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    • CommentAuthornbishara
    • CommentTimeMar 21st 2012
     
    Hi all,

    I've just had two days at Ecobuild and, as usual, it was great, but my head is fried. I went to source MHRV. I knew that my solid walled 1925 semi wasn't really as such air tight, but I reckoned that I'd improve it over time (EWI with parge coat, intello etc) and as I did so, the MHRV would become more effective.

    The reason that I'm ventilation shopping was that, as discussed on a previous thread, I've got real issues with high humidity (65-70%), mould and respiratory problems (GP thinks I now have asthma so I really need to do something about it asap). Everyone's helpful contributions made me realise just how urgent ventilation was and one or two people's positive experiences of MHRV dealing with mould, made me think that it would do the trick.

    However, I spoke to an architect I really respect at the show and he pointed out that unless I'm lower than 1 airchange per hour at 50 pascals etc etc, installing MHRV is likely to overventilate the house and I'll lose more heat than i need. He thought that Postive input ventilation was bad because the humid air then has to go through the fabric of your house, with the comcommittent danger of condensation. He therefore recommended mechanical extract ventilation.

    I talked to a lot of reps flogging ventilation kit. TBH, a lot of them were either lying or ignorant ("You don't need your house to be airtight for mhrv"), although I will give a special mention to the woman at Envirovent who really seemed to know her stuff and was happy to explain the concepts behind PIV. I now have an inner database of ventilation possibilities.

    What I'd really appreciate is some guidance on what I should do now and whether I've understood the relative merits and demerits of various possibilities correctly. This is my summary so far...


    MHRV

    Pros: heat recovery
    Cons: may over ventilate your house if not sufficiently airtight; hassle & expense of retrofit; expense of buying; expense of running 24/7 (although I think you'd turn off in summer)

    MEV
    Pros: gets rid of humid air
    Cons: gets rid of heat; offends my energy conscious soul;designed to be always on (?); hassle & expense of retrofit

    DEV (Demand Extract Ventilation)
    Pros: gets rid of humid air, less ducting and hassle, I think. Only on when you need it. Liked the German study apparently demonstrating that was more cost effective than MHRV because it wasn't on all the time (although I haven't read the paper and if I haven't read something properly, I'm a bit sceptical)
    Cons: gets rid of heat; sounds possibly overly complicated

    Single Room Heat Recovery
    Pros: heat recovery! no ducting hassle or expense
    Cons: not convinced it works; surely must have same issues as whole house MHRV in terms of airtightness?
    I found an interesting Ukrainian model, with a ceramic core, that didn't have a heat exchanger as such, but expelled the air through the core for 70s and then took air from outside through the same core for 70s. Somehow I quite liked this idea, until I saw the line that the core "moistened", as well as warmed the air. Great for continental climates that can be very dry in winter, but not so great when you're trying to get rid of the humidity.

    Positive Input Ventilation
    Pros: relatively inexpensive to buy; looked pretty simple to fit; used on a lot of social housing properties with condensation and damp to great effect. Liked the idea that you'd benefit a bit from the somewhat warmer air in the loft (although as you reduce air loss from the warm rooms below and increase your insulation, the air up there will be colder). I did wonder whether heating element might not be totally mad either- because when it's sunny in winter, I could "subsidise" from pv, depending on wattage; although I'm mindful that air isn't a great heating medium in this context & this would only work during the daytime, when I'm usually out.
    Cons: On all the time; cold(ish) air coming in to house. I do worry about what the Architect said about moisture and the fabric of the house - where does all that damp air go? It can't just dematerialise! Will this be more of a problem as I increase air tightness or should I just give up on that?

    Positive Input Ventilation with solar warming
    This was a variant one of the major manufacturers do, which reminded me somewhat of the solar venti. Essentially you put a couple of solar air panels on your south facing roof; the PIV then takes from either those (when they're warm enough) and from the loft when they're not (you can also get a version with a take on the N facing roof for summer cooling; bit optimistic imho)
    Pros: nice energy saving concept; no complicated ducting in house
    Cons: reading between the lines, I got the impression that it might not be that effective (although Solar venti appear to get great reviews for their single room version). It's pretty pricey too - and you need sufficient and appropriately orientated roof space.

    Finally....

