Indirect Evaporative Research Articles

The Effect of Indirect Evaporative Cooling Applied to Existing AHU Systems

The Effect of Indirect Evaporative Cooling Applied to Existing AHU Systems

DESIGN OF A NOVEL DEW POINT INDERECT EVAPORATVE COOLER: PRELIMINARY EXPERIMENTAL INVESTIGATIONS

Evaporative coolers may represent a promising alternative to conventional cooling technologies based on vapor compression systems. Indeed, they present lower production and operative costs, as well as lower environmental impact. The present study aims to develop a novel Dew Point Indirect Evaporative Cooler (DPIEC), by combining simplicity, hence low production costs, and higher cooling performance. The design proposed has mixed flow configuration and is made of polycarbonate plate covered with cotton cloth as wicking material. Two prototypes with different length are experimentally tested for two different water distributors. The performance of the novel DPIEC is evaluated and compared in terms of temperature drop, dew-point effectiveness, cooling capacity and compactness. The results show that the long prototype performs better in terms of temperature drop and dew point effectiveness, but yields lower cooling capacity and is less compact. In addition, it is observed that the distributor that supplies water over the system performs better, independently on the prototype. These results can serve as reference for future designs of mixed-flow DPIEC.

Experimental Study on the Performance of an Air Conditioning Unit with a Baffled Indirect Evaporative Cooler

Indirect evaporative coolers (IECs) use the latent heat of water evaporation to cool air. This system has the advantage of operating at low power without a compressor and does not increase the absolute humidity of the air. However, an IEC is difficult to use on its own because its cooling capacity is limited by the theoretical constraint of the wet-bulb temperature of the ambient air. Therefore, an air conditioning unit (ACU) was integrated with an IEC and experimentally evaluated in this study. The dry and wet channels of the IEC were integrated with an ACU evaporator and a condenser, unlike previous studies where IECs were integrated solely with either an evaporator or a condenser. This reduced the cooling load on the evaporator and helped the condenser to dissipate heat to improve the performance of the existing ACU. In addition, the IEC was equipped with baffles to improve its performance. To assess the extent of the performance improvement due to integration with the IEC, comparisons were also performed under the same experimental conditions with an ACU only. The results showed that under conditions with an indoor temperature of 32 °C, integrating the IEC with the ACU increased the average cooling capacity by 13.1% and decreased the average power consumption by 8.60% during the test period, compared to using only the ACU. Consequently, the average coefficient of performance (COP) increased by 19.5% compared to using only the ACU under the same conditions.

A Computational Analysis of Heat and Mass Transfer in an Indirect Evaporative Cooler Using the Spray Dryer Model

A Computational Analysis of Heat and Mass Transfer in an Indirect Evaporative Cooler Using the Spray Dryer Model

Numerical Analysis on Performance Improvement of a Vertical Plate Indirect Evaporative Cooler with Baffles

The performance of the Plate Indirect Evaporative Cooler (PIEC) can be effectively improved by incorporating baffles in the dry channel. However, in the dimensional influence of the baffles on PIEC performance there remains a research gap. In order to investigate the impact of baffle dimensions on the wet bulb efficiency, namely the average heat transfer coefficient and the cooling capacity of the PIEC, this paper proposed and verified a three-dimensional numerical model and method based on the species transport model and the Euler wall film model. At the same time, in order to obtain the equilibrium point between the enhanced heat transfer performance and the additional resistance induced by baffles, a comprehensive performance evaluation index is introduced. The results indicate that, under the same conditions, (1) the baffle effect on PIEC performance is significant at a lower inlet air velocity, and the wet bulb efficiency of the PIEC with baffles can be improved by 22.8%; (2) the baffle effect on PIEC performance is negative if its relative length exceeds 60% or the primary air inlet velocity surpasses 4 m/s under the conditions specified in this paper; and (3) the baffle effect on PIEC performance is significant when its channel height is lower and its channel width is larger, and the wet bulb efficiency of the PIEC with baffles can be improved by 29.3%.

