Abstract
Concerns about energy consumption and climate change make residential evaporative coolers a popular alternative to central air conditioning in arid and semi-arid climates. However, evaporative coolers have been shown to significantly increase indoor relative humidity and dust mite allergen levels in some studies, while showing no association in other studies. Improved measurement of temporal fluctuations in indoor relative humidity may help identify factors that promote mite growth in homes in dry climates. Dust samples and continuous indoor relative humidity measurements were collected from homes with central air conditioning and homes with evaporative coolers in Utah. Samples were collected over two seasons, winter/spring (Jan–Apr) and summer (July–Sept), 2014. Dust samples were analyzed for Der p 1 and Der f 1 using a two-site monoclonal antibody-based enzyme-linked immunosorbent assay (ELISA) analysis. Housing characteristics including age of home, occupant density, and age of mattresses, furniture, and carpeting were also measured. Positive Der p 1 or Der f 1 samples were found in 25.0% of the homes and there was no difference in mean allergen levels by type of air conditioning. Indoor relative humidity was significantly higher in homes with evaporative coolers compared to those with central air conditioning during the summer. Homes with evaporative coolers also spent significantly more time during summer above 55.0% and 65.0% relative humidity compared to central air homes, but not above 75.0%. Findings from this study suggest that increased humidity from evaporative coolers may not be sufficient to exceed the critical equilibrium humidity or maintain humidity excursions for sufficient duration in relatively larger single-family homes in semi-arid climates to support mite growth and reproduction.
Highlights
Exposure to house dust mite (HDM) allergens is associated with immune system sensitization; development of asthma, rhinitis, and atopic dermatitis; and exacerbation of disease symptoms in sensitized individuals [1,2,3,4,5,6,7]
We found that mean indoor relative humidity (RH) was significantly higher in homes using evaporative coolers during summer months, but levels were below the critical equilibrium humidity necessary for optimal dust mite growth
The semi-arid climate found in Utah County, Utah provides an excellent environment to test the role of evaporative cooling on indoor RH and the presence of HDM allergens since the ambient RH is below the critical equilibrium humidity required for dust mite growth
Summary
Exposure to house dust mite (HDM) allergens is associated with immune system sensitization; development of asthma, rhinitis, and atopic dermatitis; and exacerbation of disease symptoms in sensitized individuals [1,2,3,4,5,6,7]. Dermatophagoides farinae and D. pteronyssinus are the most prevalent mite species found in homes in humid temperate regions in the U.S and worldwide [8, 9]. These mite species acquire water primarily by absorbing moisture from ambient air; indoor relative humidity (RH) is a critical determinant of mite population growth [10,11,12]. Maintaining indoor RH below 50.0% year-round is recommended as a primary control strategy to avoid HDM growth and subsequent allergen exposures [2]
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