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Experimental investigation about thermal effect of colour on thermal sensation and comfort
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Experimental investigation about thermal effect of colour on thermal sensation and comfort Haiying Wang , Guodan Liu , Songtao Hu , Chao Liu PII: DOI: Reference:
S0378-7788(18)30701-1 10.1016/j.enbuild.2018.06.008 ENB 8610
To appear in:
Energy & Buildings
Received date: Revised date: Accepted date:
2 March 2018 7 May 2018 7 June 2018
Please cite this article as: Haiying Wang , Guodan Liu , Songtao Hu , Chao Liu , Experimental investigation about thermal effect of colour on thermal sensation and comfort, Energy & Buildings (2018), doi: 10.1016/j.enbuild.2018.06.008
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Highlights
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The thermal effect of colour walls has been verified by experiments. Thermal sensation vote increases at warm colours and decreases at cool colours. Subjects’ heart rate increases as colours changing from cool to warm. Use of colours may improve thermal comfort and save energy in thermal environments.
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Experimental investigation about thermal effect of colour on thermal sensation and comfort
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Haiying Wanga,*, Guodan Liua, Songtao Hua，Chao Liua
a Department of Environment and Municipal Engineering, Qingdao University of Technology, Qingdao, China
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* Corresponding author
Abstract
This study aims to find the possible influence of colour on thermal sensation and comfort. Experiments have been carried out to explore the effect. Sixteen Chinese subjects
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participated the experiments, which contained three temperature levels and seven coloured wall conditions. Subjects’ thermal sensation vote (TSV), thermal comfort vote
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(TCV) and colour satisfactory vote (CSV) were collected and heart rate (HR) was tested. The results show that coloured walls do have impact on thermal sensation and comfort in
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different air temperature conditions. Subjects’ TSV is increased at warm colours and decreased at cool colours compared to neutral colours. And TCV is also affected by
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colours. Subjects feel that cool colours are more comfortable in warm environment, and warm colours are more comfortable in cold environment. The results of CSV show that
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cool colours become more satisfactory in warm environment, while warm colours are more popular in cool environment. The variation of HR is related to temperature and colours. HR increases as temperature increases. And HR in warm colours is a little higher than that in neutral and cool colours. For a certain temperature, with colours changing from cool to warm, there is linear correlation between TSV and HR. The changes of subjective voting and physiological parameters are consistent in supporting the thermal effect of colours. Considering this effect of colours, integrating warm or cool colours in indoor spaces can optimize thermal perception against occupants’ actual thermal
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condition, which has positive significance for energy saving in building environment.
Keywords colour; hue-heat hypothesis; thermal sensation; energy saving; thermal environment
1 Introduction
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Energy saving and energy efficiency is nowadays a widespread motivation for doing research because of the importance of environmental impacts, protection of energy resources and cost control in virtually every field, especially in buildings. The main function of buildings is to provide suitable and comfortable indoor environment that people can work or live in. The demand for energy consumption in conceiving indoor comfort
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around the world is known to increase continuously. Designing buildings which require less or zero energy to achieve thermal comfort of occupants is, therefore, more challenging today.
Despite new designing and technics in lowering building energy, thermal comfort is being
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studied with more extensive essence continuously [1-4]. Related studies lead to better understanding about providing thermal comfort under various conditions and potential
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energy savings [5, 6]. As stated by de Dear, human thermal perception are mainly the psychophysical dynamics of thermal alliesthesia, which proposes that the hedonic
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qualities of the thermal environment (qualities of pleasantness or unpleasantness, or 'the pleasure principle') are determined as much by the general thermal state of the subject as
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by the environment itself [7-9]. In a study done by Höppe, simply announcing that the temperature was higher than it really did, made the occupants to start feeling warmer [10].
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In a chamber experiment, Luo et al found that subjects with perceived control tended to report more positive comfort perception [11]. These findings indicate that psychological aspect plays a role in perception of thermal environment. Colours are related with psychological meanings, which evoke various emotional feelings such as excitement, energy, and calmness [12-14]. What is more interesting is the effect of colour on temperature perception, which has been known, for almost a century, as the hue-heat hypothesis [15, 16]. The hue-heat hypothesis is the idea of psychological
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distinction between “warm colours” and “cool colours”. It considers change in subjective feeling of temperature based on colour of objects [15, 16]. The hue-heat hypothesis states that light or colour with wavelengths predominantly toward the red end of the visual spectrum is perceived as warmer, while that with wavelengths mainly toward the blue end is perceived as cooler [17]. For example, blue and green colours are considered to be cool, while yellowish and reddish hues are seen as warm. So, will colours impact people’s
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thermal sensation? To date, a considerable amount of research in the fields of experimental psychology, applied psychology and psychological ergonomics has been done about the possible influence of colours or coloured surfaces on thermal sensation and thermal comfort.
