I can't seem to find anything about supply air windows on the internet except the "Dwell Vent" website. When you follow the link to Howarth Timber, who are supposed to be making them, I can't find anything about them. What else do you know Tuna? What do you think of Bill Dunster's wind catcher things?

OK, so I design HRV for a living and so will not intrude in this thread for long... but I have to say something.

A cave is a natural home, everthing else is man made and hence there are compromises to make.

For those who say we have mild climate - try telling the huge number of elderly people who are losing their thermoregulatory ability or spend some time outside without your high tec fleeces'.

I do not care about those of us who can afford to build deep green homes (I work with straw bale builders for example and would happily live in one). I am more concerned with the vunerable, inner city poor who should have as a basic right decent homes that are easy to keep warm and have decent air quality.

HRV is not just about energy efficiency - it delivers reliable and consistent air quality with the added benefit of pollen filtration (etc) for those who need it (the near 50% of the population with allergies, including 1 in 7 children with allergic childhood asthma, many with grass pollen allergies). HRV systems have been proven to aleviate the sysmptoms of asthma sufferers (UNI Strathclyde, CEDAR centre)

Without mechanical intervention (complete or in support of a passive stack) then this relaibility is not easily achivable. Highly designed individual homes may be finely tuned, but the majority will not.

A good example is the fact (BRE 2006) that homes with trickle ventilation (ie wind and passive stack driven) with an average air leakage of n50=13 failed to achieve the required ventilation rates in 68% of homes tested (by accurate tracer gas analysis).

Of all ventilation options only HRV is fully designed for specific air flow rates to individual rooms (please correct if you know otherwise). Because it suffers little heat loss the ventilation rate is not constrained by this factor - meaning that HRV systems are designed for air quality.

Parisitic energy usage (fans) are an issue but even in the UK climate (say 1500 degree days) most systems will return a COP fo over 3 (Gas heating). Future generations of fans (later this year) are going to be so efficent this will not be an issue.

Supply air windows are an interesting concept, but there are still outstanding questions - such as what happens in summer and how do you match the optimum air flow rate (assuming you can control it) with the required ventilation rate?

If your supply air window is next to a road you will get pollution and nios directly. HRV systems should take air from a high level.

HRV system life - I recently inspected and repairs an 18 year old system that had only had filter replacements as its annual maintenence. Dusts were clear and clean and the home owner reported they had the only home in the estate without condesnation problems (apart from many people running de-humidifiers).

Air quality sensors - some HRV's have these built in (humidity and also CO2 etc, if required). This allows them to respond to occupancy. Part F does allow for demand control ventilation systems, based on air quality sensors. I do not know of any home designed this way but I do plan on doing it for my own home (Very low trickle rate with continuous air quality sensors).

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In defence of british builders - if we pay them enough and train them enough they will do the job - do not confuse them with developers; It is the exploitative nature of building in the UK that has ingrained bad attitutes in many builders.

The only way we will improve the situation it to regulate both the installation (improved building regulations and many more inspectors) and insist on maintenence regimes to be incorporated into the Home Information Packs...

Not just Finnish
http://www.biffvernon.freeserve.co.uk/air_flow_windows.htm

The point is not that MVHR systems don't work well in the UK climate, but that may not work as advertised when rolled out to 250,000 new homes each year. Paul T's "vulnerable inner city poor" are frankly unlikely to be living in homes which would be airtight enough to benefit from MVHR: it only makes sense in new housing or extensively refurbished housing and people that live in such homes are unlikely to be vulnerable, almost by definition (though they may be poor).

No what worries me is that if MV is rolled out on an industrial scale, it won't be looked after, it will break down, no one will repair it, it will be turned of in summer and never put back on in winter. In the worst cases, the units will be sabotaged or nicked and sold on. The airtight house model depends on there being a fully functioning MV system in place. What happens when it breaks down?

Posted By: Mark BrinkleyNo what worries me is that if MV is rolled out on an industrial scale, it won't be looked after, it will break down, no one will repair it, it will be turned of in summer and never put back on in winter. In the worst cases, the units will be sabotaged or nicked and sold on.

Tackling your last point first about the units being "nicked or sold on". Are you serious? What would the market me for such units if, in your pessimistic view, people aren't using them? There are no valuable parts contained within (no copper for example). If you think that's a problem in the UK, then the UK has some fundamental issues beyond fossil fuel poverty.

As for the turning off in the summer and never being turned on, this is easily solved by linking the MHRV to the heating system. Ours is controlled by a humidistat but is essentially "on" year round. We don't even touch the controls, though have set the humidistat such that we increased winter humidity levels since dryness is a problem in a cold climate. In the summer it doesn't matter if it runs or not since, gasp, the windows are sometimes open on those days when it's cool enough to open them - of which there are a lot in the UK.

As for the repair, it's no different than servicing a heating appliance. Some people won't do it and there's nothing you can do about that - after all, people still die of CO poisoning. As I've mentioned already, maintenance is trivially simple.

Finally, for flow rates, they're not critical. Balanced is best, of course, but as long as there isn't serious depressurization then there's really no problem. I'll leave it as an exercise for the reader to figure out why depressurization is more important than over pressurization.

Paul in Montreal.

