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Outside Ventilation and How it Impacts Energy Consumption
As we have mentioned previously, the right filtration system can shave a considerable amount off a building's operating costs. Low static pressure polarized-media electronic air cleaners, when replacing 80%+ high-efficiency passive filters, can influence huge savings on both fan energy and maintenance costs.
But there is also another little-utilized way in which filtration can impact even greater energy savings - by optimizing ventilation air requirements using the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) IAQ Procedure.
Ventilation rates are used in conjunction with commercial building codes and construction practices. For many decades, outside ventilation air has been the primary means of diluting indoor contaminants. There are two methods for determining the necessary outdoor air levels in ASHRAE Standard 62.2-2010 - the Ventilation Rate Procedure and the IAQ Procedure.
The Ventilation Rate Procedure is the easier of the two to apply and the vast majority of buildings are designed and operated under its guidelines. The ventilation rate standard specifies a combination of cfm per person and cfm per square foot for various types of buildings. For example, in a typical office space, the HVAC system must bring in 12-15 cfm/person of outdoor air.
When the current ventilation rates were adopted in 1989, two things were assumed: 1) the only means of dealing with contaminants in the space was by dilution with outdoor air (i.e. there was no air cleaning); and 2) the outdoor air level was sufficient to accommodate "moderate smoking" (based on 30% of the occupants smoking 1 cigarette per hour). The ventilation standard also requires that the outdoor air quality meet certain criteria, even though in practice this is something that is often undetermined or unmonitored. Today, we are increasingly apt to see scenarios whereby 1) smoking is prohibited entirely within the building, 2) low VOC-emitting building materials are used inside the building, and/or 3) outdoor ventilation air, especially in urban environments, is more polluted than the indoor air.
The IAQ Procedure is more complicated. It allows for greater fine-tuning and more efficient operation of the HVAC system and outdoor air levels. The IAQ Procedure gives designers and operators outdoor air credit for things such as no smoking, good airflow patterns, and air cleaning. But because it utilizes a series of complex calculations based on performance, it is less straightforward to use than the Ventilation Rate Procedure.
IAQ Procedure guidelines state that if outdoor air and return air are filtered simultaneously, and prescribed MERV ratings are met, then ventilation air can be adjusted. According to guidelines, if the particle level within the space is no worse than it would be using the Ventilation Rate procedure, then filtration efficiency (Dust Spot Efficiency and MERV) can be calculated at lower dilution rates. The IAQ Procedure also requires that known "contaminants of concern" (i.e. gaseous contaminants) be identified and controlled to an acceptable level. ASHRAE has developed formulas for calculating contaminant levels in a space and guidelines as to what levels are of concern. By using "mass balance" formulas in accordance with ASHRAE 62 guidelines, Dynamic has developed calculations to predict contaminant levels with Dynamic Air Cleaners. The Dynamic AirQ™ Program puts these in a format that is easy to interpret, and makes meaningful predictions for CO2 and contaminant levels. The AirQ Program also uses location specific climate and energy data to calculate potential operational savings.
Dynamic Air Cleaners have the ability to control particles, biologicals, and VOCs to ensure superior air quality and allow for significant reductions in outdoor air levels. In a typical building with no smoking and no unusual contaminant sources, outdoor air levels can often be reduced by as much as 50%. Such a reduction can yield significant operational savings in heating and cooling unconditioned outdoor air. For example, in a small office building with a 60-ton rooftop unit, annual savings can be expected in the range of $3,000 to $12,000, depending on the geographic location of the building (hot humid climates have the greatest costs/savings). That represents significant savings.
The other benefit to this approach is that contaminants in outdoor air - should they be the source of problems inside a building - are removed as air enters the building. Schools provide a good illustration. Although ventilation standards are designed to ensure that outdoor air quality meets certain criteria, there can be times, such as when idling school busses are loading or unloading, that engine exhaust fumes are drawn in with the ventilation air. The IAQ Procedure and Dynamic Air Cleaners can not only reduce the volume of outside air - but remove odors, particulates, and contaminants from the incoming outside air as well.
Dynamic Air Cleaners offer many advantages over alternatives. High-efficiency passive filters may meet requirements for controlling particulates at the reduced ventilation rate, but they usually do not address gaseous "contaminants of concern" and are likely to negatively impact energy consumption due to higher resistance to airflow. Dynamic Air Cleaners further reduce operational costs through lower static pressure drop and significantly longer maintenance intervals.
Clean air, healthier indoor conditions and reduced energy costs - the benefits are well worth it. To learn more about Dynamic Air Cleaners, the Dynamic AirQ Program, or to find out how we can conduct a comprehensive Operating Cost Analysis for your next project, call us today or visit www.DynamicAQS.com/commercial.
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