A change in paradigm, low flow fume hoods, can provide compelling benefits your lab’s bottom line without compromising safety. Are your fume hoods sucking too much money out of your labs? Safety is almost exclusive of other considerations, including energy consumption, waste and cost; you can’t argue with safety in a lab. A low flow fume hood is first and foremost a safety device with its intended purpose to keep users safe and healthy. Fume hoods create a large amount of airflow, which drives overall HVAC sizing and energy requirements within the building it’s located in. Although costs vary, with climate a contributing variable, the average annual cost of a fume hood operation is approximately $6,000. In the US alone, there are approximately 750,000 fume hoods, with an estimated annual operating cost of $4.2 billion and a corresponding 5,100 megawatts of peak electrical demand. Savings and energy use potential can be significant.
Supply and exhaust fans, space-cooling energy, space-heating energy, and depending on geographic areas, either humidification or de-humidification and terminal reheat all contribute to the energy consumption and associated operational costs of a fume hood. Ventilation is often the dominant contributor to lab energy consumption and can be roughly twice as much as lighting and other electrical loads combined. Proper ventilation is essential to protecting its workers, but too much airflow can waste significant energy and cost.
Whether new construction or retrofitting an existing lab, energy strategies must fit within the space requirements without compromise. This can often be accomplished by focusing on needs rather than want in the design process. The cost to temper a lab room’s air that the fume hood simply pumps outside directly correlates to a fume hood’s energy consumption and operational costs. The number of required air changes, which is dependent on volume and type of chemicals used, volume of heavy instrumentation/BTU’s, and the number of researchers or students are drivers behind room exhaust. Air volume (CFM) requirements within a lab also directly correlate to energy consumption of a fume hood. Costs however are typically second in importance to face velocity. It is possible to properly ventilate a lab for optimal safety, while conserving energy and saving money.
An emerging trend, in response to changing needs, desire for sustainability and conservation of energy and associated costs within the lab, fume hood manufacturers have developed and introduced energy-efficient low flow / high performance fume hoods, designed to at minimum maintain if not improve operator protection while reducing costs and conserving energy.
There can be confusion between low flow and low velocity. A low flow hood reduces exhaust volume by operating through a reduced sash opening; containment does not need to be the same with a fully opened sash for setup as it is for usage. Whereas low velocity hoods retain proper capture (4.0AIO.10) when the sash is raised for set up and face velocity drops as low as 60 fpm. Each can achieve energy savings by reducing the sash opening and corresponding exhaust volume, however a low flow hood requires proper sash management for both setup and usage so as not to waste conditioned air and energy.
A high performance CAV hood typically has higher initial set up costs, when compared to a conventional bypass hood, however its ROI can be achieved rather quickly depending on hood size and sash setting. A high performance hood in a lab is one of the most powerful ways to reduce energy consumption by providing the highest level of improved containment and airflow, which in turn allow these hoods to operate at a face velocity as low as 60 fpm.
Not only does a low flow hood operate at approximately 60% of that of a standard bypass hood, passing the ASHRAE 110 test, it can also mean a reduction in support equipment costs: less powerful blowers to purchase, maintain and replace. It also means a reduction in conditioned air pumped into the lab, which equates to smaller air conditioners, furnaces and air handlers. All this can add up to a significant domino effect on energy savings.
A hood should have low, but safe, face velocity and / or a small opening area. The lowest acceptable standard safe face velocity currently noted in any major standard is 60 fpm; nothing suggests that anything below 60 is safe. The variable then becomes opening area. A reduction in opening area reduces the required CFM, which reduces the consumption of tempered air leading to a reduction in energy consumption and operating costs.
When installed, fume hoods should be inspected in accordance to the ASHRAE110, an industry standard tracer gas mannequin method, to ensure proper ventilation. Annually hoods should be tested and recertified, ensuring air is balanced with supply and exhaust air flow in proper proportion to maintain a negative balance between lab space and the outside corridor and as well, face velocities meet design criteria. Exhaust flow must be greater than supply to create air movement from hall into the lab so as to contain any airborne contaminants. Any leakage and proper containment integrity should be evaluated with a random testing of hoods.
To justify the additional up-front costs required for low flow fume hoods, as well as other potential options in order to realize a reduction in energy consumption, some substantial, requires a cost comparison between fume hoods and life cycle cost analysis to compare total expense for the life of each system or combination of systems. Breakeven points can vary depending on climate, energy costs and usage.