ENVIRONMENTAL
9, 66-75
RESEARCH
Subjective
(1975)
Responses
to Atmospheric
D. A. MCINTYRE Electricity
Council
Research
Centre, Received
Humidity
AND I. D. GRLFFITHS~
Capenhurst, Januam
Chester,
CHl
6ES,
United
Kingdom
25, 1974
Three humidities, 20, 50, and 75% relative humidity (RH), at 2 temperatures, 23 and 28°C were set up in the environmental chamber at the Electricity Council Research Centre, Capenhurst. Subjects in the age range 16-19 years, each experienced one condition for 6 hours. Warmth votes were recorded at hourly intervals and a 16 item questionnaire was completed at the end of the morning and afternoon. Humidity did not affect the subjects’ warmth votes at 23”C, but at 28°C the warmth vote increased by 0.8 interval on the Bedford 7 point scale as the humidity increased from 20 to 75% RH; this is equivalent to an increase in temperature of 2.5”C. At 23°C the subjects distinguished between the humidities on the evaluative scales. Both the low and high humidities were found more oppressive and uncomfortable than 50% RH. At 28°C the low humidity (20% RH) condition was preferred; higher humidities were found more oppressive, more uncomfortable and more moist.
The desirability of control of atmospheric humidity has always been accepted in climates with high temperatures and humidities. New patterns of building structure and usage in this country have resulted in a wide range of humidities being found inside buildings, and it is necessary to understand the effect of unusually low or high humidities on people before considering the desirability of humidity control. The humidity of the atmosphere affects a person’s sensation of warmth. At ‘a given temperature, increasing the relative humidity (RH) increases the feeling of warmth, and this effect is more marked at higher temperatures (Nevins et al., 1966; Koch, Jennings, and Humphreys, 1960). Very much less attention has been paid to the perception of humidity at comfortable air temperatures. Koch (1963) reported an experiment in which sedentary subjects experienced a range of humidities from 15 to 95% at a constant air temperature of 25°C. They rated the environment after 3 hours on a 7 point scale running from painfully dry to wet. The subjects were not able to detect low humidities with any reliability. Fifty percent of the ‘normal humidity’ votes occurred between 32 and 50%humidities. Fifty percent of the ‘very humid’ votes occurred between 76 and 92%RH, indicating that the subjects could detect high humidities. The subjects did not evaluate the environment in terms of pleasantness or comfort. Rasmussen( 1971) carried out an experiment into the perception of humidity. Subjects were exposed to 2 humidities (30 and 70%RH) at 4 temperatures (21.1, 23.3, 25.6, and 27.8”C); th e subjects were seated and dressed in standard clothing (0.6 clo). After 3 hours they rated the environment on a 5 point scale running ’ Present
address:
Atkins
Copyright Q 1975 by Academic Printed in the United States.
Research
and Development, 66
Press. Inc. All IrIghts of reproductwn
Ashley
Road,
in any term reserved
Epsom,
United
Kingdom.
RESPONSES
TO
ATMOSPHERIC
67
HUMIDITY
from I (very dry) to 5 (very humid). An analysis of variance of the data quoted by Rasmussen shows that his subjects reliably distinguished between the two humidity levels at the highest temperature of 27.8”C, where there was a mean change of 1 scale interval on the humidity scale between 30 and 70% RH. There is a body of opinion which holds that low humidities are both uncomfortable and unhealthy. The argument is based on the drying effect of low humidities on the nasal mucosa, which is supposed to lead to discomfort, and an increased risk of infection. The evidence in this field is summarised by Elkins ( 1968), who decided that the evidence was inconclusive. However, he suggested that low humidities might be important when coincident with other health problems. In spite of the lack of evidence, the proponents of humidification claim dramatic effects for low humidities: “staff efficiency down 50X,” “very detrimental to health,” “ a complete deceleration of all body functions” (Leisinger 1970). In view of the lack of experimental evidence an experiment was set up at the Electricity Council Research Centre, Capenhurst, to investigate the subjective reactions of people to both low and high humidities. The experiment was not restricted to feelings of warmth and humidity, and covered a range of subjective responses at both comfortable (23°C) and elevated (28°C) temperatures. Three relative humidities, 20, 50, and 75% were used at each temperature, representing the greatest range commonly found in buildings. Personality of the subjects was included as a variable in the analysis, since it was hypothesised that the relatively long exposure time (6 hours) would produce differential effects between extraverts and introverts. (Eysenck 1967). EXPERIMENTAL
DESIGN
AND ANALYSIS
Physical Conditions The experiment was carried out in the E.C.R.C. environmental chamber. This is a room 3.7 x 3.7 X 2.5 m, with temperature controlled walls and ceiling. Air at controlled temperature and humidity enters the chamber through a perforated floor covering and is extracted at ceiling level. This permits high air change rates with low air velocities. A matrix of 2 temperatures and 3 humidities was used, consisting of temperatures of 23 and 28°C and relative humidities of 20, SO,and TABLE PHVS~XL
Dry bulb (“C) Condition 1 2 3 4 5 6
Meau 22.9 23.0 22.9 28.0 27.9 28.0
(i Mean radiant temperature
0.3 0.2 0.2 0 .3 0.2 0.3
Ia
CONDITIONS
Asp. wet blllb (“C) hlean
Sl)
V.P. (mbar)
RH (%I,)
11.2 16.5 19.7 14.3 20.4 “4.5
0.3 0.2 0.3 0.5 0.2 0.2
Fi.4 14.4 20.8 7.2 19.0 28.5
20 51 75 19 50 7.5
equal to air temperature;
air ve1ocit.y less than 0.1 m/second.
