Anyone got an MVHR?
Discussion
TooMany2cvs said:
And what about the poor cat? How does it get in and out?
You can now get a PassivHaus certified catflap.But if you keep pets, you're doing far too much damage to the planet to be a proper PassivHauser, anyway.
The authors of that book were my course tutors on my Architecture degree, incidentally.
I mean, you have to take everything with a pinch of salt, but it's amazing how infrequently you feel the need to open windows if you have a mhrv system.
The house is just airy and fresh feeling all the time, like you have a window open, but without the cold draft. I've got no ties to sell the products but having grown up with it, it's honestly great.
Parents house still has opening windows, and it's nice to be able to open them on the ten hottest days or the year or so, but for me you can shove 'trickle vents' and having to remember to close the bathroom window before you leave for work!
Daniel
The house is just airy and fresh feeling all the time, like you have a window open, but without the cold draft. I've got no ties to sell the products but having grown up with it, it's honestly great.
Parents house still has opening windows, and it's nice to be able to open them on the ten hottest days or the year or so, but for me you can shove 'trickle vents' and having to remember to close the bathroom window before you leave for work!
Daniel
dhutch said:
The house is just airy and fresh feeling all the time, like you have a window open, but without the cold draft.
Against which you've got to balance the research on SBS and build up of pathogens.The air may feel fresh (that's the oxygen and CO2 levels you're detecting, primarily, which MVHR deals with just fine), but the truth is that the distribution of air circulation within individual rooms is not anything like as good as it is with natural ventilation (you've usually only got one register per room). Pathogens built up in the 'dead spots' and this is suspected (with ongoing research to back it up) to be a major contributory factor with SBS.
The bottom line is that you can't have your cake and eat it: if there is enough internal air circulation for a genuinely healthy atmosphere, then our bodies are sensitive enough to detect drafts (and if done by MVHR the levels of ACHR required generate an unacceptable level of background noise, unless you use huge ducts)..
MVHR is fine, and a good idea, when used in moderation, but when used as to extremes - to achieve PassivHaus levels of energy efficiency - then it almost certainly becomes detrimental to human health. We evolved to live outside, with air that is being vigorously and continuously stirred by a turbulent atmosphere, not in hermetically sealed boxes with artificially ducted ventilation.
Blimey. Lots to think about. We're probably going to the planners in the next three months with a new build house. One thing I desperately don't want to do is end up with a house that's got something like MVHR to find out it's a totally outdated system in ten years time and a nightmare to maintain because nobody supports these systems any more.
I really don't want anything with any kind of proprietary technology in the building. No interest for example in a multi room audio system where you're reliant on one company for support/maintenance. Learnt about that the hard way with the audio system we installed in our place in London in 2005. When we sold in 2015 it still worked etc but it was pretty archaic and outdated!
I think we're probably going to appoint consultants for the heating/ventilation system as I want to make sure it's specified properly and someone's on the hook if it doesn't perform properly. Anyone got any recommendations would be interested to hear!
I really don't want anything with any kind of proprietary technology in the building. No interest for example in a multi room audio system where you're reliant on one company for support/maintenance. Learnt about that the hard way with the audio system we installed in our place in London in 2005. When we sold in 2015 it still worked etc but it was pretty archaic and outdated!
I think we're probably going to appoint consultants for the heating/ventilation system as I want to make sure it's specified properly and someone's on the hook if it doesn't perform properly. Anyone got any recommendations would be interested to hear!
If you're building a home that is relatively airtight you have no choice. I fully agree with Equus about the merits of continuing along the Passiv route, but we are where we are at the moment and it's worth reflecting on developments like central heating, which came along 50 years ago and was blamed for dry skin, colds and all sorts of ailments, could anyone conceive building a house without CH today?
A properly maintained and serviced MVHR system should function efficiently and provide a comfortable environ in all seasons and pose no health risk, in fact the absence of dampness is a key health benefit along with some semblance of respite for hay fever and asthma sufferers, if you keep the windows closed.
A properly maintained and serviced MVHR system should function efficiently and provide a comfortable environ in all seasons and pose no health risk, in fact the absence of dampness is a key health benefit along with some semblance of respite for hay fever and asthma sufferers, if you keep the windows closed.
Blue62 said:
A properly maintained and serviced MVHR system should... pose no health risk.
I'm afraid you simply can't say that. Don't believe the hype that MVHR improves air quality. Unless you suffer from hayfever or live in a location so heavily polluted with particulates that it's barely safe to go outside, it simply isn't true. It is simply impossible to deliver the sort of ventilation rates and distribution we (Architects and Building Services Engineers) would ideally like, because to do so from the limited number of registers and restricted ductwork sizes available from a practicable system would (a) cause drafts and (b) result in excessive background noise.
The systems are therefore a compromise between better energy efficiency and poorer air quality, in critical respects.