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Based on experiments, Bennet concluded that hue produced a strictly intellectual effect, a belief that one was warmer or cooler but did not affect one’s thermal comfort [18]. Fanger and Breun found in l6 subjects that a slightly lower ambient temperature (0.4℃) was preferred in extreme red light compared to extreme blue light [19]. They concluded that
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this colour effect was too small to have any physiological or practical significant. Other studies in aircraft cabin found that indoor temperature was perceived as being different
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depending on the colour of the lighting. In yellow light, room temperature was felt to be warmer than in blue light [20, 21]. Study by Huebner et al found that participants put on
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significantly more items of clothing under cold light than warm light [22]. Itten and Clark found that comfort was significantly impacted by wall colour, with participants feeling
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colder in blue/blue-green rooms [23, 24]. In more recent studies, based on a series of empirical studies in Sri Lanka, Hettiarachchi etc. found that colour temperature preference
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is a psychological response [25]. In their field studies, it was revealed that incorporating red colour in interiors of cool tropical uplands induced a comparatively warmer thermal perception. And the reverse was true in hot, humid coastal areas where factory workers demanded greater ceiling fan speeds to achieve thermal comfort in red coloured interiors than in blue [26, 27]. However, others did not observe any reliable effect of colour of the environment on the judgment of room temperature or comfort [28, 29]. And survey by Baniya et al found no support for the hue-heat hypothesis and indicated that people felt
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thermally more comfortable in an indoor workplace at the correlated colour temperature of 4000 K [17]. To summarize, existing research is ambiguous regarding the association between coloured light/wall and thermal perception. In addition, the different ways of manipulating colour, response types and methodologies employed in previous studies complicate the comparability between studies and the ability to draw final conclusions [22].
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As stated by Albers et al and Hettiarachchi et al, even though the impact of colour on temperature and comfort sensation is minimal, when utilized in a large-scale could potentially contribute to a quantifiable impact on energy savings [21, 25]. Nowadays, the 0.4℃ difference found in Fanger’s study may also lead to measurable energy saving in
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developing building thermal environment. Driven by the greater possibility of colour on thermal sensation, this study carried out experiments on the effect of different colours on thermal sensation. 2 Methodology
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In this study, coloured walls were used to simulate different ambient hue conditions. Colour fabrics were hanged close to walls. Seven colours: red, yellow, green, blue, violet,
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black and white were tested, which are shown in Fig.1. Among these colours, red and yellow are warm colours, green and blue are cool colours, while white and black are
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usually taken as neutral colours. Though in some research, violet were taken as cool colour, it is regarded as a neutral colour in this study considering the psychological and
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emotional symbolism in Chinese culture (all participants were Chinese) [30].
Figure 1 Seven colours used in experiments 2.1 Participants
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Sixteen Chinese postgraduates (10 males and 6 females) from Qingdao University of Technology with normal colour vision volunteered for the experiments. The study was approved by the University Ethics Committee and all participants provided written informed consent prior to the study. Table 1 summarizes participants’ characteristics. Table 1 Participants’ characteristics (n=16) Mean (SD)
Range
Males
Age (years) Height (cm) Body mass (kg)
24.2±0.9 177.1±4.2 69.9±7.4
23-26 168-180 57-80
Female
Age (years) Height (cm) Body mass (kg)
23.9±0.8 165.2±4.6 53.2±4.5
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Gender
22-26 160-174 45-60
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Subjects were asked to avoid alcohol, smoking, and intense physical activity at least 12 h prior to each experimental session. All subjects were required to wear typical summer clothes of short-sleeved shirt, thin trousers, underwear, sandals (an estimated clothing insulation value of 0.60 Clo, including the insulation of wooden chair).
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2.2 Experimental Chamber
Testing was carried out in a climate chamber (4.5m long× 2.5m wide × 2.0m high) which is
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located in an enclosed room. Both the room and chamber are equipped with air conditioners with temperature control. The control precision of the chamber is ±0.5°C and
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±1°C for the room. The air change rate of chamber is about 5 times per hour. As there was no natural light in the chamber, LED lights (with colour temperature about
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4000K, a more comfortable colour temperature according to Baniya et al [17]) were used. Some lights were fixed on the roof along the walls. Others were hanged over the table and
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the illumination rate at the level of table was about 500lux. The illumination was kept unchanged during test. The layout of chamber is shown in Fig.2.
Figure 2 Layout of Chamber 2.3 Experimental set-up and equipment
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The experiments were carefully arranged to overcome the main issue of some previous studies of not controlling for (all) covariates that might impact on thermal comfort. Participants were divided into 4 groups. During each test, only one group was tested. Upon arrival, the participants entered the room (with white walls) and sat in the resting
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area for 20min. Then they came into the chamber. During test, they kept siting around a table (with light-yellowish-wood colour). The subjects were allowed to read books or talk
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with each other. Their conversation were restricted that they shouldn’t talk about any content related to private sensations. The estimated metabolic rate was about 1 to 1.2
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met.
The experiments were carried out in July 2017. There were three temperature conditions:
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23°C (cool environment), 26°C (close to neutral environment) and 29°C (warm environment). Temperatures of the room and the chamber were kept same during tests.
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Before test, seven coloured fabrics were hanged layer by layer with random sequence. In similar studies, colours were changed every ten minutes [17, 22, 31]. In this study, participants were also exposed to one coloured environment for 10min. Then they were asked to fill in questionnaires and their heart rate (HR) was tested (Omron, HEM-7320) considering the influence of colour on physiological parameter [31]. After that, surface fabrics were taken off by operate staff and participants would be exposed to the next colour. The whole process of each test lasted for about 2h with constant temperature. Fig.3 shows the schedule of each test.
