Relief Air

[Dave Waterworth]

I couldn't find anything relating to Relief Air Fans / Dampers etc in the schema. I'm not sure if this is a universal convention but many buildings I've encountered have both exhaust and relief fans, i.e. I believe configured as per the first diagram from https://energy-models.com/ventilation-infiltration-exfiltration

A relief fan and an exhaust fan seem to perform the same functionality, venting air from the building to the exterior. The difference seems to be that an exhaust fan is stand-alone, a relief fan is part of the recirculation system. It could possibly be that the relief fan is driven by a pressure setpoint (i.e. it operates when pressure exceeds some setpoint) but I'm not sure.

Should relief be added as a concept, or should I just map `relief` to the `exhaust` concepts? 

[Jason Koh]

I believe this has been relatively less discussed so far. I've been using exhaust concepts only, and after a quick search, there might be significant semantic difference as described here by Trane. The main difference seems to be their purposes

- relief is for balancing the indoor air

- exhaust is for remove the indoor air (for refreshing the air)

I like the distinction, but I'm unsure how well this difference is recognized in the industry. I'd love to have others' input here while I'll poke around as well.

With regards,

Jason Koh

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[Paul Raftery]

A relief fan and an exhaust fan both remove air from a building. An exhaust fan is the term often used when the fan locally removes air that has been somehow contaminated from a specific area or areas of a building. For example, you'd find an exhaust fan connected directly to labs, kitchens, bathrooms, etc. In contrast, a relief fan removes air from the general return air coming back to the air handler (i.e. the air coming back from the whole building, including spaces like offices, hallways, etc., that could in part be reused/recirculated back into the building as long as ventilation requirements are met). The relief fans' purpose is to balance pressure within the building, essentially by removing the net airflow from the combination of air handler outdoor airflow, and exhaust airflow, and infilitration/exfiltration through the building envelope. Relief fans are common on systems that have economizers as these systems typically have high outdoor air flow rates when they are in economizing mode, which is much higher than ventilation or exhaust requirements in most cases, and so the building would be overpressurized if there was no relief fan or some other means of relief (e.g. a relief damper).

  

You can find a technical discussion of different types of relief systems here, which describes the different types of layout of return and relief fan systems. As mentioned in that article, and as with almost everything in the HVAC industry, different people/organizations/regions use different terms to describe the same physical system. Some people call a relief fan an exhaust fan, especially in systems/regions that don't typically use economizers.

For the BRICK schema, I think there is value in distinguishing between a relief fan and an exhaust fan.

Regards,

Paul

Paul Raftery | Center for the Built Environment  | (510) 725-0562

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[Gabe Fierro]

Thanks for the insight, Paul! Dave, would you be able to add Relief Fan as a concept to Brick in a PR? I feel like it makes the most sense as a sibling to Exhaust Fan.

Best,

Gabe

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[Dave Waterworth]

I've created a PR that includes both brick:Relief_Fan and brick:Relief_Damper (along with tag:Relief). I think that's all that's necessary at this stage.

[Matt Steen]

Although I've preferred to ignore relief air in favor using exhaust (EA vs. RA for return air), ASHRAE's definition aligns with Paul's description.

Exhaust Air = https://xp20.ashrae.org/terminology/index.php?term=exhaust&submit=Search

Relief Air = https://xp20.ashrae.org/terminology/index.php?term=relief&submit=Search