SBMS

I've tried to do a cooling calculation based on 30 degrees outside, 21 inside. I have more rooms but those won't be cooled. My absolute worst case peak cooling is around 21kW for the whole house (red columns). Appreciate this is unrealistic etc. I've looked around and a fair bit of wisdom indicates designing to around 75% of peak and I have done this (orange columns). This is around 16kW. This exceeds the heat pump, but then again 6kW of this is for the kitchen diner, which, when it is very hot, we are likely to have all doors open in any event, so any cooling in here is likely to be fairly pointless. This drops the design to around 10kW which a 12kW heat pump should be able to provide. In actual fact, the important rooms are master bedroom, living room, bedrooms 1 and 2 and the hallway, which only has a design cooling load of around 5kW. It has a peak load of around 9kW. I feel that an ASHP would deliver enough cooling for the house, but I do think that I'd need the FCUs on their own, cooler circuit - especially the cooling loads for the landing and halls which are driven by FCUs. Thoughts? Floor Room Orientation Floor Area (m2) UFH Available Area (m2) Cooled By Solid Ground Area - 0.10 (m2) External Wall Area - 0.15u (m2) Pitched Roof Area - 0.12u (m2) Flat Roof Area - 0.11u (m2) Window Area - 0.71u (m2) Door Area - 1.0u (m2) Velux Area - 1.0 u (m2) Rooflight Area - 0.6 u (m2) ACH Design Internal Temp Glazed Doors? Cooling Required G Value of Doors/Windows Heat Gain - External Wall (watts) Heat Gain - Pitched Roof (watts) Heat Gain - Flat Roof (watts) Heat Gain - Windows (watts) Heat Gain - Doors (watts) Heat Gain - Veluxes (watts) Heat Gain - Rooflights (watts) Heat Gain - Uncontrolled Infiltration (watts) Heat Gain - Internal (watts) Total Heat Gain (kW) Wall Gain (Design W) Pitched Roof Gain (Design W) Flat Roof Gain (Design W) Window Gain (Design W) Door Gain (Design W) Velux Gain (Design W) Rooflight Gain (Design W) Ventilation Gain (Design W) Internal Gain (Design W) Total Gain (Design kW) Ground Hallway* South 22.73 19.00 UFH 22.73 11.70 0.00 0.00 2.73 2.73 0.00 0.00 0.50 21 No Yes 0.346 15.80 0.00 0.00 755.66 0.00 0 0.00 8.223714 136.38 0.92 13.43 0.00 0.00 566.75 0.00 0.00 0.00 6.58 109.10 0.70 Ground Living Room* South 26.39 23.90 UFH 26.39 26.23 0.00 0.00 3.08 0.00 0.00 0.00 0.50 21 Yes 0.346 35.42 0.00 0.00 852.54 0.00 0 0.00 9.547902 263.90 1.16 30.10 0.00 0.00 639.41 0.00 0.00 0.00 7.64 211.12 0.89 Ground Gym* West 26.55 26.55 UFH 26.55 14.79 0.00 26.55 0.00 0.00 0.00 0.00 0.50 21 Yes 0.346 19.97 0.00 26.28 0.00 0.00 0 0.00 9.60579 318.60 0.37 16.98 0.00 22.34 0.00 0.00 0.00 0.00 7.68 254.88 0.30 Ground Open Plan Living* North and East 41.00 40.00 UFH 41.00 38.17 0.00 41.00 0.00 25.62 0.00 7.28 0.50 21 Yes Yes 0.504 51.53 0.00 40.59 0.00 6456.24 0 1310.40 14.8338 410.00 8.28 43.80 0.00 34.50 0.00 4842.18 0.00 982.80 11.87 328.00 6.24 Ground Kitchen* East 38.00 25.00 UFH 38.00 4.03 0.00 0.00 0.00 0.00 0.00 0.00 0.50 21 Yes 0.504 5.44 0.00 0.00 0.00 0.00 0 0.00 13.7484 380.00 0.40 4.62 0.00 0.00 0.00 0.00 0.00 0.00 11.00 304.00 0.32 Ground Utility/Boot Room East 12.00 6.60 UFH 12.00 20.88 0.00 0.00 0.00 1.89 0.00 0.00 0.50 21 Yes Yes 0.346 28.19 0.00 0.00 0.00 392.36 0 0.00 4.3416 72.00 0.50 23.96 0.00 0.00 0.00 294.27 0.00 0.00 3.47 57.60 0.38 Ground Snug/Playroom* East 14.39 12.70 UFH 14.39 7.93 0.00 0.00 0.00 3.15 0.00 0.00 0.50 21 Yes Yes 0.346 10.71 0.00 0.00 0.00 653.94 0 0.00 5.206302 86.34 0.76 9.10 0.00 0.00 0.00 490.46 0.00 0.00 4.17 69.07 0.57 Ground Study* South and East 10.90 9.90 UFH 10.90 19.66 0.00 0.00 1.43 3.15 0.00 0.00 0.50 21 Yes Yes 0.346 26.54 0.00 0.00 247.39 544.95 0 0.00 3.94362 65.40 0.89 22.56 0.00 0.00 185.54 408.71 0.00 0.00 3.15 52.32 0.67 First Floor First Floor Gallery Landing* South 28.00 FCU 0.00 11.70 0.00 0.00 6.70 0.00 0.00 0.00 0.50 21 Yes 0.346 15.80 0.00 0.00 1854.56 0.00 0 0.00 9.7083 168.00 2.05 13.43 0.00 0.00 1390.92 0.00 0.00 0.00 7.77 134.40 1.55 First Floor Bedroom 2* 21.00 FCU 0.00 26.49 0.00 0.00 5.23 0.00 0.00 0.00 0.50 21 Yes 0.346 35.77 0.00 0.00 905.48 0.00 0 0.00 7.281225 105.00 1.05 30.40 0.00 0.00 679.11 0.00 0.00 0.00 5.82 84.00 0.80 First Floor Bedroom 1* North and West 20.00 FCU 0.00 27.04 0.00 0.00 5.36 0.00 0.00 0.00 0.50 21 Yes 0.346 36.50 0.00 0.00 927.97 0.00 0 0.00 6.9345 100.00 1.07 31.03 0.00 0.00 695.98 0.00 0.00 0.00 5.55 80.00 0.81 First Floor Master Bedroom (incl gable)* North 23.20 FCU 0.00 39.44 24.00 0.00 8.90 0.00 0.00 0.00 0.50 21 Yes 0.504 53.24 25.92 0.00 1121.40 0.00 0 0.00 8.04402 116.00 1.32 45.25 22.03 0.00 841.05 0.00 0.00 0.00 6.44 92.80 1.01 First Floor W/W* South 9.68 None 0.00 12.35 0.00 0.00 1.43 0.00 0.00 0.00 0.50 21 Yes 0.346 16.67 0.00 0.00 395.82 0.00 0 0.00 3.356298 58.08 0.47 14.17 0.00 0.00 296.87 0.00 0.00 0.00 2.69 46.46 0.36 Second Floor Second Floor Gallery Landing* South 25.40 FCU 0.00 9.90 39.67 0.00 0.00 0.00 2.14 0.00 0.50 21 Yes 0.346 13.37 42.84 0.00 0.00 0.00 471.68 0.00 8.806815 152.40 0.69 11.36 36.41 0.00 0.00 0.00 353.76 0.00 7.05 121.92 0.53 Second Floor Bedroom 4* 40.00 FCU 0.00 29.39 62.47 0.00 0.00 0.00 4.02 0.00 0.50 21 Yes 0.346 39.67 67.47 0.00 0.00 0.00 884.4 0.00 13.869 200.00 1.21 33.72 57.35 0.00 0.00 0.00 663.30 0.00 11.10 160.00 0.93 Second Floor Bedroom 5* 31.45 FCU 0.00 17.51 58.00 0.00 0.00 0.00 2.63 0.00 0.50 21 Yes 0.346 23.64 62.64 0.00 0.00 0.00 577.808 0.00 10.9045 157.25 0.83 20.09 53.24 0.00 0.00 0.00 433.36 0.00 8.72 125.80 0.64

