MHRV & cooker hood in a kitchen

BigGeorge

Looking for suggestions for the use of an MHRV extract and a cooker hood in a kitchen in an airtight house. Quick bit of research appears to say

- If I use a cooker hood with an external vent , will this compromise airtightness? Or will an unit with internal recirc only with a charcoal filter be effective enough.

- Locating the MHRV extract head anywhere near the cooker will result in fats, dust etc... building up in the duct over time. Is this true & what can be done to get around this

Mike2006

Personally, I would not put the cooker hood through the MHRV system no matter what anyone said to me about filtration etc...

What I did was use an external air supply to the extractor fan as per usual but put a damper in the line which is only open when the extractor fan is on. When the fan is off, the damper closes.
That was my solution. Be it the correct one or not.. I achieved a value 1.45 on my airtightness test.

Mike.

murphyep

Hi Mike,
Can you tell me more about the damper you put between the vent and the extractor hood please?
Where did you source it?

Thanks,
Eddie

creedp

Hi

I have a similar issue in that my builder went ahead and installed the ducting for an external cooker hood even though I was concerned about the airtightness problems it might cause. I was intending to install one of those recirculating hoods that use a carbon filter to deal with this issue. However, my builder and MHRV guy are not very impressed by these and say they won't deal efficiently with cooking smells and particularly the risk of contamination of MHRV ducting due to frying etc.

It seems to me if a damper could be installed on the externally vented hoods that would be a very good compromise. I would be interested in where these could be sourced and whether they can be installed with standard ducting and hoods.

One final point, when the extractor hood is on a high setting could this cause sufficient negative pressure to pull air from the Kitchen MHRV extract duct? Would you also need a damper on this extract which would close once kitched hood is activated?

Thanks

Mike2006

Sorry about the delay in reply, just logged in again now...



I used 2 of these in series with a slight modification to make them more airtight....

http://www.tlc-direct.co.uk/Products/BG4BS.html


Mike.

Poor Uncle Tom

Mike2006 wrote: »

Personally, I would not put the cooker hood through the MHRV system no matter what anyone said to me about filtration etc...

What I did was use an external air supply to the extractor fan as per usual but put a damper in the line which is only open when the extractor fan is on. When the fan is off, the damper closes.
That was my solution. Be it the correct one or not.. I achieved a value 1.45 on my airtightness test.

Mike.

That is thinking on your feet, very pracitcal, but why did you use 2 in series?

Mike2006

Tom,

I put 2 in series just to give a better 'seal' as such or in case 1 failed. They were pretty cheap so I just erring on the side of caution with the second one...

Mike.

gears

creedp wrote: »

Hi

I have a similar issue in that my builder went ahead and installed the ducting for an external cooker hood even though I was concerned about the airtightness problems it might cause. I was intending to install one of those recirculating hoods that use a carbon filter to deal with this issue. However, my builder and MHRV guy are not very impressed by these and say they won't deal efficiently with cooking smells and particularly the risk of contamination of MHRV ducting due to frying etc.

It seems to me if a damper could be installed on the externally vented hoods that would be a very good compromise. I would be interested in where these could be sourced and whether they can be installed with standard ducting and hoods.

One final point, when the extractor hood is on a high setting could this cause sufficient negative pressure to pull air from the Kitchen MHRV extract duct? Would you also need a damper on this extract which would close once kitched hood is activated?

Thanks

In relation to your MVHR guy being concerned about cooking smells, should his system not change the air at a rate sufficient for smells not to build up.

creedp

gears wrote: »

In relation to your MVHR guy being concerned about cooking smells, should his system not change the air at a rate sufficient for smells not to build up.

Your right Gears, that is one of the two primary roles the system has!! Im afraid its my fault I was trying to make the point about contamination of ducting by grease etc from smelly cooking and I made a bit of a bags of it !!


Mike 2006 can I ask where these dampers are located - are they built into the external ducting or are they located where the ducting connects into the hood? Sorry its clear I am anything but technically litterate!