Modeling of Indirect Evaporative Cooling Systems: A Review

Air-to-air indirect evaporative cooling (IEC) systems are particular heat exchangers that use the latent heat of evaporation of water to cool down an air stream, without increasing its specific humidity, thus guaranteeing adequate thermohygrometric conditions in the refrigerated environment with low energy consumption. Dew-point indirect evaporative cooling (DIEC) systems are based on the IEC technology, but they recirculate a part of the air taken from the room to be refrigerated, in order to possibly achieve a lower air temperature. IEC and DIEC systems are becoming increasingly common these years, as they can ensure a good efficiency, minimizing the environmental impact of the air-conditioning system. Consequently, it has been necessary to develop models, both analytical and numerical, to quickly and accurately design this type of system and to predict their performance. This paper presents a review of the analytical and numerical models developed specifically for IEC and DIEC systems, highlighting their method, main innovations and advantages, and possible limitations. From this analysis, it emerged that analytical models have been developed since the late 1990s and only few of them are suitable for DIEC heat exchangers, while numerical models for both IEC and DIEC systems are gaining popularity in recent years. Almost all the analyzed models have been validated by comparison with numerical and/or experimental data, showing a maximum discrepancy within 10% in the majority of the cases. However, the validations were performed for a few specific cases, so in real applications it might be difficult to associate the model boundary conditions and the heat exchangers operating conditions, such as nozzles orientations, plates materials, water flow rates, and configurations. Another common limitation concerns the modeling of some properties, as wettability factor and air density, which might affect the accuracy of the results.

An Approach to Analyzing and Comparing the Cooling Performance of Two Indirect Evaporative Cooler Designs

Abstract Energy-efficient air cooling systems are always in demand. Direct evaporative coolers are energy-saving and have low cost, but in hot and humid areas, they produce an almost uncomfortable environment. Alternatively, modified indirect evaporative coolers with different technical configurations can produce better thermal output. This paper presents a simple thermodynamic approach developed to analyze, for comparison, the behavior of conventional and regenerative indirect evaporative coolers that comprise different process structures. The analysis is based on the energy balance of the coolers to consider which is more applicable for further modification. Similar performance cross-flow heat exchangers with separate air washers are adopted for both units. The two coolers are subjected to the same general summer operating conditions. The results showed that the conventional indirect evaporative cooler provided better cooling performance in terms of all thermal comparison parameters. The supply temperature trend in regenerative indirect evaporative cooler (RIEC) is higher by 23.4–34.1%, while its effectiveness is lower by 26–56% compared to that of the conventional indirect evaporative cooler (CIEC). The cooling capacity of CIEC is always higher at any air ratio value. At an equal secondary air flowrate where the primary air flowrate of RIEC is 25% more than that of CIEC, CIEC still generates lower air supply temperature and its effectiveness is higher. Thus, CIEC deserves priority attention for further development and additional improvement of performance.

Design Selection Method of Exhaust Air Heat Recovery Type Indirect Evaporative Cooler

In order to promote the engineering application of indirect evaporative cooling (IEC) in the field of building air conditioning, as well as reduce air conditioning energy consumption and carbon emissions, this paper proposes a fresh air unit using indirect evaporative cooling to achieve heat recovery from exhaust air, which gives the recommended values of air and spray water operation parameters. The indirect evaporative cooler heat and mass transfer mathematical model and numerical solution procedure were made. In summer outdoor design conditions, the fresh air outlet state parameters, cooling capacity, fresh air cooling load, wet bulb efficiency and enthalpy efficiency were numerically solved for thirty typical cities from five climate zones of China. In addition, also based on the model results for the cities in China, two representative operating conditions points of medium and high humidity were selected. Eight models of fresh air unit coolers in the air volume range of 1000–10,000 m3/h commonly used in engineering were simulated to obtain the optimal heat transfer area and size selection of ERIEC heat exchangers for fresh air units, and economic analysis was performed. The results show that the wet bulb efficiency ranges from 0.67–0.98, and increases as the outdoor design wet bulb temperature decreases; the enthalpy efficiency ranges from 0.76–1.29, and increases as the outdoor design wet bulb temperature increases; and the fresh air load that the exhaust air heat recovery type indirect evaporative cooler can bear ranges from 55–100%, which could largely decrease the cold load of the matched surface cooler. As demonstrated, the energy-saving effect is remarkable.

Experimental Characterization of the Wettability of Coated and Uncoated Plates for Indirect Evaporative Cooling Systems

Indirect Evaporative Cooling (IEC) is a very promising technology to substitute and/or integrate traditional air conditioning systems, due to its ability to provide cooling capacity with limited power consumption. Literature studies proved that a higher wettability of the IEC plates corresponds to better performance of the system. In this work, wettability of three different surfaces used for IEC systems plates—uncoated aluminum alloy (AL), standard epoxy coating (STD), and a hydrophilic lacquer (HPHI)—is studied and characterized in terms of static and dynamic contact angles. The static contact angle resulted to be the lowest for the HPHI surface (average 69°), intermediate for the STD surface (average 75°), and the highest for the AL surface (average 89°). The analysis of the dynamic contact angles showed that their transient behavior is similar for all the surfaces, and the advancing and receding contact angles obtained are consistent with the results of the static analysis. These results will be useful as input parameters in models aimed at predicting the IEC system performance, also using computational fluid dynamics.

