Heating-only fan coil(HFC)is one of the suited end users,which is not only compact but also highly efficient.And the major factors affecting the heat dissipation performance of HFC include leakage through coil bypass,...Heating-only fan coil(HFC)is one of the suited end users,which is not only compact but also highly efficient.And the major factors affecting the heat dissipation performance of HFC include leakage through coil bypass,distance between fan and coil,fan structure and air inlet type.Under natural air convection or forced,experimental studies were made on the effects of these factors upon the heat dissipation performance of HFC.The results show that:1)After reducing the leakage through coil bypass,the heat dissipation of HFC increases 16.9% under natural convection,and increases 8.3% under forced convection.2)After the distance between fan and coil be raised from 23.2cm to 41.7cm,the heat dissipation of HFC decreases 21.3% under natural convection,but increases12.8% under forced convection.3)After changing the fan structure,the heat dissipation of HFC increases 41.8% under natural convection,and the heat dissipation per motor power increases 96.1% under forced convection.4)The heat dissipations of HFC with round pass,slit and strip type of air inlet are different,whose proportion is about 100%,110%,136% under natural convection,and 100%,105%,116% under forced convection.展开更多
Curtain-sided barns with circulation fans above stall are commonly used to house dairy cows in China.Many farms equipped with circulation fans are unable to provide appropriate cooling,especially for the naturally ven...Curtain-sided barns with circulation fans above stall are commonly used to house dairy cows in China.Many farms equipped with circulation fans are unable to provide appropriate cooling,especially for the naturally ventilated shed,which can result in decreasing feed intake and milk production.For alleviating heat stress and improving animal comfort,a system consisting of an air cooler and a 30 m perforated air duct(PAD)was integrated to evenly distribute cooling air.The air was cooled by underground water and delivered to targeted zones above stall bed.The system was evaluated in an open sided dairy barn in Tianjin,China.For the stalls equipped with PAD system,air velocity reached above 1.1 m/s at 0.5 m height plane of the stall space,and was more uniformly distributed.Compared to the stalls equipped with circulation fans,the PAD system lowered air temperature by 1.5℃,and increased relative humidity by 8.1%.On average,Temperature Humidity Index(THI)and Equivalent Temperature Index(ETI)were decreased by 0.5 and 0.6,respectively.After a 15 days’operation of the system,rectal temperatures of the treated dairy cows were significantly lowered.The results also showed that the cows under PADs had a higher milk production.These findings suggest the PAD can be an effective cooling alternative for naturally ventilated dairy barns to alleviate heat stress.展开更多
The duct static pressure reset (DSPR) control method is a popular modern control method widely applied to variable air volume (VAV) systems of commercial buildings. In this paper, a VAV system simulation program was u...The duct static pressure reset (DSPR) control method is a popular modern control method widely applied to variable air volume (VAV) systems of commercial buildings. In this paper, a VAV system simulation program was used to predict the system performance and zone air temperature of two kinds of layouts that were applied to a typical floor of an existing building office in Hong Kong. The position where the static pressure sensor was placed should affect the zones temperature and energy consumption. The comparison of predictions of the two kinds of layouts indicates that with the same DSPR control method the layout of the air duct might influence the fan control result and energy savings.展开更多
In this study, we investigated the torque characteristics of large low-speed direct-drive permanent magnet synchronous generators with stator radial ventilating air ducts for offshore wind power applications. Magnet s...In this study, we investigated the torque characteristics of large low-speed direct-drive permanent magnet synchronous generators with stator radial ventilating air ducts for offshore wind power applications. Magnet shape optimization was used first to improve the torque characteristics using two-dimensional finite element analysis（FEA） in a permanent magnet synchronous generator with a common stator. The rotor step skewing technique was then employed to suppress the impacts of mechanical tolerances and defects, which further improved the torque quality of the machine. Comprehensive three-dimensional FEA was used to evaluate accurately the overall effects of stator radial ventilating air ducts and rotor step skewing on torque features. The influences of the radial ventilating ducts in the stator on torque characteristics, such as torque pulsation and average torque in the machine with and without rotor step skewing techniques, were comprehensively investigated using three-dimensional FEA. The results showed that stator radial ventilating air ducts could not only reduce the average torque but also increase the torque ripple in the machine. Furthermore, the torque ripple of the machine under certain load conditions may even be increased by rotor step skewing despite a reduction in cogging torque.展开更多
Based on the corresponding theories of engineering thermodynamics and hydro-dynamics, a careful study is made of the characteristics of air flow in different duct-embedded ways. According to critical Reynolds number, ...Based on the corresponding theories of engineering thermodynamics and hydro-dynamics, a careful study is made of the characteristics of air flow in different duct-embedded ways. According to critical Reynolds number, the atmospheric critical velocity of the duct with different diameters, which makes laminar flow different from turbulent flow, is calculated. Given the condition in which a forced flow occurs and the wind strength is larger than the atmospheric pressure gradient along the air-duct, a rational ratio of the length to the diameter is presented. Based on the above theory and field test data on soil temperature and embankment settlement, the advantages and disadvantages are discussed in details of all duct-embedded ways that might affect the stability of embankment.展开更多
基金Supported by National11th Five-Year Plan Major Scientific and Technological Issues of China(2006BAJ01A04)
文摘Heating-only fan coil(HFC)is one of the suited end users,which is not only compact but also highly efficient.And the major factors affecting the heat dissipation performance of HFC include leakage through coil bypass,distance between fan and coil,fan structure and air inlet type.Under natural air convection or forced,experimental studies were made on the effects of these factors upon the heat dissipation performance of HFC.The results show that:1)After reducing the leakage through coil bypass,the heat dissipation of HFC increases 16.9% under natural convection,and increases 8.3% under forced convection.2)After the distance between fan and coil be raised from 23.2cm to 41.7cm,the heat dissipation of HFC decreases 21.3% under natural convection,but increases12.8% under forced convection.3)After changing the fan structure,the heat dissipation of HFC increases 41.8% under natural convection,and the heat dissipation per motor power increases 96.1% under forced convection.4)The heat dissipations of HFC with round pass,slit and strip type of air inlet are different,whose proportion is about 100%,110%,136% under natural convection,and 100%,105%,116% under forced convection.
