sustainability

Article A Comprehensive Thermal Comfort Analysis of the Cooling Effect of the Stand Fan Using Questionnaires and a Thermal Manikin

Sun-Hye Mun †, Younghoon Kwak †, Yeonjung Kim and Jung-Ho Huh * Department of Architectural Engineering, University of Seoul, Seoul 02504, Korea; [email protected] (S.-H.M); [email protected] (Y.K.); [email protected] (Y.K.) * Correspondence: [email protected]; Tel.: +82-2-6490-2757 Contributed equally to this work. †


Received: 14 August 2019; Accepted: 12 September 2019; Published: 17 September 2019


Abstract: In this study a quantitative analysis was performed on the effect on thermal comfort of the stand fan, a personal cooling device that creates local air currents. A total of 20 environmental conditions (indoor temperatures: 22, 24, 26, 28, and 30 ◦C; fan modes: off, low (L) mode, medium (M) mode, and high (H) mode) were analyzed using questionnaires on male and female subjects in their 20s and a thermal manikin test. The contents of the questionnaire consisted of items on thermal sensation, thermal comfort, thermal acceptability, and demands on changes to the air velocity. This step was accompanied by the thermal manikin test to analyze the convective heat transfer coefficient and cooling effect quantitatively by replicating the stand fan. Given that this study provides data on the cooling effect of the stand fan in quantitative values, it allows for a comparison of energy use with other cooling systems such as the air conditioner, and may be used as a primary data set for analysis of energy conservation rates.

Keywords: stand fan; cooling effect; thermal comfort; questionnaire; thermal manikin

1. Introduction Indoor air velocity is one of the key physical variables affecting occupant comfort, along with dry air temperature, radiation temperature, and relative humidity [1]. However, indoor air velocity has mostly been studied with a focus on draft—air currents that cause thermal discomfort. More recently, the emphasis has been shifting to observe the positive effects of air currents in warm weather conditions that improve occupant comfort and energy conservation [2]. Konz et al. [3] found that an increase in average air current increase by 0.1 m/s (between 0.4 and 1.2 m/s) in oscillating and fixed personal fans can have equal comfort level to a maximum 0.40 ◦C increase in temperature. Hseieh [4] studied the thermal comfort according to varying temperatures and air velocities with male and female college students of medium activity level and showed that a 0.23 m/s increase of air velocity offset a 1 ◦C increase. Such a result indicates that at the same activity levels, the existence of a fan may raise the optimal indoor temperature for thermal comfort compared to situations without a fan. Toftum and Nielsen [5] conducted a study of 10 male subjects where they were exposed to average velocity gradually increasing from 0.05 to 0.40 m/s for temperatures between 11 and 20 ◦C to see if the subjects could feel the movement or air and whether it caused discomfort. In a comparison of dissatisfied responses at two different activity levels, there was less dissatisfaction at high activity levels rather than lower ones. Another study administered a questionnaire to the occupants of schools and offices in Australia. Seventy percent of the respondents answered that when the thermal sensation of the body was slightly warm or hot, they preferred a wind velocity higher than 0.2 m/s. This surpasses

Sustainability 2019, 11, 5091; doi:10.3390/su11185091 www.mdpi.com/journal/sustainability Sustainability 2019, 11, 5091 2 of 18 the air velocity suggested by ASHRAE Standard 55-2013 [6] to prevent the risk of the draft. Even at a neutral body thermal sensation, half of the respondents said that they wanted a higher air velocity than 0.2 m/s [7]. Sun et al. [8] attached a small fan to each corner of a chair to create an upward current and examined the thermal comfort and individual usage patterns of 32 college students at indoor temperatures of 22, 24, and 26 ◦C. At 26 ◦C, the subjects expressed satisfaction at the high air velocity from the fans but felt coldness at the waist for 22 and 24 ◦C. Also, the overall thermal sensation of the body was determined by the thermal sensation at the waist, arms, calves, and feet. This showed that while the lower parts of the body are less affected by the surrounding environment [9], the upper body is directly exposed to the air current, thereby playing a key role in determining the overall thermal sensation of the body. Further, when the subjects were allowed to manipulate the air velocity, 90% of them changed the air velocity within an hour. On the other hand, higher indoor air current has cooling effects, not only maintaining the thermal comfort of the occupant at a higher temperature but also lowering the cooling energy consumption of the building compared to air conditioners [2]. Further, it has been reported that air current has a positive relationship with thermal comfort in fields other than buildings (i.e., automobiles, indoors, underground mines) [10–12]. Yang et al. [13] expressed the cooling fan efficiency of fans using an index called cooling fan efficiency (CFE). They conducted a thermal manikin test with air velocity between 0.6 and 2.5 m/s at temperatures of 24, 26, 28, and 30 ◦C. The CFE appeared higher at lower temperatures and higher wind velocity, and the rise of fan air velocity not only increased the cooling effect on the human body but also the energy consumption. The thermal manikin test showed that the maximum cooling effect according to the air velocity of the fan was 2 C, proving that the stand − ◦ fan is an energy-efficient technology that satisfies thermal comfort under warm weather conditions. Zhai et al. [14] looked not only at temperatures of 26, 28, and 30 ◦C but also relative humidity levels of 60% and 80%, administering a questionnaire for subjects in an experiment using the stand fan. Eighty percent of the subjects replied that they could accommodate up to 30 ◦C and 60%, but showed discomfort at 30 ◦C and 80%, requesting higher air velocity. Ho et al. [15] used numerical simulation to analyze the indoor fluid flow and heat transfer in a room with a ceiling fan. When the ceiling fan is operational, it creates a strong circulation of air, inducing convective heat transfer and displaying an even temperature distribution. As a result, the predictive mean vote (PMV) value shifted to cool with the increase in air velocity created by the fan. That is, even in the circumstances with higher heat load, the ceiling fan has a cooling effect, making it possible to maintain thermal comfort. Various studies around the world have found that indoor temperature setting regulations can cause occupant discomfort [16], thereby leading to a negative effect of lowered productivity [17,18]. As such, to increase the productivity in high indoor temperature, further cooling through building control [19] or stand fan may be used. Therefore, this study aimed at a quantitative analysis of the cooling effect of the stand fan, a personal cooling device creating local air current, on thermal comfort. As it is not possible to objectivize or quantify all subjects at same conditions [20], this study analyzed the cooling effect of stand fan through questionnaires for subjects and an experiment using a thermal manikin.

2. Method As can be seen in Figure1, this study conducted an analysis of the indoor thermal comfort questionnaire following the operation of a stand fan and that of the cooling effect of the stand fan using a thermal manikin. The specifics are as follows:

Step O1 : Prior to studying the cooling effect of the fan and its impact on the occupant thermal • comfort, the air velocity the temperature at the location of the occupant was measured. Assuming that the occupant would be sitting, the air current was measured at the foot level (0.1 m), head level (1.1 m), and the level parallel to the fan (0.6 m), where the air current was likely to be the strongest. Step O2 : To derive the impact of stand fan operation according to indoor temperature on thermal • comfort, a questionnaire was administered to 16 university and graduate students in their 20s. Sustainability 2019, 11, 5091 3 of 18

Sustainability 2019, 11, x FOR PEER REVIEW 3 of 19 Indoor temperature conditions were 22, 24, 26, 28, and 30 ◦C, and the fan was set to off mode (O(Off),ff), lowlow modemode (L),(L), mediummedium modemode (M),(M), andand highhigh mode (H), which were combined to create 20 environmental conditions.conditions. • Step O③3 :: The The thermal thermal manikin manikin test test waswas conductedconducted in in the the environmental environmental chamber. chamber. Indoor • temperaturetemperature andand relativerelative humidity humidity represented represented the the same same conditions conditions as inas the in questionnaires.the questionnaires. The airflowThe airflow devices devices were were calibrated calibrated to the to same the same conditions conditions as the as air the velocity air velocity at the at three the three levels levels in O1 . Stepin ①O.4 : Through the thermal manikin test, the heat flux of each body part was measured and • • usedStep to④: obtain Through the coethe ffithermalcient of manikin convective test, heat the transfer.heat flux of each body part was measured and StepusedO to5 : obtain The convective the coefficient heat transferof convective coefficient heat (obtainedtransfer. through the thermal manikin test and • • theStep sensitivity ⑤: The convective of each body heat part) transfer was coefficient utilized to (obtained calculate through the cooling the ethermalffect of manikin the stand test fan and for eachthe sensitivity of the three of modeseach body (L, M, part and) was H). utilized to calculate the cooling effect of the stand fan for each of the three modes (L, M, and H). Step O6 : A comprehensive analysis of the cooling effect was derived through the questionnaire • ⑥ • andStep the: thermal A comprehensive manikin on analysis the stand of fan.the cooling effect was derived through the questionnaire and the thermal manikin on the stand fan. The above process is repeated for each set temperature (22–30 C, 2 C interval). The above process is repeated for each set temperature (22–30 ◦°C , 2 ◦°C interval).

