impact of temperature and humidity on the perception of ... · impact of temperature and humidity...

Indoor Air 1998; 8: 80–90 Copyright c Munksgaard 1998Printed in Denmark. All rights reserved

INDOOR AIRISSN 0905-6947

Impact of Temperature and Humidity on the Perception ofIndoor Air Quality

L. FANG1, G. CLAUSEN1 AND P. O. FANGER1

Abstract Sensory responses to clean air and air polluted by fivebuilding materials under different combinations of temperatureand humidity in the ranges 18-28æC and 30-70%RH were studiedin the laboratory. A specially designed test system was built anda set of experiments was designed to observe separately the im-pact of temperature and humidity on the perception of air qual-ity/odour intensity, and on the emission of pollutants from thematerials. This paper reports on the impact on perception. Theodour intensity of air did not change significantly with tempera-ture and humidity; however, a strong and significant impact oftemperature and humidity on the perception of air quality wasfound. The air was perceived as less acceptable with increasingtemperature and humidity. This impact decreased with an in-creasing level of air pollution. Significant linear correlations werefound between acceptability and enthalpy of the air at all pol-lution levels tested, and a linear model was established to de-scribe the dependence of perceived air quality on temperatureand humidity at different pollution levels.

Key words Indoor air quality; Perceived air quality;Temperature; Humidity; Perception; Ventilation.

Received 7 April 1997. Accepted for publication 3 March 1998.

C Indoor Air (1998)

IntroductionThe purpose of ventilation for offices, lecture halls,schools, and similar spaces is to provide air of a qualitythat will be perceived as acceptable. The idea is to di-lute the pollution from sources in the space by supply-ing the necessary flow of outdoor air. For many years,occupants were believed to be the only source of pol-lution. During recent years, however, the building hasalso been acknowledged as a major source of pollution.To improve indoor air quality, ventilation was usuallybelieved to be the most effective way, and the moreventilation, the better the quality of the indoor air. This

1Centre for Indoor Environment and Energy, Department of Energy Engineering, Technical University of Denmark, Building 402, DK-2800Lyngby, Denmark. Tel: π45 45931199. Fax: π45 45932166

idea came from the philosophy that it is the chemicalproperties of indoor air that determine its quality,while physical properties of the air, such as tempera-ture and humidity, influence the thermal sensations. Inventilation standards and guidelines (ASHRAE, 1989;DIN, 1994; and ECA, 1992), air temperature and hu-midity have not until now been regarded as factorsthat have any impact on perceived indoor air quality.

Yaglou et al. (1936) considered the effect of tempera-ture when they performed their classic studies forASHRAE on ventilation requirements. The requiredventilation rate obtained from their experiment wasbased on neutral thermal conditions, as they remarkedthat: ‘‘temperature, in fact, is one of the most importantfactors in air quality and unless it is controlled thequality will suffer badly, no matter what the outdoorair supply, particularly when the air is overheated’’.

The effect of temperature and humidity on the per-ception of odour intensity and air quality has been in-vestigated in several previous studies. In an earlystudy, Kerka and Humphreys (1956) used humanpanels to evaluate the odour intensity of three purevapours and of cigarette smoke. The authors foundthat the odour intensity decreased with increasing hu-midity, and for tobacco smoke, that the odour intensitydecreased slightly with an increase in air temperatureat constant water vapour pressure. Woods (1979) re-evaluated Kerka and Humphreys’ results and foundthat the perceived odour intensity was linearly corre-lated with enthalpy of the air, which revealed an im-pact of the thermal environment on the sensitivity ofthe sense of smell.

In a major study by Cain et al. (1983), the impact oftemperature and humidity on perceived air qualitywas studied for both smoking and non-smoking occu-pancy. In the study, subjective assessments of odour

Impact of Temperature and Humidity on the Perception of Indoor Air Quality

intensity and acceptability of air polluted with bioef-fluents or tobacco smoke were obtained for four en-vironmental conditions: 20æC RHÆ50%, 23æCRHÆ50%, 25.5æC RHÆ50%, and 25.5æC RHÆ70%. Theselection of environmental conditions did not allow theauthors to study the effect of humidity at moderatetemperatures. The authors concluded that for bothsmoking and non-smoking conditions, a combinationof high temperature (25.5æC) and high humidity(RHØ70%) exacerbated the odour problem. However,the observed odour intensity difference was not signifi-cant when air was polluted by tobacco smoke at differ-ent temperatures and humidities.

In a later study, Berglund and Cain (1989) concludedthat for a subjective evaluation of indoor air quality,the concentration of pollutants in the air may in someinstances prove secondary to the influence of tempera-ture and humidity. This rather surprising conclusionwas derived from the subjective responses of 20 sub-jects studied at three temperatures, three humiditiesand three activities or metabolic rates. The air was per-ceived to be fresher and less stuffy with decreasingtemperature and humidity. The effect of temperaturewas 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-point range 2–11æC than in the range 11–20æC. The airquality was typically unacceptable when the relativehumidity exceeded 50%.

Gwosdow et al. (1989) studied the physiological andsubjective responses to the respiratory air at four levelsof temperature (27æ, 30æ, 33æ and 36æC) and two levelsof relative humidity (47%, 73%). The air was suppliedby respiratory protective devices, and the studyshowed that the acceptability of the inspired air de-creased when the air temperature rose above 30æC.

Conversely, a study made by Berg-Munch and Fang-er (1982) found no significant influence of air pollutedby human bioeffluents on perceived odour intensitywhen the air temperature increased from 23æ to 32æC.The authors concluded that the ventilation require-ment is most likely independent of the temperature inspaces where bioeffluents are the dominant source ofpollution, such as in auditoria, theatres, etc., providedthat people are kept thermally neutral. Clausen et al.(1985), in their study, also observed no significantchanges in odour intensity of air polluted by tobaccosmoke, when the relative humidity varied between30% and 80%.

On the other hand, temperature and humidity mayalso influence the emission of pollutants. The effect oftemperature and humidity on the chemical emission ofbuilding materials has been reported in several studies

81

(Andersen et al., 1975; Bremer et al., 1993; Wolkoff,1997). It is likely that temperature and humidity influ-ence perceived air quality in two ways: a) the percep-tion of odour intensity and air quality; b) the magni-tude and composition of emissions. However, the in-formation available at present is insufficient forpractical applications in HVAC engineering. To investi-gate systematically the way in which temperature andhumidity may influence perceived air quality, a com-prehensive study was initiated under the Danish‘‘Healthy Buildings’’ research programme and underthe research programme ‘‘European Data Base for In-door Air Pollution Sources in Buildings’’. The studyinvestigated separately the impact of temperature andhumidity on both human perception of air quality andon emission of pollutants from building materials. Thispaper presents the results of the investigation on theimpact of temperature and humidity on the perceptionof air quality and odour intensity, with common build-ing materials as pollution sources. The results re-flecting the influence of temperature and humidity onthe emission of building materials will be publishedseparately.

MethodsPollution Sources and the Test EnvironmentsThe effect of temperature and humidity on the percep-tion of air quality and odour intensity was investigatedat three levels of temperature (18æ, 23æ, 28æC) and threelevels of relative humidity (30%, 50%, 70%RH) using thejudgements of a sensory panel of untrained persons. Theinvestigations were made with unpolluted outdoor airand with air polluted by five building materials. Thebuilding materials used as pollution sources in the ex-periment were PVC flooring, waterborne acrylic floorvarnish, loomed polyamide carpet, waterborne acrylicwall paint and acrylic sealant. The floor varnish waspainted on 12 mm thick beechwood parquet; the wallpaint was painted on 10 mm thick gypsum board; thesealant was applied to u-shaped aluminium profiles

Table 1 Area of material samples placed in each CLIMPAQ

Material Area of material (m2)

PVC flooring (loading 1) 1.2Carpet (loading 1) 0.3

(loading 2) 0.6Floor varnish (loading 1) 0.22

(loading 2) 0.66Wall paint (loading 1) 0.62

(loading 2) 1.55Sealant (loading 1) 0.015 (Ω1.5m)

(loading 2) 0.0375 (Ω3.75m)

Fang, Clausen and Fanger

Fig. 1 Principle of the modified CLIMPAQ

with an inner width and depth of 10 mm and 12 mm re-spectively. The quantities of the material loadings arelisted in Table 1. They were determined using sensoryemission data of the same materials obtained from a pre-vious study (Knudsen et al., 1996).

Experimental FacilitiesThe fundamental experimental principle was to studythe impact of temperature and humidity separately onperceived air quality/odour intensity and on pollutantemissions from building materials.

