The below chart is a representation of how these energy requirements (plug load, exhaust system energy, and cabinet exhaust airflow for biosafety cabinet exhaust and heating load) add up to total operating cost for each type of biosafety cabinet. The exact cost will vary depending on local electricity rates, climate, code requirements and what is driving the air changes in a particular laboratory, so the is for comparison purposes only.
The chart shows that a recirculating cabinet exhausted to the room (Type A2) contributes the most to the laboratory cooling load, but there is no increase to the exhaust system power because all the air is exhausted to the room. In contrast, a total exhaust cabinet (Type B2) contributes an insignificant amount to the laboratory cooling load, but it contributes significantly to the exhaust system power because 100% of the air is exhausted.
You may expect that venting a cabinet outdoors is more expensive than venting to the room, however this analysis does not show this. It is actually less costly to operate a Type A2 cabinet vented to the outdoors because the heat load associated with venting to the room is significant. When vented through a canopy connection to the exhaust system, heat is captured and released through the exhaust system, which reduces the cabinet’s heat load to the laboratory. Therefore, even if a risk assessment determines that the Type A2 cabinet can be exhausted to the room, it may be more energy-efficient to vent outside.