Dew Point Indirect Evaporative Cooler Research Articles

Experimental study of the optimal design and performance of a mixed-flow dew-point indirect evaporative cooler

Evaporative cooling technologies represent a promising alternative to face the emerging cooling energy poverty, owing to their low production and operative costs. High performance can be achieved through more complex designs, such as dew point indirect evaporative cooling (DIEC) systems. Recent literature explores improvements on these systems, like flow configuration, materials, and water distribution. This study proposes a compact mixed-flow DIEC system made of polycarbonate plates covered with two possible wicking materials. Three water distribution systems are also studied. The prototypes are experimentally characterised by varying the inlet air temperature, humidity, volume flow, and working-to-intake air ratio. The best performing design is evaluated in terms of temperature drop, dew-point effectiveness, wet-bulb effectiveness, and cooling capacity. Results are consistent with those in the literature for equivalent heat transfer areas. The use of a wicking material improves the cooling capacity by up to 1.45. The type of material is less relevant, which enables to select the most economic and accessible option. External nozzles for water distribution offers temperature drops of more than 1 °C and better cooling capacities of approximately 100 W than inlet water distributors.

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 assessment of the energy performance of a renewable air-cooling unit based on a dew-point indirect evaporative cooler and a desiccant wheel

Given the escalating energy consumption in cities worldwide, it is crucial to investigate the utilization of sustainable technologies and renewable energy sources. The number of empirical studies on the energy performance of hybrid air-cooling systems is limited. Therefore, the objective of this work is to experimentally study the energy performance of a novel renewable air-cooling unit. This prototype is mainly composed of a desiccant wheel and a dew-point indirect evaporative cooler to independently control the temperature, humidity, and carbon dioxide levels of indoor air. 64 experimental tests are carried out to fit an empirical model of this renewable air-cooling unit, focusing on outlet air conditions and the coefficient of performance. In addition, several performance indices are developed for desiccant wheel and dew-point indirect evaporative cooler: (i) moisture removal capacity; (ii) moisture removal capacity per unit of electrical power-consumption; (iii) dew-point efficiency and (iv) cooling capacity of dew-point indirect evaporative cooler per unit of electrical power-consumption. The highest values of dehumidification capacity, sensible cooling capacity and coefficient of performance for this renewable air-cooling unit are achieved for the most severe outdoor air conditions, namely 19.02 kg·h−1, 21.49 kW and 11.0, respectively. This work can serve as a reference for research on the feasibility of hybrid air-cooling systems in the scenarios of heat events and climate change world.

Multi-objective optimization of dew point indirect evaporative coolers for data centers

This study introduces a novel counter-flow dew point indirect evaporative cooler (DPIEC) tailored for data center cooling. A numerical model for DPIEC was developed in COMSOL and validated experimentally, followed by the formulation of regression models using response surface methodology. Eight critical design parameters (five operational and three geometrical) were linked to three performance evaluation indexes (outlet primary air temperature T1,out, coefficient of performance COP, and cooling capacity per unit volume Qv). The magnitude of parameter influence on the evaluation indexes was assessed. Employing the three regression models as objective functions, a genetic algorithm, implemented in MATLAB, was adopted to perform multi-objective optimization for DPIEC under four climatic conditions, yielding an array of optimal parameter combinations. The results underscored the robust predictive accuracy of the established regression models, with R2 and Adeq Precision exceeding 0.96 and 53.7, respectively. The ideal point method achieved design solutions of the DPIEC with T1,out below 21.6 °C, COP above 61.3, and Qv over 15.5 kW/m3. Compared to the original design, the optimized design featured reductions of over 13.84 %, elevations of over 23.50 %, and enhancements of over 104.10 % in these three indexes, respectively. In addition, the confirmation study of the Pareto front proved the reliability of the obtained DPIEC design reference.