    Good old fashioned single room extraction
    Pros: been used for years; quick response to humid air in kitchen/bathroom before it gets a chance to go elsewhere; only on when you need it.
    Cons: I'm not sure it would help my high humidity in my bedroom (both my kitchen and bathroom are downstairs, with a room inbetween them and the stairs. I don't have enough wall in the bathroom to mount an extractor fan and would have to do something interesting with ducting and the roof (it is only a single storey though).

    So....what have I misunderstood/what have I missed out/ what should I do?! I should add that I don't have trickle vents on my dg and I have no extraction in my bathroom or kitchen. Hell, I don't even have a letter box I've been so paranoid about air infiltration ;-)

    Thoughts and advice very gratefully recieved; tbh, I'm freaked out by the asthma thing which I am pretty confident is because of the damp and mould so I need to decide and act.

    Thanks,

    Tania
  1.  
    Hi Tania, is the house kept pretty cold? If so then you can expect higher RH levels, also have you completely ruled out that the cause is not a defect somewhere in the building (leaking pipework etc) - is there excessive moisture in any particular location? In the type of house you describe then single extract fan in kitchen/bathroom should be all that is needed to avoid damp and mould, keep the heat at reasonable levels elsewhere and problem should be sorted. Think about insulating sooner rather than later to keep fabric temps up.
    • CommentAuthordocmartin
    • CommentTimeMar 21st 2012
     
    Tania,
    Willie.Mcleod's comment is echoing what others have pointed out about heat input on your original other thread. Have you already done that and has it helped?
    Martin.
    •  
      CommentAuthorSteamyTea
    • CommentTimeMar 22nd 2012
     
    Posted By: nbisharaSo....what have I misunderstood/what have I missed out/ what should I do?! I should add that I don't have trickle vents on my dg and I have no extraction in my bathroom or kitchen. Hell, I don't even have a letter box I've been so paranoid about air infiltration ;-)

    Start thinking about getting your airtighness sorted, you can always open a window. This is a must for any 'controlled' ventilation.
    As for the technologies, there are really only two, ones without heat recovery and ones with. The whole humidity/temperature/CO2 nonsense is purely a matter of when it is on or off. Say you have a high humidity, the unit switches on, it will lower the temperature and the CO2, end off (unless you have a bonfire being fanned).

    Now think of the easiest and cheapest way to install a whole hows ventilation system.
    There is no magic bullet, we all dream of something the size of a matchbox that will do anything we want, physics is just not like that. You have to move air, so it needs a fan, you want to get heat back, so you need an exchanger, you want to control it, you need a controller, all the rest is detail and that is particular to your property.
    Simple really, get the credit card out.:wink:
    • CommentAuthorEd Davies
    • CommentTimeMar 22nd 2012
     
    Posted By: nbisharaI found an interesting Ukrainian model, with a ceramic core, that didn't have a heat exchanger as such, but expelled the air through the core for 70s and then took air from outside through the same core for 70s. Somehow I quite liked this idea, until I saw the line that the core "moistened", as well as warmed the air. Great for continental climates that can be very dry in winter, but not so great when you're trying to get rid of the humidity.


    Wouldn't blowing incoming air over a moist warm-to-tepid ceramic core be a recipe for spreading mould?
  2.  
    Posted By: nbisharaPositive Input Ventilation
    Cons: On all the time; cold(ish) air coming in to house. I do worry about what the Architect said about moisture and the fabric of the house - where does all that damp air go? It can't just dematerialise! Will this be more of a problem as I increase air tightness or should I just give up on that?
    Don't assume that architects know about building services, in my experience, very few do. Even if you rely on "natural" air leakage, the air will leak in through some holes (usually low down) & leak out through other (usually high up). The whole point is that it is entirely uncontrolled & so liable to cause condensation in the fabric!

    Positive Input Ventilation needs a defined output path. Usually this is achieved by putting trickle vents over some of the windows. These can be humidity sensitive vents, so the more humid rooms automatically get more of the air because they provide a lower resistance path to the outside.

    Posted By: nbisharaPositive Input Ventilation with solar warming
    A good option if you have a south facing roof & live in a place that gets winter sun. Don't worry about it only heating during the day. Remember that removing moisture requires heat as well as ventilation & there are very few truly renewable sources of energy that you can just turn on when you want them, like a gas boiler. It will still help to take the chill out of the house, keep it dry 24x7 & make it easier to heat when you get home.

