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Ventilation: Kitchen extract within MVHR?

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    • CommentAuthorXT600
    • CommentTimeOct 7th 2015 edited
     
    In an airtight house with MVHR, does anyone know if it's possible to fit an extractor fan to deal quickly with cooking fumes/steam? In my experience, whole house MVHR doesn't deal with kitchen extraction quickly and efficiently, and a re-circulation system is next to useless. Is their a way to fit an extractor fan, ducted directly to the outside, but with a way to seal this ducting when the fan is not in use?
  2.  
    I think you want one of these attached to a cooker hood.

    http://www.berbel.de/uk/accessories/wall-boxes.html
  3.  
    Nice bit of kit - does it cost more than the cooker hood? :cry:
    • CommentAuthorjfb
    • CommentTimeOct 8th 2015
     
    why is a recirculation system useless? in theory it should take out the oils. Ok it doesn't do the condensation but that should be done my MVHR in a reasonable time, at least it does for me (I have both MVHR and recirculation)
    •  
      CommentAuthordjh
    • CommentTimeOct 8th 2015
     
    The price doesn't look too bad - 320 euro on amazon.de - though still quite a lot of money. (Compare it with 1000 for a catflap!)

    It claims a U-value of 0.95 W/m²K and claims to be airtight but doesn't give a spec value.

    It doesn't appear to be PH certified, so all figures would have to be discounted as well.

    My wife said (unprompted) only last night that she thinks our MVHR deals with the cooking smells pretty well so I guess it depends on what and how you cook and what your personal standard/ambition is.
  6.  
    Posted By: djhso I guess it depends on what and how you cook and what your personal standard/ambition is.

    Yes that was exactly the outcome of another nearly identical discussion on here a while ago.
    • CommentAuthorCWatters
    • CommentTimeOct 8th 2015
     
    <blockquote>In an airtight house with MVHR, does anyone know if it's possible to fit an extractor fan to deal quickly with cooking fumes/steam?</blockquote>

    Sure. All that will happen is that the system will be unbalanced while it's running. We have MHVR and an extract hood in the kitchen but I suspect our house isn't as air tight as it should be. Seems to work fine. Just gives the incoming fan an easier time and spoils the heat recovery - but only when running which isn't a high percentage of the time.

    Some models of hood can be set up to either extract to recirculate. Perhaps go for one that can do either, install as an extractor and if you have issues convert it to a recirculating mode?

    If you have a wood burner "over extracting" using a powerful extractor hood could in theory can draw fumes back down the chimney - but we haven't noticed that either. The MVHR seems capable of delivering enough air.
    • CommentAuthorCWatters
    • CommentTimeOct 8th 2015
     
    Is their a way to fit an extractor fan, ducted directly to the outside, but with a way to seal this ducting when the fan is not in use?


    We have a gravity operated shutter/flap on ours. I believe you can also get electrically operated ones?
    •  
      CommentAuthordjh
    • CommentTimeOct 8th 2015
     
    Posted By: djhThe price doesn't look too bad - 320 euro on amazon.de - though still quite a lot of money.

    I just discovered the price of the carbon filters for our hood - approx £50 for the pair! To be replaced every 3-4 months in theory. So I suddenly became interested in that Berbel valve, until I realized that the other side of the wall on which our cooker hood is mounted is inside our sun room. So that starts to get very complicated.

    Any ideas on economical ways to make or buy carbon filters?
    • CommentAuthortony
    • CommentTimeOct 8th 2015
     
    Make your own charcoal?
    • CommentAuthorSimon Still
    • CommentTimeOct 8th 2015 edited
     
    I'm buying a very expensive Berbel hood for recirculation- it takes "bulk" carbon so the large filter is supposed to last around 3 years and can then be refilled (refills ere I think 60 euro)
    • CommentAuthormikrt
    • CommentTimeOct 8th 2015
     
    • CommentAuthorgravelld
    • CommentTimeOct 9th 2015
     
    Could the answer simply be that some recirculation hoods are better than others?
    •  
      CommentAuthordjh
    • CommentTimeOct 9th 2015
     
    Posted By: Simon StillI'm buying a very expensive Berbel hood for recirculation- it takes "bulk" carbon so the large filter is supposed to last around 3 years and can then be refilled (refills ere I think 60 euro)

    Do you happen to have any links to technical details of the filter? (diagrams etc) All I've found so far are single sentence descriptions.
  15.  
    You'll have to do some work on Google Translate -
    http://www.berbel.de/data/media/downloads/TechnischeDatenUmluftfilter.pdf

    They seem to be a cut above any other hoods I've come across - Dyson style centrifugal filter rather than a metal mesh, insulated external exhaust, switchable between exhaust and recirc mode (so you can extract in summer, recirc in winter) and bulk charcoal filter rather than poxy little things.

