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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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Kev M

(@kev-m)

Noble Member Member

Joined: 6 years ago

Posts: 1276

06/11/2021 8:19 am

@batalto, your latest weather comp settings sound about the same as ours now and I'm thinking of knocking it down a bit. I agree about the water; I'm all for saving a few quid but not at the expense of comfort. We have electric showers for now so not an issue for us.

Hopefully you'll stay warm with the latest adjustments.

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batalto

(@batalto)

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Joined: 5 years ago

Posts: 1092

Topic starter 06/11/2021 8:24 am

@kev-m we'll see. I'll note that last night we used 11kw and delivered 42 in heat - COP 3.88. and the night is the coldest time...

Yesterday as a whole we used 36kw and delivered 110kw in heat - COP 3.05

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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Kev M

(@kev-m)

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Joined: 6 years ago

Posts: 1276

06/11/2021 8:43 am

@batalto, my corresponding numbers are 30.6 and 4.6. I turn the room temps down during the day and through the night (something I'm going to experiment with). My delivered energy has stopped recording so I don't know COP.

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batalto

(@batalto)

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Joined: 5 years ago

Posts: 1092

Topic starter 06/11/2021 9:36 am

@kev-m I'm confused, what are those numbers then?

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Kev M

(@kev-m)

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Joined: 6 years ago

Posts: 1276

06/11/2021 10:05 am

Posted by: @batalto

@kev-m I'm confused, what are those numbers then?

30.6 kWh used yesterday 5/11/21 and 4.6 kWh used from midnight to now.

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batalto

(@batalto)

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Joined: 5 years ago

Posts: 1092

Topic starter 06/11/2021 10:09 am

@kev-m ah ok. That makes sense now

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batalto

(@batalto)

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Joined: 5 years ago

Posts: 1092

Topic starter 06/11/2021 8:53 pm

Some feedback for everyone in two charts. As a note, I've created my own measure of efficiency beyond COP. At the moment its called COP-A (or COP per degree ambient). I'll explain my reasoning below.

This graph shows the impact of radiator balancing and weather compensation adjustment down. I started looking at the balance on the 2nd of November, which you can see coincides with a big drop in COP as we had a cold night. On the 3rd I adjusted them further and reduced my weather comp to 55 degrees at -2 and 33 at 16 degrees. You can see the COP easing upwards. However I find the graph very clunky to draw any conclusions.

The solution (in my view) is to link ambient temperature and COP; as these are the two most critical to performance. What I've done is take the COP and divide it by the ambient temperature. This gives me COP per degree ambient. The lower the number, the worse the performance of your system.

As you can see, there is a much clearer outcome from this. Even with a falling ambient (or rising) you can see how efficient your system really is. If you maintain your COP but your ambient drops your COP-A has risen. I have no idea how this metric might perform over time, but at least it delivers an insight beyond COP.

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Kev M

(@kev-m)

Noble Member Member

Joined: 6 years ago

Posts: 1276

07/11/2021 8:36 am

@batalto, not sure I understand. Are you using degrees Celcius? I see what you're trying to do but what happens when ambient temp gets to, or close to, or lower than, zero?

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(@heacol)

Prominent Member Contributor

Joined: 5 years ago

Posts: 415

07/11/2021 10:05 am

@batalto Nice indication of the implacations of flow temperature, try to drop your curve even further and disable all you other levels of control by turning them up fill (except your bedrooms). Control your internal temperature by adjusting the curve. You will find a huge differance and when you find the sweetspot for your house you wil need no furter control.

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batalto

(@batalto)

Noble Member Member

Joined: 5 years ago

Posts: 1092

Topic starter 07/11/2021 10:30 am

@kev-m that's an issue to cross when I get there lol. But it's more about trying to take cop out of the theoretical and ground it in reality so you can compare day to day. If today is warmer you can easily compare using this factor

👍

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batalto

(@batalto)

Noble Member Member

Joined: 5 years ago

Posts: 1092

Topic starter 07/11/2021 8:41 pm

Another day, another filter clean. Barely anything in there today

👍

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batalto

(@batalto)

Noble Member Member

Joined: 5 years ago

Posts: 1092

Topic starter 08/11/2021 10:16 am

Curve adjusted down again last night - we are now at;

Max: 50 @ -4 degrees

Min: 25 @ 15 degrees

I might leave these alone now and track for the next week. I've made quite a few changes recently and I need to see the impacts

👍

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