Effect of Direct Neck Cooling on Psychological and Physiological State

Abstract

Intelligent neck cooler has been proposed as an energy-saving indoor air-conditioning method by direct cooling of human body. This paper reports evaluation results of intelligent neck cooler’s effectiveness regarding labor productivity and comfort in hot summer office environment. We studied through trial subjects how neck cooling affects psychology and physiology in summer heat environment. Higher comfort level and cooler hyperthermic were reported in long lasting tasks when performing neck cooling were demonstrated. These were also confirmed by better physiological response concerning sweat amount and heart rate variability.

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2015 JSME-IIP/ASME-ISPS Joint Conference on Micromechatronics for Information and Precision Equipment (MIPE 2015)
June 14-17, 2015, Kobe International Conference Center, Kobe, Japan
ABSTRACT
Intelligent neck cooler has been proposed as an
energy-saving indoor air-conditioning method by direct
cooling of human body. This paper reports evaluation
results of intelligent neck cooler’s effectiveness regarding
labor productivity and comfort in hot summer office
environment. We studied through trial subjects how neck
cooling affects psychology and physiology in summer
heat environment. Higher comfort level and cooler
hyperthermic were reported in long lasting tasks when
performing neck cooling were demonstrated. These were
also confirmed by better physiological response
concerning sweat amount and heart rate variability.
1. INTRODUCTION
Today in Japan, comfortable lifestyle and environment
realized by abundant electric power is being questioned
by energy consumption reduction policies. This has been
accompanied by augmentation of heatstroke, hypothermia
risks, and deterioration of labor productivity. Intelligent
neck cooler is a Peltier element based device that directly
cools human body [1]. The Peltier element is placed in
the neck worn part of the device that also embed sensors
measuring surrounding temperature and humidity (see
Fig. 1). Temperature is autonomously regulated using
bi-linear equation of temperature and humidity (patented
algorithm).
Several researches reported that both local cooling and
warming affect physiological indices variations [2], [3].
Also, neck cooling causes variations in brain temperature
and brain blood flow [4], [5].
We have been investigating the effectiveness of direct
neck cooling in summer conditions office environment.
We studied through trial subjects how neck cooling
affects (1) subjective evaluation on comfortable and
hyperthermic feeling, and (2) physiology environment.
Fig. 1. 1st prototype of the intelligent neck cooler, and
its mechanism’s schematic.
2. EXPERIMENTAL CONDITIONS
The environment of a typical Japanese office space in
summer heat can be reproduced using an environment
control room, in which temperature and humidity can be
set and controlled in detail. Concretely, the environment
control room temperature and humidity were respectively
set at 32℃ and 60%. Subjects were eight men and eight
women from twenties to thirties. All subjects were
healthy, wearing underwear, a full-length pants, and a
short-sleeved shirt without neck-tie (standard “cool-biz”
dress code in Japan).
Subjects were sat in the room, performing an
experimental procedure of about two hours (see Fig. 2).
The procedure begins with a phase at rest of 30 minutes
accommodating to the room environment. Then they
performed successively three tasks of 15 to 20 minutes
that have been chosen to simulate conventional
deskwork: S-A creativity test, CPT X task, and n-Back
task. The procedure ends with a 10 minutes phase at rest
(cool-down). Each subject performed the experiment
once using the neck cooler, and another time in normal
condition (not using neck cooler).
EFFECT OF DIRECT NECK COOLING ON PSYCHOLOGICAL AND
PHYSIOLOGICAL STATE
Guillaume LOPEZ*, Yuta SUZUKI*, Yasuhiro KAWAHARA**, Mikio Takahashi***, and
Hiroki Takahashi***
* College of Sciences and Engineering, Aoyama Gakuin University
5-10-1 Fuchinobe, Chuo-ku, Sagamihara-shi, Kanagawa, Japan
E-mail: {guillaume, ysuzuki}@wil-aoyama.jp
** Faculty of Liberal Arts, The Open University of Japan
Chiba, Japan
E-mail: kawahara@ouj.ac.jp
*** Takenaka Corporation, R&D Institute
Chiba, Japan
E-mail: {takahashi.mikio, takahashi.hiroki}@takenaka.co.jp
WeC-3-1

