Energy performance of a bedroom task/ambient air conditioning (TAC) system applied in different climate zones of China

doi:10.1016/j.energy.2018.06.211

Energy

Volume 159, 15 September 2018, Pages 724-736

https://doi.org/10.1016/j.energy.2018.06.211 Get rights and content

Highlights

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A CFD study was conducted on TAC system applied in different climate zones.
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RSM method was used to predict energy consumption of TAC system.
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Total energy consumption in summer ranged from 0 to 58.33 kWh in different cities.
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Increasing the t_oz can reduce energy consumption by 23.42%–36.23%.
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VAT (variable air temperature) operating mode can help save energy consumption.

Abstract

Task/ambient air conditioning (TAC) system applied to bedrooms has been investigated and its energy efficient performance reported. To promote the application of bedroom TAC to a larger region, a numerical study was carried out on a bedroom TAC system applied in five different climate zones. To simplify the numerical study, response surface methodology (RSM) was used to predict operating power of TAC based on CFD results. It's found that the daily energy consumption in the typical day was from 0 kWh in Kunming to 1.27 kWh in Shanghai, the averaged daily energy consumption varied from 0.47 kWh in June to 0.56 kWh in August for Guangzhou, and the total energy consumption in summer ranged from 0 kWh in Kunming to 58.33 kWh in Guangzhou. Meanwhile, the operating time of the TAC were also different between these five cities. In order to save energy, different set points of t_oz (average air temperature in the occupied zone) were investigated. It's found that increasing the t_oz from 24 to 25 °C can reduce energy consumption by about 23.42% in Shanghai to 36.23% in Beijing. Besides, the energy saving potential using two operating modes were compared: variable air flow rate and variable air temperature.

Introduction

The varying outdoor air temperature results to the variation of indoor air temperature due to the heat transfer through the envelope. To reduce the effect of varying outdoor air temperature, two types of method were adopted: passive cooling and active cooling. The former includes using PCM (phase change materials), changing envelope insulation, and ventilation. Lei et al. [1] investigated the building envelope with PCM, and found that PCM reduced the change of indoor air temperature and cooling load. Huang et al. [2] investigated the thermal insulation of building, and found that employing thermal insulation can significantly reduce cooling load through the building external wall. Evola et al. [3] proposed night-time ventilation to reduce the cooling load. The typical method for the latter is using air conditioners. The latter is air conditioner which has been widely used to maintain a suitable thermal environment [4]. It can be seen that, the air conditioner can weaken the variation of indoor air temperature [5]. Traditionally, full volume air conditioning (FAC) system was used. In order to reduce the energy use, task/ambient air conditioning (TAC) systems were introduced [6,7].

TAC systems have attracted increasingly research attention, due to their excellent performances in local thermal environmental control and energy saving [7,8]. On one hand, by allowing individual occupants to control their thermal environments, their individual thermal comfort preferences can be accommodated. On the other hand, the use of TAC systems also helped achieve energy saving. This was because when a full volume air conditioning (FAC) system was used, a comfortable indoor environment for everywhere in a room may be maintained. However, when a TAC system was used, only a comfortable indoor environment within an occupied zone would be maintained, but air temperatures outside the occupied zone were allowed to fluctuate to even out of comfort limits. Pan et al. [9] experimentally compared the performance of a personalized air-conditioning system, which was called an innovative partition-type fan-coil unit, with that of a central air conditioning system, in terms of thermal comfort achieved and cooling energy consumed. The experimental results indicated that the use of the personalized system can reduce the duration required in achieving the same level of thermal comfort, and save up to 45% of energy use. Pan et al. [10] studied the energy utilization of bed-based TAC system, and Mao et al. [11] carried out an experimental study on the energy utilization of a ductless bed-based TAC system. They found that both TAC had much better energy utilization than traditional air conditioning system. However, most of these studies focused on the use of TAC in a certain region which belongs to hot and humid climate zone, such as Hong Kong [10,11] and Taiwan [9]. When it comes to applying the TAC system in a larger region, the effect of different climate zones should be considered.

