Indoor Air 1998; 8: 80–90 Copyright c Munksgaard 1998 Printed in Denmark. All rights reserved INDOOR AIR ISSN 0905-6947 Impact of Temperature and Humidity on the Perception of Indoor Air Quality L. FANG1, G. CLAUSEN1 AND P. O. FANGER1 idea came from the philosophy that it is the chemical Abstract Sensory responses to clean air and air polluted by five properties of indoor air that determine its quality, building materials under different combinations of temperature while physical properties of the air, such as tempera- and humidity in the ranges 18-28æC and 30-70%RH were studied ture and humidity, influence the thermal sensations. In in the laboratory. A specially designed test system was built and ventilation standards and guidelines (ASHRAE, 1989; a set of experiments was designed to observe separately the im- pact of temperature and humidity on the perception of air qual- DIN, 1994; and ECA, 1992), air temperature and hu- ity/odour intensity, and on the emission of pollutants from the midity have not until now been regarded as factors materials. This paper reports on the impact on perception. The that have any impact on perceived indoor air quality. odour intensity of air did not change significantly with tempera- Yaglou et al. (1936) considered the effect of tempera- ture and humidity; however, a strong and significant impact of ture when they performed their classic studies for temperature and humidity on the perception of air quality was ASHRAE on ventilation requirements. The required found. The air was perceived as less acceptable with increasing ventilation rate obtained from their experiment was temperature and humidity. This impact decreased with an in- creasing level of air pollution. Significant linear correlations were based on neutral thermal conditions, as they remarked found between acceptability and enthalpy of the air at all pol- that: ‘‘temperature, in fact, is one of the most important lution levels tested, and a linear model was established to de- factors in air quality and unless it is controlled the scribe the dependence of perceived air quality on temperature quality will suffer badly, no matter what the outdoor and humidity at different pollution levels. air supply, particularly when the air is overheated’’. The effect of temperature and humidity on the per- Key words Indoor air quality; Perceived air quality; ception of odour intensity and air quality has been in- Temperature; Humidity; Perception; Ventilation. vestigated in several previous studies. In an early Received 7 April 1997. Accepted for publication 3 March 1998. study, Kerka and Humphreys (1956) used human C Indoor Air (1998) panels to evaluate the odour intensity of three pure vapours and of cigarette smoke. The authors found that the odour intensity decreased with increasing hu- Introduction midity, and for tobacco smoke, that the odour intensity The purpose of ventilation for offices, lecture halls, decreased slightly with an increase in air temperature schools, and similar spaces is to provide air of a quality at constant water vapour pressure. Woods (1979) re- that will be perceived as acceptable. The idea is to di- evaluated Kerka and Humphreys’ results and found lute the pollution from sources in the space by supply- that the perceived odour intensity was linearly corre- ing the necessary flow of outdoor air. For many years, lated with enthalpy of the air, which revealed an im- occupants were believed to be the only source of pol- pact of the thermal environment on the sensitivity of lution. During recent years, however, the building has the sense of smell. also been acknowledged as a major source of pollution. In a major study by Cain et al. (1983), the impact of To improve indoor air quality, ventilation was usually temperature and humidity on perceived air quality believed to be the most effective way, and the more was studied for both smoking and non-smoking occu- ventilation, the better the quality of the indoor air. This pancy. In the study, subjective assessments of odour 1Centre for Indoor Environment and Energy, Department of Energy Engineering, Technical University of Denmark, Building 402, DK-2800 Lyngby, Denmark. Tel: π45 45931199. Fax: π45 45932166 Impact of Temperature and Humidity on the Perception of Indoor Air Quality intensity and acceptability of air polluted with bioef- (Andersen et al., 1975; Bremer et al., 1993; Wolkoff, fluents or tobacco smoke were obtained for four en- 1997). It is likely that temperature and humidity influ- vironmental conditions: 20æCRHÆ50%, 23æC ence perceived air quality in two ways: a) the percep- RHÆ50%, 25.5æCRHÆ50%, and 25.5æCRHÆ70%. The tion of odour intensity and air quality; b) the magni- selection of environmental conditions did not allow the tude and composition of emissions. However, the in- authors to study the effect of humidity at moderate formation available at present is insufficient for temperatures. The authors concluded that for both practical applications in HVAC engineering. To investi- smoking and non-smoking conditions, a combination gate systematically the way in which temperature and