[Greenbuilding] ERV's

[David Posada]

Hi Tedd,
Thanks for your input. You raise a good point about the wind pressure from the local microclimate - something to consider.

Since ASHRAE 62.2 is trying to prevent to under-the-door infiltration of air quality issues you mention, and if the units have their own make-up air supply you could probably use door sweeps. You're right - either the bath fan or the stove hood exhaust alone could ventilate the unit in exhaust-only mode, so the question then becomes where to get the make-up air supply?

Options seem to fall into two camps - local, individual make-up air at the outer wall from a trickle vent or spot ERV, or else a central system ducted from the corridor.

For local make-up air, one might ask if the trickle vent raises questions of thermal comfort and/ or additional heat load from unconditioned outside air, and if the Spot ERV is thus a good alternative to help condition that make-up air. Other options might be based around centrally supplied make-up air, so to inform the cost-benefit comparisons it's great to hear input like yours.

David


From: Tedd Weyman [mailto:weyman_tedd at yahoo.com]
Sent: Tuesday, February 22, 2011 7:10 AM
To: David Posada
Cc: greenbuilding at lists.bioenergylists.org
Subject: ERV's

I recently decided against using a spot ERV for a 5 room, 1200' sq cottage (radiant heat) because the local wind pressures and stack effects make the pressure drives on the exterior just too overwhelming for a light weight, low-CFM, ERV. If your heat recovery and air exchange are not from a central system (i.e. powerful enough to take over the buildings climate, including ducting to all rooms), its unlikely a small ERV will be able to overcome the external environmental forces on the building your describing (i.e small apartments or condos).

A normal kitchen exhaust (if its externally vented and not just an internal filter - has 400 to 1000 CFM) and your bathroom exhaust (120+ CFM) are more (locally) powerful than a full sized, let alone a spot ERV and probably perfectly adequate to meet all the air exchange needs in small and medium sized living units. Timer controlled fresh air supply might be needed to complement/supplement the exhaust of a timed bathroom exhaust and during the cooking cycles of the kitchen exhaust.  Your under-door fresh air supply (allegedly fresh air) will defeat the spot HRV's performance (its not just a question of volume of air per minute, its the flow rate and pressures).

If you live in a apt/condo, under-the-door positive pressure from the hallway brings is ugly.  Give me independent air such as the trickle-vent or a coordinated (with exhaust) timed fresh air supply any day over the stale smells and particulates of fried fish, cigarettes, cat hair and marijuana smoke from the neighbours.

I bet there are half a dozen other things you can do per unit for the same price (investment) as the spot ERV that will more constructively affect living climate, improve the air quality, and conserve/recycle/reduce energy waste.

TW







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