JohnMo

A thing I forgot to mention With a mixed radiator and UFH, the flow coming out of the UFH (cool) will dominate how the heat pump runs, until the floor temp stabilises.

The basics on how a heat pump works. It will start and basically ramp up to full load. It will first try and get it's running delta T (difference between flow and return temperature) to within a defined pont controlled by the controller. It then only as Delta T reduces add more heat to the flow temperature. With UFH this can take hours. I would set all thermostats to 22, and let the system stabilise. Leave a couple of days. Do not do any setbacks, just let weather compensation do it's thing. You are making the heat pump run full load most the time. Doing yourself no favours. If I let my house temp drop by a full degree, heat pump or boiler would take around 24 hrs to recover. Room temperature setup, if a room is too hot, reduce the flow rate to those loops by 0.5L/min, leave again for 12 hours. Opposite for cool rooms. Use the heatmiser as a monitor system do not use for control. That is the heat pumps job. This will take some time.

What you do has to comply with current regs, as you are making a change So outcome could be, a treatment plant to replace septic tank, located in a suitable location.

Guidance on close coupled tee install dimensions, so you get proper hydraulic separation.

Cylinder and boiler are within the heated envelop of the building, so any heat losses are going into the building, so winter time heat losses don't go to waste. Summer time cylinder and pipe losses are not useful. So you need to insulate for that. Space looks very tight. I would as a minimum insulate the hot cylinder pipe top for first meter. And the flow and return from the boiler where practical.

My niece moved into a house with an electric boiler, it got removed after the first month in the house as bills were hideously expensive. Ask to look at the electric bills. But with a smart meter you get a decent time of use tariff to make costs acceptable. Octopus Cosy for example is for heat pumps or electric heating.

Couple of things jump out of your description So 80kWh divided by 24 hrs, is just over 3kW electric input. Your either running 24/7 and getting a CoP of 3.3 or you are running on a timer for short periods and getting a piss poor CoP for the hours run. New build in 2022 should be nearer 3 to 8kW for your size house. So something doesn't add up. I suspect how you are running the system is the bit that's amiss. And or how it's set up. So are you running on a time based and thermostat regime or running on weather compensation 24/7? How many thermostats do you have?

Strong suspicion the insulation details around the steelwork leave some thermal bridges. It's a big bridge if not correctly detailed. The steel at the top of the roof, could also be an issue as you have lots of gaps in the roof insulation at that area. PIR in cavity walls is easy to do badly and difficult to do well. Suspect you have a lot of small detail issues that all stack up. Window size shouldn't give you issues. But post your thermal images. Around windows, around all steels, floor to wall intersection, the walls and ceiling.

If you have MVHR the air change per house is 0.3 to 0.5. But this has about 80 to 90% heat recovery. An air test of building tightness of 10ACH would give you around 0.5ACH natural infiltration. If you looking at a grant, the MCS spreadsheet has pre added ACH figures. You want them to move on the numbers you need an airtightness test result and then argue the point.

Bit confused by this Can you draw what you mean?

Although the outer part of the frame isn't structural, would have thought it needs to be supported, not just floated. Pre insulated planks seems complications. If you have to do suspended floor why not block and beam? Add allowance in heights for insulation and screed etc. Just do it thermal bridge free. The 140mm structural bit sounds over kill.

Think you are mixing up heating and ventilation. The heating on will be making matters better rather than worse. You either need to fix the ventilation, to keep humidity in check but way more importantly the CO2 levels are going to be at an unhealthy level most likely. Or implement a purge routine. Purge routine is pretty simple, you open windows doors for 10 mins, and then close. It replaces the air, but reheats really quickly once the windows are closed again. Air contains very little energy, the fabric of the building reheats the air. A dehumidifier may remove moisture from the air, but does nothing to help the CO2.

All heat pumps are a bit steep, £7500 of free money makes that occur, everyone a piece.

Sorry looks a bit naff The window should straddle the insulation otherwise you get a big cold bridge. So sitting on the brickwork and a ventilated cavity is not good. Without careful design of you chimney it will leak heat.

As I said above min output is 17kW. 5 UFH controlled zones, it will be zero seconds cycle time.

2020/21. £670m² fully installed. All made 4 miles away. Includes 5 doors all with side glazing panels each side, a big wall of glass (12 windows) and 6 other windows, all wooden frame, nearly all 3G, except 4 glass doors which are 2G Krypton filled.

Sorry not a lover Looks good, but from a practical point of view why not just do wooden cills? And sit the window on compacfoam? Looks loads of work, for little or no gain

And 5kW for £3500

But is that because closed the UFH mixer right down to get away from 70 Deg flow temperature?

Good luck getting that to run without a big buffer. Lowest boiler output is 17kW on any of the boilers in the range. And the lowest circulation pump flow rate is 15l/min. All 5 UFH loops will not support that flow rate on there own or all together. There is usually a good reason why boiler manufacturers don't want you trying to run lots of zones direct from their boilers, because they cannot modulate to small enough outputs.

Back to my original post? Flow needed for UFH on its own is small with a mixer. In flow terms your trying to push an elephant through your front door. You are likely going to need to flow radiators and UFH at the same time. Or put your UFH on a secondary loop via a close coupled tee.

Best you get your pens and paper out, or a computer version. Or pay additional.

Shows the need for detailed drawings and a clear airtightness strategy. Don't you have room in roof and cathedral ceilings? If so do you need tonytrays? Again back to a clear drawn out strategy.

So maybe good reason it only does 3 zones. Otherwise lots of short cycling unless you are buffering to a big buffer or thermal store, which as you are S plan out most likely are not.

Lots of boilers don't use volt free. So nothing unusual there. Add it then? Think you are missing a trick, not using weather compensation and priority demand hot water.