Elsevier

Building and Environment

Volume 44, Issue 6, June 2009, Pages 1128-1134
Building and Environment

Thermal perceptions, general adaptation methods and occupant's idea about the trade-off between thermal comfort and energy saving in hot–humid regions

https://doi.org/10.1016/j.buildenv.2008.08.001Get rights and content

Abstract

A field study conducted in workplaces and residences in Taiwan is carried out to clarify two questions in detail: (1) do people in the tropical climate regions demonstrate a correlation between thermal sensation and thermal dissatisfaction the same as the PMV–PPD formula in the ISO 7730; and (2) does the difference in opportunities to choose from a variety of methods to achieve thermal comfort affects thermal perceptions of occupants? A new predicted formula of percentage of dissatisfied (PD) relating to mean thermal sensation votes (TSVs) is proposed for hot and humid regions. Besides an increase in minimum rate of dissatisfied from 5% to 9%, a shift of the TSV with minimum PD to the cool side of sensation scale is suggested by the new proposed formula. It also reveals that the limits of TSV corresponding to 80% acceptability for hot and humid regions are −1.45 and +0.65 rather than −0.85 and +0.85 suggested by ISO 7730. It is revealed in the findings that the effectiveness, availability and cost of a thermal adaptation method can affect the interviewees' thermal adaptation behaviour. According to the discussion of interviewees' idea about the trade-off between thermal comfort and energy saving, it is found that an energy-saving approach at the cost of sacrificing occupant's thermal comfort is difficult to set into action, but those ensure the occupant's comfort are more acceptable and can be easily popularized.

Introduction

After the adaptive model of thermal comfort became the spirit of changes to the current version of ASHRAE Standard 55 [1], [2], more and more researchers (e.g., Zhang et al. [3], Han et al. [4], Wong and Khoo [5], Henry and Wong [6], Yang and Zhang [7]; Cheng and Ng [8], Rangsiraksa [9], Kwok [10], de Dear and Fountain [11], Chan et al. [12], and Hwang et al. [13]) have paid attention to the study on thermally comfortable environment in the hot and humid climate, both in air-conditioned spaces and naturally ventilated spaces. According to PMV–PPD formula [14], the predicted mean vote between the limits of ±0.85 corresponds to the point where 80% of the residents feel satisfied. In line with this criterion, all the former studies determined the acceptable conditions for 80% acceptability from a linear regressive model of thermal sensation and air temperature without investigating the applicability of PMV–PPD formula to hot and humid region. Humphreys and Nicol [15] had suggested that people who live in the tropical climate regions would prefer a cooler-than-neutral thermal condition.

The merit of the PMV–PPD formula, as shown in Eq. (1), is that it reveals a perfect symmetry with respect to thermal neutrality (PMV = 0). At PMV = 0, a minimum rate of dissatisfied of 5% exists.PPD=10095.0×exp[0.03353×PMV40.2179×PMV2]

As more and more field studies have found that thermal neutrality does not correspond to the optimal condition, the application of PMV–PPD curve in cold or hot climates is under suspicion. The point is when Fanger developed the PMV–PPD model, the correlated percentages of dissatisfied was not obtained by direct inquiry but by definition. Satisfaction is synonyms to the three categories (slightly cool; neutral; slightly warm) in the middle of the seven-point scale, while cold dissatisfaction is synonyms to “cool” and “cold” categories, and warm dissatisfaction to “warm” and “hot” categories. Some studies [16], [17] tried to amend the correlation between dissatisfaction percentage and thermal sensation by redefining dissatisfaction. For example, Mayer [16] conducted a field study in Germany and gave a new definition of uncomfortable cold sensation by accessing the votes for cold, cool and slightly cool for cold climates. A new correlation between PMV and PPD for cold climate regions was also suggested in Mayer's article.

As none of the amendments made for the correlation of PMV–PPD has been suggested for hot–humid climate, a question is very important and must be answered by thermal comfort researchers: do people in the tropical climate regions demonstrate a correlation between thermal sensation and thermal dissatisfaction the same as the PMV–PPD formula in the ISO 7730? This motivated us to conduct a comprehensive field survey on occupants' thermal sensation, preference and adaptation in workplaces and residences in Taiwan. Through comparisons on measured data of field survey and original data of Fanger's experiments [18], this study is expected to examine the applicability of PMV–PPD formula in hot and humid regions and further suggest a new correlation if the formula fails to apply.

In addition to a variety of adaptation methods, occupants in residences have more opportunities to choose the methods of adaptation to achieve thermal comfort depending on their needs and their preferences. On the contrary, the methods and opportunities are limited to a certain degree in the workplaces. For example, usually in offices the control of air temperature for individuals and an electrical fan for increasing air velocity are not provided, even the clothing level is not as free for adjustment as in private spaces. Does the difference in opportunities to choose from a variety of methods to achieve thermal comfort affects thermal perceptions of occupants? It is worth to discuss in detail.

Additionally, understanding occupants' most preferred method of adaptation may help to understand the implementation result of some low-cost or zero-cost methods, as advocated by the energy related department of Taiwan government in order to reduce energy consumption in the use of A/C systems. It is also hoped that the results of this study will contribute to this goal.

Section snippets

Field experiments design

The two major approaches used to access thermal comfort are field experiments and laboratory chamber experiments. The former method is adopted in this study. Field experiments are respectively carried out in residences and workplaces. The surveyed sites scatter around Taiwan and are equipped with either HVAC systems or household air-conditioners. During the field experiments, none of the interviewees is asked to turn on, turn off, or adjust room temperature settings of the A/C system; the use

Regression analysis, neutral temperature and comfortable zone

In order to facilitate the comparison with ISO 7730 standard, which is mainly developed from data gathered in Fanger's laboratory chamber experiments, data processing in our field experiments have reached fully compliance to Fanger's approach [18]. In the approach of Fanger, to eliminate the influence of individual subjectivities, interviewees' responses were grouped into different temperature intervals with an increment of 1.1 °C (2 °F) represented by the mean temperature of each interval. In

General methods of adaptation suggested by interviewees

Fig. 3 illustrates the relative frequencies of the most preferred method of adaptation suggested by interviewees when they sense thermal uncomfortable. It was found that the interviewees demonstrated different habitual methods to achieve thermal comfort in different places. Findings obtained in offices reveal that the percentage of subjects who choose to turn on the air-conditioner (57%) is the highest, followed by opening the window (16%), using electrical fan (13%), adjusting clothing level

Conclusion

This study investigates the thermal perceptions and general adaptation methods in hot and humid regions by carrying out a field survey in workplaces and residences in Taiwan. The primary aim is to examine how the correlation between thermal sensation and thermal dissatisfaction has changed. Changes may result from the subjects' accommodation to hot and humid climate. The secondary aim is to understand the difference between occupants in workplaces and residences in the most preferred thermal

Acknowledgment

We sincerely appreciate the National Science Council for assistance in grant under the project number: NSC-96-2221-E-039-008-MY2.

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