Questionnaire (22oC - 30oC) Thermal manikin (22oC - 30oC)

① Measurement of fan speed (air velocities) ③ Adjustment of airflow device ▪ Low mode (L) ▪ Low mode (L) ▪ Medium mode (M) Calibration ▪ Medium mode (M) ▪ High mode (H) ▪ High mode (H)

④ Experiment of thermal manikin ▪ Coefficient of convective heat transfer

② Questionnaire for thermal comfort ▪ Thermal sensation ▪ Thermal comfort ⑤ Calculation of cooling effect ▪ Thermal acceptability ▪ Calculation of cooling effect according ▪ Demands on changes to the air velocity to

⑥ Comprehensive thermal comfort analysis on the cooling effect of the stand fan

Figure 1. Flow chart of the study. Figure 1. Flow chart of the study. 3. Questionnaire for Thermal Comfort 3. Questionnaire for Thermal Comfort 3.1. Setting for the Questionnaire 3.1. Setting for the Questionnaire 3.1.1. Standing Fan 3.1.1. Standing Fan The specifications of the fan used to analyze the cooling effect are as shown in Table1. As a productThe of specifications company H, theof the fan fan has used five 14-inchto analyze wings the and cooling has the effect function are as that shown allows in itsTable four 1. modes As a toproduct be adjusted of company by remote H, the control. fan has Its five height 14-inch is adjustable wings and between has the function 0.7 and 0.86 that m. allows This its study four had modes the fan’sto be centeradjusted set by at aremote 0.6-m heightcontrol. for Its the height experiment. is adjustable This isbetween the same 0.7 height and 0.86 as them. ASHRAEThis study Standard had the 55-2013fan’s center [6] uses set at to a assess0.6-m thermalheight for comfort the experiment. with the occupant This is the sitting same down.height as the ASHRAE Standard 55-2013 [6] uses to assess thermal comfort with the occupant sitting down.

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Table 1. Table 1. SpecificationsSpecifications of the ofstand the standfan. fan.

PicturePicture of the ModelModel Product Product Details Details ModelModel EFe-492R EFe-492R Air velocityAir velocity Levels 1–4 Levels 1–4 Level 1 (8 W)Level 1 (8 W) Electricity Level 2 (33 W) Electricityconsumption Level 2 (33 W)Level 3 (39 W) consumption Level 3 (39 W)Level 4 (45 W) WeightLevel 4 (45 W) 3.4 kg Weight 3.4 kg

Dimensions 0.40 (L) 0.35 (W) 0.70–0.86 (H) m × × Dimensions 0.40 (L) × 0.35 (W) × 0.70–0.86 (H) m

TheThe fan fan power power increases increases the air the velocity air velocity from fromlevel level1 to 4, 1 and to 4, this and study this studyutilized utilized only the only fan the fan powerpower from from 1 to 1 3, to leaving 3, leaving out outlevel level 4. Here, 4. Here, we express we express level 1 level as the 1 aslow the mode low mode(L), level (L), 2 levelas the 2 as the mediummedium mode mode (M), (M), and andlevel level3 as the 3 as high the mode high (H). mode Table (H). 2 Tableshows2 theshows air velocity the air according velocity according to fan to mode.fan mode.

TableTable 2. Air 2. velocityAir velocity according according to fan tomode. fan mode.

FanFan Mode Mode Air Velocity Air Velocity LevelLevel 1 1 (Low (Low mode) mode) 1.48 m/s 1.48 m/s LevelLevel 22 (Medium (Medium mode) mode) 3.55 m/s 3.55 m/s Level 3 (High mode) 4.73 m/s Level 3 (High mode) 4.73 m/s

3.1.2. Object Space 3.1.2. Object Space ToTo ensure ensure that that only only the the air air velocity velocity caused caused by by the the fan fan would would be be measured measured by by minimizing minimizing the the effect effectof crosswind, of crosswind, a single a single room room of suof ffisufficientcient size size was was chosen chosen so so that that the the experiment experiment would would be be less less a ffected affectedby other by other structures structures such assuch pillars. as pillars. The selectedThe selected room room was was a single a single room room with with the the dimensions dimensions of 6.88 m (L) 8.64 m (W) 3 m (H), with pillars (0.68 m 0.5 m) on the west and east side of the room. Desks, of 6.88× m (L) × 8.64 ×m (W) × 3 m (H), with pillars (0.68× m × 0.5 m) on the west and east side of the room.chairs, Desks, and chairs, a whiteboard and a whiteboard were piled were on thepiled western on the western wall ofthe wall room, of the making room, making the actual the actual area used for areameasurement used for measurement approximately approximately 46 m2. 46 m2.

3.1.3.3.1.3. Indoor Indoor Temperature Temperature Control Control of Target of Target Space Space TwoTwo electric electric heat heat pump pump (EHP) (EHP) devices devices installed installed on the on ceiling the ceiling were used were for used indoor for indoortemperature temperature control.control. To Toensu ensurere that that the theair current air current from from the EHP the EHPdid not did affect not atheffect occupant, the occupant, a thin avinyl thin was vinyl was installedinstalled at 2 at-m 2-m height height to create to create a temporary a temporary ceiling ceiling between between the EHP the and EHP the and occupant’s the occupant’s head. Also, head. Also, as astwo two fans fans would would not nothave have any anyeffect eff ifect they if theywere were more more than 3 than m apart 3 m apart[21], questionnaires [21], questionnaires were were administeredadministered in groups in groups of two. of two.

3.1.4.3.1.4. Questionnaire Questionnaire Conditions Conditions FigureFigure 2 shows2 shows the the position position of the of thefan fanand andthe occupant. the occupant. F indicates F indicates the fan, the and fan, O andindicates O indicates the the occupantoccupant location. location. X is Xthe is themeasurement measurement spots spots of indoor of indoor temperature temperature and humidity. and humidity. The distance The distance betweenbetween F1 F1and and F2 F2is 3.0 is 3.0m, and m, andthe thedistance distance between between the fan the and fan the and occupant the occupant is 1.5 m. is 1.5Also, m. to Also, to minimizeminimize discomfort discomfort such such as dry as dryeyes eyesthat thatmay maybe induced be induced by the by extended the extended exposure exposure to air current to air current givengiven the the length length of the of theexperiment experiment and andto account to account for the for actual the actual use of usethe offan the when fan sitting when at sitting a desk, at a desk, the fan was positioned so that the air current from it reached the occupant from the side (left). the fan was positioned so that the air current from it reached the occupant from the side (left). Sustainability 2019, 11, 5091 5 of 18 Sustainability 2019, 11, x FOR PEER REVIEW 5 of 19

MMeasurement easurem ent point point (t, RH )

N

F1F1 O1O 1 F1 F2 O1 3.0m X

F2F2 O2O 2 O2 1.5m

(a) (b)

(c)

Figure 2. Thermal comfort questionnaire according to the location of the occupant and the fan. (a) Floor Figure 2. Thermal comfort questionnaire according to the location of the occupant and the fan. (a) plan of the occupant and the fan; (b) Position of the occupant and the fan; (c) Administration of the Floor plan of the occupant and the fan; (b) Position of the occupant and the fan; (c) Administration of thermal comfort questionnaire. the thermal comfort questionnaire. The indoor environment conditions for the questionnaire is as shown in Table3. There are five The indoor environment conditions for the questionnaire is as shown in Table 3. There are five indoor temperatures: 22, 24, 26, 28, and 30 ◦C; the fan modes consisted of off, low (L), medium (M), indoorand high tempe (H).ratures: Also, the 22,relative 24, 26, 28, humidity and 30 was°C ; the kept fan within modes the consisted comfort of range off, low of 40–60%. (L), medium To ensure (M), andconsistency high (H). of Also, the temperature the relative and humidity the humidity, was kept a measurement within the comfort devices wererange installed of 40–60%. at X To to monitorensure consistencythe conditions of in the the temperature duration of and the questionnaire the humidity, process. a measurement devices were installed at X to monitor the conditions in the duration of the questionnaire process. Table 3. Indoor environment conditions for the questionnaire. Table 3. Indoor environment conditions for the questionnaire. Indoor Temperature (◦C) 22 24 26 28 30 Indoor Temperature (°C) 22 24 26 28 30 Fan mode Off, Low (L), Medium (M), High (H) Relative humidityFan (%) mode Off, Low (L), Medium 40–60 (M), High (H) Relative humidity (%) 40–60 3.1.5. Study Subjects 3.1.5. StudyStudy subjectsSubjects consisted of 16 university and graduate students, 8 male and 8 female. These studentsStudy were subjects born consisted in Korea of and 16 are university familiar and with graduate the Korean students, climate. 8 male Similar and with 8 female. Fong etThese al.’s studentsstudy [16 were], experiments born in Korea were and conducted are familiar with with students the Korean from climate. the area. Similar Table with4 shows Fong theet al.’s physical study [16],attributes experiments of the study were subjects,conducted who with were students healthy from students the area. in the Table 20s 4 with shows an averagethe physical age ofattributes 26. of the study subjects, who were healthy students in the 20s with an average age of 26.

