JohnMo

My final version of gas powered UFH, wasn't pure weather compensation as boiler just wouldn't modulate down far enough at low temperature and cycled too much to be efficient. So ran weather compensation at a fixed flow temp and a setback. Used a simple 0.1 hysterisis thermostat in the hall and let the system bounce of that a flow temp of 36, heating demand set back off and no heating demand setback on. This gave the boiler two running temps, 36 or 26, so in setback it never fired up. The 36 temperature allowed the boiler to run with no cycling. It started and stopped based on the thermostat. So a -9 day it ran for about 12 hrs, a 7 degree day a few hours. Efficiency was great. Generally running once per day.

May need it for radiators, but you just don't need to bother with low temperature UFH. Pretty easy really, solcast integrates into home assistant etc so you can get hourly forecasts. In shoulder seasons I actually ramp up day time heating to charge floor, on excess solar. Get good day time cop instead of night time cold temperatures. Heating just reverts back to WC mode when sun no longer generating enough. But floor generally full of energy to heat house as temperature drop. Completely the opposite of what we are being informed to do.

No stats anywhere other than, I believe bedrooms, but not even convinced they are in active control. My influence is flow temp via settings WC curve only. ASHP algorithm does everything else. Don't even have the ASHP controller in house; as that's built in to ASHP. The heat pump will modulate flow rate as it sees fit. Even have the UFH loop flow meters fully open to assist the heat pump looking after itself. Just designed the loops and rooms to match target temp at the same dT for every loop. Gas bills initially drove the changes, way higher than expected. Final leap to no thermostat was the electricity meter going smart with whole house battery and being able to run whole house on cheap rate electric 24/7/365, this drove me away from batch charging floor via a single thermostat, to pure weather compensation for heating and effectively a fixed flow temp for cooling.

Ask @JamesPa and others how the thermostatic valves he has in his retrofit system. Does he have issues running weather compensation - no. Think he has them in bedrooms only so he can run those rooms cooler than MCS design standards. So pretty much my favoured methodology.

Been there done that with UFH biggest disaster of all the options I tried and tested (Atag boiler). Floor timescale for change is just too long, great for radiators, utter rubbish with UFH (unless very screed and high flow temps used). The main reason I chose UFH, as opposed to radiators, where high flow temp means they do not self regulate. As this topic is about simple UFH, not sure radiators are relevant or room compensation. If your room is 23 (solar gains etc) and floor temp is 22, there is zero output to the room. A thermostat does nothing except close of flow routes available to the heat pump, generally not good. The floor stays charged up ready to release heat as room temp drops. There are obviously two views, but if I knew in 2020, what I know now, I wouldn't have a cupboard full of needless tatt, that I have removed from the heating system. Subject is simple UFH. Simple is no mixers, no more pumps than absolutely required. Open loop, no thermostats. Run a simple weather compensation curve. Have switch that allows cooling to be active if needed. ASHP will run only as required, set the logic so the circulation pumps are off during compressor off periods to get a great CoP. Plus a suitable system water capacity, to ensure decent run times. So about 30L to 40L of system water always engaged per min output kW of the heat source. The heat pump will modulate it's self, as gets closer to target flow temp, so you don't need outside influence to do that. If you don't do UFH, maybe you should explore further. Set it running it on weather compensation it looks after it's self come rain or shine. You don't need external control.

Been asking ChapGPT loads of ASHP related questions. One was related to the use of ball valve strainers (which I use) and proper inline filters (I had a Spirovent Dirt on the boiler, now sitting idle). The main comment was on pressure drop differences. Spirovent being almost zero even sized at 22mm compared to quite high on the ball valve strainer. The other question was heat pump run time, exploring UFH affects and water volumes. Short answer, as expected more water volume is better. System volume is circa 70 to 80L without volumiser. In cooling mode first run of the day was typically 12 to 14 mins, no longer. Have now installed an additional 50L water volume (around 130L total), used a cylinder that was used on the combi boiler as solar preheat for DHW. Not ideal in theory as it only has 22mm ports. The only place I could install due to layout issues was close the the ASHP. It is connected within the return piping as a volumiser. This means without mitigation the volumiser would get filled with DHW heating water - not ideal. So used a previously used ESBE Mixing valve as a diverter driven by the relay, I use on DHW signal filtering. Added the Spirovent filter while I was there. First run I left the strainer in place as well as the Spirovent, flow reduced from the 19.5L/min to 16L/min, which was worrying. However removing just the strainer from the ball valve flow jumped up to 22.5L/min. Ball valve strainers seem to be pretty rubbish and many get installed. So gained an extra 3L min flow while installing a 22mm volumiser and associated piping plus a 22mm 3 port valve. Run time after volumiser install is been dramatic. Normal first run of the day is 10 to 15 mins, today 42 mins. CoP has increased (like for like outside temp) a small amount 0.04, not big put running CoP was already high, so now achieving 6.53 this morning while running. dT has dropped from 4.4 to 3.8, so this allows me to reduce flow target temp a little and get the same heat transfer, which will reduce run time a little but gain CoP. Still need to complete the insulation, need some additional materials.

