The personal blog of Darren Scott
Posts tagged ground source heat pump
The ground source heat pump – a year on…
It’s just over a year now since our IVT Greenline HT+ E11 11kW ground source heat pump (GSHP) was installed so I thought it would be the perfect time to reflect on our experiences of owning and running a system like this, and also importantly to do some quick analysis on how much electricity we’ve used over that period compared with previous years.
If you’re interested in previous posts relating to the heat pump, take a look at these…
A bit of background…
First, though, it’s worth a re-cap on why we decided to install a ground source heat pump in the first place. During the latter part of 2011 we extended our house considerably by converting an adjoining timber-framed thatched barn into additional living space and creating an enlarged entrance hall, a new open plan living and dining space, large kitchen and utility room. Our existing central heating and hot water system was an electrically heated wet system with radiators designed to work with low-rate electricity tariffs. Although electrically powered (which sounds frighteningly expensive!), this had worked reasonably well and efficiently over the previous 12 years since installation but it was nearing end-of-life, the manufacturer had gone out of business and it was simply not big enough to satisfy the increased demands of the enlarged property. So it had to be replaced with a new system.
After looking at all the options available to us, particularly as we are off the gas grid, and comparing various traditional technologies with newer ones, a ground source heat pump emerged as the ideal choice for us.
At the time we decided on a GSHP we also planned to add a solar thermal installation to supplement the hot water. As it eventually turned out, we didn’t install solar thermal and instead opted for a 4kW (peak) solar PV array which, we were told, would be a very good companion to the heat pump.
Installation and commissioning
Our GSHP system was supplied by ICE Energy, probably the UK’s biggest and most experienced supplier of GSHPs. It was important to me that we chose a company with a lot of experience given the general lack of knowledge and even awareness of this technology, and we definitely got that with ICE Energy. Their sales, engineering and technical support staff were very knowledgeable, efficient and professional at all times so I would highly recommend them to anyone else looking for a heat pump.
The installation of the heat pump, cylinder and associated plumbing was pretty straightforward for the plumber working on our barn conversion, even though he had never installed one these before. The work associated with the installation of the ground collector pipework loops was a lot more than I had originally imagined, with some 300 tonnes of soil being moved during the course of the work: digging the three trenches, 50m long x 1m wide x 1m deep, laying 200m of coiled collector pipe “slinkies” in each trench, creating a concrete inspection chamber to house the pipework manifolds, filling the trenches back in and making good the paddock again. Having said that, it was all completed within about 4 days and even though my paddock looked like a barren wasteland for a few weeks, it didn’t take long for the re-seeded grass to grow back and look as good as it had previously.
The commissioning of the system, which included checking the basic installation, filling the collector ground loop with the heat transfer fluid and powering on the system for the first time was carried out by an ICE Energy engineer. He also talked through the basic operation of the system, how to tweak the controls and what maintenance tasks needed to be performed. There was a lot of information to take in but I also had the full manual which I read several times to make sure I absorbed the important detail.
The early days
Initial impressions of the system were very favourable. It was very quiet in operation, which was an important factor given that it is housed in specially made oak framed cupboards in our entrance hall, immediately adjacent to our main living area.
The first few months involved a lot of tweaking of the system settings in order to find an acceptable level of comfort while still trying to keep it running as economically as possible. The primary settings of the heat pump include a heat “curve” which dictates how much heat the heat pump should generate given the current outdoor temperature and the temperature of the water returning from the underfloor/radiators. The steeper the curve, the more heat it will generate at lower temperatures. There is also a “fine tune” setting which raises or lowers the heat curve (not adjusting the slope of the curve) to increase or decrease the target temperature. One other setting I tweaked was that of the domestic hot water temperature, which was initially set to 49°C. I lowered this to 47°C which was still perfectly acceptable for hot water but would squeeze a little bit more efficiency out of the system by not being required to maintain quite as high a temperature.
The installation has been problem free apart from one occasion during the first couple of weeks after installation where our new underfloor heating wasn’t reaching the desired temperature, and this turned out to be because the pressure in the unvented system had dropped. Once this was corrected we had no further problems like that.