68
MCINTYRE
AND
GRIFFITHS
75%. The walls, ceiling and floor of the chamber were maintained at air temperature. Wet and dry bulb temperatures were measured in the chamber at hourly intervals using an Assman aspirated thermometer; the conditions achieved are listed in Table 1. Air velocity was measured with a DISA low speed anemometer, and was found to be low, less than 0.1 m/second. Each of the 6 conditions was presented 3 times, and the order of presentation was randomised. Conduct
of Experiment
The subjects were students in good health, of both sexes, and with an age range of 16-19 years. Of the total of 72 subjects, 53 were male and 19 female. Each subject attended once only. Four subjects attended each session; before entering the chamber they were asked to remove any jackets or pullovers. The subjects were thus lightly clothed, with a clothing insulation value of about 0.7 clo units. During the experiment the subjects were seated, and occupied themselves reading, writing or playing cards. A wireless was provided, and smoking was allowed. Drinks from a vending machine were provided on demand; the number of drinks was recorded. A light lunch was provided, which the subjects ate in the chamber. The experiment took place in August, 1972, and a payment of &2 was made for each attendance. Each sessionlasted from 1000 to 1600 hours. On 4 occasions sublingual temperatures were taken, using the recommended procedure of replacing the thermometer until consistent readings were obtained. At hourly intervals subjects were asked to describe their feelings of warmth on the 7 point Bedford scale. TABLE
2
QUISSTIONNAIRP
Vote
no.
2 3 4 6 7 8 9 10 11 12 13 14 15 1G 17
1
End
points
7
Open Even No discomfort Fresh Bedford Scaleb
Oppressive Uneven Considerable Stagnant
W Comfortable Hot Headache: none Invigorating Steady Pleasing Draughty Skin : dry Eyes: dry Nose: clear Sweating: not, at all
Moist Uncomfortable Cold Severe Dozy Changing Annoying Still Moisl; Moist Congested Very much
discomfort
D The questionnaire was presented at 1230 and 1,530; the answers apply to the whole morning or afternoon. b Bedford Scale: 1 Much too cool; 2 too cool; 3 comfortably cool; 4 comfortable and neither cool nor warm; 5 comfortably warm; 6 t,oo warm; 7 milch too warm.
RESPONSES
TO
ATMOSPHERIC
TABLE
69
HUMIDITY
3
TIMET.U\I,E DF I’:IPEILIMENT Subjects Sublingu31 Warmth Warmth SltblinglA Warmth Lunch Sublingual Warmth Warmth Sublingual Warmth Eysenck End
10.00 10.15 10.30 11 30 12.15 12.30 13.45 13 .20 13.30 14.30 15.15 15.30 15.45 16.00
remove outer t.emperature vc>te vote temperatIn-e vote, followed
clot.hing
and enter
by full
questionnnire
temperature vot,e vote temperatcu-e vote, followed by full Personality Irivent.ory
chamber
questionnaire
Subjects wrote the time, their individual code number and their Bedford vote on a slip of paper and deposited it in a box. They were not able to refer to earlier votes, and were instructed not to discuss the conditions with each other. They were not told the nature of the experiment. At 1230 and 1530 the subjects answered 16 questions on their feelings about the conditions in the chamber. All questions were in the form of 7 point rating scales, and are listed in Table 2. This questionnaire is a shortened form of the 34 item questionnaire used in earlier experiments. The questions were made up in the form of slides and shown to the subjects using a projector; the items were presented in a new random order for each session. The answers were punched by the subjects themselves on IBM computer cards according to the instructions in the appendix. At the end of the session, the subjects completed an Eysenck Personality Inventory. which estimates personality on the 2 dimensions of introversionextraversion (E) and neuroticism (N). Form B of the questionnaire was used. The group of subjects had a distribution of scorescharacterised by z!?= 14.5, D = 4.3 and aq = 11.9, 0 = 4.3, compared with the figures of E = 13.4, cr = 4.2 and fi = 11.0, 0 = 4.8, which are quoted for students in the manual of the E.P.I. A timetable of the experiment is given in Table 3.
Analysis of Variance The data collected in this experiment were subjected to analyses of variance. While there were minor variations in the analysis for different sets of data, the basic design was the same. Separate analyses were performed for data collected at 23 and 28°C; it was not the purpose of this experiment to examine the effect of temperature per se on reactions. The analysis used was a 3 way factoria1 design; treatments were designated A (humidity), B (introversion) with repeated mea-
70
MCINTYRE
FIG.
1.
