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Showering Thermal Sensation in Residential Bathrooms

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Authors:
L. T. Wong at The Hong Kong Polytechnic University
L. T. Wong
K.W. Mui at The Hong Kong Polytechnic University
K.W. Mui
Yiu-Wing Chan
Yiu-Wing Chan
Yiu-Wing Chan
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Abstract

The thermal energy consumed by showering to the satisfaction of the showering subject, is largely dependent on the water temperature, shower duration, water flow rate, and bathroom air temperature. A research gap, between human thermal preferences and the smart use of thermal energy in high-rise urban residential bathroom environments, has been identified. This study examines the influence of a bathroom’s thermal environment on the showering subject’s thermal sensation. Of the 98 invited respondents, a total of 31 volunteers (12 females and 19 males) participated in the showering experiments, under three thermal conditions (control, colder, and warmer); their subjective thermal responses, including thermal sensation, thermal comfort, and thermal acceptability votes, were recorded. The results showed a non-linear trend of thermal sensation vote (TSV) against the bathroom air temperature. The predicted dissatisfied (PD) was asymmetrical, and the showering subjects preferred a slightly warm environment. Although the female TSV values were more sensitive than the male ones, in both the colder and warmer experiments, there were no significant gender differences. The findings of this study—including the expressions derived from the shower-water and bathroom air temperatures for the thermal comfort zone in a bathroom environment—can be used as a reference to enhance our understanding of thermal energy consumption in environmental design, and to help optimize the thermal environment in bathrooms.
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Content may be subject to copyright.
Citation: Wong, L.-T.; Mui, K.-W.;
Chan, Y.-W. Showering Thermal
Sensation in Residential Bathrooms.
Water 2022,14, 2940. https://
doi.org/10.3390/w14192940
Academic Editor: Akintunde
O. Babatunde
Received: 1 August 2022
Accepted: 16 September 2022
Published: 20 September 2022
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water
Article
Showering Thermal Sensation in Residential Bathrooms
Ling-Tim Wong , Kwok-Wai Mui * and Yiu-Wing Chan
Department of Building Environment and Energy Engineering, Research Institute for Smart Energy, The Hong
Kong Polytechnic University, Hong Kong, China
*Correspondence: horace.mui@polyu.edu.hk; Tel.: +852-2766-7783
Abstract:
The thermal energy consumed by showering to the satisfaction of the showering subject, is
largely dependent on the water temperature, shower duration, water flow rate, and bathroom air
temperature. A research gap, between human thermal preferences and the smart use of thermal energy
in high-rise urban residential bathroom environments, has been identified. This study examines the
influence of a bathroom’s thermal environment on the showering subject’s thermal sensation. Of
the 98 invited respondents, a total of 31 volunteers (12 females and 19 males) participated in the
showering experiments, under three thermal conditions (control, colder, and warmer); their subjective
thermal responses, including thermal sensation, thermal comfort, and thermal acceptability votes,
were recorded. The results showed a non-linear trend of thermal sensation vote (TSV) against the
bathroom air temperature. The predicted dissatisfied (PD) was asymmetrical, and the showering
subjects preferred a slightly warm environment. Although the female TSV values were more sensitive
than the male ones, in both the colder and warmer experiments, there were no significant gender
differences. The findings of this study—including the expressions derived from the shower-water
and bathroom air temperatures for the thermal comfort zone in a bathroom environment—can be
used as a reference to enhance our understanding of thermal energy consumption in environmental
design, and to help optimize the thermal environment in bathrooms.
Keywords: thermal sensation; thermal environment; showering; residential bathroom; hot water
1. Introduction
The concept of optimizing domestic hot water usage is often overlooked, especially
in subtropical cities, where winters are relatively short, and ambient temperatures are
generally higher [
1
,
2
]. Statistics of residential energy consumption show that 20% of the
end-use energy is for water-heating, especially for personal hygiene, such as bathing and
showering. It is known that the amount of thermal energy consumed by showering—the
most common form of bathing—is related to water temperature, shower duration, water
flow rate, and bathroom temperature [3].
A study found that the preferred shower-water temperature, which is affected by
seasonal climate change, is inversely proportional to the bathroom air temperature [
4
].
A hot shower is usually taken not only for maintaining body temperature but also for
achieving thermal comfort. Thermal sensation and comfort estimates for humans under
showers have been investigated under warmer environmental conditions. The experimental
results revealed that, in the same thermal environment, many subjects feel colder and more
uncomfortable in a shower than in a whole-body bath [
5
]. In other words, extra heat-energy
is required for meeting the thermal comfort demand resulting from a shower. A study
found that if both the bathroom air and bathwater temperatures required for a neutral
thermal preference are reached, then further air and water temperature adjustments in the
bathroom are not necessary [6].
Studies have also demonstrated that the range of desirable shower-water temperatures
is 36–41
◦
C [
3
,
7
]. A study by Masuda et al. [
8
] reported that when the skin temperature was
about 40
◦
C, different subjects had similar thermal perceptions at bathroom temperatures
Water 2022,14, 2940. https://doi.org/10.3390/w14192940 https://www.mdpi.com/journal/water
Water 2022,14, 2940 2 of 9
15
◦
C and 25
◦
C. However, the skin temperature measurements before and after bathing in a
bathroom controlled at 15
◦
C were significantly lower than those in a bathroom controlled at
25
◦
C. Moreover, a study by Herrmann et al. [
9
], that used lower shower-water temperatures
(32–39
◦
C), recorded a thermal neutral level at a higher bathroom air temperature of 28
◦
C.
