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- ESTIMATES OF AIR EXCHANGE RATES THROUGH THE USE OF TOTAL VOLATILE ORGANIC COMPOUND DECAY MEASUREMENTS
- Bradley, Christopher
Indoor air exchange rates are commonly used to assess the overall fitness of a building and assess its performance. More recently, air...
Show moreIndoor air exchange rates are commonly used to assess the overall fitness of a building and assess its performance. More recently, air exchange has become a concern due to the COVD-19 pandemic, requiring replacement air to ensure safety; especially so considering that humans spend much of their time indoors. Building science has focused on air exchange to quantify needs for thermal loads, balancing the overall tightness of a building with the amount of energy consumed. Moreover, guidelines have been created by several different organizations to maintain adequate ventilation to remove indoor air pollution, replacing it with clean outdoor air. Research focuses on how to maintain a comfortable and safe quality of indoor air while balancing the needs of the energy crisis.When installed with proper HVAC systems, air exchange rates can be set to a recommended value based upon the conditions of the environment. Buildings without mechanical ventilation face another issue, mainly that they only rely on natural ventilation and the infiltration rate. Temperature differences between the indoor and outdoor environment and the condition of wind speed and direction create pressure differences across the building envelope, influencing the infiltration rate, which can change the amount of air exchange in buildings with natural or mechanical ventilation. Currently, air exchange rates are commonly measured using tracer gases. More frequently used gases have included perfluorocarbon, sulfur hexafluoride, and carbon dioxide, though none of these have proven to be ideal tracers. Alongside this, cost and burden on the participants of these studies often limit the amount of measurements made. Numerous studies have been conducted on how to model the air exchange rate by the changes in concentrations, but accuracy depends on the amount of information available. Other attempts have been made to characterize buildings by their infiltration rate to make estimations, but other questions have arisen about the accuracy of these methods. Due to their ubiquity in indoor environments, volatile organic compounds have been suggested as a plausible tracer gas for measuring air exchange rates. The plausibility of this method raises questions, such as their behavior within the indoor environment, their ability to be measured and the cost to measure concentrations, and the analytical requirements to characterize the rates of removal as air exchange rates. However, due to the rapid increase of available technology in low cost, lightweight, high-resolution sensors, this novel method of using VOCs, especially indicators of total VOCs (TVOCs), may prove fruitful in measuring air exchange within specific microenvironments. Analysis of time-series TVOC concentration measurements taken from a study conducted in multiple residences was conducted to investigate the feasibility of using these measurements, and especially naturally occurring elevation and decay periods, as a proxy for calculating air exchange rates. Though the removal rates of these compounds fell within the range of typical air exchange rates for residential spaces, the results of this analysis suggest the method has potential but with limitations, including the unknown behavior of the individual compounds comprising TVOC measurements within the space, proximity and mixing effects, and potentially invalid comparisons to air exchange rates given from a LBLX model rather than simultaneous tracer gas tests. Future work should explore simultaneous use of TVOC measurements alongside conventional tracer gas testing to further explore the potential utility of such methods.