Investigation of a hybrid system of nocturnal radiative cooling and direct evaporative cooling

In this paper, the results of a study on a hybrid system of nocturnal radiative cooling, cooling coil, and direct evaporative cooling in Tehran have been discussed. During a night, the nocturnal radiative cooling provides required chilled water for a cooling coil unit. The cold water is stored in a storage tank. During eight working hours of the next day, hot outdoor air is pre-cooled by means of the cooling coil unit and then it enters a direct evaporative cooling unit. In this period, temperature variation of the conditioned air is investigated. This hybrid system complements direct evaporative cooling as if it consumes low energy to provide cold water and is able to fulfill the comfort condition whereas direct evaporative alone is not able to provide summer comfort condition. The results obtained demonstrate that overall effectiveness of hybrid system is more than 100%. Thus, this environmentally clean and energy efficient system can be considered as an alternative to the mechanical vapor compression systems.     

再循环蒸发冷却中再循环风量的实验研究

介绍了一种再循环蒸发冷却技术,其原理是利用一部分经间接冷却处理的空气作为二次空气直接蒸发制取冷水,用冷水反过来间接冷却室外空气。搭建了相应的实验台,针对夏季实际工况条件,实验研究了再循环风量比例对蒸发冷却效率的影响,给出了合适的再循环风量范围。     

Application of desiccant systems for improving the performance of an evaporative cooling-assisted 100% outdoor air system in hot and humid climates

The purpose of this study was to enhance the energy-saving potential of an indirect and direct evaporative cooling-assisted 100% outdoor air system (IDECOAS) by integrating it with either a solid or liquid desiccant system. The desiccant system can be installed either at the scavenger air side of the indirect evaporative cooler (IEC) to enhance its effectiveness or at the primary air side of the IEC to reduce the latent load of outdoor air. The operating energy consumption affected by the location and type of the desiccant unit integrated with IDECOAS was simulated under three different hot and humid climates using TRNSYS 17 integrated with commercial equation solver programme. And then, the most energy-conservative configuration was selected for each climate zone as the proposed system. The simulation results showed that configurations with the desiccant dehumidification unit located upstream of the IDECOAS consume 76–85% less cooling coil energy than those with the desiccant unit located downstream of the IDECOAS. It was also found that the liquid desiccant system saves 21–50% more primary energy than the solid one, when it is integrated with IDECOAS.     

间接蒸发冷水机组设计开发及性能分析

基于间接蒸发冷却技术设计了高温冷水机组,其驱动源为室外干空气而非电能,冷水机组的理论出水温度可无限接近进口空气的露点温度。建立了数学模型,并提出了系统的串联冷水流程,以更充分地利用室外干空气的能量。合作开发了第一台间接蒸发冷水机组,通过测试得到了实际机组的性能。最后分析了冷水机组作为湿度独立控制空调系统的高温冷源在中国西部及其他地区的应用。     

间接蒸发冷却技术——中国西北地区可再生干空气资源的高效应用

通过间接蒸发冷却技术制备冷水,解决常规间接蒸发冷却系统风道占用空间大、风机耗电高的问题,是在干燥地区推广应用蒸发冷却技术的关键.介绍了间接蒸发冷却冷水制备技术的原理、研发机组的实测性能及其在工程中的实际应用效果.综述了目前间接蒸发冷却技术的应用状况和推广前景.所研发的间接蒸发冷水机出水温度16～19℃,达到室外湿球温度和露点温度的平均值,可作为空调的冷源.这种间接蒸发冷水机及其系统在西北地区已经实现了规模化推广.     

