JohnMo

Without having a well insulated house, the running cost of a heat pump could be huge. Are you sure, done the maths to make sure it's right for you. You don't say if you are on electric, oil or gas heating presently? If you get your annual heating usage in kWh, divide by around 2.5, then multiply by day rate electric cost, you will get a close approximate of the ASHP running cost.

+2, about friends, different rates of work and expectations, for a couple of weeks is ok, for months on end, could drive you up the wall. Are you down sizing to a six bed house for retirement? UFH is easy enough, it sits above the ground floor installation and in the screed. Have a u value circa 0.1, this will limit downwards heat loss. You mentioned outer skin of building, how are you building the structure? Light, big windows are great, but the downside can be over heating. Even with big overhangs, the sun when it in the west and low can cause over heating, so watch for that. We have a well sound proofed internal walls, but a door open circumvents all that. So I would not get to hung up about it, if you have 70mm stud walls, use 25mm sound insulation job done. All the things mentioned about airtightness, contractors in the main have no clue about airtightness, don't care, don't understand the issue, generally think you are daft wanting an airtight house. Bamboo, lots of weedkiller, one that attacks the roots

But is it really mvhr, as it seems to a MEV system with heat pump, doesn't seem to be doing the supply air. If you are going this route it really needs to be MVHR, and the air after the heat recovery, used for the heat pump. There are systems that do this.

If a manufacturer combined the rainpower (but would need higher efficiency) into a PV panels, sun out power, wet day power, dull dry day not much power.

Daft question - Local isolation valve closed?

Where do you live, that a typical roof has 70 tonnes of water on the roof? That's a lot of water, are sure your maths is correct? A typical house may have a footprint of 70m2, so would need a 1m deep storage tank over the whole roof. Not sure you would get planning permission. Not sure what you would do with water when you finished driving the turbine, you could store it and pump it back up again, then it becomes a battery.

You be worth having a read of the regs, to make sure you have the required ventilation strategy in place https://www.gov.scot/publications/building-standards-2017-domestic/3-environment/314-ventilation/

The regulations state the size minimum for the shower, use that dimension and add to drawing. Activity space then adjoins the defined shower space.

But they are all estimated, the estimate will change hugely, based on building shape, size, build type, external and internal finish, flat roof, pitch roof, insulation levels, ventilation/ airtightness, heating type (gas, ASHP,gshp, UFH radiators) etc etc. Two different kitchen designs can change a build budget by £50k, the amount windows can change it again by £20 to 30k with ease, uPVC or Ali clad can change it again by the same amount. My thoughts are for a basic start point. £2k to £2.5k per M2 with someone else doing all the work will be a basic ok performance house, so 400k for 200m2 two storey. Add a good 10 to 15% on for single storey but depends on roof complexity (our roof added about 25% to m2 cost). The more bells and whistles and any changes you make along the way will add quite quickly. The above assumes limited or no landscaping, painted internally a single colour.

What about a solar assist heat pump, they are generally around 2kW, come with 2 off 2x1m panels for outside though and they need to be mounted. Or if you like engineering something, could you use a car Aircon condenser and car fan, instead, mount in a custom box. Use it to heat a 50/100 litre cylinder with coil and take the UFH water from that. Or a Willis heater, CoP 1 though, so may be costly to run. Or an all in one air to air heat pump, for cooling and heating. But that doesn't used the UFH. But no outside unit.

Is the cartridge adjustable, our is a different make but behind the temperature knob is an adjustable temperature screw, if that is adjusted the wrong way it is just be hot all the time. Worth a read of the instructions

Something like this - other makes available. Would be my recommendation. https://www.vent-axia.com/range/lo-carbon-nbr-dmev-dmeve Runs continuously and is silent, humidity stat options available.

No particular warning on my Titon units. My thoughts are. For what it saves why switch off and risk not switching on when you have closed the windows. Mvhr sucks in moisture from wet rooms, so be definition the extract side is wet or damp. Switching off for a prolonged period would allow these damp areas to generate bugs, mould etc. Neither is healthy for the unit or you.

We had one similar to that, was great. £2k or put kettle on at your required temp, it's hot when you back from a visit to the toilet.

What are you referring to "these"? dMEV fans go in the following rooms. Utility, bathroom, shower room, en-suites, kitchen, anywhere where moisture is generated. The combination of all the fans must give an air change of 0.3 an hour. So calculate the internal volume of the house, divide by 0.3,this will give you are target M3/HR flow rate. Read building regs related to ventilation that will tell you exactly what is needed, for flow rates in each room, but base any discussion on an airtightness of less than 5.

One thing not mentioned is during winter you will get very little hot water from PV. As it doesn't generate much.

I would say they both look cramped. How about putting the bath where the sink is, or where the toilet is on the first sketch. then sink and toilet where the bath is.

All vaulted, except a small part of hall. Spray foam insulation between and under rafters.

I have wet UFH, electric towel rads. If I did it again, I would do electric towel and electric UFH.

Based on that figure, the fans specified as intermittent are fine. But with a polystyrene ICF build you may be a lot more air tight and could end up with mould, poor air quality etc. As a minimum I would get dMEV installed, these fans will fit into the existing/planned holes in the wall, match the windows you may have already been installed/ordered, with trickle vents and give you the least hassle. Best of all they are silent. The way dMEV works, the fans run at a low speed continuously, extracting air from the wet rooms. Air is drawn in through tickle vents in dry room windows. The air cross flows through the house/under doors etc. and out through the wet room fans. Think you are aiming for 0.3 ACH through the ventilation system.

Easy to work out read building regs for your region. In Scotland it's basically 0.5 ACH. So calculate the internal volume, divide by 2. That's the basic normal flow, add 25% for boost. Choose a unit that flows your boost figure at about 70% or lower it's rated capacity. Extract in wet rooms and kitchen, supply everywhere else. As Dave say semi rigid is easy to install, just plan ahead.

Had MVHR flow rates set per Scottish planning the other day. As soon as the guy left I put mine on to setback (mid way between min speed and current set point). Considerably lower flow rates, closer to passivhaus and no noticeable increase in CO2 levels, in living space and bedrooms.

Out of interest what airtightness figure was used to get an 88 from SAP?

Not sure of the rules where you are, but in Scotland if your final airtightness is 3 or better you would have to have it installed. ICF builds tend to be quite airtight. dMEV is a good option if worse than 3, anything from 3 to 5. This would require trickle vents, and continuously running (silent) fans in wet rooms and kitchen. This can be made to run on condition (humidity etc), so run at a low output, until required. We have MVHR, my wife has COVID, and somehow I don't. Not sure if it's the continuous ventilation or I'm lucky so far.

https://ecostream.org.uk/d-mvhr/ Not used or seen