JohnMo

Your main bedroom I would do 40m³/h other bedrooms 20m³/h. That gives 80m³/h. I will get to lounge in a latter Extract, kitchen 48m³/h and bathroom 32m³/h. So fully balanced and not over ventillated. Lounge depends on your layout. Ideally you would've as through flow. That is excess air from upstairs (48m³/h) would flow through the lounge to the kitchen. For this to work you need a path from the stairway through lounge to kitchen. If that doesn't work because of layout, you need a supply in lounge and extra extract in bathroom and kitchen to balance flows. Boost set 20% above normal Have you undercut doors?

It's not quite what it seems. You have an external ASHP this is the first point of heat or cool, the other units add to this heat e

Sand is good, pretty much self compacting, if I needed to dig down below it, our borehole was 34m of pure sand. We are built on top of a sand dune that is now inland 8 miles. Don't waste your time or money on insulation, 100mm thick concrete slab, so it can take a car, even if you don't use for a car. Job done. Put a thermal top on or work harder.

You may end up with a system that moves in and out of balance depending on what the heat pump is doing. Plus the flow from MVHR is at an order magnitude lower than the heat pump, so will little or no impacts. Keep it simple don't overthink it.

I think you are looking at steady state, which is only one set of circumstances. The floor energy output is its area and floor surface to room dT. As the heat demand increases because it's colder outside, the only variable to output is floor to room dT. So floor temperature has to increase to compensate for additional heat losses. That is why weather compensation exists. On a set flow temperature I can charge the floor for 2 hours on a mild day and the house stays warm all day. On a very cold day heating runs all day. So you either need to change how long you add heat or flow temperature or both to compensate for different floor output required. Maintaining a set flow return dT will just give a fixed output which only meet one fixed output kW.

Started on our build route with passive style insulated raft in mind. But soon found no suppliers any where near me. Structural engineer scratching his head, big shipping costs, specialist contractor costs and accommodation not small. So then just went the route of a thermal bridge free conventional strip foundations. Had to do some thinking myself and feed this into the design, but all pretty straightforward. Advantages Bog standard stuff for our structural engineer. Standard stuff for local contractors, ease of construction. Everything available off the shelf Pretty cheap Disadvantages None, it has no thermal bridges, down, up or sideways.

This is what I did. Found out what the kitchen company sold (makes of appliances). Got a subscription to "Which", compared the makes and different models. Made my choice, based on what I thought was important to me and my wife. Buying by committee on a forum, just a waste of time and effort, your wife, husband or whatever will say yes or no, so they need to be involved in the process, with unbiased tested input (such as Which).

Question why are you adding a thin bit of insulation. Is this just causing issues and not resolving anything. If your sub floor squeaks fix the issue. The insulation isn't going to.

Bunch of info in here conventions-for-u-value-calculations.pdf You basically have two surface resistants, floor and void below floor to add in. Plus you need to include the P/A ratio into the calculation. Other than that, I think your trying to hard. Are you thinking this hard for you roof insulation? Which is no different. The only difference is UFH temperature is the mean flow temperature a roof is inside building temperature. Flow direction is either up or down.

That temperature is way to high, turn you mixer flow temp down.

You will soon find out if it's ok. Would monitor you gas consumption over the next couple of weeks to see what happens. Then there will not be a surprise bill in a month's time if it's running rubbish.

Number radiators or bedrooms is a bit meaningless less. For heating, heat demand, you need to do a heat loss calculation. But unless you have a wall missing any of the referenced boilers is fine. But for hot tap water you need to look at flow rates and boiler turn down for heating. This will give a good compromise. But with a 4 bed house, I would look elsewhere and you may be better with a storage combi. Similar size, better flow of DHW.

Thermostat or sensor on buffer is only used to stop and start ASHP. The house thermostat for heating starts and stops the circulation pump on the heating side. 2 port buffer - Heated water is always available for heating straight away. If flow either side is the same all water bypasses the buffer. Only if a zone closes does any excess water flow into and out of buffer. Acts to increase cycle time, more efficient than continuously mixing water in the buffer.

You definitely have flow because the hot pipes are hot and the flow shows flow. Reasons for being cooler It's been balanced to give the heat required - dT changed. Bigger dT than the other loops. Easy way to fix is open the flow slightly. But if rooms are up to temperature are just making problems?

