Commercial Building pressurization question

[Dan Gratton]

Can anyone advise me on where to get information on how to pressurize a commercial building using the HVAC system? Or alternatively, how to do this using the HVAC system?

[Scott Gilligan, CMI]

Most HVAC systems only recirculate the indoor air and condition it as it passes over the evaporator coils. They do not draw in outside air. Even if you set all the units to the blower setting, all you would be doing is recirculating. You need to introduce outside air and have it remain in the building to get an elevated pressure. You will still probably need a blower door system in order to accomplish this. If you just want to pressurize the building, say for a thermal imaging scan, you might not need all the gauges and a calibrated fan. You might be able to get by with blower door frames and a high volume fan like they use in mold or other haz-mat remediation.

Can you please explain a litlte more why you need to pressurize a commercial building and we might be able to give you the best answer or point you in the right direction?

[Wayne B. Wilson]

Dan
My buildings that i looked after where all Pressurized, Fans going 24 /7 Yes they had outside air supplied. we set dampers to allow 15 % outside air. Required for commercial back then. Have you checked to see if it was pressurized? normalay you can acually hear it when you crack a window or door .

[Dan Gratton]

Thanks guys. I am doing some thermal imaging of commercial building envelopes and wanted to pressurize the building using the HVAC system.

[Joe Farsetta]

Scott,

They do not draw in outside air.

This depends on the configuration. In the settings I find myself in nowadays, we do bring in outside air...

[Marcel R. Cyr]

Joe is correct in stating most Commercial buildings take on outside air.
First of all it needs to meet the requirements of air exchange for the occupants of the building.
Now if you wish to pressurize the Building, the help of a Contol Technician might be required to achieve that.

Exfiltration aiflow is determined by building construction and differential pressure across the envelope. Even a small differential pressure across a leaky envelope can result in significant exfiltration regardless of building size. On the other hand, a very large differntial pressure across a very tight envelpe results in very little exfiltration, again regardless of building size. With these points in mind, any size building can be pressurized provided the envelope is tight enough and provided that the outdoor air intake and supply fan can deliver airflow in excess of local exhaust, exfiltration, and return airflow.

Good luck.

Marcel

[Scott Gilligan, CMI]

Guess it is all relative to what size building we are talking about and the type of HVAC system installed. Most of the buildings I see around here have split systems on the roof or PTAC's. Air handlers are tucked away in ceiling cavities, hallways, or in a mechanical room someplace. The larger rooftop units typically intorduce fresh air into the building. Guess we are missing a critical bit of information here in order to give accurate suggestions.

[Nick Gromicko]

Ever been in an Embassy Suites hotel? That particular layout has so much stack effect that the vacuum pulled on the first floor outside doors is so strong that without outside make-up air, you wouldn't be able to open them. They would feel locked.

[Bruce M. Graham, III]

most package units will have an economiser with barometric relief as well as other control systems in place. Some buildings will have a seperate stair well pressurization system as well.

[Jason Yost]

You should educate yourself on ASHRAE Standards for more information on pressurization of buildings. Mr. Cyr did a good job of introducing to the conversation some important principles to understand. While there are general formulas for calculating the necessary exchange of air these calculations are not the only thing that determines whether or not a building is being pressurized properly. One area may require negative pressure (like a kitchen vs. a bedroom) in relation to another area. What is the purpose of the inspection? What are your Client's expectations?

[bskinner]

When i was doing construction we got a contract to build a Japanese resturant. One where they cook in front of you. It had 16 cooking stations. When we got finished. It took us another week just to get the air flow fine tuned because we had to calibrate Ventilation systems with return air and the HVAC system. When we turned on all the vents for the first time it took 3 people to open an exterior door. And when you did get the door open the air coming in felt like 60mph winds.
That week was not fun.