Alan Ambrose

Thanks John

Err, CVC was what Nick recommended. @JohnMo interesting on your use of co2 monitor, I expect I'll need to do similar. Is it possible to post your link again for the eBay sensor - it just gives me 'error page'. BTW CVC quoted an extra £190 for the humidity sensor, which makes the total about £680 more than the Zehnder unit. I'd love to see what's in the sensor - I bet there's less than £10 of parts there. I've got the unfortunately named SHT35 humidity sensor in other parts of the build - the chip is about £6.

Curious - I can't think why it's ok for hot feeds but not for recirculating.

Ah interesting, I hadn't clocked the bit about the humidity sensor - a bit dumb that it wouldn't have. BTW cheapest places I could find were TradeSparky for the Zehnder and CVC for the Brink. This thing? https://www.ventilationland.co.uk/en_GB/p/brink-excellent-rv-humidity-sensor/5791/ Seems expensive. I was planning boost in the bathrooms and kitchen and maybe a co2 sensor in our bedroom as I think my other half is very sensitive to this - she wants the bedroom window open all year round - even in minus degrees.

Congrats, looks v tidy. >>> My understanding is that a female port (where a rubber seal and seat for that seal is absent) requires the mating male to be tapered thread (BSPT) and wrapped with thread sealer to make the joint I don't think that's right. My understanding is not to mix parallel and tapered unless you need a temporary bodge. I think most threads used in residential are parallel. Both parallel and tapered will need good thread sealer and I've used some cheap parts in the past that needed a bunch of thread sealer to work. That's all consistent with the instructions you quoted which said, in effect, 'don't use tapered parts here'.

OK for anyone 'following along at home' I decided on the Brink unit. I was leaning towards Zehnder but the physical size was an important factor considering the slopey attic it needs to fit into. I figured I needed 30cm above the unit to cope with the ducting. Not yet sure what I'll do re controls - the branded controls are stupidly expensive imo. I'll probably run CAT6 to the places where we want controls and/or sensors and assume I'll figure out the wiring later.

This is what it thinks about the mounting issue and that sounds good to me:

Ah thanks Mike. For anyone following along in future, this is what Gemini thinks, but having looked more closely at Ubbink's offering, I don't see any reason why it can't be shortened - it looks just like a bit of flexible insulated pipe that has some ends formed in it - and I think you could do that forming by hand without a problem.

A related question - has anyone here used (or felt the need for) some kind of sound absorbing feet or mounts in addition to whatever is on the bottom of the boxes?

Oh yeah I was only looking at Ubbink ones duh, I see DEC has a range e.g. Flexible silencer non-woven with connection diameter: 180 mm length 500mm 72620518 | Ventilationland Actually, maybe DEC is actually supplying Ubbink anyway as they look so similar.

Was going to use these to connect my MVHR box to the ducting (either 180mm foam ducts for external or the 180mm connectors on the plenums): Ubbink Aerfoam Insulated Mass Flow Ductwork Sound Attenuator 180mm These are nominal 1m and stretchy of course. The best connections I can see would bend to about 0.5m long - can I shorten them OK by cutting and forming something a bit like the factory ends?

>>> why are you limited to export volume? Well the DNO will always limit, even if it's only to 17kW on single phase - it's a risk thing with local voltages apparently. And we have planning permission to cover one roof and the 'cartlodge' with panels.

@Beelbeebub Yeah, that's pretty much what I want to do for similar reasons. Presumably you had to limit the export in software but had a much larger inverter?

So, am I right in thinking that the old way of looking at the problem was to optimise for max summer output i.e. S facing and make the most of the panels you’ve got. And the max self consumption route is: panels are cheap, spread panels east-west for long output during the day; have max panels for usable output in the shoulder seasons; and then a bit of battery to cope with occasional dull days and to keep the heat pump running overnight. Almost ‘off grid’ for 3 seasons, with a bit of backup help from the grid in winter?