In fact, research efforts have focused on the thermophysiological responses to shower-
water temperatures (e.g., 40–42
◦
C), rather than neutral air temperatures (
≤
25
◦
C) [
5
,
10
,
11
].
Although the air temperature in a bathroom affects both energy and human health [
12
],
the thermal responses of showering subjects at different air temperatures were not studied
in detail.
There is a gap in our knowledge of human thermal preferences and the smart use of
thermal energy in high-rise urban residential bathroom environments. To meet sustain-
ability challenges in cities dominated by high-rise housing developments, the modelling
of factors affecting the use of energy in buildings must be based on thermal sensation
studies reflecting realistic bathroom conditions. The objective of this study was to examine
the influence of a bathroom’s thermal environment on the showering subject’s thermal
sensations. This study generated new data on the thermal response of showering subjects,
based on measurements and experimental data available from open literature. The survey
subjects and the experimental procedure are described in Section 2. The measurement
results are presented in Section 3, with the thermal responses of the showering subjects
estimated at a range of air and water temperatures. Concluding remarks are presented in
Section 4.
2. Materials and Methods
To generate new data on the thermal response of showering subjects at a new air-
temperature range, this study recruited volunteers for the experiment, using a protocol
described in this section.
2.1. Subjects of Investigation
A pre-screening interview survey was conducted, to collate details of showering habits.
Shower-water temperature, time spent in the shower, and time spent on other activities
in the bathroom were recorded for a year. A sample of the survey questions is shown in
Appendix A. Invitations were sent via online platforms, and 98 participants completed
the survey. The showering habits of these participants covered all the possible options;
therefore, they can be seen as representative samples. Among those participants, 12 females
and 19 males (corresponding to an acceptance rate of 32%) took part in the subsequent
showering experiments, and their details are summarized in Table 1. The average heights
and weights were 1.56 m and 54.6 kg for the females (body mass index (BMI) = 22.6) and
1.74 m and 66.8 kg for the males (BMI = 22.2), respectively. The showering experiments
included three different experiments (control, colder, and warmer) arranged on different
days in different bathroom air temperatures. None of the showering subjects were told
about the experimental conditions, to minimize participant bias. Ethical approval was
obtained for the study protocols from the Human Subjects Ethics Sub-Committee of the
Hong Kong Polytechnic University (Reference Number HSEAR20201015003).
Table 1. Subject information.
Gender Count Height (m) Weight (kg) BMI Age
Female 12 1.47–1.62 43–64 19.3–27.3 24–45
Male 19 1.65–1.84 52–86 17.2–26.6 24–55
2.2. Conditions and Procedures
The size of the bathroom used in the experiments was 2.1 m
×
1.5 m—the typical size
of a local residential bathroom in high-rise buildings. It comprised two areas (sitting and
showering) separated by a showering curtain, as shown in Figure 1. Inside the bathroom,
Water 2022,14, 2940 3 of 9
there was an exhaust fan for ventilation, and a thermal ventilator for indoor temperature
and velocity controls.
Water 2022, 14, x FOR PEER REVIEW 3 of 9
2.2. Conditions and Procedures
The size of the bathroom used in the experiments was 2.1 m × 1.5 m—the typical size
of a local residential bathroom in high-rise buildings. It comprised two areas (sitting and
showering) separated by a showering curtain, as shown in Figure 1. Inside the bathroom,
there was an exhaust fan for ventilation, and a thermal ventilator for indoor temperature
and velocity controls.
Figure 1. The bathroom (2.1 m × 1.5 m).
The air temperature in the bathroom could be set to: the control condition (mean air
temperature ≈26 °C); the colder condition (mean air temperature ≈18 °C in the colder
months, from December to March); or the warmer condition (mean air temperature ≈30
°C in the warmer months, from March to September).
Figure 2 illustrates the 35 min experimental procedure, based on an experimental
protocol adopted in previous studies, that required the subject to sit for at least 15 min,
shower for at least 10 min, and spend at least 10 min on after-shower drying [11]. Upon
entering the sitting area of the bathroom, the showering subject was briefed on the exper-
iment details. Sitting in the bathroom for at least 20 min enabled the subject to reach a
thermally stable state, in which the thermal sensation vote was estimated to be 0, −3, and
1 for the control, colder, and warmer conditions, respectively, based on the environmental
conditions, and on the metabolic rate of 1.1 Met and clothing value of 0.6 clo [13].
Figure 2. Experimental procedure.
The physical environmental parameters (air temperature Ta in °C; black globe temper-
ature Tg in °C; relative humidity RH in %; and air velocity Va in ms−1) and shower-water
temperature Tc (°C) at the showerhead outlet were recorded continuously throughout the
experimental procedure. The shower-water temperature, measured at the showerhead out-
let, was set according to the choice of the showering subject. The outdoor air temperature
was also measured. The indoor mean radiant temperature Tr (°C) was determined by [14]:
𝑇𝑟= 𝑇𝑔+ 2.35√𝑉𝑎(𝑇𝑔−𝑇𝑎)
(1)
The thermal sensation of the showering subject was recorded after each showering
session, using a 7-point semantic differential scale for thermal comfort [13], i.e., Cold (−3),
Figure 1. The bathroom (2.1 m ×1.5 m).