    Very expensive, though much cheaper from Germany than anywhere in the UK. Mine is coming from acasa.de. email them for a shipping quote to the UK on info@ascasa.de

    You might want to wait until mine actually turns up before ordering.....
    •  
      CommentAuthordjh
    • CommentTimeOct 9th 2015
     
    Thanks for that. They do seem impressive and I haven't read any bad reports. The price of the filters (BUF 150 etc) doesn't seem outrageous so I'm tempted.
    • CommentAuthorCWatters
    • CommentTimeOct 10th 2015
     
    Some makes say the filters can be put in the dishwasher. Perhaps worth considering.
    • CommentAuthorbillt
    • CommentTimeOct 10th 2015
     
    That'll be the grease filter. You wouldn't want to put the carbon filter in there!
    • CommentAuthorXT600
    • CommentTimeOct 11th 2015
     
    Thanks for all your comments, the Berbel system looks good and at least gives me an option to offer to my customer. On airtight dwellings I have worked on previously I haven't been too impressed by the way MVHR deals with cooking extraction.
  20.  
    The carbon filters in our Elica twin recirculating hood is just this stuff (but 6mm thick) with a cloth cover.

    http://www.ebay.co.uk/itm/DIY-ACTIVATED-CARBON-IMPREGNATED-FOAM-FILTER-SHEET-12mm-THICK-18-x-12-/260987352067?hash=item3cc40ef403

    They are washable in the dishwasher and are supposed to last for 3 years but I found that whilst they were very effective at absorbing odours when new I was not so impressed after they were washed.

    The discussion here has prompted me to take another look at how I might improve performance.

    There is plenty of space between the wire mesh filter and the fan above,about 6 or 7cm. so I must look at making some sort of a holder or bag that I can refill with activated charcoal media.

    You can get activated carbon in nugget form quite cheap from aquarium suppliers, I am guessing that as the nuggets will not be packed that tight they will still allow plenty of airflow but will give lots of carbon material to absorb cooking smells?
    • CommentAuthorwookey
    • CommentTimeNov 1st 2015
     
    Re the hourses for courses comment above. I bought a cooker hood extractor for previous house/kitchen and it was a waste of money. We never turned it on unless there was something like a burned toast disaster, and we have windows for that which work just as well. Partly because it was quite noisy, but mostly because we never felt the need, and always resented blowing hot air outside. This house doesn't have one at all and we've not missed it.

    We also bunged up the in-window extractor (aka 'windy hole') a few years ago and even that's still mostly OK although it was nominally temporary (it's just taken 3 years to get round to doing the MVHR). The only problem is some condensation on external window, and sometimes a general 'rank bin smell', especially if you've been away for a while. So I'm expecting MVHR to be plenty of ventilation and deal with both of those issues. We shall see.
    • CommentAuthorwookey
    • CommentTimeApr 3rd 2016
     
    So, coming back to this, can I buy an air valve with a grease-filter in it, just to keep the worst of the mank out of the MVHR pipe+filters? All I've found so far is this in-line box:
    http://www.i-sells.co.uk/in-line-filter-box-eu-grade-150mm (at £120)

    or this inline round filter:
    http://www.growland-hydroponics.com/Duct-Filter-150mm (at €46 which is a bit more reasonable, €15 for new filters)

    I was hoping for an air-valve that just had a filter in the back of it, without costing a fortune. That could be unscrewed to change as needed.

    Also, should I worry about air throughput vs grease-collecting efficacy?
    •  
      CommentAuthordjh
    • CommentTimeApr 4th 2016
     
    I believe conventional wisdom is to separate the grease trap from the MVHR. i.e. put the grease trap directly over the hob and the MVHR extract terminal somewhere else.

    I bought a conventional cooker hood and fitted it in recirculation mode. The plan was to fit its optional grease filters but the ones I bought were the wrong size and I haven't bothered trying to find the correct ones. We don't use the hood much at all. The latest plan was to buy an external component and bulk grease trap material as discussed earlier in the thread. Note that there are different types of filter material; I don't know/remember which are good for grease.