Evaporation-Assisted Humidification–Dehumidification Cycles for Desalination Application in Tropical and Subtropical Regions

The present study aims to evaluate the performance of evaporation-assisted humidification–dehumidification (E-HDH) desalination, specifically direct evaporative (DE-HDH), indirect evaporative (IE-HDH), and Maisotsenko evaporative (ME-HDH) systems. To achieve this, a thermodynamic modeling approach is utilized, which incorporates the wet bulb effectiveness method, psychrometric relationships of humid air, and equations that govern heat and mass balance. The key performance indicators of the studied E-HDH desalination systems are estimated concerning operating parameters. The results show that the ME-HDH system is capable of producing a comparatively higher water production rate (WPR) ranging between 0.01 and 7.92 g/s as compared to the DE-HDH and IE-HDH systems. The sensible cooling flux was observed to be high at a dry-bulb temperature (Tdb) of 50 °C and relative humidity (RH) < 0.2, having a value of 5.26 kW for the DE-HDH system, followed by the ME-HDH system (3.23 kW) and the IE-HDH system (3.11 kW) due to relatively high mass flow rates. The latent heat flux was observed to be relatively high in the case of the ME-HDH system. Minimum specific energy consumption was observed from the ME-HDH system, and consequently, a maximum gain output ratio (3.32) was realized. In addition, the study realized that an increment in air velocity and wet bulb effectiveness significantly improves the WPR. In accordance with the climatic conditions of the studied Saudi Arabia cities, it has been realized that Al-Hofuf and Riyadh produce relatively high WPRs with minimum energy consumption. In the case of Al-Hofuf, the average WPR was recorded as 185.51 kg/day, followed by Riyadh (180.33 kg/day). The energy required was estimated to be 0.042 kWh/kg and 0.034 kWh/kg for both cities, accordingly.

Prediction and Analysis of Dew Point Indirect Evaporative Cooler Performance by Artificial Neural Network Method

The artificial neural network method has been widely applied to the performance prediction of fillers and evaporative coolers, but its application to the dew point indirect evaporative coolers is rare. To fill this research gap, a novel performance prediction model for dew point indirect evaporative cooler based on back propagation neural network was established using Matlab2018. Simulation based on the test date in the moderately humid region of Yulin City (Shaanxi Province, China) finds that: the root mean square error of the evaporation efficiency of the back propagation model is 3.1367, and the r2 is 0.9659, which is within the acceptable error range. However, the relative error of individual data (sample 7) is a little bit large, which is close to 10%. In order to improve the accuracy of the back propagation model, an optimized model based on particle swarm optimization was established. The relative error of the optimized model is generally smaller than that of the BP neural network especially for sample 7. It is concluded that the optimized artificial neural network is more suitable for solving the performance prediction problem of dew point indirect evaporative cooling units.

On the performance improvement of an inverted Brayton Cycle using a regenerative heat and mass exchanger

Recovery of the low-temperature waste heat for electricity generation has been gaining a significant interest. An Inverted Brayton Cycle (IBC) is often employed to convert the low-temperature waste-heat to electricity while the thermal efficiency and specific work output are poor. In this paper, a new energy recovery scheme is introduced incorporating the IBC with a Regenerative Heat and Mass Exchanger (RHME). The RHME is a heat and mass exchanger that consolidates a recuperator (for thermal efficiency improvement) and an Indirect Evaporative Cooler (for enhanced specific work). Numerical models for RHME and the IBC were judiciously developed where possible condensation in the product air channel was accounted for. The model was validated with the experimental data and the cycle was investigated for various waste-heat sources (50–150 °C). When compared to a conventional air-cooling IBC system, incorporating the current energy recovery scheme increases the thermal efficiency from 8.13% to 14.36% and specific work output from 10.38 to 12.46 kJ/kg equivalent to 76.63% and 20.1% improvements, respectively. The unprecedented performance improvement is realised from the exploitation of the regenerative and air-saturation (cooling) mechanisms for both energy recovery and cooling of the working fluid.

