A New Approach to Saving Energy and Enhancing Safety

Over the past five to ten years, research facility design has been adapting to changing laboratory practices. Today’s modern laboratory, especially in the life sciences, operates with fewer fume hoods due to the prevalence of microchemistry, or the use of minute quantities of chemicals, and computational chemistry. Additionally, thermal loads in labs have dropped due to the reduced plug loads of more energy efficient equipment such as LCD monitors instead of CRTs, more efficient freezers, and higher efficiency lighting. The result of all these changes is that the minimum air change rate is now often the dominant or controlling factor for determining average, and in many cases, design values for supply and exhaust air flow volumes in laboratories.

While acknowledging the increasing importance of this factor, there continues to be great debate over the correct value for the minimum air change rates (ACH) for laboratories. Air change rates are often set to a single value between 6 and 12 ACH for a laboratory with no hard guidelines or standards to rely on. The truth is, there is no single correct rate of air changes for even a specific lab room. The dynamic nature of any individual lab space precludes that one “correct” value is appropriate at all times or for all conditions.

The “correct” value varies based on the specific conditions of the lab at a given point in time. For example, if a spill of a solvent or volatile chemical occurs, or chemists are doing work on a bench top that should be done in a hood, a higher room air change rate is desirable. In a spill situation, a rate far above 6 or 8 ACHs, such as 16 ACHs, can provide superior dilution performance at the time of the incident and for a period of time afterwards. When the situation calls for it, a higher air change rate is much more effective in reducing contaminant levels quickly. However, the majority of the time, under normal operating conditions, lab room air is typically clean, and a minimum of 2 ACH would be “correct.” Diluting cleanroom air with clean supply air achieves no benefit and wastes significant amounts of energy.

Consequently, the best theoretical approach regarding minimum air change rates for labs would be to determine the rate based on the real time quality of the air in the laboratory. This would allow airflow in a lab to vary based on all the situational factors affecting lab airflow, as opposed to only the status of the hoods and the thermal load. Implementing a dynamic approach to controlling minimum air change rates requires the ability to measure a unique set of indoor air parameters, such as total volatile organic compounds (TVOCs), particles, carbon dioxide, and humidity, and to integrate this information with the building management system.

Until now, such an approach similar to demand control ventilation (DCV) but applied to laboratories has not been feasible or cost effective primarily due to the quality and quantity of sensors necessary to safely implement this approach. In addition, the associated calibration and maintenance costs rendered it impractical to populate a large number of sensors throughout a facility.