    On our MVHR, it's the incoming air filter that gets dirty. I've had to clean that a couple of times already, but the extract filter is still clean. So I don't think there's much dirt getting into the extract vents. I've taken a couple off and had a look at the duct but it seems to be clean as well. So far!
    • CommentAuthorGreenfish
    • CommentTimeApr 4th 2016 edited
     
    We have a conventional freestanding cooker hood above the hob in recycle mode (no pipe to outside), that traps the grease and the MVHR extract elsewhere in the room deals with the smells. Used whenever we use the hob (daily), MVHR boot when smelly. The MVHR filters are clean after a year of use, both in and out but a rural location with lovely clean sea air. The in filter does get wet when we have days of mizzle in autumn. The MVHR extract terminal in the kithcen is also fairly clean.

    We didn't have the carbon filters to fit when hood was installed - they didn't come with it as I expected - so there was a delay before got around to that. During that extended period grease did collect on the hood as well as the metal grease filters, and a patch on the ceiling where the casing meets the ceiling. Effectively recycled air was passing out the casing there and leaving a mark, that motivated me to act. Since fitting the carbon filters and sealing that gap all has been well, so at least I know that the carbon filters do something. Also the metal grease filters do get mucky, I wouldn't like to not have a hood.

    What does wind me up is having to put the whole house in MHVR boost just to deal with the cooking smells, the downside of a whole house balanced system I guess. Experience with airtight house and WBS convinces me that a simple cooker extractor with single pipe to outside would not work. It would not be able to pull air from the room without an opening to supply air for it to draw on.
    • CommentAuthorCWatters
    • CommentTimeApr 4th 2016
     
    We have a separate extractor fan for the kitchen hood. I figure it's not used for a high percentage of the time so who cares if the MVHR is temporarily unbalanced.
    • CommentAuthorGreenfish
    • CommentTimeApr 4th 2016 edited
     
    Would take a pretty powerful separate extractor to unbalance my whole house MVHR! How airtight are you CWatters? Where is the air the hood extracts coming from? A hole in the wall?

    Even if I open a window I don't get air flow unless there is a wind blowing directly at it. I have to open 2 windows to get flow. A rarely discussed aspect of airtightness less than 1 (units I forget). You need a powerful fan to create a negative pressure enough to move greasy smelly air out the house.
    • CommentAuthorwookey
    • CommentTimeApr 4th 2016 edited
     
    I believe conventional wisdom is to separate the grease trap from the MVHR.


    Right, but I don't like cooker hoods (noisy, 90% pointless). We have one but it has never been used - in fact I'm not sure if it works (I think it does but the bulb doesn't). VTW does not want to turn one on every time she cooks, and neither do I.

    But we do now have MVHR, at least in winter. And over a decade or so lard does slowly collect in the corners of the room, so some will now end up in the vent pipe. A filter in the valve seems like a good idea (Assuming that loss of efficiency is not too high).

    Are we saying there there is no such thing because what I want is 'weird'. So that 45€ in-line jobbie is as good as it gets? (In which case I should have done this whilst fitting the pipework, rather than assuming I could find a filtering-terminal later !)

    Mind you, If I had the right filter-material, attaching some to a ring the right size and shoving it up the pipe shouldn't be that hard...
    •  
      CommentAuthordjh
    • CommentTimeApr 4th 2016
     
    Posted By: wookeyA filter in the valve seems like a good idea (Assuming that loss of efficiency is not too high).

    I would check the pressure loss due to the filter before spending too much money on it. There seems a fair chance it will unbalance your MVHR to a greater degree than is acceptable.

    So that 45€ in-line jobbie is as good as it gets? (In which case I should have done this whilst fitting the pipework, rather than assuming I could find a filtering-terminal later !)

    That unit looks like it is designed so that you change the filter by side access, so probably not ideal for mounting in the ceiling.

    If you want a quick and dirty test, you could try cutting a circular piece of a sponge and stuffing that in the pipe?
  29.  
    We're considering a Siemens hood, v minimal, set flush in the false ceiling. It can be ducted either to the outside or back into the room through a smaller matching vent with a carbon filter. Not cheap, though!

    Another option is a similar cheaper hood from a different company. It's is only supposed to duct to outside, but I can't see why it wouldn't work with the Siemens recirculation vent. Any reasons why not?
  30.  
    Posted By: GreenfishWould take a pretty powerful separate extractor to unbalance my whole house MVHR! How airtight are you CWatters? Where is the air the hood extracts coming from? A hole in the wall?


    Have you looked at the specs of Cooker Hoods?

    My Sentinal Kinetic Plus MVHR has, I think, a 173w power consumption at Max and the building regs spec for my c200m2 house was a flow rate of 229m3/h

    http://www.siemens-home.co.uk/productlist/cooking/cooker-hoods lists extract rates of up to 800m3/h - I think that's more than enough to cause an issue.

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