Air Change Rates and Interzonal Flows in Residences, and the Need for Multi-Zone Models for Exposure and Health Analyses

Liuliu Du,Jo-Yu Chin,Michael Breen,Toby Lewis,Edith Parker,Thomas Robins,Christopher Godwin,Stuart Batterman,Wilma Brakefield

doi:10.3390/ijerph9124639

Abstract

Air change rates (ACRs) and interzonal flows are key determinants of indoor air quality (IAQ) and building energy use. This paper characterizes ACRs and interzonal flows in 126 houses, and evaluates effects of these parameters on IAQ. ACRs measured using weeklong tracer measurements in several seasons averaged 0.73 ± 0.76 h−1 (median = 0.57 h−1, n = 263) in the general living area, and much higher, 1.66 ± 1.50 h−1 (median = 1.23 h−1, n = 253) in bedrooms. Living area ACRs were highest in winter and lowest in spring; bedroom ACRs were highest in summer and lowest in spring. Bedrooms received an average of 55 ± 18% of air from elsewhere in the house; the living area received only 26 ± 20% from the bedroom. Interzonal flows did not depend on season, indoor smoking or the presence of air conditioners. A two-zone IAQ model calibrated for the field study showed large differences in pollutant levels between the living area and bedroom, and the key parameters affecting IAQ were emission rates, emission source locations, air filter use, ACRs, interzonal flows, outdoor concentrations, and PM penetration factors. The single-zone models that are commonly used for residences have substantial limitations and may inadequately represent pollutant concentrations and exposures in bedrooms and potentially other environments other where people spend a substantial fraction of time.

Highlights

With few exceptions, previous indoor air quality (IAQ) studies have assumed that residences and other small buildings are well mixed spaces throughout which pollutant concentrations are uniform, allowing the building to be represented as a single zone [1,2,3,4]
The distribution of air change rates (ACRs) (Figure 2) show that most values fell in a narrow range, e.g., only 10% of measurements were below 0.2 h−1 and 1% exceeded 4 h−1, and measurements were lognormally distributed (p = 0.32, Anderson-Darling test)
This paper presents results and analyses of a large survey of homes in Detroit, Michigan investigating air exchange rates (ACRs) and interzonal flows, two important factors relevant to indoor air quality (IAQ), as well as energy and comfort

Summary

Introduction

Previous indoor air quality (IAQ) studies have assumed that residences and other small buildings are well mixed spaces throughout which pollutant concentrations are uniform, allowing the building to be represented as a single zone [1,2,3,4] While this assumption facilitates analyses and may be reasonable for some purposes, it is highly idealized. The existence of localized emission sources within buildings, such as cigarette smoking or chemical use occurring in only portions of a building, is likely to produce pollutant differentials [4,5] Pollutants such as particulate matter (PM) and ozone, which have relatively high deposition or removal rates, are sensitive to age-of-air and other factors that affect pollutant removal and lifetime [6,7] and that serve to increase spatial variation. Areas of buildings that are either partially decoupled from the rest of the building, or that have air change rates (ACRs) that differ from the building as a whole, may differ in concentration, a result of varying rates of dilution, deposition or transport in the building [2,5]

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