Smart air supply terminal for floor-standing room air conditioners based on the identification of human positions
Introduction
Floor-standing air conditioners (FSACs) are the most popular, widely used, and affordable air conditioners among all types [1,2]. In the past 10 years, with the development of the economy and power supply capacity of China, air conditioning has been widely implemented in houses, schools, offices, and commercial buildings [3]. In 2019, China's output of room air conditioners was 218.662 million, an increase of 4.3% over the previous year [4]. By the end of 2019, every 100 households in China had 115.6 household air conditioners on average [5]. In Hong Kong, China, 32% of the total electricity was used for air conditioning in 2018 [6]. It is predicted that the number of global air conditioners is likely to increase from 1.6 billion at present to 5.6 billion by 2050 [7]. A smart terminal with a relatively low cost and simple structure for FSACs would benefit more than 21% of the world population, so this topic has received wide interest.
The existing research concerning the use of FSACs has the following aspects. Some studies involve optimization of the refrigerant [8,9] and the fan shell parameters [10,11] (such as the thickness and deflection angle of the inlet air deflector, volute curvature, vortex wall angle, and distance from the vortex wall to the fan) of indoor air conditioner units. Some new air conditioners have reduced the draft sensation while ensuring the cooling effect. These methods are available for saving energy or improving efficiency to some extent, but it is time-consuming and expensive to transform an existing air conditioner. Yang et al. [12] introduced personal air-conditioning and sensing technology to an FSAC and suggested a new control algorithm. Zhang et al. [13] used an FSAC and a portable air cleaner to examine the indoor air purification effects of a cleaner according to the installation location of each device. Gao et al. [14] investigated the thermal comfort of FSACs by varying the angle of the guide vanes installed on an FSAC and the installed positions. In addition, some new air distribution methods have been proposed in recent years. Buildings should be ventilated with as much fresh air as possible to dilute SARS-CoV-2-laden aerosols [15,16]. Lin et al. [17,18] proposed stratum ventilation characterized by a fresh air layer directly delivered to the working and breathing area of humans. Li et al. [19,20] proposed air curtain ventilation in which jet flow is delivered to the working area in the form of horizontal diffusion caused by impacting the ground after adhering to a vertical wall. Personalized ventilation [21,22] has been studied to provide a satisfactory local microenvironment for individuals and various other forms of air distribution. As shown above, very few studies have investigated how to reduce the draft sensation of an FSAC from the external environment. How to learn from the established forms of air distribution and refine the FSAC from the external perspective remains a problem to be solved.
Humans are the object and target for air distribution in civil and office buildings but are also the most uncertain obstacle [23]. Air jets are entrained in the room and contact the wall. With the increasing height of the air outlet, the air supply velocity decreases, and the cross-section of the air jet increases. In other words, different parameters of the air jet are required for different relative positions between the air supply outlet and any humans present. Thus, it is necessary to introduce technology to identify human positions. Information on the behaviors of humans in the room has been used to optimize the start/stop operation of the air conditioner system to effectively save energy [24]. Erickson et al. [25] determined the number of passengers by using passive infrared sensors and video tracking systems and then estimated the corresponding required ventilation rate. Mutis et al. [26] developed a new method of visual sensor occupancy perception based on human motion analysis, which could control the indoor air quality more effectively. Meng et al. [27] proposed a real-time estimation method for the human load in a building space and a predictive control strategy for air conditioners integrated with image information. Kim et al. [28] developed a human-adaptive air conditioner that creates a comfortable thermal environment for humans by measuring human factors with a nonterminal indoor positioning system. These studies show that human identification can be effectively combined with an air conditioner system, to improve thermal comfort for humans, realize demand-based air supply, or save energy consumption. However, there has been little research on combining human body recognition and the air supply of FSACs to set the air supply to the appropriate parameters. This work aims to solve this problem.
