BSC efficiency yields rewards for owners, environment Part 1: AC vs. DC motor technology By Dave Phillips Laboratories today are facing new challenges. Safety and reliability continue to be paramount, yet there is a growing need worldwide for improved energy efficiency. Laboratory facilities are high energy users, consuming up to 103 more energy per ft2 than many commercial office buildings (according to “A Design Guide for Energy-Efficient Research Laboratories,” published by Lawrence Berkeley National Laboratory’s Center for Building Science). Energy consumption by lab infrastructure and equipment may impact the environment over time, and biological safety cabinets (BSCs) are no exception. Today’s BSCs have become critical to research and have evolved through the years, with many improvements in safety containment performance, ergonomics, and serviceability. However, while BSCs are now among the most effective and commonly used primary containment devices in laboratories, modern technologies are required to achieve maximum energy efficiency. Environmental impacts Paying for energy to power appliances is an essential outlay for all laboratories, and key daily decisions can influence and determine a building’s rates of energy consumption for many years to come. The International Energy Agency has estimated that approximately 95% of carbon dioxide emissions come from energy combustion and contribute to the majority of the global warming potential of greenhouse gases that are released into the atmosphere. Globally, greenhouse gas emissions have increased more than four-fold in the last half of the 20th Century, and they are still growing. The International Energy Agency has also estimated that 85% of the world’s extra energy needs over the next 25 years will be met by fossil fuels and that, without action, global energy demand and carbon emissions will both grow by 60%. However, sustainable lower carbon consumption could be achieved through more efficient use of energy. As biological safety cabinets become essential equipment in more and more labs, BSC energy use is contributing more to the energy profile of science buildings. Photo courtesy of Thermo Fisher Scientific. Click to enlarge. Designed to consume less energy One of the key objectives in the design of Class II biological safety cabinets is to create a product that is energy-efficient and cost-effective. Crucial goals include reducing energy consumption, minimizing the use of environmentally damaging substances, and optimizing the useful life of the cabinet. This leads to a reduction in energy bills, lower demand, and a smaller environmental footprint, thereby helping to reduce the environmental impacts associated with carbon dioxide and other emissions. Although manufacturers have made many improvements in the energy efficiency of BSCs during recent years, lab owners and managers should consider all available technologies and usage patterns to ensure maximum savings. A BSC consumes energy in three ways: electricity for operation, additional cooling required, and conditioning of replacement air for exhaust. The BSC energy consumption for operation is proportional to the required intake velocity of the class and type of the cabinet and the area of the opening, how the BSC chamber is maintained when not being used, and the use of ultraviolet radiation. The predominant energy consumption related to the external exhausting of BSCs arises from the heating and cooling of the makeup air (the quantity of air drawn into the laboratory to make up for extracted air), and from the fan power required for the extraction processes. Therefore, the greatest energy efficiency can be achieved when these are minimized, and users should not choose BSCs that are more sophisticated than required by the laboratory application. Improved energy efficiency through better motors One of the first points to consider in achieving maximum energy efficiency is how much the BSC is used. All BSCs have an operational mode with the fans at operational speed and the sample chamber illuminated. The major differentiator in energy consumption among various BSC models is whether the electric fan motor is an alternating current (AC) or direct current (DC) motor. AC motors were originally chosen for BSCs because of their desirable maintenance characteristics. Although DC motors were more efficient at the smaller sizes used in BSCs and offered better control, the DC motors available at the inception of the BSC had brushes requiring regular replacement. The AC motors did not require this maintenance and so became the motor of choice for BSCs. Within the past five years, brushless DC motors have become available, allowing DC motors to take their rightful place in BSC design. Compared with AC motors, DC motors are more efficient and offer more accurate speed control. DC motors are also smaller, providing manufacturers with the opportunity to design applications within a compact footprint. In addition, BSCs with DC motors require as little as 26% of the energy of comparable AC motor designs, since they draw less current and consume less power. Cabinets using this technology also operate much more efficiently at low speeds. Therefore, the first energy saving technology lab owners should employ with regard to BSCs is the use of DC motors. The more the BSC is used, the more cost savings the DC choice provides. In addition, BSCs with DC motors deliver improved performance, reliability, and reduced noise levels. Improved energy consumption The second key BSC energy consideration is how the sample chamber is maintained when not in use. While some users and procedures allow the BSC to be completely shut down, other procedures require that the sample chamber be continuously protected even when not in use. Energy consumption can be slightly reduced in these cases even in cabinets with AC motors by turning off the fluorescent lights. Field surveys indicate that this simple step can reduce energy consumption by almost 100 W. While AC motor designs cannot reduce the fan speed and energy consumption significantly for non- operational times, BSCs using DC motors can. Modern BSCs that employ DC motor technology can provide a reduced-flow mode whereby the window is partially or totally closed and the fan speeds greatly reduced. This mode circulates a very small amount of air through the BSC to allow maintenance of the clean sample chamber. Loading of the filters at this setting is minimal to nonexistent, and energy consumption is reduced to <10% of the operational consumption of traditional AC motor designs. This means that users who need to maintain the sample chamber even when not working in the BSC would benefit the most from a BSC with a reduced flow capability. Table 1. Impact of AC and DC motor usage on energy consumption of biological safety cabinets. Source: Thermo Fisher Scientific. Click to enlarge. A hidden cost to operating a BSC is from cooling the air in the laboratory. Fans and lights in BSCs generate heat in amounts directly related to the energy consumed. For example, a typical 4-ft-wide Class II BSC will generate from 1,900 to 2,900 BTUs/hr. This heat must then be dissipated, and since most modern laboratories are filled with a wide variety of equipment, additional cooling may even be necessary beyond the summer months. Use of energy- efficient motors and lower energy reduced-flow modes can decrease the BTUs generated by as much as 75%. In Table 1 (above, left), the comparative impact of AC and DC motors and the usage pattern of a BSC can be seen. The first column contrasts the energy consumption and typical cost of a BSC with DC motor technology to that of a unit with AC motor technology for a BSC used constantly, year-round. The DC-motor BSC consumes 65% less electricity. The second column shows the energy consumption a BSC with DC motor technology and a BSC with AC motor technology for an application requiring the operation of a BSC 40 hr/week for 50 weeks/yr, and maintenance of the sample chamber even when not operating. The BSC with DC motor technology uses 87% less electricity than the BSC with AC motor technology because of the greater capability for a reduced-flow mode with DC motors. Even within each type of motor technology, we see a reduction in energy use when the BSC is not fully operational around the clock (as in column 1). There is an 8% reduction for the AC motor technology and a 64% reduction for the BSC with DC motor technology. The third column shows the energy consumption a BSC with DC motor technology and a BSC with AC motor technology for an application requiring the operation of a BSC 40 hr/week for 50 weeks/yr and completely turned off when not operating. The BSC with DC motor technology uses 64% less electricity than the BSC with AC motor technology. As expected, a reduction in energy use would occur with both types of motor technologies. Fig. 1. Estimated annual cost of operating one BSC utilizing DC motor technology vs. AC motor technology. Source: Thermo Fisher Scientific. Click to enlarge. In general, the energy savings in using a BSC with DC motor technology vs. AC technology can be ~65%, and even as much as 87% for applications where the BSC is operated during normal work hours, but must maintain the sample chamber cleanliness when not in operation. The resulting reductions in annual operating cost are graphically illustrated in Fig. 1 (left). In conclusion, comfort, health, and safety requirements are no longer the only objectives when choosing and using a BSC, and environmental conditions for experimental work are equally important. Laboratories are high consumers of energy, so reducing overall energy usage is critical for a cost-efficient laboratory. BSCs with the latest energy-efficient technologies and optimal design specifications offer maximum performance and capacity, reducing energy use and heat emission by ~60% compared with traditional BSCs. A reduction in energy consumption allows relative reductions in carbon dioxide emissions, as well as optimizing the efficiency and operation of the biological safety cabinet and ultimately, the lab building. Next month, Part 2 of this article will examine the benefits and energy costs associated with different exhaust methods and optimizing the use of UV germicidal lights within BSCs. Dave Phillips is a technical applications specialist-laminar flow with Thermo Fisher Scientific. The company provides a complete range of lab products and solutions, including biological safety cabinets (www.thermo.com/bsc).