Optimizing Laboratory Exhaust Systems

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The creation of sustainable, high-performance and efficient buildings is growing in importance for companies and governments around the world for both economic and environmental reasons. In particular, laboratories are the focus of many of these reduction efforts as they are some of the largest consumers of energy due to the specialized equipment and ventilation systems required for safety and compliance.

Consider this: buildings are currently the largest consumers of energy on the planet, accounting for a staggering 42 percent of energy usage worldwide and generating approximately 40 percent of global greenhouse gas emissions. Compared to a typical commercial office building, the average laboratory facility uses 10 times more energy per square foot, with some laboratories accounting for as much as 100 times more energy use.1 While much of this is due to specialized equipment, a significant amount of energy consumption—up to 80 percent—is due to ventilation systems.2,3

While much attention is focused on air supply and conditioning, exhaust systems have traditionally received the least amount of attention in terms of energy optimization because they only make up one part of the ventilation system. However, exhaust energy comprises up to 40 percent of a ventilation system’s energy use, and as much as 30 percent of a laboratory’s energy consumption, presenting a significant opportunity for laboratories to realize operational energy savings as well as more sustainable operations.

The importance of optimizing laboratories: Financial and beyond

Taking into consideration the amount of energy a laboratory ventilation system uses, reducing any possible waste through energy reduction can provide laboratories with a tangible return on investment in operational costs alone. But beyond the obvious financial benefits, it is also important to consider the emphasis by today’s consumers and the federal government to operate in a sustainable manner. For this reason, corporate responsibility and environmental protection are also large considerations for any company operating in today’s economy.

In addition, the potential for reducing impact on the climate in laboratories alone is enormous. The U.S. Environmental Protection Agency (EPA) estimates that if half of the laboratories in the U.S. reduced energy use by 30 percent—a goal that it considers possible—it would be comparable to reducing national energy consumption by 84 trillion BTUs. That’s enough energy to power 840,000 households and is equivalent to removing 1.3 million cars from U.S. highways or preventing 56 million trees from being harvested.2

Laboratory exhausts and energy consumption

Reducing the energy use of laboratory exhaust systems can be achieved by addressing two primary issues: design of exhaust stacks and power maintenance of the systems.

Historically, the exhaust stacks have been kept short for aesthetic reasons. However, because plume rise is directly related to stack height, shorter stacks increase the exhaust load, resulting in wasted energy. If a stack is taller, less power is required to reach the desired plume height, whereas with shorter stacks, more energy is required.4 This is critical because laboratories must maintain a minimum exhaust velocity to ensure safety and effectiveness. The American National Standards Institute (ANSI)5 recommends a minimum exit velocity of 3,000 feet per minute (fpm), and the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) puts the figure at between 2,000 and 3,000 fpm.6

A second reason for the high energy consumption of exhaust systems is that they are typically maintained at full power on a constant basis—in many laboratories, 24 hours per day, 7 days a week. Furthermore, these settings are usually based on worst-case scenarios for wind conditions and contaminants. In the case of wind, the worst conditions only occur a small percentage of the time. For contaminants, the EPA states: “An overly conservative judgment about the potential toxicity of an exhaust stream may result in a high-energy-use exhaust system as volume flow or exit velocity is increased unnecessarily.” The agency recommends that the exhaust flow be based on scientific measurements of actual contaminants, adjusting it accordingly to achieve “an exhaust system that yields acceptable air quality while consuming a minimum amount of energy.”7

Considering the above factors, it is very likely that in most laboratories, exhaust flow is set higher than needed a high percentage of the time, resulting in a significant amount of energy waste.

Adding up the savings

While mathematical modeling and wind tunnel tests can provide valuable predictive data on exhaust safety and engineering savings, the real test is in actual use. Field data suggests that the energy savings from optimized exhaust systems can be substantial.

Based on the experience of operating research laboratories that have used air quality monitors in their exhaust flow, it has been found that worst-case airflow rates are needed only about 12 hours per year—which means that lower set points could be used if proper monitoring is in place—as much as 99 percent of the time. For example, one laboratory was able to reduce the exhaust-related energy use to just 10 percent of previous levels through the use of a staged variable air volume (VAV) system with anemometer control. This resulted in annual savings of $81,000 plus an additional bonus of $90,000 from the company’s utility company for conservation incentives.

While the potential for realized savings is dependent on each laboratory, its system and air quality requirements, there is a clear opportunity to reduce costs and environmental impact by optimizing exhaust systems.

Strategies for reducing energy use

By using an automated monitoring and control system, it is often possible to safely reduce energy use in laboratory exhaust systems by as much as 50 percent or more, which would reduce a laboratory’s total energy use by 15 percent. There are several proven concepts within the market, and one such example is based on the paper “Labs for the 21st Century,” authored by Brad Cochran, Ron Petersen and John Carter of Cermak Peterka Petersen (CPP). The paper offers three effective strategies for accomplishing a safe reduction of energy use, based on replacing CV systems with variable volume exhaust systems,8 including passive variable volume exhaust, active VAV with anemometer and active VAV with chemical monitor.

“Labs for the 21st Century” is just one example of several successful concepts for reducing energy in laboratory exhaust systems. However, before being able to execute such a strategic plan for reducing energy within a laboratory facility, today’s laboratory managers are often met with the challenge of justifying the cost of installing new equipment to reduce energy while improving ROI. The following steps will assist laboratory managers and facilities professionals in executing similar projects within their buildings:

1) Engage with a building professional that has knowledge of laboratory environments and understands your company and building’s unique needs and challenges.

2) Perform an audit of your existing exhaust systems to identify areas for improvement.

3) Based on the findings of the audit, create a plan that shows the current amount of energy being used by laboratory exhaust fans, and show the ROI and environmental savings that can be achieved by optimizing the fan system.

4) Once the upgraded equipment is in place, properly train staff on the system to ensure that the equipment is being used correctly for the maximum amount of energy savings.

5) Continuously monitor and look for areas of improvement based on actual aboratory operations.

Conclusion

For compliance and safety reasons, air quality is essential in any laboratory, and exhaust systems play an important role in meeting this requirement. At the same time, exhaust systems are a major contributor to laboratory energy use.

Laboratories can reduce energy use significantly by optimizing their exhaust systems, with the use of modern technologies such as VAV controls, airflow and contaminant sensors, and building automation systems that can adjust airflow for actual conditions. Combined with dispersion analysis studies—using either mathematical models or physical wind tunnels—design engineers can specify exhaust airflows that will reduce energy usage to gain significant operational and environmental savings, while ensuring safe and compliant operations.

Published In

Going Greener Magazine Issue Cover
Going Greener

Published: April 1, 2013

Cover Story

Going Greener

Equipment vendors continue making strides to reduce energy use and consumables.

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