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Figure 3 Schedule of test In a questionnaire, the subjects were asked for their thermal sensation, thermal comfort and colour satisfaction. Thermal sensation votes (TSV) are based on the ASHRAE/ISO seven-point thermal sensation scale, which is defined hot (+3), warm (+2), slightly warm (+1), neutral (0), slightly cool (-1), cool (-2) and cold (-3). For thermal comfort vote (TCV),
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there are fewer verbal explanations, namely very comfortable (0), just comfortable (1), just uncomfortable (2), and very uncomfortable (3). Like TCV, colour satisfaction vote (CSV) is based on four levels: very satisfied (0), just satisfied (1), just unsatisfied (2), and very unsatisfied (3). Before experiments, the participants were given a detailed explanation of
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the contents of the questionnaire and the voting so that they could fully understand. Air temperature, velocity and relative humidity were measured by multi-parameter
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ventilation meter (Model 8386, TSI Inco., Minnesota, USA). For temperature sensor, the testing range is -17.8-93.3°C and the accuracy is ±0.3°C; for relative humidity, the testing
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range is 0-95% and the accuracy is ±3%; for velocity, the testing range is 0～50 m/s and the accuracy is ±3.0% of reading or ± 0.015m/s, whichever is greater. Mean radiant
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temperature was tested by black-bulb thermometer (JTR04, JT Technology, Beijing, China). The testing range is 5-150°C and the accuracy is ±0.5°C.
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The statistics of tested environmental parameters are shown in Table 2. Table 2 Tested environmental parameters Experiment conditions
Tested environmental parameters Air temperature (°C)
23°C
26°C
29°C
22.9±0.3
26.3±0.2
29.1±0.4
Relative humidity (%)
50±3.9
52±4.6
58±3.5
Mean radiant temperature (°C)
23.1±0.3
26.4±0.3
29.3±0.5
Air velocity (m/s)
0.11±0.04
0.10±0.05
0.13±0.04
3 Results and discussions
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3.1 Thermal sensation vote The mean values of TSV in three temperature conditions are shown in Fig.4. TSV, undoubtedly, was affected by temperature. It increased significantly as temperature increased (P<0.001). And the influence of colour was also significant (P<0.05). Compared with TSV of neutral colours, TSV of cool colours became lower and TSV of warm colours were the highest in three temperature conditions. Maximum difference of TSV among
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colours were 0.92, 0.74 and 1.03, corresponding to 23°C, 26°C and 29°C.
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Figure 4 TSV for different colours
For neutral colours, the effect of black, white and violet on TSV were almost the same.
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The differences of TSV among the three colours in different temperatures were quite small. More specifically, TSV of white was a little bit higher than that of black and violet. The
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reason could be that white feels brighter than the other two and may give an impression of warmer. For cool colours of blue and green, TSV of blue were lower than that of green at
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23°C and 26°C, and were the same at 29°C. For warm colours of red and yellow, TSV of yellow were always a little higher than that of red. The results are consistent with the
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findings of Winzen et al, where they also found that yellow and blue hues seem to be more useful for increasing and decreasing temperature sensation respectively [20]. The average TSV for different kinds of colours were shown in Fig.5. According to the figure, with the increase of temperature, the difference of TSV between warm colour and neutral colour became bigger. The difference increased to 0.78 at 29°C. And the difference between cool colours and neutral colours tended to decrease. 29°C was a hot condition, in which the use of warm colours could intensify hot sensation, and the effect of
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cool colour on regulating TSV was to weaken.
Figure 5 Average values of TSV under cool, neutral and warm colours 3.2 Thermal comfort vote
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The mean TCV of subjects are shown in Fig.6. The votes were related with temperature and colours. As 26°C was a more suitable temperature compared to 23°C and 29°C, it had the lowest TCV, which means that the subjects felt more comfortable. The TCV in each temperature condition were also changing according to colours. In cool environment
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(23°C), TCV of cool colours were high, followed by neutral colours, the lowest were warm colours, and the opposite was the case in warm environment (29°C). The downward
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concave line showed the variation of TCV with colours and temperature. It indicated that subjects felt that cool colours were more comfortable in warm environment, and warm
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colours were more comfortable in cold environment.
Figure 6 Changes of TCV The changes of TSV with TCV were also analyzed as shown in Fig.7. The polynomial fit showed that the two variables were correlated significantly. When TSV is 0, TCV has the
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lowest value. When TSV increases or decreases further, TCV will increase, which means that subjects feels less comfortable. The results are consistent with the existing thermal comfort theory and findings [32, 33, 34], in which TSV has similar relations with TCV. This
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indicated that the subjective vote of the subjects in the experiments were reliable.
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Figure 7 Changes of TCV with TSV 3.3 Colour satisfaction vote
The statistics of CSV is shown in Fig.8. CSV for cool colours raised as temperature decreased. And for warm colours, the change of CSV were the opposite. The results of
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CSV showed that subjects’ felt cool colours more satisfactory in warm environment, while warm colours were more popular in cool environment. It was consistent with the previous
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analysis of TSV and TCV.
