Laboratory Exhaust and Fume Hood Requirements
A newly installed fan exhaust system serving a laboratory or factory above 10,000 cfm must be able to turn down to the regulated minimum circulation rate. Variable air volume fume hoods in intensive labs need automatic sash closure within 5 minutes.
Why lab exhaust is regulated separately
A laboratory exhausts air continuously for safety, and every cubic foot thrown out has to be replaced with conditioned makeup air. That makes lab exhaust one of the largest energy loads in any building that has it — and unlike most loads it runs at full rate around the clock unless something is designed to turn it down.
The code's approach is not to reduce safety ventilation. It is to require the capability to run at less than full rate when full rate is not needed.
The 10,000 cfm threshold
The requirement applies to newly installed fan exhaust systems serving a laboratory or factory greater than 10,000 cfm. Note that it says laboratory or factory — a manufacturing exhaust system of that size is caught by the same provision.
The system must be a variable airflow system capable of reducing zone exhaust and makeup airflow rates to the regulated minimum circulation rate. The floor is set by the safety requirement, not by the energy code — the energy code simply requires the system to be able to reach it.
Four routes, and they map onto the test forms
Compliance can be shown four ways:
- meet all discharge requirements in ANSI Z9.5-2012
- a power limit of 0.85 W/cfm with air treatment devices, or 0.65 W/cfm for other systems
- wind-speed based control using anemometers
- contaminant concentration-based control using sensors
Those routes are visible in the acceptance test family: NRCA-PRC-14c1-F covers simple turndown, 14c2-F wind responsive, 14c3-F contaminant monitoring, with 14a-F as the summary and 14b-F for test and balance. Which form you complete follows directly from which route you chose, so choosing the route is also choosing the test.
The two power limits are worth reading carefully. A system with air treatment devices gets the looser 0.85 W/cfm allowance, because the treatment itself imposes pressure drop the fan has to overcome. Everything else is held to 0.65.
Wind-responsive control is the interesting one
Exhaust discharge has to disperse safely, and how much velocity that needs depends on the wind. A system that assumes worst-case wind runs at worst-case rate permanently. Measuring actual wind speed with anemometers lets it discharge at a lower rate when conditions allow — which is a real saving on a system that never otherwise turns down.
Fume hood sashes close themselves
Variable air volume fume hoods in intensive labs must have an automatic sash closure system with presence detection that closes the sash within 5 minutes of no detection.
The reason is that an open sash on a VAV hood is the single largest exhaust demand in a lab, and hoods are routinely left open when nobody is working at them. Automating the sash removes the dependence on habit. Fume hood acceptance is tested on NRCA-PRC-15-F.
What this means for programme
Every one of these is an acceptance test, and all of the PRC family carry the -F suffix — so a field technician may perform them rather than a certified acceptance test technician. That is useful on lab work, where the specialist commissioning the exhaust system is usually the person best placed to demonstrate it.