Thanks Nick - that post was from 2022 and our current build - we're going again, so different house.

What did you do in the end? Separate ac units?

Yes it’s large around 480sqm internal space (rooms in roof). To be fair they’ve calculated a higher heat load using their standard MCS calculator of around 10kw. Heatpunk calculated 9.8kw. I will work it with them, would rather not switch and they’re a good outfit and we used them on last build. any advice on calculating an average cooling demand?

Worth saying that these are just the output capacity of the fan coils not the cooling/heating demand for the room.

We touched on this before on another thread where I got ripped apart as my cooling load was enormous as I had done it on a worst case basis which I think you’d said wasn’t realistic. Heat loss is around 7kW (it’s a big house). Installer is sizing for an 12kW arotherm I think - and that’s probably sensible with DHW and a bit of headroom. Will probably need it this large for cooling. I’m going to do some more work on this cooling demand and try and get an average cooling load demand - I have a heat loss calculation which is fine but must admit am struggling to model the average heat gain on the worst day. Any hints on how to easily model this?

Thanks - does The heat pump need to be aware of multiple circuits or is this done via manifolds and blending etc?

Still getting my head around all this so be kind..! As I understand it, I’m pushing cool water round the system. My thinking is to have UFH downstairs and then around 7 fan coil radiators in bedrooms and landing spaces. I will lag all pipes to the FCUs (possibly prelagged piping). Don’t know size had assumed 15mm (standard?). I can have a single circuit when cooling but the temperature of the water in that circuit is going to be dictated by the UFH and danger of dew/condensation so consensus seems to be to run that at 15 degrees. If I had one single circuit my FCUs would also receive 15 which inhibits their cooling capacity a fair amount. I think that some heat pumps (we are probably going for an aroTherm) support cooling two circuits. The first circuit would do the UFH at 15 and the second would do the FCUs at 10 degrees. I assuming the ASHP would be producing 10 degree water and it would be blended to warm it for the UFH circuit. All of the above is my assumption and about the limit of my understanding without yet speaking to the installer.

I’m at the stage of specifying the system and I’d need to decide whether to run two circuits or not, at this stage? The fan coil units I am looking at output 1.6kw cooling for example with an input temp of 10 degrees. If I run these at 15 or 16 I assume that output will drop something like 20%? Hence wondering if I should run two circuits

If lagging pipes why not run fan coils at a lower temperature, and ignore dew point?

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?