For neutral colours, the change of black were different from white and violet. CSV for
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black were almost the same in three temperature environments. Large areas of pure black are rarely applied in building interiors because the depressing sensation it brings. And this
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sensation would not be changed in different temperatures. Thus, it was understandable that the influence of black on CSV at different temperatures was almost constant. The
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changes of CSV of white and violet were similar to cool colours. Both white and violet can arouse emotions similar to cool colours, for example, calmness [12]. This might be the reason that white and purple become more satisfactory when the temperature was raised up. Besides, white had the lowest vote at 26°C and 29°C among all colours, which meant that white was the most preferred colour. Combined with the analysis of TSV and TCV, it was found that although cool colours could make people feel cooler and more comfortable in warm/ hot environment, the subjects in this study considered white to be more satisfactory. The reason might be that most of the indoor environments in which the
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Figure 8 Statistics of CSV
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subjects live and stay were painted in white and they had good adaptability to white.
For about half of conditions, CSV were in the range of 1 (just satisfied) to 2 (just
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unsatisfied), which implies that these colour environments were not quite satisfactory. The colours used in experiments have high colour saturation, except for white. Study of AL-Ayash et al found that vivid colours (with high colour saturation) were more arousing than pale colours (with lower colour saturation) [31]. And their participants felt more
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positive in the pale colour conditions compared to the vivid colour conditions, because pale colours were perceived to be pleasant, fresh, calm, relaxed, light, cool and less sharp.
used in experiments.
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3.4 Heart rate
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This may explain why subjects in this study were not very satisfy with the vivid colours
Fig.9 shows the changes of HR under different experimental conditions. And the average
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values are shown in Fig.10. From these two figures, the variation of HR was related to temperature (P<0.0005)) and colours (P<0.05).
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Mean HR increased with the increase of temperature. The effect of ambient temperature on blood pressure was in accordance with physiological rules [35, 36]. In normal temperature environment, when temperature increases the need to cool the body down will increase too. In higher temperatures, blood flow is directed closer to the surface of the skin so that blood can be cooled down. Therefore, human heart beats faster to accelerate blood circulation and regulate body temperature. When colour changed from cool colour to neutral colour and warm colour, HR also
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increased. According to studies by AL-Ayash et al, hue induces significant changes in HR [31]. They have found that red and yellow increases HR whereas blue decreases HR. This was same with what we found in this study. The results supported the notion that colour has impact on the physiology of people who stayed in the coloured room. In addition, several colour studies have indicated that long-wavelength colours such as red and yellow are more arousing than short-wavelength colours such as blue and green [37, 38]. In
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neutral colours, the corresponding HR of violet was lower, this may due to the short wavelength of voilet. This character of violet is similar to blue and green. In fact, in some
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studies violet was taken as cool colour [21].
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Figure 9 Changes of HR
Figure 10 Average HR for different colours
As both TSV and HR were affected by colours, so correlation between them was analyzed further. The correlations was indicated in Fig.11. At a certain temperature, with colours changing from cool to warm, there was a linear correlation between TSV and HR (with minimum P<0.006 for three linear relations). From physiological point, different colours interfere with psychology and emotion to a certain extent, resulting in corresponding
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changes in HR and TSV.
(The coloured dots corresponding to the colour conditions)
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Figure 11 HR and TSV
In the above analysis and discussion of experimental results, some explanations may be speculative. The effect of colour on emotion and psychology can be complicated. Besides the hue-heat response, there are other appearance attributes about colour, i.e. lightness
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(heavy/light), chroma (active/passive) and individual colour preference (like/dislike) [13,39]. The neutral colour of white and black may give different impression about
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lightness and chroma. These characters of colour haven’t been fully considered in the experiments. Therefore, the interpretation of some experimental results cannot go deeper.
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are certain.
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However, the effects of warm and cool colours on thermal sensation and thermal comfort
Usually, the perception of thermal environment is mainly through thermal regulation
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system of human body. People can also experience their surrounding through perception, cognition, and construct meaning through colour. There have been many studies on the application of interior decoration colours, but the main consideration focuses on space function, visual and psychological feeling, and the combination of thermal sensation is rare. Considering the hue-heat effect, the psychological and emotional changes brought by vision will have influence on the perception of thermal environment to some extent. The use of good colour design might contribute to a more positive mood, and thus make the thermal environment of building more comfort and pleasant with less energy consumption.
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4 Conclusions The main goal of the present research is to investigate the effects of different colours on people’s thermal sensation. The experimental results supports the hue-heat hypothesis. And colours do have impacts on thermal sensation in different temperature environments. Compared with neutral colours, warm colours intend to make people feel warmer, while cool colours have the opposite effect. Both subjective voting and physiological index of
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HR support the conclusion. Integrating warm or cool colours in cool or warm indoor spaces can psychologically induce an optimized thermal perception against the actual thermal condition in occupants, which has positive significance for energy saving of thermal environment.
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Inevitably, this study has some limitations. First, the number of participants was 16. The size of the sample is considered small. Besides, all subjects are Chinese in the age of twenties. According researches, emotional sensation of colour is affected by age and culture background [13, 39, 40]. Therefore, the results may not be applicable to people
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with different age and cultural background. Besides, colours with lower colour saturation should be studied further In order to facilitate practical application.
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Thus, further research is needed to investigate these points. In addition, the quantitative study of the effect of colour on thermal environment is necessary, so as to facilitate the
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combination of colour in thermal environment design.
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Acknowledgement
This study has been financially supported by the National Natural Science Foundation of
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China with contract number of 51678314 and 51778305, and by China Scholarship Council (201700810003). The authors would also want to thank those participants who volunteered for the experiments.