There are many indexes for evaluating the air distribution in a room, including the ventilation efficiency (energy utilization), air velocity uniformity coefficient, air temperature uniformity coefficient, age of air, predicted mean vote (PMV), predicted percentage of dissatisfied (PPD), air diffusion performance index (ADPI), and fast cooling effect index (FCEI) [[29], [30], [31], [32], [33], [34]]. In the evaluation of the air supply of floor-standing room air conditioners, two factors should be considered. One is air accessibility; that is, air should be supplied to the working area where humans are located. The other is the draft sensation; that is, the draft sensation should be reduced at the position of the air supply. None of the above indexes considers the two factors at the same time, so an evaluation index to describe the two factors mentioned above is needed.
This study introduces a new smart terminal for FSACs based on the identification of human positions in the room. A series of optimizations are made to the smart terminal, and finally, an optimal form is determined. A targeted air supply evaluation index for evaluating the effect of air supply in the occupied zone is proposed. The indoor air velocity distribution and the air velocity target value (AVTV) before and after installing the smart terminal are analyzed by using numerical simulation and full-scale experiments. Compared with other existing manually controlled terminals purchased online, the terminal proposed in this paper produces a significantly low AVTV and reduces the draft sensation of humans in the room while ensuring the cooling effect. This paper provides a new perspective on the air distribution of the most common FSAC in the world.
Section snippets
Idea generation
Taking a real room as an example, this section proposes all the concepts involved, such as the air velocity target value (AVTV), and the occupied zone, and introduces the preliminary idea and implementation process of the smart terminal, which may reduce the draft sensation of traditional floor-standing room air conditioners.
Research methods
The research methods for air distribution in the room mainly include numerical simulation and experimental research [35]. In this study, numerical simulation is used to optimize the four factors mentioned in Table 1 and calculate the air velocity contour of the room theoretically. A full-scale experiment is used to verify the accuracy of the numerical simulation and the air supply effect in the occupied zone after the terminal is installed. The combination of these two methods makes this study
Results
To determine the optimal parameters of the terminal, an orthogonal experiment was designed in this section, and CFD numerical simulation was used to determine the four parameters described in Table 1 (the distance L between the terminal and the air outlet, the rotation angle θ, the width × height W × H of the baffle and the opening width B).
Discussion
The following work is carried out to analyze and verify the effect of the smart terminal on creating a good air velocity field in the room. Section 5.1 analyzes the air velocity contour calculated by CFD numerical simulation before and after the installation of the terminal. Section 5.2 verifies and compares the experimental results and numerical simulation results. Section 5.3 compares the air velocity target values of the smart terminal with several other terminals that were purchased online
Conclusions
In view of the draft sensation caused by the direct impact of cold air from floor-standing room air conditioners (FSACs) on humans and the uncertainty of the positions of occupants in rooms, this paper proposes a new smart terminal. The main conclusions are as follows:
This study proposes a new smart terminal that can be automatically adjusted according to the different positions of occupants in a room. This terminal is adjusted periodically and automatically based on the different positions of
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This research project was sponsored by the Opening Funds of State Key Laboratory of Building Safety and Built Environment and National Engineering Research Center of Building Technology (Grant No. BSBE2019-08), the National Key R&D Program of China (Grant No. 2017YFC0702800), the National Natural Science Foundation of China (Grant Nos. 51878533 and 51508442), the Natural Science Foundation of Shaanxi Province (Grant No. 2019JM-233), the Industrialization Fund of Shaanxi Provincial Department of
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2023, Applied Thermal EngineeringCitation Excerpt :Particularly in hot summer, as a large amount of heat is transferred from the external walls to the indoor environment, it is likely to cause overheating around the area near the exterior wall, and then produce a large-scale indoor circulation, which can increase the air velocity in the occupied area and consequently provoke draught risk [22,23]. In addition, the optimization for the supply vane angle of FSAC is generally for several people in a small office in literature [18,24]. However, in practice, FSAC system is generally installed in medium-sized and large rooms with many people because of its high cooling capacity.