The performances of a refrigeration unit relying on compressors working in parallel have been investigated considering the influence of the compressor volumetric efficiency and isentropic efficiency on the compression...The performances of a refrigeration unit relying on compressors working in parallel have been investigated considering the influence of the compressor volumetric efficiency and isentropic efficiency on the compression ratio.Moreover,the following influential factors have been taken into account:evaporation temperature,condensation temperature and compressor suction-exhaust pressure ratio for different opening conditions of the compressor.The following quantities have been selected as the unit performance measurement indicators:refrigeration capacity,energy efficiency ratio(COP),compressor power consumption,and refrigerant flow rate.The experimental results indicate that the system refrigeration capacity and COP decrease with a decrease in evaporation temperature,increase of condensation temperature,and increase in pressure ratio.The refrigerant flow rate increases with the increase in evaporation temperature,decrease in condensing temperature and increase in pressure ratio.The compressor power consumption increases with the increase in condensing temperature and increase in pressure ratio,but is not significantly affected by the evaporation temperature.展开更多
In hot arid countries with severe weather, the summer air conditioning systems consume much electrical power at peak period. Shifting the loads peak to off-peak period with thermal storage is recommended. Model A of r...In hot arid countries with severe weather, the summer air conditioning systems consume much electrical power at peak period. Shifting the loads peak to off-peak period with thermal storage is recommended. Model A of residential buildings and Model B of schools and hospitals were used to estimate the daily cooling load profile in Makkah, Saudi Arabia at latitude of 21.42°N and longitude of 39.83°E. Model A was constructed from common materials, but Model B as Model A with 5 - 8 cm thermal insulation and double layers glass windows. The average data of Makkah weather through 2010, 2011 and 2012 were used to calculate the cooling load profile and performance of air conditioning systems. The maximum cooling load was calculated at 15:00 o’clock for a main floor building to a 40-floor of residential building and to 5 floors of schools. A district cooling plant of 180,000 Refrigeration Ton was suggested to serve the Gabal Al Sharashf area in the central zone of Makkah. A thermal storage system to store the excess cooling capacity was used. Air cooled condensers were used in the analysis of chiller refrigeration cycle. The operating cost was mainly a function of electrical energy consumption. Fixed electricity tariff was 0.04 $/kWh for electromechanical counter, and 0.027, 0.04, 0.069 $/kWh for shifting loads peak for the smart digital counter. The results showed that the daily savings in consumed power are 8.27% in spring, 6.86% in summer, 8.81% in autumn, and 14.55% in winter. Also, the daily savings in electricity bills are 12.26% in spring, 16.66% in summer, 12.84% in autumn, and 14.55% in winter. The obtained maximum saving in consumed power is 14.5% and the daily saving in electricity bills is 43% in summer when the loads peak is completely shifted to off-peak period.展开更多
This paper presents the evaluation of the “capacity to the total energy consumption per bit ratio” of multiple antennas systems with distributed fashion. We propose an adequate geometric channel modeling for the wir...This paper presents the evaluation of the “capacity to the total energy consumption per bit ratio” of multiple antennas systems with distributed fashion. We propose an adequate geometric channel modeling for the wireless communication system which operates in indoor propagation environment with scatterers. The channel model is derived in function of both the line of sight (LOS) and the non line of sight (NLOS) components. The aim of this paper is to study the limits in the gain concerning the capacity to the total energy consumption ratio when additional antennas are implemented in the communication system. To do so, we have evaluated by simulations both the capacity and the total energy consumption per bit. Then, we have determined the capacity to the total energy consumption ratio. Finally, the computational capacity to the total energy ratio is obtained for different system