JohnMo

You will get a small temperature drop across the plasterboard, but not much. So the polythene will be at room temperature all the time, except in the case of poor insulation, a high degree of wind wash and thermal bridges, then it could be closer to outside temp. But shouldn't happen in a well designed house. With a decent ventilation system your internal humidity should be above 60% RH (dMEV or MVHR). In winter with building standards ventilation flow rates (with heat recovery) you may struggle to get much above 30 to 40% RH in really cold weather. As said do an interstitial condensation calculation, you can mess with lots of different materials, different temperature and different ventilation rates to see the effect. What I found interesting when you start to control max humidity at no more than 65%, it doesn't really matter what the internal temperature is you don't get condensation. If you don't control humidity, you start getting condensation at 18 deg, which could be the temperature of your bedroom. I used on from really useful software, which is free to use in demo mode.

There a rip off because the government will chuck £5k towards installers. The installers hike up the price and say 'but we are now giving you £5k off because of the grant. Technically not any different from an A2A heat pump, slightly different heat exchanger and no fan coil unit inside the house. So actually simpler, but generally cost more. You can get them at a reasonable price, you need to shop around and DIY install as mentioned above, rather than going for a grant. You really don't want to over size them.

My garage is very silver inside. Ceiling 25mm PIR boards screwed with spreader washers to ceiling rafters, then joints taped. Above that is 100mm of mineral wool. Walls, 100mm accoustic mineral wool in vertical wall timber, then covered in a foil membrane. Insulated roller doors, insulated side door. Garage not heated, but may use an electric heater at odd times.

I'm in Scotland so had to meet 0.5ach.

My average over the 4 months is 2kW, so 68m3! Big Can't imagine the temperature staying at 90 degC for long. So in reality to take account of losses maybe 50% as big again.

Not much of a fan for the ventilation you are producing, you will end with the worst of all worlds. 2x power required, for extract and supply, but no heat recovery to offset the ventilation losses and electric use. I would ditch the PIV. Then three options, vent fans with heat recovery, such as these (link below) you will need one at least in each room, wet and dry rooms - dMVHR. https://www.ventilationland.co.uk/product/40954/decentralised-mvhr-unit-o100-mm-with-switch.html?utm_source=googleshoppingUK&utm_campaign=googleshopping-FeedUK&gclid=Cj0KCQjwzqSWBhDPARIsAK38LY9sv8y5tPeyEPH6lJdO42VQvR7AagTCv5jhXEym6Mpwy0W1M5whOLAaAv7EEALw_wcB Full MVHR. dMEV, but condition based ventilation, so passively controlled vents inwards that response to humidity and the same for fan extract side . This way ventilation will be limited to what is needed. This will limit ventilation losses, and only require power to vent fans in wet rooms. You need to get good cross flow for this to be effective.

Don't get involved let the contractor do it. If he hits anything it's on his shoulders not yours. Mine hit a main 10" water line , the cost to repair was down to him and his insurance. If you start saying do this, do that, you are in charge - it then your fault and your shoulders, your money.

In theory, but in practice the holes you make in it, means it's not airtight, plus you would need to seal skirting level. Instead of guessing do if I need this or need that, get an interstitial condensation assessment. Either download a free trial copy or get your house designer to do it. Are you going for an airtight build? Have you looked at ventilation?

All insulation has acoustic properties. The more dense it is, the better normally. PIR is rubbish. We used rockwool flexi in our internal walls, seems to do the job quite well, equally suited to ceilings. Ideally you need an air gap either side of the insulation, that helps with the acoustics.

That sound like a good plan, hope there many hundreds

Recent topics on sand thermal storage and a mention of inter seasonal store on another topic has got me thinking. I live on an old sand dune (sea now 6 miles away). So have more sand than you shake a stick at. So my thoughts are 1. Dig big hole. 2. Line with 200mm PIR, or 300mm polystyrene. 3. Insert big tube coil, use same coil for charging in summer and extract heat in winter. Add suitable valves. 4. Back fill hole with sand, cap with more insulation. 5. With a spare solar thermal panel charge over summer. 6. Pump through same coil in winter to extract heat. Use heat stored to provide some heating load to UFH. UFH only needs a mean flow temp of 26/27 degrees for coldest day. Is it practical or would need to huge and not cost effective? Any thoughts

Nice design, but not sure how practical for a passivhaus. Has a passivhaus designer drawn up the design? I think overall you may struggle to get passivhaus heating requirements, your perimeter to floor space ratio is the wrong end of the scale, three long oblongs, with lots of room in roof; when the ideal shape is a single cube. Your U values will all need to be sub 0.1 to get anywhere close. You have lots of wall/roof to get airtight also. The glazing will kill the thermal properties in the cold and overheat you in the spring, summer and autumn.

