Personal comfort systems (PCSs) are gaining popularity due to their better comfort and great energy-saving potential, as compared to conventional air conditioning systems [1
]. A PCS efficiently cools or heats local body parts of people so as to keep the whole body comfortable [4
]. As a result, people have more chances to avoid discomfort stimulations of the non-neutral environment. Such a feature leads to a high energy-efficiency because only a small amount of energy is consumed by a PCS to condition the local body parts rather than the whole indoor environment and the set point temperature range of air conditioning systems (for maintaining the background environment in buildings) is widened. As proved by many studies, extending the set point temperature contributes to great energy conservation in air conditioning system [4
A personal cooling system is an important part of PCS. In recent years, many studies have been carried out on personal cooling. Huang et al. [8
] proposed a new airflow management technique to supply cool airflow for passengers in a car. The local airflow met the individual requirements of passengers in different zones thus satisfying all of them. Cui et al. [9
] undertook a field investigation on passengers’ comfort and behaviors on ten air planes. The results indicated that passengers tended to use the personalized nozzles to ameliorate the warm discomfort. Oh et al. [2
] conducted a series of experiments on the air-conditioning system which supplied cool air in cars, then they found it saved more than 20% energy. Likewise, through CFD simulation, Ghosh et al. [1
] claimed that personal cooling could reduce both the airflow and the cooling load in the automobile thus improving the energy-efficiency of the air-conditioning system.
Besides the application in mobile vehicles and aircrafts, more personal cooling systems and devices have been studied in building environments. Chen et al. [10
] simulated the energy performance of a kind of personal ventilation system. They found the best condition was achieved when the supply air of personal ventilation was at 20 °C while the background environment was at 26 °C. Besides, around 10% energy consumption was saved when the indoor temperature increased from 23 to 26 °C. Chakroun et al. [11
] tried to add personalized evaporative coolers to a room with chilled ceiling and displacement ventilation. They reported that personal cooling contributed to a 17.5% energy savings at 21 °C since the supply air temperature of displacement ventilation was increased. However, Yang et al. [12
] stated that if the personal cooling system consumed too much extra energy, the total energy may increase although the indoor temperature was elevated. Schiavon and Melikov [13
] introduced a new index for evaluate the cooing capacity and the energy use of personal fans. This index made it possible to compare the performances of different fans. Watanabe et al. [14
] designed a kind of ventilated chair with two small fans which directly cooled buttocks and backs of users. It was then proved through the experiments that the chair made participants feel neutral in the environment at 28 °C. Likely, Boerstra et al. [15
] claimed that desk fans could meet 90% acceptable requirement by ASHRAE Standard 55 [16
] for occupants in office room as indoor temperature went up to 28 °C [16
]. Further, Atthajariyakul and Lertsatittanakorn [5
] conducted tests on small fans. They pointed out that the usage of small fans allowed people to have a neutral thermal sensation in the environment at up to 28 °C and it could help save up to 1959.51 GWh/year of electricity in Thailand. Dalewski et al. [17
] studied the combination of personal ventilation cooling with displacement ventilation and they found personal ventilation cooling significantly improved thermal comfort in warm environments and most of the participants found the indoor environment acceptable even when it was at a temperature of 29 °C. Similar to the study of Watanabe et al. [14
], Pasut et al. [18
] combined office chairs and small energy-efficient fans (merely 2 W) to maintain comfort. The obtained results from experiments indicated that subjective comfort was still maintained in the environment at 29 °C. He et al. [19
] used small desk fans as complementary cooling for a radiant ceiling system. It was demonstrated that the desk fans could be regarded as an energy-efficient solution for maintaining comfort when the cooling ceiling was unable to fully cool the indoor environment.
Some other researchers have attempted to explore the performance of personal cooling systems in hotter environments. Based on the results from experiments, Zhai et al. [20
] drew the conclusion that both floor fans and ceiling fans could improve comfort and perceived air quality in the hot environment at the temperature of 30 °C. Huang et al. [22
] held the similar opinion that increased air movement by desk fans significantly reduced the warmth sensation when air temperature was as high as 32 °C. Different from most of previous studies, He et al. [23
] designed a new type of personal cooling system (a radiant cooling desk) which adopted radiant cooling panels to cool the users. The results showed that most of participants with this system voted on the acceptable side in the environment at 32 °C and the warm sensation was significantly lowered. Moreover, Wang and Song [24
] tested four personal cooling strategies (including fans and some wearable devices) in extremely hot environments (36 °C and 40 °C) by using a manikin. They found that using fans and evaporative cooling clothing simultaneously presented the best cooling effect.
As reviewed above, personal cooling is a practical approach to maintaining users’ comfort in warm environments. Nevertheless, fans and personal ventilation are the dominant topic in previous studies while other personal cooling systems account for a small proportion. Thus, there is a need to explore other different ways of personal cooling. Besides, some indexes for evaluating PCSs have been proposed, and they could be better and more universal if they could be used for evaluating different systems in terms of comfort and energy efficiency simultaneously. For example, the new index proposed by Schiavon and Melikov [13
] is only for evaluating personal fans, while the Corrective Energy & Power index (CEP) proposed by He et al. [25
] is only for personal electrical heating systems. More importantly, understanding the comments and the willingness of people with personal cooling will be pretty helpful for the development and application of personal cooling systems, but this point is usually ignored in previous studies. Some field investigations [26
] showed that some people used personal cooling strategies (personal fans) to adapt to the ambient environment. However, few studies have really paid attention to understanding how people feel about personal cooling and what influences their willingness to adopt personal cooling.
The purposes of this study are listed below:
To compare the comfort performances of several personal cooling systems, i.e., radiant cooling desk, desk fans and their combinations, in warm environments;
To propose an improved CEP index which is possible to compare various personal cooling systems (not only those in this study);
To understand how people feel about personal cooling and how they decide to adopt it.
To achieve these purposes, a series of experiments involving physical measurements, questionnaires and feedback was carried out in a real office environment. Then, with some results of our previous studies [23
], three types of personal cooling systems (i.e., radiant cooling desk, desk fan and their combination) were compared. Afterwards, an improved CEP
index was proposed to evaluate and compare various personal cooling systems. Besides, the comments of people who participated in the experiments were obtained and analyzed under two modes (i.e., they needed to pay for the personal cooling systems or not). Logistic regression was used to identify which factors influenced the willingness to adopt personal cooling.