公共建筑空调系统节能措施探讨

介绍了中国公共建筑中央空调系统能耗现状,分析了中国公共建筑中央空调系统在设计和运行管理中存在的问题,包括空调冷热负荷、空调系统新风量、空调冷热源、水系统和风系统的维护保养等,并提出了相应节能措施。     

大型超市空调冷热源选择的对比研究

本文研究了大型超市建筑夏季空调冷负荷的主要影响因素,并以上海市某一大型超市建筑为例,分析其夏季空调负荷的分布规律,并针对不同的冷热源选择方案,结合超市建筑的空调负荷特点,提出了多种空调冷热源方案的适用性,可为大型超市空调冷热源的设计提供参考.     

公共建筑空调冷热源工程适用性的调查分析

对我国不同气候区6个城市的96栋公共建筑空调冷热源状况进行了调研.目前我国公共建筑的空调冷源主要以电为能源的蒸汽压缩式制冷冷水机组,以燃油和燃气为能源的溴化锂吸收式冷热水机组、各种类型的热泵机组也占有一定的比例,蓄冷技术和区域供冷技术应用不多.建筑类型决定了其使用功能,气候条件决定建筑的使用环境条件,均会影响空调冷热源...     

Performance enhancement of a subcooled cold storage air conditioning system

This article experimentally investigates the enhancement of thermal performance for an air conditioning system utilizing a cold storage unit as a subcooler. The cold storage unit is composed of an energy storage tank, liquid-side heat exchanger, suction-side heat exchanger and energy storage material (ESM), water. When the cooling load is lower than the nominal cooling capacity of the system, the cold storage unit can store extra cold energy of the system to subcool the condenser outlet refrigerant. Hence, both the cooling capacity and coefficient of performance (COP) of the system will be increased. This experiment tests the two operation modes: subcooled mode with energy storage and non-subcooled mode without energy storage. The results show that for fixed cooling loads at 3.05 kW, 3.5 kW and 3.95 kW, the COP of the subcooled mode are 16.0%, 15.6% and 14.1% higher than those of the non-subcooled mode, respectively. In the varied cooling load experiments, the COP of the subcooled cold storage air conditioning system is 15.3% higher than the conventional system.     

水上和水下提取次表层海水冷量的对比和分析

夏季的酷热迫使人们耗费大量能源以维持狭窄的温度环境,城市空调负荷节节攀升;近在身边的海中,表层以下巨大的水团静静地安卧,闲置着天然的冷量.冷媒水与海水在海中进行换热,是实现水下直接提取海洋冷量的构想.与陆上提取冷量方案的对比,可以证明其技术优势和节能效果.水下取冷方案甚至可应用于高盐度海区,并提高海水与冷媒水的换热温差,以提升海水冷量利用率;采用自来水作为冷媒水,不需要对海水进行处理,也不会出现管道堵塞的故障;作为空调系统回水的自来水,又可用作其它工业或生活用途.该方案在提供相同冷媒水流量的条件下,输水耗功减少幅度达到90%.     

Thermal storage in an air conditioning system with dual energy storage unit

在自行搭建的双蓄能实验平台上进行了制冷兼蓄热实验研究,对比了制冷兼蓄热模式和一般制冷模式,探讨了不同冷冻水流量和不同风机盘管风量对机组性能的影响.实验结果表明:蓄热对机组制冷端的影响很小,但是由于回收了大量的冷凝热,使得机组的综合能效比得到大幅提高,因此蓄热对空调节能具有较大作用.此外,在制冷兼蓄热模式下,冷冻水流量或风机盘管风量越大,机组的综合能效比越大,当风量为1033 m³/h,冷冻水流量为972 L/h时,机组综合能效比高达7.06.     

