building air exchange rate

[hnewman]

Can someone help me with a solid reference to usual and customary engineered air exchange rates for large buildings. I'm a health physicist trying to defend what I think is a reasonable exchange rate of 10/hour to a regulatory agency. This is the case for the building as now engineered. Is there any credible scenario where the building would be used and would not have such an exchange rate? What is the normal range for commercial buildings?
Thanks
Harry Newman

 

[quark]

The air exchange rate as far as residential buildings are concerned, will be set as per the CO2 percentage in the exhalation of a healthy human being.(taken as an average)
There is a regulation to what should be the maximum CO2 percentage in the air.

Based on this calculation it was derived that 16 cfm fresh air is required per person.

If you are taking fresh air from outside always 10ACPH can be high.

As it is difficult to put the formula here I can forward it to you if I have your e-mail id.

 

[hnewman]

Thanks quark

The building is currently a R&D lab with hoods in every roon. The actual exchange rate currently is 10/hour. I am getting called on the possibility that some time in the future the bldg may not be used for the same function and therefore have a lower exchange rate (this affects the modeling work I am performing for residual contaminants).

I really need something hard I can point the reviewers to.

Thanks
Harry

 

[ChasBean1]

hnewman, 1 cfm per square foot is standard total supply air to a building for air conditioning (to satisfy the typical office building thermal loads). This is noted in ASHRAE and well known in HVAC engineering. The average space with 9-foot ceilings set up for adequate cooling and ventilating would have 6.7 ACH supply. Outside air is typically a variable percentage of that. I would guess a year's average outside air concentration of 30% of the total supply - giving 2 ACH of outside air.

Also, ASHRAE 62 establishes design criteria for outside air based on occupancy, and estimates 7 people per 1,000 ft2, with a minimum 20 cfm of outside air per person. Do the math and this only gives about .9 ACH of outside air.

In general, a certain air exchange rate is less of a "need" than the result of the HVAC systems doing what they need to do. There are, however, certain ACH requirements for certain facilities (per AIA - such as 6 total ACH for x-ray rooms). Put a lab hood in that x-ray room and you'll probably get over 20 ACH resulting from the volume of hood exhaust. 5-7 ACH total might typically result from normal, office-type space conditioning.

Hopefully this helps some.