Variation
of mean
AND
GRIFFITHS
TIME
OF
warmth
DAY
vote
with
time
of day.
sures on C (time of day). The form of analysis given by Winer ( 1962, p. 337) was followed. Subjects were allocated to subgroup B, or Bz (introversion or extraversion) on a post hoc basis. The 12 subjects who experienced a single level of humidity (factor A) were divided at the median for the group on the basis of their Personality Inventory scores for extraversion. The range of medians among the groups was small. RESULTS
Warmth
Votes
The subjects recorded their warmth vote on the Bedford Scale 6 times at hourly intervals throughout the experimental session. The answers were subjected to a 3 way analysis of variance, with treatments humidity X introversion X time of day (3 X 2 X 6). The results are shown graphically in Figs. 1 and 2. Increasing
MUCH ToocooL
20%
50%
RELATIVE
FIG.
2.
Variation
of mean
warmth
75%
HUMIDITY
vote
with
humidity.
RESPONSES
TO
.AThlOSPHElR.\TINC S;c.\rxs of meal, votes
OF SIGNIFICANT J~>FFECTS ON REHPOKSIC TO
Tahle
GRIFFITHS
Ten-
OF TIME
Time
of day
hM
PM
:IND HUMIDITY
Humidity
]NX-
1
S-ale
i.rlre
Oppressive
Open No discomfort.
Considerable
Fresh Dry Comfortahle Headache: Pleasing Skin: dry
St.agnant) Moist Uncomfortable Severe Annoying Moist
Eyes:
7
dry
* Significant ** 11 *** 11
none
hluist,
discomfort,
23 28 23 28 23 28 28 28 28 23 28 28
Low
.5.3***
4.1 3 .2
5.1*** 3. !a*
4.5 1.7 4.4
.;.4*** 2, g*** 4.7*
High
4 0 3.1 3.0 3.7 3.2
2.6 .5 2 2.2 4.5 3.0 4.4
3.5 * 5.6 ** 2,s * 5.3 4.0 (lOS?o)
5.2
***
3.1 A 1 3.1
3.a 5.2 2.7
4.3 6.2 4.1
*
3 3
4.6
Medium
*
at :i:,l level. /i ,c; (1 it ($;;, “ :
on the dry-moist scale, but an increase in rating of moistness of the skin was found. The scales open-oppressive and discomfort both produced changes significant at the 5% level. Both showed a minimum at the 50% RH level, with both high and low humidities rated as worse. A similar effect was found with the scale fresh-stagnant, but this was only significant at the 10% Ievel. The sensitivity to humidity of this analysis is rather low, since repeated measures were not used for the humidity levels. Several time of day effects were found. From the summary in Table 5, it can be seen that the subjects did not like the afternoon. They found the afternoon session more oppressive, more uncomfortable, more stagnant, more annoying, and it gave them more headaches. All these effects occurred at 28°C except for the increase in the fresh-stagnant rating, which occurred at 23°C. Sublingual
Temperature
Body temperature is known to vary throughout the day; differences between extraverts and introverts have also been observed (Blake 1971). The sublingual temperature of each subject was measured on 4 occasions during the session. The results were analysed by a three way analysis of variance (humidity X extraversion X time of day, repeated measures on time of day). Separate analyses were performed for results obtained at 23 and 28°C. The only significant result was the effect of time of day at 28°C (p < 0.1%). The variation is shown in Fig. 3. Drinks Subjects were provided with drinks on demand. Analysis showed that significantly more drinks were demanded at 28°C than at 23°C. The mean number of
RESPONSES
FIG.
3. Variation
TO
ATMOSPHERIC
of mean sublingual
HUMIDITY
temperature
73
with time of day.
drinks for the sessionwere 2.0 (23°C) and 2.7 (2S”C), p < 0.05. A significant, but nonhypothesised interaction between temperature, personality and humidity was found.