2015 JSME-IIP/ASME-ISPS Joint Conference on Micromechatronics for Information and Precision Equipment (MIPE 2015)
June 14-17, 2015, Kobe International Conference Center, Kobe, Japan
During the experiment, comfort/discomfort sensation,
thermic sensation, and sweat sensation were evaluated at
regular intervals using both self-assessment by a Visual
analog scale (VAS) and physiological information
measurement (sweat, heart rate variability). Thermic
sensation scale ranges from 0 for cold sensation to 10 for
hot sensation. In the same way, comfort/discomfort scale
ranges from 0 for discomfort to 10 for comfort (see Fig.
3). Thermic sensation and comfort/discomfort sensation
were self-assessed 30 minutes after entering the room and
after each task using VAS.
All results presented in sections 3 and 4, were validated
using Welch's t-test. It is a statistical hypothesis test used
to determine if two sets of unequal variance data sets are
significantly different from each other.
Fig. 2. Experimental procedures and schedule
Fig. 3. VAS used for evaluation of thermal sensation
and comfort/discomfort feeling
3. NECK COOLING EFFECT ON COMFORT
LEVEL AND HYPERTHERMNIC SENSATION
3.1 Evaluation of effect on comfort level
We compared the VAS self-assessment of the 16
subjects for comfort/discomfort sensation in both normal
and neck cooling conditions 30 minutes after entering the
environment control room. More than 80% of the
subjects self-assessed a higher comfort level in neck
cooling condition (see Fig. 4,5).
Fig. 4. Comparison of comfort/discomfort sensation in
a summer heat room after accommodation phase
Fig. 5. Comparison of comfort/discomfort sensation in
a summer heat room after S-A creativity test
Moreover, one-tailed t-test confirmed statistical
significance (P(T<t) = 0.001) of better comfort level in
neck cooling conditions. Statistical significance could
also be confirmed (P(T<t) = 0.029) for neck cooling
positive effect on comfort sensation when performing
deskwork task, such as S-A Creativity test.
3.2 Evaluation of effect on hyperthermic sensation
We compared the VAS self-assessment for thermic
sensation (cold/hot) of the 16 subjects in both normal and
neck cooling conditions. Figure 5 shows the thermic
sensation evaluated the S-A Creativity test.
Fig. 6. Comparison of thermic sensation in a summer
heat room after S-A creativity test
More than 85% of the subjects self-assessed a colder
sensation in neck cooling condition. Moreover, one-tailed
t-test confirmed statistical significance of lower thermic
sensation level in neck cooling condition, both after
accommodation phase (P(T<t) = 0.001) and after S-A
Creativity test (P(T<=t) = 0.053), confirming the positive
thermal effect of neck cooling in heat summer office
environment, whatever the activity is.
p
< 0.05
p < 0.05
p < 0.05

2015 JSME-IIP/ASME-ISPS Joint Conference on Micromechatronics for Information and Precision Equipment (MIPE 2015)
June 14-17, 2015, Kobe International Conference Center, Kobe, Japan
4. NECK COOLING EFFECT ON PHYSIOLOGY
4.1 Evaluation of sweat amount
Sweat amount were measured during the whole
experiment every 2 seconds by difference method using a
ventilated capsule-type sweat sensor (SNT-200, Rousette
Strategy Inc.). We compared the average sweat amount
during the whole experiment for 14 subjects
(measurement error occurred for 2 subjects) when neck
cooling was performed or not (See Table 1). Sweat
amount was slightly lower when neck cooling was
performed. One-tailed t-test confirmed statistical
significance (P(T<=t) = 0.06) of lower average sweat
amount in neck cooling condition.
4.2 Evaluation of heart rate variability
The evolution of heart rate variability as sympathetic
nervous system activity index, and comfort/discomfort by
VAS evaluation have been compared. Ratio of
consecutive heart rate intervals (RRI) that difference is
greater than 50 milliseconds (PNN50) was used as
sympathetic nervous system activity index. A high
PNN50 ratio represents a state when the activity of
parasympathetic nervous system is dominant compared to
sympathetic nervous system.
Average PNN50 ratio was calculated every 5 minutes
during the whole 2 hours experiment, such obtaining 24
samples. Each sample is the average PNN50 of all 16
subjects during the same 5 minutes period of the
experiment, such the analysis result is independent from
the subject. Figure 6 shows that when comfort level
assessment is high, PNN50 ratio is also high with an
acceptable correlation of 0.57. Figure 7 shows also that
PNN50 ratio is significantly higher when performing
neck cooling, such demonstrating a better comfort level
(P(T>t) = 0.01) .
Fig. 6. Relation between comfort level self-assessment
and PNN50
Fig. 7. Comparison of average PNN50 during the
experimental procedure with or with neck cooling
9. CONCLUSION
We evaluated through trial subjects’ experiments how
neck cooling affects psychology and physiology in
summer heat environment. More than 80% of 16 subjects
reported significantly better comfort level (0.05 level) in
neck cooling condition. Heart rate variability index
PNN50 reflected significantly higher values when
performing neck cooling, showing to be a promising
index for real-time assessment of hyperthermic comfort
level at rest or during deskwork tasks.
ACKNOWLEDGEMENT
This research was partly supported by Japan New
Energy and Industrial Technology Development
Organization (NEDO).
REFERENCES
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Table 1 Comparison of the effect of neck cooling on
sweat amount during the experiment
Average sweat
amount [g/m2/min]
Sweat amount
variance [g/m2/min]
Neck cooling 17.04 6.41
No Neck
cooling 18.02 2.01