Sounds similar to ours, but without the split level. I just put in way less UFH pipes in bedrooms, as the design temp of the room was lower, which what we wanted, converse could be true also if you wanted bedrooms hotter, for strange reason. Just less heat added to room at same flow temperature; pretty much the same as you do for radiators.

Foil lined is basically a plastic covering. So use a paint suitable for plastic or a primer suitable and any suitable paint for the primer over it. I just bought some of this for painting some outside plastic, covers really well and great finish. No primer used. https://amzn.eu/d/jcqODve

That's the difference you get paid for it, so you better get it right first time. 😁 I used all the wisdom at the time 2020, when we installed our heating system, thermostats etc, f'ing waste of time and money. Caused more issues than they fixed (boiler short cycling, under and over swing of room temps), worked my way down to one thermostat, now have none, one switch from cool to heat, now we are on a heat pump. Plus a home assistant relay, which is used to soak up excess PV and charge floor at a great CoP - plus zero cost heating 30% of the time in the shoulder season. Sorry against what you think, thermostats are tat, used for high temp heating systems. Just aren't needed running weather compensation and low flow temps.

Doubt it. Your floor output just drops to zero as the it gets solar gain. On a 7 Deg day the floor surface is only going to because degree or so warmer than the room. Switching a loop off is a waste of time. The time frame to have any affect is way longer than than the solar gain lasts. Just run it all open loop on WC and leave the system to look after it's self. Now on year three with proportionally more glass. In late winter I was actually running the heating at a higher flow temp of excess PV, even though the house was warm. Then as it dropped to -3 overnight (back at WC flow temps) the heat pump actually switched itself off. Spread the pipes out further instead of all bunched up.

Images help, if you could add that would be great. Also does this steel post act as a thermal bridge?

So glad I built single storey - one or two levels of thought process deleted.

Not nice with chips, but pretty nice with ice-cream

Are you sure about that with an ASHP? You need to keep the return temp as low as possible for as long as possible to a get a decent CoP. You would kill CoP pretty quick. Can see an argument to push back in the centre the tank but not the bottom.

Had a gate made either ceder or larch. Anyway did yacht varnish. 18 months later lots had peeled off and plenty had gone black. Two days later had it scrapped off and used ceder oil, applied every two years after that and looked as good as new.

Just your local pie shop. We can get macaroni cheese pies here, there great. The chip shop even fries them!

Sorry once I finished building I was more interested in real pies of any description.

PHE work well due to the turbulent flow at the plates inside the exchanger. Using the change in density as the fluid heats may not/will not give the turbulent flow needed on the cylinder side especially at heat pump temperatures. So may be as good as useless. I would add a DHW suitable pump, and pump from bottom connector through PHE and into top outlet connection. The equivalent area of a PHE when compared to a 3m² cylinder coil is about 1 to 1.2m².

Are you sure, if you have a dMEV fan you don't need any other ventilation, you move from intermittent to continuous section in building regs.

Why? Ours has been there 3 years and looks as good as the day it went in. Will be pretty pissed if it only lasts 10 years.

Just seen this bit, sounds like an easy way to get a rotten deck - warm humid air pumped in

Why bother pushing the air outside? Carbon filter and one with decent grease filter, and do it as recirculating? No idea what your ventilation strategy is, if not MVHR, add a dMEV fan to kitchen and let it slowly tick away and auto boost on rising humidity.

To be frank if you don't know your airtightness and it's better than 3m³/m² at 50Pa I really wouldn't bother. I would do keep it simple dMEV in every wet room. No trickle vents in this rooms. I would choose Greenwood CV2 or CV3 only as these are silent in use and automatically boost intelligently -raising humidity. Either wall or window trickle vents in all dry rooms, but they should be humidity activated. This will sweep humidity from rooms in use only via ventilated only, minimising heat loss. Pennies a year to run no filters, no ducts to run etc.

Ultimately the floor output has to be considered when compared to the whole house demand, so for example. House 200m² and heat demand of 3kW would require the floor output to be 3000W / 200, or 15W per m², if the whole house had UFH, but as you are on 3 storeys of equal floor area (assumed) on each floor you now need 3x the output from ground floor UFH. So 45W per m². If on 200mm centres for the UFH loops that would be approx 40 degs flow temp on the coldest day and the UFH would provide heating for the whole house. 150mm centres would drip that be a couple of degrees.

Not sure who is leading you down that path? But it's nonsense. Your UFH system should be manifold, floor loops and that is pretty much it. All run in weather compensation on a fully open system, certainly no buffer. A volumiser may add running time when warm outside. No actuators or thermostats are needed. All heat pump will flow at 25 some at 20 in heating mode. The way UFH works is via dispersion of heat within the screed. The further it has the travel the more the temperature drops via radial conduction.