Fig. 2 Schematic diagram of the air-conditioning system for CLIMPAQs

82

The experiments were carried out in a climatechamber (3.6¿2.5¿2.55 m3) which was designed for airquality studies (Albrechtsen, 1988). Inside the chambera specially designed test system was built. It consistedof 10 modified CLIMPAQs (Chambers for LaboratoryInvestigations of Materials, Pollution and Air Quality)(Gunnarsen et al., 1993). The CLIMPAQ is a1.005¿0.25¿0.22 m3 test box made of glass. Each of themodified CLIMPAQ had a diffuser to release the airfor exposure of the subjects, and each of them wasequipped with two independent air-conditioning sys-tems: one supplied 0.2 L/s of clean air, conditioningthe 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 airflowreleased from the CLIMPAQ and controlling the tem-perature and humidity of the air in the diffuser. Thetest material was placed in the CLIMPAQ which wassupplied with conditioned clean air, giving an airchange of 17 hª1 in each CLIMPAQ. The principle ofthese modified CLIMPAQs is shown in Figure 1.

The principle of the air-conditioning system for theCLIMPAQs is shown in Figure 2. The air was pre-con-ditioned collectively by a multi-dew-point air-condi-tioner that can provide 20 airflows with different dew-point temperatures. The multi-dew-point air-condi-


Fig. 3 Example of air-conditioning processes for the nine temperature and humidity conditions

tioner consists of two conditioned air supply systems:one supplied cold and dry air (10æC, 30%RH) to airreservoir A, the other supplied warm and humid air(29æC, 90%RH) to air reservoir B. The temperature, hu-midity and pressure were kept constant at the two airreservoirs. The air from the two reservoirs was thenmixed through 20 sets of mixing valves and split into20 flows. By adjusting the valves, the proper mixingrate and flow rate could be obtained, which gave eachairflow a required absolute humidity and flow rate;however, the temperatures were kept lower than re-quired. The airflows were then sent to the CLIMPAQsand heated locally by the electric heaters in each CLIM-PAQ to obtain the required temperatures and relativehumidities. Therefore, this air-conditioning systemcould simultaneously provide 20 airflows, each withany combination of temperature and humidity in therange 10æC, 30%RH to 29æC, 90%RH. An example ofthe air-conditioning processes that give a required ma-trix of the nine temperature and humidity combi-nations is illustrated on the psychrometric chart shownin Figure 3. The whole system was automatically con-trolled by a computer which maintained a stability of∫0.2æC temperature, ∫3% relative humidity and ∫2%airflow rate respectively for each parameter controlledin the system.

83

To avoid polluting the air by the equipment itself,all the surfaces that were in contact with the air in themulti-dew-point air-conditioner, the CLIMPAQs andthe tubes connecting both parts were made of glass,stainless steel or Teflon. Only distilled clean water wasused to humidify the air; the water boiler and all pipessupplying the steam were also made of stainless steeland were cleaned before use. While the system wasin operation, the overpressure inside the water boilerguaranteed that no pollutants could be introduced intothe water from the supply air. Furthermore, the watertemperature was kept above 100æC, thus preventingmicroorganisms from accumulating in the water.

Forty untrained subjects (30 males and 10 females)were recruited to assess the air quality. The subjectswere randomly selected; they were university studentsaged between 20 and 35 years and in good health;seven of them were cigarette smokers smoking maxi-mum 10 cigarettes per day. Because the experimentswere performed only once a week, the whole experi-ment lasted for two months. From time to time, sub-jects were unable to participate in individual experi-ments due to illness or other reasons. Each time thenumber of subjects participating in the experimentvaried from 33 to 40. Before the experiment, the sub-jects were instructed not to eat very spicy food within


24 hours; they were also requested not to use strongperfume. Smoking and drinking coffee were notallowed one hour prior to an experiment.

Experimental ProceduresIn testing the impact of temperature and humidity onperception, the ambient temperature and humidity in-side the climate chamber were set at 18æC and 30%RHrespectively; the air change rate in the climate chamberwas set at 56 hª1 to achieve a good environment withvery low background pollution. All the CLIMPAQswere ventilated by equal airflows with identical tem-perature and humidity (23æC and 50%), but the air re-leased from the diffusers for exposure was recon-ditioned to the nine different levels of temperature andhumidity by mixing with equal flows of conditionedclean make-up air after each CLIMPAQ. The CLIM-PAQs were either empty or loaded with materials.When the CLIMPAQs were empty, the subjects wereexposed to clean air conditioned at different tempera-tures and humidities. When the CLIMPAQs were load-ed with materials, the subjects were exposed to pol-luted air with different temperatures and humidities.The nature of the pollutants was varied by using differ-ent types of material and the concentration of the pol-lutants was varied by changing the material loading.In this way, 10 air samples with different pollutantcompositions giving a range of acceptability were pre-pared (including clean air which was not polluted bythe materials); each air sample was further conditionedinto 9 different temperature and humidity levels, andthe impact of temperature and humidity on perceptionof these air samples was then tested.

