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VOLUME 13, NUMBER 4 HVAC&R RESEARCH JULY 2007
623
Indoor Temperature, Productivity, and
Fatigue in Office Tasks
Shin-ichi Tanabe, DrEng Naoe Nishihara, PhD Masaoki Haneda
Fellow ASHRAE
Received January 1, 2006; accepted March 16, 2006
The current status of Japanese office buildings is taken as an example and the balance of envi-
ronmental concerns and office productivity are discussed. To promote the effort for energy con-
servation, it is important to estimate the indoor environmental quality from the aspect of office
workers’ productivity. Our experiments on the effect of moderately high temperature on produc-
tivity are noted. They showed that the effects of thermal environment on task performance were
contradictory among the task types. However, the subjects complained of the feeling of mental
fatigue more, and more cerebral blood flow was required to maintain the same level of task per-
formance in the hot condition than at a thermal neutral condition. For evaluating task perfor-
mance, the cost of maintaining performance, namely, fatigue and mental effort, is important in
evaluating and predicting productivity. For long periods of exposure, indoor air temperature
has effects on workers’ performance.
INTRODUCTION
Indoor environmental quality may affect physiological and psychological processes that, in
turn, may affect performance of tasks that may interact with other factors to affect overall pro-
ductivity (Parsons 1993). Seppänen and Fisk (2003) developed a conceptual economic model
for owner-occupied buildings that shows the links between improvements in indoor environ-
ment quality and financial gains. It is very important to consider the effect of indoor environ-
mental quality on office workers’ health and productivity.
Earlier studies about the effect of thermal conditions on productivity were done mainly by
field study. They showed that accident rates were high or output rate decreased in hot environ-
ments (Chrenko 1973; Vernon, 1919). Some reviews and a summarized model for the effects
of the thermal environment on mental performance showed that mental performance
decreases with heat (Parsons 1993; Wyon 1986; Seppänen and Fisk 2003). On the other hand,
it was also reported that performance of mental tasks is generally unaffected by heat (Pepler
and Warner 1968; Sundstrom 1987). Productivity research is somewhat confusing because the
results are sometimes conflicting (Lorsch and Abdou 1994; CIBSE 1999). The difference of
task types or workers’ psychological factors, such as motivation level, may affect the results.
In our study, we tried to evaluate the effect of thermal environment on productivity, not only
by task performances, but also by physiological measurements, psychological measurements,
and structural analysis of fatigue.
In this paper, the current status of Japanese office buildings is taken as an example and the
balance of environmental concerns and office productivity are discussed by introducing our
previous subjective experiments on the effect of moderately high temperature on office work-
ers’ productivity.
Shin-ichi Tanabe is a professor and Masaoki Haneda is a graduate student in the Department of Architecture and Naoe
Nishihara is a research associate in the Research Institute of Science and Engineering at Waseda University, Tokyo, Japan.
©2007, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in HVAC&R Research, Vol. 13,
No. 4, July 2007. For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without
ASHRAE’s prior written permission.
624 HVAC&R RESEARCH
CURRENT STATUS OF JAPANESE OFFICE BUILDINGS
With the intent of energy conservation, the Japanese government recommended keeping an
office temperature setting of 28°C in summer. If we keep an office temperature setting of 28°C,
we may reduce expenditure for energy cost by 1~2%, which would be no more than 50 $/m2 per
year and accounts for only 4% of real-estate rental service (Murao et al. 2003). As a result,
reduction in the quality of the office environment will occur. It will decrease the office worker’s
productivity and have much effect on income, which accounts for 68.9% of real-estate rental
service. Since a building owner’s interest is to raise income or to reduce expenditure, nobody
will take that risk.
How does reduction of energy use in controlling the indoor environment affect productivity in
the office? We must balance environmental concerns and office productivity.
