Preparing for 2nd winter in new build house.

sbm74 · 2025-09-19T07:39:51Z

Firstly, apologies for what is likely to be a long post. We have a complex setup that will take a bit of explanation. We completed our new build in Sussex almost a year ago and moved in at the end of November 2024. The house is brick and block construction and was still very much drying out when we moved in given the wet weather we had had all through the build and the traditional plastering method that was used internally. We have two separate mains power supplies entering the property: one supplies the power for the house and one EVCP and the other supplies the ASHP, some AC and another EVCP. We have solar PV and a Powerwall 2 on the house phase. This means that the ASHP does not benefit from any other power sources. The ASHP and UFH system was designed by Nu-Heat (we didn’t have a choice in this) and they have provided a room-by-room heat loss calculation. Most of the rooms have thermostats. Until I found this forum, we had 4 zones in the house: reception rooms, bathrooms, bedrooms and unused rooms. Having read some of the posts here, I’m reducing the number of zones. The ASHP phase is on the Cosy Octopus tariff, so we have to set back all zones during the expensive period in the afternoon. Currently the set back is significant enough to stop the ASHP coming on at all. As I mentioned, we don’t have any alternative power source on this phase, so it’s entirely dependent on the grid. I realise that such a large set back is likely to be adversely affecting the efficiency of the heat pumps. I’d be grateful for any advice from other users of this tariff. I’ve attached a photo of our heat curve. Firstly, it looks like the maximum supply temperature that’s been set by the installer is very high at 60°. I feel like I should reduce this. I’m also considering undertaking the task that is detailed on this forum of using the thermostats as limiters and just using the weather compensation curve on the heat pump. I’ll wait until the weather is colder. The Weather Control setting is currently off. There isn’t a lot of information about what this actually does, but it would seem that it checks the weather forecast and adapts its behaviour accordingly. I would be grateful if anyone has any knowledge of this feature and whether it’s worth enabling. If I believe the year-to-date data provided by the heat pumps, I have a SCOP of 4.24. I don’t know how accurate this is likely to be and we haven’t hit any cold weather since the spring. My main question is am I doing everything I can to make the system as efficient as possible? I am a bit of a tech geek, but this is the first time we’ve had a heat pump so I’m still learning. On the other hand, I don’t want to be completely obsessive over this (I have that tendency) so I’m not planning to constantly tweak. I just want to be sure it’s set up efficiently and then I can leave it alone. We are happy with the temperature in the house for the most part. Our bills were higher than we’d like last winter, but I know that is in part due to the house drying out. Thanks in advance for your help with this. Forum Handle: sbm74 Manufacturer: NIBE Model: 2x F2040-16 Type: ASHP Arrangement: Mono Area of Country: West Sussex Home Type: House Size: 650m2 Insulation Level: 2024 Cavity wall new-build Heat Loss Calculation: 22.1kW @ Amb. Temp, of: -3 °C Type of Controller: Room thermostats Type of Control: Room Temperature System Type: UFH throughout Total Output of Heat Emitters: kW Buffer Tank or Low Loss Header: BT 215 litre Secondary Pumps: 1 DHW return Solar PV System: 4.2kW on different phase Power Diverter: No Battery System: Tesla Powerwall 2 14kWh on different phase.

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Air Source Heat Pumps (ASHPs)

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sbm74

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Topic starter 19/09/2025 12:34 pm

The setting is on the room stats. That room has 2 loops. The ASHP is using weather compensation so the OAT would have to be around -15° before it got to 60°. According to the heat loss calcs the maximum flow temp should be 50°.

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