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[39] Gao X, Xin JH, Sato T et al. Analysis of cross-cultural color emotion. Color Res Appl
[40] Rikard Küller, Seifeddin Ballal, Thorbjörn Laike et al. The impact of light and colour on psychological mood: a cross-cultural study of indoor work environments. Ergonomics 2006; 49(14): 1496–1507
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Experimental investigation about thermal effect of colour on thermal sensation and comfort Haiying Wang , Guodan Liu , Songtao Hu , Chao Liu PII: DOI: Reference:
S0378-7788(18)30701-1 10.1016/j.enbuild.2018.06.008 ENB 8610
To appear in:
Energy & Buildings
Received date: Revised date: Accepted date:
2 March 2018 7 May 2018 7 June 2018
Please cite this article as: Haiying Wang , Guodan Liu , Songtao Hu , Chao Liu , Experimental investigation about thermal effect of colour on thermal sensation and comfort, Energy & Buildings (2018), doi: 10.1016/j.enbuild.2018.06.008
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Highlights
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The thermal effect of colour walls has been verified by experiments. Thermal sensation vote increases at warm colours and decreases at cool colours. Subjects’ heart rate increases as colours changing from cool to warm. Use of colours may improve thermal comfort and save energy in thermal environments.
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Experimental investigation about thermal effect of colour on thermal sensation and comfort
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Haiying Wanga,*, Guodan Liua, Songtao Hua，Chao Liua
a Department of Environment and Municipal Engineering, Qingdao University of Technology, Qingdao, China
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* Corresponding author
Abstract
This study aims to find the possible influence of colour on thermal sensation and comfort. Experiments have been carried out to explore the effect. Sixteen Chinese subjects
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participated the experiments, which contained three temperature levels and seven coloured wall conditions. Subjects’ thermal sensation vote (TSV), thermal comfort vote
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(TCV) and colour satisfactory vote (CSV) were collected and heart rate (HR) was tested. The results show that coloured walls do have impact on thermal sensation and comfort in
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different air temperature conditions. Subjects’ TSV is increased at warm colours and decreased at cool colours compared to neutral colours. And TCV is also affected by
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colours. Subjects feel that cool colours are more comfortable in warm environment, and warm colours are more comfortable in cold environment. The results of CSV show that
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cool colours become more satisfactory in warm environment, while warm colours are more popular in cool environment. The variation of HR is related to temperature and colours. HR increases as temperature increases. And HR in warm colours is a little higher than that in neutral and cool colours. For a certain temperature, with colours changing from cool to warm, there is linear correlation between TSV and HR. The changes of subjective voting and physiological parameters are consistent in supporting the thermal effect of colours. Considering this effect of colours, integrating warm or cool colours in indoor spaces can optimize thermal perception against occupants’ actual thermal
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condition, which has positive significance for energy saving in building environment.
Keywords colour; hue-heat hypothesis; thermal sensation; energy saving; thermal environment
1 Introduction
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Energy saving and energy efficiency is nowadays a widespread motivation for doing research because of the importance of environmental impacts, protection of energy resources and cost control in virtually every field, especially in buildings. The main function of buildings is to provide suitable and comfortable indoor environment that people can work or live in. The demand for energy consumption in conceiving indoor comfort
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around the world is known to increase continuously. Designing buildings which require less or zero energy to achieve thermal comfort of occupants is, therefore, more challenging today.
Despite new designing and technics in lowering building energy, thermal comfort is being
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studied with more extensive essence continuously [1-4]. Related studies lead to better understanding about providing thermal comfort under various conditions and potential
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energy savings [5, 6]. As stated by de Dear, human thermal perception are mainly the psychophysical dynamics of thermal alliesthesia, which proposes that the hedonic
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qualities of the thermal environment (qualities of pleasantness or unpleasantness, or 'the pleasure principle') are determined as much by the general thermal state of the subject as
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by the environment itself [7-9]. In a study done by Höppe, simply announcing that the temperature was higher than it really did, made the occupants to start feeling warmer [10].
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In a chamber experiment, Luo et al found that subjects with perceived control tended to report more positive comfort perception [11]. These findings indicate that psychological aspect plays a role in perception of thermal environment. Colours are related with psychological meanings, which evoke various emotional feelings such as excitement, energy, and calmness [12-14]. What is more interesting is the effect of colour on temperature perception, which has been known, for almost a century, as the hue-heat hypothesis [15, 16]. The hue-heat hypothesis is the idea of psychological
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distinction between “warm colours” and “cool colours”. It considers change in subjective feeling of temperature based on colour of objects [15, 16]. The hue-heat hypothesis states that light or colour with wavelengths predominantly toward the red end of the visual spectrum is perceived as warmer, while that with wavelengths mainly toward the blue end is perceived as cooler [17]. For example, blue and green colours are considered to be cool, while yellowish and reddish hues are seen as warm. So, will colours impact people’s
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thermal sensation? To date, a considerable amount of research in the fields of experimental psychology, applied psychology and psychological ergonomics has been done about the possible influence of colours or coloured surfaces on thermal sensation and thermal comfort.
