Three approaches to improve existing ventilation and filtration systems in buildings were evaluated to assess their impact on energy use and indoor air quality. A test method to evaluate existing carbon dioxide (CO2) based demand control ventilation (DCV) systems was developed and demonstrated. Six commercially available controllers were tested to demonstrate the test method and provide directly comparable results. Most of the commercially available controllers had marginal or poor performance for CO2 control and excessive damper movement. Notably, a proportional-integration (PI) algorithm configured and tested by the research team achieved superior performance with CO2 control 92% of the time and damper movement 1.5 times an ideal controller.
DCV systems are often paired with an economizer function that increases outdoor air to save cooling energy when the outdoor air is within temperature and/or enthalpy conditions set by the controller. A major shortcoming of economizer controls is they do not consider outdoor air pollution levels. The rule-based IAQ-Energy Controller, which includes an economizer and DCV and consideration of outdoor particulate matter (PM) was developed and evaluated (see figure). The performance of the IAQ-Energy Controller was modeled for a single-zone HVAC system in a classroom environment in 14 US cities for five years with historical weather and PM2.5 data (2018 to 2022). In addition to optimizing ventilation rate control, the IAQ-Energy controller approach includes modulating the speed of an internet-connected portable air cleaner (PAC). Relative to the Economizer + DCV Controller, the IAQ-Energy Controller had the biggest impacts in regions impacted by wildfire smoke and reduced average indoor exposure to PM2.5 on the worst day of the year in Stockton, San Francisco, and Seattle by 10.8, 19.0, and 24.3 µg/m3, respectively.
Finally, filtration performance of do-it-yourself (DIY) box fan filters deployed across a university campus were assessed over an academic year. Four DIY air filters were constructed from box fans and air filters with a minimum efficiency reporting value (MERV) of 13 and deployed in four spaces and operated 9 hours a day. The particle size dependent clean air delivery rate (CADR) and single pass filtration efficiency for each box was measured in a laboratory before deployment and every 10 weeks, for a total of five measurements over 40 weeks. We found that these DIY box fan filters maintain robust performance over time, with each air filter maintaining at least 60% of its initial CADR at the end of the 40-week study, even with daily operation in environments with modest particle concentrations. CADR values for particles of 1.0-3.0 µm optical diameter averaged 34% higher than CADR values for 0.35-1.0 µm particles, aligning with MERV 13 filter size-dependent filtration expectations. Reductions in CADR over time were attributed to a reduction in filtration efficiency. The long-term robustness of DIY box fan air filters demonstrates their validity as a cost-effective, high performance, alternative to portable high efficiency particulate air (HEPA) filters.