基金This study was funded by National High Technology Research and Development Program(2013AA10230602)China Agricultural Research System(CARS-36).A special thank for all the help from Hailin Dairy Farm,Tianjin,China,where the field evaluation was conducted.
文摘Curtain-sided barns with circulation fans above stall are commonly used to house dairy cows in China.Many farms equipped with circulation fans are unable to provide appropriate cooling,especially for the naturally ventilated shed,which can result in decreasing feed intake and milk production.For alleviating heat stress and improving animal comfort,a system consisting of an air cooler and a 30 m perforated air duct(PAD)was integrated to evenly distribute cooling air.The air was cooled by underground water and delivered to targeted zones above stall bed.The system was evaluated in an open sided dairy barn in Tianjin,China.For the stalls equipped with PAD system,air velocity reached above 1.1 m/s at 0.5 m height plane of the stall space,and was more uniformly distributed.Compared to the stalls equipped with circulation fans,the PAD system lowered air temperature by 1.5℃,and increased relative humidity by 8.1%.On average,Temperature Humidity Index(THI)and Equivalent Temperature Index(ETI)were decreased by 0.5 and 0.6,respectively.After a 15 days’operation of the system,rectal temperatures of the treated dairy cows were significantly lowered.The results also showed that the cows under PADs had a higher milk production.These findings suggest the PAD can be an effective cooling alternative for naturally ventilated dairy barns to alleviate heat stress.
文摘The duct static pressure reset (DSPR) control method is a popular modern control method widely applied to variable air volume (VAV) systems of commercial buildings. In this paper, a VAV system simulation program was used to predict the system performance and zone air temperature of two kinds of layouts that were applied to a typical floor of an existing building office in Hong Kong. The position where the static pressure sensor was placed should affect the zones temperature and energy consumption. The comparison of predictions of the two kinds of layouts indicates that with the same DSPR control method the layout of the air duct might influence the fan control result and energy savings.
基金Project supported by the National Natural Science Foundation of China（No.51377140） the National Basic Research Program（973）of China（No.2013CB035604）
文摘In this study, we investigated the torque characteristics of large low-speed direct-drive permanent magnet synchronous generators with stator radial ventilating air ducts for offshore wind power applications. Magnet shape optimization was used first to improve the torque characteristics using two-dimensional finite element analysis（FEA） in a permanent magnet synchronous generator with a common stator. The rotor step skewing technique was then employed to suppress the impacts of mechanical tolerances and defects, which further improved the torque quality of the machine. Comprehensive three-dimensional FEA was used to evaluate accurately the overall effects of stator radial ventilating air ducts and rotor step skewing on torque features. The influences of the radial ventilating ducts in the stator on torque characteristics, such as torque pulsation and average torque in the machine with and without rotor step skewing techniques, were comprehensively investigated using three-dimensional FEA. The results showed that stator radial ventilating air ducts could not only reduce the average torque but also increase the torque ripple in the machine. Furthermore, the torque ripple of the machine under certain load conditions may even be increased by rotor step skewing despite a reduction in cogging torque.
文摘Based on the corresponding theories of engineering thermodynamics and hydro-dynamics, a careful study is made of the characteristics of air flow in different duct-embedded ways. According to critical Reynolds number, the atmospheric critical velocity of the duct with different diameters, which makes laminar flow different from turbulent flow, is calculated. Given the condition in which a forced flow occurs and the wind strength is larger than the atmospheric pressure gradient along the air-duct, a rational ratio of the length to the diameter is presented. Based on the above theory and field test data on soil temperature and embankment settlement, the advantages and disadvantages are discussed in details of all duct-embedded ways that might affect the stability of embankment.
