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ASHP in Hampshire

batalto · 2021-04-22T13:28:11Z

Hi all, Just wanted to talk you through our upcoming ASHP installation. We live on the south coast, just outside of Portsmouth. The house is a detached home of around 260m2 in footprint. The bottom floor was an extended bungalow and we added a second floor. The first floor is standard construction, brick cavity that's filled and double glazed. The upper floor is made of Structurally Insulated Panels (SIPs) with triple glazing. We had to use SIPs because they are lightweight and so wouldn't affect the shallow bungalow foundations. As an upside SIPS are also extremely efficient in retaining heat and have a very low U value, 0.18. The loft has 200mm of insulation in the middle beneath the floor and 400mm of insulation for everywhere else. We have 8.4kW of solar PV on the roof and 7kWh of battery storage (Pylontech batteries). We also have a Solic solar PV heat controller, which will dump excess solar power into the tank before we export. We've just had our EPC done and we scored very highly A (93) that also provided a heat demand of 34w/m2 which tallies with our ASHP assessment of 36w/m2. The ASHP is a 12kw Midea with a stated SCOP of 3.36 supplied and installed by J A Rees, sourced from Freedom Heat Pumps - total cost just under £10k. We will be replacing our current 32kW gas system boiler and hot water cylinder and using the green homes grant for £5k of the cost and I will paying the other £5k. We qualify for the highest RHI so would expect to get roughly £7200 back over the next 7 years. The boiler will be retained as a backup heating system and isolated from the ASHP system. We have been told this is fine with the RHI as its a backup and not hybrid. The heating is currently set to 45 degrees and we have had no problems. Our main living area has a large bifold door system and west facing. This means we have significant heat loss in the winter and for 2 months its very cold and this makes the room chilly, but not cold. All the other months the solar gain is significant, heating the room and the rest of the house. With the conventional boiler the room is chilly, so I am expecting issues in January heating up the room. We might need to come up with a plan for this room, possibly some thick curtains. The install will be next week and should be very straightforward. The ASHP will go on the drive next to the current power intake. The pipework will go straight through the wall into the current boiler room and tap into the current pipework. The tank will need replacement for one with a larger coil, but more or less everything else will remain the same. The aim is 2 days. Currently our gas is 2.5p and electricity is 14p and the current boiler is 58% efficient (according to the boiler) - this leads to a bill of around £1250 for both gas and electricity for the year. With the ASHP, boiler efficiency and assuming a worse SCOP of 2.7 on the current tariff we expect the bill to fall to just under £1,000 (34,000kw of gas to 7,000kw of electricity). This cost includes a standing charge for gas even though we wont be using it. My plan after we have got used to the ASHP is to upgrade the batteries and add 7kw extra, then move to a new tariff. Agile GO is very interesting as I could fill my batteries at night and expend them during the day. The batteries would store 11.4kw (14kW @ 80% Depth of Discharge). I have estimated this would further drop my bills down to £780

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Air Source Heat Pumps (ASHPs)

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Derek M

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10/11/2021 11:44 am

@batalto

The thermostat is set at 21.5 degrees and the house is being held at 21 and has been for over 24 hours.

Good morning Batalto,

Very useful data.

As a check, try increasing your thermostat setpoint to say 23C and see if the indoor temperature increases. If it does then your system is not fully operating on weather compensation.

You could try make the slope of your weather compensation shallower, by changing the left hand end to 50C @ -10C.

Don't change the slope immediately, increase the thermostat setting and wait several hours or more to see the effect.

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batalto

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Topic starter 10/11/2021 11:49 am

@kev-m actually I used LESS power. You can see from below the details of the days.

And of course as soon as I said it, I was wrong. My heating got the house to 21.5, so I've adjusted the weather curve down a tiny bit from 25@20, to 25@18. I'll wait to see the impact. Also yesterday I adjusted the hot water from 55 to 53 and that seems to be fine as well. Its not perfect as ambient is an average of the whole day - It could have been a cold night and a warm day and still average 13 vs 13 all day. However for my needs its close enough to be interesting.

12kW Midea ASHP - 8.4kw solar - 29kWh batteries
262m2 house in Hampshire
Current weather compensation: 47@-2 and 31@17
My current performance can be found - HERE
Heat pump calculator spreadsheet - HERE

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batalto

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Topic starter 10/11/2021 11:54 am

@derek-m It doesnt matter what I set the thermostat to. Originally I had it on 22, but moved it to 21.5 to prevent a boiling house if the experiment went totally wrong. So far my nest app says the heating was being called for "23.5 hours" yesterday. It is showing 21 steady in the house downstairs. I've left upstairs on normal thermostat as its so warm up there anyway its not really ever on. When it does come on, it warms up pretty quickly.

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batalto

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Topic starter 11/11/2021 12:03 am

Checked the filter today and it was pretty much totally clean - so I think the gunk is now cleaned out. The system is basically silent now as well, whereas before it made a high pitched noise in the main return pipe. I assume this was just a restricted flow issue.

House seems to be totally fine today, however the temps seem to creep up in the day. Now evening has come it's back to holding at 21. Not sure what to do as it seems to be a solar gain issue. However it wasn't a major issue as it was only 0.5° above target. A stated I've adjusted my curve a little bit. I'll be leaving it alone for the next few days and seeing the impact. However any tweaks will be around the edges.

Current setting 50°@-3° and 25°@18°

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batalto

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Topic starter 11/11/2021 12:39 pm

room temperature hit 21.5 again today, so trimmed the weather comp at the bottom end a little. Its not exactly sunny, so solar gain should be negligible today. Now the house is up to temperature it'll be interesting to see how it holds. slowly slowly dialling in. Just need a cold snap to see how we are really getting on

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Kev M

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11/11/2021 2:14 pm

@batalto,

we're a tiny bit cooler indoors today on the same flow temps. I think it's because it's damps and misty. Not enough to worry about though. Like you say, this is too easy, we need some proper winter weather.

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batalto

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Topic starter 12/11/2021 10:10 am

Ran through the night with a COP of 4.2 - Lost some heat downstairs though, the temperature dropped to 20. So I've adjusted my curve 1 degree upwards; 25 @ 17

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Derek M

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12/11/2021 10:17 am

Posted by: @batalto

Ran through the night with a COP of 4.2 - Lost some heat downstairs though, the temperature dropped to 20. So I've adjusted my curve 1 degree upwards; 25 @ 17

Good morning Batalto,

The wind speed was higher last night in our area, and I have noticed that it appears to have added about 5C to the required water flow temperature.

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batalto

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Topic starter 12/11/2021 10:28 am

@derek-m there is a bit of cycling on the system due to the super mild weather (ambient was 13 overnight). However its very wet today, so interesting to see how we get on. The house is well up to temperature now.

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Kev M

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12/11/2021 10:37 am

@batalto,

The overnight peaks are very similar to mine. What's the peak between 6 and 9? HW or the curve being moved?

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batalto

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Topic starter 12/11/2021 10:44 am

@kev-m It'll be a mix of hot water (for the showers), my wife's hair dryer, washing machine going on etc. This measures power in 5 min intervals, so its prone to being a bit spikey. You think 2/3kw for hot water being heated plus a 2kw hair drier and you're getting up there. Interestingly I am still running on battery, so my power is still 5p/kw

SOC = State of charge e.g. %