Is Your Lab Exhaust System Doing More Work Than It Needs To?

Laboratory exhaust systems are among the major energy consumers in research buildings, and they run continuously. In facilities with a single fume hood or low hood density, the architecture of that exhaust system is often carried over from designs built for much larger, centralized laboratories. A recent whitepaper evaluates whether that default assumption holds up when analyzed at the single-hood scale.

What every lab exhaust system must do

Laboratory fume hood exhaust systems have two jobs: keep contaminants contained at the hood opening, and safely disperse exhaust air above the roofline. U.S. standards like ANSI/AIHA Z9.5 and ASHRAE define what those outcomes must look like, and they allow for more than one compliant architecture to achieve them.

How that flexibility plays out depends largely on how the hood itself operates.

How a single fume hood operates

A four-foot laboratory fume hood, one of the most common configurations in university and research labs, does not run at the same airflow all day. Airflow varies directly with sash position, from minimum to near-full sash opening, and exhaust systems are expected to cover that full range continuously, around the clock.

That operating range is where the two main exhaust architectures start to diverge.

Two compliant architectures

Architecture A: Constant fan speed with bypass damper A centrifugal fan runs at constant speed. When hood airflow demand decreases, a bypass damper introduces dilution air upstream of the fan to keep total airflow constant. This requires additional hardware: damper assemblies, actuators, airflow sensors, and control logic.

Architecture B: Fan-speed modulated exhaust An EC fan adjusts speed directly in response to sash position, varying airflow across the full operating range. No bypass hardware is required.

Both architectures are fully compliant with safety standards. What differs is how each one responds when hood demand drops, and what that means over time.

What a representative analysis found

Using a typical laboratory operating profile, with the hood at low sash conditions the majority of the time and systems running 24 hours a day, the two architectures behave very differently.

In Architecture A, fan power remains essentially unchanged regardless of sash position. In Architecture B, as fan speed drops, power drops sharply at low sash, in line with fan affinity laws. That difference in power draw, sustained across a full year of continuous operation, is reflected in the energy figures in the whitepaper.

The capital picture follows a similar pattern. Architecture A requires substantially more equipment and control components than Architecture B for a single-hood installation, a difference that carries through into maintenance costs and redundancy requirements. The full breakdown is in the whitepaper.

Want the full picture?

The whitepaper includes exact airflow ranges, annual energy and cost figures, detailed capital cost tables, maintenance considerations, and redundancy analysis.

📄 Download the full whitepaper → Performance-Based Energy Analysis of Single-Hood Laboratory Exhaust Architectures