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General: Trickle Vent Position

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    • CommentAuthorCX23882
    • CommentTimeJul 17th 2015 edited
     
    Hi,
    I'm planning to fit a PIV unit. Currently there are no trickle vents or wall vents, so I'm planning on fitting a trickle vent per window.

    I've attached a plan sketch of the bedroom, showing the door and window, with two positions marked A and B.

    Position A is where the opening casements are - a top opener and side opener below it.
    Position B is above the fixed pane, towards the corner.

    I was thinking that position B is optimal, being diagonally opposite the door, but position A is easier to fit (on the top opener), and being directly opposite the door, might offer less resistance.

    Does it make much difference where the trickle vents go, particularly with PIV?

    Thanks
    • CommentAuthortony
    • CommentTimeJul 17th 2015
     
    How rich are you? You will be a lot less rich blowing all that heat out of your house

    Best place for a trickle vent is in the bin.
    •  
      CommentAuthorfostertom
    • CommentTimeJul 17th 2015
     
    What's PIV?
    • CommentAuthorEd Davies
    • CommentTimeJul 17th 2015
     
    Various things. In this case I assume positive input ventilation.
    •  
      CommentAuthorfostertom
    • CommentTimeJul 18th 2015
     
    Or passive? Maybe it's a 'natural' vent system, which requires a definite inlet as well as drawing stuff out. In that case, something like trickle vents wd be necessary. You can get self-contained ones which only open when internal humidity rises.
    •  
      CommentAuthordjh
    • CommentTimeJul 18th 2015
     
    What's the advantage of PIV over MEV?
    • CommentAuthorEd Davies
    • CommentTimeJul 18th 2015
     
    Pretty sure it's usually “positive” rather than “passive”. If it was “passive” then it wouldn't just be “input”, surely?
    •  
      CommentAuthorfostertom
    • CommentTimeJul 18th 2015
     
    Where's the OP gone? (next question - what's OP?)
  9.  
    Organic pasta.
    • CommentAuthorTriassic
    • CommentTimeJul 19th 2015
     
    Ordinary Portland?
    • CommentAuthorCX23882
    • CommentTimeJul 19th 2015 edited
     
    Yes, Positive Input Ventilation. It's just for background ventilation. The inlet goes in a central location, but the air needs somewhere to go, other than through cracks into the cavity etc. I was going to go for the Aereco humidity-sensitive trickle vents.

    I considered several other options.

    Passivent is not feasible due to low-pitched roof and surrounding property heights.

    MEV was ruled out because there are already kitchen and bathroom extractors fitted, plus PIV has the benefit of pre-heating the air somewhat from the loft, as opposed to MEV where the input is straight from outside in the window/wall vents.

    MHRV was a contender, but again, ruled out because of existing extractors, plus the significantly higher cost.
    • CommentAuthorringi
    • CommentTimeJul 19th 2015
     
    Most building have more leakage then is needed for a PIV system to operate.

    If you are so draft proofed that a PIV system does not work, then single room MHRV may be an option.

    But don't rule out installing a "full" MHRC system with the extractors in all the wet rooms, but the inlets only in the hallways, or rooms that are easy to get duct to.
    •  
      CommentAuthordjh
    • CommentTimeJul 20th 2015
     
    Posted By: CX23882Yes, Positive Input Ventilation. It's just for background ventilation. The inlet goes in a central location, but the air needs somewhere to go, other than through cracks into the cavity etc.

    What is your house made of? As you say, PIV tends to cause air to be forced out through cracks, so it can be problematic if there is anything that can rot in the exterior construction.
    • CommentAuthorCX23882
    • CommentTimeJul 20th 2015
     
    It's standard brick and block (probably steel wall ties), with blown mineral wool insulation, and the top of the cavity open to the loft space. The inner surface is wet plastered and generally sound condition, other than surface damage from previous wallpapering. Some rooms were done with Zinsser Gardz before re-emulsioning.

    All of the windows having cloaking profiles siliconed on.

    The floor is solid concrete slab with solid screed on top.

    All penetrations through the ceiling are caulked.
    •  
      CommentAuthorfostertom
    • CommentTimeJul 20th 2015
     
    Agree with ringi.
    • CommentAuthorringi
    • CommentTimeJul 21st 2015
     
    Positive Input Ventilation (PIV) has been proven time and again to work a lot better in real life then the measured RH reduction says it should. It seems that the measured RH is not reduced that much by most PIV systems, but that mold and damp problems are reduced by more then the measured RH would lead you to expect.

