Our air source heat pump efficiency and performance

by Mars

We’ve covered the reasons why we chose an air source heat pump to heat our property and what the installation entailed. Today, we delve into the all-important subject of our air source heat pump efficiency and performance, sharing some tips that we’ve learnt along the way.

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Luffy 1 December 2020 - 14:58

Thanks both. I’ve sent the link onto Hugh to watch. Ours is a new build and will be as airtight as we can make it, but it’s still interesting to hear of your experiences in terms of efficiency leaving it on 24 x7 and keeping all rooms at the same temperature.

Mars 2 December 2020 - 09:18

Given that you’re building from scratch, I’m sure your property will be really well insulated and your system will be really efficient. Looking forward to hearing about your ASHP installation when the time comes.

Luffy 1 December 2020 - 17:17

Hugh said:

You mentioned that, when the radiators came on in one of your rooms, the radiators in the other rooms struggled. Not sure whether you know this, but old timer plumbers used to tune the radiators around the house using their second valve. They turned down the second valve in the radiators closer to the boiler, to make sure that all the radiators got their fair share of the hot water.
I have noticed that some younger plumbers either don’t know this or don’t care, because most houses are smaller and most boilers are more powerful.
Apologies if you already know this.

Mars 2 December 2020 - 09:24

Thanks for the feedback and for Hugh’s comments. I had read about turning down (partially closing) the second/exit valves on rads, and this is something I tried last winter, very unsuccessfully. I may just revisit that again this week because I have a slightly better understanding of our internal piping now. We only have one room that doesn’t come to temperature consistently (TV room), and I’m thinking of partially closing exit valves in a portion of the house that we don’t use very regularly, but that’s very warm.

Mars 3 December 2020 - 08:54

I have a quick (and silly) question for Hugh. For the exit (second valve that doesn’t have the TRV) which way do I turn them to partially close them. Is the premise still righty-tightly to close them, and left to fully open them?

Luffy 3 December 2020 - 15:35

Hugh says– Yep. They are conventional valves. Clockwise to close, anticlockwise to open

Mars 3 December 2020 - 15:45

Awesome. Thank you.

Luffy 3 December 2020 - 15:36

He also said that it’s best to expect the unexpected when it comes to your previous owners DIY!

Mars 3 December 2020 - 15:47

With the previous owner’s DIY skills all we expect is drama (and 9 out of 10 times we’re right). Fingers crossed.

Mark Crooks 2 December 2020 - 07:25

It’s nice to see the cat decided to contribute at the end!

Interestingly with one supplier who gave me a quote for a 14kW ASHP system, I asked them to supply me with reports for running the system at 21º and 22º. Like you we have chillophobia!

They both came back with exactly the same power usage.

Although they thought the calculations were correct perhaps it’s more likely that the software used to generate the reports is pre set to use 21º as a temp.

Is it possible for you to calculate the percentage of power that is used by the ASHP that comes from the solar panels?

Mars 2 December 2020 - 09:33

Yes, Olive decided to wake up as we were wrapping up – just in time for biscuits.

Very interesting about the power usage. We had our pump serviced yesterday, and I was able to get some good tips and insights from the engineer which I’m going to share either the blog or YouTube.

For the last question, the ASHP/solar calculation is not possible to work out for us, because we can’t see where the solar electricity goes – it will satisfy overall demand, so we don’t know if it pushes to the fridge, TV or ASHP – as a guess, during autumn and winter, 95% will be pushed to the ASHP as it runs 24/7. Come to think of it, that’s not overly important in the greater scheme of things, because the solar is utilised to reduce our electricity bill and overall consumption.

Feed-in-Tariff payments and changing electricity provider » My Home Farm 10 December 2020 - 13:22

[…] consume in excess of 15,000 kWh of electricity per year (mainly due to our air source heat pump) so it’s imperative that we are always on the best possible tariff. This means that once a year […]