Table 4 compares the warmth votes found in this experiment with those found by other experimenters. Differences in overall level of warmth between experiments occur because of differences in clothing insulation and metabolic rate; it is the changes due to temperature aud humidity within experiments that are of interest. Nevins et al. (1966) f ound a strong effect of humidity on warmth vote at both 23 and 2S”C. At 23°C his subjects were voting cool, yet still showing a change of 0.5 of a warmth scale interval between 20 and 75% RH. Koch et al. ( 1960) found no effect of humidity on warmth at 23”C, in agreement with our results. Fanger’s ( 1972) equation was used to predict warmth votes at the humidity levels used in this experiment. Best agreement was obtained by assuming a metabolic rate of 70 W/mS and a clothing insulation of 0.75 clo units. This figure for metabolic rate is somewhat higher than that usually assumed for sedentary subjects; either our subjects were unusually active or preferred a lower temperature than those on which Fanger’s equation is based. Fanger’s equation predicts a change of 0.3 of an interval over the range 20-75% RH at 23°C; this is a small change, and would be difficult to detect using an experiment with independent measures. All results agree on the importance of RH in warmth sensation at 2S”C. Our results produced a change of 0.S of an interval over the range of humidity 20-75%. The questionnaire results (Table 5) indicate that at 28”C, the subjects could reliably detect the change in RH. There was a 2 point change in the dry-moist vote, as well as increases in skin: dry-moist and eyes: dry-moist votes. The low humidity condition was preferred. There was a monotonic increase of discomfort and oppressiveness as the RH increased from 20 to 75%.At an elevated temperature both discomfort and oppressivenessincrease with warmth. An earlier experiment (McIntyre and Griffiths, 1972) found a regression coefficient of the openoppressive vote on warmth vote of 0.64. TnbIe 4 shows a change in warmth vote of AM’ = 0.8 between 20 and 75% RH at 28”C, and we should expect this to produce a change in oppressiveness vote of 0.64 ATY = 0.5. The change found
74
MCINTYRE
AND
GRIFFITHS
of 1.6 is much larger than this, indicating that the increase in humidity produces a feeling of ‘oppressiveness’ which cannot be explained by a simple increase in warmth. At the comfortable temperature of 23°C the humidity is only perceived directly in the skin: dry-moist scale, which increased from 3.1 to 4.3. The open-oppressive scale showed a minimum for 50% RH; both low to high humidities were related scale. This as more oppressive. A similar shape was found for the discomfort provides evidence to show that low humidities are found undesirable at temperatures which are otherwise comfortable. At 28°C conditions in the afternoon were rated worse than in the morning on a variety of scales. This probably mainly results from spending 6 hours in an experimental chamber in conditions which were “too warm.” There were no significant interactions of time of day and humidity on the subjective rating scales. This implies that a difference of given magnitude in humidity produces the same subjective response after 3 or 6 hours of exposure. Thus increasing the exposure time from 3 to 6 hours does not produce an improvement in the detectability of humidity differences. In this experiment subjects each attended once only. This experimental design avoids various problems where the subject’s previous experience affects his subsequent ratings. However, it does reduce the sensitivity of the experiment as compared with a repeated measures design, in which each subject experiences all conditions. With the 12 subjects per condition used in this experiment, it was possible to detect changes in vote between conditions of about one interval. CONCLUSIONS
This investigation differs from previous experiments in the literature in having used a greater variety of subjective rating scales than was previously the case. This has resulted in a demonstration that humidity has more subjective correlates than warmth and perceived humidity. People can detect changes in atmospheric humidity at a comfortable air temperature (23°C)) and find a level of 50%more comfortable and less oppressive than either 20 or 75%.The effect of humidity on warmth sensation at this temperature is small. At a higher temperature (2S”C), increasing the humidity from 20% makes people feel warmer and lesscomfortable. APPENDIX
How to Anwer the Questions When you have experienced the environmental conditions under test you can indicate your opinion of these conditions by answering a set of questions. The questions are shown to you as a set of slides and most questions are in the form: Hot 1
7 Cold 44
To indicate your response to this you punch a hole in the preperforated card: the
RESPONSES
TO
ATMOSPHERIC
HUMIDITY
75
number at the bottom of the slide tells you which column to punch, (columns are vertical and the numbers are at the top or long side of the card) and your answer is a number between 1 (Hot) and 7 (Cold). In our example, 4 would indicate that you found it neither hot nor cold, 5 would indicate that you found it a little cold, and so on. Some questions are shown with an exact meaning for each number (such as ‘comfortably cool,’ 5), but most leave this to you. If you have any difficulties with the questions, ask the experimenter. In the scales which run from 1 to 7 it is useful to remember that the middle or neutral category is 4. REFERENCES BLAKE, M. J. F. ( 1971). Temperament and time of day. In “Biological Rhythms and Human Performance” (W. P. Colquhoun, Ed.), Academic Press, London. ELKINS, R. H., AND LONGLEY, M. Y. (1968). Eifects of h umidity on health. American Gas Association Inc. Conference 25 Feb. 2968. Catalogue No. M 30000-l. EYSENCK, H. J. ( 1967). “Biological Basis of Personality” Charles C Thomas, Springfield, Illinois. FANGER, P. 0. ( 1972). “Thermal Comfort.” McGraw-Hill, New York. KOCH, W. (1963). Humidity sensations in the thermal comfort range. Architect. Sci. Rev., March 1963, pp. 33-34. KOCH, W., JENNINGS, B. H., AND HUMPHREYS, C. M. ( 1960). Sensation responses to ten]perature and humidity under still air conditions in the comfort range. ASHRAE Trans. 66, 264-287. LEISINGER, F. M. ( 1970). Humidifiers for the home. Heating Ventilating Eng., 44, 232-236. MCINTYRE, D. A., AND GRIFFITHS, I. D. (1972). Subjective response to radiant and convective environments. Enuiron. Res. 5, 471-482. NEVINS, R. G., ROHLES, F. H., SPRINGER, W., AND FEYERHEIM, A. M. (1966). A ten)perature-humidity chart for thermal comfort of seated persons. ASHRAE J. April, 55-61. RASMUSSEN, 0. B. (1971). “Man’s subjective perception of air humidity.” Fifth International Congress for Heating Ventilating and Air Conditioning. Polyteeknisk Forfag, Copenhagen. WINER, B. J. (1962). “Statistical Principles in Experimental Design.” McGraw-Hill, New York.
