearly basis for peace of mind, however if this needs to be a dedicated service engineer will depend on the heat pump manufacturer.

Sorry I can't be clearer.

John

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andypippa

andypippaComment left on: 4 September 2011 at 9:41 pm

I've been told by my installer that i have to pay into a yearly maintenance schedule in order to qualify for the rhi when it finally arrives.  Is this not necessary or correct then?

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John Barker-Brown

John Barker-Brown from Kensa Engineering LtdComment left on: 3 August 2011 at 10:18 am

Thanks Bob, a valid cautionary note from you.

I suppose it comes down to my pet hate which is immersion heaters in heat pumps, something which we have never done here at Kensa. If the compressor fails and there are no immersion heaters, the client knows the unit has failed as the heat pump doesn't work and his building feels cold. 

Obviously it's far better not to have a failure in the first place and a good brand of reliable compressor should help mitigate this.

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Bob Irving

Bob IrvingComment left on: 3 August 2011 at 9:23 am

I think that the most important bit of maintenance for a GSHP is to check that it's working correctly. I know of one, kept in an outbuilding, where the compressor failed and it ran on the auxiliary heaters for a fortnight before anyone noticed, fortunately in the summer.... It would be nice if there was something other than a tiny red light to indicate this sort of fault, but if it was inside, I suppose the owners might notice that the compressor was not running.

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