A few months ago, I was in a meeting with Mark Davis, the civil servant in charge of the Zero Carbon consultation. He said, ‘In all the conversations I’ve had about Zero Carbon no one has ever protested that you can have too much energy efficiency!’ The people around the table laughed and nodded but I put my hand up to disagree and tried to make the following case:
Requiring extremely high levels of efficiency, such as currently proposed for the Zero Carbon definition, will also require the use of mechanical ventilation with heat recovery (MVHR). And this is potentially a very bad thing.
In a typical building, heat is lost in two ways: conduction through the building fabric and heat loss through air changes (i.e. warm stale air goes out and cold fresh air comes in).
You can reduce the conduction losses by adding more insulation. Easy peasy.
On the ventilation side, you can reduce losses by increasing the airtightness – but only up to a point. In a typical house, you need something like half an air change an hour or the space will begin to feel stuffy. Where there is insufficient ventilation, there is also a higher likelihood of mould growth and poor air quality. So you can make your house super airtight but people will still need fresh air.
One way to reduce heat loss through air changes is by using MVHR ventilate the house, catching the heat in the outgoing air and transferring it to the incoming fresh air. This type of system can work very well. So well, in fact, that in a well designed house you can do away with your boiler and wet heating system altogether and replace it with a small heating coil in the ventilation system. And that’s exactly what the passivhaus strategy is based on.
The standard of efficiency proposed for all homes from 2016 is so high that you can’t get there just by adding more insulation. You have to use MVHR.
But living in a passivhaus isn’t for everyone. In the government report on low carbon building standards for Scotland, the authors noted:
Although having many examples of ‘PassivHaus’ (2,500 in total) in his own country, one of our European members was most insistent that you could not impose ‘PassivHaus’ living habits on home owners and occupiers. The main issue associated with ‘PassivHaus’ is that to realise the enhanced energy performance and to avoid mould growth arising from condensation, the occupants must be prepared to adjust their lifestyle to rely solely on mechanical ventilation with heat recovery (MVHR), including frequent changes of filters and the associated running costs. In his country there was significant subsidy for those who elected to build and occupy such houses, but most importantly these people had made the decision themselves and had not been forced to live this way through regulation.
Hat tip to House 2.0.
The responsibility and level of awareness required to properly drive a passivhaus shouldn’t be underestimated. As Michael Willoughby noted on a recent visit to a passivhaus in Frankfurt:
And then there was all that kit in the basement housed in a room larger than my kitchen. What was it all? Could your average homeowner drive a property with all those pipes and dials? Perhaps Germans weren’t to be trusted either; there was talk of guying the system so inhabitants thought they had turned off the ventilation while nothing much had happened at all.
Oh dear.
I think we can say with certainty that before we take the step of requiring every new home to install MVHR from 2016, we need to ask people whether they’re willing to live in this way. Because if they’re not (and my strong suspicion is most people won’t be), they will simply open the windows – wiping out the benefits of MVHR and creating heat demands that the system can’t cope with. Or worse, they’ll live in a mouldy sealed box.
Can you have too much efficiency? Hell yes. And that’s just what we’ll have unless we make a strong case in the Zero Carbon consultation.
carbon limited 
Anyone know what ‘guying the system’ means?
I emailed Michael to ask and he says he meant to say “gaming”. I don’t know if that helps, but I think the gist is clear.
Great post. I have been thinking along these lines for some time, but you have nailed it.
I have written this up on my blog and added in some of my own thoughts on Passivhaus and the demands it places on occupants.
Sorry, I haven’t quite got the hang of this Trackback lark yet.
Cheers,
Chris
Passivhaus for not so passive occupants…
I would like to have attended the Passivhaus seminar at BRE Watford today, but I had other commitments I couldn’t change. I’ve been interested in Passivhaus since examining it as a possible starting point for the Welsh housing industry to meet the …
I’m very new to this so forgive me if this is a dumb question…
Would it not be possible to design an automated system to detect whether or not the internal environment of the house is becoming conducive to mould growth? e.g. measuring air humidity and the electrical conductivity of surfaces which are likely to attract condensation (a proxy for dampness) etc. If the system detects that mould growth is becoming likely then it alerts the users. If the users fail to act then the system would go into a fail-safe mode where, for example, the MHVR would automatically go into summer override mode (which I presume would reduce the chances of condensation building up in the MHVR unit) until the user changes the filter or gets the system serviced. Maybe modern MHVR units already do this?