Experimental investigation of two-stage indirect/direct evaporative cooling system in various climatic conditions

Cooling performance of two-stage indirect/direct evaporative cooling system is experimentally investigated in the various simulated climatic conditions. For this purpose, a two-stage evaporative cooling experimental setup consisting of an indirect evaporative cooling stage (IEC) followed by a direct evaporative cooling stage (DEC) was designed, constructed and tested. Due to the wide variety of climatic conditions in Iran, two air simulators were provided to simulate outdoor design condition of different cities in primary and secondary air streams. Results show that under various outdoor conditions, the effectiveness of IEC stage varies over a range of 55–61% and the effectiveness of IEC/DEC unit varies over a range of 108–111%. Aspects of achieving comfort conditions and power saving have been investigated with related excess water consumption. Considering the evaporative comfort zone, this system can provide comfort condition in a vast region in Iran where direct evaporative alone is not able to provide summer comfort condition. More than 60% power saving could be obtained by this system in comparison with mechanical vapor compression systems with just 55% increase in water consumption with respect to direct evaporative cooling systems. This system can fill the gap between direct evaporative cooling systems and mechanical vapor compression systems as an energy efficient and environmentally clean alternate.     

Study on a novel thermally driven air conditioning system with desiccant dehumidification and regenerative evaporative cooling

Existing desiccant cooling systems reduce the temperature of process air either by adopting evaporative coolers or incorporating vapor compression systems. While the former is restricted by inaccurate control, the latter still consumes certain quantity of electric power. To solve this problem, a thermally driven air conditioning system, which combines the technologies of rotary desiccant dehumidification and regenerative evaporative cooling, has been proposed and investigated. In addition to dehumidification, the system is capable of producing chilled water, thereby realizing separate temperature and humidity control without increasing electrical load. To find out the characteristics of produced chilled water and evaluate the feasibility and energy saving potential of this novel system, a mathematical model has been developed. Case studies have been conducted under Air conditioning and Refrigeration Institute (ARI) summer, ARI humid and Shanghai summer conditions. It is found that the system can achieve a thermal COP higher than 1.0 and an electric COP about 8.0. The temperature of chilled water produced by the system is around 14–20 °C. This chilled water can be used with capillary tube mats for radiant cooling. It is suggested that the system can also be designed as a standalone chilled water plant. As a desiccant dehumidification-based chilled water producing technology, this would expand desiccant cooling to a boarder niche application. The effects of chilled water flow rate, air distribution ratio, inlet air conditions and regeneration temperature have been analyzed in detail. Reachable handling regions, which will be helpful to system design and optimization, have been obtained.     

间接蒸发冷却方案的比较研究

根据数值模拟计算结果,比较了间接蒸发冷却器(IEC)和回热式间接蒸发冷却器(RIEC)的温度、换热效率火、用效比。结果表明RIEC的火用效比略低于IEC,但能得到更低的温度。这两种方案都有非常显著的节能潜力。     

Energy saving potential of an indirect evaporative cooler as a pre-cooling unit for mechanical cooling systems in Iran

The performance of indirect evaporative cooling system (IEC) to pre-cool air for a conventional mechanical cooling system has been investigated for four cities of Iran. For this purpose, a combined experimental setup consisting of an IEC unit followed by a packaged unit air conditioner (PUA) was designed, constructed and tested. Two air simulators were designed and used to simulate indoor heating load and outdoor design conditions. Using of experimental data and an appropriate analytical method, the performance and energy reduction capability of combined system has been evaluated through the cooling season. The results indicate IEC can reduce cooling load up to 75% during cooling seasons. Also, 55% reduction in electrical energy consumption of PUA can be obtained.     

地铁用间接蒸发冷却器换热性能影响因素

为解决地铁站冷却塔设置难题,提出了一种采用低速电机驱动旋转布水装置的间接蒸发冷却器,在两种布置方式下,对其换热性能进行了单因素实验,并运用正交实验法对较优布置方式下影响换热器换热的因素进行了分析。结果表明:两种布置方式下,喷嘴与蒸发冷却器的间距、两组换热管束间距均存在最佳值,喷嘴双侧旋转布水优于单侧旋转布水;换热器平行气流布置且喷嘴双侧旋转布水为较优布置方式,此时,换热器换热量随喷水量、转速、空气速度、冷却水进口温度的增加以及喷水温度、空气温度的降低而增大,其中,冷却水进口温度对换热器换热影响最为显著,其他因素对其换热的影响从主到次顺序为:喷水量、空气温度、空气速度、喷水温度、转速、冷却水流量。     

