空调系统中热湿处理过程的(火用)评价方法及应用

提出对热、湿处理过程进行单独(火用)评价的概念,并构建了相应评价指标.以某一次回风空调系统的典型夏季空气处理过程为例,在热力学极限意义上阐明了对热、湿处理进行单独(火用)评价的实施过程,计算结果表明该空气处理过程的显热(火用)效明显高于潜热(火用)效,潜热(火用)效低下的原因主要在于再热显热(火用)损和冷凝水(火用)损...     

Experimental analysis of energy recovery for humidity control in split A/C system

This study presents a proposed idea about making use of the thermal energy rejected by the condenser in a water-cooled split-air-conditioning systems to decrease the relative humidity of the cold air supplied by such air conditioners. Most of split air-conditioner systems cool air without controlling its humidity. An amount of heat is rejected from the air conditioner, through the condenser, into the surrounding in order to allow the refrigerant to cool down and condense, thus, part of the lost energy can be exploited to decrease the relative humidity of the sub-cooled air that leaves the evaporator as saturated humid air. Four variables, viz. the coil type (single or double), the amount of flowing water, water, temperature, and the cooled air velocity were studied to find out the optimum conditions required for this purpose. The requisite amount of heat that may adjust the relative humidity of the conditioned air was also determined. The experimental results suggest an optimum design of a heat exchanger for performing the use of the heat rejected from the condenser to achieve the aim. As a result, the proposed heat recovery concept can be worthily adopted to achieve economic results in large-scale systems.     

Influence of building parameters and HVAC systems coupling on building energy performance

The performance of different HVAC systems varies when coupled with different buildings. This paper examines the relationship between building heating and cooling load and subsequent energy consumption with different HVAC systems. Two common HVAC systems in use throughout the UK office building stock, variable air volume (VAV) system and fan coil (FC) with dedicated outside air system, have been coupled with a typical narrow plan office building with and without daylight control and for both cellular and open plan.The results presented in this paper clearly indicate that it is not possible to form a reliable judgment about building energy performance based only on building heating and cooling loads. For the two investigated systems, variable air volume system and fan coil with dedicated outside air system, the difference between system demand and building demand varied from over −40% to almost +30% for cooling and between −20% and +15% for heating. If a heat recovery unit is used, the difference in heating performance is even greater, rising to −70%.     

Evaluating the low exergy of chilled water in a radiant cooling system

In this paper, in order to make guidelines for designing a low-energy radiant cooling system with an air-handling unit (AHU) for dehumidification, we investigated the impact of various air-conditioning parameters on the exergies of chilled water supplied to radiant panels and a cooling coil. The cooling load, thermal comfort index PMV, relative humidity, area of radiant panels, sensible heat factor (SHF), temperature and air-flow rate of supply air of the AHU, and presence/absence of total heat exchanger were considered. We used computational fluid dynamics (CFD) code in order to analyze the indoor air-flow and thermal environments, and added models for the calculation of thermal transfer to radiant panels and a cooling coil. Furthermore, a feedback control algorithm was introduced to calculate the surface radiant panel temperature, targeting the average PMV of the task area in an office room. As a result, the impact of various air-conditioning parameters on the exergies of chilled water were demonstrated quantitatively. As an example, by reducing the cooling load rate from 100% to 57% and 27%, the exergy of chilled water decreased by 47% and 67%, respectively.     

机械泵驱动分离式热管应用于空调冷量回收

为了探究机械泵驱动分离式热管对空调系统冷量回收和除湿能力的影响,搭建了四组该热管系统进行实验,其循环工质为R134a。在入口空气干球温度28.5℃、相对湿度60%的条件下,当运行热管由0增加到4组时,系统的机器露点由11.7℃降到8.2℃,供风温度由11.7℃升到24.1℃,系统的除湿能力增加了29.5%。指数δ(热管系统回收的冷量与制冷机蒸发器的制冷量之比)达到66.0%。研究结果表明,机械泵驱动分离式热管可以显著提高空调系统除湿能力,降低系统能耗。     

A comparative study of different control strategies for indoor air humidity

There has been a rising concern in controlling the high indoor humidity of hot and humid countries. When an air-conditioned space experiences only part of its design heat load, its humidity tends to rise as a result of the air-conditioning system trying to control the indoor temperature by reducing its cooling capacity. In this study, the part-load dehumidification performances of three temperature control strategies are compared, namely, chilled water flow control, bypass air control and the variable air volume control. Coil simulations are employed to study the part-load performance of these control strategies. The coil model has been validated with experimental data to within ±6.5%. The relative humidity of a space depends of factors such as design sensible heat factor of the space, temperature control strategy employed and load condition experienced by the space. Simulation results have indicated that chilled water control strategy results in the highest indoor humidity throughout the range of conditions studied while variable air volume system provides highly effective dehumidification performance of the cooling coil. Bypass air control appears to be a good option for adoption as it is able to provide an acceptable humidity over a wide range of load conditions without having to affect the air movement within the space.     