Sure, it’s not a perfect solution and I agree that MHVR shouldn’t be forced onto unwilling people.
Very thought provoking – particularly as we are about to retro-fit an MVHR system as part of our renovation. Just a couple of points, from my limited understanding.
“the occupants must be prepared to adjust their lifestyle to rely solely on mechanical ventilation with heat recovery (MVHR), including frequent changes of filters and the associated running costs.”
Isn’t this similar to the adjustments that people have to make to live with other heating systems? e.g. the planning and conservation of heat required when working with Storage Heaters, or the regular (expensive) servicing and replacement of your Gas boiler? Or the regular sweeping of your chimney if you’re using more traditional methods? Sure this is a new system to most people in the UK, but once it is in widespread use people will build up the innate knowledge that we currently have for Central Heating, and wit will be no more difficult to use or service than our current systems.
The controls undoubtedly need to become as simple as those for Central Heating – although I saw a report recently saying that most people do not understand their Central Heating controls, so maybe that’s not a great aim!
Sometimes I put up a post and think, this will definitely get some comments, and then nothing happens. Other times, like with this post, I put something up expecting people to doze off halfway through and then lots of comments appear.
@Jack
I think some kind of alert for users could be a good idea and might help people avoid unhealthy conditions. But I don’t think it would help them to use the system properly in the first place. This leads on to…
@lepotager
…the next comment. I’m not sure I’d put MVHR in the same category as typical central heating. People are used to having a source of heat in their homes. As you hint, many people don’t use it in the way it was intended (e.g. cranking the thermostat to 30 when they want the heat on and turning it down to 10 when they’ve cooked themselves). But the boiler as a heat source is a pretty intuitive concept.
I think most people simply ignore their boilers and only notice their existence when they stop working. In my opinion, MVHR is a much greater leap in terms of how you use it, how often you must maintain it, and the consequences of ignoring it.
To my mind, the idea that people aren’t using their boiler controls properly only supports the argument that many people won’t use MVHR in the way engineers and manufacturers’ intend, especially if they didn’t ask for it in the first place.
On a side note:
It’s interesting that you’re using MVHR in a renovation. Was air tightness a concern? How have you guys approached it?
Two things leap to mind here.
1) We only got central heating ( and indoor toilets for that matter) in the last 50 years. We adapted. Most people wouldnt know how to build a coal fire these days, yet it was that or die of cold in the fifities.
2) Passivhaus may need MVHR for heating, but people can still open their windows. If no other house-wide heating system is provided, people will soon switch on to which windows they can leave open and when. I saw PH’s in Germany with the windows open in Feb, and still only using 40kWh/m2/yr- far less than current part L. And that was on biomass.
Basically, we can soon educate people in change- its only the Daily Mail that makes us think we cant- and they will get it.
Maintenance, on the other hand…….(I’m thinking smoke alarm batteries and cooker hood filters, here). I predict a phenomenon of millions of cases of IAQ related illnesses in A&E! Passivhaus will be the next smoking, or obesity!
[…] Bayley sums up the opportunity that passive offers, but raises the main problems with it: can we deliver the standard and will anyone want them? Both are considerable hurdles: the first supposes a “a quality of detailing hitherto unknown to our native builders” as Bayley put it. The second has been raised for some time, and was voiced by my parents-in-law whilst I was watching the programme at the weekend. There were fundamental misgivings about controlling the air supply of the interior of the house. Casey at Carbon Limited summed up this issues well in a post last week. […]
did anyone get to said BRE event? (http://www.bre.co.uk/eventdetails.jsp?id=2606)
This is what a senior product designer emailed to me:
I went to a very interesting seminar at the BRE in Watford yesterday re the German PassivHaus code being recommended by the BRE to be incorporated into the UK Building Regs for housing. Not sure if you had anyone there but it seemed like hot stuff to me.