EFFECT OF HIGH TEMPERATURE ON
TASK PERFORMANCE AND FATIGUE (SHORT EXPOSURE)
Method
To study the effect of moderately high temperature on task performance and fatigue, a subjec-
tive experiment was conducted in a climate chamber. College-age subjects, 20 males and 20
females, participated in the experiment. The chamber was conditioned at operative temperatures
of 25.5°C, 28.0°C, and 33.0°C with still air. Prior to these three conditions, a practice session at
an operative temperature of 25.5°C was conducted. Relative humidity was controlled around
50%. Subjects wore a uniform with an insulation value of 0.76 clo. Task performance tests on a
computer were conducted for 1.5 hours.
The experimental procedure is shown in Figure 1. After entering the climate chamber, sub-
jects waited in a sedentary position for 30 minutes and then reported their first thermal sensation
in the chamber and their feeling of fatigue. Four tests were carried out: the addition test for ten
minutes, the positioning test for five minutes, the text typing test for five minutes, and the
Walter Reed Performance Assessment Battery test (PAB) (Thorne et al. 1985) for about 15 min-
utes. After each test, an intermission of five minutes was taken and the subjects reported their
thermal sensation, their feeling of fatigue, and their evaluation of the task load. Subjects filled in
Figure 1. Experimental procedure showing the effect of moderately high temperature on
task performance and fatigue.
VOLUME 13, NUMBER 4, JULY 2007 625
the sheets for evaluation of subjective symptoms of fatigue 30 minutes after entering the climate
chamber as a “before” task and after all computer tasks were finished as an “after” task.
Subjective votes on thermal sensation using ASHRAE scales of male subjects were 0.1±0.83
for 25.5°C, 1.2±0.69 for 28.0°C, and 2.5±0.49 for the 33.0°C condition and those of female sub-
jects were –0.6±1.03 for 25.5°C, 1.1±0.78 for 28.0°C, and 2.5±0.63 for the 33.0°C condition. At
25.5°C, the average values of the thermal sensation vote and the sweating sensation vote of
female subjects were significantly lower than that of male subjects (p < 0.01).
Task Performances
For female subjects, there was no significant difference in the performance of all computer
tasks under the environmental conditions. For male subjects, there was no significant difference
in the performance of the addition test and the positioning test under the environmental condi-
tions. With regard to the performance of PAB, there was no significant difference under all envi-
ronmental conditions except for “four choice serial reaction time.” The performance of this test
at 33.0°C was significantly lower than at 28.0°C (p < 0.05) for male subjects. The performance
of the text typing test at 25.5°C was significantly lower than at 28.0°C and 33.0°C (p < 0.05) for
male subjects. The performance of the addition task, text typing, and “four choice serial reaction
time” (PAB) are shown in Figures 2, 3, and 4. In this study, the effects of thermal environment
on task performance were contradictory among the task types as in previous findings (Lorsch
and Abdou 1994; CIBSE 1999). It is difficult to evaluate the effect of thermal environment on
productivity by measuring only task performance.
Evaluation of Subjective Symptoms of Fatigue
To evaluate the feeling of fatigue, subjects filled in the sheets of “Evaluation of Subjective
Symptoms of Fatigue” (Yoshitake 1973). It consists of three categories: group I consists of ten
terms about “drowsiness and dullness,” group II consists of ten terms about “difficulty in con-
centration,” and group III consists of ten terms about “projection of physical disintegration.” By
the order of the rate of them, three types of fatigue feeling were estimated (Yoshitake 1973):
I>III>II for a general pattern of fatigue, I>II>III for a typical pattern of fatigue for mental work
and overnight duty, and III>I>II for a typical pattern of physical work.
The general rate of complaints before the task was the highest at 33.0°C, the next highest at
28.0°C, and the lowest at 25.5°C. The order among the categories of subjective symptoms of
fatigue is shown in Table 1. Before the task, at 25.5°C and 28.0°C, I>III>II was observed in both
female and male subjects. On the other hand, at 33.0°C, it was I>II>III in both female and male
subjects. For male subjects after the task, the type of fatigue was I>II>III under all environmen-
tal conditions. For female subjects, it was I>III>II at 25.5°C and 28.0°C and I>II>III at 33.0°C.
The subjects complained of a feeling of mental fatigue and complained the most just being in the
room with an operative temperature of 33.0°C.