The materials were used one type at a time. Beforethe test, each type of material was ventilated con-tinuously (24h/day) at 23æC and 50%RH for twoweeks, since the previous studies showed that bothchemical and sensory emission of the materials testedtended to become stable after being ventilated for 14days (Tirkkonen et al., 1996; Bluyssen et al., 1996;Knudsen et al., 1996; Wolkoff, 1997). In the firstweek, each type of material was ventilated collec-tively; an identical quantity of a given type of testmaterial was then placed in each of the nine CLIM-PAQs and ventilated for another week to achievequasi steady-state emission at the CLIMPAQ. Sincetemperature, humidity and airflow rates inside eachof the nine CLIMPAQs were controlled so that theywere identical, the same air pollution could be ex-pected in all nine airflows. During each experiment,the subjects were exposed to air with the same pol-lution but with different levels of temperature andhumidity; therefore, any difference in perceived

84

odour intensity and air quality would be caused onlyby an impact of temperature and humidity on per-ception. This experiment was repeated with each ofthe five different test materials, each material beingtested at two levels of loading (see Table 1), exceptfor PVC flooring where only one level was tested. Inaddition, there was always one empty CLIMPAQ ar-ranged to determine odour intensity and ac-ceptability of the clean background air at 23æC and50%RH.

On each experimental day, each subject made thesensory assessments within one hour. After a brief ex-posure to the air released from the CLIMPAQs, thesubjects assessed their immediate perception andmarked the continuous odour intensity and ac-ceptability scales (Figure 4) to judge each assessed airsample. Each air sample was randomly assigned forassessment by the subjects, and the subjects were notallowed to compare the assessment of different airsamples.

Before the subjects voted on the acceptability of theair, they were asked the following question: Imaginethat during your daily work you would be exposed to the airfrom the diffusers. How acceptable is the air quality? Theacceptability scale was slightly modified from thatused by Gunnarsen and Fanger (1992) by splitting ‘‘justacceptable’’ and ‘‘just unacceptable’’ at the centre of thescale to avoid the vote on both ‘‘just acceptable’’ and‘‘just unacceptable’’ and make it possible to count PDusing the percentage of the votes on the unacceptableside. The mean acceptability of the subject votes can beused to describe perceived air quality and can also beconverted to Percentage of Dissatisfied (PD) (Gunnars-en and Fanger, 1992) or decipol (Fanger, 1988).

Fig. 4 Odour intensity and acceptability scales used by the sen-sory panel during the experiment


Fig. 5 Perception of odour intensity of clean air and air polluted by the five building materials at different temperatures and humidities

ResultsThe Influence of Temperature and Humidity onOdour Intensity of AirThe observed impact of temperature and humidity onthe perception of odour intensity was presented by fit-ting the response surfaces of the mean odour intensityvotes obtained for the nine combinations of air tem-perature and humidity. Different response surfaceswere fitted for the air with different compositions (e.g.clean air and air polluted by the five building materialsat different loadings). Figure 5 shows sensory re-sponses for clean air and air polluted by the five ma-terials, each at one pollution level, arranged in orderof increasing odour intensity. The nine data pointsshown on each surface are the mean votes of 33 to 40subjects. The Average Standard Deviation of the Means(ASDM) is also given on each figure. The response sur-faces in Figure 5 show that temperature and humidityhad little influence on perception of odour intensity.Especially when air was polluted by the materials, theodour intensity of the air seems independent of the air

85

temperature and humidity. For clean air the odour in-tensity slightly increased with increasing air tempera-ture and humidity.

To analyse the statistical significance of the impact oftemperature and humidity on the perception of odourintensity, analysis of variance was performed for themean odour intensity votes of the subjects. This analy-sis showed that the impact of both temperature andhumidity was not significant at the level of P∞0.05when air was polluted by building materials; however,for clean air this impact was found statistically signifi-cant at a level of P∞0.05.

The Influence of Temperature and Humidity on theAcceptability of AirThe response surfaces of the mean perception of airquality in the temperature and humidity ranges 18–28æCand 30–70%RH are shown in Figure 6. The figure showsthe mean acceptability votes of the same air samples asused for odour intensity assessment and arranged in thesame order as in Figure 5. The response surfaces in Fig-


Fig. 6 Perception of acceptability of clean air and air polluted by the five building materials at different temperatures and humidities

ure 6 show that the air was always perceived as less ac-ceptable with increasing temperature and humidity, andthat this impact was less pronounced with increasinglevel of air pollution (indicated by decreased ac-ceptability). Analysis of variance showed that the im-pact of both temperature and humidity is highly signifi-cant (P∞0.002) at all the pollution levels tested. Further-more, the interaction of temperature and humidity isalso significant at a level of P∞0.05.

