Green Building Forum - Purpose of filters for MVHR systems and the reduction of interior dust

Purpose of filters for MVHR systems and the reduction of interior dust

Shevek — Fri, 22 Feb 2013 11:21:37 +0000

What's the purpose of filters for MVHR systems? Are they to filter the incoming air for the occupants or the equipment? Or both? Can you get filters that filter our pollution or is it just relatively large particles like pollen? (We're probably installing Paul MVHR)

Purpose of filters for MVHR systems and the reduction of interior dust

CWatters — Fri, 22 Feb 2013 12:37:57 +0000

We live in the countryside in central england. Our MHRV system is quite crude by modern standards. The input filter is a very coarse filter (way too coarse to trap pollen) and it manages to clog up in about 4 months with a mixture of dust, flys and moths etc.

The ones on the room extract vents are much finer and are intended to stop the duct work filling up with dust. They seem to need cleaning about once every 4 weeks.

Purpose of filters for MVHR systems and the reduction of interior dust

tony — Fri, 22 Feb 2013 12:45:11 +0000

Dust is the problem, our filters are so efficient that we hardly get any dust in the house now.

There is a cost in maintaining them, I feel that it is worth it.

I would rather see the dust in the filters than in my nose or lungs.

Purpose of filters for MVHR systems and the reduction of interior dust

Shevek — Fri, 22 Feb 2013 13:38:29 +0000

Are we at risk of creating unnaturally sterile environments? Is there any research into this?

Purpose of filters for MVHR systems and the reduction of interior dust

djh — Fri, 22 Feb 2013 13:42:12 +0000

Shevek asked: "What's the purpose of filters for MVHR systems? Are they to filter the incoming air for the occupants or the fans? Or both? Can you get filters that filter our pollution or is it just relatively large particles like pollen? (We're probably installing Paul MVHR)"

The basic reason is to stop dust clogging up the heat exchanger and collecting in the ducts, but you can also buy pollen filters.

The supplier kind of answers the question:

http://www.greenbuildingstore.co.uk/media/page_content/MVHR/Pricelist/MVHR-filters-pricelist-October-2011.pdf

Purpose of filters for MVHR systems and the reduction of interior dust

Shevek — Fri, 22 Feb 2013 14:09:25 +0000

Posted By: tonyDust is the problem, our filters are so efficient that we hardly get any dust in the house now.

Do you think this is mostly because it's filtering incoming air or because it's extracting dust?

Or maybe it's not related to MVHR filtration at all but is rather a product of having an air-tight construction, which controls the ingress of dust through cracks, but of course is also properly ventilated? Perhaps there tends to be less carpet in houses with MVHR?

Purpose of filters for MVHR systems and the reduction of interior dust

Shevek — Fri, 22 Feb 2013 14:09:34 +0000

Also, do you think a house ventilated with PVHR (like Ventive) would remove dust in a similar fashion to MVHR systems?

Purpose of filters for MVHR systems and the reduction of interior dust

fostertom — Fri, 22 Feb 2013 14:17:14 +0000

Must be

Posted By: Shevekbecause it's filtering incoming air

you can't 'extract' dust unless you stir it up, or catch it before it settles, a tall order with the negligible air velocities of MHRV.

So any kind of whole-house ventilation with well filtered inlet would eliminate external dust in the house, but would do nothing to remove the dust that's created indoors - dead skin etc!

Purpose of filters for MVHR systems and the reduction of interior dust

Shevek — Fri, 22 Feb 2013 14:18:44 +0000

Posted By: fostertom

you can't 'extract' settled dust - so any kind of whole-house ventilation with well filtered inlet would eliminate external dust in the house, but would do nothing to remove the dust that's created indoors - dead skin etc!

Right, so why is it that people with MVHR systems tend to report having far less dust in their houses? Is it really just the incoming filter? And what about reports of dirty room extract filters. Why are they getting dirty if not much dust is not being extracted? (see CWatters comment above)

Purpose of filters for MVHR systems and the reduction of interior dust

fostertom — Fri, 22 Feb 2013 14:21:50 +0000

Fair comment - BTW I added to my post while you were replying to it!

Purpose of filters for MVHR systems and the reduction of interior dust

RobinB — Fri, 22 Feb 2013 14:57:45 +0000

I find our MVHR house about as dusty as the old Victorian house before it. I expected a big improvement - the filters do get quite dirty. I don't dust often. I blame the cat.

Purpose of filters for MVHR systems and the reduction of interior dust

Shevek — Fri, 22 Feb 2013 14:59:10 +0000

Interesting. Is your incoming air filtered Robin?

Purpose of filters for MVHR systems and the reduction of interior dust

barney — Fri, 22 Feb 2013 15:11:03 +0000

As a broad premise, you would almost certainly want filters of around Eu5 or Eu7 grade protecting both the fans and the heat exchanger (so supply side and extract side).

above that the fan power required to drive air through increasing high grade filtration becomes a major burden.

You cannot get high levels of filtration on passive ventilation - the stack effect doesn't provide enough driving force

regards

Barney

Purpose of filters for MVHR systems and the reduction of interior dust

RobinB — Fri, 22 Feb 2013 15:38:51 +0000

Yes it is. Maybe I'm just lazy with the house work.

Purpose of filters for MVHR systems and the reduction of interior dust

Simon Still — Fri, 22 Feb 2013 18:46:03 +0000

Posted By: RobinB I blame the cat.

I blame our cat for a lot. Her ability to hold large amounts of earth in her paws, carry it (without spilling any) up two flights of stairs, to then deposit it on our bed never ceases to amaze.

Purpose of filters for MVHR systems and the reduction of interior dust

Viking House — Fri, 22 Feb 2013 22:15:09 +0000

Its usually dustier in summer and people don't put filters on their open windows. The reality is that only 50% of people change their filters. The main reason for filters is to keep ducts clean.

Purpose of filters for MVHR systems and the reduction of interior dust

borpin — Sat, 23 Feb 2013 07:08:13 +0000

Posted By: ShevekWhat's the purpose of filters for MVHR systems? Are they to filter the incoming air for the occupants or the equipment? Or both? Can you get filters that filter our pollution or is it just relatively large particles like pollen? (We're probably installing Paul MVHR)

Most units come with a G4 Filter to protect the unit. An F7 filter may be an option and this would filter pollen to some extent but this reduces the efficiency of the unit as it has to work harder to get the air through. My Helios 500 has the option of fitting an F7 and I may get one for the summer.

Purpose of filters for MVHR systems and the reduction of interior dust

Shevek — Sun, 24 Feb 2013 16:17:48 +0000

Posted By: Viking HouseIts usually dustier in summer and people don't put filters on their open windows. The reality is that only 50% of people change their filters. The main reason for filters is to keep ducts clean.

Good points.

All of this points to misconception that MVHR results in this dusty houses it seems to me. This was one of the major pros I had in my own head at least. Now I think I'm leaning more toward putting PVHR (e.g. Ventive) in.

Purpose of filters for MVHR systems and the reduction of interior dust

djh — Wed, 27 Feb 2013 20:28:57 +0000

Posted By: Simon StillI blame our cat for a lot. Her ability to hold large amounts of earth in her paws, carry it (without spilling any) up two flights of stairs, to then deposit it on our bed never ceases to amaze.

I think the trick is to lick your paws so the dust sticks to them, walk it upstairs, then curl up on the bed for a while until your paws dry and the dust falls off.

Scratching yourself is also good for generating a bit of dust and giving your staff something to do.