The use of air conditioning and refrigeration systems improved the standard of living. However, the system contributes to global warming by releasing potential global warming refrigerants directly and powering the sys...The use of air conditioning and refrigeration systems improved the standard of living. However, the system contributes to global warming by releasing potential global warming refrigerants directly and powering the system. There is an obligation, like UN Kyoto Protocol, EU MAC Directive and Japan METI Directive to find an alternative low-GWP refrigerant with excellent thermophysical properties. In this paper, the global warming effect of an air-conditioning system is analyzed theoretically using few low-GWP refrigerant mixtures. New refrigerant mixtures are formed based on low GWP, high volumetric capacity, and refrigerating effect. After analyzing, refrigerant blends of R1234yf/R32 (40/60, 50/50, and 60/40 by wt%) and R1234ze/R32 (40/60, 50/50, and 60/40 by wt%) are found promising to replace the widely used R410A. The best performance of the refrigerant blend is found for R1234yf/R32 (40/60). These analyses are crucial for selecting suitable refrigerants for domestic air conditioning systems.展开更多
To explore the relationship between summer office set air-conditioning temperature and energy consumption related to air conditioning use to provide human thermal comfort,a comparison experiment was conducted in three...To explore the relationship between summer office set air-conditioning temperature and energy consumption related to air conditioning use to provide human thermal comfort,a comparison experiment was conducted in three similar offices at temperatures of 24,26 and 28 ℃ respectively. A thermal comfort questionnaire survey was conducted. It is demonstrated that air-conditioner energy consumption at the set temperature of 28 ℃ is 113% and 271% lower than at 26 ℃ and 24 ℃,respectively. A linear relationship exists between air-conditioner energy consumption and the indoor and outdoor temperature difference. When comfortably dressed,over 80% of research participants accept the set temperature of 28 ℃. The regression analysis leads to a neutral temperature of 26.2 ℃ and an acceptable temperature of 28.2 ℃ for over 80% of the research participants subjects,indicating that the current 26 ℃ set temperature for offices in summer,required by Chinese General Office of the State Council,can be increased to 28 ℃. Moreover,analysis of predicted mean vote(PMV) index shows that a set temperature of 27 ℃,not 26 ℃,is sufficiently comfortable for office staff wearing long-sleeve shirts,long pants and leather shoes.展开更多
DC-inverter split air-conditioner is widely used in Chinese homes as a result of its high-efficiency and energy-saving. Recently, the researches on its outdoor unit have focused on the influence of surrounding structu...DC-inverter split air-conditioner is widely used in Chinese homes as a result of its high-efficiency and energy-saving. Recently, the researches on its outdoor unit have focused on the influence of surrounding structures upon the aerodynamic and acoustic performance, however they are only limited to the influence of a few parameters on the performance, and practical design of the unit requires more detailed parametric analysis. Three-dimensional computational fluid dynamics（CFD） and computational aerodynamic acoustics（CAA） simulation based on FLUENT solver is used to study the influence of surrounding structures upon the aforementioned properties of the unit. The flow rate and sound pressure level are predicted for different rotating speed, and agree well with the experimental results. The parametric influence of three main surrounding structures（i.e. the heat sink, the bell-mouth type shroud and the outlet grille） upon the aerodynamic performance of the unit is analyzed thoroughly. The results demonstrate that the tip vortex plays a major role in the flow fields near the blade tip and has a great effect on the flow field of the unit. The inlet ring＇s size and throat＇s depth of the bell-mouth type shroud, and the through-flow area and configuration of upwind and downwind sections of the outlet grille are the most important factors that affect the aerodynamic performance of the unit. Furthermore, two improved schemes against the existing prototype of the unit are developed, which both can significantly increase the flow rate more than 6 %（i.e. 100 m3·h～（-1）） at given rotating speeds. The inevitable increase of flow noise level when flow rate is increased and the advantage of keeping a lower rotating speed are also discussed. The presented work could be a useful guideline in designing the aerodynamic and acoustic performance of the split air-conditioner in engineering practice.展开更多
