Craigdhu installed a heat pump in 2019.

What technology have you installed?

A 6 kW Nibe ground source heat pump.

We have 500 m of pipe buried 1.2 m deep in a very marshy bit of ground which should make it more efficient this is more ‘oblong’ than trench, but it has the same effect.

The heat pump is connected to underfloor heating and used about 200 W during spring 2020, while an additional 1.5 kW was used when the domestic hot water was being heated.

The 6 kW is made up of 1.5 kW for heating the house and a potential of 4.5 kW for hot water but that is so it can do a boost every 2 weeks.  In practice the heating uses about 200 W and the hot water cycles on and off at 1.5 kW. The hot water tank is 180 litres and is part of the unit (picture 1)

We already had underfloor heating.

Where do you live and what kind of house is it?

The house is 1.5 story 3-bed croft house and is about 12 years old. It has a cavity wall which was built with reasonably good insulation, but not as good as it would be in a newer build. After a thermal survey by LEG, 3 years ago, we have worked at improving cool spots, reducing drafts and added more curtains to larger windows.

What system was replaced?

The previous system was a ‘wet electric’ system, with 12 kW electric immersion heaters running the underfloor heating.

When was it installed?

Summer/autumn  2019

Installation cost?

It cost about £14,000 including digging the hole for the coil of the pipe (which we laid ourselves with help of friends and family), purchase of unit, materials and installation.  It also includes the cost of the Energy Performance Certificate and an electrician to disconnect the old system and connect the new one.

Did any grants/support help with the cost?

The system is eligible for Renewable Heat Incentive (RHI) and over 7 years this is expected to cover the capital costs.  To get this you need to use an approved installer who will calculate how much RHI you will receive.  It is based on the theoretical requirement of your house, not on the electricity you actually use.  Your house also needs to have an up to date Energy Performance Certificate.

What difficulties did you encounter getting the installation carried out?

Planning permission was not required and we used an experienced local installer, Lochaber Renewables from Arisaig, who organised everything except digging the hole and laying the pipe. We were quoted for 2 types of Ground Source Pump and for an Air Source Pump, and were able to discuss what would work best according to the local ground conditions.

We had already had a free survey done by the Energy Savings Trust and it was really on their recommendation that we investigated the Ground Source Heat Pump.

Getting the pipes into the house was slightly complicated because the heating system was at the back of the house, while the underground coils were at the front and there is a solid concrete floor for the underfloor heating. We had to bring them in at ceiling height and drop them into the pump from above (Pic 1).

The unit that holds the pump just fitted into the cupboard (pic 2) which used to hold the hot water tank and it did take some acrobatics from Graham, the installer, to attach all the different pipes. We needed an electrician to connect the pump and it has its own meter so you can see how much electricity it uses.

How long did it take?

It took us a while to decide what we were going to do and which version to use. We dug the hole and laid the pipe in June when we had a digger on site doing another job and by mutual agreement the installation of the Nibe unit took place over 2 days in early October.

Has it been effective?

In a nutshell the house is warmer than it was before and it costs much less to heat. We have the system set at 18°C and that gives a good background heat. You can easily change the settings but mostly you don’t need to (pic control panel).  We still use our wood burner on cold or miserable days and in the evenings, but much less than we used to. Below is a winter cost comparison.  We don’t yet know what the costs will be for the summer, but the pump will automatically switch itself off whenever it is warm outside and the water heating is very efficient.

4 Month: December – March Comparison of kWh

Over the past few years we have used between 3100 and 4200 kWh on heating during these 4 months.  This year the pump has taken 1150 kWh to run the heating.  Our tariff has changed so a direct cost comparison is difficult but effectively the costs have dropped by nearly 70% and that equates to a saving of £350 at 14p per kWh for 4 months.

Would you recommend the system?

Absolutely, if you have some space in appropriate ground for the coil of pipes or the correct ground conditions for a bore hole (which is likely to be more expensive, but also more efficient).  You also have to have enough capital to invest in a long term saving.  You will receive your capital back from RHI.

I would also recommend Lochaber Renewables for advice, installation and support.

Pic 1. The pipework coming in at ceiling level to avoid breaking into the solid floor.

Pic 2. The new unit which just fits into the cupboard which housed the old hot water tank.


LEG Comments

This looks like a cosy and efficient system. Having suitable outside space for coils and underfloor heating already installed makes the Ground Source Heat Pump a relatively easy choice!

The up front cost can be funded by the Home Energy Scotland loan, with £10,000 at 0% available for heat pumps. Along with the Renewable Heat Incentive this makes it very accessible for people to change to renewable heating!

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