California Air Resources Board

PROJECT SUMMARY:

CARB will be holding a research seminar on how Building Energy Code requirements for multifamily buildings impact indoor air quality (IAQ), energy use and greenhouse gas (GHG) emissions. The energy code requirements studied include air tightness and ventilation strategies for multifamily units.

Unlike single-family homes, units in multifamily buildings have many shared walls with neighboring units. These shared walls provide airflow connections between units and can allow for unwanted transfers of air pollutants. Through field measurements and model simulation, this study investigated how compartmentalization (or enhanced air tightness of individual units) between units in multifamily buildings and ventilation strategies impact IAQ, energy usage, and GHG emissions. The results showed that multifamily units with tighter compartmentalization than the current requirement in the CA Building Energy Codes were achievable and could provide some benefits. Improved compartmentalization could reduce inter-unit air pollutant transfer, energy use, and GHG emissions in multifamily buildings; but it may increase the concentration of air pollutants generated within a unit due to decreased infiltration from outdoors. Therefore, other complementary measures such as enhanced ventilation should be considered together with compartmentalization in future code updates. This study provides important information to inform the development of modern building standards in support of meeting California’s air quality, climate, and energy efficiency goals.

Background:

Multifamily housing represents more than 50% of new residential housing in California annually. Because multifamily construction differs substantially from single-family construction, achieving healthful IAQ as well as significant energy conservation and GHG reductions is more challenging in multifamily buildings. Improved compartmentalization refers to increasing the level of sealing from each multifamily unit to adjacent units, other interior spaces, and the exterior, such that each unit is effectively its own compartment. Title 24-2019 (the CA Building Energy Codes), effective January 1, 2020, required that all new-construction multifamily units either: a) meet a compartmentalization requirement of 0.3 cfm50/ft2, or b) provide balanced ventilation to each dwelling unit in order to achieve energy, greenhouse gas and IAQ benefits. However, the value for the current compartmentalization requirement was based on estimated air-sealing feasibility instead of evidence for specific IAQ improvements. Also, under this code newly constructed multifamily buildings can bypass compartmentalization requirements by installing balanced ventilation systems, which still allows for leakage between units and infiltration due to wind and stack effects. This study was designed to test the impacts of the current Building Energy Code requirements about compartmentalization on providing indoor air quality, energy and GHG emission benefits.

Biography

The principal investigator, Mark Modera, PhD, is the Associate Director of the Western Cooling Efficiency Center (WCEC), University of California, Davis. Dr. Modera was a Professor in the Departments of Civil & Environmental Engineering and Mechanical & Aerospace Engineering from 2009 to 2019 and served as the Director of the WCEC from 2008 to 2019. His current research projects encompass (i) HVAC-equipment efficiency improvement; (ii) alternative cooling technologies, (iii) thermal energy distribution and air leakage, (iv) water management technologies and strategies, (v) aerosol particle production analysis and application to sealing.

The co-principal investigator, Deborah Hall Bennett, PhD, is a Professor and the Division Chief in the Department of Public Health Sciences, University of California, Davis. Dr. Bennett’s research focuses on the fate, transport, and exposure of organic compounds and particulate matter in the indoor environment, including direct consumer product use, within the context of both environmental epidemiology and environmental risk assessment. She utilizes both modeling and measurement techniques, bridging the gap between these two lines of inquiry. She has been a leader in indoor fate and transfer modeling and have also conducted numerous field studies in the indoor environment and environmental exposures.