    Positive Input Ventilation (PIV) is a "quick fix" solution to a problem home, (not building, as the problem is often with the people living their not the building itself.) Given a choose, I would never design a building to use PIV.

    PIV can be installed in most small homes for under £500, only needing access to the building for a few hours and not needing to making good any painting etc.

    (A home that is not dump, does not need as much heating to "feel" warm, hence calculated heat loses may not match up with real life. Likewise if a PIV system stops people leaving windows open all day... )
    • CommentAuthorCX23882
    • CommentTimeAug 11th 2015 edited
     
    Thanks for all the replies. I've gone for a PIV system, which seemed like the best fit for this property.

    Time will tell if it helps in the colder months, but I've actually been grateful to have it during the warmer weather since it is great for flushing out the warm air overnight.

    The bathroom extractor is also much more effective. Steam is gone from the windows within 5 minutes, even with the window closed.

    For the trickle vents, I ended up just fitting them in the top of the opening casements. There wasn't enough space in the outer frame, short of attempting to drill right through from the outside in.

    I can see the attraction of MVHR, but the deciding factors against it for me were:
    - cost. PIV was well within budget. MVHR is just too much at this point.
    - airtightness. A test is expensive, and it's likely to be poor anyway due to existing kitchen vents, even if obvious unintentional cracks have been repaired.
    - legionnella. PIV by the nature of how it works has negligable risk, not so sure about MVHR.
    - more ducting to install (admittedly fairly easy in a bungalow) and to ensure cleanliness.
    • CommentAuthorgravelld
    • CommentTimeAug 11th 2015
     
    Sorry, why couldn't you just fill in the existing vents? Surely this would be an important part of the ventilation design anyway?
    • CommentAuthorCX23882
    • CommentTimeAug 11th 2015 edited
     
    Of course you could fill the existing vents, and remove the kitchen extractor and fit a recirculating hood, and remove the bathroom extractor and replace with an MVHR extract point, as well as the other unknown leaks, but that, combined with the cost means it wasn't the most sensible option.

    I haven't seen anything that says that MVHR offers significant energy savings over PIV or MEV, in a retrofit.
    •  
      CommentAuthordjh
    • CommentTimeAug 11th 2015
     
    Posted By: CX23882legionnella. PIV by the nature of how it works has negligable risk, not so sure about MVHR

    Legionella is only a risk in hot water systems, nothing to do with ventilation.
    • CommentAuthorgravelld
    • CommentTimeAug 11th 2015
     
    Posted By: CX23882I haven't seen anything that says that MVHR offers significant energy savings over PIV or MEV, in a retrofit.
    It's not so much the retrofit as the characteristics of the dwelling post retrofit, I think, i.e. what air permeability you end up with.
    • CommentAuthortony
    • CommentTimeAug 11th 2015
     
    Deliberately blowing cold air into a house and letting it force warm air out through all the cracks is insane and a sport only for the rich.
    • CommentAuthorEd Davies
    • CommentTimeAug 11th 2015 edited
     
    Posted By: CX23882I haven't seen anything that says that MVHR offers significant energy savings over PIV or MEV, in a retrofit.
    To the extent that there's any mechanical ventilation required MVHR can provide a saving.

    Agreed that it'll be a smaller saving in comparison to the overall losses but in absolute terms (watts rather than percentage) it'll be the same for the same ventilation rates.

    In a way you might expect a bigger absolute saving via MVHR in a retrofit over a new-build with a similar level of airtightness. This is presuming that the new build has better insulation and therefore lower losses by conduction. Lower conduction losses will result in higher inside surface temperatures and therefore less potential for condensation and consequently a (slightly) lower need for ventilation giving a smaller potential saving by MVHR.

    (Edit to add: even for nominally the same U-values you'd hope a new build would have less in the way of cold bridges than a retrofit so still need a bit less ventilation.)
    • CommentAuthorringi
    • CommentTimeAug 11th 2015 edited
     
    Posted By: tonyDeliberately blowing cold air into a house and letting it force warm air out through all the cracks is insane and a sport only for the rich.


    Firstly the air is pre-warmed in the loft,

    But the real benefit is when windows can be left closed in winter, so by blowing in a LITTLE air in a controlled way allow much less heat lose then if windows are left open.

    PIV systems are a compromise. MVHR is clearly the correct option for a new build, or a complete refit. However a PIV system is often a lot better than nothing.