The air temperature in the bathroom could be set to: the control condition (mean air
temperature
≈
26
◦
C); the colder condition (mean air temperature
≈
18
◦
C in the colder
months, from December to March); or the warmer condition (mean air temperature
≈
30
◦
C
in the warmer months, from March to September).
Figure 2illustrates the 35 min experimental procedure, based on an experimental pro-
tocol adopted in previous studies, that required the subject to sit for at least 15 min, shower
for at least 10 min, and spend at least 10 min on after-shower drying [
11
]. Upon entering the
sitting area of the bathroom, the showering subject was briefed on the experiment details.
Sitting in the bathroom for at least 20 min enabled the subject to reach a thermally stable
state, in which the thermal sensation vote was estimated to be 0,
−
3, and 1 for the control,
colder, and warmer conditions, respectively, based on the environmental conditions, and
on the metabolic rate of 1.1 Met and clothing value of 0.6 clo [13].
Water 2022, 14, x FOR PEER REVIEW 3 of 9
2.2. Conditions and Procedures
The size of the bathroom used in the experiments was 2.1 m × 1.5 m—the typical size
of a local residential bathroom in high-rise buildings. It comprised two areas (sitting and
showering) separated by a showering curtain, as shown in Figure 1. Inside the bathroom,
there was an exhaust fan for ventilation, and a thermal ventilator for indoor temperature
and velocity controls.
Figure 1. The bathroom (2.1 m × 1.5 m).
The air temperature in the bathroom could be set to: the control condition (mean air
temperature ≈26 °C); the colder condition (mean air temperature ≈18 °C in the colder
months, from December to March); or the warmer condition (mean air temperature ≈30
°C in the warmer months, from March to September).
Figure 2 illustrates the 35 min experimental procedure, based on an experimental
protocol adopted in previous studies, that required the subject to sit for at least 15 min,
shower for at least 10 min, and spend at least 10 min on after-shower drying [11]. Upon
entering the sitting area of the bathroom, the showering subject was briefed on the exper-
iment details. Sitting in the bathroom for at least 20 min enabled the subject to reach a
thermally stable state, in which the thermal sensation vote was estimated to be 0, −3, and
1 for the control, colder, and warmer conditions, respectively, based on the environmental
conditions, and on the metabolic rate of 1.1 Met and clothing value of 0.6 clo [13].
Figure 2. Experimental procedure.
The physical environmental parameters (air temperature Ta in °C; black globe temper-
ature Tg in °C; relative humidity RH in %; and air velocity Va in ms−1) and shower-water
temperature Tc (°C) at the showerhead outlet were recorded continuously throughout the
experimental procedure. The shower-water temperature, measured at the showerhead out-
let, was set according to the choice of the showering subject. The outdoor air temperature
was also measured. The indoor mean radiant temperature Tr (°C) was determined by [14]:
𝑇𝑟= 𝑇𝑔+ 2.35√𝑉𝑎(𝑇𝑔−𝑇𝑎)
(1)
The thermal sensation of the showering subject was recorded after each showering
session, using a 7-point semantic differential scale for thermal comfort [13], i.e., Cold (−3),
Figure 2. Experimental procedure.
The physical environmental parameters (air temperature T
a
in
◦
C; black globe temper-
ature T
g
in
◦
C; relative humidity RH in %; and air velocity V
a
in ms
−1
) and shower-water
temperature T
c
(
◦
C) at the showerhead outlet were recorded continuously throughout the
experimental procedure. The shower-water temperature, measured at the showerhead out-
let, was set according to the choice of the showering subject. The outdoor air temperature
was also measured. The indoor mean radiant temperature T
r
(
◦
C) was determined by [
14
]:
Tr=Tg+2.35√VaTg−Ta(1)
The thermal sensation of the showering subject was recorded after each showering
session, using a 7-point semantic differential scale for thermal comfort [
13
], i.e., Cold (
−
3),
Cool (
−
2), Slightly Cool (
−
1), Neutral (0), Slightly Warm (+1), Warm (+2), and Hot (+3).
In addition, the showering subject was required to describe the feeling of comfort (Com-
fortable/Slightly Uncomfortable/Uncomfortable/Very Uncomfortable) and the overall
thermal acceptability (Acceptable/Unacceptable).
Water 2022,14, 2940 4 of 9
3. Results and Discussion
3.1. Pre-Screening Interview
A total of 98 participants (55 females and 43 males) completed the pre-screening
interview survey. Table 2summarizes the survey results. The total time spent in the
bathroom (21.6–27.4 min) was similar to the design experiment time of 25 min. The average
time spent in the bathroom before showering (including using the toilet, washing up,
brushing teeth, etc.) was 8.9 min (SD = 5.2); this was comparable to the pre-showering time
of 7–10 min adopted by a previous study [
5
]. While the female participants spent a longer
time on the pre-showering activities than the male participants (M= 9.3 min, SD = 5.6 vs.
M= 8.3 min, SD = 4.6), there was no significant difference relating to gender (p= 0.34,
t-test).
Table 2. Screening interview aspects and responses.
