Operating Instructions

Controlling Laboratory Air Flow

Siemens Building Technologies, Inc. 3-7

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Do not reduce fume hood flow if ventilation is being set back.

Finally, before implementing ventilation setback, a building manager should estimate the

energy savings available. Some key factors are described in the following sections.

Amount of setback possible

When determining the amount of setback possible, consider the following questions:

• How much of a reduction has the Safety Official endorsed?

• Is a corresponding reduction in exhaust possible?

The supply airflow doesn't only dilute contaminants; it also balances the exhaust flow. This

means that correct pressurization is required, even when the need for ventilation is reduced.

The general exhaust may be reduced as part of the ventilation setback strategy; however,

that does not affect the fume hoods or any other exhaust devices. It is possible that the

minimum exhaust will not allow supply flows as low as the minimum air change rate.

NOTE:

If the laboratory does not have a general exhaust, it may be impossible to reduce

the ventilation as the supply flow has to track the exhaust devices.

Hours of unoccupied operation

The hours of unoccupied operation for laboratories can vary greatly, but most laboratories are

occupied less than half the time. These long unoccupied periods can make even a small

reduction in flow cost-effective. An important consideration is how spaces are used.

Cost of conditioning supply air

The cost of conditioning supply air is usually the largest part of the cost savings. The energy

savings depend on outside air conditions. The savings also depend on the particular HVAC

system and the way it runs. What is the supply air temperature, and what do you spend to

achieve it? If the energy source is free heat from a co-generation plant, you will get a different

result than if the energy source is expensive chilled water.

Cost of moving supply and exhaust flows

The cost of moving supply and exhaust flows into and out of a room can be significant even

in cases where the cost of conditioning the supply air is not. Reducing flow requirements at

the fans can also lead to energy savings.