configurations. We have shown that the gain in capacity increases with the number of antennas but it stills be limited by the total energy consumption. The limits for increasing the number of transmit antennas are determined in function of the separation distances between the transmitter and the receiver sides of the communication system. Optimal power allocation strategy via water-filling algorithm has been carried out for evaluating the capacity to energy ratio. We find by simulation that optimal power allocation brings a gain in the addressed metric reaching a level of about 1.7 at transmit signal to noise ratio of 8 dB if comparing to the case when transmit energy is equally split among transmit antennas.展开更多
Earth tubes are earth-to-air heat exchangers that are frequently utilized in energy conscious low-rise buildings, but are scarcely reported for tall buildings. The feasibility of applying earth tube cooling to tall bu...Earth tubes are earth-to-air heat exchangers that are frequently utilized in energy conscious low-rise buildings, but are scarcely reported for tall buildings. The feasibility of applying earth tube cooling to tall buildings in a hot summer and cold winter climate zone was studied in this paper. Firstly, the designed cooling load of a tall building was obtained from the energy simulation using the baseline and the modified models with applicable energy efficiency measures. Based on the load, the required cooling capacity, the overall section area and the effective length of the earth tube system was deduced from the heat transfer and fluid flow calculation analytically. Then the performance of the earth tube system was crosschecked and verified via the Computational Fluid Dynamics (CFD) simulation. In the CFD simulation, earth tubes with different diameters and lengths, as well as a full-scale earth tube model with surrounding soil above the depth of constant temperature, were investigated. The outlet air temperatures of the full-scale models were computed with the consideration of different axial distances between adjacent tubes. Meanwhile, multiple conceptual design schemes and the tunnel construction method for the earth tube system were proposed from the perspective of performance enhancement, constructability, efficiency and economy. It revealed that earth tube systems are conditionally feasible for some tall buildings if their design guidelines for climate, underground spaces, construction method, friction of tube interior surface, optimization of effective length and axial distance, as well as synergy with other energy efficiency measures are followed. Even the cooling capacity of earth tubes degrade with time due to the accumulated heat underground, but in a hot summer and cold winter climate zone it can still possibly produce cooled air for a tall building with a Floor Area Ratio of less than 7 effectively in summer.展开更多
为降低数据中心制冷系统的能耗,搭建了一种磁力泵驱动的两相冷却复合制冷装置,并对其进行了实验研究。结果表明,室外温度15℃时,泵循环模式的EER随冷凝器迎面风速先增大后减小,当风速为1 m/s时EER获得最大值。在热负荷为7.3 k W条件下,...为降低数据中心制冷系统的能耗,搭建了一种磁力泵驱动的两相冷却复合制冷装置,并对其进行了实验研究。结果表明,室外温度15℃时,泵循环模式的EER随冷凝器迎面风速先增大后减小,当风速为1 m/s时EER获得最大值。在热负荷为7.3 k W条件下,实验获得了两种运行模式的最佳转换温度;最后以哈尔滨和石家庄地区为例,模拟计算出泵驱动模式的全年最佳运行时间比。展开更多
基金supported by the National Natural Science Foundation of China(No.41877251)the Key project of Natural Science Foundation of Tianjin City(No.6JCZDJC39000).
文摘The performances of a refrigeration unit relying on compressors working in parallel have been investigated considering the influence of the compressor volumetric efficiency and isentropic efficiency on the compression ratio.Moreover,the following influential factors have been taken into account:evaporation temperature,condensation temperature and compressor suction-exhaust pressure ratio for different opening conditions of the compressor.The following quantities have been selected as the unit performance measurement indicators:refrigeration capacity,energy efficiency ratio(COP),compressor power consumption,and refrigerant flow rate.The experimental results indicate that the system refrigeration capacity and COP decrease with a decrease in evaporation temperature,increase of condensation temperature,and increase in pressure ratio.The refrigerant flow rate increases with the increase in evaporation temperature,decrease in condensing temperature and increase in pressure ratio.The compressor power consumption increases with the increase in condensing temperature and increase in pressure ratio,but is not significantly affected by the evaporation temperature.