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Based on experiments, Bennet concluded that hue produced a strictly intellectual effect, a belief that one was warmer or cooler but did not affect one’s thermal comfort [18]. Fanger and Breun found in l6 subjects that a slightly lower ambient temperature (0.4℃) was preferred in extreme red light compared to extreme blue light [19]. They concluded that
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this colour effect was too small to have any physiological or practical significant. Other studies in aircraft cabin found that indoor temperature was perceived as being different
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depending on the colour of the lighting. In yellow light, room temperature was felt to be warmer than in blue light [20, 21]. Study by Huebner et al found that participants put on
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significantly more items of clothing under cold light than warm light [22]. Itten and Clark found that comfort was significantly impacted by wall colour, with participants feeling
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colder in blue/blue-green rooms [23, 24]. In more recent studies, based on a series of empirical studies in Sri Lanka, Hettiarachchi etc. found that colour temperature preference
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is a psychological response [25]. In their field studies, it was revealed that incorporating red colour in interiors of cool tropical uplands induced a comparatively warmer thermal perception. And the reverse was true in hot, humid coastal areas where factory workers demanded greater ceiling fan speeds to achieve thermal comfort in red coloured interiors than in blue [26, 27]. However, others did not observe any reliable effect of colour of the environment on the judgment of room temperature or comfort [28, 29]. And survey by Baniya et al found no support for the hue-heat hypothesis and indicated that people felt
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thermally more comfortable in an indoor workplace at the correlated colour temperature of 4000 K [17]. To summarize, existing research is ambiguous regarding the association between coloured light/wall and thermal perception. In addition, the different ways of manipulating colour, response types and methodologies employed in previous studies complicate the comparability between studies and the ability to draw final conclusions [22].
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As stated by Albers et al and Hettiarachchi et al, even though the impact of colour on temperature and comfort sensation is minimal, when utilized in a large-scale could potentially contribute to a quantifiable impact on energy savings [21, 25]. Nowadays, the 0.4℃ difference found in Fanger’s study may also lead to measurable energy saving in
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developing building thermal environment. Driven by the greater possibility of colour on thermal sensation, this study carried out experiments on the effect of different colours on thermal sensation. 2 Methodology
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In this study, coloured walls were used to simulate different ambient hue conditions. Colour fabrics were hanged close to walls. Seven colours: red, yellow, green, blue, violet,
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black and white were tested, which are shown in Fig.1. Among these colours, red and yellow are warm colours, green and blue are cool colours, while white and black are
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usually taken as neutral colours. Though in some research, violet were taken as cool colour, it is regarded as a neutral colour in this study considering the psychological and
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emotional symbolism in Chinese culture (all participants were Chinese) [30].
Figure 1 Seven colours used in experiments 2.1 Participants
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Sixteen Chinese postgraduates (10 males and 6 females) from Qingdao University of Technology with normal colour vision volunteered for the experiments. The study was approved by the University Ethics Committee and all participants provided written informed consent prior to the study. Table 1 summarizes participants’ characteristics. Table 1 Participants’ characteristics (n=16) Mean (SD)
Range
Males
Age (years) Height (cm) Body mass (kg)
24.2±0.9 177.1±4.2 69.9±7.4
23-26 168-180 57-80
Female
Age (years) Height (cm) Body mass (kg)
23.9±0.8 165.2±4.6 53.2±4.5
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Gender
22-26 160-174 45-60
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Subjects were asked to avoid alcohol, smoking, and intense physical activity at least 12 h prior to each experimental session. All subjects were required to wear typical summer clothes of short-sleeved shirt, thin trousers, underwear, sandals (an estimated clothing insulation value of 0.60 Clo, including the insulation of wooden chair).
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2.2 Experimental Chamber
Testing was carried out in a climate chamber (4.5m long× 2.5m wide × 2.0m high) which is
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located in an enclosed room. Both the room and chamber are equipped with air conditioners with temperature control. The control precision of the chamber is ±0.5°C and
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±1°C for the room. The air change rate of chamber is about 5 times per hour. As there was no natural light in the chamber, LED lights (with colour temperature about
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4000K, a more comfortable colour temperature according to Baniya et al [17]) were used. Some lights were fixed on the roof along the walls. Others were hanged over the table and
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the illumination rate at the level of table was about 500lux. The illumination was kept unchanged during test. The layout of chamber is shown in Fig.2.
Figure 2 Layout of Chamber 2.3 Experimental set-up and equipment
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The experiments were carefully arranged to overcome the main issue of some previous studies of not controlling for (all) covariates that might impact on thermal comfort. Participants were divided into 4 groups. During each test, only one group was tested. Upon arrival, the participants entered the room (with white walls) and sat in the resting
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area for 20min. Then they came into the chamber. During test, they kept siting around a table (with light-yellowish-wood colour). The subjects were allowed to read books or talk
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with each other. Their conversation were restricted that they shouldn’t talk about any content related to private sensations. The estimated metabolic rate was about 1 to 1.2
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met.
The experiments were carried out in July 2017. There were three temperature conditions:
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23°C (cool environment), 26°C (close to neutral environment) and 29°C (warm environment). Temperatures of the room and the chamber were kept same during tests.
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Before test, seven coloured fabrics were hanged layer by layer with random sequence. In similar studies, colours were changed every ten minutes [17, 22, 31]. In this study, participants were also exposed to one coloured environment for 10min. Then they were asked to fill in questionnaires and their heart rate (HR) was tested (Omron, HEM-7320) considering the influence of colour on physiological parameter [31]. After that, surface fabrics were taken off by operate staff and participants would be exposed to the next colour. The whole process of each test lasted for about 2h with constant temperature. Fig.3 shows the schedule of each test.