Gender 55 Females 43 Males
Time spent in the bathroom before taking
a shower (including using the toilet,
washing up, brushing teeth, etc.)
9.3 min (SD = 5.6) 8.3 min (SD = 4.6)
Time spent in the shower 14.4 min (SD = 6.4), Summer
18.1 min (SD = 6.9), Winter
13.3 min (SD = 7.1), Summer
16.3 min (SD = 7.1), Winter
Time spent in the bathroom 23.7 min (SD = 9.7), Summer
27.4 min (SD = 10), Winter
21.6 min (SD = 9.7), Summer
24.7 min (SD = 9.4), Winter
Prefer a higher shower-water
temperature in winter than in summer
Yes = 44
No = 4
Maybe = 7
Yes = 31
No = 4
Maybe = 8
Prefer a lower shower-water temperature
in summer than in winter
Yes = 27
No = 14
Maybe = 14
Yes = 29
No = 6
Maybe = 8
The average times spent in the shower were 13.9 min (SD = 6.7) in summer and
17.3 min (SD = 7.0) in winter. A previous field measurement study reported that, with an
outdoor temperature drop of 6
◦
C, the shower duration was 10% [
15
]. In this study, there
was no significant difference in the showering time relating to gender, either in summer
(p= 0.42, t-test) or in winter (p= 0.23, t-test).
Although 75 participants preferred a higher shower-water temperature in winter than
in summer, 8 participants expressed otherwise. Furthermore, 56 participants preferred
a lower shower-water temperature in summer than in winter, while 20 participants did
not. The results indicated that the preferred shower-water temperature could be seasonally
influenced. However, in a previous field measurement study, no significant difference in
the preferred shower-water temperature had been found, with an outdoor temperature
drop of 7 ◦C [15].
3.2. Thermal Responses
Table 3summarizes the experimental results of the control, colder, and warmer case
averages, with standard deviation given in brackets. Determined by the following expres-
sion, where V
a
(ms
−1
) is the average air velocity, T
a
(
◦
C) is the indoor air temperature and
Tr
(
◦
C) is the indoor mean radiant temperature, the operative temperature T
op
(
◦
C) in the
bathroom was [14]:
Top =Tr+Ta√10Va
1+√10Va
(2)
Water 2022,14, 2940 5 of 9
Table 3. Results.
Parameter Control Colder Warmer
Outdoor daily mean temperature Tod (◦C) 17.4 (0.7) 17.7 (0.7) 30.7 (1.4)
Indoor air temperature Ta(◦C) 25.8 (0.3) 17.7 (0.7) 29.8 (0.2)
Indoor mean radiant temperature Tr(◦C) 25.4 (0.2) 17.3 (0.6) 29.4 (0.2)
Average air velocity Va(ms−1)0.57 (0.02) 0.55 (0.05) 0.57 (0.02)
Operative temperature Top (◦C)
Overall
Female
Male
25.7 (0.3)
25.6 (0.2)
25.7 (0.3)
17.6 (0.6)
17.6 (0.7)
17.6 (0.7)
29.7 (0.2)
29.7 (0.2)
29.7 (0.2)
Relative humidity RH (%) 80 (4) 81 (3) 80 (2)
Shower-water temperature Tw(◦C)
Overall
Female
Male
38.8 (0.7)
39.2 (0.6)
38.6 (0.7)
38.8 (0.7)
39.2 (0.6)
38.6 (0.7)
38.8 (0.7)
39.2 (0.6)
38.6 (0.7)
Thermal sensation vote TSV
Overall
Female
Male
0 (0)
0 (0)
0 (0)
−0.71 (0.64)
−0.90 (0.67)
−0.60 (0.61)
0.68 (0.65)
0.80 (0.62)
0.60 (0.68)
Thermally comfortable
Slightly thermal uncomfortable
Female
Male
Female
Male
12
19
0
0
5
17
7
2
7
16
5
3
Thermally acceptable
Thermally unacceptable
Female
Male
Female
Male
12
19
0
0
10
19
2
0
11
19
1
0
Note: Standard deviation in brackets.
In the experiments, the T
op
and relative humidity (RH) values were maintained be-
tween 25.2–26.1
◦
C and 75–85% for the control cases, 16.7–18.8
◦
C and 76–85% for the
colder cases, and 29.4–30.0
◦
C and 78–83% for the warmer cases. The findings revealed
that females preferred a higher shower-water temperature (39.2
◦
C, SD = 0.6) than males
(38.6
◦
C, SD = 0.7) (p= 0.016, t-test). In the control cases, the most preferred shower-water
temperature—a temperature at which all showering subjects felt thermally neutral (i.e.,
thermal sensation vote TSV = 0), comfortable, and acceptable—was 38.8
◦
C (SD = 0.7). It
was also employed in the subsequent colder and warmer experiments.
All subjects in the control cases expressed that the thermal environment was neutral,
comfortable, and acceptable. In the colder cases, however, 9 (out of 12) females and 10 (out
of 19) males felt slightly cool or cool. Among those female subjects, 7 stated they were
slightly uncomfortable, while 2 expressed that the thermal environment was unacceptable.
Among those male subjects, only 2 felt cool, yet they accepted the thermal environment.