Aim: To investigate the effect of air-conditioner exposure on semen quality. Methods: The data came from the healthy male volunteers, aged 22 to 30 years, who went to centers for maternity and children health for prem...Aim: To investigate the effect of air-conditioner exposure on semen quality. Methods: The data came from the healthy male volunteers, aged 22 to 30 years, who went to centers for maternity and children health for premarital physical examination in Shanghai, Henan, Zhejiang and Hebei from December 1998 to February 2000. The sampling size is 304. Results: Among the subjects, 90 (29.6 %) had air-conditioner at home and the rest did not. X2-test and multiple logistic regression analyses showed that, the difference between the exposure and control groups was statistically significant in semen volume, sperm density and proportion of sperm with normal morphology. The three indexes were lower in the exposure group. Conclusion: Air-conditioner exposure possibly influences the semen quality.展开更多
A subgroup H of G is called s-conditionally permutable in G if for every Sylow subgroup T of G, there exists an element x ∈ G such that HTK = T^KH. In this paper, we investigate further the influence of s-conditional...A subgroup H of G is called s-conditionally permutable in G if for every Sylow subgroup T of G, there exists an element x ∈ G such that HTK = T^KH. In this paper, we investigate further the influence of s-conditionally permutability of some 2-maximal subgroups of the Sylow subgroup of G, on the structure of finite groups. New criteria for a group G being p-nilpotent are obtained.展开更多
More and more studies reported that there were insufficient ventilation and excessive CO_2 concentration in air-conditioned residential buildings, but few solutions were provided. This study investigates the overnight...More and more studies reported that there were insufficient ventilation and excessive CO_2 concentration in air-conditioned residential buildings, but few solutions were provided. This study investigates the overnight evolution of CO_2 concentration in air-conditioned residential buildings and then focuses mainly on the evaluation of three ventilation strategies, including overnight natural ventilation, short-term mechanical ventilation and short-term natural ventilation. On-site measurements were conducted in a typical residential bedroom in Hong Kong in September. The indoor and outdoor CO_2 concentration, air temperature and relative humidity as well as the outdoor wind speed during the measurements were analysed. Ventilation rates were calculated based on the time series of CO_2 concentration. This study confirms that additional ventilation is usually needed in air-conditioned residential buildings. Overnight natural ventilation with even a small opening is associated with excessive energy consumption and deteriorated indoor thermal environment. Short-term natural ventilation strategies are inefficient and uncontrollable. Compared to the best short-term natural ventilation strategy, a reasonably designed short-term mechanical ventilation strategy requires only a 41% of ventilation period to complete one full replacement of indoor air and to reach a lower indoor CO_2 concentration. Nighttime case studies and a theoretical analysis suggest that a few several-minute mechanical ventilation periods could potentially maintain an acceptable indoor air quality for a normal sleeping period of 8 h.展开更多
A subgroup H of a group G is called s-conditionally permutable in G if for every Sylow subgroup T of G there exists an element x ∈ G such that HTx = TxH. Using the concept of s-conditionally permutable subgroups, som...A subgroup H of a group G is called s-conditionally permutable in G if for every Sylow subgroup T of G there exists an element x ∈ G such that HTx = TxH. Using the concept of s-conditionally permutable subgroups, some new characterizations of finite groups are obtained and several interesting results are generalized.展开更多
Let G be a finite group. Fix a prime divisor p of IGI and a Sylow p-subgroup P of G, let d be the smallest generator number of P and Ma（P） denote a family of maximal subgroups P1, P2 , Pd of P satisfying ∩^di=1 Pi...Let G be a finite group. Fix a prime divisor p of IGI and a Sylow p-subgroup P of G, let d be the smallest generator number of P and Ma（P） denote a family of maximal subgroups P1, P2 , Pd of P satisfying ∩^di=1 Pi = Ф（P）, the Frattini subgroup of P. In this paper, we shall investigate the influence of s-conditional permutability of the members of some fixed .Md（P） on the structure of finite groups. Some new results are obtained and some known results are generalized.展开更多