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Table 4. Physical attributes data of subjects (* standard deviation). Table 4. Physical attributes data of subjects (* standard deviation). Sex Number of Subjects Age Height (m) Weight (kg) SexFemale (F) Number of Subjects8 25 Age ± 1 * 158.8 Height ± 2.7 *(m) 53.8 Weight± 7.8 * (kg) Female (F) 8 25 1 * 158.8 2.7 * 53.8 7.8 * Male (M) 8 28 ± 2 * 176.5 ± 3.8± * 76.9 ± 8.2± * Male (M) 8 28 2 * 176.5 3.8 * 76.9 8.2 * ± ± ± F + MF + M 1616 26 ± 2*2 * 167.6 167.6 ± 9.7 *9.7 *65.3 ± 65.3 14.2 *14.2 * ± ± ± To ensure psychological variables such as stress did not affect the comfort assessment, study To ensure psychological variables such as stress did not affect the comfort assessment, study subjects were recommended to have at least 7 h of sleep the previous night. It was notified prior to subjects were recommended to have at least 7 h of sleep the previous night. It was notified prior to the experiment that they were to wear underwear, half-sleeves, long summer pants (excluding jeans), the experiment that they were to wear underwear, half-sleeves, long summer pants (excluding jeans), socks, and slippers. Those with longer hair were required to tie their hair. During the questionnaire, socks, and slippers. Those with longer hair were required to tie their hair. During the questionnaire, the occupants’ activities were limited to light reading and writing; they were not allowed to leave the occupants’ activities were limited to light reading and writing; they were not allowed to leave their their spots during the experiment. spots during the experiment. 3.1.6. Questionnaire Procedures 3.1.6. Questionnaire Procedures The procedures for the questionnaire are as shown in Figure 3. Fan mode started at Off, and The procedures for the questionnaire are as shown in Figure3. Fan mode started at O ff, and changed to Low, Medium, and High in that order. “▼” indicates the administration of the changed to Low, Medium, and High in that order. “H” indicates the administration of the questionnaire. questionnaire. Each subject took 15 min to adapt to indoor temperature before operating the fan, and Each subject took 15 min to adapt to indoor temperature before operating the fan, and they were they were given a 5-min break before the change to the fan mode within the room. Once the given a 5-min break before the change to the fan mode within the room. Once the questionnaires questionnaires were collected for the four fan modes under one temperature conditions, the indoor were collected for the four fan modes under one temperature conditions, the indoor temperature was temperature was adjusted. The subjects were allowed at this point to leave the space for a 25–30-min adjusted. The subjects were allowed at this point to leave the space for a 25–30-min break. If the subjects break. If the subjects complained of severe cold or heat they filled out the survey immediately, complained of severe cold or heat they filled out the survey immediately, stopping the experiment and stopping the experiment and allowing the subjects to take a break. allowing the subjects to take a break.

▼ ▼ ▼ ▼

Off Low Medium High

Break Break

Figure 3. Questionnaire procedure according to fan mode. Figure 3. Questionnaire procedure according to fan mode. 3.1.7. Questionnaire Contents 3.1.7.As Questionnaire can be seen Contents in Table5 , the contents of the questionnaire constituted of thermal sensation, thermal comfort, thermal acceptability, and demands on changes to the air velocity. A questionnaire As can be seen in Table 5, the contents of the questionnaire constituted of thermal sensation, was administered over 20 times according to changes in the experiment conditions. thermal comfort, thermal acceptability, and demands on changes to the air velocity. A questionnaire was administered over 20 times according to changes in the experiment conditions. Table 5. Questionnaire contents and possible responses.

ItemTable 5. Questionnaire Content contents and possible responses. Possible Responses 1 Thermal sensation (TS) 7-point scale ( 3, 2, 1, 0, 1, 2, 3) Item Content · Possible Responses− − − Strongly comfort 1 Thermal sensation (TS) · 7-point· scale (−3, −2, −1, 0, 1, 2, 3) Comfort 2 Thermal comfort (TC) · Strongly· comfort Discomfort · Comfort· 2 Thermal comfort (TC) Strongly discomfort · Discomfort· Strongly acceptability · · StronglyAcceptability discomfort 3 Thermal acceptability (TA) · · StronglyUnacceptability acceptability · · AcceptabilityStrongly unacceptability 3 Thermal acceptability (TA) · · UnacceptabilityMore · 4 Demands on changes to the air velocity· StronglyNo unacceptability · · More Less 4 Demands on changes to the air velocity · · No Sustainability 2019, 11, 5091 7 of 18

3.2. Questionnaire Results

3.2.1. Thermal Sensation (TS) The first item on the questionnaire asked about the general thermal sensation. The subjects were instructed prior to the experiment to express thermal sensation on a scale of –3 (cold), 2 (cool), 1 − − (slightly cool), 0 (neutral), +1 (slightly warm), +2 (warm), and +3 (hot). Table6 shows the average thermal sensation and thermal comfort among the 16 study subjects according to fan mode. According to the ASHRAE Standard 55-2013 [6], thermal sensation from 1 to +1 is regarded as representing − comfort when assessing the indoor thermal environment through a questionnaire. However, when compared to the second item thermal comfort, subjects selected a thermal sensation in the range of 2 − to 0 when they answered that the thermal environment was comfortable. Such a low thermal sensation appears to be due to the age group of the subjects (who were in their 20s), indicating that that 2 − (cool) is pleasantly cool. Also, as the experiment was conducted during July in the summer, a cooler sensation may have been preferred.

Table 6. Average TS according to fan mode and proportion of “Comfort” responses.

Indoor Responses within Responses within Fan Mode Average TS Temperature ( C) 1~1 Range (%) 2~0 Range (%) ◦ − − Off 2.19 20 20 L 2.31 30 30 30 M 0.94 80 80 H 0.19 90 90 − Off 0.81 58 58 L 0.25 83 83 28 M 0.63 92 100 − H 1.00 83 100 − Off 0.25 92 92 L 0.69 100 100 26 − M 1.31 58 100 − H 1.88 17 75 − Off 0.63 75 100 − L 1.31 58 92 24 − M 2.31 17 67 − H 2.75 8 25 − Off 1.94 25 67 − L 2.50 17 33 22 − M 3.00 0 0 − H 3.00 0 0 −

3.2.2. Thermal Comfort (TC) and Thermal Acceptability (TA)

Figure4 shows the proportion of the responses to each item of the questionnaire. At 22 ◦C, more than 75% of the responses did not show thermal comfort, with the exception of the L mode, and no one felt strong comfort at H mode. Even when the fan was not in operation, the proportion of those who reported strong comfort was 44%, less than half. This indicates that for thermal comfort the fan should not be operated. In contrast, the responses in the comfort range was 75%, but those who showed “strong comfort” represented 19%, indicating that the operation of the fan did not have a positive impact on the thermal comfort of occupants. That is, at 22 and 30 ◦C occupants cannot feel thermal comfort, making them the limit temperatures on use of the fan. These results are similar to those of a previous study [14]. Sustainability 2019, 11, 5091 8 of 18 Sustainability 2019, 11, x FOR PEER REVIEW 8 of 19

100 100 Comfort Acceptability Strongly comfort Strongly acceptability

75 75

50 50 Response rate [%] rate Response Response rate [%] rate Response 25 25

0 0 Off L M H Off L M H Off L M H Off L M H Off L M H Off L M H Off L M H Off L M H Off L M H Off L M H 30 28 26 24 22 30 28 26 24 22 Fan mode by temperature Fan mode by temperature (a) (b)

100 More 75 Less

50

25

0

-25

Response rate [%] rate Response -50

-75

-100 Off L M H Off L M H Off L M H Off L M H Off L M H 30 28 26 24 22 Fan mode by temperature (c) Figure 4. Percentage of responses to questionnaire. (a) Thermal comfort; (b) Thermal acceptability; (c) Figure 4. Percentage of responses to questionnaire. (a) Thermal comfort; (b) Thermal acceptability; (c) Demands on changes to the air velocity. Demands on changes to the air velocity.