水冷式表冷器传热研究（3）：半干半湿工况热力计算

将已较成熟的水冷式表冷器干工况和湿工况热力计算理论与干、湿工况的分界是点“表冷器空气初状态的露点温度”结合起来,建立了半干半湿工况热力计算公式。其特点在于把湿工况段转换为等价干工况处理。     

Performance of combined displacement ventilation and cooled ceiling liquid desiccant membrane system in Beirut climate

The performance of the chilled ceiling (CC) displacement ventilation (DV) systems is constrained by latent load removal capacity and cost of supply air dehumidification to prevent condensation on the ceiling. In this study, a liquid desiccant dehumidification membrane cycle (LDMC) is mathematically modelled to replace the CC and remove directly latent and sensible load from indoor space through the membrane. The desiccant system is coupled with the DV system. An optimized operational strategy is adopted while allowing ceiling temperature to drop to lower values than conventional CC/DV. The optimized LDMC-C/DV system was implemented in an office space in Beirut climate. It was found that decreasing the membrane liquid desiccant temperature resulted in a significant decrease in the total cooling energy of the system, while increasing the solar heating energy of the desiccant regeneration. At optimal set points, a decrease of 49% in energy consumption was observed compared to the conventional CC/DV system.     

Membrane heat exchanger in HVAC energy recovery systems, systems energy analysis

The thermal performance of an enthalpy/membrane heat exchanger is experimentally investigated. The heat exchanger utilizes a 60gsm Kraft paper as the heat and moisture transfer surface for HVAC energy recovery. The heat exchanger sensible, latent and total effectiveness have been determined through temperature and moisture content measurements. The annual energy consumption of an air conditioner coupled with an enthalpy/membrane heat exchanger is also studied and compared with a conventional air conditioning cycle using in-house modified HPRate software. The heat exchanger effectiveness are used as thermal performance indicators and incorporated in the modified software. Energy analysis showed that an air conditioning system coupled with a membrane heat exchanger consumes less energy than a conventional air conditioning system in hot and humid climates where the latent load is high. It has been shown that in humid climate a saving of up to 8% in annual energy consumption can be achieved when membrane heat exchanger is used instead of a conventional HVAC system.     

Experimental study on a residential temperature-humidity separate control air-conditioner

According to the temperature and moisture characteristics and current problems experienced in the Yangtze River Area, a temperature-humidity separate control air conditioner was developed. This unit can remove indoor sensible heat and latent heat load separately, and adjust indoor temperature and humidity respectively, thus improve indoor comfort and reduce energy consumption. The air-conditioner consists of an air cooling evaporator and a water cooling evaporator. Orthogonal experiments were designed to study the influence of outdoor temperature, indoor temperature, indoor humidity, compressor frequency, and refrigerant distribution ratio in air cooling evaporator (RDRAE) on the unit performance. The results showed that the dehumidification capacity ranged from 0 to 4.02 kg/h; the EER ranged from 2.71 to 4.57; the cooling capacity ranged from 6822 to 13,080 W. The results can help to make the control logic of the unit, and be used as the basis of energy consumption calculation. Units with temperature and humidity separate control could save about 15.6% of the cooling energy consumption against traditional residential air-conditioner, and 47.8% against the traditional residential air-conditioner that could control both indoor temperature and humidity.     

建筑内表面吸放湿过程对室内环境和空调负荷影响的仿真研究

提出了一个考虑室内表面材料吸放湿过程的建筑热湿过程简化模型,介绍了对室内空气湿度及空调负荷的仿真分析。仿真结果表明,室内表面材料吸放湿过程有明显的降低湿度变化幅度的作用,对潜热负荷的影响较大     

西北干旱地区的空调系统节能设计

针对西北地区独特的气候特点,分别提出了蒸发冷却+置换通风和蒸发冷却+干式风机盘管2种空调系统形式可在喀什地区实际工程中应用。通过对比发现,第1种系统形式比传统电制冷空调系统节能53%,第2种系统形式比传统电制冷系统的制冷机房内设备节能71%,2种系统节能效果显著。通过对送风状态点露点分析,蒸发冷空调系统无凝结水产生,可避免室内环境污染。蒸发冷却空调系统的独特优势决定了其在西北地区的广泛应用前景。     

Simulation and analysis on thermodynamic performance of surface water source heat pump system

This work established a thermodynamic performance model of a heat pump system containing a heat pump unit model, an air conditioning cooling and heating load calculation model, a heat exchanger model and a water pump performance model based on mass and energy balances. The thermodynamic performance of a surface water source heat pump air conditioning system was simulated and verified by comparing the simulation results to an actual engineering project. In addition, the effects of the surface water temperature, heat exchanger structure and surface water pipeline transportation system on the thermodynamic performance of the heat pump air conditioning system were analyzed. Under the simulated conditions in this paper with a cooling load of 3400 kW, the results showed that a 1 °C decrease in the surface water temperature leads to a 2.3 percent increase in the coefficient of performance; furthermore, an additional 100 m of length for the closed-loop surface water heat exchanger tube leads to a 0.08 percent increase in the coefficient of performance. To decrease the system energy consumption, the optimal working point should be specified according to the surface water transportation length.     