为降低城市化进程中楼宇储能投资成本,提出一种基于共享储能服务的智能楼宇(intelligent buildings,IBs)双层优化配置方法。首先,建立计及寿命周期的共享储能电站(shared energy storage station,SESS)模型;其次,基于楼宇建筑物热惯性,...为降低城市化进程中楼宇储能投资成本,提出一种基于共享储能服务的智能楼宇(intelligent buildings,IBs)双层优化配置方法。首先,建立计及寿命周期的共享储能电站(shared energy storage station,SESS)模型;其次,基于楼宇建筑物热惯性,构建含空调系统的IBs数学模型;然后,综合考虑SESS与IBs的差异化利益诉求,建立基于SESS的IBs双层优化模型。上层模型目标函数旨在降低SESS的规划成本,下层模型目标函数旨在降低IBs的年运行成本,并采用卡罗需-库恩-塔克(Karush-Kuhn-Tucher,KKT)条件将原双层优化问题转换为单层混合整数线性规划问题进行求解。最后,以3个IBs社区的四季典型日为例,对比分析不同优化配置方法对于IBs运行和SESS配置结果的影响。结果表明,在满足IBs用户温度舒适性的同时,所提双层优化配置方法可充分满足SESS运营商与IBs的差异化利益诉求,实现双方的共赢。展开更多
文摘The use of air conditioning and refrigeration systems improved the standard of living. However, the system contributes to global warming by releasing potential global warming refrigerants directly and powering the system. There is an obligation, like UN Kyoto Protocol, EU MAC Directive and Japan METI Directive to find an alternative low-GWP refrigerant with excellent thermophysical properties. In this paper, the global warming effect of an air-conditioning system is analyzed theoretically using few low-GWP refrigerant mixtures. New refrigerant mixtures are formed based on low GWP, high volumetric capacity, and refrigerating effect. After analyzing, refrigerant blends of R1234yf/R32 (40/60, 50/50, and 60/40 by wt%) and R1234ze/R32 (40/60, 50/50, and 60/40 by wt%) are found promising to replace the widely used R410A. The best performance of the refrigerant blend is found for R1234yf/R32 (40/60). These analyses are crucial for selecting suitable refrigerants for domestic air conditioning systems.
基金Project(50838009) supported by the National Natural Science Foundation of ChinaProjects(2006BAJ02A09,2006BAJ02A13-4) supported by the National Key Technologies R & D Program of China
文摘To explore the relationship between summer office set air-conditioning temperature and energy consumption related to air conditioning use to provide human thermal comfort,a comparison experiment was conducted in three similar offices at temperatures of 24,26 and 28 ℃ respectively. A thermal comfort questionnaire survey was conducted. It is demonstrated that air-conditioner energy consumption at the set temperature of 28 ℃ is 113% and 271% lower than at 26 ℃ and 24 ℃,respectively. A linear relationship exists between air-conditioner energy consumption and the indoor and outdoor temperature difference. When comfortably dressed,over 80% of research participants accept the set temperature of 28 ℃. The regression analysis leads to a neutral temperature of 26.2 ℃ and an acceptable temperature of 28.2 ℃ for over 80% of the research participants subjects,indicating that the current 26 ℃ set temperature for offices in summer,required by Chinese General Office of the State Council,can be increased to 28 ℃. Moreover,analysis of predicted mean vote(PMV) index shows that a set temperature of 27 ℃,not 26 ℃,is sufficiently comfortable for office staff wearing long-sleeve shirts,long pants and leather shoes.
基金Supported by Program for Changjiang Scholars and Innovative Research Team in University,Ministry of Education of China(PCSIRT)
文摘DC-inverter split air-conditioner is widely used in Chinese homes as a result of its high-efficiency and energy-saving. Recently, the researches on its outdoor unit have focused on the influence of surrounding structures upon the aerodynamic and acoustic performance, however they are only limited to the influence of a few parameters on the performance, and practical design of the unit requires more detailed parametric analysis. Three-dimensional computational fluid dynamics（CFD） and computational aerodynamic acoustics（CAA） simulation based on FLUENT solver is used to study the influence of surrounding structures upon the aforementioned properties of the unit. The flow rate and sound pressure level are predicted for different rotating speed, and agree well with the experimental results. The parametric influence of three main surrounding structures（i.e. the heat sink, the bell-mouth type shroud and the outlet grille） upon the aerodynamic performance of the unit is analyzed thoroughly. The results demonstrate that the tip vortex plays a major role in the flow fields near the blade tip and has a great effect on the flow field of the unit. The inlet ring＇s size and throat＇s depth of the bell-mouth type shroud, and the through-flow area and configuration of upwind and downwind sections of the outlet grille are the most important factors that affect the aerodynamic performance of the unit. Furthermore, two improved schemes against the existing prototype of the unit are developed, which both can significantly increase the flow rate more than 6 %（i.e. 100 m3·h～（-1）） at given rotating speeds. The inevitable increase of flow noise level when flow rate is increased and the advantage of keeping a lower rotating speed are also discussed. The presented work could be a useful guideline in designing the aerodynamic and acoustic performance of the split air-conditioner in engineering practice.