An analysis of the heat transfer rate and efficiency of TE (thermoelectric) cooling systems

The heat transfer rate and efficiency of TE (thermoelectric) cooling systems were investigated. The emphasis of the present study is focused on the use of large-scale TE refrigerators for air conditioning applications. A one-dimensional heat transfer analysis was performed to determine the cooling power and electricity consumption of the TE elements. The constant-property results are in good agreement with the variable-property solutions for TE materials and temperatures typical for air conditioning applications. A heat transfer analysis was also carried out for TE refrigerators equipped with a heat exchanger. Both parallel- and counter-flow heat exchangers were considered. Fluid temperature variations of these two flow arrangements were found to be quite different, but the efficiencies and cold fluid exit temperatures differed only slightly when a uniform current was used for all TE elements. If the length of the heat exchanger exceeds an optimal value, the cold fluid temperature begins to rise and the efficiency drops for both parallel- and counter-flow arrangements. The second law of thermodynamics was applied to the optimization of TE refrigerators operating between two constant-temperature reservoirs and between two flowing fluids. It was found that if a TE cooling system incorporates a heat exchanger, a nonuniform current distribution should be used to achieve the maximum efficiency and the lowest cold fluid temperature. The optimization results for TE refrigerators operating between two constant-temperature reservoirs are not applicable to TE cooling systems between two flowing fluids. The most energy-efficient current distribution for the parallel-flow arrangement is the one which increase in the direction of the cold fluid.     

Optimized solar-powered liquid desiccant system to supply building fresh water and cooling needs

This paper studies the feasibility of using a solar-powered liquid desiccant system to meet both building cooling and fresh water needs in Beirut humid climate using parabolic solar concentrators as a heat source for regenerating the liquid desiccant. The water condensate is captured from the air leaving the regenerator. An integrated model of solar-powered calcium chloride liquid desiccant system for air dehumidification/humidification is developed. The LDS model predicted the amount of condensate obtained from the humid air leaving the regenerator bed when directed through a coil submerged in cold sea water. An optimization problem is formulated for selection and operation of a LDS to meet fresh water requirement and air conditioning load at minimal energy cost for a typical residential space in the Lebanon coastal climate with conditioned area of 80 m² with the objective of producing 15 l of fresh drinking water a day and meet air conditioning need of residence at minimum energy cost. The optimal regeneration temperature increases with decreased heat sink temperature with values of 50.5 °C and 52 °C corresponding to sink temperatures of 19 °C and 16 °C.     

风冷式太阳能吸收式制冷机性能模拟研究

在环境温度和太阳辐射动态变化的情况下,对制冷量为5 kW的风冷式太阳能吸收式制冷机的性能进行了模拟,得出了集热器出口水温和热水储槽温度随时间变化的规律曲线以及在此规律的影响下吸收式制冷机的性能曲线.模拟结果表明风冷式太阳能吸收式制冷机在理论上是切实可行的,但是环境温度的变化以及风冷系统的散热能力对系统性能有较大的影响,环境温度的升高会使需要风冷降温的冷凝器、吸收器温度升高,从而提高了发生温度的要求,这不利于太阳能的利用和系统的制冷.为此需要强化冷凝器和吸收器的散热效果,来降低境温度对系统的不利影响.     

Modeling cooling coils

Finned-tube heat exchangers commonly used as cooling coils in air conditioning systems undergo complex heat transfer and dehumidification. Due to the presence of water film on the outside surface of the coils, the general approach for an analysis of dry surface is not adequate to predict the performance of such coils. This paper presents a modeling procedure for cooling coils with dehumidification based on the approach of Threlkeld. In order to verify the calculational results of the model, experiments were conducted with an aim to determine the outlet air conditions as well as some other parameters required as the inputs to the model. Comparison between the simulation and experimental results reveals that the model is accurate and suitable for predicting the performance of cooling coils with dehumidification.     

