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...environment. comparison was based on three factors--human comfort, energy consumption, and human productivity. The setpoint control was only concerned with the first two factors, while the PMV control considered human productivity as well. Computer simulation techniques were employed to obtain the thermal environments created by the two control methods. The simulation results led to comparison of human comfort and energy consumption. For human productivity, a financial analysis was developed. The financial loss due to reduction in productivity under the simulated environment was estimated. More financial loss represented poorer performance in productivity. It was found that the conventional control caused significant reduction in human productivity even when an acceptable thermal comfort level was achieved. Severe financial loss resulted, accounting for a 9% drop in net profit. On the other hand, the PMV control performed well for both human comfort and human productivity. Only a 0.4% profit drop was observed that compensated the extra energy consumption. Much better overall performance was yielded. Therefore, it is strongly recommended to consider human productivity in the design of future air-conditioning control as well as human comfort and energy consumption.
INTRODUCTION
Air conditioning is very common in modern buildings. Its original purpose was to maintain thermally comfortable environments for people inside while keeping energy consumption as low as possible. So far, human thermal comfort and energy consumption are the only two criteria adopted to govern the control and operation of a system. However, human productivity is becoming more and more important, particularly in a commercial office. Employers urge their staff to achieve higher productivity to generate more profits for the companies, while employees themselves want to perform better for reward. It is reasonable to expect that air-conditioning control should consider human productivity as well as human comfort and energy consumption.
Research on human productivity has long been conducted. Dating back to 1910, the New York State Commission on Ventilation conducted a series of experiments to evaluate various effects on human performance. In four of the experiments, 32 male subjects and 7 female subjects wearing the same clothing were invited to perform mental tasks and typewriting under controlled thermal environments. Their performances were measured under two different temperature settings, -20[degrees]C and 24[degrees]C. The conclusion drawn at that time was that human performance was not affected by heat stress (New York State Commission on Ventilation 1923).
Several decades later, several researchers (Pepler and Warner 1968; Holmberg and Wyon 1969; Johansson and Lofstedt 1969) obtained an opposite finding when they carried out performance tests under conditions with and without moderate heat stress. The tests were normal schoolwork such as reading and comprehension. They all agreed that such heat stress lowered the performance of children in these tests. In 1974, Wyon validated this finding by re-analyzing the previous experimental results from the New York State Commission on Ventilation. He applied the Wilcoxon matched-pairs signed-ranks test to find out the difference of performance in typing conducted by the 39 test subjects under the two temperature settings (i.e., -20[degrees]C and 24[degrees]C). The test had not yet been invented in the 1920s when the Commission analyzed the data. It was designed for the comparison of measurements of a single sample (Wilcoxon 1945) that fully satisfied Wyon's analysis. By using this test, Wyon confirmed that the testing subjects performed less typing under the higher temperature setting (i.e., 24[degrees]C), which created heat stress for the same clothing condition. This matched with the finding of Pepler and Warner (1968), Holmberg and Wyon (1969), and Johansson and Lofstedt (1969).
In another study, Wyon et al. (1975) claimed that testing subjects with different clothing would adjust the air temperature to achieve the same mental performance as well as the same level of thermal comfort. Two groups of subjects wore two sets of clothing--0.6 and 1.15 clo. They performed mental tasks inside a climate chamber for 2.5 hours. The tasks included calculation tests, word memory tests, and cue-utilization tests. During the testing period, they were allowed to adjust the air temperature. The group with lighter clothing preferred the temperature to be 23.2[degrees]C, while the preferred temperature of another group was 18.7[degrees]C. It was found that both groups attained the same level of mental performance as well as thermal comfort. This implied that the test subjects performed mental tasks equally under the same level of thermal comfort. However, the thermal environment adjusted by the subjects did not corresponded to the zero predicted mean vote (PMV), the neutral thermal comfort condition estimated by Fanger's comfort equation (Fanger 1972). In fact, Wyon's valuable experimental results were employed by later researchers to discover the important finding of a relationship between thermal environment and human working efficiency.
In 1982, Jokl (1982) defined four hygrothermal microclimates and discussed their effects on human performance. The zones were cold microclimate, optimal microclimate, hot perspiration climate, and hot microclimate. The optimal microclimate corresponded to the balance of heat generation and heat consumption inside a human body. The imbalance of heat would result in other microclimates. There would be an increase in human performance in the optimal microclimate while a loss in performance occurred in others. Jokl realized that environmental conditions affected the efficiency of workers. Also, he called for an economic study to evaluate the impact of working environments on human efficiency.
In 1994, Lorsch and Abdou (1994) investigated the effect of air temperature on occupant productivity. They claimed that an air-conditioning system could improve the working conditions in both industrial and office work locations to raise occupant productivity by 5% to 15%. However, temperatures providing optimum comfort might not necessarily give rise to maximum efficiency. This matched with Wyon's previous research finding (Wyon et al. 1975). They did not mention how to adjust the air temperature to improve the working efficiency. One major reason was that no well-defined relationship between thermal environment and human performance had been developed at that time. Also, no economic study had been developed for the evaluation urged by Jokl (1982).
Two years later, Wyon (1996) summarized his previous findings on the effect of air temperature on human performance. He recalled that thermal conditions providing optimal comfort (i.e., zero PMV value) might not give rise to maximum efficiency. Testing subjects had better performance in typing tasks and mental tasks at 20[degrees]C. He also suggested that productivity loss was a function of both air temperature and the type of activity. A set of experimental data was created that was useful for later research into human productivity.
In 1997, Fisk and Rosenfeld carried out a literature review to conclude a solid relationship between indoor environments and the working performance of occupants. They estimated that there would be an annual productivity gain of US$12-125 billion by improving working environments. Such improvement also reduced the occurrence of sick building syndrome, allergies, asthma, and respiratory infection inside a building, which contributed to potential annual savings of US$17-43 billion. A similar study was conducted in Finland by Seppanen (1999), who emphasized the negative consequence of poor indoor thermal environments. He estimated that Euro 2.7 billion was lost due to a reduction in productivity under poor indoor environments. These researchers reported the economic impact of poor thermal environments on human productivity. Anyway, there was no analytical method developed for quantitative evaluation on the productivity.
In 2002, Niemela et al. conducted a field test to evaluate the effect of air temperature on human productivity in two call centers of a telecommunication office. In one of the centers, there were two zones with different average room air temperatures. The north zone had an air temperature of 23.6[degrees]C, while the south zone's temperature was 25.2[degrees]C. It was found that the productivity of workers in the north zone was about 5% higher. In another center, an extra cooling unit was installed to lower the room air temperature from the original setting of 25.1[degrees]C to the value close to the temperature in the north zone of the first center. A similar rise of productivity of 7% was observed. Site results obtained in this research served as a useful reference in this...
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