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Figure 3 Schedule of test In a questionnaire, the subjects were asked for their thermal sensation, thermal comfort and colour satisfaction. Thermal sensation votes (TSV) are based on the ASHRAE/ISO seven-point thermal sensation scale, which is defined hot (+3), warm (+2), slightly warm (+1), neutral (0), slightly cool (-1), cool (-2) and cold (-3). For thermal comfort vote (TCV),
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there are fewer verbal explanations, namely very comfortable (0), just comfortable (1), just uncomfortable (2), and very uncomfortable (3). Like TCV, colour satisfaction vote (CSV) is based on four levels: very satisfied (0), just satisfied (1), just unsatisfied (2), and very unsatisfied (3). Before experiments, the participants were given a detailed explanation of
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the contents of the questionnaire and the voting so that they could fully understand. Air temperature, velocity and relative humidity were measured by multi-parameter
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ventilation meter (Model 8386, TSI Inco., Minnesota, USA). For temperature sensor, the testing range is -17.8-93.3°C and the accuracy is ±0.3°C; for relative humidity, the testing
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range is 0-95% and the accuracy is ±3%; for velocity, the testing range is 0～50 m/s and the accuracy is ±3.0% of reading or ± 0.015m/s, whichever is greater. Mean radiant
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temperature was tested by black-bulb thermometer (JTR04, JT Technology, Beijing, China). The testing range is 5-150°C and the accuracy is ±0.5°C.
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The statistics of tested environmental parameters are shown in Table 2. Table 2 Tested environmental parameters Experiment conditions
Tested environmental parameters Air temperature (°C)
23°C
26°C
29°C
22.9±0.3
26.3±0.2
29.1±0.4
Relative humidity (%)
50±3.9
52±4.6
58±3.5
Mean radiant temperature (°C)
23.1±0.3
26.4±0.3
29.3±0.5
Air velocity (m/s)
0.11±0.04
0.10±0.05
0.13±0.04
3 Results and discussions
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3.1 Thermal sensation vote The mean values of TSV in three temperature conditions are shown in Fig.4. TSV, undoubtedly, was affected by temperature. It increased significantly as temperature increased (P<0.001). And the influence of colour was also significant (P<0.05). Compared with TSV of neutral colours, TSV of cool colours became lower and TSV of warm colours were the highest in three temperature conditions. Maximum difference of TSV among
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colours were 0.92, 0.74 and 1.03, corresponding to 23°C, 26°C and 29°C.
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Figure 4 TSV for different colours
For neutral colours, the effect of black, white and violet on TSV were almost the same.
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The differences of TSV among the three colours in different temperatures were quite small. More specifically, TSV of white was a little bit higher than that of black and violet. The
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reason could be that white feels brighter than the other two and may give an impression of warmer. For cool colours of blue and green, TSV of blue were lower than that of green at
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23°C and 26°C, and were the same at 29°C. For warm colours of red and yellow, TSV of yellow were always a little higher than that of red. The results are consistent with the
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findings of Winzen et al, where they also found that yellow and blue hues seem to be more useful for increasing and decreasing temperature sensation respectively [20]. The average TSV for different kinds of colours were shown in Fig.5. According to the figure, with the increase of temperature, the difference of TSV between warm colour and neutral colour became bigger. The difference increased to 0.78 at 29°C. And the difference between cool colours and neutral colours tended to decrease. 29°C was a hot condition, in which the use of warm colours could intensify hot sensation, and the effect of
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cool colour on regulating TSV was to weaken.
Figure 5 Average values of TSV under cool, neutral and warm colours 3.2 Thermal comfort vote
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The mean TCV of subjects are shown in Fig.6. The votes were related with temperature and colours. As 26°C was a more suitable temperature compared to 23°C and 29°C, it had the lowest TCV, which means that the subjects felt more comfortable. The TCV in each temperature condition were also changing according to colours. In cool environment
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(23°C), TCV of cool colours were high, followed by neutral colours, the lowest were warm colours, and the opposite was the case in warm environment (29°C). The downward
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concave line showed the variation of TCV with colours and temperature. It indicated that subjects felt that cool colours were more comfortable in warm environment, and warm
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colours were more comfortable in cold environment.
Figure 6 Changes of TCV The changes of TSV with TCV were also analyzed as shown in Fig.7. The polynomial fit showed that the two variables were correlated significantly. When TSV is 0, TCV has the
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lowest value. When TSV increases or decreases further, TCV will increase, which means that subjects feels less comfortable. The results are consistent with the existing thermal comfort theory and findings [32, 33, 34], in which TSV has similar relations with TCV. This
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indicated that the subjective vote of the subjects in the experiments were reliable.
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Figure 7 Changes of TCV with TSV 3.3 Colour satisfaction vote
The statistics of CSV is shown in Fig.8. CSV for cool colours raised as temperature decreased. And for warm colours, the change of CSV were the opposite. The results of
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CSV showed that subjects’ felt cool colours more satisfactory in warm environment, while warm colours were more popular in cool environment. It was consistent with the previous
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analysis of TSV and TCV.