Posted By: Mark BrinkleyIf they become mandatory in all new homes, then there will be a healthy resale market for the units, in order to get a new building finalled. Rather like what used to happen with the automatic door closers needed to get the fire rating and removed once the building inspector had issued the completion notice.

Mark,

if you gave this a moment's thought you'd realize how ridiculous your assertion is. Have you ever seen a HRV? Any idea how it's installed? It is installed either in the basement (over here where we have basements) or, more likely in the UK, in the attic. It is not something small and visible like a door closer that can easily be removed. The cost of an HRV is pretty small too - equivalent, say, to a window. I fail to see how there could be a resale market since you're also implying that people in the UK wouldn't want them anyway. It is not something that is trivial to retrofit so I really can't understand what this mythical resale market is.

Your whole tone suggests that people in the UK are too stupid to operate and maintain such devices. I'm sure similar statements were made about central heating systems 40 years go. People in Canada are no brighter than people in the UK but I've never heard anyone here suggest not installing a HRV because it might be difficult to maintain or operate. They are very simple devices with little to go wrong. Even if one failed and wasn't noticed for several weeks, there is little chance of damage. Regularly scheduled maintenance at the start of the heating season is all that's required. This is true of all gas boilers anyway - it would be trivial to do both at the same time.

Are you suggesting it's better in the UK not to even try to "build tight, ventilate right"? Remember when smoke detectors were first installed? There were many public awareness campaigns of the need to change the batteries annually. Education is the key (both for the architects and builders in the first place and the end users). Your tone just sounds like defeatism. People like you are key to the education process - I think you should step up to the plate rather than down.

Paul in Montreal.

Can temporary sub-optimal levels of ventilation be mitigated through the use of naturally hygroscopic materials like un-fired earth and untreated timber? Internal air quality can also be improved by plants.

Air quality can only be improved by plants in that they can remove CO2 add O2 and water. They do not remove pollutants and in many cases add VOCs

Natural materials can buffer moisture in the internal air and some breathing walls can remove it and send it outside but in moderation ( not when there are problems)

Plants are nice inside buildings but so is fresh air

I cannot understand our resistance to MHRV it is like breathing fresh out door air all the time but at indoor temperatures

That is a mighty big if. If I were you I would fit the ducting just in case.

For block quotes, you should select the "html" button in the "format comments as ..." section below.

Paul.
p.s. you can go back and edit your posts and then select that button and it will fix everything up

PaulT, we considered HRV for our refurb but after much humming and haring (spelling?) dismissed it for a number of reasons among them that we live close enough to the sea for salt air to scorch leaves and corrode most metals in just a few months, I assumed that this aggressive atmosphere would have a similar effect on the heat exchanger? I know that systems include filters but would they cope with a very coastal environment?

Mark S,

I assume you are referring to the systems where they add an electric post-heater onto the incoming ducting, in effect a warm air heating system. That was what I witnessed in Hanover during the BRE's PassivHaus study tour this time last year. I guess in that situation you would have a useful failsafe to ensure that the MVHR unit was serviced. But is PH so prescriptive that you have to heat in such a way? Is this indeed the future?

Mark B,
PH is not so prescriptive per-se but for the most economic solution this is the ideal. Elec resistance heating was used in one PH when I went on the BRE PH tour (no. 2). The rest albeit larger schemes used wood pellets and district heating. Gas, with hydronic feed to post-heater distribution, and compact heating units (incorporating heat pumps and MVHR) are the best low carbon option that I'm aware of. Is it the future; it is one possible future.

Mark

Bowman - good point about sea air; We use electrostatic pre-filters which should help. Also the plastic cores should not corrode and are washable, salt being disolvable. We are installing a system in Filey and will ask if we can monitor the situation.

Biff - sorry I have spec'd French Oak windows with shuters (as complete units) - These will perform better than triple glazing. the shutters will be mechanic, yet another system(!), but will allow me to use the central controller to adjust solar gain and heat losses automaticaly (OK, not practical for most, but I am developing a luxury version of an ECO home as a demonstration of what can be done).

I think the most important point to make is that PassivHaus does not mean Passive House!

The German is a proven engineering solution. They have built a proven conceptual model that works, although it is not problem free and may need adjusting for the UK climate. the ventilation rate is a good example, in Germany they use a lower ventilation rate as the Climate is much drier in winter; This is also the case in Canada where the the rate is 0.4 ach (?). (UK 0.5)

When considering ventilation though, a word of warning - we have just about the smallest homes in the 'Western developed world' (new builds around 70m2, 1920 UK 100m2 +, progress?). This means that the air resevoir is smaller and, combined with a humid climate there is greater risk of air quality problems.

Heating - the electric air heater is more amatter of convenience and cost; If you already have a distribution system why bother? Well, you lose the ability to heat zones to different temperatures, so if the bathroom is 'cold' (consider thermal comfort when getting out of the shower) the whole house gets heated to a higher temperature. This is a good example of diminishing returns - in super insulated home the thermostat gets turned up.

My approach will still be to fit an underfloor perimeter heating loop and wire up bathrooms, etc; cheap(er) to do now than regret it later.

Posted By: Chris WardleAre individual personal preferences and aspirations legitimate reasons for adopting solutions that might be considered sub-optimal from an energy efficiency point of view?

Certainly if they are NOT sub optimal from an energy efficiency point of view!

But even if they are?