文摘Aim: To investigate the effect of air-conditioner exposure on semen quality. Methods: The data came from the healthy male volunteers, aged 22 to 30 years, who went to centers for maternity and children health for premarital physical examination in Shanghai, Henan, Zhejiang and Hebei from December 1998 to February 2000. The sampling size is 304. Results: Among the subjects, 90 (29.6 %) had air-conditioner at home and the rest did not. X2-test and multiple logistic regression analyses showed that, the difference between the exposure and control groups was statistically significant in semen volume, sperm density and proportion of sperm with normal morphology. The three indexes were lower in the exposure group. Conclusion: Air-conditioner exposure possibly influences the semen quality.
基金The Scientific Research Foundation of Sichuan Provincial Education Department of China(No.08zb082)
文摘A subgroup H of G is called s-conditionally permutable in G if for every Sylow subgroup T of G, there exists an element x ∈ G such that HTK = T^KH. In this paper, we investigate further the influence of s-conditionally permutability of some 2-maximal subgroups of the Sylow subgroup of G, on the structure of finite groups. New criteria for a group G being p-nilpotent are obtained.
文摘More and more studies reported that there were insufficient ventilation and excessive CO_2 concentration in air-conditioned residential buildings, but few solutions were provided. This study investigates the overnight evolution of CO_2 concentration in air-conditioned residential buildings and then focuses mainly on the evaluation of three ventilation strategies, including overnight natural ventilation, short-term mechanical ventilation and short-term natural ventilation. On-site measurements were conducted in a typical residential bedroom in Hong Kong in September. The indoor and outdoor CO_2 concentration, air temperature and relative humidity as well as the outdoor wind speed during the measurements were analysed. Ventilation rates were calculated based on the time series of CO_2 concentration. This study confirms that additional ventilation is usually needed in air-conditioned residential buildings. Overnight natural ventilation with even a small opening is associated with excessive energy consumption and deteriorated indoor thermal environment. Short-term natural ventilation strategies are inefficient and uncontrollable. Compared to the best short-term natural ventilation strategy, a reasonably designed short-term mechanical ventilation strategy requires only a 41% of ventilation period to complete one full replacement of indoor air and to reach a lower indoor CO_2 concentration. Nighttime case studies and a theoretical analysis suggest that a few several-minute mechanical ventilation periods could potentially maintain an acceptable indoor air quality for a normal sleeping period of 8 h.
基金supported by National Natural Science Foundation of China (Grant No. 10771180)Scientific Research Fund of Sichuan Provincial Education Department (Grant No. 08zb059)Research Programme of Chengdu University of Information Technology
文摘A subgroup H of a group G is called s-conditionally permutable in G if for every Sylow subgroup T of G there exists an element x ∈ G such that HTx = TxH. Using the concept of s-conditionally permutable subgroups, some new characterizations of finite groups are obtained and several interesting results are generalized.
基金Supported by the National Natural Science Foundation of China (Grant No.11071229)the Natural Science Foundation of the Jiangsu Higher Education Institutions of China (Grant No.10KJD110004)the Postgraduate Innovation Grant of Xuzhou Normal University
文摘Let G be a finite group. Fix a prime divisor p of IGI and a Sylow p-subgroup P of G, let d be the smallest generator number of P and Ma（P） denote a family of maximal subgroups P1, P2 , Pd of P satisfying ∩^di=1 Pi = Ф（P）, the Frattini subgroup of P. In this paper, we shall investigate the influence of s-conditional permutability of the members of some fixed .Md（P） on the structure of finite groups. Some new results are obtained and some known results are generalized.
文摘为降低城市化进程中楼宇储能投资成本,提出一种基于共享储能服务的智能楼宇(intelligent buildings,IBs)双层优化配置方法。首先,建立计及寿命周期的共享储能电站(shared energy storage station,SESS)模型;其次,基于楼宇建筑物热惯性,构建含空调系统的IBs数学模型;然后,综合考虑SESS与IBs的差异化利益诉求,建立基于SESS的IBs双层优化模型。上层模型目标函数旨在降低SESS的规划成本,下层模型目标函数旨在降低IBs的年运行成本,并采用卡罗需-库恩-塔克(Karush-Kuhn-Tucher,KKT)条件将原双层优化问题转换为单层混合整数线性规划问题进行求解。最后,以3个IBs社区的四季典型日为例,对比分析不同优化配置方法对于IBs运行和SESS配置结果的影响。结果表明,在满足IBs用户温度舒适性的同时,所提双层优化配置方法可充分满足SESS运营商与IBs的差异化利益诉求,实现双方的共赢。