The best you can say for MVHR is that it's the least worst option currently available IF you require a ventilation strategy to support the very highest levels of energy efficiency and building airtightness.
I mean, I've never lived in a house the was airtight to 'modern standards' and there is a chasme between the minimum legal airtightness (bearly more than your average 30-40yo house) and Passiv Haus standards.
However adding mhrv to and house can surely not make it worse? It's the airtightness of the house that may cause issues. Not the mhrv system.
My 1938 ex-council house that has been replastered and fitted to a very low standard was super drafty by modern standards and certainly required noticeable more heating on a windy day than the equiv temp still day. Like 2-3 times as much heating. That's obviously crap. So there is a need for some sort of limits and or testing.
Ventilation systems have been around for hundreds of years, and mhrv for decades. The company 'villavent' who main my parents system 30years ago is still trading and was abltto supply a pair of replacement fans a year or so ago. So I wouldn't worry about it becoming out of date or unmaintainable. Worst case you replace the whole unit, like fitting a new boiler to a ch system.
Daniel
However adding mhrv to and house can surely not make it worse? It's the airtightness of the house that may cause issues. Not the mhrv system.
My 1938 ex-council house that has been replastered and fitted to a very low standard was super drafty by modern standards and certainly required noticeable more heating on a windy day than the equiv temp still day. Like 2-3 times as much heating. That's obviously crap. So there is a need for some sort of limits and or testing.
Ventilation systems have been around for hundreds of years, and mhrv for decades. The company 'villavent' who main my parents system 30years ago is still trading and was abltto supply a pair of replacement fans a year or so ago. So I wouldn't worry about it becoming out of date or unmaintainable. Worst case you replace the whole unit, like fitting a new boiler to a ch system.
Daniel
dhutch said:
However adding mhrv to and house can surely not make it worse?
No, adding it cannot make things worse.Using it (as the only form of ventilation; or worse still, designing the house in such a way that it relies upon it) is what can make things worse.
If you add it to a really old and leaky house, you're pretty much wasting your money, though: there will be enough ventilation happening through air leakage, during the heating season, and that leakage won't stop if you add MVHR. So even if your MVHR is operating at 90% efficiency, that basically means that you're spending several £thousand to add another 10% to your heat loss.
Don't get me wrong: I'm not anti-MVHR, per se, it's just that it only really comes into its own at very high levels of airtightness and insulation, and there are all sorts of reasons why it makes sense not to spend the extra money/effort on high airtightness and MVHR, and to instead let nature take its course to a greater degree.
Sounds fair.
Obviously if the house is airtight as an ox, and the mhrv isn't moving enough to keep the people well, that's no good. And it's hard to know what the minimum is and there is a driver to keep it low. I don't really know how and when that becomes an issue.
If the house is stupid drafty and changing its air every 45minutes without any extra ventilation then adding mhrv is a bit like using a hosepipe in a rainstorm as your not going to get damp anyway. Or benefit from the heat exchanger.
However my gut feeling is that there is wide spectrum of houses where they are airtight enough that they feel nicer with a bit more air movement, a baseline air turnover that isn't effected by windspeed, and recovers most of the heat. The cost of the unit isn't insignificant, but they aren't mad money, and certainly most of the work is in getting the ducting in.
Who knows. Seems to work where I've seen it.
Daniel
Obviously if the house is airtight as an ox, and the mhrv isn't moving enough to keep the people well, that's no good. And it's hard to know what the minimum is and there is a driver to keep it low. I don't really know how and when that becomes an issue.
If the house is stupid drafty and changing its air every 45minutes without any extra ventilation then adding mhrv is a bit like using a hosepipe in a rainstorm as your not going to get damp anyway. Or benefit from the heat exchanger.
However my gut feeling is that there is wide spectrum of houses where they are airtight enough that they feel nicer with a bit more air movement, a baseline air turnover that isn't effected by windspeed, and recovers most of the heat. The cost of the unit isn't insignificant, but they aren't mad money, and certainly most of the work is in getting the ducting in.
Who knows. Seems to work where I've seen it.
Daniel
Equus said:
As a general rule, we try to base the technical design of buildings on more than gut feeling, these days. 
The problem with that being that you end up with buildings that are technically capable and meet required standards, but not necessarily facilitate comfortable living. Trickle vents that need to closed when windy, and then opened again, no where to dry clothes in the house, poor soundproofing between bedrooms, etc. Daniel
dhutch said:
The problem with that being that you end up with buildings that are technically capable and meet required standards, but not necessarily facilitate comfortable living.
I agree totally: and ironically that's the problem with MVHR (and PassivHaus)... they may give you what you think are acceptable air change rates on paper, but the internal circulation isn't adequate in practice.None the less, it's better to understand and work to some sort of technical baselines, rather than to just design things by a feeling in your water.
It is because we have done the technical analysis that we are now learning that the ACHR rates offered by MHVR in a high airtightness building in fact aren't adequate, and we can adjust our strategies to suit.
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