The responses on TC and TA were mostly similar. At an Off mode of 22 ◦C, 75% of the responses The responses on TC and TA were mostly similar. At an Off mode of 22 °C , 75% of the responses indicated comfort, but the responses on acceptability did not reach 75%. At an H mode of 26 ◦C, the indicatedcomfort responses comfort, but were the 69%, responses but acceptability on acceptability was over did 75%.not reach 75%. At an H mode of 26 °C , the comfort responses were 69%, but acceptability was over 75%. 3.2.3. Demands on Changes to the Air Velocity 3.2.3. Demands on Changes to the Air Velocity Figure4c shows the demands on changes to the air velocity. Here, the proportion of positive ( +) responsesFigure indicate 4c shows more, the demands and the negative on changes ( ) responsesto the air velocity. indicate Here, less. the proportion of positive (+) − responsesAt O ffindicateand L modesmore, an ofd 30 the◦C, negative most responses (−) responses demanded indicate a strongerless. air velocity, but at M and H modes,At Off 50% and of theL modes occupants of 30 did °C , notmost demand responses a stronger demanded air velocity a stronger although air velocity, the thermal but at discomfort M and H modes,had not 50% yet of been the relieved.occupants Also, did not no respondentsdemand a stronger wanted air a highervelocity wind although velocity the atthermal H mode discomfort at any of hadthe temperaturenot yet been conditions.relieved. Also, no respondents wanted a higher wind velocity at H mode at any of the temperature conditions. 4. Thermal Manikin Experiment 4. Thermal Manikin Experiment 4.1. Experiment Overview 4.1. ExperimentA thermal Overview manikin test was conducted to quantify the cooling effect of the stand fan. This experimentA thermal measured manikin the test heat was flux conducted in each body to part, quantify which the was cooling used to effect calculate of the the stand convective fan. This heat experimenttransfer coe measuredfficient and the the heat cooling flux einffect. each body part, which was used to calculate the convective heat transfer coefficient and the cooling effect. 4.2. Thermal Manikin Experiment

4.2.4.2.1. Thermal Environmental Manikin Experiment Chamber

4.2.1. TheEnvironmental thermal manikin Chamber test was conducted in an environment chamber within the research facility. This chamber constitutes of an airflow device (0.7 m 0.48 m) with three fans stacked on top of each The thermal manikin test was conducted in an environment× chamber within the research facility. other as seen in Figure5a, and a thermal manikin (“Newton”), as seen in Figure5b,c. The size of the This chamber constitutes of an airflow device (0.7 m × 0.48 m) with three fans stacked on top of each other as seen in Figure 5a, and a thermal manikin (“Newton”), as seen in Figure 5b,c. The size of the Sustainability 2019, 11, 5091 9 of 18 Sustainability 2019, 11, x FOR PEER REVIEW 9 of 19 chamber isis 3.33.3 mm (L)(L) × 2.9 m (W) × 2.92.9 m (H) as shown in Figure 5 5d.d. TheThe environmentenvironment controlcontrol withinwithin × × thethe chamberchamber isis asas shownshown inin TableTable7 7..

(a) (b) (c)

Airflow device 2.9 2.9 m

Thermal manikin

3.3 m (d)

Figure 5. Thermal manikin in the test chamber. (a) Airflow device; (b) Thermal manikin (front); (Figurec) Thermal 5. Thermal manikin manikin (back); (ind )the Plan test of chamber. the test chamber. (a) Airflow device; (b) Thermal manikin (front); (c) Thermal manikin (back); (d) Plan of the test chamber. Table 7. Environment control inside the chamber. Table 7. Environment control inside the chamber. Chamber Environment Control Specification Chamber EnvironmentAirflow device Control 0.6–6Specification m/s Temperature 40–80 C Airflow device − 0.6◦ –6 m/s Humidity 20–95% Temperature −40–80 °C 4.2.2. Environmental ConditionsHumidity 20–95% The temperature conditions inside the chamber were adjusted between five temperatures of 22, 4.2.2. Environmental Conditions 24, 26, 28, and 30 ◦C, and air velocity mode constituted of four modes, off, low, medium, and high. ExperimentsThe temperature were conducted conditions for ainside total the of 20 chamber environment were adjusted conditions between that combined five temperatures the two. Given of 22, the24, 26, limitations 28, and 30 in space,°C , and the air standing velocity fanmode was constituted replaced withof four the modes, airflow off, device low, withinmedium, the and chamber. high. IndoorExperiments temperature, were conducted relative humidity, for a total and of air20 velocityenvironment were keptconditions as the samethat combined as what was the usedtwo. forGiven the questionnairethe limitations survey. in space, The the clothing standing of fan the was thermal replaced manikin with was the madeairflow to device be similar within to the the instructed chamber. clothingIndoor temperature, for the questionnaire relative humidity, in Figure2 c,and as air can velocity be seen wer in Figuree kept5 b,c.as the Fourteen same as body what segments was used ( iforis thethe body questionnaire segments), survey. as can be The seen clothing in Table of8 , the were thermal used for manikin the thermal was manikin made to test be to similar measure to the the heatinstructed flux and clothing derive fo ther the convective questionnaire heat transfer in Figure coe 2cffi,cient. as can be seen in Figure 5b,c. Fourteen body segments (𝑖 is the body segments), as can be seen in Table 8, were used for the thermal manikin test to measure the heat flux and derive the convective heat transfer coefficient. Sustainability 2019, 11, x FOR PEER REVIEW 14 of 19

32 C] o Sustainability 2019, 1130, x FOR PEER REVIEW 14 of 19 Sustainability 2019, 11, x FOR PEER REVIEW 14 of 19 Sustainability 2019, 11, x FOR PEER REVIEW 14 of 19 Sustainability 2019, 1128, x FOR PEER REVIEW 14 of 19 32 32

C] 32 o C] 32 o

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o 30 30 30 2428 28 28 28 26 2226 26 26 24 2024 24 24 22 22 1822 22 20 20 1620 Temperature of weightedcooling effectTemperature [ 20 18 OffLMHOffLMHOffLMHOffLMHOffLMH 18 18 18 30 28 26 24 22 16 Temperature of weightedcooling effectTemperature [ 16 Temperature of weightedcooling effectTemperature [ 16 OffLMHOffLMHOffLMHOffLMHOffLMHFan mode by temperature Sustainability 2019 11 of weightedcooling effectTemperature [ 16 OffLMHOffLMHOffLMHOffLMHOffLMH , , 5091 of weightedcooling effectTemperature [ OffLMHOffLMHOffLMHOffLMHOffLMH10 of 18 OffLMHOffLMHOffLMHOffLMHOffLMH30 28 26 24 22 30 28 26 24 22 Sustainability 2019, 11, x FOR PEER REVIEW 30 28Fan mode 10by 26 oftemperature 19 24 22 30 28Fan mode by 26 temperature 24 22 Figure 7. Temperature of weighted coolingFan mode effect by accordingtemperature to fan mode by each indoor set-point Table 8. Body segments for measurement points. Fan mode by temperature Table 8. Body segmentstemperature. for measurement points.