太阳能吸收式空调系统的经济性分析

针对一个特定的对象,进行了太阳能吸收式空调系统寿命周期内的模拟计算及影响因素的分析,结果表明：（1）单纯太阳能空调（无采暖与热水供应）的经济性很差,太阳能空调与供热的复合系统的经济性要优于单纯的太阳能空调系统;（2）太阳能采暖与空调的复合系统,采暖与供冷的负荷比对系统的经济性有很大影响,即使在最佳的负荷比时仍无法和常规的系统竞争;（3）太阳能与生活热水系统的负荷系统中,热水负荷所占比重越大,经济性越好,当太阳能空调使用生活热水系统夏季多余的热量时,太阳能空调系统经济上可以和天然气锅炉＋电动制冷机竞争,并具有很好的节能性和环境效益。     

Experimental studies on a novel roof pond configuration for the cooling of buildings

A new evaporation based passive cooling technology was tested. The technology is based on the exposure of “floating” wetted cloth to the ambient air. It was compared to various other passive cooling techniques, with very favorable results. Two identical shallow ponds were constructed. One of them was covered with white cotton towels stretched on a densely perforated PVC panel supported by pieces of waterproof polystyrene keeping it just floating on the water surface. Five comparable experiments of different cooling techniques have been carried out. The results indicate that the new cooling technique performed slightly better than the pond with movable insulation, which is widely considered as one of the best roof cooling techniques based on evaporation. It seems that the higher efficiency of the tested technique is due to the thermal stratification created in the water inside the pond, which more effectively resists the transfer of heat gains from the sun and ambient air into the deep water of the pond. In turn, the water temperature near the floor of the pond is lower, thus heat flow from the building to the pond is increased. During the experiment, all the ponds which were compared were ranked according to performance (from best to worse): shaded pond with towels floated on it, pond with towels floated on it and pond with movable insulation, shaded open pond, open pond, covered pond.     

空调新技术耦合应用的节能分析

为了探讨空调新技术较之常规空调技术所体现出来的节能效果,选取了武汉地区六个应用不同空调技术的工程实例并做了具体计算,结果表明地源热泵、水源热泵、变频技术、蓄能技术、热回收技术在空调系统中的运用能够起到很好的节能效果,提出了空调系统能耗系数与单位空调面积能耗量的经验关系式,给出了实现绿色空调的措施。     

Feasibility study of hybrid fuel cell and geothermal heat pump used for air conditioning in Algeria

Hybrid Energy System (HES) is mainly based on proton exchange membrane fuel cell (PEMFC) technology, which is supplied by a fuel reforming process for hydrogen production, starting from natural gas. The exhaust heat from the PEMFC is evacuated to a thermal storage tank (TST) mixed with water provided by geothermal source, The bath (Hammam) Sidi Aïssa 47 °C, TST hot water maintained to 47 °C is used in a fan coil for canteen heating in Si Ben Salah School located in Saïda (NW of Algeria). Cooling is assured by the air conditioning sub-system made of a fan coil and heat pump using cool water tank. The experimental analysis of the air conditioning device is done for canteen application for cooling and heating modes. The feasibility study shows that using the geothermal sources located in Northern Algeria and low temperature PEMFC for air conditioning is a promising solution.     

An open reversed Brayton cycle with regeneration using moist air for deep freeze cooled by circulating water

This paper presents an open reversed Brayton cycle with regeneration using moist air for deep freeze cooled by circulating water, and proves its feasibility through performance simulation. Pinch technology is used to analyze the cooling of the wet air after compressor and the water used for cooling wet air after compressor. Its refrigeration depends mainly on the sensible heat of air and the latent heat of water vapor, its performance is more efficient than a conventional air-cycle, and the utilization of turbo-machinery makes it possible. The adoption of this cycle will make deep freeze easily and reduce initial cost because very low temperature, about ?55 °C, air is obtained. The sensitivity analysis of coefficient of performance to the efficiency of compressor and the efficiency of compressor, and the results of the cycle are also given. The simulation results show that the COP of this system depends on the temperature before turbine, the efficiency of compressor and the efficiency of compressor, and varies with the wet bulb temperature of the outdoor air. Humid air is a perfect working fluid for deep freeze with no cost to the user.     

