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Health risks associated with passive houses

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2 hours ago, Ferdinand said:


 

I think the key thing is what we in software development call Maintainabilty, in this context the ability to change all the services without destroying the fabric. I try to do that in my small way when renovating.



 

Going off topic here, but when I lay my upstairs flooring (chipboard and carpet) I will leave a strip of boards probably 300mm wide that are only screwed down around the perimeter of each room and can be lifted should I need to add e.g any extra wiring.  I did this in my previous house and it worked well. the only reason I did not do it in the present house was we have UFH upstairs.

 

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I have just been reading this thread in catching up.  Some interesting perspectives, and controversial opinions. Some general comments / responses.

  • The audience in this forum is a highly biased one: people interested in self-build development. Moreover,  those who want to take an interest in the informed opinion of peers.
  • From my personal research the main risks with MVHR relate to poor maintenance and ignorance of the occupiers. I don't think this is relevant to most visitors to this forum.
  • IMO,  the risks in modern well sealed houses are in those without correctly operated MVHR (and closed trickle vents, etc.).
  • @Sensus comments about the risks of condensation due to poor airflow and dead zones in MVHR-fitted houses, seem anecdotal rather than evidence based.  They have no underpinning in the physics of gas diffusion.  It just doesn't work that way.  Heat exchange drops the RH of input air at 0°C and RH 60% to something like 20% at 20°C. The walls in a house like mine are typically within 1°C of room temp.   Even the surfaces nearer cold bridges around the windows will only get down to say 15°C under the most extreme conditions.  Gas defusion and micro circulation means that the AH in the room will rarely vary a few %.   The only material condensation occurs in the MVHR unit itself,  and this is designed to discharge it safely.  Yes,  we will be adding to the moisture levels by inhabitation, but only to comfortable and safe levels. 
  • On a different point in some regions decent self-build plots are extremely difficult to come by.   We were lucky enough to a have a garden large enough to split, and survived the LPA cat and mouse game to get planning permission.  The other alternative here is to buy a rundown property,  demolish and rebuild.   The local LPA is really only interested in supporting large developments in designated development villages. 
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If anyone wants to do their own research and draw their own conclusions on some of this then you could do better than start here. ...

 

http://hope.epfl.ch/

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How does the circulation of air via MVHR compare to the effects of convection? Of course in a PH you don't have the heating on (or it is a very low background heat through UFH) so there will be less convection happening than an ordinary house.

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@Sensus, this document http://www.ibp.fraunhofer.de/content/dam/ibp/de/documents/Publikationen/Fachzeitschriften/mold_growth_predictiontcm45-35017.pdf - if I underestand it correctly - states that below 60% RH probability of mould growth is close to 0. Also, it seems to imply humidity should stay quite high for 6 hours a day for the growth to actually occur. If (if!) this is correct than with MVHR our localised 100% RH after shower or kettle or washing will not last that long.

 

In my leaky house I actually hardly ever see RH below 60% between October and March. Right now I have 67% at 21.9C next to me with the window open and it is not going down. Yes, it is not healthy but there is nothing I can do about it. At least with better air tightness MVHR can help somewhat.

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There is currently an active thread over at the other place (Green Building Forum) on this subject, which references this paper:

 

https://www.researchgate.net/publication/268098972_Passive_Houses_What_May_Happen_When_Energy_Efficiency_Becomes_the_Only_Paradigm_CH-12-032

 

Quote

Passive Houses: What May Happen When Energy Efficiency Becomes the Only Paradigm (CH-12-032)

Conference Paper (PDF Available) · January 2012with59 Reads

Conference: ASHRAE 2012 Winter Conference
  • Hugo_Hens.png

 

Thread:http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14342&page=1

Edited by Ferdinand

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That's quite an old study that was discussed over at eBuild, JH referred to it quite a few times.

 

I don't agree with the title. Came down to poor installation of the underground duct.

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Condensation is an odd thing - RH is another. 

 

If you boil a kettle or use a shower you get a very dramatic rise in RH to the point of saturation UNLESS you are extracting the moisture at a rate that RH cannot be maintained. 

 

What normally occurs is that water vapour condenses on the first available surface and by capillary action - unless it is a sealed/tiled surface - the water is drawn into the material. Once in the material, the condensate has to evaporate which requires the latent heat to be sufficient to cause the vapourisation to happen - this is where your issues will lie as the temperature differential is not enough. As the material stays damp for a sufficient period and is usually moistened on a cyclical basis then you start to see why mould forms. 