Mike2006

Hi,

No probs.

I positioned both dampers with a 50mm gap between them just at the outside air outlet (external wall, just inside the wall grille).

Reason I put them there is for easy of access later on if need be...

Mike.

creedp

Thanks Mike

Wally Runs

Now, just to throw in a bit here. I have HRV and a recirculation hood in the kitchen. There is a HRV extraction point in near the hob but not above it. The kitchen is part of a large open plan living area (50m2). It has been in a year now and so far no signs of grease in the extraction point of the HRV. A little dusty but no more than the others.

With regard smells and moisture there have yet to be problems. This was a big worry of ours at the time. The hood we installed is from IKEA (Whirlpool) and has a long life filter that you can wash in the dishwasher to re-invigorate it. So far so good. We could not vent from where the hood was located as it would have had a very long run. We cook quite a bit.

murphyep

Hi Mike2006,
What modifications did you make to these two dampers from tlc direct.
I got two from them before xmas and am getting ready to install them this week.

Thanks,
Eddie

Mike2006

Eddie,

I wrapped plumbing tape (pvc) all around the outside of them to give them a good seal to the inside of the 4" duct. Otherwise there would have been a slight gap or at best a hard plastic to hard plastic seal...

Also, make sure that you install them in the correct direction and with the hinged part vertical (this will stop accidental opening or sticking)


Mike.

mechelec

The filters in most HRU's are not made to take grease etc. from the kitchen. It is recommended to duct the cooker hood seperatly.

Introducing dampers such at the ones discussed above would increase the pressure on the duct run, adding two would certainly have some effect. This is probably not critical in a very short run but worth considering if your run is several meters. B-regs is 30l/s intermittent vent direct over a cooker in a kitchen.

Correct me if I am wrong but it is my understanding that any intentional vents can be sealed over during your air pressure test, thus not affecting the end result.

The test is intended to check for leaks in the construction such as gaps around windows etc.

It is my opinion that passive hit and miss type vents should be installed in any occupiable rooms in tandem with your MVHR system. These can be closed normally. Otherwise the building is practically unoccupiable if the power goes off.

I have come across systems turned off by occupants that didn't understand what it was for, wanted to reduce ESB bills, thought it was noisy etc.

just do it

Mike2006 wrote: »

Sorry about the delay in reply, just logged in again now...



I used 2 of these in series with a slight modification to make them more airtight....

http://www.tlc-direct.co.uk/Products/BG4BS.html


Mike.

Mike2006 wrote: »

Hi,

No probs.

I positioned both dampers with a 50mm gap between them just at the outside air outlet (external wall, just inside the wall grille).

Reason I put them there is for easy of access later on if need be...

Mike.

Mike2006 wrote: »

Eddie,

I wrapped plumbing tape (pvc) all around the outside of them to give them a good seal to the inside of the 4" duct. Otherwise there would have been a slight gap or at best a hard plastic to hard plastic seal...

Also, make sure that you install them in the correct direction and with the hinged part vertical (this will stop accidental opening or sticking)


Mike.

Great idea Mike, I'm going to try it out.

cuculainn

Hi Mike,

Just looking at the valves you installed..Can you tell me if when close they provide a complete seal? i.e completely air tight?

I am looking at either a recirculating hood or a system similar to what you have done

Is it a case of external air pressure will force it tight closed?

THnaks

Mike2006

Cuculainn,

It is not 100% airtight as it is only spring loaded with hard plastic-to-hard plastic seal, but it is quite a good level of airtightness for the required application.

Taking the airtightness level of the 2 dampers and the filter of the hood itself into account, I would think that the leakage losses are negligible.

Mike.

galwaytt

t

Mike2006 wrote: »

Sorry about the delay in reply, just logged in again now...



I used 2 of these in series with a slight modification to make them more airtight....

http://www.tlc-direct.co.uk/Products/BG4BS.html


Mike.