区域供冷与蓄冷技术发展动态

  目的  空调能耗渐趋增加,是电网峰谷电量差的主要原因之一,分析区域供冷及蓄冷技术的特点及在主动调节空调制冷系统的用电量分布,减小用电高峰负荷的作用,为区域供冷的规划、设计及运行提供参考。  方法  采用蓄冷工程调研文献综述及实际案例分析相结合的方法。分析了水蓄冷、盘管外融冰蓄冷技术的特点,区域供冷的资源秉性以及应遵循的原则。  结果  研究表明:区域供冷及蓄冷技术在中国发展大有可为,水蓄冷系统灵活方便,宜利用电价机制鼓励用户自己投资建设。盘管外融冰蓄冷系统的单位蓄冷规模初投资和生命周期总费用均随着蓄冷系统规模增加呈现下降趋势,但变化趋势渐趋平缓。区域供冷项目应规划先行,且视为本区域全部成员资源利益最大化的项目,须全员参与,才可获得最大利益,并全员共享。  结论  所提区域供冷与蓄冷技术可为实际应用提供指导。     

水源热泵在空调系统中应用的经济性分析

本文对水源热泵的能耗进行了分析,表明水源热泵机组的性能系数与水源的温度直接相关,讨论了水源热泵在嵊州市空调系统集中供冷供热的可行性,对集中冷热水供水系统夏季空调工况与冬季热泵工况的经济性进行了计算与分析,结果表明,嵊州市利用水源热泵建立集中冷热水供水系统的社会经济效益显著,具有重要的节能与环保意义。     

Liquid Cooled Cold Plates for Industrial High-Power Electronic Devices—Thermal Design and Manufacturing Considerations

Electronics cooling research has been largely focused on high heat flux removal from computer chips in the recent years. However, the equally important field of high-power electronic devices has been experiencing a major paradigm shift from air cooling to liquid cooling over the last decade. For example, multiple 250-W insulated-gate bipolar transistors used in a power drive for a 7000-HP motor used in pumping or in locomotive traction devices would not be sufficiently cooled with air-cooling techniques. Another example is a “hockey puck” SCR of 63 mm diameter used to drive an electric motor that could dissipate over 1500 W and is difficult to cool with air because of the shape of the device. Other devices include radio-frequency generators, industrial battery chargers, printing press thermal and humidity control equipment, traction devices, mining devices, crude oil extraction equipment, magnetic resonance imaging, and railroad engines. This article classifies the cold plates into four types: formed tube cold plate, deep drilled cold plate, machined channel cold plate, and pocketed folded-fin cold plate. The article further discusses selection of cold plate type and channel configuration, and some of the relevant manufacturing issues. It is recommended that the thermal designer be involved in the early stages during the electrical design and layout of the devices.     

Numerical investigation on the heat and mass transfer in a direct evaporative cooler

A simplified mathematical model is developed to describe the heat and moisture transfer between water and air in a direct evaporative cooler. The mass of evaporated water is treated as a mass source of air flow, and the related latent heat of water evaporation is taken as a heat source in the energy equation. The momentum caused by water evaporation is taken into account in the momentum equations. The effective air viscosity and diffusion coefficient are decided experimentally. The models and methods are validated by comparing the numerical results with those of experiment for the same evaporative cooler. The influences of the inlet frontal air velocity, pad thickness, inlet air dry-bulb and wet-bulb temperatures on the cooling efficiency of the evaporative cooler are calculated and analyzed.The cooling effects of the direct evaporative cooler are predicted for use in four different regions in northwest China using the present numerical method and local weather data for air conditioning design. The predicted results show the direct evaporative cooler with high performance pad material may be well applied for air conditioning with reasonable choices for the inlet frontal velocity and pad thickness.