9, 66-75
RESEARCH
Subjective
(1975)
Responses
to Atmospheric
D. A. MCINTYRE Electricity
Council
Research
Centre, Received
Humidity
AND I. D. GRLFFITHS~
Capenhurst, Januam
Chester,
CHl
6ES,
United
Kingdom
25, 1974
Three humidities, 20, 50, and 75% relative humidity (RH), at 2 temperatures, 23 and 28°C were set up in the environmental chamber at the Electricity Council Research Centre, Capenhurst. Subjects in the age range 16-19 years, each experienced one condition for 6 hours. Warmth votes were recorded at hourly intervals and a 16 item questionnaire was completed at the end of the morning and afternoon. Humidity did not affect the subjects’ warmth votes at 23”C, but at 28°C the warmth vote increased by 0.8 interval on the Bedford 7 point scale as the humidity increased from 20 to 75% RH; this is equivalent to an increase in temperature of 2.5”C. At 23°C the subjects distinguished between the humidities on the evaluative scales. Both the low and high humidities were found more oppressive and uncomfortable than 50% RH. At 28°C the low humidity (20% RH) condition was preferred; higher humidities were found more oppressive, more uncomfortable and more moist.
The desirability of control of atmospheric humidity has always been accepted in climates with high temperatures and humidities. New patterns of building structure and usage in this country have resulted in a wide range of humidities being found inside buildings, and it is necessary to understand the effect of unusually low or high humidities on people before considering the desirability of humidity control. The humidity of the atmosphere affects a person’s sensation of warmth. At ‘a given temperature, increasing the relative humidity (RH) increases the feeling of warmth, and this effect is more marked at higher temperatures (Nevins et al., 1966; Koch, Jennings, and Humphreys, 1960). Very much less attention has been paid to the perception of humidity at comfortable air temperatures. Koch (1963) reported an experiment in which sedentary subjects experienced a range of humidities from 15 to 95% at a constant air temperature of 25°C. They rated the environment after 3 hours on a 7 point scale running from painfully dry to wet. The subjects were not able to detect low humidities with any reliability. Fifty percent of the ‘normal humidity’ votes occurred between 32 and 50%humidities. Fifty percent of the ‘very humid’ votes occurred between 76 and 92%RH, indicating that the subjects could detect high humidities. The subjects did not evaluate the environment in terms of pleasantness or comfort. Rasmussen( 1971) carried out an experiment into the perception of humidity. Subjects were exposed to 2 humidities (30 and 70%RH) at 4 temperatures (21.1, 23.3, 25.6, and 27.8”C); th e subjects were seated and dressed in standard clothing (0.6 clo). After 3 hours they rated the environment on a 5 point scale running ’ Present
address:
Atkins
Copyright Q 1975 by Academic Printed in the United States.
Research
and Development, 66
Press. Inc. All IrIghts of reproductwn
Ashley
Road,
in any term reserved
Epsom,
United
Kingdom.
RESPONSES
TO
ATMOSPHERIC
67
HUMIDITY
from I (very dry) to 5 (very humid). An analysis of variance of the data quoted by Rasmussen shows that his subjects reliably distinguished between the two humidity levels at the highest temperature of 27.8”C, where there was a mean change of 1 scale interval on the humidity scale between 30 and 70% RH. There is a body of opinion which holds that low humidities are both uncomfortable and unhealthy. The argument is based on the drying effect of low humidities on the nasal mucosa, which is supposed to lead to discomfort, and an increased risk of infection. The evidence in this field is summarised by Elkins ( 1968), who decided that the evidence was inconclusive. However, he suggested that low humidities might be important when coincident with other health problems. In spite of the lack of evidence, the proponents of humidification claim dramatic effects for low humidities: “staff efficiency down 50X,” “very detrimental to health,” “ a complete deceleration of all body functions” (Leisinger 1970). In view of the lack of experimental evidence an experiment was set up at the Electricity Council Research Centre, Capenhurst, to investigate the subjective reactions of people to both low and high humidities. The experiment was not restricted to feelings of warmth and humidity, and covered a range of subjective responses at both comfortable (23°C) and elevated (28°C) temperatures. Three relative humidities, 20, 50, and 75% were used at each temperature, representing the greatest range commonly found in buildings. Personality of the subjects was included as a variable in the analysis, since it was hypothesised that the relatively long exposure time (6 hours) would produce differential effects between extraverts and introverts. (Eysenck 1967). EXPERIMENTAL
DESIGN
AND ANALYSIS
Physical Conditions The experiment was carried out in the E.C.R.C. environmental chamber. This is a room 3.7 x 3.7 X 2.5 m, with temperature controlled walls and ceiling. Air at controlled temperature and humidity enters the chamber through a perforated floor covering and is extracted at ceiling level. This permits high air change rates with low air velocities. A matrix of 2 temperatures and 3 humidities was used, consisting of temperatures of 23 and 28°C and relative humidities of 20, SO,and TABLE PHVS~XL
Dry bulb (“C) Condition 1 2 3 4 5 6
Meau 22.9 23.0 22.9 28.0 27.9 28.0
(i Mean radiant temperature
0.3 0.2 0.2 0 .3 0.2 0.3
Ia
CONDITIONS
Asp. wet blllb (“C) hlean
Sl)
V.P. (mbar)
RH (%I,)
11.2 16.5 19.7 14.3 20.4 “4.5
0.3 0.2 0.3 0.5 0.2 0.2
Fi.4 14.4 20.8 7.2 19.0 28.5
20 51 75 19 50 7.5
equal to air temperature;
air ve1ocit.y less than 0.1 m/second.