In the warmer cases, 8 (out of 12) female subjects felt slightly warm or warm. While 5 of
them were slightly uncomfortable, only 1 of them expressed that the thermal environment
was unacceptable. Although 3 (out of 19) male subjects felt slightly uncomfortable in the
warmer environment, no male subjects found the thermal environment unacceptable.
As exhibited in Table 3, even though the female TSV values in both the colder and
warmer experiments (TSV =
−
0.90, SD = 0.67, and TSV = 0.80, SD = 0.62, respectively)
were more sensitive than the male ones (TSV =
−
0.60, SD = 0.61, and TSV = 0.60, SD = 0.62,
respectively), there were no significant gender differences (p= 0.21, t-test).
According to Figure 3,TSV was more sensitive in a warm environment than in a
cold one. Figure 3a shows a non-linear trend of TSV against the air temperature. An
average TSV drop of
−
0.71 was recorded for an average air temperature drop of 8.1
◦
C
from a neutral air temperature T
a
= 25.8
◦
C, with an average shower-water temperature
T
w
= 38.8
◦
C, corresponding to a TSV gradient of
−
0.088
◦
C
−1
. An average increment of
Water 2022,14, 2940 6 of 9
TSV = +0.68 was recorded for an increment of 4
◦
C for both T
a
and T
op
, corresponding to a
TSV gradient of +0.17 ◦C−1.
Water 2022, 14, x FOR PEER REVIEW 6 of 9
thermal sensation vote TSV = 0), comfortable, and acceptable—was 38.8 °C (SD = 0.7). It
was also employed in the subsequent colder and warmer experiments.
All subjects in the control cases expressed that the thermal environment was neutral,
comfortable, and acceptable. In the colder cases, however, 9 (out of 12) females and 10 (out
of 19) males felt slightly cool or cool. Among those female subjects, 7 stated they were
slightly uncomfortable, while 2 expressed that the thermal environment was unaccepta-
ble. Among those male subjects, only 2 felt cool, yet they accepted the thermal environ-
ment.
In the warmer cases, 8 (out of 12) female subjects felt slightly warm or warm. While
5 of them were slightly uncomfortable, only 1 of them expressed that the thermal environ-
ment was unacceptable. Although 3 (out of 19) male subjects felt slightly uncomfortable
in the warmer environment, no male subjects found the thermal environment unaccepta-
ble.
As exhibited in Table 3, even though the female TSV values in both the colder and
warmer experiments (TSV = −0.90, SD = 0.67, and TSV = 0.80, SD = 0.62, respectively) were
more sensitive than the male ones (TSV = −0.60, SD = 0.61, and TSV = 0.60, SD = 0.62, re-
spectively), there were no significant gender differences (p = 0.21, t-test).
According to Figure 3, TSV was more sensitive in a warm environment than in a cold
one. Figure 3a shows a non-linear trend of TSV against the air temperature. An average
TSV drop of −0.71 was recorded for an average air temperature drop of 8.1 °C from a
neutral air temperature Ta = 25.8 °C, with an average shower-water temperature Tw = 38.8
°C , corresponding to a TSV gradient of −0.088 °C−1. An average increment of TSV = +0.68
was recorded for an increment of 4 °C for both Ta and Top, corresponding to a TSV gradient
of +0.17 °C−1.
Figure 3b illustrates the results from a previous experimental study by Herrmann et
al. [9] (Tw = 32.4, 33.9, 35.4, 36.9, 38.4 °C, and at Ta = 28 °C); the TSV gradient estimates were
−0.33 °C−1 for the colder test conditions and +0.73 °C−1 for the warmer test conditions [9].
Figure 3. Subjective thermal responses to the showering environment: (a) thermal sensation votes
of 12 females and 19 males at Tw = 38.8 °C (SD = 0.7 °C) and at Ta = 17.7, 25.8, 29.8 °C; (b) thermal
sensation votes of 30 subjects at Tw = 32.4, 33.9, 35.4, 36.9, 38.4 °C and at Ta = 28 °C; the values reported
by Herrmann et al. [9] are shown for comparison.
Figure 4 shows the fractional counts of the showering subjects, who felt slightly un-
comfortable with the thermal environment they were exposed to, against TSV. The results
gave a more sensitive TSV in a colder environment, i.e., 41% at TSV = −1 (slightly cool and
uncomfortable) vs. 38% at TSV = +1 (slightly warm and uncomfortable). Similarly, the
above-mentioned previous study reported a more sensitive TSV in a colder environment,
i.e., ~50% at TSV = −1 vs. 20% at TSV = +1 [9].
Figure 3.
Subjective thermal responses to the showering environment: (
a
) thermal sensation votes
of 12 females and 19 males at T
w
= 38.8
◦
C (SD = 0.7
◦
C) and at T
a
= 17.7, 25.8, 29.8
◦
C; (
b
) thermal
sensation votes of 30 subjects at T
w
= 32.4, 33.9, 35.4, 36.9, 38.4
◦
C and at T
a
= 28
◦
C; the values
reported by Herrmann et al. [9] are shown for comparison.
Figure 3b illustrates the results from a previous experimental study by Herrmann
et al. [
9
] (T
w
= 32.4, 33.9, 35.4, 36.9, 38.4
◦
C, and at T
a
= 28
◦
C); the TSV gradient esti-
mates were
−
0.33
◦
C
−1
for the colder test conditions and +0.73
◦
C
−1
for the warmer test
conditions [9].