It’s fair to say that the house, particularly in the old part with traditional radiators, was cooler than it had been previously during this initial running-in period but we eventually found the settings that worked for us under all conditions and we’ve not changed them since. In fact, that is one of the selling points of a system like this – once it is set up, you shouldn’t ever need to touch it again!
Maintenance
There is virtually no maintenance to be carried out on the GSHP and I believe this is true for the whole life of the system. You do have to check a couple of particle strainer filters a couple of times a year, one external to the heat pump unit on the ground loop circuit, and one internal to the unit. This is a straightforward task and should only take around 30 mins at most to complete.
Electricity consumption
So, we finally get onto our electricity consumption over the last year. Bearing in mind the house is now almost twice as big as it was previously with a larger space to heat and more appliances and lighting, I’m very happy to report that our electricity consumption has actually gone down over the last year by around 30%! I’ve got to say I am very pleasantly surprised by this and I had feared quite a few times that we would be using more electricity.
Our solar PV system will have had some impact on these figures due to the fact we will have used our own generated electricity some of the time rather than having to import it. But this is probably not a significant factor as the times when we were generating the most electricity were a few hours during sunny Spring and Summer days when the heat pump wasn’t on much. Looking at seasonable usage, I suspect the savings are largely down to the efficiency of the GSHP when compared with our previous system. I haven’t had chance to calculate the coefficient of performance (CoP) for our system yet but this is something I would like to do in the future.
Don’t get me wrong – we still use a lot of electricity, much more than a lot of households use I would imagine – but the important and re-assuring thing is that we are now using considerably less than we did before. And given that our only fuel is electricity, this bodes well for the future.
Savings and subsidies
Finally, I just wanted to say a little about the financial aspects of this system. In total, it probably cost us around £15K for the installation of the GSHP, which is quite a sizable up front investment, however this was offset slightly by a £1,250 installation grant under the Renewable Heat Premium Payment (RHPP) scheme operated by the UK Government. In addition to this, if all goes to plan, the new Renewable Heat Incentive (RHI) scheme should start in Summer 2013 which will provide an annual payment towards the cost of the installation, similar to the Feed-in-Tariff (FiT) scheme for Solar PV installations, over a proposed 7 year period (compared with the 20+ years for solar). This would more than cover the cost of installation of the GSHP system, and when combined with the solar FiT payments we are already receiving, will cover the cost of all of our energy usage over the next few years.
Another ground source heat pump update
So… we’ve been living with our IVT Greenline HT+ E11 11kW ground source heat pump for another week or so now and I happy to report that it’s still performing admirably.
The outside temperature is just below 0°C and the house is nice and warm, with the new part of the house with underfloor heating at around 20°C.
The glycol based heat transfer fluid which collects heat from the ground is currently entering the heat pump at 1.3°C and after heat has been extracted from it, it is being returned to the ground loop at -1.9°C.
We currently have the hot water temperature set to 48°C but I’m going to try lowering that to 47°C in an effort to squeeze a bit more efficiency out of the system for no noticeable impact.
I’m also watching the electricity meter and compressor operating times like a hawk but so far my gut feel is that we’re using less electricity than we were over a similar period of cold weather last year.
The heat pump throws a wobbler!
All has been well with my new ground source heat pump system since it was commissioned at the beginning of January although it has needed a fair bit of tweaking of controls to get everything working as desired. It’s taken me a couple of weeks to really understand how all the different settings work together to produce the end results, but I think I’m almost there with it now…
That was until the underfloor heating simply refused to get warm a couple of days ago!
The target temperature being shown by the heat pump for the underfloor circuit looked perfectly reasonable yet the actual temperature reading from the sensor next to the shunt / mixer valve controlling the underfloor supply was way too low. And it simply refused to get anywhere near the target temperature despite regardless of any settings changes I made. After previously thinking I’d got the heat pump operation and control completely sussed, this was a bit of a let down.
After speaking with the excellent technical support team at ICE Energy they decided it would be best if an engineer came out to check the shunt valve, so an appointment was booked.
Shortly afterwards I just happened to be looking over the heat pump installation and I noticed that the pressure gauge for the unvented system had dropped from the normal of around 2 bar to just over 0.25 bar. This wasn’t right so I corrected it and lo and behold, the temperature of the underfloor circuit started to rise!
