[Greenbuilding] ERV's and air handlers

[John Straube]

It is effective and practical to use the air handlers and ductwork to distribute air. It is quite reasonable to inject the fresh air on the return side of the AHU and not uncommon,
Two challenges with the approach.  If you inject the air into the ductwork, the AHU would need to be running to distribute the air.  It is rare that the low ventilation air flows will move properly through ducts designed for heating/cooling.  We have solved this my using a FanCycler control (google it) so that the ERV runs on a duty cycle to deliver air, and triggers the AHU to run on low speed if needed.
Second issue, is where the exhaust air comes from.  A good solution if the duct run is not long, is to exhaust from the bathroom, but any hallway or open space is also OK. 
I dont know what the LR return duct is. 

On 2011-02-25, at 10:29 AM, J Messerschmidt wrote:

> Since you are all talking about ERV's, I thought I'd ask a question.  The (conventional) mechanical engineer of a house I'm currently building didn't have an ERV spec'd.  Since I'm tightening it up, I recommended one so he added it to one of three air handlers. 
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> I see on the plans that there is a direct duct coming from the outside into the ERV and then into the air handler.  Another duct leads from a LR return duct to the ERV and then to the outside.  Disregarding the fact that this is on only one of the units, it is an effective solution to go through the air handlers?  If so, then should I lobby to add it to the other units?
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> John
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> From: greenbuilding-bounces at lists.bioenergylists.org [mailto:greenbuilding-bounces at lists.bioenergylists.org] On Behalf Of David Posada
> Sent: Tuesday, February 22, 2011 1:30 PM
> To: 'Tedd Weyman'
> Cc: greenbuilding at lists.bioenergylists.org
> Subject: Re: [Greenbuilding] ERV's
>  
> 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?
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> 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.
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> 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.  
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> David
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> 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).
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> 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).
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> 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.
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> TW
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Dr John Straube, P.Eng.
Associate Professor
University of Waterloo
Dept of Civil Eng. & School of Architecture
www.buildingscience.com

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