The impact of temperature and humidity on percep-tion was further studied by correlating acceptabilitywith the thermodynamic property ‘‘enthalpy’’ whichrepresents the energy content of the moist air. Highlysignificant linear relations were found at all testedlevels of the different pollutants. The linear regressionsof acceptability versus enthalpy of the assessed air atfive selected pollution levels are shown in Figure 7. Atlow enthalpy (low temperature and/or humidity) thepollution level is the key factor that influences the per-ception of air quality, while air pollution becomes lessimportant for the perceived air quality when enthalpyof the air increases. Beyond a certain level of enthalpy,

86

for instance at 28æC and 70%RH, temperature and hu-midity are the key factors that determine the perceivedair quality; in this case, the air was perceived as unac-ceptable whether the air was clean or not.

Models can be created to predict perceived air qual-ity, using the data obtained from the experiment. The

Fig. 7 Acceptability of air related to enthalpy at the selected pol-lution levels of different materials


Table 2 Coefficients of equation (1) for air with different compositions

Tested air Coefficients of Eq. 1 Significant level(with different pollution source) P∞

a b

Background air (clean) ª0.033 1.662 0.0000polluted by floor varnish (loading 1) ª0.026 1.268 0.0001polluted by wall paint (loading 1) ª0.025 1.162 0.0000polluted by carpet (loading 1) ª0.024 1.030 0.0001polluted by carpet (loading 2) ª0.023 0.966 0.0001polluted by PVC flooring (loading 1) ª0.021 0.941 0.0002polluted by sealant (loading 1) ª0.020 0.743 0.0009polluted by floor varnish (loading 2) ª0.019 0.722 0.0002polluted by wall paint (loading 2) ª0.018 0.713 0.0010polluted by sealant (loading 2) ª0.013 0.263 0.0080

models should include three factors – air pollution,temperature and humidity – to determine perceived airquality. A simple linear model was first considered byusing the results from Figure 7. The linear model de-fined the acceptability of the air as a function of en-thalpy by the following equation:

AccΩaEπb (1)

where: AccΩacceptability of the airEΩenthalpy of the air (kJ/kg)

a,b are coefficients which will be different for the airwith different pollutants and pollution levels.

To determine the two coefficients, linear regressionswere made between the acceptability and enthalpy fortested air with the 10 different compositions. The coef-ficients a and b from the 10 linear regressions are listedin Table 2.

The two coefficients are different at different levelsof air pollution; however, a highly significant linearcorrelation was found between the two coefficients(Figure 8). A linear regression of the coefficients a andb can be expressed as:

Fig. 8 Linear correlation between coefficients a and b

87

bΩª69.419a–0.594, (rΩ0.991, P∞0.00004) (2)

Substituting for b in eq. (1), one obtains:

AccΩaE–69.419a–0.594 (3)

Rewriting eq. (3) for a reference condition of 23æC,50%RH, for which EΩ45.39KJ/kg, the perceptionmodel can be expressed as:

AccΩAcc0ª0.0247(E-45.39)ª0.0416Acc0(Eª45.39) (4)

where Acc0 is the acceptability of the air at 23æC and50%RH; E can be calculated from air temperature andhumidity by using perfect gas laws as follows:

EΩhaπW ¡ hg (5)where:

haΩ1.006t, the enthalpy of dry air;hgΩ2501π1.84t, the enthalpy of water vapour;WΩ0.622Pw/(P0–Pw), the humidity ratio;PwΩ0.01jPws, the partial pressure of water vapour;PwsΩthe saturation pressure of water vapour,by the Antoine equation, PwsΩe(23.58–4043/(tπ273.15–37.58)).

Thus we obtain the following equation to calculate en-thalpy from temperature and relative humidity of theair:

EΩ1.006tπ0.622(2501π1.84t) ¡0.01je(23.58–4043/(tπ273.15–37.58))

P0–0.01je(23.58–4043/(tπ273.15–37.58))(6)

where: tΩair temperature (æC)jΩrelative humidity (%)P0Ωatmospheric pressure (Pa),(typically P0Ω101324Pa)

Eq. (4) indicates that the acceptability of the assessed


air is influenced by a linear combination of sensorypollution, temperature and humidity (expressed by en-thalpy) and the interaction of the three factors. Also, itcan be seen that when EΩ45.39 kJ/kg (e.g. tΩ23æC, jΩ50%), then AccΩAcc0. Acc0 is used here as a factor in-dicating the air pollution level. Acc0 can also be ar-ranged to be the acceptability of the air at any tempera-ture and humidity by adjusting the other terms of theequation. The enthalpy correction introduced by themodel makes it possible to predict the perceived airquality at any level of temperature and humidity bymeasuring acceptability of the air at a single level oftemperature and humidity. The model can also be usedtogether with an emission model and the comfortequation of perceived air quality (Fanger, 1989; ECA,1992) to calculate the ventilation requirement or thesensory pollution load.

