Evaporative Cooler Use Influences Temporal Indoor Relative Humidity but Not Dust Mite Allergen Levels in Homes in a Semi-Arid Climate

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.

Associations between evaporative cooling and dust‐mite allergens, endotoxins, and β‐(1 → 3)‐d‐glucans in house dust: A study of low‐income homes

“…56 In contrast, occupant densities for middle-income homes in Utah were 1.72 residents/100 m 2 . 22 Thus, it appears that low RH in homes in dry climates, even when evaporative coolers are used, discourages dustmite growth unless there are compounding housing factors, such as high occupant density.…”

“…The bioaerosol profile of an individual home varies widely based on multiple housing factors, including geographical location, [7][8][9][10][11][12] presence of indoor or outdoor animals, 7-16 living on a farm, 7,13 number of occupants, [8][9][10][11]14 cleanliness and presence of cockroaches, 8,15 presence of carpeting or rugs, 10,13 and other factors. 20,22 The higher RH from evaporative coolers may create an ecological niche for HDMs to survive in arid and semi-arid climates, 17,20 potentially exposing home occupants to mite allergens. [17][18][19][20] Evaporative coolers are predominantly used in climates with low relative humidity (RH) and seasonally high outdoor temperatures 21 such as the Rocky Mountain States in the US.…”

“…Residential evaporative coolers remove heat from dry ambient air by drawing the air across a wetted filter media, resulting in lower indoor air temperature, but higher RH. 20,22 The higher RH from evaporative coolers may create an ecological niche for HDMs to survive in arid and semi-arid climates, 17,20 potentially exposing home occupants to mite allergens. 23 Furthermore, untreated evaporative cooler sump water provides a growth medium for Gram-negative bacteria during summer months 24 and may be a significant source of residential endotoxin load in homes.…”

Differential effects of air conditioning type on residential endotoxin levels in a semi-arid climate

“…Conversely, evaporative “swamp” coolers, which are commonly used in dry climates, increase indoor RH and may promote bacterial growth. Evaporative coolers work by pulling hot, dry ambient air into the home through wet filters, resulting in lower air temperature, but higher RH . Furthermore, high levels of Gram‐negative bacteria have been found in evaporative cooler sump water .…”

“…Evaporative coolers work by pulling hot, dry ambient air into the home through wet filters, 25 resulting in lower air temperature, but higher RH. 26,27 Furthermore, high levels of Gram-negative bacteria have been found in evaporative cooler sump water. 28 However, to date, there are little data on the relationship between evaporative cooler use and house dust endotoxin levels.…”