Jennifer Ross 23 December 2020 - 14:16

Great videos thank you. We live in a rural area in Scotland and are off the gas grid. When we bought our 3 bed detached property 4 years ago we were led by our hearts rather than our heads. We have an electric wet heating system and a separate hot water system (which is effectively an immersion heater). We do not have underfloor heating. We installed a wood burning stove in the living room so we have one warm room throughout the winter – at least when the fire is lit!
Generally we live in a cold house with one warm room. The hall temperature is usually around 14 degrees. With heating on for two hours a day during the winter months (Nov-March) our electricity consumption is c. 11,000 KwH annually. In the winter our smart meter shows up to £10 a day electricity cost with hot water constantly being boosted so that we can have a bath or hot shower and the heating on for 2 hours a day. We don’t go out to work so we end up wearing lots of layers to stay warm.
One year after moving here the Scottish Power power head exploded (literally) and we nearly had a major fire. This was caused by a massive overload on the entire electrical system – as a result of the new system which had been put in by the previous owners and which was legally unsafe. Since then we have limped along on half of each system (hot water and heating). We honestly don’t believe that we could any system worse than the one we have. Almost anything must be better! Hence our interest in an ASHP. Its been very helpful to listen to your experience and to hear your discussion. The main issue for us is around insulation. Our house was built in 1990 but it was economised on and we don’t know whether it has cavity wall insulation. The roof space is well insulated but there are dormer windows and velux windows upstairs and we think the insulation there is very poor. With the heating being on for such a short length of time everything gets cold – the walls the floors etc.
Given what I say above, how big an issue is insulation? Is it worth us thinking about ASHP at all? Sorry – you probably can’t answer that question but any thoughts would be gratefully received.

Mars 28 December 2020 - 10:06

Thank you for your comments and feedback Jennifer.

As an initial comment, the 11,000kWh you’re consuming is high. By comparison, we’re doing about 15,000kWh annually (the bulk of which is consumed by the ASHP which runs 24/7 over winter).

On the subject of insulation, it’s been very important for us. We see significant improvements in efficiency when we spend time getting rid of drafts. Wall insulation will definitely help, but more importantly do you have double glazing and do you have any notable drafts. Is the house reasonably airtight? It’s probably not surprising the walls are cold if the heating is coming on for two hours a day.

If you satisfy enough of the criteria above, the ASHP should work for you. If anything, you won’t be adding a huge amount to your existing annual consumption (which means running cost wise you’ll be similar) but the house will be warmer than it is now, especially if you run the pump 24/7.

Based on what you said, I don’t think it would hurt to get one or two installers to come out and have a look, because the ASHP could potentially work for you.

Jennifer Ross 28 December 2020 - 16:23

Many thanks for your quick response Mars. The high consumption is the result of the installation of two electric Amptec boilers (which feed the radiators with hot water) and a megaflo boiler which provides hot water to the rest of the house. The Amptec operates like an electric shower. It is a hugely inefficient way of heating a house as two hours of heating is similar to running an electric shower for two hours. We do have double glazing but much of it now needs replacing. It’s okay but could be better. Even where we have replaced it the rooms lose heat quickly – but then they are never very warm to begin with. We don’t have any noticeable drafts and we have double doors at front and back. I understand about the need to increase insulation and we have done our best. Perhaps underfloor insulation would also help.
On another note it seems odd, given the government’s ban on gas boilers in new houses after 2025, that there is not more innovation in the sector of electric house heating. Unless developers start to actually properly insulate houses people are going to find their heating costs rocketing. Or is there something I’m missing here!?

Wout Mertens 6 March 2021 - 13:38

Some tips:
– To check if you have wall cavity insulation, simply drill a hole somewhere inconspicuous and check with a flashlight. Just fill the hole afterwards, or leave it for if you’ll let someone fill it up. Ideally you’d have 5cm or more of airgap with few mortar bridges between the inner and outer wall.
– You can buy an endoscope for 10-15$ from China, this just plugs into your Android phone or computer and you can inspect the walls better. Very handy https://www.aliexpress.com/wholesale?SearchText=endoscope+camera+usb+c
– For about 100EUR you can get a Shelly 3EM power monitor, which will give you realtime per-phase and total kW consuption, which helped me discover some problematic devices. It earned its price back the first week in my case (which is of course both sad and great) https://shelly.cloud/products/shelly-3em-smart-home-automation-energy-meter/
– I’m very much considering a thermal camera like the HT-102 which is pretty low resolution but should still help find cold spots due to gaps or insulation issues.
– Consider using local water heaters next to the shower etc so that you only heat the water you use
– Air-to-air heatpumps are more efficient, you can also get mobile models fairly cheaply to test the waters, but make sure the incoming and outgoing air don’t mix

Air Source Heat Pump Performance for 2020 » My Home Farm 1 January 2021 - 21:52

[…] recently spoke about the general performance and efficiency of our air source heat pump (ASHP), but with 2020 behind us, we have a full year of data that we […]


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