    David
    • CommentAuthornbishara
    • CommentTimeMar 22nd 2012
     
    <blockquote><cite>Posted By: Ed Davies</cite><blockquote><cite>Posted By: nbishara</cite>I found an interesting Ukrainian model, with a ceramic core, that didn't have a heat exchanger as such, but expelled the air through the core for 70s and then took air from outside through the same core for 70s. Somehow I quite liked this idea, until I saw the line that the core "moistened", as well as warmed the air. Great for continental climates that can be very dry in winter, but not so great when you're trying to get rid of the humidity.</blockquote>

    Wouldn't blowing incoming air over a moist warm-to-tepid ceramic core be a recipe for spreading mould?</blockquote>

    Yeah, I had that thought, too; shame, quite liked the idea for a while.

    Loved steamy tea's matchbox - yep, I just need to get to the point where I can accept the non existence of it (& cheap effective heat pumps, Ewi, triple glazing etc etc ;-) and whip out the visa to get a reasonable compromise

    And Doc, absolutely agree; I've been under heating and I have tried to remedy that & been running the dehumidifer a lot more. You've made me realise that it didn't help recently that my ch wasn't working for over a week, despite my best efforts to get it fixed. I will Ewi in the future, but it's fairly obvious that I need to address ventilation now (and as I've yet to find an Ewi installer I'd trust, I think I need to do the ventilation first)
    • CommentAuthornbishara
    • CommentTimeMar 22nd 2012
     
    Positive Input Ventilation needs a defined output path. Usually this is achieved by putting trickle vents over some of the windows. These can be humidity sensitive vents, so the more humid rooms automatically get more of the air because they provide a lower resistance path to the outside.

    Ha! Thanks for that David, that really makes sense to me & addresses the architect's concern; all the piv companies seem to assume that it's going to dematerialise !
    • CommentAuthorwookey
    • CommentTimeMar 26th 2012
     
    One option is the passive (or active) ventilation with controlled vents that Aereco do. This is actually quite clever and looks almost like a low-energy system that could work. Humidity-controlled vents that are entirely passive, then a constant-pressure fan so it stops if the vents are all closed. I guess that's MEV, but 'clever MEV'. Ah, I see that's what you called 'Demand controlled ventilation'. Didn't seem overcomplicated to me. No idea if it works better than HRV or not. 'It depends', probably.

    Why will MHRV over-ventilate if your house is not tight enough? If you have a model with separately controllable input and output speeds you should be able to allow for quite a lot of 'excess' air. The catch is that you lose exchanger efficiency because some fraction of the air isn't coming in that way, but I don't see how you get 'too much' ventilation (unless airtightness is terrible)
    • CommentAuthorjms452
    • CommentTimeMar 27th 2012
     
    Posted By: wookeyWhy will MHRV over-ventilate if your house is not tight enough? If you have a model with separately controllable input and output speeds you should be able to allow for quite a lot of 'excess' air. The catch is that you lose exchanger efficiency because some fraction of the air isn't coming in that way, but I don't see how you get 'too much' ventilation (unless airtightness is terrible)


    I agree - The over ventilation argument seems to me a theoretical one - i.e. if you have black mould growing on your walls due to high internal humidity it doesn't seem like you are over ventilating!

    That said, in your case where you already have mechanical ventilation, I would suggest getting your PIV working well (with defined extract paths) as will be hugely cheaper than MVHR.
    • CommentAuthorTimSmall
    • CommentTimeMar 27th 2012
     
    I don't think there's any one correct answer, a lot of it depends on the shape of your house.

    Having tried out various other solutions, I believe a couple of the bigger eco retrofit organisations now routinely use one or two single room MVHR units (I have some personal experience of them too, and they really do work), e.g. one in the bathroom, and one in the kitchen,

    Maybe consider the Envirovent Retrovent, or (if you have deeper pockets) Viking House's unit. Both are intelligent designs with high efficiency exchangers, and which respond to the conditions where they are installed, and use little energy (and produce little noise) when lots of ventilation isn't needed.

    If you haven't done-so already, get some cheap (£10 or less) humidity meters and scatter them around the place. If you're not sure about the single room MVHR, then just fit one to start off with, and see how much difference it makes.