Manufacturing and experimental analysis of a dew-point indirect evaporative cooler using fused deposition modelling 3D printing and polymeric materials

Evaporative cooling (EC) is an interesting alternative for reducing energy consumption and CO2 emission associated with the cooling of building. In the present work, a prototype of an innovative dew-point indirect evaporative cooler (DIEC) was manufactured by additive manufacturing technology. This prototype was made up of two types of materials: (a) one porous, with high water absorption capacity, polyvinyl alcohol (PVA) with felt, and therefore, high capacity of generate EC; and (b) another with high hydrophobic properties, polylactic acid (PLA) with bronze. The materials were characterised in terms of thermal, water absorption properties and morphological properties. Prior to manufacturing, a design of experiments was conducted in order to find the optimal manufacturing parameters. The prototype was produced through an innovative process, based on the simultaneous use of two extruders, and the manufacture of a porous layer of felt by dissolving the PVA matrix where the felt was initially embedded. Finally, the energy performance of the prototype was experimentally analysed, reaching values of dew-point effectiveness up to 0.9 and energy efficiency ratio up to 22.74 at 45 °C outside dry bulb temperature. These results show that additive manufacturing is promising for developing competitive compact and highly energy efficient DIEC systems.

Impact of air distribution on dew point evaporative cooler thermal performance

A new geometry of the dew-point indirect evaporative cooler structure was proposed which enables uniform distribution of water in the working channels and application in traditional air handling units. This arrangement requires a complicated structure of the product channel in which the air is cooled. The airflow direction changes and complicated structure it is associated with local losses affecting the total pressure loss. High-pressure drop limits the use of this dew point evaporative cooler as an alternative source of cooling. Therefore, a verified method based on numerical fluid dynamics (CFD) was used to determine the pressure drop and air distribution in the exchanger. The combination of the CFD method and modified ε-NTU allows the thermal performance of the device including the uniformity of air distribution, cooling capacity, and coefficient of performance to be determined. Finally, the appropriate exchanger dimensions, i.e., the channel height, or final distribution regulation may be found depending on the exchanger application.

Experimental analysis of dewpoint indirect evaporative cooler operating with solar panel

M-cycle (Maisotsenko cycle) based indirect evaporative cooling system can significantly enhance the natural ecosystem. The operating cost of dewpoint indirect evaporative cooler (Dewpoint-IEC) is low for space air cooling systems. Dewpoint-IEC is inexpensive, energy efficient, and ecological friendly. This study illustrates the experimental evaluation of Dewpoint-IEC working with varying operating conditions. The system designed for up to 1 Ton cooling capacity of the system which has coefficient of performance and energy efficiency ratio up to 6 and 20. The experimentation of Dewpoint-IEC is investigated in terms of the relative humidity and ambient temperature. The results indicate that the effectiveness of the Dewpoint-IEC system is increased with decrease the relative humidity and increase the ambient air temperature. The highest experimental values of wet bulb and dewpoint effectiveness of the system is 1.11 and 0.76. The maximum resulting values of EER, COP, and cooling capacity is 19, 6.1, and 3.3 kW, respectively. Based on experimental results, the system is a feasible option in hot summer days. Moreover, the power consumption of the Dewpoint-IEC is 70 W which can be achieved by combining the system with solar panels. So, current research also shows that Dewpoint-IEC integrated with solar panel recommends off-grid solution as well.

Simulation of a desiccant air-conditioning system integrated with dew-point indirect evaporative cooler for a school building

In this study, a desiccant based air-conditioning system supported by a dew-point indirect evaporative cooler, a direct evaporative cooler, two heat recovery units was investigated during a complete cooling season for air-conditioning of a school building located in Adana, Turkey. A mathematical model of the air-conditioning system was developed by deriving new equations for modelling two key components of the system, namely desiccant wheel and dew-point indirect evaporative cooler using the available correlations and experimental data. Effectiveness of desiccant wheel and dew-point evaporative cooler, heat transfer rates realized in the main system components, the thermal energy requirement to drive the system and cooling performance of the system are investigated thoroughly. The effect of desired building indoor air temperature and mixing ratio of exhaust air on the operation and performance of the system was detailed. The results show that it is possible to obtain desired comfort conditions within the building during complete cooling season with the air-conditioning system considered. The monthly average thermal COP is maximum in October with 0.78 and minimum in July with 0.22. The seasonal thermal COP of the system is 0.43.

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.