of high temperature (25.5æC) and high humidity humidity may influence perceived air quality, a com- (RHØ70%) exacerbated the odour problem. However, prehensive study was initiated under the Danish the observed odour intensity difference was not signifi- ‘‘Healthy Buildings’’ research programme and under cant when air was polluted by tobacco smoke at differ- the research programme ‘‘European Data Base for In- ent temperatures and humidities. door Air Pollution Sources in Buildings’’. The study In a later study, Berglund and Cain (1989) concluded investigated separately the impact of temperature and that for a subjective evaluation of indoor air quality, humidity on both human perception of air quality and the concentration of pollutants in the air may in some on emission of pollutants from building materials. This instances prove secondary to the influence of tempera- paper presents the results of the investigation on the ture and humidity. This rather surprising conclusion impact of temperature and humidity on the perception was derived from the subjective responses of 20 sub- of air quality and odour intensity, with common build- jects studied at three temperatures, three humidities ing materials as pollution sources. The results re- and three activities or metabolic rates. The air was per- flecting the influence of temperature and humidity on ceived to be fresher and less stuffy with decreasing the emission of building materials will be published temperature and humidity. The effect of temperature separately. was linear and stronger than the effect of humidity. The effect of humidity on freshness, stuffiness, and ac- ceptability of the air quality was smaller in the dew- Methods point range 2–11æC than in the range 11–20æC. The air Pollution Sources and the Test Environments quality was typically unacceptable when the relative The effect of temperature and humidity on the percep- humidity exceeded 50%. tion of air quality and odour intensity was investigated Gwosdow et al. (1989) studied the physiological and at three levels of temperature (18æ,23æ,28æC) and three subjective responses to the respiratory air at four levels levels of relative humidity (30%, 50%, 70%RH) using the of temperature (27æ,30æ,33æand 36æC) and two levels judgements of a sensory panel of untrained persons. The of relative humidity (47%, 73%). The air was supplied investigations were made with unpolluted outdoor air by respiratory protective devices, and the study and with air polluted by five building materials. The showed that the acceptability of the inspired air de- building materials used as pollution sources in the ex- creased when the air temperature rose above 30æC. periment were PVC flooring, waterborne acrylic floor Conversely, a study made by Berg-Munch and Fang- varnish, loomed polyamide carpet, waterborne acrylic er (1982) found no significant influence of air polluted wall paint and acrylic sealant. The floor varnish was by human bioeffluents on perceived odour intensity painted on 12 mm thick beechwood parquet; the wall when the air temperature increased from 23æ to 32æC. paint was painted on 10 mm thick gypsum board; the The authors concluded that the ventilation require- sealant was applied to u-shaped aluminium profiles ment is most likely independent of the temperature in spaces where bioeffluents are the dominant source of pollution, such as in auditoria, theatres, etc., provided Table 1 Area of material samples placed in each CLIMPAQ that people are kept thermally neutral. Clausen et al. 2 (1985), in their study, also observed no significant Material Area of material (m ) changes in odour intensity of air polluted by tobacco PVC flooring (loading 1) 1.2 smoke, when the relative humidity varied between Carpet (loading 1) 0.3 (loading 2) 0.6 30% and 80%. Floor varnish (loading 1) 0.22 On the other hand, temperature and humidity may (loading 2) 0.66 Wall paint (loading 1) 0.62 also influence the emission of pollutants. The effect of (loading 2) 1.55 temperature and humidity on the chemical emission of Sealant (loading 1) 0.015 (Ω1.5m) building materials has been reported in several studies (loading 2) 0.0375 (Ω3.75m) 81 Fang, Clausen and Fanger The experiments were carried out in a climate chamber (3.6¿2.5¿2.55 m3) which was designed for air quality studies (Albrechtsen, 1988). Inside the chamber a specially designed test system was built. It consisted of 10 modified CLIMPAQs (Chambers for Laboratory Investigations of Materials, Pollution and Air Quality) (Gunnarsen et al., 1993). The CLIMPAQ is a 1.005¿0.25¿0.22 m3 test box made of glass. Each of the modified CLIMPAQ had a diffuser to release the air for exposure of the subjects, and each of them was equipped with two independent air-conditioning sys- Fig. 1 Principle of the modified CLIMPAQ tems: one supplied 0.2 L/s of clean air, conditioning the temperature and humidity inside the CLIMPAQ; the other supplied 0.7 L/s of make-up air, recon- ditioning the temperature and humidity of the airflow with an inner width and depth of 10 mm and 12 mm re- released from the CLIMPAQ and controlling the tem- spectively.