Performance enhancement of a cross flow dew point indirect evaporative cooler with circular finned channel geometry

Efficient geometric design has a significant influence on heat transfer characteristics in heat exchanging devices. Performance of a dew point evaporative cooler can be significantly enhanced through geometric modification(s) of dry channel in order to achieve desired cooling effect. In this regard, the current study reports experimental analysis of a finned cross flow dew point indirect evaporative cooler (IEC) working under wide range of operating conditions. The system is designed for a cooling capacity of about 1 kW using circular Aluminum fins which are deployed in the dry channels of IECwf; thereby increasing around 5% in terms of the surface area for enhancement of heat transfer process. While another heat and mass exchanger is used in the dew point Indirect Evaporative Cooler without having extended surfaces (IECwof). Both experimental setups are investigated under similar operating conditions in terms of ambient air temperature (varying between 30 and 45 °C), air humidity (ranging between 10 and 12 g/kg), velocity (varied from 2 to 6 m/s) and water temperature (25–35 °C). Performance of both IECwf & IECwof is investigated in terms of cooling capacity, temperature drop of product air, wet bulb effectiveness, dew point effectiveness and thermal coefficient of performance. The results show that the IECwf has achieved average value of supply air temperature 16.5 °C with cooling capacity of 692 W which are around 25% and 18% enhanced compared to IECwof, respectively. The resulted average COP is 11.24 for IECwf. This efficient dew point IECwf is better suited for residential, commercial and industrial purposes in hot and dry regions.

Approach for Integrating Indirect Evaporative Cooling System into Contemporary Architecture

Nowadays, the knowledge of building ecology focuses on energy efficiency and how to integrate environmental and climatic parameters into HVAC and thus enhances space qualities such as comfort ability. The aim of this paper is to demonstrate the rule of Indirect Evaporative Cooling systems in sustainability of contemporary architecture in hotarid and hot-humid climate. An approach for integrating a novel Sub-Wet Bulb Temperature Evaporative cooler into contemporary architecture is presented. The system uses porous clay materials, as wet media, embedded with heat pipes heat exchangers, the supply air and working air flows were staged in separate ducts and in counter flow direction. Modelling and experimental results show that supply air would be cooled to below wet bulb temperature achieving a considerable cooling capacity and effectiveness. This performance would make the system a potential alternative to conventional mechanical air conditioning systems in buildings.

Operational mode optimization of indirect evaporative cooling in hot climates

This study experimentally investigates the performance of an indirect evaporative cooling fresh air-handling unit at different modes of operation under harsh climatic conditions experienced in Qatar. Temperature and relative humidity are measured at various points within the fresh air handling unit for each mode of operation and, the measured data are stored and analyzed. Cooling performance indices are evaluated in terms of temperature difference across the heat exchanger, dry and wet bulb temperature effectiveness, thermal conductance, and cooling load. Different modes of operation are achieved by pre-treatment of the secondary air using either mist injection, water shower, or a combination of mist and water shower. It is found that indirect evaporation can achieve reductions of up to 43% of the unit's cooling capacity compared to dry operation. A sequence of operations to sustainably optimize energy consumption and reduce carbon emissions is determined.

The Effect of Dry and Wet Bulb Temperature Variation on the Performance of the Indirect Evaporative Cooler

The research is about designing and building up an evaporative cooling system, working by two- stages evaporative cooling system using outer air (pure air). The system is founded by designing and making a heat exchanger of orthogonal flow from Aluminum sheets of (30*60*40) cm, which represents the first stage of the system (indirect stage). The second stage (direct stage) of the system is represented by making an equipment of air washing (cylindrical) with (45 height, 60 width, 3 thickness) cm. The cooling system pulls outer air by a Centrifugal fan. The air passes through the heat exchanger pipes to be cooled tangibly (without moistening). Then it goes over the equipment of air washing to be cooled and cools the specified space. Computer software was designed by FORTRAN Language (FORTRAN 90) to predict the evaporative air cooler performance to know the proper environmental and design conditions of the system. Some variables were made to study their effect on the thermal performance of the system. The studied variable is to change the volumetric flow rate of air from (750 cfm) to (2000 cfm) of the dry side, and from (750 cfm) to (2500 cfm) of the wet side. The pipe length was changed from (20 cm) to (45 cm), and its diameter from (0.5 cm) to (3 cm). Those were the design changes. On the environmental changes, we studied the effect of changing the temperature on the dry or wet bulb of the system. The study is taken place in Tikrit University (34. 35N; 43.37 E), to determine the suitability of the weather conditions of the region for the work of the system. It was taken place in the late August for two consecutive days, with readings of 24 hours. The results show that the best quantity of the air supplied, which represent the best performance of the system (750 cfm) and (1000 cfm) for the wet side when the diameter (1-1.5 cm) and length is (45 cm). The results show also the possibility of the work of this system for the region mentioned because it is characterized by its hot and dry climate in the summer, as the efficiency of evaporative evaporator increases the hot and dry environment by 80%.

