Darryl Beals and I recently attended the 2013 I²SL (International Institute for Sustainable Laboratories) conference (formerly Labs 21 conference) in Minneapolis, MN. It was a pleasure being back in Minneapolis where I went to college at the University of Minnesota. The weather was perfect in the high 70s and I had a chance to catch up with some old friends in the evenings after attending seminars all day.
As you can imagine with a conference focused on lab sustainability, much of the 3-1/2 days of seminars and workshops was focused on saving energy in laboratories. As much as 2/3 of the energy usage of a typical research campus is from the laboratory space that is typically less than 1/5 of the buildings on campus. There is a lot that can be done to improve energy efficiency in new and existing laboratories, but one area that is of special interest to me is to reduce airflow. Electricity is our highest cost driver these days, with natural gas prices being historically low across the country. As most engineers are aware from the fan laws any reduction of airflow amounts to a reduction in fan energy to the third power. For instance, a 25% reduction in CFM will reduce fan power usage by 58%. This is savings you can get excited about!
One big opportunity for savings in airflow is in the laboratories themselves. The first step to reducing air flow is to have a lab with Variable Air Volume (VAV) controls to allow varying the flow of air to and from the lab based on the cooling loads and fume hood sash position while maintaining safe minimum airflow during occupied and unoccupied times. With a VAV system and by sizing equipment for the actual expected loads in the space and establishing minimum Air Change Per Hour (ACPH) based on science, airflow can often be greatly reduced. Many times engineers use a minimum ACPH in the lab, such as ACPH of 6, based on a rule of thumb rather than informed understanding of the work actually being done in the lab. Ideally the facility owner would consult with an Industrial Hygienist to determine safe minimum ACPH during occupied and unoccupied times. At the conference, the University of California (UC) – Irvine presented the success they have had reviewing lab air changes with their Industrial Hygienist to reduce ACPH in 85% of 1,610 lab rooms. Often times this reduction in airflow is in conjunction with an air contaminant monitoring system that will increase airflows in the event of a chemical spill or other accident.
Some of speakers at the conference focused on how further reductions in airflow can be made by reducing the minimum exhaust from fume hoods. Assuming you have a variable flow fume hood, the minimum exhaust when the sash is closed is determined by the AIHA/ANSI Z9.5 standard. The latest version (2012) of this standard allows a minimum range from 150 ACPH to 375 ACPH. This equates to about 10 CFM/SF to 25 CFM/SF of fume hood bench top surface with a typical hood. The old ANSI Z9.5 standard required 25 CFM/SF minimum. The new standard allows significantly lower minimum exhaust air flow in less hazardous fume hoods. The facility’s Environmental Health and Safety personnel or Industrial Hygienist should be consulted to establish the correct minimum fume hood flow. Where many fume hoods are in a lab, this minimum flow can have significant affect on unoccupied and even occupied minimum supply air flow.
Reducing airflow is one area of “low hanging fruit” where lab energy efficiency can be greatly improved. If you have a facility that is currently running with a constant volume lab, you could experience significant energy savings by converting to variable volume and making the above improvements. Sometimes budget gets in the way of full implementation of variable flow in existing laboratories. In those cases, you can take a step-by-step approach as we are doing at Purdue Wetherill Laboratory of Chemistry. In this case, exhaust fans have been prepared for variable flow operation and await future phases to implement variable flow within each lab. As explained at the I²SL conference, these improvements, along with some other items, allowed UC Irvine to save 50% or more in energy costs in their labs.