SBMS

Is it necessary to get a heat pump that can run two independent circuits when doing cooling? One for UFH and one for fancoils - to run at different temperatures? If so, are there any downsides to this setup when it comes to heating?

One challenge is the builder often takes you to a 'satisfied' customer. That customer might have been totally hands off, not inspected work, and have no clue as to what issues are lurking in the building fabric...

Does it need a vapour barrier as well?

That looks good thanks, just realised I have been looking at the exterior stuff which is why it was 2-3x as expensive!

Considering fan coil units in bedrooms for cooling via ASHP (instead of a2a system). appreciate that many don’t run below dew point and don’t worry about insulated pipework. I’m a bit belt and braces so want pipework insulated. Is standard pipe lagging sufficient, or is a specialist product needed or something very expensive like the pre insulated pipework like ecoflex? I read that a vapour barrier is very important which I’m guessing standard pipe lagging doesn’t provide?

We discounted a2a for heating after a couple of AC contractors said that they wouldn’t have it for heating over UFH as it just isn’t as nice. I was planning on UFH downstairs and AC upstairs for cooling and supplementary heating but am now thinking more of fan coils and using the heat pump for cooling…

Rick - would strongly advise against this position and sending a letter like this. At this stage your builder is possibly preparing themselves for legal proceedings. In this instance you are absolutely advised to commit as little as possible to written (or even verbal form). I would advise that you don’t continue with this contractor under any circumstances - and get yourself in a headspace where you’ve accepted you need to find someone else. reading your contract you can’t unilaterally terminate the contract as there is the provision for remediation. My first course would be to request a without prejudice conversation with your builder. Within this conversation (have a third party present such as your SE, architect or a friend) set out that from your point of view the trust and relationship has degraded to a point of no return and you do not under any circumstances want the builder to continue. Explain that if that isn’t agreeable you will exercise clause 37 and at the builders Cost they will be required to replace all posi rafters and fit them to the satisfaction of your SE. State that Pasquill have advised they are likely not recoverable. This is an expensive exercise for the builder. Others may suggest you try and get them to cover the cost of doing the job right. Personally I wouldn’t trust them anywhere near my site. I would seek a negotiated exit and write off getting any money back. Alternatively, if the builder doesn’t agree I would advise you exercise clause 37 immediately. I doubt that they will remediate within 14 days but if you don’t follow the provisions of your contract your builder can pursue you. I would advise a letter that is entirely factual, unemotional and succinct if you need to serve a breach notice. I can help draft one if you need. Accept your relationship with your builder is over.

Agreed! But thought I’d contribute the actual law which is that any letting out (and your neighbours for example decided to let someone at council know!) would trigger the CIL. But like @nod says if no one knows then it’d be unlikely anyone would enforce. Just go into it eyes wide open and accept the risk 👍

Yes, letting your house out for any period of time is explicitly listed as a disqualifying event in the legislation: the letting out of a whole dwelling or building that is self-build housing or self-build communal development; see https://www.gov.uk/guidance/community-infrastructure-levy?#para094

I’d want to make sure they’ve got the dpm continuity right. Our DPM is turned up the inner face of the blockwork and lapped over the DPC, how do they do this if pouring the slab first? I suppose they could leave it long and then integrate it into the inner block after? in any event I’d check with your BC first.

This looks like a good product. Looks good for sealing round windows too?

I am I was responding to the OP!!

Or use a posi rafter roof. Best of both worlds - manufactured off site, can be arbitrarily deep (ours are 304mm) and span from ridge to wall plate:

We are using pro clima intello plus.

We are looking at triple glazing options. Front of house has a fair amount of south facing glazing and there is a glass option that has a g value of 0.43 (43% solar energy let through) and lets 63% of light through (VLT). We will likely go for this for the front elevation. At the moment there is little cost difference to doing the rear as well. The alternative is a triple glazing with 0.61 g value (61% solar energy let through) and lets 73% of light through. This is a 0.6 Ug value whereas the other glazing is 0.5Ug. Will a 63% VLT be noticeably darker?

Yes agreed. I think MCS lets you discount rooms heated by other sources in heat pump design (MCs 3005). But I think you’re right that BUS requires 100% heat from heat pump. There’s a weird cross over I think that is unclear as to whether MCS when designed for BUS requires it and that’s probably an installer interpretation. Still on the fence about cooling with ASHP and sticking fancoils upstairs and ditching the AC.

It’s actually relevant for us as some rooms we may put AC in so wouldn’t be heated by heat pump.

I guess as long as it is sized to heat it doesn’t actually have to deliver heat to that room to be eligible for the grant though?

How come? Are you not allowed this?

We are using 22mm steico universal boards with pro clima solitex plus.

What size outdoor unit do you have @Thorfun?

Good point. It made a mistake and I’ve time shifted it now. But it does still make me think… it’s pretty hard to model correctly the cooling load.

Thanks @JohnMo I didn’t realise it was that automated. That’s interesting. I got chat gpt to model my cooling requirements during summer and it spat out this graph taking in my heat loss and cooling data along with this description of how it generated it. It still has a peak of around 13.4kW. 🔍 The whole-house 24-hour cooling load profile I plotted is not based on full peak (worst-case) loads Instead, it is based on: A synthetic sinusoidal profile interpolated between average and peak cooling loads – using column W (Average Load) as the baseline – and column AD (Peak Load) as the afternoon high 📈 What does that mean? At 4:00 AM, each room is assumed to demand only its average load (e.g., from internal gains or mild solar). By 15:00, each room is assumed to hit its peak load (from full solar and ventilation gains). The curve is room-by-room, then summed.

So if you switch the pump into cool mode but then the DHW falls for heat it reverts back to heat mode (and then back again to cool mode when water is heated)?

Do the units natively support switching from heat to cooling or is it work to ‘put the heat pump in cooling mode’? by my estimation it’d be around 4k for the fan coil units needed for cooling with ASHP versus significantly more (10k+) for a2a system.