68
MCINTYRE
AND
GRIFFITHS
75%. The walls, ceiling and floor of the chamber were maintained at air temperature. Wet and dry bulb temperatures were measured in the chamber at hourly intervals using an Assman aspirated thermometer; the conditions achieved are listed in Table 1. Air velocity was measured with a DISA low speed anemometer, and was found to be low, less than 0.1 m/second. Each of the 6 conditions was presented 3 times, and the order of presentation was randomised. Conduct
of Experiment
The subjects were students in good health, of both sexes, and with an age range of 16-19 years. Of the total of 72 subjects, 53 were male and 19 female. Each subject attended once only. Four subjects attended each session; before entering the chamber they were asked to remove any jackets or pullovers. The subjects were thus lightly clothed, with a clothing insulation value of about 0.7 clo units. During the experiment the subjects were seated, and occupied themselves reading, writing or playing cards. A wireless was provided, and smoking was allowed. Drinks from a vending machine were provided on demand; the number of drinks was recorded. A light lunch was provided, which the subjects ate in the chamber. The experiment took place in August, 1972, and a payment of &2 was made for each attendance. Each sessionlasted from 1000 to 1600 hours. On 4 occasions sublingual temperatures were taken, using the recommended procedure of replacing the thermometer until consistent readings were obtained. At hourly intervals subjects were asked to describe their feelings of warmth on the 7 point Bedford scale. TABLE
2
QUISSTIONNAIRP
Vote
no.
2 3 4 6 7 8 9 10 11 12 13 14 15 1G 17
1
End
points
7
Open Even No discomfort Fresh Bedford Scaleb
Oppressive Uneven Considerable Stagnant
W Comfortable Hot Headache: none Invigorating Steady Pleasing Draughty Skin : dry Eyes: dry Nose: clear Sweating: not, at all
Moist Uncomfortable Cold Severe Dozy Changing Annoying Still Moisl; Moist Congested Very much
discomfort
D The questionnaire was presented at 1230 and 1,530; the answers apply to the whole morning or afternoon. b Bedford Scale: 1 Much too cool; 2 too cool; 3 comfortably cool; 4 comfortable and neither cool nor warm; 5 comfortably warm; 6 t,oo warm; 7 milch too warm.
RESPONSES
TO
ATMOSPHERIC
TABLE
69
HUMIDITY
3
TIMET.U\I,E DF I’:IPEILIMENT Subjects Sublingu31 Warmth Warmth SltblinglA Warmth Lunch Sublingual Warmth Warmth Sublingual Warmth Eysenck End
10.00 10.15 10.30 11 30 12.15 12.30 13.45 13 .20 13.30 14.30 15.15 15.30 15.45 16.00
remove outer t.emperature vc>te vote temperatIn-e vote, followed
clot.hing
and enter
by full
questionnnire
temperature vot,e vote temperatcu-e vote, followed by full Personality Irivent.ory
chamber
questionnaire
Subjects wrote the time, their individual code number and their Bedford vote on a slip of paper and deposited it in a box. They were not able to refer to earlier votes, and were instructed not to discuss the conditions with each other. They were not told the nature of the experiment. At 1230 and 1530 the subjects answered 16 questions on their feelings about the conditions in the chamber. All questions were in the form of 7 point rating scales, and are listed in Table 2. This questionnaire is a shortened form of the 34 item questionnaire used in earlier experiments. The questions were made up in the form of slides and shown to the subjects using a projector; the items were presented in a new random order for each session. The answers were punched by the subjects themselves on IBM computer cards according to the instructions in the appendix. At the end of the session, the subjects completed an Eysenck Personality Inventory. which estimates personality on the 2 dimensions of introversionextraversion (E) and neuroticism (N). Form B of the questionnaire was used. The group of subjects had a distribution of scorescharacterised by z!?= 14.5, D = 4.3 and aq = 11.9, 0 = 4.3, compared with the figures of E = 13.4, cr = 4.2 and fi = 11.0, 0 = 4.8, which are quoted for students in the manual of the E.P.I. A timetable of the experiment is given in Table 3.
Analysis of Variance The data collected in this experiment were subjected to analyses of variance. While there were minor variations in the analysis for different sets of data, the basic design was the same. Separate analyses were performed for data collected at 23 and 28°C; it was not the purpose of this experiment to examine the effect of temperature per se on reactions. The analysis used was a 3 way factoria1 design; treatments were designated A (humidity), B (introversion) with repeated mea-
70
MCINTYRE
FIG.
1.