文摘In hot arid countries with severe weather, the summer air conditioning systems consume much electrical power at peak period. Shifting the loads peak to off-peak period with thermal storage is recommended. Model A of residential buildings and Model B of schools and hospitals were used to estimate the daily cooling load profile in Makkah, Saudi Arabia at latitude of 21.42°N and longitude of 39.83°E. Model A was constructed from common materials, but Model B as Model A with 5 - 8 cm thermal insulation and double layers glass windows. The average data of Makkah weather through 2010, 2011 and 2012 were used to calculate the cooling load profile and performance of air conditioning systems. The maximum cooling load was calculated at 15:00 o’clock for a main floor building to a 40-floor of residential building and to 5 floors of schools. A district cooling plant of 180,000 Refrigeration Ton was suggested to serve the Gabal Al Sharashf area in the central zone of Makkah. A thermal storage system to store the excess cooling capacity was used. Air cooled condensers were used in the analysis of chiller refrigeration cycle. The operating cost was mainly a function of electrical energy consumption. Fixed electricity tariff was 0.04 $/kWh for electromechanical counter, and 0.027, 0.04, 0.069 $/kWh for shifting loads peak for the smart digital counter. The results showed that the daily savings in consumed power are 8.27% in spring, 6.86% in summer, 8.81% in autumn, and 14.55% in winter. Also, the daily savings in electricity bills are 12.26% in spring, 16.66% in summer, 12.84% in autumn, and 14.55% in winter. The obtained maximum saving in consumed power is 14.5% and the daily saving in electricity bills is 43% in summer when the loads peak is completely shifted to off-peak period.
文摘This paper presents the evaluation of the “capacity to the total energy consumption per bit ratio” of multiple antennas systems with distributed fashion. We propose an adequate geometric channel modeling for the wireless communication system which operates in indoor propagation environment with scatterers. The channel model is derived in function of both the line of sight (LOS) and the non line of sight (NLOS) components. The aim of this paper is to study the limits in the gain concerning the capacity to the total energy consumption ratio when additional antennas are implemented in the communication system. To do so, we have evaluated by simulations both the capacity and the total energy consumption per bit. Then, we have determined the capacity to the total energy consumption ratio. Finally, the computational capacity to the total energy ratio is obtained for different system configurations. We have shown that the gain in capacity increases with the number of antennas but it stills be limited by the total energy consumption. The limits for increasing the number of transmit antennas are determined in function of the separation distances between the transmitter and the receiver sides of the communication system. Optimal power allocation strategy via water-filling algorithm has been carried out for evaluating the capacity to energy ratio. We find by simulation that optimal power allocation brings a gain in the addressed metric reaching a level of about 1.7 at transmit signal to noise ratio of 8 dB if comparing to the case when transmit energy is equally split among transmit antennas.
文摘Earth tubes are earth-to-air heat exchangers that are frequently utilized in energy conscious low-rise buildings, but are scarcely reported for tall buildings. The feasibility of applying earth tube cooling to tall buildings in a hot summer and cold winter climate zone was studied in this paper. Firstly, the designed cooling load of a tall building was obtained from the energy simulation using the baseline and the modified models with applicable energy efficiency measures. Based on the load, the required cooling capacity, the overall section area and the effective length of the earth tube system was deduced from the heat transfer and fluid flow calculation analytically. Then the performance of the earth tube system was crosschecked and verified via the Computational Fluid Dynamics (CFD) simulation. In the CFD simulation, earth tubes with different diameters and lengths, as well as a full-scale earth tube model with surrounding soil above the depth of constant temperature, were investigated. The outlet air temperatures of the full-scale models were computed with the consideration of different axial distances between adjacent tubes. Meanwhile, multiple conceptual design schemes and the tunnel construction method for the earth tube system were proposed from the perspective of performance enhancement, constructability, efficiency and economy. It revealed that earth tube systems are conditionally feasible for some tall buildings if their design guidelines for climate, underground spaces, construction method, friction of tube interior surface, optimization of effective length and axial distance, as well as synergy with other energy efficiency measures are followed. Even the cooling capacity of earth tubes degrade with time due to the accumulated heat underground, but in a hot summer and cold winter climate zone it can still possibly produce cooled air for a tall building with a Floor Area Ratio of less than 7 effectively in summer.
文摘为降低数据中心制冷系统的能耗,搭建了一种磁力泵驱动的两相冷却复合制冷装置,并对其进行了实验研究。结果表明,室外温度15℃时,泵循环模式的EER随冷凝器迎面风速先增大后减小,当风速为1 m/s时EER获得最大值。在热负荷为7.3 k W条件下,实验获得了两种运行模式的最佳转换温度;最后以哈尔滨和石家庄地区为例,模拟计算出泵驱动模式的全年最佳运行时间比。
