Size matters (at least for interior air flow pathways): The indoor air quality and energy implications of compartmentalization in multi-unit residential buildings

Interior building airtightness affects energy consumption and indoor air quality (IAQ) in multi-unit residential buildings (MURBs). Coupled CONTAM-EnergyPlus simulations were used to assess energy and IAQ performance for 4-storey and 20-storey MURBs for a Toronto, Canada climate. Different interior and exterior partition and door airtightness values and mechanical ventilation systems were assessed (including in-suite heat recovery ventilators (HRVs), pressurized corridor systems (PC) and direct-to-suite ducted systems (DTS). Three contaminants were emitted in all suite zones (CO2, NO2 and PM2.5). IAQ was assessed using annual average zone contaminant concentrations and the annual average fraction of suite concentration that originated from other zones, to quantify inter-zonal contaminant transport. Annual average suite fractional CO2 concentrations ranged from 3 to 35% for all airtightness and mechanical ventilation configurations; NO2 and PM2.5 ranges were 2–23% and 0–12%, respectively. HRV cases had the lowest space conditioning energy use intensities (EUI) and annual average suite fractional concentrations, compared to the respective PC and DTS cases. Interior partition and elevator/stairwell door airtightness had minimal effects in the 4-storey cases, but significantly reduced space conditioning EUI and fractional suite concentrations in the 20-storey cases, especially for cases with “loose” building envelope airtightness. Tightening interior/exterior partitions reduced inter-zonal contaminant transport, but increased source zone concentrations by reducing dilution. The results generally corroborate previous studies and highlight the importance of tightening both suite and shaft partitions, especially in tall buildings, and coupling compartmentalization with adequate mechanical ventilation.