Is there ever a problem where you would like to have more panels but your DNO-agreed inverter size and the max oversize of panel capacity for your mppts limits your shoulder seasons generation?

Suggest just call up, describe the problem in round terms, send them a few pics and ask them to take a look and give an opinion. Maybe an informal opinion and recommendation rather than a report. They may charge for their time but it’s probably money well spent. They’ll like dealing with you if they don’t have to explain the basic laws of physics 😀.

By which I mean large overcapacity of panels. Object being to provide almost all power in the summer & shoulder seasons - only using imported power in the winter?

OK a bit more info: + the Zehnder unit has the benefit of not being 'handed' (as it's switchable) but the drawback is that it's quite a lot physically taller - 850mm vs. 650mm. + the Brink unit seems to be consistently £600 more expensive than the Zehnder. + the Brink Vigor / Flair etc brand confusion doesn't inspire confidence. Which organisation will be supporting? Neither was my experience of their duct system which seem half-baked ... just like someone on their design team had never ever tried to install it. + both Brink & Zehnder seem to need an extra bit of electronics for web control. Although, in the end the built-in RS485 / Modbus might be the best control solution. According to Google AI (which I have not verified) the Brink units need an actual internet connection for the app to work, the Zehnder units don't. While the bigger physical size is a pain, I'm leaning towards the Zehnder unit.

Don't know whether you got @saveasteading 's point: If you hire in machines, hire surveyors or other 'knowledge workers', buy tools etc then you can't claim back the VAT - these are examples of things that are not on the self-build VAT-reclaim list. If a trade does this for you in the course of doing some work involving labour then they can claim back the VAT but their supply will still be zero-rated to you. That is, you've saved the VAT over buying directly. The other factor though I think is this - it takes a fair amount of time and effort to hunt for good prices / compare products etc. Most trades won't bother knowing they're just going to bill straight through anyway. You have a much bigger incentive to keep your own bill down.

p.s. the lowest point of any cable overhanging the entrance + the ground level underneath for any tall vehicle height checks. Plus the location of any known external services for service design e.g. where is the nearest Openreach pole with fibre on it, ditto power, water.

@john0wingnut >>> how I am going to run an intumescent strip along the top with ventilation mesh Envirograf do a combined mesh / intumescent product if that helps.

>>> So do I need the windows as well as the ridge and eaves for No 3? Sorry missed that. Can’t see any reason to unless you think you might have a battle over ‘overlooking’ or need to establish some similarity to the neighbours e.g. building a new end-of-terrace. In any case once the surveyors have done their set-up, marked their stations, taken gps coords of those, recorded points say on a 2m grid for ground levels, features, fences, poles, pipes etc etc etc … a few extra points will (should) make zilch difference to the price. You may want to use the same surveyors to mark out your design, so you might ask them about that process. Also, you might like to set-up a hard-to-disturb datum level (we used scaffold poles) at a known round number absolute level. Then you can calc other levels from that with a laser whenever you need.

@Owain1602 >>> What are you going to do at the heads of the windows? We used thin stainless strip as per an earlier ‘ub discussion. Quite a bit of work, but done now. Much cheaper than intumescent of course and seems to me anything fireproof will work (maybe not in the regs though) as you don’t need the expandability of intumescent.

>>> I raised the subject of "automatic fire suppression". Would be interested to hear about that. FYI, just spoke to Envirograf - they asked what the BCO said and actually agreed with him ... but said that for belt-and-braces a strip under the eaves and gables and at the bottom of the cladding was good. Also the windows etc. But then they are selling the stuff. 😀 p.s. Envirograf said there was a v good illustration on the NHBC website. Envirograf couldn't / wouldn't send me a link or copy. And I can't find it. Think I'm going with a strip at the top of the cladding only. >>> External cavity measures are borderline irrelevant for a regular domestic dwelling of 1 or 2 stories, in my own opinion. Might depend on how generally flammable the build is, but kind of agree - esp. as we're one storey and all rooms except bathrooms have a door to the outside.