DiscussionFigure 5 and Figure 6 indicate that the decrease of per-ceived air quality (acceptability of the air) due to in-creasing air temperature and humidity was not causedby an increased odour intensity of the air. A coolingeffect in the respiratory tract may help to explain thereason. It is well known that chemical pollutants influ-ence perception of the air by acting directly on the ol-factory and chemical sense, and lead to the perceptionof odour or irritation. Temperature and humidity, how-ever, change the energy content of the inspired air andprovide a changed cooling of the respiratory tract. Ingeneral, the effect of the thermal exchanges on inhal-ation is to cool the mucosa if the temperature of theinhaled air is below the mucosal temperature which isnormally at a level of 30æ to 32æC (Mcfadden, 1983;Proctor and Andersen, 1982). The observed linear cor-relation between acceptability and enthalpy of the airimplies that the cooling of the mucosa is essential forthe perception of acceptable air quality. Within thetemperature and humidity ranges tested, the morecooling the respiratory tract was exposed to, thefresher and more acceptable was the air perceived. Aninsufficient cooling may be interpreted as a local warmdiscomfort in the respiratory tract and lead to the in-haled air being perceived as unacceptable. Recently,Toftum et al. (1997) studied jointly the respiratory ther-mal sensation and the perceived comfort due to respir-atory cooling. The experiment led to almost the sameresults as those of the present study. A similar linearcorrelation between air freshness and enthalpy was ob-served by Berglund and Cain (1989). The present studyfurther indicated that when the respiratory cooling ef-fect decreases to a certain level, the air will be per-

88

ceived as very poor whether it is clean or polluted,and increasing the ventilation rate would be a wasteof energy without any improvement in perceived airquality. In this case, decreasing air temperature andhumidity would succeed where decreasing the pol-lution level could fail to achieve acceptable air quality.

The present study shows that air quality ac-ceptability is very sensitive to temperature and hu-midity, while the perception of odour intensity of ma-terials seems to be almost independent of air tempera-ture and humidity. The experiment used buildingmaterials as air pollution sources. However, if the im-pact of temperature and humidity on acceptability ofair is due to the cooling effect in the respiratory tract,the results obtained from this study would probablyalso apply to conditions with other pollution sources.For air polluted by human bioeffluents and tobaccosmoke, the studies made by Berglund and Cain (1989)and Cain et al. (1983) confirmed that the acceptabilityof air was also decreased significantly with increasingair temperature and humidity. Cain’s study also ob-served the odour intensity using the butanol odour in-tensity scale and the continuous line-marking odourintensity scale. The odour intensity of the air pollutedby tobacco smoke assessed using the butanol odour in-tensity scale showed little difference between twolevels of air temperature and humidity. For occupancyodour, the odour intensity increased with increasingair temperature and humidity. However, in Cain et al.’sstudy, the impact of temperature and humidity on theemission from the occupants was confounded with theimpact on perception. Therefore, the increased odourintensity was most likely due to the increased emissionfrom the occupants when they were exposed to higherlevels of air temperature and humidity. The study ofBerg-Munch and Fanger (1982), and Clausen et al.(1985), using the same odour intensity scale as thepresent study, confirmed that odour intensity was in-sensitive to air temperature and humidity when airwas polluted by occupants or tobacco smoke.

Kerka and Humphreys’ result (1956) showed thatodour intensity of tobacco smoke decreased with in-creasing air temperature and humidity. This result isinconsistent with that found in the present experimentand in other studies. However, the odour intensity ob-served by Kerka and Humphreys changed very littlewith temperature, and the relative humidity effect wasmore evident at the higher temperatures. Since onlysix subjects were used as a sensory panel making thejudgement, the observed difference in odour intensitymay not be statistically significant. However, theanalysis of variance for the odour intensity data of to-bacco smoke was not reported in their paper. It is


therefore difficult to judge whether the observed vari-ation of odour intensity is an intrinsic effect of tem-perature and humidity or not.