管式间接蒸发冷却器在兰州的性能测试与分析

本实验在兰州地区针对二次空气为室外新风的管式间接蒸发冷却器进行研究,在一定实验条件下,得出这种管式间接蒸发冷却器效率和温降随二次／一次风量比和淋水量的变化关系。在所取实验风量中得出当一次空气风量为9000m^3／h时,最佳二次／一次风量比为0．7,效率达到71％,温降达到9．1℃,此时管式间接蒸发冷却器的效率和温降达到最高。在这种情况下改变淋水量,若一、二次空气风量都一定,淋水量越大,冷却器的效率和温降越高,当淋水量达到4．6m^3／h时,再增大淋水量,冷却器效率和温降没有太大的改善。这样就进一步验证了二次空气为室外新风的管式间接蒸发冷却器在兰州地区的适用情况,同时也为这种类型的管式蒸发冷却器在其他地区的适应性提供了参考。     

Numerical study of a M-cycle cross-flow heat exchanger for indirect evaporative cooling

In this paper, numerical analyses of the thermal performance of an indirect evaporative air cooler incorporating a M-cycle cross-flow heat exchanger has been carried out. The numerical model was established from solving the coupled governing equations for heat and mass transfer between the product and working air, using the finite-element method. The model was developed using the EES (Engineering Equation Solver) environment and validated by published experimental data. Correlation between the cooling (wet-bulb) effectiveness, system COP and a number of air flow/exchanger parameters was developed. It is found that lower channel air velocity, lower inlet air relative humidity, and higher working-to-product air ratio yielded higher cooling effectiveness. The recommended average air velocities in dry and wet channels should not be greater than 1.77 m/s and 0.7 m/s, respectively. The optimum flow ratio of working-to-product air for this cooler is 50%. The channel geometric sizes, i.e. channel length and height, also impose significant impact to system performance. Longer channel length and smaller channel height contribute to increase of the system cooling effectiveness but lead to reduced system COP. The recommend channel height is 4 mm and the dimensionless channel length, i.e., ratio of the channel length to height, should be in the range 100 to 300. Numerical study results indicated that this new type of M-cycle heat and mass exchanger can achieve 16.7% higher cooling effectiveness compared with the conventional cross-flow heat and mass exchanger for the indirect evaporative cooler. The model of this kind is new and not yet reported in literatures. The results of the study help with design and performance analyses of such a new type of indirect evaporative air cooler, and in further, help increasing market rating of the technology within building air conditioning sector, which is currently dominated by the conventional compression refrigeration technology.     

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.     

水蓄冷式末端盘管热泵机组空调系统

介绍一种水蓄冷式空调系统，使用风机盘管与水冷热泵一体的空调机组末端装置，实现了蓄冷空调模式与末端热泵空调模式并存与互补。与普通风机盘管式空调系统类似，但末端具有电制冷能力，能实现制冷供暖，蓄热蓄冷，大温水循环，有效回收利用余热     

适用于湿工况的风机盘管简化换热模型

针对半集中式空调系统风机盘管的换热计算问题,通过干湿工况转换方法,设计了一种适用于湿工况的风机盘管换热模型.根据能量平衡和热传递原理,简化了该换热模型,使换热量仅由冷水流量、进水温度、盘管风量和进风温度等独立控制变量确定.在实际风机盘管上进行了仿真验证,得到了不同工作条件下的换热曲线.实验结果表明,该简化换热模型计算精度较高.     

蒸发冷却与毛细管辐射供冷复合式空调

本文介绍了蒸发冷却与毛细管辐射供冷的概况,并根据西北地区的气候特点,提出了一种将两者相复合的半集中式空调系统方案,阐述了该方案中蒸发冷却与毛细管辐射供冷相复合的特点,同时指出该空调系统在我国西北地区具有十分广阔的应用前景.     