 

Taking the points about airflow, unless you want to do a full 3D model of  room and understand it's fluid dynamics then most MVHR placement is just shy of borderline guesswork ... Extracts are regularly placed over or very near to hot spots for vapour generation, and yet this may not be the most suitable place for fully extracting from the room.  

 

I have a shower that has an extractor directly above it yet due to the shape of the cubicle we still get tiny patches of black mould appear on the silicone in the top corners - the extract is doing its job but fluid dynamics tells me there is a significant slow down in air flow from extraction, and this cannot compete with the secondary air flow caused by heat rising from the hot shower - I could increase the airflow but this would still only have an effect if I had a perfectly circular shower with an extract that was the same size and the tray was perforated to allow a linear airflow from below me - I would hazard a guess that 99% of showers are actually sealed at the base so in a practical situation the laws of fluid dynamics go out of the window ..! 

 

 

 

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8 minutes ago, PeterW said:

we still get tiny patches of black mould appear on the silicone in the top corners - the extract is doing its job but fluid dynamics tells me there is a significant slow down in air flow from extraction, and this cannot compete with the secondary air flow caused by heat rising from the hot shower 

 

Or, could you have 3D cold bridging in the corners causing a significant cold point that is below dew point for more of the time?

Edited by IanR

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Just now, IanR said:

While 

 

Or, could you have 3D cold bridging in the corners causing a significant cold point that is below dew point for more of the time?

 

Highly unlikely given the two outer walls are insulated - and internal - with 100mm rock wool and the loft sits above with over 400mm above an unventilated false ceiling. 

 

Computational fluid dynamics can show the flow in a box is not even and has significant "cold spots" where flow reduces - this is exacerbated at low flow rates so MVHR doesn't really stand much chance when it comes to ensuring a clean extract. 

 

I think there is a lot more science to this than the manufacturers and the "designers" of some of the systems want to admit to and they just don't understand it - or more likely can't make it understandable for Joe Public in a simple and effective way. 

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11 minutes ago, Sensus said:

 

All quite correct. But of course there's also quite a big gap (40%!) between 100% RH and 60% RH.

 

And at risk of becoming boring by repetition, it's not the mold we should be worrying about: the mold is just an unsightly indicator of the real problem, and the thresholds on that are not so clear-cut.

 

I know I will appear boring and yet : every single house I lived in so far had mould and smell and RH levels above 60%. And I can quite clearly see for myself that the house with (old) cavity insulation is better for us than the one without it which was in turn better than two with solid walls. So my point is somehow I am pretty certain I will be better of in the house with good insulation, good air-tightness and MVHR because on top of everything some people are indeed from Venus :-) and unfortunately my wife is not a big fun of open windows in October. And even open window does not help much on cold rainy day.

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32 minutes ago, Sensus said:

thermal mass

If you can't put a sensible unit on it, the term should not be used, ever.

There has been long discussions about this.:D

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22 minutes ago, Sensus said:

But once again I would repeat that health and wellbeing is not a simple matter of mold...and too dry can be just as harmful as too damp.

 

The big problem I have with PH is that (to achieve anything close to the predicted efficiency) it demands its occupants conform to the environment it creates.

 

I was always taught that my buildings should serve their occupants, not the other way around. :(

Honestly, I find it really, really hard to imagine a house in Britain that is too dry. Well, in the South East. I would be very curious to see one.

Also, again, it is not difficult to add moisture. Way easier, than to get rid of it.

 

 

These are the choices as I see them:

1) Air-tight (not necessarily PH) : one has all the tools to have comfortable life in such house - it is warm all year around and MVRH is there to for ventilation. One is free to open windows and/or put in humidifier if required. Also one is free to use the house, i.e. put furniture anywhere in the house not worrying about cold spots in the built-in wardrobe. 

2) Standard : one has nothing of any use apart from windows that may or may not help depending on season. Put your furniture next to the wall at your own risk because unless every single occupant is a fan of having open windows all day long AND during showers etc. you will get all the harmful stuff one of the obvious sign of which may be mould.

 

So... choose your poison. I know which one I prefer.

 

And which one of those would you call serving its occupants? But you clearly see different choices, don't you?

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10 minutes ago, Sensus said:

 

Yes, I currently (until we develop massively more sophisticated MVHR) see the choices as between diffuse and highly variable ventilation (at some cost in energy efficiency) versus heavily constrained and insufficiently diffuse ventilation (at a small cost in terms of energy efficiency).