Figure 7. Temperature of weighted cooling effect according to fan mode by each indoor set-point Figure 7. Temperature of weighted cooling effect according to fan mode by each indoor set-point ThermalThermal Manikin Manikin temperature.Figure 7. Temperature i Segmentof weighted Segment cooling effect according to fan mode by each indoor set-point Figuretemperature. 7. Temperature Table 11. ofStandardized weighted cooling regression effect accordingcoefficients to fanfor eachmode body by each segment indoor [23]. set-point temperature. temperature.① Head ● O1 Head TableI 11. StandardizedSegment regression coefficientsStandardized for each body Regression segment [23]. Coefficients Table 11. Standardized regression coefficients for each body segment [23]. 1 ②Table 11.R(right) Standardized-hand regression coefficients for each body segment [23]. ①O2 R(right)-hand TableI 11. StandardizedSegmentHead regression coefficientsStandardized for each Regression body segment0.93 Coefficients [23]. I Segment Standardized Regression Coefficients ③I L(left)-handSegment Standardized Regression Coefficients ②①OI3 L(left)-handR(right)-handSegmentHead Standardized Regression0.93 0.86 Coefficients ① Head 0.93 ① Head 0.93 ④③①② R-forearmR(right)-handHead 0.930.86 ● ● ②O4 R(right)-handR-forearmL(left)-hand 0.86 1.00 ② R(right)-hand 0.86 7 6 ④②③ R(right)-handL(left)-hand 0.861.00 ⑤③5 L-forearmR-forearm 1.00 ● ③O L(left)-handL-forearm 1.00 ③④ L(left)-hand 1.00 ⑤④ L(left)-handR-forearmL-forearm 1.00 0.98 8 ⑥④O6 R-upperR-upperR-forearm arm arm 1.00 ④⑤ R-forearmL-forearm 0.981.00 ● ● ⑥⑤ R-forearmL-forearmR-upper arm 1.000.98 0.87 ⑦⑥⑤ L-forearm 0.98 5 4 ⑤⑥O7 L-upperL-upperR-upperL-forearm arm arm 0.870.98 ⑦⑥ R-upperL-upper arm arm 0.87 0.93 ⑥⑦ R-upper arm 0.87 ⑧⑦O8 R-upperL-upperTorso arm 0.870.93 ●3 ● ⑧ TorsoL-upper arm 0.93 2 ⑧⑦ L-upperTorso arm 0.93 0.90 ⑦⑧ L-upperTorso arm 0.930.90 ● ● O9 R-thighTorso 0.90 ⑨⑨⑧ R-thighTorso R-thigh 0.90 0.89 ⑧⑨ R-thighTorso 0.890.90 10 9 ⑨ R-thigh 0.89 ⑩⑨ L-thighR-thighL-thigh 0.89 0.88 ⑩⑩ L-thighR-thighL-thigh 0.890.88 ⑩ L-thigh 0.88 ⑪⑩ L-thighR-calfR-calf 0.890.88 0.89 ⑪⑪ L-thighR-calf 0.880.89 ⑪ R-calf R-calf 0.89 ⑫⑪ R-calfL-calfL-calf 0.890.86 0.86 ● ● ⑫ L-calf 0.86 ⑫⑬⑫ L-calf 0.86 12 11 ⑬⑫ L-calf R-footL-calfR-foot 0.860.95 0.95 ⑬ R-foot 0.95 ⑬⑭ R-footL-foot 0.970.95 ⑬⑭ R-foot R-footL-footL-foot 0.950.97 0.97 ●14 ●13 ⑭ L-foot 0.97 ⑭ L-foot 0.97 5. Discussion ⑭ L-foot 5. Discussion 5. 5.Discussion Discussion 5. Discussion 4.2.3. Airflow Device 5.1. Comfort Conditions of Stand Fan Use 4.2.3. Airflow Device 5.1. Comfort Conditions of Stand Fan Use 5.1.5.1. Comfort Comfort ConditionsConditions ofof Stand Stand Fan Fan Use Use 5.1. ComfortThe above Conditions results of may Stand be Fan combined Use to categorize the comfort conditions as seen in Table 12. To Tomaintain maintain the the same same conditions conditions as the as thequestionnaire, questionnaire,The above resultsthe theair may airflow flow be was combined was made made to to come tocategorize come from from thethe thecomfort left. conditions as seen in Table 12. ThermalTheThe aboveabovesensation results (TS) may maybetween be be combined combined−2 and 0,to thermalcategorizeto categorize comfort the comfortthe (TC) comfort responses conditions conditions of as “comfort” seen as in seenTable (strong in 12. Table 12. left.The The airflow airflow device device was was calibrated calibrated soso thatthatThermal thetheThe airflowairflow abovesensation wouldresults (TS) create may between be the the combined same− same2 and air air 0,to velocity velocitythermalcategorize ascomfort as thethe the comfort stand (TC) responses conditions of as “comfort” seen in Table (strong 12. ThermalcomfortThermal sensation+sensation comfort) (TS)over(TS) between75between %, and − 2 −TA 2and andresponses 0, thermal0, thermal of “acceptable”comfort comfort (TC) (strongly(TC)responses responses acceptable, of “comfort” of acceptable)“comfort” (strong (strong standfan fan from from the the position position of of the the manikin. manikin. TableTableThermalcomfort9 9 comparescompares +sensation comfort) the the (TS)over air air between 75velocity velocity %, and −of2 ofTA theand the responses stand 0, stand thermal fan fan ofand “acceptable”comfort and the the (TC) air (stronglyresponses acceptable, of “comfort” acceptable) (strong overcomfort 75% + werecomfort) regarded over as75 comfort%, and TAconditions responses and of marked “acceptable” as *. ** (stronglyindicates thatacceptable, over 50% acceptable) reported comfortcomfortover 75% + + comfort)werecomfort) regarded overover as75 75 comfort%, %, and and TAconditions TA responses responses and of marked “acceptable” of “acceptable” as *. ** (stronglyindicates (strongly thatacceptable, over acceptable, 50% acceptable) reported acceptable) airvelocity velocity ofof thethe airflowairflow devicedevice in the chamber.over Using75% Using were the the regardedair air velocity velocity as comfortmeasurements measurements conditions at at 0.1, and 0.1, 0.6, marked 0.6, and and as 1.1 *. ** m indicates that over 50% reported overoverstrong 75% 75% comfort, were were regarded indicating as asthe comfort comfort ideal comfort conditions conditions conditio and and markedns. Themarked idealas *. **ascomfort indicates*. ** indicates condit thations over that (**) 50% wereover reported met50% at reported 1.1from m from the ground,the ground, root root mean mean square square error errorstrong (RMSE) (RMSE) comfort, and and mean indicating mean bias biasthe error ideal error (MBE) comfort (MBE) were conditio were used used tons. analyzeThe to ideal the comfort conditions (**) were met at Offstrong and comfort, L modes indicating of 24 °C, theL and ideal M comfortmodes of conditio 26 °C, ns.and The M andideal H comfort modes ofcondit 28 °C.ions * indicates(**) were anmet Off at strongstrongOff and comfort, comfort, L modes indicating of 24 °C, theL the and ideal ideal M comfortmodes comfort of conditio 26 conditio °C, ns.and Thens. M andTheideal H ideal comfort modes comfort ofcondit 28 °C. conditions * indicates(**)ions were (**) anmet wereOff at met at analyzesimilarity the similarity between between the two setsthe two of values. sets ofOff Basedvalues. and L on Basedmodes the assessmenton of the24 °C, assessment L and that M the modesthat air the velocity of air 26 velocity°C, of and the Mof stand and fanH modes of 28 °C. * indicates an Off Offmode and of L26 modes °C, L modeof 24 °C,of 28 L and°C, andM modes H mode of of26 30°C, °C, and where M and the H subjects modes offelt 28 some °C. * heat. indicates an Off the stand fan for the questionnaire was similarOffmode and to of Lthat 26 modes °C,of theL modeof airflow 24 of°C, 28 Ldevice, °C, and and M the H modes modeexperiments ofof 3026 °C, °C, were where and Mthe and subjects H modes felt some of 28 heat. °C. * indicates an Off for the questionnaire was similar to that mode of the of airflow 26 °C, L device, mode of the 28 °C, experiments and H mode were of 30 carried °C, where out. the subjects felt some heat. mode of 26 °C, L mode of 28 °C, and H mode of 30 °C, where the subjects felt some heat. carried out. mode of 26 °C, L mode of 28 °C, and H mode of 30 °C, where the subjects felt some heat.

Table 9. Comparison of air velocity between the stand fan and the airflow device. RMSE: root mean Tablesquare 9. Comparison error; MBE: of mean air velocity bias error. between the stand fan and the airflow device. RMSE: root mean square error; MBE: mean bias error. Off (m/s) Low (m/s]) Medium (m/s) High (m/s) Height Height Off (m/s) Low (m/s]) Medium (m/s) High (m/s) [m] Survey Manikin Survey Manikin Survey Manikin Survey Manikin [m] Survey Manikin Survey Manikin Survey Manikin Survey Manikin 0.1 0.10.05 0.05 0.16 0.16 0.10 0.100.22 0.220.22 0.220.22 0.220.24 0.240.22 0.22 0.6 0.07 0.19 0.48 0.41 1.57 1.44 1.98 1.87 0.6 0.07 0.19 0.48 0.41 1.57 1.44 1.98 1.87 1.1 0.04 0.17 0.16 0.31 0.27 0.37 0.32 0.45 1.1Average 0.04 0.05 0.17 0.17 0.16 0.250.31 0.310.27 0.690.37 0.680.32 0.850.45 0.85 AverageRMSE 0.05 0.100.17 0.25 0.110.31 0.69 0.090.68 0.85 0.85 0.10 RMSEMBE 0.10 0.10 0.11 0.100.09 0.080.10 0.09 MBE 0.10 0.10 0.08 0.09 4.3. Experiment Results 4.3. Experiment Results 4.3.1. Convective Heat Transfer Coefficient 4.3.1. Convective Heat Transfer Coefficient Convective heat transfer coefficient (hc) can be derived from the thermal manikin test. According Convective heat transfer coefficient (ℎ푐) can be derived from the thermal manikin test. According to a previous study [22], hc according to the change in air velocity can be derived as in Equation (1) to a previous study [22], ℎ푐 according to the change in air velocity can be derived as in Equation (1) n ℎ = h퐵c ×=푣B푛 v (1) (1) 푐 × Sustainability 2019, 11, x FOR PEER REVIEW 14 of 19

32 C] o Sustainability 2019, 1130, x FOR PEER REVIEW 14 of 19

2832 C] C] C] C] o o o o 2630

2428

26 2226

24 20 22 18 20 16 Temperature of weightedcooling effectTemperature [ Sustainability18 OffLMHOffLMHOffLMHOffLMHOffLMH2019, 11, 5091 11 of 18