EFFECT OF THE DIFFICULTY LEVEL OF TASKS AND
HIGH TEMPERATURE ON CEREBRAL BLOOD FLOW
Near Infrared Spectrometer
The near infrared spectrometer (NIRS) is shown in Figure 5 (Nishihara and Tanabe 2004). Near
infrared light was produced by laser diodes and carried to the tissue via optical fibers (Elwel 1995).
The light emerging from the tissue was returned to the instrument through another optical fiber by
detector, and incident and integrated values of transmitted light intensities were recorded every
second. The sampling rate was 2,000 times per second. Changes in the concentration of the chro-
mophores oxygenated hemoglobin “ΔO2Hb” and deoxyhemoglobin “ΔHHb” were calculated by
626 HVAC&R RESEARCH
Figure 2. The performance of the addition task.
Figure 3. The performance of the text typing test.
Figure 4. The performance of the “four choice serial reaction time” (PAB) test.
VOLUME 13, NUMBER 4, JULY 2007 627
the modified Beer-Lambert equation in µM = 10–6 mol units (Delpy et al. 1988). The changes in
concentration of total hemoglobin were calculated: Δtotal Hb = ΔO2Hb + ΔHHb. The probes were
placed on the subject’s forehead.
Previous studies reported that increase of ΔO2Hb and Δtotal Hb and decrease of ΔHHb were
the typical findings by NIRS during the brain activation and mental work (Villringer et al. 1993;
Kido 1995). The mechanism was explained as follows (Sakatani 2002): brain blood is necessary
for brain activity but there are few stocks of glucose and O2 in brain. So it is necessary to supply
them by blood flow. The ΔO2Hb and Δtotal Hb become higher in brain activity. The consump-
tion of O2 in brain activity is much smaller than the increased rate of cerebral blood flow. So,
ΔHHb becomes relatively lower in brain activity.
From the studies of the split-brain, the left brain is more dominant for linguistic abilities, cal-
culations, and math and logic abilities, where the right brain is more dominant for spatial ability
(Oono 1996), and it was also reported that the language center of most right-handed people is on
the left side of the brain (Kubota 1982; Sakano, 1982).
Cerebral Blood Flow and the Level of Difficulty of Tasks
The relationship between changes in cerebral blood oxygenation and the level of difficulty of
a task was evaluated in a subjective experiment. Four tasks were given to the subjects: sin-
gle-digit addition, double-digit multiplication, triple-digit addition, and triple-digit multiplica-
tion. It was evaluated that the more difficult the type of task, the more oxygenated hemoglobin
Table 1. The Order Among the Three Categories of Subjective Symptoms of Fatigue
Male/Female
Conditions Group I, % Group II, % Group III, % Order among
Three Categories
Before Task
25.5°C 15.5/16.5 3.5/1.5 5.5/5.5 I>III>II / I>III>II
28.0°C 23.0/26.5 5.0/8.0 7.0/11.0 I>III>II / I>III>II
33.0°C 24.0/32.0 12.0/14.0 11.5/12.0 I>II>III / I>II>III
After Task
25.5°C 21.5/31.5 14.0/12.5 13.5/14.0 I>II>III / I>III>II
28.0°C 28.0/31.5 15.5/15.0 13.5/18.5 I>II>III / I>III>II
33.0°C 24.5/34.0 21.5/19.0 14.5/16.5 I>II>III / I>II>III
Figure 5. The NIRS.
628 HVAC&R RESEARCH
and total hemoglobin concentration were required for their performance. There was a significant
correlation between the subjective value of mental demand for tasks and the left-side Δtotal Hb.
The change rate of total hemoglobin during each task is shown in Figure 6. It is shown that tasks
involving a higher mental demand require a higher cerebral blood flow. The correlation between
the values of change rates of mental demand and left-side Δtotal Hb, based on the single-digit
addition task, are shown in Figure 7. Monitoring cerebral blood oxygenation changes could be
applied to the evaluation of the input-side parameter of productivity to indicate the degree of
mental effort required to perform the task.
Effect of High Temperature on Cerebral Blood Flow
Another subjective experiment was conducted to study the effect of a moderately hot environ-
ment on cerebral blood flow.