Variation
of mean
AND
GRIFFITHS
TIME
OF
warmth
DAY
vote
with
time
of day.
sures on C (time of day). The form of analysis given by Winer ( 1962, p. 337) was followed. Subjects were allocated to subgroup B, or Bz (introversion or extraversion) on a post hoc basis. The 12 subjects who experienced a single level of humidity (factor A) were divided at the median for the group on the basis of their Personality Inventory scores for extraversion. The range of medians among the groups was small. RESULTS
Warmth
Votes
The subjects recorded their warmth vote on the Bedford Scale 6 times at hourly intervals throughout the experimental session. The answers were subjected to a 3 way analysis of variance, with treatments humidity X introversion X time of day (3 X 2 X 6). The results are shown graphically in Figs. 1 and 2. Increasing
MUCH ToocooL
20%
50%
RELATIVE
FIG.
2.
Variation
of mean
warmth
75%
HUMIDITY
vote
with
humidity.
RESPONSES
TO
.AThlOSPHElR.\TINC S;c.\rxs of meal, votes
OF SIGNIFICANT J~>FFECTS ON REHPOKSIC TO
Tahle
GRIFFITHS
Ten-
OF TIME
Time
of day
hM
PM
:IND HUMIDITY
Humidity
]NX-
1
S-ale
i.rlre
Oppressive
Open No discomfort.
Considerable
Fresh Dry Comfortahle Headache: Pleasing Skin: dry
St.agnant) Moist Uncomfortable Severe Annoying Moist
Eyes:
7
dry
* Significant ** 11 *** 11
none
hluist,
discomfort,
23 28 23 28 23 28 28 28 28 23 28 28
Low
.5.3***
4.1 3 .2
5.1*** 3. !a*
4.5 1.7 4.4
.;.4*** 2, g*** 4.7*
High
4 0 3.1 3.0 3.7 3.2
2.6 .5 2 2.2 4.5 3.0 4.4
3.5 * 5.6 ** 2,s * 5.3 4.0 (lOS?o)
5.2
***
3.1 A 1 3.1
3.a 5.2 2.7
4.3 6.2 4.1
*
3 3
4.6
Medium
*
at :i:,l level. /i ,c; (1 it ($;;, “ :
on the dry-moist scale, but an increase in rating of moistness of the skin was found. The scales open-oppressive and discomfort both produced changes significant at the 5% level. Both showed a minimum at the 50% RH level, with both high and low humidities rated as worse. A similar effect was found with the scale fresh-stagnant, but this was only significant at the 10% Ievel. The sensitivity to humidity of this analysis is rather low, since repeated measures were not used for the humidity levels. Several time of day effects were found. From the summary in Table 5, it can be seen that the subjects did not like the afternoon. They found the afternoon session more oppressive, more uncomfortable, more stagnant, more annoying, and it gave them more headaches. All these effects occurred at 28°C except for the increase in the fresh-stagnant rating, which occurred at 23°C. Sublingual
Temperature
Body temperature is known to vary throughout the day; differences between extraverts and introverts have also been observed (Blake 1971). The sublingual temperature of each subject was measured on 4 occasions during the session. The results were analysed by a three way analysis of variance (humidity X extraversion X time of day, repeated measures on time of day). Separate analyses were performed for results obtained at 23 and 28°C. The only significant result was the effect of time of day at 28°C (p < 0.1%). The variation is shown in Fig. 3. Drinks Subjects were provided with drinks on demand. Analysis showed that significantly more drinks were demanded at 28°C than at 23°C. The mean number of
RESPONSES
FIG.
3. Variation
TO
ATMOSPHERIC
of mean sublingual
HUMIDITY
temperature
73
with time of day.
drinks for the sessionwere 2.0 (23°C) and 2.7 (2S”C), p < 0.05. A significant, but nonhypothesised interaction between temperature, personality and humidity was found.