蒸发冷却新风空调集成系统

分析了对蒸发冷却技术的一些误解，介绍了新风集成系统，单风道、双风道、三风道集成系统等几种方案，在此基础上提出一种借鉴了独立新风系统设计思想的蒸发冷却新风空调集成系统方案。     

Indirect evaporative cooling potential in air–water systems in temperate climates

Recent developments have prompted a review of evaporative cooling technology as an effective means of cooling modern deep plan buildings. Prominent among these developments is the success of high temperature sensible cooling systems, particularly, chilled ceilings, which require a supply of cooling water at 14–18 °C. Crucial to the success of evaporative cooling technology, as a significant means of cooling in modern applications, is the ability to generate cooling water, in an indirect circuit, at a temperature which closely approaches the ambient adiabatic saturation temperature (AST) or wet bulb temperature (WBT). Recent experimental research has demonstrated that it is technically viable to generate such cooling water at a temperature of 3 K above the ambient AST.While the frequency of ambient AST occurrence can be obtained from meteorological sources, there is little in-depth analysis of the potential for this form of cooling water generation, based on the approach temperatures which have now been shown to be viable. The decision to use an evaporative cooling system depends largely on an assessment, in-depth, of net energy saved against capital expended. Such an assessment requires detailed data on the availability of cooling water, generated by evaporation, for each location. This paper quantifies evaporative cooling availability in-depth for a northern and southern European city, Dublin and Milan and suggests a method of analysing such data for any world wide location, for which suitable meteorological records are available. The paper, incorporates recent experimental research findings and bases the availability analysis on meteorological test reference weather year data.The results of this research confirm a major potential for the generation of cooling water by evaporative means, which can be used to provide effective cooling of deep plan buildings by means of contemporary water based sensible cooling systems, such as fan coil systems, radiant chilled ceiling panels and ceiling cooling convectors (chilled beams). While the technique offers most potential in locations with a northern European temperate climate, it has significant potential to contribute to cooling in some southern European cities, during the non-summer months and also at other times, particularly where load shaving techniques are incorporated.     

A numerical study of daytime passive radiative coolers for space cooling in buildings

A passive daytime radiative cooler is made of a sky facing surface which can preserve the indoor air temperature below ambient without energy consumption by simultaneously reflecting solar radiation and emitting thermal radiation to the universe through the atmospheric window located between 8–13 μm of the electromagnetic spectrum. After the first demonstration of radiative cooling under direct sunlight, a solar mirror coated with a mid-infrared (MIR) emissive thin film has become the standard device architecture. This study firstly reviews recent developments in daytime passive radiative cooling, followed by describing the development of an energy balance mathematical model to study the potential application of passive radiative coolers in HVAC systems of buildings. Some micro-channels are fabricated on the back side of the passive radiative cooler, allowing fluid to flow in an isolated loop such that the coolant can be chilled and transported to the demand side for spacing cooling. This leads to the partial replacement of conventional vapor compression refrigeration by the radiative cooling panel. Considering the steady state energy balance within the radiative cooling panel integrated HVAC systems, the cooling performance and indoor air temperature are evaluated by numerical analysis. A 100 m2 passive radiative cooling panel could chill water for the cooling of air, reducing indoor air temperature by 10 °C, equivalent to a net cooling power of 1600 W. This study suggests that the proposed passive radiative cooling system should be used to pre-cool the ambient hot air such that the overall energy consumption of a traditional air-conditioning system can be reduced. The findings promise the application of passive daytime radiative cooling in building HVAC systems.     

利用盐溶液制备冷水的冷水机组

在间接蒸发冷却装置的基础上，设计了利用盐溶液制备冷水的冷水机组，使得间接蒸发冷却技术能够应用于非干燥地区，并运用了热回收技术达到节能目的。通过对不同室外工况下冷水机组性能的模拟，发现COP对室外空气含湿量最敏感。最后模拟分析了在北京地区使用时此冷水机组的整体性能。