Including the influence of temperature and hu-midity in ventilation requirements may be of practicalsignificance in optimizing energy utilization. To pro-vide a certain perceived air quality, the ventilation re-quirement may be decreased by decreasing the air tem-perature and/or the humidity. Obviously, this will leadto a reduction in energy consumption in the winter.Even in summer, the amount of energy saved by de-creasing the ventilation rate may compensate for theincreased energy required to further cool or dehumid-ify the reduced flow of supplied outdoor air, and com-pensate for the increased heat gain due to the lowerroom air temperature. Therefore, above a minimumventilation requirement for health, there may be an op-timum level of indoor air temperature and humidity atwhich a minimum consumption of energy for heating,ventilation and air-conditioning can be achieved for agiven level of perceived air quality. The optimum tem-perature and humidity will of course depend, inter alia,on the outdoor air temperature and humidity, the ther-mal transmittance (U-factor) of the external wall, andthe indoor air pollution load.

A great effort was made to avoid any pollutioncoming from the humidification system of the test fa-cility. The unpolluted air supplied to the CLIMPAQsat 28æC, 70%RH and at 18æC, 30%RH was chemicallyanalysed to further check whether any pollutants hadbeen introduced by humidification of the air. Thechemical analysis revealed very low concentrations ofVOCs and no significant difference of the TVOC con-centrations between the most humid and the driestcondition, which further proved that the humidifi-cation system, as designed, did not pollute the air. Theobserved impact of humidity on the perception of airquality was a true effect of humidity as such.

The first impression on entering a space has tra-ditionally been the basis for ventilation standards as ameasure of perceived air quality. The evaluation isusually relative to clean background air of prior ex-posure, but the temperature and humidity of the back-ground air has not yet been defined. The present inves-tigation of perceived air quality was relative to cleanambient air at 18æC and 30%RH as a background inthe climate chamber. This arrangement gives the bestperceived quality of the background air in the tem-perature and humidity ranges tested in the experiment.However, the results of the experiment may vary withthe temperature and humidity of the background air.Furthermore, the judgements in this study were madeby exposing only the face to the air released from the

89

diffusers. This exposure is somewhat artificial com-pared to practice when the whole body is exposedwhen people enter a room. The present results need tobe validated under such conditions. A further study istherefore suggested to test the impact of temperatureand humidity on the perception of air quality duringimmediate and longer whole-body exposure with dif-ferent prior exposure temperature and humidity en-vironments.

ConclusionsO Temperature and humidity have little influence on

perception of odour intensity of air polluted bybuilding materials.

O Temperature and humidity have a strong and sig-nificant impact on the perception of indoor air qual-ity; at a constant pollution level, the perceived airquality decreases with increasing air temperatureand humidity.

O The impact of temperature and humidity on the per-ception of air quality decreases with increasing levelof air pollution, while the influence of pollution onperceived air quality decreases with increasing airtemperature and humidity.

O At a constant pollution level, the acceptability of theair was found to be linearly correlated with the en-thalpy of the air.

O A model was established predicting the effect oftemperature and humidity on acceptability.

O Further studies on whole-body exposure on a fullscale are recommended.

AcknowledgementsThis study was supported financially by the DanishTechnical Research Council as part of the research pro-gramme ‘‘Healthy Buildings’’, and by the EuropeanDIXIE as part of the research programme Joule II‘‘European Data Base for Indoor Air Pollution Sourcesin Buildings’’.

ReferencesAlbrechtsen, O. (1988) ‘‘Twin climatic chambers to study sick

and healthy building’’. In: Proceedings of Healthy Buildings‘88, Stockholm, Vol. 3, pp. 25–30.

Andersen, I., Lundquist, G.R. and Mølhave, L. (1975) ‘‘Indoorair pollution due to chipboard used as a construction ma-terial’’, Atmospheric Environment, 9, 1121–1127.

ASHRAE (1989) Ventilation for Acceptable Indoor Air Quality,Atlanta, GA, American Society of Heating, Refrigeratingand Air Conditioning Engineers (ASHRAE standard 62–1989).

Berglund, L. and Cain, W.S. (1989) ‘‘Perceived air quality and


the thermal environment’’. In: Proceedings of IAQ ’89: TheHuman Equation: Health and Comfort, San Diego, pp. 93–99.

Berg-Munch, B. and Fanger, P.O. (1982) ‘‘The influence of airtemperature on the perception of body odour’’, Environ-ment International, 8, 333–335.

Bluyssen, P.M., Cornelissen, H.J.M., Hoogeveen, P., Wouda,J.F. van der Wal (1996) ‘‘The effect of temperature on thechemical and sensory emission of indoor materials’’. In:Proceedings of Indoor Air ’96, Nagoya, International Confer-ence on Indoor Air Quality and Climate, Vol. 3, pp. 619–624.