    (If you can feel the air movement from a PIV system, it is very likely it is set on to high a setting.)
    • CommentAuthortony
    • CommentTimeAug 12th 2015
     
    Or pre cooled from in the loft!
    • CommentAuthorCX23882
    • CommentTimeAug 13th 2015 edited
     
    Do you think there is any benefit of injecting a bit of expanding foam either side of the trickle vent slot, to reduce air movement inside the frame? I'm presuming that the individual chambers run all the way around the perimeter.

    I appreciate I've just cut a 2800mm2 hole through from inside to the outside, but is it worth going from "2800mm2 hole, all chambers connected" to "2800mm2 hole, and chambers isolated" for the effort of a couple of squirts of foam? I'm on the fence because the glazing opening has a 5mm tolerance between the DGU and the frame anyway, with nothing but a bit of beading and wedge gasket.

    RE MVHR - it was just way out of budget. There are more important things to spend money on (usable flooring being a big one). Trickle vents on their own would be insufficient, based on my experience with the night lock position. PIV seemed ideal, and can't be that bad running-cost wise given how many social housing properties have had it fitted.

    RE legionella; fair enough. Presumably a correctly-installed MVHR wouldn't be condensing water in the system or ducts, and the temperatures are too low anyway? Is there any need to clean the ducts of other "nasties" though?
    •  
      CommentAuthordjh
    • CommentTimeAug 13th 2015
     
    Posted By: CX23882RE legionella; fair enough. Presumably a correctly-installed MVHR wouldn't be condensing water in the system or ducts, and the temperatures are too low anyway? Is there any need to clean the ducts of other "nasties" though?

    MVHR systems do condense water out of the exhaust air sometimes. That's why they have a condensate drain. As you say, the temperatures in an MVHR system are too low for legionella and there isn't enough water involved. But the main reason it's not a problem is that legionella is spread by droplet infection, and there's no mechanism for an MVHR to produce a droplet spray. By contrast, showers and water-cooled air-conditioning condensers do produce droplet sprays, which is why they are sometimes problematical.

    There shouldn't be any great need to clean the ducts in normal circumstances; the biggest risk is during the construction process itself, AFAIK. Plus don't extract air straight from a cooker into the ducts!

    Some ducts are lined with anti-bacterial coatings, supposedly to be extra safe.
    • CommentAuthorCX23882
    • CommentTimeOct 27th 2015 edited
     
    Just a quick message to report that the PIV and trickle vent combination is working great.

    All windows have remained closed since the temperatures began to drop, and the trickle vents are automatically opening and closing with humidity (but generally 80-100% open), and there has been zero condensation on any window overnight (only 3 were fitted with trickle vents, all the others are left without). The Drimaster is currently set to speed 3, which is what is suggested for the volume.

    I know that PIV is frowned upon here for not being "green" enough, but the heat losses aren't enough to make MVHR worthwhile for me. My heating is set to come on at 15°C overnight, and so far, in spite of some 3 and 4°C nights, it hasn't clicked on, so the heat loss can't be that disasterous. This is supported by my actual consumption:
    In August 2014, I used 158kWh gas for heating, August 2015, 64kWh.
    In September 2014, 190kWh, September 2015, 96kWh.
    The majority of this is from central heating, since the washing machine is cold fill, dishes are washed by dishwasher, and the shower is cold-fed electric.

    In spite of the comparatively large gas usage last year, I was still suffering severe condensation. It made no difference whether the windows were closed, or locked open. Windows wide open is never an option in a bungalow. Windows locked open is less than ideal too. It's not totally positive - the trickle vents do let in a bit more noise - not excessive, but it is there. But again, that's compared to a closed window, not one that has been locked open. This is somewhere that MVHR wins.

    Overall, I am satisfied. The environment is more comfortable, since it is set for the temperature that I want, instead of a temperature high enough to hold the excessive moisture in the air.

    I cleaned the input-side filter a fortnight or so after installing the Drimaster, and it was covered in fibres from the loft insulation. I've checked a few times since, and it's relatively clean, so presumably it was just from stirring things up during the installation. No sign of any fibres getting through the filter into the outlet.
    •  
      CommentAuthordjh
    • CommentTimeOct 27th 2015
     
    Well done. And thanks for reporting back - it may well be useful to somebody else in future.
    • CommentAuthortony
    • CommentTimeOct 27th 2015
     
    How is your energy consumption being influenced?

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