Performance assessment of a desiccant air-conditioning system combined with dew-point indirect evaporative cooler and PV/T

In this study, a new solid desiccant air-conditioning system configuration integrated with direct and dew-point indirect evaporative coolers and water-cooled photovoltaic-thermal solar collectors (PV/T) is proposed and simulated for a building located in Adana, a humid and hot city on Mediterranean coast of Turkey. New multiple linear regression equations are developed for the performance of desiccant wheel and dew-point indirect evaporative cooler, which are the two crucial components of the air-conditioning system and used in hourly simulations. Building set temperature, exhaust air mixing ratio, suitable warm air source for preheating regeneration air and optimum connection strategy of PV/T collectors to each other are examined in detail. Hourly and daily thermal coefficient of performance (COPth), solar fraction, primary energy consumption and specific primary energy consumption are calculated to evaluate the energetic performance of the system. COPth of the system ranges from 0.28 to 0.40 during the day, with a daily COPth of 0.34. 69% of the thermal energy required to regenerate desiccant wheel can be generated by the PV/T water collectors.

Experimental research on the cooling performance of a new regenerative dew point indirect evaporative cooler

This paper presents an experimental investigation of a new regenerative dew point indirect evaporative cooler that uses a polymer plant fibre composite material and a pure counter-flow heat exchange structure. The wet bulb efficiency, dew point efficiency and cooling capacity of the cooler were tested and analysed under various working conditions, such as a dry area, moderate humidity area and high humidity area conditions in an enthalpy laboratory. The experimental results show that the wet bulb efficiency reaches 105.6% and the dew point efficiency reaches 76% under standard drying conditions (dry-bulb temperature of 38 °C and wet-bulb temperature of 23 °C) and when the secondary air/primary air volume ratio is equal to 1.1, the cooling capacity is 2.83 kW, the dry-bulb temperature drop can reach 15.2 °C. Simulating the experimental results of the working conditions of Urumqi and a standard dry environment shows that the application of dew point indirect evaporative cooling technology in hot and dry areas has great advantages and broad application prospects. • The cooler is made of polymer plant fiber composite material, which has high-efficiency hydrophilicity. • The cooler is a pure countercurrent heat exchange structure to improve the heat and mass transfer efficiency. • The performance of the cooler under different environmental parameters was studied experimentally. • The experimental results show that the wet bulb efficiency reaches 105.6% and the dew point efficiency reaches 76% under standard drying conditions.

Comparative analysis of sustainable desiccant – Evaporative based ventilation systems for a typical Qatari poultry house

Direct evaporative cooling is the typically adopted ventilation system in poultry houses in hot climates. This type of cooling is inefficient during period of relatively high humidity resulting in degraded thermal comfort and air quality for the chicken. This work investigates two sustainable ventilation systems that are adequate to hot and humid climates to enhance the poultry indoor conditions. System I consists of the conventional direct evaporative cooler integrated with packed bed desiccant dehumidifier whilst system II integrates a dew-point indirect evaporative cooler with the packed desiccant bed. To determine the most cost-effective cooling system and ventilation strategy, both systems were sized and their operation optimized for a case study of a typical modular poultry house in Qatar hot humid climate. The selection of the better performing system was based on the consumption of water, electricity and thermal energy during the cooling season while ensuring that the same thermal and air quality conditions were attained within the poultry house by both systems. This was achieved by developing and validating mathematical models for the mass and energy balances of the poultry house as well as the systems’ subcomponents. The models were integrated and a genetic algorithm optimizer was used to find the best performance of system I and system II to compare their performance. Accordingly, it was found that system II was able to meet the poultry house thermal and air quality requirements at 35 % lower operating cost as compared to system I over the entire Qatari cooling season.

Energy efficiency analysis of a multifunctional hybrid open absorption system for dehumidification, heating, and cooling: An industrial waste heat recovery application

Rising energy consumption for heating, dehumidification, and cooling applications has created a scientific gap to develop new hybrid energy systems which can utilize the available waste heat or renewable energy resources. In this study, a new multifunctional hybrid open absorption system is proposed to utilize the waste heat from moist air or flue gases to supply hot water for heating and to dehumidify the ambient air for further industrial or space cooling applications at the expense of any external heat source for regeneration requirement. This multifunction system consists mainly of two open column absorbers (primary and secondary), condenser, regenerator, heat exchangers and Maisotsenko cycle based dew point indirect evaporative cooler. The secondary absorber recovers the latent heat from moist gas and the primary absorber dehumidifies the ambient humid air for air-conditioning or other cooling applications. Absorbed water vapors from the absorbers are condensed to get the recovered water by transferring the vapor’s latent heat to the circulating water which can be used for heating applications. The thermodynamic and process models of this system are developed to analyze its performance in detail. The effects of important inlet parameters are studied on different performance parameters and the results highlight that the system is capable to provide 176.9 kW heating capacity at the thermal coefficient of performance of 2.223 with heat recovery efficiency of 87.1%. Moreover, this system can recover 115.2 kg/h water in the form of condensate with recovery efficiency of 76.36% and cooling capacity of 9.873 kW can be achieved at system design specifications.