    BTW, I've also fitted a couple of whole house MVHRs too, but think I'd still recommend the single room MVHRs in most situations.
    •  
      CommentAuthorCitrus
    • CommentTimeMar 30th 2012
     
    That's interesting to hear, as I'm looking at trying to increase ventilation in a 4-storey house with no loft, and the thought of trying to squeeze whole-house MVHR in as a retrofit was terrifying. We'll be working on air tightness first, but as we know the house has damp issues it seems worth fitting single room MVHR to help in the meantime, and possibly long-term if it seems to be doing the job.
  3.  
    I am interested in this thread as I just bought a 1950s ex council house concrete-block cavity wall, rendered (gable end mock stone face on the concrete blocks) which no one wanted to buy probably because of patches of mould on the walls owing to condensation. (Double-glazed, no active ventilation in kitchen or bathroom). I am now thinking of installing single roome HRV systems to address the problem but need to know more about the detailed way they work. I was a bit concerned that the units may recover heat when it may not actually be needed. Sorry I am hazy on detail, and need to do more research, but I gather the units are factory set to recover heat when the outside ambient temperature is a certain level and it sounded to me quite high. I am the sort of person that has to have the bedroom window partly open even if it is minus six outside. Any pearls of wisdom to help me consider this approach would be helpful. It also seems like most of the houses in this area have a similar problem, as occupants don't understand the issues of moisture and condensation. My next door neighbour has a horrendous problem with mould growing indoors. I am hoping I may be able to show people round here what they need to do.
    •  
      CommentAuthorDamonHD
    • CommentTimeApr 17th 2012
     
    As to "the units may recover heat when it may not actually be needed" you can always turn them off and open a window.

    With my new bathroom MHRV when it is warmer outside we do just that; on the recent cold days it helps keep the internal temperature up and we turned the central heating off at the end of last month.

    Rgds

    Damon
  4.  
    Posted By: suegreenbuildingI am the sort of person that has to have the bedroom window partly open even if it is minus six outside.
    This is probably because the internal air quality is poor due to insufficient ventilation & this is the only way you can stop it feeling "stuffy". If you get the ventilation sorted then you probably won't need to open the windows as much & you can just enjoy the warmer temperatures. That said, there are a number of MVHR units which have a programmable summer bypass, but I've not seen it on a single room unit.

    David
  5.  
    If I can turn it off then that is fine. Thanks all for your comments.
    •  
      CommentAuthorjoe90
    • CommentTimeApr 22nd 2012
     
    Is it not possible for a controller for MVHR to only switch it on if the air is "bad" (CO2/RH) so if you open a window or simply by using the house, doors open etc the MVHR does not come on. This is surely "green" as it does not waste power running the unit when its not required?
    • CommentAuthorGaryB
    • CommentTimeApr 22nd 2012
     
    Joe90:

    The Vortice Prometeo range has automatic CO2 and RH boost function. There may be other systems out there with similar controls - if not, you can add an RH sensor in the duct (CO2 sensors tend to be too expensive) to boost the vent rate - we did this with Nuaire units on a 19 unit CSH Level 3 social housing project we designed.

    It will not turn itself off but the background ventilation and the boost ventilation rates can be set separately on the controller between 1% and 100% speed so there is no reason why you cannot set it up to give a trickle ventilation rate of 1% - except that Building Regs will require a minimum background vent rate for 'whole house' ventilation.

    If I had one in my own house I would certainly set it up in this way as there would be running cost savings when the house was unoccupied.
  6.  
    Posted By: joe90Is it not possible for a controller for MVHR to only switch it on if the air is "bad" (CO2/RH) so if you open a window or simply by using the house, doors open etc the MVHR does not come on. This is surely "green" as it does not waste power running the unit when its not required?


    Ventaxia do the following:

    http://www.vent-axia.com/range/sentinel-totus-demand-energy-recovery-ventilation

    It has heat recovery like a MHRV unit, but the vents only open when required - i.e. occupancy of a bathroom/toilet on the extract or the CO2/humidity levels of a bedroom on the supply.

    I have an old leaky house that I'm slowly sealing up, but it will never be airtight enough for MHRV, so this seems to be the ideal solution for us.

    Ouch! I've just seen the price!
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