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.     

Feasibility study of a novel dew point air conditioning system for China building application

The paper investigated the feasibility of a novel dew point evaporative cooling for air conditioning of buildings in China regions. The issues involved include analyses of China weather conditions, investigation of availability of water for dew point cooling, and assessment of cooling capacity of the system within various regions of China. It is concluded that the dew point system is suitable for most regions of China, particularly northern and west regions of China where the climate is hot and dry during the summer season. It is less suitable for Guangzhou and Shanghai where climates are hot and humid. However, an air pre-treatment process involving a silica-gel dehumidification will enable the technology to be used for these humid areas. Lower humidity results in a higher difference between the dry bulb and dew point of the air, which benefits the system in terms of enhancing its cooling performance. Tap water has adequate temperature to feed the system for cooling and its consumption rate is in the range 2.6–3 litres per kWh cooling output. The cooling output of the system ranges from 1.1 to 4.3 W per m³/h air flow rate in China, depending on the region where the system applies. For a unit with 2 kW of cooling output, the required air volume flow rate varies with its application location and is in the range 570–1800 m³/h. For a 50 m² building with 60 W/m² cooling load, if the system operates at working hours, i.e., 09:00 to 17:00 h, its daily water consumption would be in the range of 60–70 litres. Compared with mild or humid climates, the dry and hot climates need less air volume flow rate and less water.     

On-site experimental testing of a novel dew point evaporative cooler

Technologies which utilise the advantages of evaporative cooling to reduce the temperature of air without the addition of moisture have existed for some time. These systems use a heat exchange media between the evaporation of water process and cooling of air. Research has been conducted on a number of systems utilising these technologies in various configurations and it has been demonstrated that temperatures of the incoming air can approach its dew point temperature. This is considerably lower than the wet bulb temperature which is the limit achieved with conventional direct evaporative cooling systems. Prototypes have been built to demonstrate the principles and temperatures achievable, but the technology has never been developed due to its high cost and complexity. These disadvantages have been addressed in a newly developed indirect evaporative cooler. The paper presents results obtained from testing a prototype cooler installed in both a commercial and residential application in a wide range of ambient conditions. The performance characteristic of the indirect evaporative cooler in regards to its outlet temperatures and electrical energy efficiency is presented.     

Speculation in the feasibility of evaporative cooling

The use of evaporative air cooling, for residential air conditioning, cannot be taken for granted in all situations. It depends on the climatic conditions and the specific nature of application. This work establishes a general foundation for judging the feasibility of evaporative cooling with different evaporative-system configurations, under different climatic conditions and for different applications. Two feasibility criteria were stipulated; the rate of air supply to space and the indoor relative humidity. Systematic procedures are presented for evaluating the required air-flow rate and predicting the achievable indoor condition. Explicit mathematical expressions are derived to define the limitations on outdoor conditions for any allowable specific air flow. The impacts of various pertinent factors are investigated. These include the required indoor temperature, the quality of space load represented by its SHF and the performance index of the system. Computer programs were devised to automate, hence facilitate, the repetitive computations and to evade the graphical work on the psychrometric chart. Samples of program results are graphically displayed.     

Experimental investigation of a novel desiccant cooling system

Desiccant based air conditioning systems are a suitable way to improve indoor air quality due to its superior humidity control. In this study, a novel desiccant based air conditioning system is designed and tested experimentally to improve the indoor air quality and reduce energy consumption. In the system studied, a heat exchanger, which is not used in this type of systems, for pre-heating the regeneration air with exhaust air is used. This paper reports results of initial operation and operational procedures. The performance of the system and its components is discussed.     

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.     

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.     