Bremer, J., Witte, E., and Schneider, D. (1993) ‘‘Measurementand characterisation of emissions from PVC materials forindoor use’’. In: Proceedings of Indoor Air ’93, Helsinki, Inter-national conference on Indoor Air Quality and Climate,Vol. 2, pp. 419–424.

Cain, W.S., Leaderer, B.P., Isseroff, R., Berglund, L.G., Huey,R.J., Lipsitt, E.D. and Perlman, D. (1983) ‘‘Ventilation re-quirements in buildings – I. Control of occupancy odourand tobacco smoke odour’’, Atmospheric Environment, 17,1183–1197.

Clausen, G., Fanger, P.O., Cain, W.S. and Leaderer, B.P. (1985)‘‘The influence of aging, particle filtration and humidityon tobacco smoke odour’’. In: Proceedings of CLIMA 2000,Copenhagen, Vol. 4, pp. 345–349.

DIN (1994) Raumlufttechnik Gesundheitstechnische Anforderung-en (VDI- Luftungsregeln), Berlin (DIN 1946, Teil 2).

ECA (European Collaborative Action ‘‘Indoor Air Qualityand its Impact on Man’’) (1992) Guidelines for VentilationRequirements in Buildings, Luxembourg, Office for Publi-cations of the European Communities (Report No. 11).

Fanger, P.O. (1988) ‘‘Olf and decipol – the new units for per-ceived air quality’’, ASHRAE Journal, October, pp. 35–38.

Fanger, P.O. (1989) ‘‘The new comfort equation for indoor airquality’’, ASHRAE Journal, October, pp. 33–38.

Gunnarsen, L. and Fanger, P.O. (1992) ‘‘Adaptation to indoorair pollution’’, Environment International, 18, 43–54.

Gunnarsen, L., Nielsen, P.A. and Wolkoff, P. (1993) ‘‘Designand characterisation of the CLIMPAQ chamber for labora-

90

tory investigations of materials, pollution and air quality’’.In: Proceedings of Indoor Air ’93, Helsinki, International Con-ference on Indoor Air Quality and Climate, Vol. 2, pp. 507–512.

Gwosdow, A.R., Nielsen, R., Berglund, L.G., Dubois, A.B. andTremml, P.G. (1989) ‘‘Effect of thermal conditions on theacceptability of respiratory protective devices on humansat rest’’, American Industrial Hygiene Association Journal,50(4), 188–195.

Kerka, W.F. and Humphreys, C.M. (1956) ‘‘Temperature andhumidity effect on odour perception’’, ASHRAE Trans-actions, 62, 531–552.

Knudsen, H.N., Kjaer, U.D. and Nielsen, P.A. (1996) ‘‘Char-acterisation of emissions from building products: long-term sensory evaluation, the impact of concentration andair velocity’’. In: Proceedings of Indoor Air ’96, Nagoya, Inter-national Conference on Indoor Air Quality and Climate,Vol. 3, pp. 551–556.

Mcfadden, E.R., jr. (1983) ‘‘Respiratory heat and water ex-change: physiological and clinical implications’’, Journal ofApplied Physiology, 54(2), 331–336.

Proctor, D.F. and Andersen, I.B. (1982) The Nose: Upper AirwayPhysiology and the Atmospheric Environment, Amsterdam, El-sevier.

Tirkkonen, T., Andersen, T.E., Saarela, K., Clausen, G. andKnudsen, H. (1996) ‘‘VOC emissions from selected ma-terials in different chambers’’. In: Proceedings of Indoor Air’96, Nagoya, International Conference on Indoor Air Qual-ity and Climate, Vol. 3, pp. 613–618.

Toftum, J., Jørgensen, A.S. and Fanger, P.O. (1998) ‘‘Effect ofhumidity and temperature of inspired air on perceivedcomfort’’, Energy and Buildings (in press).

Wolkoff, P. (1998) ‘‘Impact of air velocity, temperature, hu-midity, and air on long-term VOC emissions from buildingproducts’’ Atmospheric Environment (in press).

Woods, J.E. (1979) ‘‘Ventilation, health & energy consump-tion: a status report’’, ASHRAE Journal, July, pp.23–27.

Yaglou, C.P., Riley, E.C. and Coggins, D.I. (1936) ‘‘Ventilationrequirements’’, ASHVE Transactions, 42, 133–162.

impact of temperature and humidity on the perception of ... · impact of temperature and humidity...

Documents