Yes, the "zoning with ASHP" topic again...

ccap · 2025-04-27T08:39:33Z

I know this general issue has been much discussed on this forum and various YouTube channels. However, as I am currently having a ASHP system designed I'm struggling to come to a decision on a few specifics. House is being completely renovated and will be up to current insulation standards or close enough throughout. Adding extra living space in a newly constructed roof so house will be 3 storey. Most of the house is basically in a box with the roof on top, so it's quite efficient in terms of heating, with heat rising up from ground to first then to second floor. Heat loss is approx 11kw so looking at either a Vaillant Arotherm 12kw or a equivalent Viessman model. We'll have UFH on the ground floor, bathrooms and landing with UFH on first floor, then rads for first floor bedrooms and all of second/attic floor all with standard TRVs (I think). I want to have it mostly open loop but with the option of increasing temps in some of the bedrooms as and when required. The kids will be in the attic rooms so when they are sleeping or out at school 19 degrees 24/7 will be fine, but at weekends or during school holidays they are likely to spend a lot more time in their rooms and we'll want 21 degrees. However, for the master bedroom and spare bedroom a constant 19 degrees will probably be fine as nobody is in there during the day. Although it would be nice to have our bedroom a bit warmer for an hour or so in the morning. To complicate things further, we will have an Aga running 24/7 in the kitchen during winter (an older Econ7 storage heater model that heats bricks up at night on cheap electricity) plus two multi-fuel burners, one in the kitchen/dining room, one in the lounge. I have a Heat Geek (HG) working on the system design. I agree with him that we should run this system as open loop as possible, with no buffer and no need for a volumizer due to the system volume we have already. HG is suggesting we control only by weather compensation, and there is no thermostat or control in the house whatsoever. This is where I'm starting to struggle a bit! My issues/questions: If the system runs on weather compensation only I know I can change the curve and make things run comfortably for most of the time. However, what happens on a winter's day when there are 8 or 10 guests (plus the four of us) in the house, ovens all on cooking a big dinner, sun shining in through the various south facing Velux windows and patio doors, and a log burner going? HG has suggested simply opening windows and yes, this is a simple solution. But it seems silly to be wasting heat when the whole point of doing the system design is to be as economical as possible. I know I can go to the UFH manifold and turn down specific UFH pipe runs and this will likely be done for the kitchen area where the Aga will be on all the time. But I don't want to have to go to the manifold and start messing with valves every time the sun comes out! From what I can gather regarding the controls for the ASHPs we're looking at, you can program a heating schedule. If there is no internal thermostat what are you actually programming?? Simply ON/OFF times? With my previous more traditional heating systems I am used to programming different temps at different times of the day, so cooler at night and warmer when you wake up and in the day. If there is no internal thermostat whatsoever then this is not possible is it?? If we want more control over the bedrooms on the top floor is there a smart thermostat system out there that we can use to adjust the temps and have timers and/or boost function? Ideally a wall thermostat on the landing between the two rooms that will gradually open/close the TRVs in the rooms rather than simple ON/OFF. I suspect that with this being the top floor, a lot of the heat will come from downstairs anyway, so we could regularly be in a situation where the top floor is warm enough while heat is required on the ground floor. OR a thermostat/controller that controls the whole pipe loop to those radiator. If we have the whole downstairs and some of the middle floor running as open loop, what happens if we have one or both log burners running? Ideally the UFH would reduce during these times and concentrate heating to the other areas of the house. Opening windows to let the excess heat out seems like a strange way to do things! Do the manufacturer supplied controllers for either the Vaillant or the Viessman allow you to combine control from both an internal main thermostat AND a weather compensation control? Weather compensation is the primary control but if internal temp gets to certain point then it can modulate down the ASHP. And/Or the whole system just runs a degree or two warmer/cooler at certain times of the day. Is there really any problem with having several zones in the house that you run "open" and together the vast majority of the time, but only control individually for specific reasons? I know any "solutions" could marginally reduce COP but there...

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Mars

(@editor)

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30/04/2025 9:44 pm

@ccap as an aside, I think you pose some interesting questions and I will put it before the panel on this week's podcast recording.

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