For neutral colours, the change of black were different from white and violet. CSV for
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black were almost the same in three temperature environments. Large areas of pure black are rarely applied in building interiors because the depressing sensation it brings. And this
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sensation would not be changed in different temperatures. Thus, it was understandable that the influence of black on CSV at different temperatures was almost constant. The
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changes of CSV of white and violet were similar to cool colours. Both white and violet can arouse emotions similar to cool colours, for example, calmness [12]. This might be the reason that white and purple become more satisfactory when the temperature was raised up. Besides, white had the lowest vote at 26°C and 29°C among all colours, which meant that white was the most preferred colour. Combined with the analysis of TSV and TCV, it was found that although cool colours could make people feel cooler and more comfortable in warm/ hot environment, the subjects in this study considered white to be more satisfactory. The reason might be that most of the indoor environments in which the
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Figure 8 Statistics of CSV
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subjects live and stay were painted in white and they had good adaptability to white.
For about half of conditions, CSV were in the range of 1 (just satisfied) to 2 (just
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unsatisfied), which implies that these colour environments were not quite satisfactory. The colours used in experiments have high colour saturation, except for white. Study of AL-Ayash et al found that vivid colours (with high colour saturation) were more arousing than pale colours (with lower colour saturation) [31]. And their participants felt more
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positive in the pale colour conditions compared to the vivid colour conditions, because pale colours were perceived to be pleasant, fresh, calm, relaxed, light, cool and less sharp.
used in experiments.
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3.4 Heart rate
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This may explain why subjects in this study were not very satisfy with the vivid colours
Fig.9 shows the changes of HR under different experimental conditions. And the average
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values are shown in Fig.10. From these two figures, the variation of HR was related to temperature (P<0.0005)) and colours (P<0.05).
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Mean HR increased with the increase of temperature. The effect of ambient temperature on blood pressure was in accordance with physiological rules [35, 36]. In normal temperature environment, when temperature increases the need to cool the body down will increase too. In higher temperatures, blood flow is directed closer to the surface of the skin so that blood can be cooled down. Therefore, human heart beats faster to accelerate blood circulation and regulate body temperature. When colour changed from cool colour to neutral colour and warm colour, HR also
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increased. According to studies by AL-Ayash et al, hue induces significant changes in HR [31]. They have found that red and yellow increases HR whereas blue decreases HR. This was same with what we found in this study. The results supported the notion that colour has impact on the physiology of people who stayed in the coloured room. In addition, several colour studies have indicated that long-wavelength colours such as red and yellow are more arousing than short-wavelength colours such as blue and green [37, 38]. In
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neutral colours, the corresponding HR of violet was lower, this may due to the short wavelength of voilet. This character of violet is similar to blue and green. In fact, in some
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studies violet was taken as cool colour [21].
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Figure 9 Changes of HR
Figure 10 Average HR for different colours
As both TSV and HR were affected by colours, so correlation between them was analyzed further. The correlations was indicated in Fig.11. At a certain temperature, with colours changing from cool to warm, there was a linear correlation between TSV and HR (with minimum P<0.006 for three linear relations). From physiological point, different colours interfere with psychology and emotion to a certain extent, resulting in corresponding
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changes in HR and TSV.
(The coloured dots corresponding to the colour conditions)
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Figure 11 HR and TSV
In the above analysis and discussion of experimental results, some explanations may be speculative. The effect of colour on emotion and psychology can be complicated. Besides the hue-heat response, there are other appearance attributes about colour, i.e. lightness
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(heavy/light), chroma (active/passive) and individual colour preference (like/dislike) [13,39]. The neutral colour of white and black may give different impression about
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lightness and chroma. These characters of colour haven’t been fully considered in the experiments. Therefore, the interpretation of some experimental results cannot go deeper.
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are certain.
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However, the effects of warm and cool colours on thermal sensation and thermal comfort
Usually, the perception of thermal environment is mainly through thermal regulation
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system of human body. People can also experience their surrounding through perception, cognition, and construct meaning through colour. There have been many studies on the application of interior decoration colours, but the main consideration focuses on space function, visual and psychological feeling, and the combination of thermal sensation is rare. Considering the hue-heat effect, the psychological and emotional changes brought by vision will have influence on the perception of thermal environment to some extent. The use of good colour design might contribute to a more positive mood, and thus make the thermal environment of building more comfort and pleasant with less energy consumption.
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4 Conclusions The main goal of the present research is to investigate the effects of different colours on people’s thermal sensation. The experimental results supports the hue-heat hypothesis. And colours do have impacts on thermal sensation in different temperature environments. Compared with neutral colours, warm colours intend to make people feel warmer, while cool colours have the opposite effect. Both subjective voting and physiological index of
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HR support the conclusion. Integrating warm or cool colours in cool or warm indoor spaces can psychologically induce an optimized thermal perception against the actual thermal condition in occupants, which has positive significance for energy saving of thermal environment.
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Inevitably, this study has some limitations. First, the number of participants was 16. The size of the sample is considered small. Besides, all subjects are Chinese in the age of twenties. According researches, emotional sensation of colour is affected by age and culture background [13, 39, 40]. Therefore, the results may not be applicable to people
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with different age and cultural background. Besides, colours with lower colour saturation should be studied further In order to facilitate practical application.
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Thus, further research is needed to investigate these points. In addition, the quantitative study of the effect of colour on thermal environment is necessary, so as to facilitate the
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combination of colour in thermal environment design.
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Acknowledgement
This study has been financially supported by the National Natural Science Foundation of
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China with contract number of 51678314 and 51778305, and by China Scholarship Council (201700810003). The authors would also want to thank those participants who volunteered for the experiments.
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