Simplified predicting models on Energy-saving Potential of Indirect Evaporative Coolers in Hong Kong

An Indirect Evaporative Cooler (IEC), when used as a precooling unit in the fresh air system, can achieve heat recovery through the use of exhaust air and is attractive for energy saving. In hot and humid areas, the IECs can also realize considerable latent heat recovery due to the possible condensation. Based on statistical data derived by numerical models of different types of IECs, this research developed simplified models for predicting the annual energy saving potential of IECs applied in practices in hot and humid areas. Results showed that the predicted values of simplified models can agree well with the simulated values. By integrating the fitted regression equations to building energy consumption simulation, a case study of a wet market in Hong Kong was conducted. Consequently, the IEC can achieve 43.8 ~ 56.4% energy saving to the HVAC system.

The Thermoheliodome – “Air conditioning” without conditioning the air, using radiant cooling and indirect evaporation

The Thermoheliodome is an experimental pavilion that explores cooling without air conditioning. The two research aims were to explore the use of indirect evaporative cooling and the geometric reflection of radiant cooling. For evaporative cooling we utilize a cooling tower outside of the pavilion to indirectly supply water chilled near the wet-bulb temperature. The radiant cooling system is made up of 55 coaxial chilled pipes each located in the central axis of cones with reflective surfaces that spectrally reflect the surface of the pipes and expand their radiant view factor to the occupants inside the pavilion. The specific geometry was digitally fabricated using an industrial robot and hot-wire foam cutter. The mean radiant temperature (MRT) was shown to be significantly decreased using thermal imaging cameras and with a novel scanning MRT sensor. The radiant cooling delivered from the fluid is maximized by reflection and concentration of heat emitted by occupants on the pipes, while the convective cooling of the air is minimized because only the small pipes are cooled and the reflecting surfaces are not, so the convective heat transfer surface area is small. Under typical indoor office conditions the ratio of radiant to convective cooling is slightly greater than one. For the Thermoheliodome the radiant ratio was greater than 10. Occupant surveys found that although the air temperature was not modified, they felt that inside the space there is a cooling sensation (p≤0.01). The day of the survey they felt on average 3°C cooler.

On the Merkel Equation: Novel ε-Number of Transfer Unit Correlations for Indirect Evaporative Cooler Under Different Lewis Numbers

An innovative relationship between the effectiveness (ε) and number of transfer unit (NTU) was presented in this work for indirect evaporative cooler (IEC). This relationship is featured by its simplicity in use and has noniterative procedure to be implemented as the traditional one in the literature. The new model can be implemented in sizing and rating design of the IEC at different Lewis numbers with a reasonable accuracy. General integral equation, which is similar to that of Merkel equation, is developed in this model. The new relationship was verified through comparison with experimental and numerical work reported in the available literature for closed or indirect cooling tower (ICT), as an example of IEC. Additionally, the predicted results of the present model were compared to those obtained from the traditional numerical models at different Lewis numbers. The simulated results from the new model show a satisfactory agreement with those obtained from the experimental work of less than 10%. The new correlations can be implemented easily in predicting the thermal design and performance of IEC in any simulation program or in real site.

Experimental study on two type of indirect evaporative cooling heat recovery ventilator

Heat recovery ventilator is a feasible way to ease the contradiction between indoor air quality and fresh air handling energy consumption. The paper presents an experimental analysis of a heat recovery ventilator which uses only sensible heat exchanger combined with indirect evaporation cooling (IEC) technology. In this study, two different placement methods (horizontal and vertical) prototypes of heat recovery ventilator combine with IEC were made and the structure and related parameters of the two prototypes were introduced specifically. Then, the porotypes were test on the test rig with different summer operating conditions. Additionally, based on the experimental resulting, the energy consumption saving capability in different China’s regions of the two prototypes were evaluated by a specific net energy saving parameter, and the result shows that both vertical and horizontal IECs can reduce energy consumption during cooling seasons in most regions of China.