I called ICE Energy back and explained what I had found and they told me that an air lock or low pressure would cause the symptoms I’d been experiencing, which was reassuring.
So fingers crossed, that little hiccup is fixed now. And, as equally important I am back to being confident I know how the system works again!
Our ground source heat pump is now alive!
After several months of research, product sourcing, price negotiation, grant and subsidy research, extensive groundworks and final installation, I am very pleased to announce that our ground source heat pump has now been commissioned and is up and running providing heating and domestic hot water for the whole house!
Commissioning
The process of commissioning the heat pump is quite lengthy and involves several steps including:
- checking the basic installation
- making final electrical connections to the heat pump
- filling the ground loop with the water/glycol heat transfer fluid
- test running the pump components
- setting initial heat pump controller settings
- heating the contents of the 300 litre hot water cylinder using the in-built immersion heaters to bring it close to working temperature
All of this was carried out by Ben, a very knowledgeable and competent engineer from ICE Energy and after all the steps were completed the heat pump was powered up and it got up to speed in no time at all.
Initial impressions
The first thing I was relieved to notice was that the heat pump is very quiet. As it is situated in the new enlarged hallway next to the new family room I was praying that it wouldn’t be too loud so as to be noticeable. I had previously been told that it would not sound any louder than a typical fridge but I was still slightly apprehensive given it’s position in the house. However I’m happy to say that it is absolutely fine from a noise perspective. Additionally, it will be enclosed in a purpose built cupboard with the potential for further internal soundproofing so noise will not be an issue.
The second thing I noticed was how quickly it got up to speed heating up both the new underfloor heating and existing radiators in next to no time.
One minor worry we’d had in our minds throughout the installation of this system was whether it would provide sufficient heat for the radiators in the existing part of the house (2/3 of the total house split over 2 floors). As the temperature of the water output from the heat pump is lower than that from other hot water boilers typically used with radiators, we’d been told that the radiators would never get as hot as previously, feeling only lukewarm to the touch. However, since the heat pump was switched on the radiators have felt no cooler than before which was quite a surprise!
The control system for the heat pump is very different to controls found on traditional heating systems, with numerous temperature sensors monitoring the outdoor and indoor temperatures, flow and return temperatures for the ground loop heat transfer fluid, radiators and underfloor heating and using these in combination with various heat curve settings in order to determine how much heat is required from the pump. The wealth of control settings is quite overwhelming but apparently once the system is established we should hardly, if ever, need to adjust these settings.
In conclusion
Overall, I’d say the house has been hotter than we expected since the heat pump took over from the old system, which is reassuring given our initial concerns about how it would cope with so many radiators.
Although the heat pump was configured with an initial range of settings I’m sure there will be lots of tweaking (in consultation with ICE Energy’s excellent technical support line) over the next few weeks until we get to a point where we are comfortable with everything.
More on the ground source heat pump ground loop installation
Following on from my previous post about the work starting on the installation of the ground loop for our ground source heat pump system, here are a few more timelapse videos of the groundworks.
Now that the work is almost complete, one comment I will make is that the scale of the work involved is much bigger than I had originally expected. I knew the numbers involved – 150m of trench in total, 1m wide by 1m deep, 60 tonnes of sand etc. – but until you actually see how much soil is moved and effort involved, you don’t appreciate the scale of it.
Having said that, the guys doing the work have been very efficient and the paddock is well on its way to being back to its state before, minus the grass of course which will have to be grown from seed again once the work is complete.
The ground source heat pump ground loop gets installed!
If you’ve read any of my previous posts, you’ll know that we’re installing a ground source heat pump as part of our barn conversion. Well, the installation of the ground loop collector pipes started in the last couple of days and I siezed the opportunity to shoot some short timelapse videos of the work being done.
The videos linked below show how the 50m x 1m x 1m trenches are dug and how the 200m of pipe loop in each trench is laid as 1m diameter coiled “slinkies” on a bed of 100mm sand. The videos are only short (they were shot with a 15 second interval between each timelapse frame) but are HD so make sure to select the 720p HD option on playback.
I’ve just bought a ground source heat pump!
As the title says, I’ve just entered the world of renewable energy and microgeneration technologies by buying a ground source heat pump – a longer blog post with all the details to follow…