Exergetic modeling and experimental performance assessment of a novel desiccant cooling system

New approaches to space conditioning of buildings are required to resolve economic, environmental, and regulatory issues. One of the alternative systems that is brought to agenda is the desiccant cooling systems, which may provide important advantages in solving air conditioning problems. This study deals with the performance analysis and evaluation of a novel desiccant cooling system using exergy analysis method. The system was designed, constructed and tested in Cukurova University, Adana, Turkey and has been successfully operated since 2008. This system consists of a desiccant wheel, heat exchangers, fans, evaporative cooler, electric heater unit and refrigeration unit. The exergy transports between the components and the destructions in each of the components of the desiccant cooling system are determined for the average measured parameters obtained from the experimental results. Exergy efficiencies of the system components are determined in an attempt to assess their individual performances and the potential for improvements is also presented. The exergetic efficiency values for the whole system on the exergetic product/fuel basis are calculated to range from round 32% to 10% at the varying dead (reference) state temperatures of 0-30 °C.     

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。     

Experimental study of cooling effects of a passive evaporative cooling wall constructed of porous ceramics with high water soaking-up ability

As a passive cooling strategy aimed at controlling increased surface temperatures and creating cooler urban environments in summer, the authors developed a passive evaporative cooling wall (PECW) constructed of porous ceramics. These ceramics possess a capillary force to soak water, which means that their vertical surface is wet up to a level higher than 100 cm when their lower end is placed in water. The present paper describes an experiment that clarifies the cooling effects of a prototype PECW constructed of pipe-shaped ceramics. The PECW is capable of absorbing water and allows wind penetration, thus reducing its surface temperature by means of water evaporation. Passive cooling effects such as solar shading, radiation cooling, and ventilation cooling can be enhanced by incorporating PECWs into the design of outdoor or semi-outdoor spaces in parks, pedestrian areas and residential courtyards. The following findings were understood from an experimental data collected over a summer period. Wet vertical surfaces of the ceramic pipe reached a height of over 1 m at an outdoor location exposed to solar radiation. Wet surface conditions can be maintained throughout successive sunny days during summer. A slight difference in the vertical surface temperatures of the ceramic pipe was found. The air passing through the PECW was cooled, and its temperature can be reduced to a minimum value by several degrees during summer daytime. It was also found that the surface temperature of the shaded ceramic pipe can be maintained at a temperature nearly equal to the wet-bulb temperature of outdoor air.     

蒸发冷却半集中式空调系统的控制方案

介绍了蒸发冷却半集中式空调系统的流程。基于该系统不同季节的运行模式,设计了自控方案,以保证该空调系统的安全性和节能性。详细介绍了控制内容和硬件配置。利用组态软件完成PC机与PLC之间的通讯,实现了系统集中控制、数据记录和打印等功能,能为现场设备维护人员提供详细的资料,简化操作、维护工作。工程应用实践表明,该自控系统运行稳定,能达到预期效果。     

基于蒸发冷却的辐射供冷/热实验台设计探讨

对基于蒸发冷却的辐射供冷/热半集中式空调系统实验台进行了简要介绍,并对实验台的新风系统和水系统设计进行了详细说明.分析了该实验台在中湿度地区不同季节的运行模式,指明了该实验台的特点.     

Experimental study of practical applications of a passive evaporative cooling wall with high water soaking-up ability

Aimed at controlling the increase in urban surface temperature and creating comfortable urban environments in summer, the authors have developed a passive evaporative cooling wall (PECW) constructed of porous ceramics. These ceramics enable their vertical surfaces to be wet up to a level higher than 100 cm when their lower end is placed in water. Our previous study has demonstrated the cooling performance and applicability of a prototype PECW constructed of pipe-shaped ceramics (ceramic pipes). The present paper presents a PECW unit system which can be easily installed for practical applications. Experiments were conducted using experimental PECW units. Experimental results show that the ceramic pipe developed in this study possessed a higher water-holding and soaking-up ability than the previous one. Wet surfaces of the new ceramic pipe reached a height of over 130 cm at an outdoor location exposed to solar radiation on sunny summer days. Furthermore, the air passing through the PECW unit was cooled, and its temperature can be reduced by around 2 °C during summer daytime. These results indicate that the proposed PECW can be broadly applied to various urban locations.     