16 30 28 26 24 22

Temperature of weightedcooling effectTemperature [ 16

Temperature of weightedcooling effectTemperature [ 16 Temperature of weightedcooling effectTemperature [ Temperature of weightedcooling effectTemperature [ OffLMHOffLMHOffLMHOffLMHOffLMH OffLMHOffLMHOffLMHOffLMHOffLMHFan mode by temperature 2 where hc is the coefficient of convective heat transfer (W/m K), v is the air velocity (m/s), and B and n 30 28 26 24 22 are the coefficients. Fan mode by temperature Figure 7. Temperaturehc value forof weighted each body cooling part effect and indooraccording temperature to fan mode conditionsby each indoor were set-point organized by B, n and the temperature.coeffi cient of determination R2 (see Table 10[23]). Figure 7. Temperature of weighted cooling effect according to fan mode by each indoor set-point temperature. temperature.Table Table 10.11. CoeStandardizedfficient of regression convective coefficients heat transfer for for each each body body segment segment [23]. according to indoor temperature (Highlight cells imply little correlation between air velocity increase and h [23]. TableI 11. StandardizedSegment regression coefficientsStandardized for each body Regression segment [23]. Coefficientsc ① I 22Segment◦CHead Standardized 24 ◦C Regression 260.93◦ CCoefficients 28 ◦C 30 ◦C ①i ②① B R(right)-handnHeadR 2 B n R2 B0.93 0.86n R2 B n R2 B n R2 ③② R(right)-hand 0.86 O1 7.47R(right)-hand 0.37L(left)-hand 0.93 7.56 0.39 0.94 7.280.86 0.401.00 0.78 7.80 0.37 0.94 8.06 0.38 0.94 ③ ④③O2 9.13L(left)-hand 0.21R-forearm 0.79 9.19 0.19 0.79 9.251.00 0.231.00 0.85 9.41 0.22 0.80 9.84 0.22 0.81 ④O3 9.61 0.60R-forearm 0.98 9.97 0.55 0.97 9.871.00 0.62 0.98 10.21 0.60 0.97 11.05 0.61 0.98 ⑤ R-forearmL-forearm 1.00 0.98 ⑤O4 6.83 0.16L-forearm0.61 7.05 0.12 0.60 7.200.98 0.18 0.63 7.53 0.14 0.51 8.11 0.16 0.58 ⑥⑤ L-forearm 0.98 ⑥O5 5.10 0.94R-upper 0.99 arm 5.20 0.97 0.99 5.20 0.940.87 0.99 5.26 0.95 0.99 5.84 0.92 0.99 ⑥ R-upper arm 0.87 ⑦O6 4.71 0.02 0.00 4.78 0.01 0.01 4.92 0.10 0.20 5.01 0.05 0.07 5.38 0.10 0.23 ⑦ L-upperL-upper arm arm 0.93 0.93 O7 2.52L-upper 1.44 0.99arm 2.82 1.38 0.99 2.66 0.93 1.44 0.99 2.62 1.45 0.99 3.04 1.40 0.99 ⑧ Torso 0.90 ⑧O8 0.60 0.90Torso 0.96 0.61 0.96 0.97 0.740.90 0.87 0.97 0.83 0.81 0.96 1.20 0.66 0.96 ⑨ ⑨O9 1.21 0.85R-thighR-thigh 0.67 1.24 0.85 0.70 1.280.89 0.810.89 0.62 1.08 0.88 0.62 0.89 0.87 0.50 ⑩ ⑩ 1.64 0.95L-thighL-thigh 0.91 1.64 1.00 0.89 1.470.88 1.010.88 0.89 1.25 1.04 0.85 0.89 1.14 0.79 ⑪ 1.41 0.61R-calfR-calf 0.76 1.55 0.57 0.79 1.820.89 0.510.89 0.66 2.02 0.46 0.69 3.75 0.24 0.43 ⑫ 1.57 0.90L-calfL-calf 0.91 1.76 0.85 0.90 1.940.86 0.810.86 0.87 2.15 0.74 0.83 4.22 0.48 0.75 ⑬ ⑬ 3.27 0.22R-footR-foot 0.67 3.52 0.19 0.60 3.580.95 0.230.95 0.64 4.05 0.19 0.63 4.79 0.13 0.44 ⑭ L-foot 0.97 ⑭ 3.12 0.30L-footL-foot 0.77 3.44 0.25 0.67 3.490.97 0.290.97 0.71 3.91 0.25 0.71 4.77 0.19 0.61 Avrage 2.68 0.62 0.92 2.77 0.62 0.93 2.83 0.62 0.91 2.95 0.59 0.91 3.49 0.54 0.90 5. Discussion 5. Discussion 5.1. Comfort ConditionsThe hand of Stand value Fan Use shows significant changes according to the adjustments in air velocity. Head and 5.1. Comfortforearm Conditions follow of Stand values Fan Use follow with a higher value. On the other hand, h value for most of the lower The above results may be combined to categorize the comfort conditions as seen in Tablec 12. ThermalThe abovesensationbody results appears (TS) maybetween to be combined relatively−2 and 0, thermal lessto categorize aff ectedcomfort bythe (TC) the comfort increaseresponses conditions inof air“comfort” velocity. as seen (strong in Table 12. Thermalcomfort sensation+ comfort)An over(TS) interesting 75between %, and aspect −TA2 andresponses in the0, thermalh coffor “acceptable” di comfortfferent body(strongly(TC) partsresponses acceptable, derived of acceptable)“comfort” through the (strong thermal manikin test comfortover 75% + werecomfort)is that regarded the over opposite as 75 comfort %, and side conditions TA of responses the and body marked of from “acceptable” as direct *. ** indicates contact (strongly that with over acceptable, the 50% air reported flow acceptable) has a very low R2 value strong comfort, indicating the ideal comfort conditions. The ideal comfort conditions (**) were met at overstrong 75% comfort, were(highlighted regarded indicating in asthe Tablecomfort ideal 10comfort ).conditions That conditio is, the andns. coe Themarkedffi idealcient ascomfort of *. convective ** indicates conditions heat that (**) transferwereover met50%in at reported the body parts opposite Off and L modes of 24 °C, L and M modes of 26 °C, and M and H modes of 28 °C. * indicates an Off strongOff and comfort, L modesto the indicating of air 24 flow °C, L appearedthe and ideal M modes comfort to have of 26 conditio no°C, correlation and ns.M andThe H toideal modes the comfort air of velocity 28 °C. condit * indicates fromions the (**) an standard wereOff met point at when the fan mode of 26 °C, L mode of 28 °C, and H mode of 30 °C, where the subjects felt some heat. Off and L modesis in operation. of 24 °C, L Also, and M such modes body of parts26 °C, seems and M to and increase H modes as the of 28 air °C. velocity * indicates of the an fan Off increase. To look mode of 26 at°C, the L mode value of for 28 the °C, whole and H body, mode the of results30 °C, where are similar the subjects to the findingsfelt some of heat. previous researchers, with an n value range of 0.5–0.6. Also, the B value appeared to increase as the indoor temperature increased.

4.3.2. Cooling Effect by the Stand Fan Cooling effect by the stand fan may be expressed as the difference in equivalent temperature (teq)[24]. Here, the equivalent temperature is defined as, “The uniform temperature of the imaginary enclosure with air velocity equal to zero in which a person will exchange the same dry heat by radiation and convection as in the actual non-uniform environment” [25]. Assuming that the before and after test of the thermal manikin test is equivalent to the stand on/off state, the cooling effect (teq) the difference in equivalent temperature are calculated as per Equations (2)–(4).

∆teq = t t (2) eq,On − eq,O f f . qt teq = tsk (3) − hcal

hcal = hc + hr (4) Sustainability 2019, 11, 5091 12 of 18

where ∆teq is the equivalent temperature difference (◦C), teq,On is the equivalent temperature when fan is on (◦C), teq,O f f is the equivalent temperature when fan is off (◦C), teq is the manikin-based equivalent . 2 temperature (◦C), is the manikin-based skin temperature (◦C), qt is the sensible heat loss (W/m ), hcal is 2 2 the coefficient of dry heat transfer (W/m K), and hr is the coefficient of radiant heat transfer (W/m K). . In this study, tsk and qt used the values derived through the thermal manikin test, hc was calculated using Equation (1), and hr was assumed to be the widely accepted value regardless of the position of the human body: 4.7 W/m2K[26]. According to ASHRAE [27], emissivity can be assumed, and explicit solutions for hr are rarely obtained for clothed subjects due to the difficulties in measuring average 2 clothed body surface temperature. Therefore the value hr = 4.7 W/m K has been widely accepted as a reasonable whole-body estimate for general purposes. Figure6 shows the cooling e ffect on each body part according to air velocity. The lower the indoor temperature and the stronger the fan speed, the more significant the cooling effect. As the airflow comes from the left, the left side of the body displayed a more significant cooling effect than the right side. In particular, the right arm and hand, which is level with the height of the fan, showed the most cooling effect. In the case of the thighs and calves, the left and right did not show much difference and had similar values. In the case of the right arm (especially in the upper right arm covered by clothing), there was little difference in cooling effect between different fan speeds. The cooling effect remained close to 0 ◦C, showing that airflow mostly did not reach the body part. Figure7 is a schematization of the cooling e ffect in each set temperature for 20 test conditions. This was calculated using Equation (5) to represent the cooling effect according to value, taking into consideration the aggravated value by the surface of the body part. Here, si was based on the analysis of the sensitivity of each body segment [23] using the standardized regression coefficient (SRC) equation [28], as can be seen in Table 11.