Numerical study of a novel dew point evaporative cooling system

Dew point evaporative cooling system is an alternative to vapor compression air conditioning system for sensible cooling of ventilation air. This paper presents the theoretical performance of a novel dew point evaporative cooling system operating under various inlet air conditions (covering dry, moderate and humid climate) and influence of major operating parameters (namely, velocity, system dimension and the ratio of working air to intake air). A model of the dew point evaporative cooling system has been developed to simulate the heat and mass transfer processes. The outlet air conditions and system effectiveness predicted by the model using numerical method for known inlet parameters have been validated with experimental findings and with recent literature. The model was used to optimize the system parameters and to investigate the system effectiveness operating under various inlet air conditions.     

热湿负荷发生系统原理和构建

在搭建HVAC领域的空气焓差法实验室时,试验房间需要有可以控制的显热负荷和潜热负荷,来满足试验各种模拟负荷的需要。然而单纯的负荷发生只能提供热量,而无法得知提供热湿功率的大小。所以有必要对其提供的热湿负荷进行监测,以供试验研究参考使用。全面介绍了热湿负荷发生器原理、功率采集、负荷变化控制、负荷调试、采集控制过程等。经试验验证提出的构建方法,能较好并及时地提供所需负荷,但仍然存在延迟以及稳态误差等问题。     

Performance analysis of earth-pipe-air heat exchanger for summer cooling

Earth-pipe-air heat exchanger (EPAHE) systems can be used to reduce the cooling load of buildings in summer. A transient and implicit model based on computational fluid dynamics was developed to predict the thermal performance and cooling capacity of earth-air-pipe heat exchanger systems. The model was developed inside the FLUENT simulation program. The model developed is validated against experimental investigations on an experimental set-up in Ajmer (Western India). Good agreement between simulated results and experimental data is obtained. Effects of the operating parameters (i.e. the pipe material, air velocity) on the thermal performance of earth-air-pipe heat exchanger systems are studied. The 23.42 m long EPAHE system discussed in this paper gives cooling in the range of 8.0-12.7 °C for the flow velocities 2-5 m/s. Investigations on steel and PVC pipes have shown that the performance of the EPAHE system is not significantly affected by the material of the buried pipe (pipe). Velocity of air through the pipe is found to greatly affect the performance of EPAHE system. The COP of the EPAHE system discussed in this paper varies from 1.9 to 2.9 for increase in velocity from 2.0 to 5.0 m/s.     

An experimental study of a novel dew point evaporative cooling system

A novel dew point evaporative cooling system for sensible cooling of the ventilation air for air conditioning application was constructed and experiments were carried out to investigate the outlet air conditions and the system effectiveness at different inlet air conditions (temperature, humidity and velocity) covering dry, temperate and humid climates. The results showed that wet bulb effectiveness ranged between 92 and 114% and the dew point effectiveness between 58 and 84%. A continuous operation of the system during a typical day of summer season in a hot and humid climate showed that wet bulb and dew point effectiveness were almost constant at about 102 and 76%, respectively. The experiment results were compared with some recent studies in literature.     

The characteristics of space cooling load and indoor humidity control for residences in the subtropics

For residential buildings located in the subtropics, it is more challenging and difficult to deal with space latent cooling load than space sensible load, using a room air conditioner (RAC), partly due to hot and humid climates. This paper reports a simulation study on the characteristics of space cooling load and indoor humidity control for residences in the subtropics, using a building energy simulation program. Both the weather conditions and the typical arrangements of high-rise residential blocks in subtropical Hong Kong were used in the simulation study. The simulation results on both the space cooling load characteristics and the hourly application sensible heat ratio (SHR) in the living/dining room and the master bedroom in a selected west-facing apartment under different operating modes of RACs in the summer design day are presented. The problem of indoor humidity control due to the mismatching between an application SHR and an equipment SHR in the two rooms both in the summer design day and during part load operations and the influences of indoor furnishings acting as moisture capacitors on indoor RH level are discussed.     

The effect of heat-pipe air-handling coil on energy consumption in central air-conditioning system

A study was carried out to investigate the effect of heat-pipe air-handling coil on energy consumption in a central air-conditioning system with return air. Taking an office building as an example, the study shows that compared with conventional central air-conditioning system with return air, the heat-pipe air-conditioning system can save cooling and reheating energy. In the usual range of 22–26 °C indoor design temperature and 50% relative humidity, the RES (rate of energy saving) in this office building investigated is 23.5–25.7% for cooling load and 38.1–40.9% for total energy consumption. The RES of the heat-pipe air-conditioning system increases with the increase of indoor design temperature and the decrease of indoor relative humidity. The influence of indoor relative humidity on RES is much greater than the influence of the indoor design temperature. The study indicates that a central air-conditioning system can significantly reduce its energy consumption and improve both the indoor thermal comfort and air quality when a heat-pipe air-handling coil is employed in the air-conditioning process.     

柴油机驱动复合空调系统尾气露点的确定

分析了柴油机尾气中硫酸蒸气的生成机理和确定尾气露点的必要性，并介绍了柴油机区动复合空调系统时的尾气露点的确定。