The seminar was attended by a diverse set of people ranging from R&D boffins through UK house builders and architects and even UK glazing manufacturers to German manufacturers and agents (!)
We were asked to formulate written answers to questions prepared by BRE in response to the CLG carbon zero consultattion document. These answers are to be collated and submitted to CLG as the consensus view of the ‘voice of construction’. The whole thing smacked heavily of orchestration by BRE who have association with PassivHaus.
However, if that was the plan, it back-fired badly and the group reacted in the best of British ……. In fact the consensus reflected quite a radical position. Firstly, the relevance of the whole focus on carbon was challenged and effevctively replaced by energy efficiency and conservation. Carbon is after all a UK problem in a European context; not such an issue in other countries, eg. France with nuclear power. The general drift was that the C4SH should be redrafted (some suggested scrapped) to shift the onus for managing carbon and energy generation issues back to the energy producers and unburden designers and builders to allow them to focus on producing energy-efficient buildings. This actually supports the PassivHaus approach but sensibly, most people thought it should not be referenced by name and that any change to BRs should cite technical performance targets.
Interestingly, I gather the event (on Feb 19th event) was timed (on purpose or otherwise) to co-incide with an official Zero Carb Hub consultation nearby in Watford.
Thoughts?
@casey PS thanks for revealing to the whole world my shaky grasp of words that are real and words that are pretend, by the way.
In response to Casey’s very interesting comments re MHRV.
Try living in a house where it’s installed – absolutely the most comfortable living conditions you can imagine, especially if you’ve lived in any pre-70’s council house (probably applies to any house built pre-war as well!?)
– You don’t need to open windows in the winter, unless you’ve burnt the toast. Do you?
– Doesn’t really matter if you open a window in summer either
– It is very simple – not to be confused with the German Passivhaus/BMW/top of the range/fully loaded way of doing things
However, I do agree that anybody can, and will, turn it off because they don’t understand what it does, or perhaps, don’t really care. Perhaps passive ventilation can be the answer?
In my case, I’ve not told my partner where the switch is!
Interesting discussion. I think one mitigation, as Jason Hawkes points out, is that the windows *do* open, if you need to make the house leaky.
But if you think about it from the other side, the alternative to requiring mechanical ventilation is to leave holes in the envelope, meaning you can never get beyond a certain level of energy efficiency. I think PH has solved this, really, by making sure the windows still open. That is, you can have holes in your house, but you get to decide when they’re open or not.
BTW, my understanding is that the new California Energy Efficiency Building Code (aka “Title 24”) either requires or will implicitly require, due to other rules, mechanical ventilation in homes.
Casey – BTW, do you have other concerns about mechanical ventilation besides the “frequent changes of filters and the associated running costs” (where presumably running costs are significantly less than the costs of running the furnace/boiler that would have been there otherwise) and the acclimatization issues – getting used to not having to open the windows?
Do you think there are health issues or quality of life issues associated with MVHR?
Nils, I’ve been pondering your question for a few weeks now. I even started a blog post about it but didn’t finish. I think my issues come down to a few things.
I am concerned about people adapting to it, taking an interest in the systems, and making sure they use them properly.
But overall, it’s not MVHR but passivhaus I have a problem with. There’s been a lot of hype in the UK around this, with the editor of BSD asking if passivhaus is the answer to zero carbon. And it’s not! It’s just a route to very thermally efficient homes. You still have to deal with DHW and electricity (and the rest of your heat load).
Also the aim of excluding wet heating systems pushes developers down the electric heating route. Because of the higher carbon intensity of grid electricity, it emits almost 3x as much carbon as gas. So I’m concerned about that.
I think it’s a valid strategy and in the fantasy self-build I’m planning I would probably include MVHR. But, it’s fair to say, I’ve got issues.