P   14 ∆tT A s i=1 eq,i × sur f ,i × i ∆tT = (5) eq,w P14   i=1 Asur f ,i

T where ∆teq,w is the weighted cooling effect from body surface at indoor set-point temperature (T) T (◦C), ∆teq,i is the cooling effect on the body segment at indoor set-point temperature (T)(◦C), Asur f ,i is 2 the surface of the body segment [m ], si is the sensitivity of body segment, T is the indoor set-point temperature (i.e., 22, 24, 26, 28, 30) ( C), and i is the body segments (i.e., 1 = head, 2 = R-hand, , ◦ ··· 14 = L-foot). As can be seen in Figure7, the cooling e ffect is present for all but Off modes in every indoor set-point temperature. At 30 and 28 ◦C, the cooling effect of Off, L, M and H modes did not surpass 2 ◦C. However, H mode of 24 ◦C had the cooling effect higher than 2 ◦C, making it cooler than Off mode of 24 ◦C. Further, M and H mode of 24 ◦C may be cooler than the Off mode of 22 ◦C. Overall, the lower the temperature, the higher the cooling effect according to fan mode. Sustainability 2019, 11, 5091 13 of 18 Sustainability 2019, 11, x FOR PEER REVIEW 13 of 19

(a) 22oC (b) 24oC ∆푡푒푞 ∆푡푒푞 ① Head ① Head -16.0 -16.0 ⑦ L-upper arm ⑥ R-upper arm ⑦ L-upper arm ⑥ R-upper arm

⑤ L-forearm -10.0 ④ R-forearm ⑤ L-forearm -10.0 ④ R-forearm

-4.0 -4.0 ③ L-hand ② R-hand ③ L-hand ② R-hand

2.0 2.0

⑩ L-thigh ⑨ R-thigh ⑩ L-thigh ⑨ R-thigh

⑫ L-calf ⑪ R-calf ⑫ L-calf ⑪ R-calf

⑭ L-foot ⑬ R-foot ⑭ L-foot ⑬ R-foot Low Low ⑧ Torso ⑧ Torso Medium Medium High High

(c) 26oC (d) 28oC ∆푡푒푞 ∆푡푒푞 ① Head ① Head -16.0 -16.0 ⑦ L-upper arm ⑥ R-upper arm ⑦ L-upper arm ⑥ R-upper arm

⑤ L-forearm -10.0 ④ R-forearm ⑤ L-forearm -10.0 ④ R-forearm

-4.0 -4.0 ③ L-hand ② R-hand ③ L-hand ② R-hand

2.0 2.0

⑩ L-thigh ⑨ R-thigh ⑩ L-thigh ⑨ R-thigh

⑫ L-calf ⑪ R-calf ⑫ L-calf ⑪ R-calf

⑭ L-foot ⑬ R-foot ⑭ L-foot ⑬ R-foot Low Low ⑧ Torso ⑧ Torso Medium Medium High High

(e) 30oC ∆푡푒푞 ① Head -16.0 ⑦ L-upper arm ⑥ R-upper arm

⑤ L-forearm -10.0 ④ R-forearm

-4.0 ③ L-hand ② R-hand

2.0

⑩ L-thigh ⑨ R-thigh

⑫ L-calf ⑪ R-calf

⑭ L-foot ⑬ R-foot Low ⑧ Torso Medium High

Figure 6. 6. CoolingCooling effect effect (∆ (푡∆푒푞t)eq on) on each each body body segment segment according according to indoor to indoor set-point set-point temperature. temperature. (a) (22a) °C 22; ◦(bC;) 24 (b )°C 24; (◦cC;) 26 (c )°C 26; (◦dC;) 28 (d °C) 28; (e◦)C; 30 ( e°C) 30. ◦C. Sustainability 2019, 11, x FOR PEER REVIEW 14 of 19

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] C o 26 30 24 28 22 26 20 24 18 22 16

Temperature of weightedcooling effectTemperature [ 16 Temperature of weightedcooling effectTemperature [ Temperature of weightedcooling effectTemperature [ Temperature of weightedcooling effectTemperature [ Temperature of weightedcooling effectTemperature [ 20 OffLMHOffLMHOffLMHOffLMHOffLMH 18 30 28 26 24 22 Fan mode by temperature 16 Temperature coolingof[ effect weighted Temperature Off L M H Off L M H Off L M H Off L M H Off L M H Figure 7. Temperature of30 weighted cooling28 effect according26 to fan 24mode by each22 indoor set-point temperature. Fan mode by temperature

Figure 7. TableTemperature 11. Standardized of weighted regression cooling coefficients effect according for each body to fan segment mode [23]. by each indoor Figureset-point 7. temperature.Temperature of weighted cooling effect according to fan mode by each indoor set-point I Segment Standardized Regression Coefficients temperature.I Segment Standardized Regression Coefficients ①Table 11. StandardizedHead regression coefficients for each body0.93 segment [23]. ② ②ITable 11. Standardized SegmentR(right)-hand regression coefficients Standardized for each Regression body0.86 segment Coefficients [23]. ③ ③O1I HeadL(left)-handSegment Standardized 0.93Regression1.00 Coefficients ④O2 R(right)-hand 0.86 ① R-forearmHead 1.000.93 O3 L(left)-hand 1.00 ⑤ L-forearm 0.98 O②4 R-forearmR(right)-hand 1.000.86 ⑥ R-upper arm 0.87 O③5 L-forearmR-upperL(left)-hand arm 0.98 0.871.00 ⑦O6 R-upperL-upper arm arm 0.87 0.93 ④ L-upper arm 0.93 O7 L-upperR-forearm arm 0.931.00 ⑧ Torso 0.90 O⑤8 TorsoL-forearm 0.900.98 ⑨ R-thigh 0.89 O⑥9 R-thighR-upperR-thigh arm 0.890.890.87 ⑩ L-thighL-thigh 0.880.88 ⑦ L-upperL-thigh arm 0.880.93 ⑪ R-calfR-calf 0.890.89 ⑧ R-calfTorso 0.890.90 ⑫ L-calfL-calf 0.860.86 ⑨ R-thigh 0.89 ⑬ R-footR-foot 0.950.95 ⑩ L-thigh 0.88 ⑭ L-footL-foot 0.970.97 ⑪ R-calf 0.89 ⑫ L-calf 0.86 5. Discussion 5. Discussion ⑬ R-foot 0.95 ⑭ 5.1.5.1. Comfort Comfort Conditions Conditions of of Stand Stand Fan Fan LUse Use-foot 0.97 The above results may be combined to categorize the comfort conditions as seen in Table 12. 5. DiscussionTheThe above above results results may may be be combined combined to to categorize categorize the the comfort comfort conditions conditions as as seen seen in in Table Table 12. 12 . ThermalThermal sensationsensation (TS)(TS) between between 2− and2 and 0, thermal0, thermal comfort comfort (TC) (TC) responses responses of “comfort” of “comfort” (strong comfort(strong − comfort+5.1.comfort) Comfort + comfort) over Conditions 75 %,over andof Stand75 TA %, responsesFanand Use TA responses of “acceptable” of “acceptable” (strongly (strongly acceptable, acceptable, acceptable) acceptable) over 75% overwere 75% regarded were regarded as comfort as conditionscomfort conditions and marked and marked as *. ** indicatesas *. ** indicates that over that 50% over reported 50% reported strong The above results may be combined to categorize the comfort conditions as seen in Table 12. strongcomfort, comfort, indicating indicating the ideal the comfort ideal comfort conditions. conditio Thens. ideal The comfort ideal comfort conditions condit (**)ions were (**) met were at O metff and at Thermal sensation (TS) between −2 and 0, thermal comfort (TC) responses of “comfort” (strong OffL modes and L ofmodes 24 C, of L 24 and °C, M L modes and M ofmodes 26 C, of and 26 °C, M and and H M modes and H of modes 28 C. of * indicates28 °C. * indicates an Off mode an Off of comfort + comfort)◦ over 75 %, and TA ◦responses of “acceptable” (strongly◦ acceptable, acceptable) mode26 C, of L 26 mode °C, ofL mode 28 C, of and 28 H°C, mode and H of mode 30 C, of where 30 °C, the where subjects the subjects felt some felt heat. some heat. over◦ 75% were regarded◦ as comfort conditions◦ and marked as *. ** indicates that over 50% reported

strong comfort, indicating the ideal comfort conditions. The ideal comfort conditions (**) were met at Off and L modes of 24 °C , L and M modes of 26 °C , and M and H modes of 28 °C . * indicates an Off mode of 26 °C , L mode of 28 °C , and H mode of 30 °C , where the subjects felt some heat.

Sustainability 2019, 11, 5091 15 of 18

Table 12. Selection of fan mode for optimal thermal comfort condition.

