joth

The mixing valve it the one the Welshman recommended on here a while back: Esbe ARA662 actuator 230v 50hz 120 sec https://www.wolseley.co.uk/product/esbe-ara662-actuator--230v-50hz-120-sec-(1)/ The Mitsubishi FTC6 controls it all, with thermistors on all the flow and return pipes plus in the uvc and buffer tank. You just set a desired flow temp per zone and it does the right thing when the zone calls for heat.

I would assume so, how as would you do it? That's what our setup will look like; approx 17C for UFH and 7C for Comfopost is what we had panned. @joth Are these temperatures fixed in your setup or can you adjust them, based on for example the relative humidy? I Yes this is ecodan with a small low loss header tank and electronic mixing valve, so I can freely run any temp on each zone down to 5°C In retrospect I larger (100L+) buffer tank would have been worth it, as I'm using the fan coil cooling more than expected (see other thread on bedroom overheating) but it's only rated about 1kW cooling so the ashp short cycles a bit driving it alone without the UFH cooling load. Also the buffer could have been cooled during solar generation time and then discharged overnight. Maybe I'll do that another time. The ecodan cloud API does allow for setting the flow temps so could do this automatically if I wanted I guess. I'm currently looking to use the API to configure heat vs cooling mode as needed.

I'm using 15°C in the UFH and 8°C in the fancoil

A simpler option is to have a new small unvented cylinder heated from the ASHP and take the UVC input from the TS. So if the TS is hot (stove or solar active) the ASHP won't have to work, but if they're not it does. (i.e. same idea as the on demand electric heater but ASHP friendly). It's still a lot of systems to maintain, but you _may_ be able to get the MCS installer to do this (basically tell the to take the UVC "cold in" feed from the TS and otherwise it looks like a bog standard install) is the gargantuan TS specified to enable multi-day storage e.g. to cover less sunny days, or because the daily demand is very high (running a guest house)? And what is the peak demand (5 showers running at once?). This sort of thing is probably influences the choices a lot.

Just a thought - you might get some more responses if you make a straw-man proposal or ask a more specific design question. You mention the goal of adapting the heating system to use an ASHP. Is that space-heating only, or DHW too? My initial thought would be to split the UFH from the legacy system and drive that exclusively from the ASHP. If the heating demand is low, that (plus the heat loss from the TS, assuming it's in the thermal envelope) maybe sufficient space heating for day to day. MVHR post heaters and towel rads could get the same treatment, depending how much they're actually doing / needed. Heating a one tonne TS from an ASHP sounds a miserable task. If the solar thermal doesn't heat it enough in winter and the stove rarely used, adding an on-demand electric boiler to the output of it would allow it to ride through the darkest months and still have the use of those parts for DHW when the stove or sun is available.

My understanding this is far more about flood prevention at large, than solving a specific hot spot at the end of your driveway in particular. See https://www.building.co.uk/comment/suds-law-sustainable-drainage-systems/5038190.article - As more land is paved over, more water ends up in the city drains and running out via large rivers creating flood risks along them, rather than getting into the ground locally and thus into the aquifer that feed smaller streams and sustaining the wildlife there. The SuDs laws are intended to have more water go into local soak away, and less down the LPA drains. No individual building application will make or break it, but at large they need to be enforcing the spirit of it in order to achieve a net reduction (or at least, no increase) in water heading out to LPA drains. If you richer in time than cash, one idea would be to submit a schedule with the acco at the top of the drive only, see if they approve that, if not resubmit it half way down, and then a couple feet from the bottom. They may get the idea and open a conversation about what they would consider acceptable . The major cost of doing it lower down is you'll need to dig your own soakaway much much lower under your plot in order to allow the run off to flow back under the drive into it.

I honestly think if you can get through the entire rest of the build and have to hold out a couple months using a temporary £50 oven before the perfect one gets back in stock, you'll be delighted (Also, in a multi year project, storing an oven or american fridge and not having it get bashed up is a challenge, and you may even find it's obsolete or been superseded by the time installed) What I did when about 4 months out from kitchen fitting was phone applianceworldonline.com and negotiated a package deal for the whole lot. They gathered them in stock over a few months, then kept them in their warehouse until the nominated day I needed them. They're going to charge a fee to hold them for 24 months though.

IKWYM - they're slowly working their way around our town, but say they have no plans to do our street. I think it's because we're in a conservation area and all the cables are underground. Most the town is on overhead pylons and it seems relatively simple for them to pull the fibre to each pole, and then drop it into individual houses as and when requested. Unfortunately our contractor accidentally ripped the old OR copper cable out when digging the soak away, so I'm now on the fence if I get them to pull a new copper wire in anyway. We're currently on VM but with 2 of use working from home both days now, having a redundant fail over seems tempting. (Last time I needed it 4G failover was not a success last time I needed it, as too much of my setup did not like being behind carrier grade NAT)

I imagine everyone here assumes you're after triple glazed windows with no trickle vents, and installed fully airtight between the frame and the building. Note that none of those things are standard practice or ensured by building regs / Fensa certificates, so if this is not what you're looking for you may need to spell out the building performance requirements a bit more.

