Energy Balance in Class II Biosafety Cabinets

Biosafety cabinets require a relatively high amount of energy to run, because they require airflow to maintain containment and protection, and they are typically operated continuously to preserve aseptic conditions. Biosafety cabinets also impact the energy requirements of a facility’s HVAC system, which contributes the high energy consumption. To determine the total energy consumption of a biosafety cabinet, both the plug load of the cabinet and the energy used by the HVAC system must be calculated.

The most common types of class II biosafety cabinets are Type A2 and Type B2, and they vary in energy requirements because of how they operate. In addition to a risk assessment, it is important to consider all your laboratory’s heating, cooling and air change requirements when selecting the appropriate type of biosafety cabinet.

Calculating Biosafety Cabinet Plug Load Energy Cost

The electrical energy required to run a biosafety cabinet is referred to as plug load. Plug load is measured in watts (W) and is calculated by multiplying voltage (V) by operating amperage (A). The cost of cabinet power is simply the total watts necessary to run the unit (V x A) converted to kilowatt hours (kWh) per year (W / 1000 × 24 hours × 365 days). Using the local kWh electricity rate, you can calculate the total cost to power the unit and easily compare different types of class II biosafety cabinets.

Exhaust and Supply Airflow

The amount of air supplied to the lab in order to replace the air exhausted and cool the space due to heat loading is calculated by determining the amount of flow (CFM) required, and then determining the annual cost using your facility’s average cost per CFM.

Either the biosafety cabinet exhaust, the laboratory cooling load or the air change requirement will determine the amount of supply air required (and therefore, the cost associated with conditioning the air). If the laboratory flow rate is driven by the cabinet’s exhaust requirement, then the cooling load will most likely be satisfied. If the laboratory is heat load driven, the cost of the biosafety cabinet exhaust should be included in the cost of the exhaust used to cool the space. The amount of energy associated with the conditioned supply air is about the same whether it is used to satisfy the cabinet’s heat contribution to the laboratory or to satisfy the cabinet’s intake / exhaust requirement.

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.