Modeling the resiliency of energy-efficient retrofits in low-income multifamily housing

Abstract

Residential energy efficiency and ventilation retrofits (eg, building weatherization, local exhaust ventilation, HVAC filtration) can influence indoor air quality (IAQ) and occupant health, but these measures' impact varies by occupant activity. In this study, we used the multizone airflow and IAQ analysis program CONTAM to simulate the impacts of energy retrofits on indoor concentrations of PM_2.5 and NO₂ in a low-income multifamily housing complex in Boston, Massachusetts (USA). We evaluated the differential impact of residential activities, such as low- and high-emission cooking, cigarette smoking, and window opening, on IAQ across two seasons. We found that a comprehensive package of energy and ventilation retrofits was resilient to a range of occupant activities, while less holistic approaches without ventilation improvements led to increases in indoor PM_2.5 or NO₂ for some populations. In general, homes with simulated concentration increases included those with heavy cooking and no local exhaust ventilation, and smoking homes without HVAC filtration. Our analytical framework can be used to identify energy-efficient home interventions with indoor retrofit resiliency (ie, those that provide IAQ benefits regardless of occupant activity), as well as less resilient retrofits that can be coupled with behavioral interventions (eg, smoking cessation) to provide cost-effective, widespread benefits.

Keywords: CONTAM; building simulation; energy-efficient retrofits; healthy housing; indoor air quality; indoor retrofit resiliency; multifamily housing.

Figure 1.

Twenty-four-hour average concentrations of total indoor PM_2.5 modeled in Unit A of a low-rise, stacked townhouse apartment building over a week during heating (top panel) and cooling seasons (bottom panel). Each line displays the change in pollutant concentrations from the pre-retrofit (baseline) condition to several post-retrofit conditions by window-opening activity. Post-retrofit conditions include: (1) weatherization only (building sealing, window/door replacements), (2) weatherization plus exhaust fans operating in the kitchen and bathroom during cooking and showering events, respectively, (3) weatherization and higher efficiency HVAC particle filtration (MERV 4 upgraded to MERV 7), and (4) all retrofits (weatherization, exhaust fans, and upgraded HVAC filtration). HVAC filtration was not operational during the cooling season.

Figure 2.

Twenty-four-hour average concentrations of total indoor NO₂ modeled in Unit A of a low-rise, stacked townhouse apartment building over a week during heating (top panel) and cooling seasons (bottom panel). Each panel displays the change in pollutant concentrations from the pre-retrofit (baseline) condition to several post-retrofit conditions by window-opening activity. Post-retrofit conditions include: (1) weatherization only (building sealing, window/door replacements), and (2) weatherization plus exhaust fans operating in the kitchen and bathroom during cooking and showering events, respectively.

Figure 3.

Source-specific 24-hr average concentrations of PM_2.5 and NO₂ from outdoor air infiltration, cooking activities, and cigarette smoking simulated in Unit A of the low-rise, stacked townhouse apartment building in the heating season under several occupant activity scenarios and retrofit conditions, including a) pre-retrofit (i.e., no retrofits), b) post-retrofit weatherization only, c) post-retrofit weatherization plus exhaust fan utilization, d) post-retrofit weatherization plus improved HVAC particle filtration (MERV 4 upgraded to MERV 7), and e) post-retrofit weatherization, exhaust fan utilization, and improved HVAC filtration.

Figure 4.

Source-specific 24-hr average concentrations of PM_2.5 and NO₂ from outdoor air infiltration, cooking activities, and cigarette smoking simulated in Unit A of the modeled low-rise, stacked townhouse apartment building in the cooling season under several occupant activity scenarios and retrofit conditions, including a) pre-retrofit (i.e., no retrofits), b) post-retrofit weatherization only, and c) post-retrofit weatherization plus exhaust fan utilization.