Bear in mind that if the towel rads are all over the house, and if it's a well insulated house, this could add quite a bit to summer overheating. If you do do that obviously insulate all this extra pipework We decided just to go with electric towel rads, and not plumb them in at all. I have them set to run for 40mins after anyone uses the shower/bath, and remain turned off the rest of the time, to avoid any unnecessary heating.

An alternative approach is to use an enthalpy heat exchanger (So "energy recovery" rather than heat recovery) and then you don't need a condensate drain. BTW depending what other things you have in the utility room, you may need more drainage anyway? I was surprised by the number of tundish and overflows needed for heating system, water softener, etc, and with condensate dripping off basically everything when using active cooling I kinda wish I'd just tanked the room and set a drain into the tiled floor.

Is the garage inside the airtightness & thermal envelope? Normally they're not as an airtight garage door is borderline impossible. But putting the MVHR unit outside the airtight boundary will be awkward as it's (potentially) a lot of pipework to detail airtightness for (depending on manifold locations etc), and also the unit is more efficient if inside the thermal envelope and any warm-side ducting outside the thermal envelope would need to be insulated. tl;dr: Utility room is likely the better choice.

Yes, that's why said "all else being equal" (or at least attempted to, sorry about the typo). This is exactly what the calculation in my original post is accounting for. 1 ACH is shifting 10W per °C difference in temperature between the supply air and the room temperature, which is effectively negligible for removing the 160W of body heat. Even in bypass mode in winter it's rarely going to exceed 150W so only just keep up (and of course, we'd not use bypass mode in winter, so in practice it's only around 10W in winter and a bit more in summer, on cool nights at least. Hence why with very efficient heat recovery, the overheating issue is actually going to be worse in winter than summer) I'm increasingly sure I don't

Can I check those units and values? Assuming 106 m3 then that's a substantial volume (vaulted ceiling?) -- about 3x our master room, so all else equally I'd estimate it'd take 3x as long for 2 people to heat up the air by 1ºC. It takes 2-3 hours for our room to get unbearable, so with a 3x larger room, I can easily see it getting through the night OK using daytime only purge. Obviously this will depend a lot on the outdoor temps overnight (worst case it'd actually be heating up the room by leaving the windows open) but for us, windows open makes a radically large difference. If it wasn't for the nearby train line, and wanting closed windows with triple glazing and additional sound insulation to block that out, this would be the solution (if a weird one to have to use in heating season) Well this year it was still unusually cold here in early May and my post was based on the very cold month + of experimentation leading up to that date. But yeah since then the experiment of sleeping in another room / house on a couple occasions has pretty much pinpointed it as a body heat issue. Also, the temperature graphs I have make it clear the temperatures sits stable when empty, but then starts to climb the moment the room is occupied. We also have a central atrium with a skylight that I now have automatically open when stack venting is required. This works like a champion for the house as a whole, but there's just not enough free airway from the bedroom to the atrium to balance out. I'm going to investigate putting a "chimney" like duct out of the bedroom feed up to a high point in the atrium near the skylight, to allow some passive circulation of air too (and also provide a better outlet for the forced-air circulation from the fancoil) Thanks for the replies, very helpful to know how others manage things in a passive (like) house

Yes, it does it on a whole building level, not room by room (AFAICT - I am not a PHPP expert). At the whole-building level we're totally fine - 2 people in a 4 bed house, no overheating experienced (except when there's a heatwave). The issue is on a per-room basis. PHPP has the "Heating Load" -> "Risk determination of group heating for a critical room", which a) does not have any allowance fort the largest source of heat in bedrooms, the occupants, and b) only deals with heating demand, not cooling demand. (The "Cooling load" tab has no such critical room risk calculator) It reports 3% overheating risk at 25 ºC. But again, this is a whole-house risk. What we see is 99% risk for one specific room, even on the days the rest of the house is sat at a nice comfortable 19ºC. Again, the internal insulation between floors and in the stud walls is actually hampering rather than helping here. No, and I really don't see it would help: My calculations in the OP say at MVHR circulation rates it would need to be delivering 4ºC air in order to keep up with 160W of heat source, which could only be achieved by having the ASHP running 365 days a year in cooling mode - very much against the ethos of a passive house! This is really interesting. Can I ask how the bedrooms specifically connect to the stack ventilation? e.g. do you have to open the bedroom windows to have this work ? And like ProDave, do you find you need to do this in the (occupied) bedrooms in winter as well as in summer? Or do you have some other way to promote more airflow through the room - besides the standard MVHR outlet and door gap - such that the bedroom windows can remain closed, yet still maintain a comfortable temperature? (or are the bedrooms particularly high volume, which would greatly increase the time it takes to warm up from body heat? or anything else that would aid this?) Thanks