Infiltration air for small commercial space acceptable? 1

[doopedeng]

Hi All,
I'm in Eastern Canada and wonder what you all think of using exhaust fans to provide the ASHRAE 62.1 required fresh air for small commercial tenant fit-up spaces? Some here think providing fresh air through window/door leaks is fine, as long as the heat source for the space can accommodate that extra load. I rather think the fresh air should be controlled and tempered properly with an HRV/ERV or makeup air unit, but this approach is costly for small spaces, so I struggle with my argument.

The National Building Code of Canada, Part 6 states "In ventilation systems that exhaust air to the outdoors, provision shall be made for the admission of a supply of makeup air in sufficient quantity so that the operation of the exhaust system and other exhaust equipment or combustion equipment is not adversely affected," so this does not exclude exhaust-only approach. The code also references ASHRAE 62.1, which doesn't seem to exclude using infiltration as a source of the outdoor air requirements, so I don't believe the code or its references specifically exclude this approach. I would very much appreciate your thoughts on this approach.

Thanks in advance,
Dooped

 

[GMcD]

The Code is a Minimum Standard and should not be used as a design guide. You are in eastern Canada. It gets cold there, right? How does all that cold air leaking through cracks in the envelope affect the integrity of the envelope - think condensation in the walls and other places. Same thing in the summer - hot and humid air outside being drawn through into a potentially colder air conditioned space? Again, how will condensation and building envelope integrity be affected? How will you calculate and "prove" how much air is leaking through the envelope to verify you have enough fresh air to show you comply with the minimum requirements? Assuming = making an a$$ out of U and me. Depending on your local jurisdiction, you may have to comply with the National Energy Code for Buildings - which has a lot of requirements for tightening up the building envelope to PREVENT air leakage and infiltration. Here in BC we have the BC Building Code and the City of Vancouver Building Bylaw, both of which refer to similar ASHRAE ventilation and energy standards as well, but even the Provincial Codes are quite explicit about tightening the envelopes, and every building I've worked on, even single family dwellings since the mid-80's, always had a dedicated source of fresh make-up air that was measurable, controllable, and able to be balanced. Here in Vancouver they are starting to go Passivhaus for some new buildings - how much air leaks through a Passivhaus envelope? Right....

 

[dbill74]

Verify with your AHJ, but I'm pretty sure the phrase "provision shall be made for the admission of makeup air" prohibits your idea to rely on infiltration and would require the use of makeup air fan, louver(s), etc.

Also, if you have too much outside or exhaust air, you will find doors don't close properly, whistle, or require strong arms to open. Depending on the space, I've usually found that amount of outside air required ASHRAE usually exceeds the amount of exhaust air needed.

This is the kind of thing you should be talking to a senior engineer in your organization about for proper guidance in designing ventilation systems.

 

[doopedeng]

GMcD, I agree. Your post outlines exactly my position on this matter. I don't like the idea of bringing in uncontrolled outside air through the envelope for fear of mold and decay issues down the road. I suppose I could follow the lead of the Passivhaus or building science community and simply provide an open path (intake louver) for the makeup air. In my neck of the woods, most contractors and developers have gotten away with sub-standard practices for a long time and the AHJ's are just starting to catch up. I start my designs to meet or better code requirements but the client doesn't always see it the same way, based on "that's the way I've always done it" approach. Old school, to be sure!

dbill74, I agree and have had problems with too much under/over pressurization in the past. This remains a concern where airflow gets high enough, but in this particular instance, I don't believe it will affect the doors.

Thanks for your input!
Dooped

 

[Drazen]

How small system could be so costly for small spaces? They are not, good sizing/specifying sometime spends more time than the whole installation work, if work hours would be comparison.