多级蒸发冷却空调系统在西北地区的应用

介绍了多级蒸发冷却空调系统的几种形式，对在新疆某工程使用的三级蒸发冷却空调系统运行情况作了测试，比较了三种运行方式的效果，得出该系统的适宜和适用的地域。     

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.     

Experimental study of the performance of porous materials to moderate the roof surface temperature by its evaporative cooling effect

The change of urban surfaces from permeable to impermeable materials, i.e. asphalt or concrete, has caused the rising of surface temperatures, particularly in densely developed cities. The consequences of this problem lead to higher energy consumption, especially for cooling purposes and other environment related issues. This paper aims to investigate the performance of several non-porous and porous potential roofing materials, to determine which ones might best be used to create a more effective system by utilizing their moisture absorption and evaporation capabilities. Here, four kinds of materials—pebbles, silica sand, volcanic ash, and siliceous shale—were tested to evaluate their moisture and thermal performance, including the effects from different particle sizes. First, the necessary physical properties and pore characteristics were obtained. Thus, each material, under simple boundary conditions, was evaluated in an evaporation experiment, to determine comparative moisture and thermal behavior. Next, cyclic experimentation was conducted, in which variations of temperature, relative humidity and simulated solar radiation were included. The measurement results showed that porous materials can satisfactorily lower surface temperature. Among the tested samples, siliceous shale of both small and large particle diameter was found to lower the daily average surface temperature by up to 6.8 and 8.6 °C, respectively. The better performance of large size particles could possibly be caused by the ventilation occurring within the material layers and high solar penetration through the large gaps between particles, which would release more latent heat when compared to materials of smaller particle size. Finally, analysis of surface energy balance suggested that water contents, solar absorptivity, and wind effects all have significant influences on cooling the surface temperature.     

Experimental study on dehumidifier and regenerator of liquid desiccant cooling air conditioning system

A new type of air conditioning system, the liquid desiccant evaporation cooling air conditioning system (LDCS) is introduced in this paper. Desiccant evaporation cooling technology is environmental friendly and can be used to condition the indoor environment of buildings. Unlike conventional air conditioning systems, the system can be driven by low-grade heat sources such as solar energy and industrial waste heat with temperatures between 60 and 80 °C. In this paper, a LDCS, as well as a packed tower for the regenerator and dehumidifier is described. The effects of heating source temperature, air temperature and humidity, desiccant solution temperature and desiccant solution concentration on the rates of dehumidification and regeneration are discussed. Based on the experimental results, mass transfer coefficients of the regeneration process were experimentally obtained. The results showed that the mean mass transfer coefficient of the packing regenerator was 4 g/(m² s). In the experiments of dehumidification, it was found that there was maximal tower efficiency with the suitable inlet humidity of the indoor air. The effective curves of heating temperature on the outlet parameters of the regenerator were obtained. The relationships of regeneration mass transfer coefficient as a function of heating temperature and desiccant concentration are introduced.     

Energy performance evaluation of a novel evaporative cooling technique

High summer conditioning consumption is becoming a tough and critical issue and consequently there is a need to provide buildings with new technologies for energy saving. Current European and Italian legislation is also working in this direction. We present a preliminary experimental evaluation of the energy performance of a new technology which is capable of canceling conduction gains through walls: “water-evaporative walls”, which are not only able to prevent the entrance of energy fluxes from the exterior to the interior, but also to reduce wall temperatures to below the values found indoors. This solution basically suggests equipping standard ventilated façades with a proper water-evaporative system, which exploits the latent heat of water evaporation, in order to absorb summer cooling loads. From the technological point of view, it requires the insertion of a water spraying system and a proper insulating layer in the ventilated air chamber. The insulation will act not only as a standard insulating material, but also as a porous surface to store water sprayed by the system and then gradually release it when needed for cooling. The experimental analyses showed the effectiveness of this technology, which decreases the overall summer energy load in buildings by canceling conduction loads.