 

Or to put it more concisely, as a choice between health and wellbeing of the occupants, versus energy efficiency and reduced bills.

 

I don't mind the use of MVHR as a supplementary system (and in conjunction with a proper heating system, that has the capacity and flexibility to allow occupants to rapidly adjust their envuronment), but that's contrary to the 'steady state', negligible energy input ethos/recipe of PassivHaus, and it's PassivHaus we're discussing here (notwithstanding the tangential forays into plotfinding, planning, the economics of room-in-roof construction and loft condensation! :D).

 

Surely it is a BALANCE not a choice since get varying amounts of both.

 

And the balance point needs to be adjustable e.g. Someone with asthma may prefer a different level of r.h. whilst someone with bad hay fever may want more heavily filtered air a la Saab.

 

Superinsulation means we start from heating bills of say 100 £££ a year rather than 600 £££.

 

Ferdinand

Edited by Ferdinand

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6 minutes ago, Sensus said:

 

Yes, I currently (until we develop massively more sophisticated MVHR) see the choices as between diffuse and highly variable ventilation (at some cost in energy efficiency) versus heavily constrained and insufficiently diffuse ventilation (at a small cost in terms of energy efficiency).

 

Or to put it more concisely, as a choice between health and wellbeing of the occupants, versus energy efficiency and reduced bills.

 

OK, then clearly a simple question. What standard does guarantee this health and well-being yet not makes occupants servants of their house? British, international, your own - anything you like.

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@oldkettle

 

I would define it as the ability of the occupants to create their desired environment, but tempered by reasonableness / practicality.

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3 minutes ago, Sensus said:

 

None, yet.

 

But building to current, basic building regulations with 'normal' levels of airtightness is potentially a better compromise than PassivHaus.

 

My personal (and professional) opinion is that PassivHaus is too far biased toward energy efficiency over occupant wellbeing.

Fair enough. I find it impossible to "defend" PH standard (which obviously does not need my defence) because I have not enough understanding of it, but since there is nothing do compare it with I personally have a winner :-) As a few people here said, there is no PH police. People are clearly free to setup their environment the way they like within the restrictions their building provides. I much prefer the limits set as high as possible because it is easy to lower them to any level. But this is just my choice and it does not matter because I can't have it in my current house anyway.

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11 minutes ago, Ferdinand said:

@oldkettle

 

I would define it as the ability of the occupants to create their desired environment, but tempered by reasonableness / practicality.

 

Sure, agreed :-) 

 

BTW, big fan of maintainability myself (both in SW and building tech). Still looking for a standard solution to have access to inter-floor space when laminate or cork floor is laid :-(

Edited by oldkettle

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If one were to build a leaky house on purpose, where would be the best place to put the leaks?

This is not an entirely facetious remark: my neighbour was complaining that his house has been built 'too airtight' and he is counting on the sparky and plumber making a few holes.

I find it hard to believe that these randomly placed holes are going to result in a better environment than a planned, active, ventilation system.

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PassivHaus Institut claims there to be 60,000 Certified buildings in use in 2016.

 

Checking the EU market, there were 880,000 Residential HRV units installed in 2015. Around 25% were localised/room only HRVs, with 75% being centralised systems. Germany, Austria, Switzerland being the more mature markets, UK expanding fast (double-digit growth), but lagging behind. 

 

Understandably HRV's are concentrated in Northern EU. [Non-heat recover ventilation units being nearly double the volume, but concentrated more to Southern EU.]

 

Hardly a small market.

 

There's a few sizable studies into MVHR/low energy homes/zero carbon homes that do detail MVHR issues with poorly maintained systems and lack of knowledge of occupants, but none suggest systemic/technology issues. However the one study that reports it, shows that even in houses with sub-optimal MVHR performance the air quality is better than the naturally ventilated houses in 80% of the those tested.

 

This is not a new technology, it is not even a niche technology. If there were inherent flaws in the technology the data would be there to demonstrate it. If it's available I'd like to see it so that I am better informed.

 

Without doubt there will be "local" issues with individual builds, there are too many variables for there not to be.

 

PH principles put occupant comfort at the centre of its strategy, along with energy efficiency and affordability. The PHPP software aids making the decisions and compromises that come into balancing those three competing requirements. Most telling though is that it also informs the heating requirements for a building. If it didn't accurately analyse the environment and predict the energy usage then those people relying on it to size the heating systems would find themselves with properties they were unable to heat sufficiently. If that were the case there would be quite a few of those 60,000 customers very understandably making their voices heard... But I don't hear them... I must assume the PHPP software to be relatively accurate. But why wouldn't it be, it's "only" physics after all.