Table 4 compares the warmth votes found in this experiment with those found by other experimenters. Differences in overall level of warmth between experiments occur because of differences in clothing insulation and metabolic rate; it is the changes due to temperature aud humidity within experiments that are of interest. Nevins et al. (1966) f ound a strong effect of humidity on warmth vote at both 23 and 2S”C. At 23°C his subjects were voting cool, yet still showing a change of 0.5 of a warmth scale interval between 20 and 75% RH. Koch et al. ( 1960) found no effect of humidity on warmth at 23”C, in agreement with our results. Fanger’s ( 1972) equation was used to predict warmth votes at the humidity levels used in this experiment. Best agreement was obtained by assuming a metabolic rate of 70 W/mS and a clothing insulation of 0.75 clo units. This figure for metabolic rate is somewhat higher than that usually assumed for sedentary subjects; either our subjects were unusually active or preferred a lower temperature than those on which Fanger’s equation is based. Fanger’s equation predicts a change of 0.3 of an interval over the range 20-75% RH at 23°C; this is a small change, and would be difficult to detect using an experiment with independent measures. All results agree on the importance of RH in warmth sensation at 2S”C. Our results produced a change of 0.S of an interval over the range of humidity 20-75%. The questionnaire results (Table 5) indicate that at 28”C, the subjects could reliably detect the change in RH. There was a 2 point change in the dry-moist vote, as well as increases in skin: dry-moist and eyes: dry-moist votes. The low humidity condition was preferred. There was a monotonic increase of discomfort and oppressiveness as the RH increased from 20 to 75%.At an elevated temperature both discomfort and oppressivenessincrease with warmth. An earlier experiment (McIntyre and Griffiths, 1972) found a regression coefficient of the openoppressive vote on warmth vote of 0.64. TnbIe 4 shows a change in warmth vote of AM’ = 0.8 between 20 and 75% RH at 28”C, and we should expect this to produce a change in oppressiveness vote of 0.64 ATY = 0.5. The change found
74
MCINTYRE
AND
GRIFFITHS
of 1.6 is much larger than this, indicating that the increase in humidity produces a feeling of ‘oppressiveness’ which cannot be explained by a simple increase in warmth. At the comfortable temperature of 23°C the humidity is only perceived directly in the skin: dry-moist scale, which increased from 3.1 to 4.3. The open-oppressive scale showed a minimum for 50% RH; both low to high humidities were related scale. This as more oppressive. A similar shape was found for the discomfort provides evidence to show that low humidities are found undesirable at temperatures which are otherwise comfortable. At 28°C conditions in the afternoon were rated worse than in the morning on a variety of scales. This probably mainly results from spending 6 hours in an experimental chamber in conditions which were “too warm.” There were no significant interactions of time of day and humidity on the subjective rating scales. This implies that a difference of given magnitude in humidity produces the same subjective response after 3 or 6 hours of exposure. Thus increasing the exposure time from 3 to 6 hours does not produce an improvement in the detectability of humidity differences. In this experiment subjects each attended once only. This experimental design avoids various problems where the subject’s previous experience affects his subsequent ratings. However, it does reduce the sensitivity of the experiment as compared with a repeated measures design, in which each subject experiences all conditions. With the 12 subjects per condition used in this experiment, it was possible to detect changes in vote between conditions of about one interval. CONCLUSIONS
This investigation differs from previous experiments in the literature in having used a greater variety of subjective rating scales than was previously the case. This has resulted in a demonstration that humidity has more subjective correlates than warmth and perceived humidity. People can detect changes in atmospheric humidity at a comfortable air temperature (23°C)) and find a level of 50%more comfortable and less oppressive than either 20 or 75%.The effect of humidity on warmth sensation at this temperature is small. At a higher temperature (2S”C), increasing the humidity from 20% makes people feel warmer and lesscomfortable. APPENDIX
How to Anwer the Questions When you have experienced the environmental conditions under test you can indicate your opinion of these conditions by answering a set of questions. The questions are shown to you as a set of slides and most questions are in the form: Hot 1
7 Cold 44
To indicate your response to this you punch a hole in the preperforated card: the
RESPONSES
TO
ATMOSPHERIC
HUMIDITY
75
number at the bottom of the slide tells you which column to punch, (columns are vertical and the numbers are at the top or long side of the card) and your answer is a number between 1 (Hot) and 7 (Cold). In our example, 4 would indicate that you found it neither hot nor cold, 5 would indicate that you found it a little cold, and so on. Some questions are shown with an exact meaning for each number (such as ‘comfortably cool,’ 5), but most leave this to you. If you have any difficulties with the questions, ask the experimenter. In the scales which run from 1 to 7 it is useful to remember that the middle or neutral category is 4. REFERENCES BLAKE, M. J. F. ( 1971). Temperament and time of day. In “Biological Rhythms and Human Performance” (W. P. Colquhoun, Ed.), Academic Press, London. ELKINS, R. H., AND LONGLEY, M. Y. (1968). Eifects of h umidity on health. American Gas Association Inc. Conference 25 Feb. 2968. Catalogue No. M 30000-l. EYSENCK, H. J. ( 1967). “Biological Basis of Personality” Charles C Thomas, Springfield, Illinois. FANGER, P. 0. ( 1972). “Thermal Comfort.” McGraw-Hill, New York. KOCH, W. (1963). Humidity sensations in the thermal comfort range. Architect. Sci. Rev., March 1963, pp. 33-34. KOCH, W., JENNINGS, B. H., AND HUMPHREYS, C. M. ( 1960). Sensation responses to ten]perature and humidity under still air conditions in the comfort range. ASHRAE Trans. 66, 264-287. LEISINGER, F. M. ( 1970). Humidifiers for the home. Heating Ventilating Eng., 44, 232-236. MCINTYRE, D. A., AND GRIFFITHS, I. D. (1972). Subjective response to radiant and convective environments. Enuiron. Res. 5, 471-482. NEVINS, R. G., ROHLES, F. H., SPRINGER, W., AND FEYERHEIM, A. M. (1966). A ten)perature-humidity chart for thermal comfort of seated persons. ASHRAE J. April, 55-61. RASMUSSEN, 0. B. (1971). “Man’s subjective perception of air humidity.” Fifth International Congress for Heating Ventilating and Air Conditioning. Polyteeknisk Forfag, Copenhagen. WINER, B. J. (1962). “Statistical Principles in Experimental Design.” McGraw-Hill, New York.