Figure 4shows the fractional counts of the showering subjects, who felt slightly
uncomfortable with the thermal environment they were exposed to, against TSV. The
results gave a more sensitive TSV in a colder environment, i.e., 41% at TSV =
−
1 (slightly
cool and uncomfortable) vs. 38% at TSV = +1 (slightly warm and uncomfortable). Similarly,
the above-mentioned previous study reported a more sensitive TSV in a colder environment,
i.e., ~50% at TSV = −1 vs. 20% at TSV = +1 [9].
Water 2022, 14, x FOR PEER REVIEW 7 of 9
Figure 4. Fractional counts of thermal discomfort; the values reported by Herrmann et. al. [9] are
shown for comparison.
Figure 5 graphs the predicted dissatisfied (PD) as the fractional counts of the unac-
ceptable votes for the thermal conditions in the bathroom. An asymmetrical PD was rec-
orded, and there were more sensitive responses in a colder showering environment than
in a warmer one. Comparatively, the PD values on the warm side were lower than those
reported by Herrmann et al. [9]. Moreover, the PD in a residential environment is shown
in the figure for comparison [16]. For the positive TSV values, lower PD values were found
in this study, indicating a slightly warm environment was favored.
Figure 5. Predicted dissatisfied PD; the values reported by Herrmann et. al. [9] and by Lai et. al.
[16] are shown for comparison.
3.3. Thermal Comfort Zone
The TSV for a showering environment is given by the following expression, where Ta
(°C) and Tw (°C) are the air and shower-water temperatures, respectively, with Ta,o (°C)
and Tw,o (°C) representing their respective values in a state of thermal neutrality (i.e., TSV
= 0) [17]:
(3)
Determined experimentally in this study, ca and cw are the unit changes of TSV for the
air and shower-water temperatures, respectively:
Figure 4.
Fractional counts of thermal discomfort; the values reported by Herrmann et al. [
9
] are
shown for comparison.
Figure 5graphs the predicted dissatisfied (PD) as the fractional counts of the un-
acceptable votes for the thermal conditions in the bathroom. An asymmetrical PD was
recorded, and there were more sensitive responses in a colder showering environment than
in a warmer one. Comparatively, the PD values on the warm side were lower than those
reported by Herrmann et al. [
9
]. Moreover, the PD in a residential environment is shown in
Water 2022,14, 2940 7 of 9
the figure for comparison [
16
]. For the positive TSV values, lower PD values were found in
this study, indicating a slightly warm environment was favored.
Water 2022, 14, x FOR PEER REVIEW 7 of 9
Figure 4. Fractional counts of thermal discomfort; the values reported by Herrmann et. al. [9] are
shown for comparison.
Figure 5 graphs the predicted dissatisfied (PD) as the fractional counts of the unac-
ceptable votes for the thermal conditions in the bathroom. An asymmetrical PD was rec-
orded, and there were more sensitive responses in a colder showering environment than
in a warmer one. Comparatively, the PD values on the warm side were lower than those
reported by Herrmann et al. [9]. Moreover, the PD in a residential environment is shown
in the figure for comparison [16]. For the positive TSV values, lower PD values were found
in this study, indicating a slightly warm environment was favored.
Figure 5. Predicted dissatisfied PD; the values reported by Herrmann et. al. [9] and by Lai et. al.
[16] are shown for comparison.
3.3. Thermal Comfort Zone
The TSV for a showering environment is given by the following expression, where Ta
(°C) and Tw (°C) are the air and shower-water temperatures, respectively, with Ta,o (°C)
and Tw,o (°C) representing their respective values in a state of thermal neutrality (i.e., TSV
= 0) [17]:
𝑇𝑆𝑉 = 𝑐𝑎(𝑇𝑎− 𝑇𝑎,𝑜) +𝑐𝑤(𝑇𝑤− 𝑇𝑤,𝑜)
(3)
Determined experimentally in this study, ca and cw are the unit changes of TSV for the
air and shower-water temperatures, respectively:
Figure 5.
Predicted dissatisfied PD; the values reported by Herrmann et al. [
9
] and by Lai et al. [
16
]
are shown for comparison.
3.3. Thermal Comfort Zone
The TSV for a showering environment is given by the following expression, where
T
a
(
◦
C) and T
w
(
◦
C) are the air and shower-water temperatures, respectively, with T
a,o
(
◦
C) and T
w,o
(
◦
C) representing their respective values in a state of thermal neutrality (i.e.,
TSV = 0) [17]:
TSV =ca(Ta−Ta,o)+cw(Tw−Tw,o)(3)
Determined experimentally in this study, c
a
and c
w
are the unit changes of TSV for the
air and shower-water temperatures, respectively:
ca=0.17 Ta>Ta,o
0.088 Ta<Ta,o,cw=0.73 Tw>Tw,o
0.33 Tw<Tw,o(4)
By applying T
a
= 25.8
◦
C and T
w
= 38.8
◦
C in a state of thermal neutrality to
Equations (3) and (4), two thermal comfort zones for PD = 0.05 (TSV =
−
0.62 and 0.82)
and PD = 0.10 (TSV =
−
0.91 and 1.11), as shown in Figure 6, were determined. The higher
thermal neutral temperature found in this study—as compared with the thermal neutral
temperature reported by Herrmann et al. [
9
] for French consumers—indicated that the
showering subjects in this study generally preferred a warm showering environment. This
is consistent with the findings of some previous local survey studies, in which all winter
showers and over 90% of summer showers were hot showers [3,4].