Thermal Thermal Comfort (TC; %) Strongly Comfort Indoor Set-Point Fan Sensation Strong Acceptable + Conditions Temperature (◦C) Mode Comfort Total (TS) Comfort Acceptable (%) of Fan Use Off 2.19 19 0 19 19 L 2.31 13 0 13 19 30 M 0.94 38 13 50 50 H 0.19 56 19 75 75 * − Off 0.81 31 13 44 44 L 0.25 56 19 75 75 * 28 M 0.63 38 63 100 100 ** − H 1.00 38 56 94 100 ** − Off 0.25 69 19 88 88 * L 0.69 38 50 88 94 ** 26 − M 1.31 31 69 100 100 ** − H 1.88 25 44 69 75 − Off 0.63 25 75 100 100 ** − L 1.31 6 75 81 81 ** 24 − M 2.31 38 6 44 63 − H 2.75 13 6 19 31 − Off 1.94 31 44 75 69 − L 2.50 19 19 38 44 22 − M 3.00 0 6 6 13 − H 3.00 6 0 6 13 −

5.2. Cooling Effect of the Stand Fan The cooling effect results from the thermal manikin test were compared to the questionnaire results. First, the expected sensible indoor temperature that assumes that the indoor temperature decreased from the cooling effect of the stand fan was calculated using the following Equation (6).

T Tp = T ∆t (6) − eq,w where Tp is the expected sensible indoor temperature (◦C). Figure8 compares the expected sensible indoor temperature and TS for each set temperature. Here, the expected sensible indoor temperature reflects the cooling effect of each fan mode on the indoor temperature, and TS is the average value of the 16 subjects. As can be seen from O1 and O2 of Figure8, the TS values of O ff mode at 28 and 26 ◦C were respectively 0.81 and 0.25. The expected sensible indoor temperature at Off mode of 28 ◦C turned out to be lower than H mode of 30 ◦C, but the questionnaire results show that the subjects felt slightly warm. Similarly, the expected sensible indoor temperature at Off mode of 26 ◦C turned out to be lower than M and H mode of 28 ◦C, but the questionnaire results showed the subjects felt slightly warm. At 26 and 28 ◦C, it appears that subjects felt cooler when there was air current compared to when there is not, even if the sensible indoor temperature is low. Such results are connected to the demand for air velocity change appearing as “more” in Off mode of 26 ◦C, and Off and L modes of 28 ◦C. However, in situations with indoor temperature such as 30 ◦C, a smaller air flow was felt to be hotter than none, as can be seen from O3 of Figure8. The TS for M mode of 28 ◦C, L mode of 26 ◦C, and Off mode of 24 ◦C were almost identical. This implies that the expected sensible indoor temperature may be different, but what the human body feels is similar. At low indoor temperature, high velocity created an excessive cooling effect. That is, M and H modes of 26 C and L, M, and H modes of 24 C produced a TS below 1. At a very low indoor ◦ ◦ − temperature, the subjects responded that it was very cold regardless of the stand fan. Sustainability 2019, 11, 5091 16 of 18

As previously mentioned, the existing study considers 1~+1 TS to represent comfort, and the − expected sensible indoor temperature was calculated to be 24.00–27.66 ◦C. However, the M and H modes of 26 ◦C each showed expected sensible indoor temperatures of 24.17 and 23.48 ◦C, but the TS was lower than 1. Further, H mode of 28 C and L mode of 24 C had TS slightly below 1, but was Sustainability 2019, 11−, x FOR PEER REVIEW ◦ ◦ − 16 of 19 analyzed to be sufficiently acceptable (see Figure4b).

32 4 ] Thermal sensation

℃ ② [ 30 3 Expected sensible indoor temperature ① 28 2

26 1

24 0

22 -1

③ Thermal sensation 20 -2

18 -3

Expected Expected sensible indoor temperature 16 -4 Off L M H Off L M H Off L M H Off L M H Off L M H 30 28 26 24 22 Fan mode by temperature

Figure 8. Comparison of expected sensible indoor temperature and thermal sensation according to fan modeFigure by 8.each Comparison indoor set-point of expected temperature. sensible indoor temperature and thermal sensation according to 6. Conclusionsfan mode by and each Future indoor Worksset-point temperature.

ThisAs can study be conductedseen from a① comprehensive and ② of Figure analysis 8, the of TS the values cooling of eff Offect ofmode the localat 28 air and currents 26 °C fromwere therespectively stand fan. 0.81 The and study 0.25. consisted The expected of a questionnaire sensible indoor for temperature male and female at Off subjects mode of in 28 their °C turned 20s and out a thermalto be lower manikin than test.H mode Comfort of 30 conditions°C , but the for questionnaire each set indoor results temperature show that were the subjects derived. felt The slightly main resultswarm. areSimilarly, summarized the expected as follows: sensible indoor temperature at Off mode of 26 °C turned out to be lower than M and H mode of 28 °C , but the questionnaire results showed the subjects felt slightly The stand fan was most effective at M and L modes of 28 ◦C, Off and L modes of 26 ◦C, and Off •warm. At 26 and 28 °C , it appears that subjects felt cooler when there was air current compared to mode of 24 ◦C. In situations with an indoor temperature of 28 ◦C, a stand fan would be able to whencreate there a is su not,fficient even cooling if the esensibleffect. indoor temperature is low. Such results are connected to the demandIt was for possible air velocity to confirm change that appearing the human as “more” body feels in Off cooling mode when of 26 airflow°C , and is Off created. and L However,modes of •28 °C . However, in situations with indoor temperature such as 30 °C , a smaller air flow was felt to be with a set indoor temperature that is 30 or 22 ◦C the cooling effect due to airflow may produce ③ hotterdi ffthanerent none results, as can than be expected. seen from of Figure 8. The TS for M mode of 28 °C , L mode of 26 °C , and Off mode of 24 °C were almost identical. This impliesThese that data the will expected prove usefulsensible for indoor generating temperature and operating may be a cooling different, strategy. but what Further, the byhuman providing body anfeels interpretation is similar. of the cooling effect in quantifiable values, it may be possible to use these data for a comparisonAt low withindoor the temperature, energy use ofhigh other velocity cooling created systems an suchexcessive as air cooling conditioning effect. andThat for is, use M and as the H primarymodes of material 26 °C and for assessingL, M, and the H energymodes consumption of 24 °C produced rate. Future a TS studiesbelow − on1. energyAt a very use low would indoor not onlytemperature, allow for the a suggestion subjects resp ofonded energy-conserving that it was very cooling cold methodsregardless that of the take stand comfort fan.conditions into account,As previously but also a more mentioned, accurate the analysis existing of study energy considers consumption. −1~+1 TS to represent comfort, and the Authorexpected Contributions: sensible indoorS.-H.M. temperature and Y.K. (Younghoon was calculated Kwak) analyzedto be 24.00 the– results27.66 °C and. However, wrote the full the manuscript; M and H Y.K.modes (Yeonjung of 26 °C Kim) each performed showed theexpected experiments sensible and indoor discussed temperature the resultss and of 24.17 implications and 23.48 at all °C stages;, but the J.-H.H. TS advisedwas lower on all than tasks −1. and Further, double-checked H mode theof 28 results °C and and L the mode whole of manuscript. 24 °C had TS All slightly authors proofreadbelow −1, the but paper. was Acknowledgments:analyzed to be sufficientlyThis work accep was supportedtable (see by Figure the National 4b). Research Foundation of Korea (NRF) grant funded by the Korea government (No. NRF-2017R1A2A2A05001443; and NRF-2019R1C1C1010956). Conflicts6. Conclusion of Interest:s andThe Future authors Works declare no conflict of interest. This study conducted a comprehensive analysis of the cooling effect of the local air currents from the stand fan. The study consisted of a questionnaire for male and female subjects in their 20s and a thermal manikin test. Comfort conditions for each set indoor temperature were derived. The main results are summarized as follows: Sustainability 2019, 11, 5091 17 of 18

Abbreviations

Nomenclature 2 Asur f : i Surface area of body part (m ) B Coefficient 2 hc Coefficient of convective heat transfer (W/m K) 2 hdry Coefficient of dry heat transfer (W/m K) 2 hr Coefficient of radiant heat transfer (W/m K) i Body segments n Coefficient R2 Coefficient of determination si Sensitivity of body part teq Manikin-based equivalent temperature (◦C) teq,on Equivalent temperature when fan is on (◦C) teq,o f f Equivalent temperature when fan is off (◦C) T ∆teq,w Aggravated cooling effect at indoor set-point temperature (T)(◦C) T ∆teq,i Cooling effect for the body part at indoor set-point temperature (T)(◦C) tsk Manikin-based skin temperature (◦C) T Indoor set-point temperature (◦C) Tp Expected sensible temperature (◦C) . 2 qt Sensible heat loss (W/m ) v Air velocity (m/s) Acronyms and Abbreviations H High mode of stand fan L Low mode of stand fan M Medium mode of stand fan MBE Mean bias error PMV Predictive mean vote RMSE Root mean square error SRC Standardized regression coefficient TA Thermal acceptability TC Thermal comfort TS Thermal sensation

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