Twelve right-handed male subjects were exposed in a climate chamber to two operative tem-
perature levels of 26.0°C and 33.5°C. Subjects experienced these two conditions in balanced
order. Before experiencing these two conditions, they participated in a practice session under an
operative temperature of 26.0°C the first time. Experimental conditions are listed in Table 2. In
this study, in order to increase their motivation to the same level, the subjects were informed that
Figure 6. The change of total hemoglobin during each task.
Figure 7. The correlation between the values of change rates of mental demand and
left-side total Hb, based on the single-digit addition task.
VOLUME 13, NUMBER 4, JULY 2007 629
the top six performers of the computer tasks could earn one hour’s worth of bonus. Therefore, it
could be assumed that subjects were highly motivated.
The experimental procedure is shown in Figure 8. After adaptation to the thermal environ-
ment for 50 minutes, three types of calculation task (single-digit addition, triple-digit addition,
and triple-digit multiplication) were assigned to subjects.
Subjects evaluated the environment at 33.5°C as hotter and stuffier compared to that at
26.0°C. There were no significant differences in task performance between 26.0°C and 33.5°C
conditions. According to the evaluation of subjective symptoms of fatigue, the subjects com-
plained of the feeling of mental fatigue more at operative temperature of 33.5°C than 26.0°C.
The results of ΔtotalHb during triple-digit addition and triple-digit multiplication tasks are
shown in Figure 9. The comparison between the levels of difficulty levels of the tasks revealed
that Δtotal Hb was significantly higher for triple-digit multiplication at 26.0°C (p < 0.03), which
supports the previously mentioned experiment. The increase of ΔtotalHb was significantly
higher at 33.5°C than that at 26.0°C for both task types (p < 0.02 for addition and p < 0.04 for
multiplication). Hot environments may require more cerebral blood flow to maintain same level
of task performance.
Table 2. Experimental Conditions
Air
Temperature, °C
Radiant
Temperature, °C
Operative
Temperature, °C
Relative
Humidity, % CO2, ppm
Practice 25.6 (0.11) 25.8 (0.09) 25.7 (0.10) 23 (4.7)*704 (46)
26.0°C 26.2 (0.71) 26.4 (0.67) 26.3 (0.69) 48 (0.2) 652 (35)
33.5°C 33.7 (0.10) 33.6 (0.04) 33.6 (0.07) 43 (1.1) 690 (71)
(standard deviation)
Icl of the experimental clothes were 0.76 clo.
*In only the practice session, there was trouble with the humidifier.
Figure 8. The experimental procedure to study the effect of a moderately hot environ-
ment on cerebral blood flow.
630 HVAC&R RESEARCH
EFFECT OF HIGH TEMPERATURE ON
TASK PERFORMANCE AND FATIGUE (SIX-HOUR EXPOSURE)
Experimental Method
To study the relationship between the task performance decrement and the work time, six
hours of subjective experiment was conducted in a climate chamber. Fifteen college-aged male
subjects participated in this experiment. The conditions were set by the combination of operative
temperature in the chamber and the amount of clothing insulation; they were 25.0°C with
1.0 clo, 28.0°C with 1.0 clo, and 28.0°C with 0.7 clo. Prior to these experimental conditions, a
practice was conducted at conditions of 25.0°C with 1.0 clo.
The experimental procedure is shown in Figure 10. After entering the chamber, the subjects
waited for 30 minutes in a sedentary position and then reported their first thermal sensation in
the chamber and their feeling of fatigue. Subjects were then assigned nine sessions of addition
tasks. In each session, the subjects worked for 30 minutes on the task and reported their thermal
sensation, their feeling of fatigue, and their evaluation of the task load in five minutes.
Figure 9. The results of ΔtotalHb during triple-digit addition and triple-digit multiplica-
tion tasks.
Figure 10. The experimental procedure to study the relationship between the task perfor-
mance decrement and the work time.
VOLUME 13, NUMBER 4, JULY 2007 631
Task Performance
The task assigned in this experiment was one-digit addition, which was programmed in com-
puters. The task performance for each subject was evaluated by his normalized performance to
precisely reflect the performance change of each subject. The normalized performance was cal-
culated from Equation 1.
