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A PILOT STUDY OF THE INFLUENCE OF RESIDENTIAL HAC DUTY CYCLE ON INDOOR AIR QUALITY (AE)
Citation:
THORNBURG, J., C. E. RODES, P. LAWLESS, C. D. STEVENS, AND R. W. WILLIAMS. A PILOT STUDY OF THE INFLUENCE OF RESIDENTIAL HAC DUTY CYCLE ON INDOOR AIR QUALITY (AE). ATMOSPHERIC ENVIRONMENT. Elsevier Science Ltd, New York, NY, 38(11):1567-1577, (2004).
Impact/Purpose:
The primary study objectives are:
1.To quantify personal exposures and indoor air concentrations for PM/gases for potentially sensitive individuals (cross sectional, inter- and intrapersonal).
2.To describe (magnitude and variability) the relationships between personal exposure, and indoor, outdoor and ambient air concentrations for PM/gases for different sensitive cohorts. These cohorts represent subjects of opportunity and relationships established will not be used to extrapolate to the general population.
3.To examine the inter- and intrapersonal variability in the relationship between personal exposures, and indoor, outdoor, and ambient air concentrations for PM/gases for sensitive individuals.
4.To identify and model the factors that contribute to the inter- and intrapersonal variability in the relationships between personal exposures and indoor, outdoor, and ambient air concentrations for PM/gases.
5.To determine the contribution of ambient concentrations to indoor air/personal exposures for PM/gases.
6.To examine the effects of air shed (location, season), population demographics, and residential setting (apartment vs stand-alone homes) on the relationship between personal exposure and indoor, outdoor, and ambient air concentrations for PM/gases.
Description:
A simple methodology was developed to collect measurements of duty cycle, the fraction of time the heating and air conditioning (HAC) system was operating, inside residences. The primary purpose of the measurements was to assess whether the HAC duty cycle was related to reductions in indoor particulate matter (PM) concentrations. A miniature temperature logger placed on an HAC outlet vent monitored changes in temperature as the system cooled or heated the residence. Temperature step changes signaling duty cycle periods were identified using spreadsheet macros. Parallel measurements of 24-hour integrated air exchange rates (AERs) and indoor PM2.5 and PM10 concentrations were collected to determine relationships with the duty cycle. The mild temperatures (mean = 18.7 °C) present during the Spring season of the RTP PM Panel Study and personal comfort preferences caused low and variable daily duty cycles (mean = 0.061, std. dev. = 0.054) in both heating and cooling mode. Warmer ambient temperatures during the Fall season of the Tampa Asthmatics Children Study (TACS) resulted in cooling-only HAC operation, with a higher mean duty cycle of 0.21 (std. dev. = 0.11). Statistically significant linear relationships were observed between daily average duty cycle and the ambient temperature for both studies. Duty cycle exhibited a strong diurnal pattern commensurate with ambient temperature fluctuations. Duty cycles were positively associated with the residence AERs for heating-mode operations, but negatively associated when operating in cooling mode. Personal preferences contributed to the variability in the relationship between duty cycle and air exchange rate. The relationship between duty cycle and PM2.5 or PM10 indoor-outdoor ratios were not statistically significant. The association of duty cycle with indoor-outdoor ratio was confounded by the short time span (mean of 10.3 minutes for the TACS) of HAC system operation and the presence of strong indoor sources altering the indoor concentration levels.