HVAC Systems for VI Mitigation: Performance and Reliability Considerations
For commercial and industrial buildings subject to vapor intrusion (VI) of subsurface volatile organic compounds (VOCs), the heating, ventilating, and air conditioning (HVAC) system may be an option for VI prevention or mitigation. The HVAC system could be appropriate as a VI engineering control when other typical mitigation options, such as sub-slab depressurization (SSD), are technically infeasible or costly. A key to the effective use of and reliance on HVAC systems for VI prevention, in addition to adequate design capacity, is the recognition that as a mechanical system, certain operating parameters are critical. HVAC systems can either improve or exacerbate an indoor air quality issue due to VI. Therefore, a thorough understanding of the factors that can influence HVAC system performance must be achieved and controlled over the long term. Performance can be compromised by unintended changes in operating conditions (e.g. air exchange, pressure), or modifications arising from changes in building use and/or occupancy. As with any mechanical system, unintended changes in operations can be caused by equipment malfunction, inadequate maintenance, or other factors that affect building air flow and pressure. Even if an HVAC system is not the primary means of VI mitigation, it should be considered in all VI assessments because it is so fundamental to indoor air quality, which is the ultimate concern of VI mitigation. The presentation will include the results of a recent study to evaluate the consistency and reliability of HVAC systems to maintain acceptable indoor air quality in several buildings that would otherwise be affected by VI.