Didn't look at your profile, now see you are in Hungary. Very different from the UK. Many different climates here. High external humidity drives a lot of defrosting also. If you are doing a buffer, 2 port would be my only choice. Set heat source to only manage buffer temperature. Heating system to only draw from buffer, via a second pump. Reversing for heat or cool, shown as a 3 port but same is true for a 2 port

You pay a person to generate. You can measure off the drawings calculate what you need, some will then add 10%, have loads of waste you pay for.

Just sounds complex. My on/off isn't really on/off, as far the boiler knows, it's weather compensation and setback weather compensation. There is always an outside temperature which the boiler controls against, but the temperature is basically fixed. On/off thermostat moving between the two set points of normal WC and setback. PDHW just interrupting the outside weather temperature.

I have a Polypipe UFH controller (rebranded Tech Controller/Roth controller) which is Opentherm and or on/off. My basic issue is the boiler is a combi, but I use it as a system boiler. The Opentherm knows it's a combi, so the control is tailored to the combi.

The on off thermostat and temperature ramping up is discussed here on page 5.Hints Tips & Fault Codes.pdf PDHW will work with any configuration for heating, so on/off thermostat, Opentherm controller (Atag controller for example) or load compensation (same as weather compensation but using inside temperature for reference) Another read h too big to upload https://www.google.com/url?sa=t&source=web&rct=j&opi=89978449&url=https://www.atagheating.co.uk/wp-content/themes/atag/hubfs/Appliance%20Technical%20Guide%20Pre%202019.pdf&ved=2ahUKEwi1xfGl4biLAxVkVEEAHQFyBAwQFnoECB8QAQ&usg=AOvVaw1gl0y29TTeKTIoqVVZ3xGC

Something isn't correct here. 2.5m³/h would indicate about 12kW heat pump, and that isn't a low energy 150m² house. Why all the complications of floor and ceiling and A2A heat pump? If you need dehumidification that is the role of ventilation, what is you ventilation system? Delete the need for a buffer. Do you need floor and ceiling heating and cooling and A2A? Do you need zones? The efficient design would be UFH (heat and cool) run as a single zone, or with fan coils in bedrooms for heat or cool (no UFH in bedrooms). Correctly sized heat pump, this would depend on proper heat loss calcs. It could be sized for batch charging floor or WC. No buffer No ceiling system

@SimonD Got the boiler running Opentherm and as you found getting the flow temperature wrong and you get plenty of cycling. In the end the Opentherm ran no different to my simulated weather compensation (resister instead of outside sensor). So just reverted back to on/off, this also gave me PDHW which didn't work on Opentherm. So now just operate at a fixed flow temp of 37.8, control via a resistor, WC is on setback when thermostat is satisfied (setback will never allow boiler to refire). To do PDHW, a relay switches resister out of circuit and the boiler ramps to about 56 degs. This was last night, wobbly bit up to 3am was the heat pump on at the same time, doing defrosting. The peak around 5.30 was cylinder heating. Charging a floor via UFH (no mixer, but boiler is behind a CCT). Basically runs once per day (if outside is below 5 degs for 6 hours) maybe twice if super cold.

Atag, great boilers. Return temp drives condensing. Most Atag boilers have modulating output and have modulation of circulation pump, so almost manages dT itself. They work very differently depends on running against a thermostat or weather compensation. On WC the flow temp is almost rock solid, on thermostat operation it will keep adding to flow temp approx 10 mins after starting and will go up to max temperature set in the controller Poor advice, flow temperature does not directly affect condensing, return temp only does. Avoid if you can. One big zone or two large ones are the way to go. The bigger volume the better, you also need good flow, so a nice open system give the boiler plenty of opportunities to move the heat and it be absorbed. With an Atag you just need the Atag controller, and TRVs on the radiators. Just keep everything simple

If your pretty airtight go that route otherwise... My view is dMEV done well or MEV. Both working conditional demand - CO2 and or humidity, with self actuating air inlets either through wall or trickle Video https://youtu.be/CGP_1rsOzDI?si=37tNvRjRVN1sBFNQ

@Stevenwithav Back to my first question?

Just giving information based on doing that and paying the huge bills while understood what was happening. Been there, got the tee shirt. Big zones good, small zones bad for the bank balance.