Water 2022,14, 2940 8 of 9
Water 2022, 14, x FOR PEER REVIEW 8 of 9
𝑐𝑎= { 0.17 𝑇𝑎> 𝑇𝑎,𝑜
0.088 𝑇𝑎< 𝑇𝑎,𝑜, 𝑐𝑤= {0.73 𝑇𝑤> 𝑇𝑤,𝑜
0.33 𝑇𝑤< 𝑇𝑤,𝑜
(4)
By applying Ta = 25.8 °C and Tw = 38.8 °C in a state of thermal neutrality to Equations
(3) and (4), two thermal comfort zones for PD = 0.05 (TSV = −0.62 and 0.82) and PD = 0.10
(TSV = −0.91 and 1.11), as shown in Figure 6, were determined. The higher thermal neutral
temperature found in this study—as compared with the thermal neutral temperature re-
ported by Herrmann et al. [9] for French consumers—indicated that the showering sub-
jects in this study generally preferred a warm showering environment. This is consistent
with the findings of some previous local survey studies, in which all winter showers and
over 90% of summer showers were hot showers [3,4].
Figure 6. Estimates of predicted dissatisfied PD = 0.05 and PD = 0.10 at thermal neutral Ta = 25.8 °C
and Tw = 38.8 °C; the value reported by Herrmann et. al. [9] is shown for comparison.
4. Conclusions
This study examined the influence of the thermal environment in a bathroom on the
thermal sensations of the showering subjects, who comprised 12 females and 19 males.
The showering subjects participated in the showering experiments under three thermal
conditions, i.e., the control, colder, and warmer experiments. The results showed a non-
linear trend of thermal sensation vote (TSV) against the bathroom air temperature. An
average TSV drop of −0.088 °C−1 was recorded for an average air temperature drop from
the neutral air temperature Ta = 25.8 °C, with an average shower-water temperature Tw =
38.8 °C. An average TSV increment of +0.17 °C−1 was recorded for an increment air tem-
perature. The predicted dissatisfied (PD) was asymmetrical, and the showering subjects
preferred a slightly warm environment. Two example thermal comfort zones at PD = 0.05
and 0.1 were estimated, using Equation (3) for the shower-water temperature of 34–42 °C,
and the air temperature of 18–34 °C. Despite the fact that the female TSV values were more
sensitive than the male ones, in both the colder and warmer experiments, there were no
significant gender differences. The expressions derived in this study for the thermal com-
fort zone in a bathroom environment can be used as a reference to enhance our under-
standing of showering subjects’ thermal sensation in environmental design, and to help
optimize the thermal environment in bathrooms.
Author Contributions: Conceptualization, L.-T.W.; Data curation, L.-T.W. and Y.-W.C.; Formal
analysis, L.-T.W.; Funding acquisition, L.-T.W. and K.-W.M.; Investigation, L.-T.W.; Methodology,
L.-T.W. and K.-W.M.; Project administration, K.-W.M.; Supervision, L.-T.W.; Writing—original
draft, L.-T.W., K.-W.M. and Y.-W.C.; Writing—review & editing, K.-W.M. All authors have read and
agreed to the published version of the manuscript.
Figure 6.
Estimates of predicted dissatisfied PD = 0.05 and PD = 0.10 at thermal neutral T
a
= 25.8
◦
C
and Tw= 38.8 ◦C; the value reported by Herrmann et al. [9] is shown for comparison.
4. Conclusions
This study examined the influence of the thermal environment in a bathroom on the
thermal sensations of the showering subjects, who comprised 12 females and 19 males.
The showering subjects participated in the showering experiments under three thermal
conditions, i.e., the control, colder, and warmer experiments. The results showed a non-
linear trend of thermal sensation vote (TSV) against the bathroom air temperature. An
average TSV drop of
−
0.088
◦
C
−1
was recorded for an average air temperature drop
from the neutral air temperature T
a
= 25.8
◦
C, with an average shower-water temperature
T
w
= 38.8
◦
C. An average TSV increment of +0.17
◦
C
−1
was recorded for an increment
air temperature. The predicted dissatisfied (PD) was asymmetrical, and the showering
subjects preferred a slightly warm environment. Two example thermal comfort zones at
PD = 0.05 and 0.1 were estimated, using Equation (3) for the shower-water temperature
of 34–42
◦
C, and the air temperature of 18–34
◦
C. Despite the fact that the female TSV
values were more sensitive than the male ones, in both the colder and warmer experiments,
there were no significant gender differences. The expressions derived in this study for the
thermal comfort zone in a bathroom environment can be used as a reference to enhance
our understanding of showering subjects’ thermal sensation in environmental design, and
to help optimize the thermal environment in bathrooms.
Author Contributions:
Conceptualization, L.-T.W.; Data curation, L.-T.W. and Y.-W.C.; Formal
analysis, L.-T.W.; Funding acquisition, L.-T.W. and K.-W.M.; Investigation, L.-T.W.; Methodology,
L.-T.W. and K.-W.M.; Project administration, K.-W.M.; Supervision, L.-T.W.; Writing—original draft,
L.-T.W., K.-W.M. and Y.-W.C.; Writing—review & editing, K.-W.M. All authors have read and agreed
to the published version of the manuscript.
