The Proceedings of the 8th International Conference on
Indoor Air Quality and Climate - Indoor Air'99 (1999)

EVALUATION AND SUPPRESSION OF FUNGAL GROWTH
IN AN AIR CONDITIONER

K Abe(*1), T Seki(*2) and S Sugawara(*2)

(*1) Institute of Environmental Biology
(*2) Mitsubishi Electric Corporation

Abstract (pdf)_>>

ABSTRACT

Using a fungal index, the microclimate was assessed in an air conditioner when cooled. The fungal index is a parameter for detecting and assessing fungal growth in the environment. The index was the highest in the wet environment inside the air conditioner. To suppress fungal growth, a program to dry the inside after cooling was developed. The fungal index was lowered using the drying program. Fungal contamination in air conditioners can be decreased.

INTRODUCTION

The ducts and filters inside air conditioners can become contaminated by fungi. Since the relative humidity of the air increases when cooled, the relative humidity is high within the cooling unit and in the cooled air outlet of air conditioners during use, promoting the growth of fungi. As air conditioners have become a source of fungal contamination indoors, it is necessary to decrease fungal growth in air conditioners.

METHOD

Measurement of fungal index

A fungal detector for wet environments was prepared by placing the spores of the biosensors and their nutrients on a polystyrene plate covered by non-woven fabric using a double sided adhesive sheet with holes. Two strains, Eurotium sp. J-183 and Alternaria sp. S-78, were used as biosensors. The detectors were placed in exposed areas inside the air conditioners for 24 hours or 5 days, and the fungal index was measured, using the
strain, which showed the high response to the exposed environment.

Air-conditioned rooms and drying program of air conditioner

The rooms were maintained with a climate typical of July. The air conditioners were cooled 2 hours from 8:00 to 10:00 and 4 hours from 17:00 to 21:00 everyday. The drying program was as follows, 15-min. air circulation and 20-min. heating with low wind velocity followed every cooling period.

RESULTS AND DISCUSSION

Fungal index in the air conditioner during cooling

Table 1 shows the fungal indices in the air conditioner in the room set in a climate typical of late July. ○ and ■ indicate fungal indices measured by xerophilic Eurotium sp. J-183 and non-xerophilic Alternaria sp. S-78, respectively, showing whether the surveyed environment was suitable for xerophilic fungi or non-xerophilic fungi. All wet environments in the air conditioner showed a high fungal index, and the growth of non-xerophilic fungi was suggested.

Table 1. Fungal index in air conditioners

Survey site				Fungal index
Air conditioned room	Air conditioner	Inlet grill		15 ○
		Filter		64 ○
		Drain pan	Brim, not dipped in water	80 ○■
			Bottom, dipped in water	120　■
			Expanded polystyrene	150　■
			Urethane rubber insulation	170　■
		Heat exchange fin		120　■
		Fan		120　■
		Inner back side		100　■
	Center of room			12　○

Exposure period of fungul detectors was 5 days or 24 hours. ○：Fungal index measured by Eurotium sp.J-183. The growth rate of J-183 was more rapid than S-78. ■：Fungal index measured by Alternaria sp.S-78. The growth rate of S-78 was more rapid than J-183.

Effect of drying program

Table 2 shows the fungal index in the air conditioner with or without drying in rooms maintained at climates typical of early July. The drying program lowered the fungal index in every surveyed site. The probability of fungal growth in air conditioners was lowered. Prevention of fungal contamination in air conditioners is possible using drying programs after cooling.

Table 2. Fungal index in air conditioners with or without drying program

Survey site		without drying	with drying
Inlet grill		-	-
Filter		-	-
Drain pan	Brim, not dipped in water	38 ○	-
	Bottom, dipped in water	80 ■	-
	Expanded polystyrene	80 ■	-
	Urethane rubber insulation	80 ■	-
	drain exit	80 ■	20 ○
Fan		80 ■	14 ■
Inner back side		80 ■	-
Center of room		-	-

Keywords: Air conditioning, Biological contaminants, Fungi,Microbial contamination,

Exposure period of fungal detector was 5 days. The upper and lower limits to detect the fungal index were 80 and 10, respectively.

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