Ground source heat pump update

I think we might have finally got there with the ground source heat pump.  It has taken some time to sort this out and I am glad that not all of the decisions on the renovation have been quite as tortuous as this one!

So why has this been so difficult?

• First of all, we had the debate over air source vs ground source.  We thought that the difference in price between the two would have favoured an air source heat pump.  However, having looked into it became clear the difference was not as big as first thought.  Given that we have a one acre field adjoining the property, it seemed a shame not to use a ground source heat pump.
• The next issue related to the provision of a 3 phase electricity supply.  It turned out once the initially estimates had been done that we needed a 24Kw unit.  Unfortunately, this is too big for a normal single phase supply and we needed a 3 phase supply.  We had heard stories of it costing thousands to get a 3 phase supply installed, so we thought that we ought to get this sorted out BEFORE ordering a ground source heat pump.  This took a while to get the quote from Northern Power Grid. More information here.  To be fair to them, it took me a while to fathom out the form!  Lots of questions that I didn’t know the answers to!  Anyway, the cost for installing a 3 phase supply (and modifying the existing single phase supply) is £2,600.  So not cheap, but not a showstopper.
• Almost there…..but now there are questions over the depth of the soil in the field.  We need at least 100cms of soil to go on top of the ground loops. We thought that there might be a problem because of the amount of soil in the others that we had dug.  So there was nothing for it, but to dig a number of test holes.  We did this last weekend and found that there is between 700-900mm of soil before you reach the bed rock.  It has taken until today to establish that around 800mm will be sufficient, so once the sand is added to the bottom of the trench to hold the pipes, we won’t be that far off.  We also have soil to come out of the garden when the footings and foundations are dug for the extension.  This soil could be put on top of the existing soil to raise the overall ground level.
• Then the last concern is over whether we are going to quailify for RHI.  I have covered this elsewhere on the blog, so I won’t bore you again here.  To qualify for RHPP, there must never have been gas on site.  Since we do have gas onsite (even though the boilers have been removed), we don’t qualify for RHPP.  RHI is due to in next  be introduced next Spring, but earlier indications seem to be that we WILL qualify for RHI.  We can’t say definitely, but we have decided to take a punt.  RHI is likely to be worth around £2,500 per year to us for 7 years.  So well worth having!  This document on the Government’s DECC website is the closest that I have seen to confirming that we are eligible even though the property has had a gas supply in the past.

So after all that I think we are just about ready to place the order for the underfloor heating and the ground source heat pump.  At last!

And now for some gratuitous photos of digging holes in a field!!

Only 700mm of soil covering the bedrock

Another skill to add to my CV!

In total, I dug 9 holes across the back of the field. The depth of the soil ranged from 600mm to 1300mm – it averaged 700-800mm in most of the locations.