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    • #31715
      Robert Prewett
      Participant

        I am looking to install an MEV system for a client as part of a retrofit project (project description below).
        While MVHR components and help are now relatively easy to come by, I wondered if anyone had experience of procuring MEV components. A number of manufactures produce the 'box' and have fan power rating that look attractive (0.35 W/l/s). Ducting from lindab is easy.
        But how about inlet grills fro walls. W Feist recently showed some damped ones as used in Sweden. Does anyone know where I might find them?
        Allowing air in through window trickle vents is not adjustable, and the existing triple glazing does not have any. Besides I hate trickle vents both for their looks and their poor build quality.
        The 2 story house about 320m3 is well insulated and will soon be triple glazed all round.
        Subject to testing I suspect we may hit air tightness is about 3ach at 50pa, so in that ‘no mans land’, where MVHR is not worth it but air quality may be an issue if we continue to rely on infiltration.
        The house suffers with some condensation problems in the kitchen dining space – due to a combination of less than perfect glazing bars on a rooflight and assumed low ventilation rates. The future work will tend to worsen this effect- hence the choice of an MEV system.
        Any experience or pearls of wisdom welcome!

      • #38631
        Mark Siddall
        Participant

          Bob,
          A good question to which I have no answer. I too would be interested to hear about peoples experience on MEV and the procurement of suitable components. (Like you it strikes me that MEV will be suited to many retrofits that are not going to achieve the standards of airtightness that could warrant MVHR).

          ….my biggest worry is causing drafts that could the lead to discomfort and turning down/off the MEV (and then poor IAQ and the damp issues that you mention.)

          At what standard of airtightness should one consider providing inlets and dampers? Can MEV not work off the 'leaky' (3ach@50pa) building? How much open area do you need to adequate ventilation? (I suspect that putting to many new holes in the building – albeit controlled – could undermine some of the benefits of MEV.)

          Mark

        • #38632
          Nick Grant
          Participant

            Bob

            I have emailed you a brochure on vents designed for MEV but have not used them. FrischLuftKomfort might show up in Google.

            Unless Alan or others disagree, I'd be with Mark on pulling the air thru' the fabric, need a few Pa resistance so that wind and stack don't dominate.

            Nick

          • #38633
            Tom Foster
            Participant

              Interesting, about deliberately pulling thro the fabric in a not-perfectly airtight house – makes sense.

              However, for such a situation, I've been considering some German trickle vents whose name I can't recall just now, but used in Prince Charles' eco-demo house at BRE – these are humidity controlled, seem high quality so shd seal well when not activated by humidity. If the MEV is also humidity activated, they should work in tandem, on the principle that humidity level is a reliable proxy/indicator also for CO2, pongs and toxins that need venting.

              Consider instead of MEV, natural stack ventilation, with room-extract grilles humidity activated – in fact that was what I've been intending to couple with the German trickle vents. The project is just out to tender, so need to settle this one.

            • #38634
              Robert Prewett
              Participant

                Tom,
                I'd be interested to know about the German inlets on the Princes house if you can dig that out.

                Bob

              • #38635

                I'd try to get components from Sweden where MEV was compulsory in new construction 35 yrs ago

              • #38636
                Anonymous

                  Hi All,

                  I'd be reluctant to reply on ventilating bedrooms through fabric leaks. In my experience fabric leaks are unexpected and can be anywhere. For example draw in to the airing cupboard from betweent the floors due to leaky joist ends. If the a bedroom has been refurbished new skirting boards and maybe fitted carpert, the line of least resistance will be where all the pipes go through the floor.

                  Fundimentally my point is that good and reliable ventilation in bedrooms is important to comfort and well being.

                  Andrew

                • #38637
                  Alan Clarke
                  Participant

                    Bob
                    does your building control officer have a view? Ours does on similar project and they are insisting on 2500mm2 of vent per habitable room. I estimate with a test result of 3ach@50Pa (not yet achieved) that the deliberate vents will only provide 20% of the total leakage area, so will be of limited use in ensuring that ventilation ends up where you think you want it.

                    Plan A had refurbishment of Victorian sash windows with vacuum double glazing – these would have provided air inlets to each room without trickle vents. Plan B has secondary glazing and old windows untouched – I'm thinking we could put controllable trickle vents just in the secondary glazing, maybe keeping both BCO and conservation officer (house is listed) happy?

                    Note in this house we are using decentralised continuous extract – full ductwork distribution wasn't compatible with retaining historic fabric – should work just as well, and has potential benefit that main bathroom can be boosted whilst guest bathroom stays at lower vent rate.

                    Alan

                  • #38638
                    Alan Clarke
                    Participant

                      I have emailed you a brochure on vents designed for MEV but have not used them. FrischLuftKomfort might show up in Google.

                      Nick

                      Is this brochure from Lunos? http://www.lunos.de/

                    • #38639
                      Paul Mallion
                      Participant

                        Passivent do a range of trickle vents with dampers and internal controls. Can't vouch for quality, they were going to run a training event for the Kent AECB but pulled out last minute, chickens. Speak to your local rep to the right spec, as the base models don't have dampers, you need to spec the wind resistant non squeaking non flappy acoustic damper.

                        On a related subject, can anyone confirm the ventilation requirements for an internal gas meter? I am getting conflicting advice, gas regs state vent meter cupboard to exterior with 0.5m2 opening, but this is not good for airtightness. House will have MEV, but not sure how airtight it may be.

                      • #38640
                        Mark Siddall
                        Participant

                          Peter,
                          I've been reading a PhD on indoor air quality in New Zealand homes; the standard house type is a bungalow. The studies undertaken suggest that PSV does not work as there is not enough stack. Wind is the dominant driver of air changes. The PhD quite clearly showed that

                          1) More than 1.25 ach/hr is required to maintain IAQ when using natural ventilation options; and even then it is not ideal. These findings were supported by on site measurements in a number of homes throughout the country. (In the study, for the passive stack option, between 80,000mm2 and 105,000mm2 of trickle vent and stack ventilator were required dependent upon local climate.)
                          2) Unheated naturally ventilated bedrooms suffer from even less ideal IAQ as stack effect is not suitably exploited.
                          2) When using MEV or MVHR it is benefitial to have improved airtightness. The study examined airtightness standards down to an n50 of 1 ac/h. As airtightness improved so did the effectiveness of the ventilation strategy. Under this scenario 7.5l/s (0.5 ac/h) proved acceptable.
                          3) between MEV and MVHR, MVHR – as balanced ventilation – displayed the best opportunity for ventilation effectiveness (regardless of airtightness.)
                          4) MEV trickle vent area for the house was 15,400 mm2. 100m2 3 bed home. This was maintained for all airtightness options ranging between an n50 of 1 and 6.5.

                          Whilst demand led scenarios were not explored in the PhD I hope that this is of assistance.

                        • #38641
                          Mark Siddall
                          Participant

                            Alan/Nick,
                            I've been looking over the Lunos website. The Lunotherm unit looks pretty good http://www.lunos.de/?page_id=282&lang=en The advantages is that, with it being a through the wall unit, air flows can be measured more easily. The challenge with this unit could be, in some cases, that it has been designed for external insulation.

                            The challenge with trickle vent supply (say http://www.aereco.co.uk/products/air-inlets) is that finding a hood that can go over.

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