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An article on a PH house overheating does not equal PHPP being unable to accurately predict solar gain. On the study I found and read regarding the block of housing association flats that were the subject of Telegraph story a while ago, it was not the tools at fault, but lack of experience from the PH Designers. There will be localised issues with any design/build process, mistakes happen.

 

PHPP however gives you the tools to predict and test solutions so that risks are reduced. It's to be applauded, not condemned.

 

Solar gain issues are present in many standard building regs builds. My current property, with it's room in roof, will regularly see 30 degrees in summer, when it's only mid-twenties outside. But nobody will have done any thermal modelling, so there's no one to blame.

Edited by IanR

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Well, it won't surprise many of you to hear that some of this thread has whistled well over my head, but I've read it all and I'm actually quite encouraged by that which I have understood. It seems likely to me, as so often is the case when opposing opinions are articulated, that the truth (in this case best practice) lies somewhere between the two, and that (hopefully) is just about where my build should end up.

 

The ambition for me was to create a house that delivers the best possible environment for my wife, rather than the most energy efficient possible. Her health problems include chronic asthma, eczema, severe allergies and bronchiectasis (a degenerative lung condition). Due to a very rare 'syndrome' she has no sweat glands, so rapid temperature/humidity swings play havoc (and not just with her asthma), and just to add insult to injury she is T2 Diabetic (despite weighing little over 6 stone) and has high blood pressure, reflux and osteoarthritis. 

 

As I set about researching the home I should build, air quality was, unsurprisingly, my main concern. Ebuild certainly informed my opinion, but I decided quite early that PH levels of air-tightness, insulation and energy efficiency were not for us. Yes we'll have a well insulated home; yes we'll have MVHR with F9 filtering (oversized so hopefully capable of more ACH than may be prescribed as we REALLY don't want to be opening windows); and yes we'll have it reasonably airtight (I'm aiming for around 2 and if we achieve better I may well engineer some 'leaks'). I don't expect the house will demand too much heat input from the UFH (driven by ASHP) but I'm quite happy to force a need for more by bypassing the MVHR unit's heat exchanger in winter (using the summer bypass, not by opening windows!) if that proves to help air circulation (due to the additional convection) and management of humidity levels. As for solar gain, I wait to see whether the SageGlass (electrochromic) glazing on the southern elevation proves to be as good as the manufacturer claims at regulating unwanted SG at warmer times of the year, whilst allowing us to benefit from it on sunny winter days. Finally, as we're building a chalet bungalow, it was a no-brainer to go with a warm roof throughout, even in the non-habitable spaces.

 

Time will tell whether the 'gut feeling' that has largely steered my decisions will provide the home that can give my wife the best environment for her wellbeing, but this thread has at least convinced me that I have a fighting chance.

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Go for good air tightness or you will let allergens in!

 

go for the good filters that you are planning, there will be a cost, change regularly.

 

go for a good air handler, Genvex and a good designer, Europeans seem better than here though there is a very good company here.

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9 hours ago, NSS said:

The ambition for me was to create a house that delivers the best possible environment for my wife, rather than the most energy efficient possible. Her health problems include chronic asthma, eczema, severe allergies and bronchiectasis (a degenerative lung condition). Due to a very rare 'syndrome' she has no sweat glands, so rapid temperature/humidity swings play havoc (and not just with her asthma), and just to add insult to injury she is T2 Diabetic (despite weighing little over 6 stone) and has high blood pressure, reflux and osteoarthritis. 

 

Hi NSS, my Wife like yours suffers from bronchiectasis, and has been on long courses of Antiobiotics many times over the past 4 years since it was diagnosed and although building our house wasn't a driver for a better standard of health we made sure that we could get a good flow of air via the MVHR to hopefully try and alleivate the chances of recuring chest infections.  The strange thing that we have found is that moving from our old house and into a draughty cold caravan and then into the new house, so far in the past 12 months their has not been one recurrence yet, whereas before every 6-9 months she would be on a course of antibiotics for 1-3 months or longer.  Our fingers are crossed that maybe there was something in the old house triggering it, or just the fact that quality of air in our new house is better but something had definitely improved the situation.

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An anecdote is not evidence, but my regular bouts of sinusitis stopped dead the moment we moved into the new house (which is 0.6ACH airtight with MVHR).  I'd had 2-5 attacks a year for the last 10-15 years, but haven't had a single one since moving into the new house a year ago.

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