Due to the temperature in different climate zones are significantly different, which results in different performance of building envelope and air conditioning system. Some researchers studied the building envelope in different cities of China. Yang et al. selected five cities: Harbin, Beijing, Shanghai, Kunming and Hong Kong, and studied the energy performance of building envelope [12]. It was found that the heat gain through the building envelope varied from 1.0 kW h/m² in Kunming to 23.5 kW h/m² in Beijing. Su et al. investigated the heat gain or a room using double-skin façade in four cities of China: Harbin, Beijing, Shanghai, and Guangzhou [13]. The different impacts of the design of façade on heat gain were observed in different cities. Zeng et al. studied the annual energy of building using green roof in Harbin, Beijing, Chongqing and Guangzhou representing four different climate zones [14]. The study results showed the performance of roof was closely related to the climates, and recommended suitable optimal parameters of roof for each city. Yu et al. studied the energy and thermal performance for office building envelop (EETPO) in three cities (Shenyang, Wuhan and Guangzhou) in different climate zones of China, and found that the maximum EETPO values were different from 0.2 W/m³K in Shenyang to 1.733 W/m³K in Guangzhou. Besides, the cooling system performances in different climate zones were also investigated. Ge et al. [15] investigated the air cooling system in six cities in China. The different relations between energy consumption and air temperature and relative humidity were displayed in these cities. Lam et al. [16] simulated the cooling load of a generic office building in five cities of China (Harbin, Shanghai, Hong Kong, Beijing, Kunming). The monthly variation of cooling load and obvious difference between these five cities were showed due to their different climate zones. Hence, for a bedroom TAC system, its energy performance is supposed to be different when it's applied to different climate zones. Therefore, it's necessary to investigate this issue for better application of TAC.

To address this concern, a numerical study on a previously developed bedroom TAC system was carried out. The objective of this study was to investigate the energy performance of the bedroom TAC system applied in different climate zones. In this study, firstly, China as a typical country which has a very large area and significantly different climate zones, was selected as the investigated country. Secondly, the CFD study was carried out on the bedroom TAC using the environmental parameters. Thirdly, predictive models of energy consumption were established using RSM method. Afterwards, the energy performance of the TAC system in different cities were predicted and analyzed.

Section snippets

Aims and methodology

The methodology of this study is shown in Fig. 1. The study was carried out in four steps: environmental parameter calculation, CFD simulation, predictive model establishment and energy consumption analysis. Firstly, typical cities in five climate zones were selected and the integrated temperature of envelope outside surface (EOT) was calculated. This temperature was set as the input parameter of the CFD simulation. Secondly, according to the ranges of supply air temperature, supply air flow

Results and analysis

Using the simulated air temperature, humidity and flow distributions inside the experimental bedroom from the CFD method, the P_o and t_oz values for the 27 simulation cases were calculated and summarized in Table 4.

Effects of set points

Fig. 15 shows the energy consumption of TAC in the typical day in five cities with two different set points: t_oz = 24 and t_oz = 25 °C. It can be seen that increasing t_oz results in the decrease in energy consumption. The decreased value can reach to around 1000 kJ (0.30 kWh) in Beijing, Shanghai and Guangzhou, as shown in Fig. 13. And the largest decrease of 1084.74 kJ (0.30 kWh) was found in Beijing, with a percentage of 36.23% accounting for the energy consumption. Therefore, increasing the

Conclusions

A numerical study on the energy performance of TAC system applied in different climate zones of China were carried out in this paper. Based on the CFD simulation results, RSM method was used to establish the predictive model of energy consumption. Considering the different environmental parameters of the selected five cities, RSM method was an effective methodology to save computation cost to obtain the final energy consumption values in different cities based on the limited number of CFD

Acknowledgements

The study was supported by the Fundamental Research Funds for the Central Universities (Project No.: 18CX02077A), Shandong Provincial Natural Science Foundation, China (Project No.: ZR2016EEQ29), Research Foundation for Talents of China University of Petroleum (East China) (Project No.: YJ201501018), and National Natural Science Foundation of China under Grant No. 51606044.

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Energy performance of a bedroom task/ambient air conditioning (TAC) system applied in different climate zones of China

Highlights

Abstract

Introduction

Section snippets

Aims and methodology

Results and analysis

Effects of set points

Conclusions

Acknowledgements

Appl Energy

Appl Energy

Energ Procedia

Build Environ

Build Environ

Energy Convers Manag

Build Environ

Energy Build

Energy Build

Energy Build

Appl Energy

Sol Energy

Energy Build

Energy Build

Energy Convers Manag

Energy Build

Energy Build

Appl Energy

Build Environ

Appl Energy

Build Environ

Energy Build