Normalized performance (1)
where
xA,i = number of correct answers during the session i for subject A
= average number of correct answers of the subject A among all sessions
sA= standard deviation for the number of correct answers of the subject A among all sessions
Figure 11 shows the result of normalized performance. The performance in the first session
was compared with the sessions after that using one-way ANOVA and then Fisher’s protected
LSD when a statistically significant result was found. The level of significance was set at
p < 0.05. The normalized performance did not change significantly at 25.0°C with 1.0 clo over
time. However, the performance was significantly lower after the sixth session (each p < 0.05) at
28.0°C with 1.0 clo. Also, the performance was significantly lower after the third session (each
p < 0.05) at 28.0°C with 0.7 clo.
DISCUSSION
Seppänen et al. (2003) reported that 1.0°C of room air temperature rise is equivalent to a
decline of 2% in working performance. Recently, Kobayashi et al. (2005) reported one year of
observation in a call center. The relationship between indoor air temperature and the average
call response rate was analyzed. An increase in indoor air temperature of 1.0°C decreased the
average call response rate by 0.16 calls/h. When indoor air temperature was 25.0°C, the average
call response rate was 7.75 calls/h. When air temperature goes up to 26.0°C, the average call
response rate falls to 7.59 calls/h, and the decline in the workers’ performance is calculated as
2.1% per 1°C. The result of this research agreed quite well with the model of Seppänen.
Figure 11. The result of normalized performance.
SA,i
xA,ixA
–
sA
-------------------- 10×50+=
xA
632 HVAC&R RESEARCH
Even if task performance is maintained in a hot and dissatisfying environment, the work-
ers’ fatigue and level of mental effort will increase depending on the level of performance
decrement. That might be the reason why short-time exposure subjects could maintain per-
formance. On the other hand, for long exposure, indoor air temperature has effect on work-
ers’ performance.
CONCLUSIONS
1. In this study, the current status of Japanese office buildings is taken as an example and the
balance of environmental concerns and office productivity is discussed. To promote the effort
for energy conservation, it is important to estimate indoor environmental quality from the
aspect of an office worker’s productivity.
2. Subjective experiments were conducted to evaluate the effect of a moderately hot environ-
ment on productivity. The effects of the thermal environment on task performance for a short
exposure were contradictory among task types as in previous findings. It is difficult to evaluate
the effect of thermal environment on productivity by measuring only task performance.
According to the evaluation of subjective symptoms of fatigue, the subjects complained of
mental fatigue more at an operative temperature of 33.0°C than at 25.5°C and 28.0°C.
3. By monitoring cerebral blood oxygenation, an increment in oxygenated hemoglobin, an
increment in total hemoglobin, and a decrement in deoxygenated hemoglobin were found at
operative temperature of 33.5°C. In the previous study, it was reported that these findings
were the typical ones during brain activation.
4. The relationship between changes in cerebral blood oxygenation and the level of difficulty of
a task was evaluated in subjective experiments. Monitoring cerebral blood oxygenation
changes could be applied to the evaluation of the input-side parameter of productivity to indi-
cate the degree of mental effort required to perform the task.
5. A subjective experiment was conducted to study the effect of a moderately hot environment
on cerebral blood flow. Twelve right-handed male subjects were exposed in a climate cham-
ber to two operative temperature levels of 26.0°C and 33.5°C. Hot environments may require
more cerebral blood flow to maintain the same level of task performance.
6. During long exposure, indoor air temperature has effect on workers’ performance.
ACKNOWLEDGMENTS
This study was partially funded by the Grant-in-Aid for Scientific Research (A) of the JSPS
(No. 14205085). The authors thank Yuko Yamamoto, Koji Tanaka, Masaya Nishikawa, Yuko
Hagiwara, Mayumi Hayakawa, Asako Tanaka, Eisuke Togashi, Satoshi Hyodo, Akihiro Kawa-
mura, Tomofumi Kumata, and Masanori Ueki for their assistance.
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