SBMS

How come all MVHr designers size off the volume of the house, not the number of occupants?

Thanks. Never really thought about from perspective of number of people in house. Family of four with 2 dogs so my gut is that although it’s a large house, something like the q600 would suffice. @JohnMo why did you go for two units out of interest (and how on earth did you get that for 2k!)

What would you aim for? I did do my heat loss calcs targeting 0.3ACH as it was a ‘healthy minimum’. I suppose this reduced the need for a larger unit even more?

So if the house volume was, say, 900m3 and I was aiming for 0.5ACH the unit would need to do 450m3? (Obviously would want to run it around 70% so probably would need 645m3?) when they do their sizing do they account for target ACH?

Not sure what you mean by over ventilation? Re your comment on price over 20 years, it’s not really the motivation for the MVHR. More because we are aiming for high air tightness so need MVHR and the comfort element.

Also - can anyone help with a very simple way to size a unit based on the size of the house? I see figures on the units like 600m3/h airflow and 108l/s requirement for building regs - how can I calculate the requirements for the house?

Currently looking at MVHR options for our build. Around 390m2 Over three floors (room in roof) so we have been given two options from BPC for MVHR: 2x Zehnder Q450 (total price 7901) 1x Komfovent r700 (total price 6000) same ducting for both options. The zehnder is 95% heat recovery but the komfovent is 83%. However I would prefer to only have a single unit and there is a price differential of 2k which I probably wouldn’t make up in heat recovery costs vs the equipment cost difference over lifetime of the unit. I also don’t know if electricity running costs would be greater with 2 units. Anyone been in a similar situation or have any advice as to which route to proceed?

Is your ‘airtightness membrane’ a VCL? I think I read the differential of the vapour resistivity between the inside (membrane) and outer (OSB sarking) needs to be around 5:1 to ensure vapour migrates out. It’s worth just checking this because if it’s at risk of condensation at least you know it’s down to makeup and not poor workmanship (design not build). Knowing doesn’t fix your problem though. I’m surprised that even with MVHR you still have a problem as that should help. I would suggest your nuclear option is to fit a dehumidifier and keep that running. You can get ones that are wall mounted and the condensate outlet can be plumbed in.

Where is your roofing membrane?? Should be under your counter battens/on top of your sarking boards?

Thanks - it’s all contained in the system itself as it’s effectively a swim spa. So filtration etc is done within the gubbins - like a massive hot tub. No separate pump room required. Heating is done via a supplied ASHP. Ventilation is not supplied and I need to look at a dehumidifier and vent system separately. Is that a single block wall basement that your pool was dropped into? how did you waterproof the basement area?

Getting my SE to design it and can then get it quoted up. Will report back!

Absolutely amazing result and fantastic news. Fair play to the other person that dealt with this. I bet your build just become a lot brighter! After that you’ll be able To deal with any issues that come up and think at least it wasn’t as bad as your last 24 hours!

Do you work for an inflatable pool company??

I think 90cm would feel a bit more like walking in a bath - I was thinking 140cm was pretty shallow. On site today and the groundworker has dug our foundations down to about 1100mm from DPC. The hole was dry as a bone at least…

Did you receive a full liability notice and was it in your name?