Funding:
This research was funded by the Research Grants Council of the Hong Kong Special
Administrative Region, China (Project no. 15217221, PolyU P0037773/Q86B).
Institutional Review Board Statement:
Ethical approval was obtained for the study protocols from
the Human Subjects Ethics Sub-Committee of the Hong Kong Polytechnic University (Reference
Number HSEAR20201015003).
Informed Consent Statement:
Informed consent was obtained from all subjects involved in the study.
Data Availability Statement:
The data presented in this study are available on request from the
corresponding author.
Conflicts of Interest:
The authors declare that they have not known competing financial interests or
personal relationships that could have appeared to influence the work reported in this paper.
Water 2022,14, 2940 9 of 9
Appendix A. Sample Survey Questions
What is your gender? (Female/Male)
In the past 12 months, how long on average time you stay in the bathroom before
taking a shower? (In minutes)
In the past 12 months, how long on average time you spend for a summertime shower?
(In minutes)
In the past 12 months, how long on average time you spend for a wintertime shower?
(In minutes)
Do you prefer a higher showering water temperature in winter than in summer?
(Yes/No)
Do you prefer a lower showering water temperature in summer than in winter?
(Yes/No)
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... Previous surveys on showering behaviors in different seasons indicated that people prefer to shower longer and increase the water temperature in winter [42]. Radiators or other types of heaters were usually used in the bathroom in winter to keep a comfortable thermal showering environment. ...
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... These were according to the comfortable temperature range of showering water identified by Wong et al. [42]. Using these values, the occupant's thermal sensation vote (TSV) during showering can be calculated based on the following equation [42]: ...
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  • Apr 2013
  • ENERG BUILDINGS
Much of the energy utilised in domestic water heating is wasted to the drainage system by applications such showers, baths, dishwashers etc. The recovery of this waste heat from domestic waste water flows has been shown to be a viable method of improving the energy efficiency of buildings. However, many existing systems only operate satisfactorily when the heat exchanger is in a vertical orientation due to the nature of waste water flow within drain pipes. This orientation requirement presents a barrier to the full scale implementation of this technology as many dwellings may not have sufficient space to accommodate a vertical heat exchanger in their waste drainage system. This paper outlines the development and analysis of a horizontal drain water heat recovery system for domestic showers. The results of the investigation show that it is possible to recover energy from horizontal shower drains using a drain water heat recovery device at a satisfactory level of efficiency. The results also demonstrate that such a system may be economically viable depending on a number or external factors. The implementation of this technology on a national level was shown to have the potential to reduce energy usage and CO2 emissions significantly.
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Research on Hot Water Issues in Residential Buildings in Subtropical Taiwan
Article
  • May 2005
Countries in subtropical areas always overlook the issue of building hot water supply systems due to the short winter and high average temperature. However, the hot water supply system is still identified as requisite residential building equipment in subtropical countries such as Taiwan. Previous research with an overview of residential water usage revealed that building hot water consumes a great amount of energy and some critical problems are disregarded. This paper focuses on the residential building hot water supply system using Taiwan as a subtropical area example. Several significant hot water supply system features are presented with the quantitative parameters from Taiwan.
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An evaluation model for indoor environmental quality (IEQ) acceptance in residential buildings
Article
  • Sep 2009
  • ENERG BUILDINGS
The indoor environmental quality (IEQ) in residential buildings is examined from the prospect of an occupant's acceptance in four aspects: thermal comfort, indoor air quality, noise level and illumination level. Based on the evaluations by 125 occupants living in 32 typical residential apartments in Hong Kong, this study proposes empirical expressions to approximate the overall IEQ acceptance with respect to four contributors, namely operative temperature, carbon dioxide concentration, equivalent noise level and illumination level, via a multivariate logistic regression model. A range of IEQ acceptances for regular residential conditions is determined and the dependence of the predicted overall IEQ acceptance on the variations of the contributors is discussed. The proposed overall IEQ acceptance can be used as a quantitative assessment criterion for similar residential environments where an occupant's evaluation is expected.
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Water and Energy Interactions
Article
  • Nov 2011
Human habitations require energy and water, which are increasingly interdependent. Energy systems have changed from using water for mechanical energy to building dams to provide irrigation water for agriculture and hydroelectricity. Large volumes of water are required to cool thermal electricity-generating stations - whether coal, natural gas, nuclear, or solar powered. Changes in cooling technology are reducing water withdrawals while increasing water consumption. Water produced from fossil fuel production represents environmental challenges and supply opportunities. Some renewable energy sources, such as wind turbines and photovoltaics, have far lower water requirements. Increasing development of biofuels creates a direct connection between water and energy systems. Energy, mostly for pumps, is necessary for supplying potable water and treating wastewater. Pumping from deeper underground as well as removing more contaminants (e.g., medicines, agricultural chemicals) and salt requires more energy. Water and wastewater treatment can dominate electricity demand in municipalities. Water reuse requires energy for treatment and pumping. Life cycle assessments and integrated resource planning strive to account for the total impacts.
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