Mike - I like that

Question - does that fit ok into a sd 115mm Wavin pipe ?

gman2k

mechelec wrote: »

It is my opinion that passive hit and miss type vents should be installed in any occupiable rooms in tandem with your MVHR system. These can be closed normally. Otherwise the building is practically unoccupiable if the power goes off.

I think your opinion on this is unreasonable and excessive.

To say that a building is practically un-occupable in the rare event of a power cut is excessive and bad advice imho.

whelzer

Mike/Galway or anybody else who has tried this. Did you guys order from the provided link or is there a supplier over here.

If not anyone in Dublin fancy sharing the postage? £13 stg seems a lot...

Mike2006

galyaytt - They fir into a wavin pipe but are not a tight fit. I used plumbers taps (pvs around the circumference of the vent to give a tight fit.


whelzer - I purchased from tlc-direct. Bought a few other bits and pieces as well so it wasn't too bad.

Mike.

just do it

I put the damper in a few weeks ago when there was a cold wind blowing into the kitchen through the extractor. It worked straight away. It was a good bit too narrow for the pipe (too much for just plumber's tape) so I sealed all around it with caulk. It's worked a treat.

I was concerned that the extractor mightn't work as well but there's been no problems there. Still sucks out just as much steam at the first speed setting i.e. the slowest. Happy days:D

BigGeorge

Is there any sort of powered damper shutter that would give a better seal that anyone has seen or is the inline spring loaded one the best option?

Gulliver

There is a hardware store in Ballina that stocks these in the trade counter area for €6.30.



Brilliant idea, Mike2006, haven't got around to installing it yet.

FergusD

I'm no ventilation specialist, but I'm guessing you probably should look for a larger shutter (pi*r*r and all that)? My cooker hood takes a 5 inch pipe reduced from 6 inch, I presume that by further reducing it to 4 you are reducing it's extract capability?

Thanks,

Fergus.

Carlow52

FergusD wrote: »

I'm no ventilation specialist, but I'm guessing you probably should look for a larger shutter (pi*r*r and all that)? My cooker hood takes a 5 inch pipe reduced from 6 inch, I presume that by further reducing it to 4 you are reducing it's extract capability?

Thanks,

Fergus.

AFAIK the dampers are on the external intake that Mike2006 has added to the system so any mismatch between a 6" outlet and the 4" inlet will be taken from the house.
[12/04/11: that is wrong, they are on outlet]
You are right about the problem if u go from 6 to 5 to 4 on the outlet

What does interest me is where is the fresh air intake positioned so as the external air is delivered as close as possible to the hood.

FergusD

From re-reading the post, they are on the outlet. I wasn't getting into all this HRV stuff to do with negative pressure and whether there should be an air inlet etc. (personally I wouldn't get too hung up on that), I was purely commenting on the effectiveness of the hood extracting and how a 4" damper might be replaced with a 5" model. I don't know if it makes a huge difference to the hood, but here's my thinking.

The cross sectional area for a 5" pipe is:
62.5*62.5*3.14 = 12266mm2

For a 4" pipe this is:
50*50*3.14 = 7850mm2

I'm guessing that this size of reduction may be significant?

Fergus.

Carlow52

FergusD wrote: »

From re-reading the post, they are on the outlet. I wasn't getting into all this HRV stuff to do with negative pressure and whether there should be an air inlet etc. (personally I wouldn't get too hung up on that), I was purely commenting on the effectiveness of the hood extracting and how a 4" damper might be replaced with a 5" model. I don't know if it makes a huge difference to the hood, but here's my thinking.

The cross sectional area for a 5" pipe is:
62.5*62.5*3.14 = 12266mm2

For a 4" pipe this is:
50*50*3.14 = 7850mm2

I'm guessing that this size of reduction may be significant?

Fergus.

+1
the math is all here
http://www.engineeringtoolbox.com/

Having thought about it again they must be on outlet so will edit post:(