That's some pretty thin insulation especially at the blue line. Plasterboard skimmed will give you reasonable airtightness, but only if no sockets or lights, these will leak like a seize. It is not moisture tight, so water vapour will pass straight through. If it was my house 1. VCL the whole roof fully tape all joints. If the walls are timber, same applies. 2. Install service Battons (counter directions to roof joists), 45 x 50mm, once services are installed insulate with 50mm mineral wool. This will help reduce the repeat thermal bridges, caused by the rafters. 3. Normal plasterboard in dry areas, wet areas with moisture resistant. 4. The wall that is blue, double the insulation thickness. Consider more insulation everywhere, you only insulate once, heating costs all the time.

It's amazing the difference the roof lights make to the temperature, my plant room is a room in roof, is not plaster boarded, so zero thermal mass, has boiler, MVHR unit, solar inverter and a 160L buffer, which is heated by solar during the summer, to preheat DHW, so cylinder, piping and inverter can kick a fair amount of heat into the room. But just checked the temp, had full sun on the roof since 6 this morning (no clouds) it's 24 degC. The room is sealed with an airtight insulated loft access hatch. There is an MVHR extract in there and vent to the rest of the house. The rest of the house is around 22 degC. So stopping the sun getting in should have a big effect.

Or just rip out the rads and replace with fan coils for heating and possibly cooling. Then no need for bigger rads. Possibly no need to do anything in bedrooms as they have a low heat demand anyway. Leave rads as they are or use same size with fins at the back. I would dig out the ASHP specs, and see what load shifting actually means in dollars over a 10 year period, to see if it makes sense based on the extra capital expenditure. And add into the equation HT split as Nick mentioned.

I also looked at Lunos, and to meet building regs flow rates it was big money. Just looked at the manual for the the linked ones, the power consumption is 1.5W in normal running and 2W in boost, so well low. You need a unit in each room, as you can't generate a cross flow between rooms. You maybe 2 in a large living room.

Just had my drive done, not seen the invoice yet, but ready to fall over. Tarmac first 8m from the road, with drainage. Then remaining drive in crushed lime stone.

They all can. This what I was referring too https://www.diy.com/departments/yale-white-metal-window-ventilation-lock-pack-of-2/254525_BQ.prd?ds_rl=1272379&gclid=Cj0KCQjwzqSWBhDPARIsAK38LY9-w6TVjzd8dsE8KkZEYVeyCYJHSLpBKRbWcLE20_O009I_qRiovwIaAjyLEALw_wcB&gclsrc=aw.ds&storeId=1217

Dump your current radiators, double the size at least, by using twin panels, with fins. Operate the heat pump at a much lower temp to get a decent CoP. Trying to charge the thermal store to that temp will get a rubbish CoP, but it is unlikely you would ever reach that temp so the heat pump will run for ever trying to a thermostat that is not reachable. The above means you can dump the thermal stores, and get lower running costs. As above UVC for DHW.

I would size for the whole heat loss. You can always decrease flow temp to down rate the system. The thing with UFH loop spacing, is the closer the spacing the lower the mean flow temp for a given W/m2. Also closer spacing results in more pipe and more water in the floor. Which may move you away from any buffer requirements. My heating requirements are 3.1kW on a -5 deg day. But I have 192m2 of UFH at 300mm spacing. My mean design flow temp is 26 degC. A spacing of 150mm would have dropped the mean flow temp to 24 degC. The loops are in 100mm concrete. The system response is slow. Down side of wide spacing is a slow reaction time, if you want on off timers, go for a close spacing. It the W/m2 that is the criteria you need to post.

I took the opinion, that if the electrician did it all and it went bang or something was not quite right, there was only a single person responsible, no he did, she did, not my fault governor.

Do you have a drawing of what you are proposing, it sounds like you may be introducing a big thermal bridge.

Sorry bit of a drag up an old thread. We have a Harlequin Hydroclear 6, 2 people in the house. The blower runs 24/7 (55W) so looking to reduce that. PV covers the running cost during the day, so would leave it running during daylight hours. So what's the best way to add a timer? Is it a normal time switch?

Simple really Electrician installs the electrical side, he can then sign as the competent person on the G98 form. This cover part P and any equivalent in Scotland. G98 gives you permission to install PV and generate, as long as you retrospectively complete the required paperwork within a given timeframe. Anyone can physically install the panels, but you need the electrician who is signing the G98 form, to do all electrical connections also.

What fun you have