Performance characterization and optimization of counter-flow dew point indirect evaporative cooler through response surface methodology

The optimal performance of dew point indirect evaporative cooler with respect to the operational environment is a challenging task as the same is affected by many parameters. This paper reports the regression modeling and optimization of a counter flow indirect evaporative cooler using the response surface methodology. Experimentation is conducted using the central composite design and regression models are statistically evaluated for adequacy and found within 7% maximum error limit as compared with literature. Results show that supply temperature and cooling capacity increase with increasing inlet air velocity and inlet air temperature. Moreover, dew point and wet bulb effectiveness have a direct relationship with inlet air temperature and an inverse relationship with inlet air velocity. After validation, the regression models are subjected to single-objective and multi-objective optimization based upon the desirability function technique. The multi-objective formulation reveals that optimal performance of the system is achieved at 41.31 °C inlet air temperature, 3.61 m/sec inlet air velocity, 12 g/kg inlet air humidity, and 24.48 °C water temperature. Finally, an operational envelope is proposed to evolve a zone for the best-suited operation of such a device which ensures a reasonable cooling capacity within 1.5 – 2.5 kW while enabling thermal comfort for the conditioned space.

Integrated solar – Windcatcher with dew-point indirect evaporative cooler for classrooms

This work investigates the performance of a novel passive ventilation and cooling system for a classroom in hot and semi-arid climate. The system integrated a combined solar chimney – windcatcher system with a fan-assisted cross-flow dew point indirect evaporative cooler (DP-IEC) to condition the fresh air supplied to the space. The classroom exhaust, driven by the solar chimney, was used to cool a double layer window and reduce the radiation asymmetry. A mathematical model was developed to size the system’s components and optimize its hourly operation to achieve the required thermal comfort and indoor air quality at minimal fan energy and DP-IEC water consumption. The integrated model was validated with published data in the literature. The validated integrated model was used to simulate the proposed system for a typical classroom in the semi-arid climate of Beqaa, Lebanon. It was found that the cooling system was able to meet the space thermal and air quality requirements throughout the summer with a temperature of 24.8 °C (±0.3 °C), a relative humidity ranging between 43% and 58%, and a CO2 level less than 900 ppm. Moreover, the radiation asymmetry was less than 3.5 ℃ which is within the acceptable range (less than10 °C). The system’s highest energy and water consumptions of 3.6 kWh/day and 185 L/day occurred during the peak load month of July where the DP-IEC was operated with a high fresh air flowrate of 1 kg/s with no bypass throughout most of the day. Over the summer period (May to September), the system achieved 70% reduction in operational cost as compared to the conventional systems.

A solar regenerated liquid desiccant evaporative cooling system for office building application in hot and humid climate

In this paper, we provide the thermal analysis and design methodology of a liquid desiccant assisted dew point indirect evaporative cooling system. The purpose of the system is to serve as an alternative for conventional vapour-compression based building air conditioning systems in providing satisfactory human thermal comfort conditions in the hot and humid climatic regions. The main features of the study are the following: i) novel incorporation of a forced parallel flow direct solar regenerator and a dew point indirect evaporative cooler within the same air conditioning unit; ii) detailed thermal modelling of each of the system components with fewer simplifying assumptions compared to earlier works; iii) large cooling capacity (~18.8 TR) under harsh climate; and, iv) a comprehensive year-round case study for system operation in a hot and humid location (Kolkata, India). Our thermal model is validated with a reference model study. The maximum room air temperature predicted by the current system for year-long analysis is 26.7 °C. The thermal COP of the system for diurnal operation in the most humid month of a calendar year (July) varied between 0.40 and 0.96. The cooling system can prevent overheating of the conditioned space, as specified by ASHRAE Standard 55–2017, throughout the year.

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.

Sustainable cooling system for Kuwait hot climate combining diurnal radiative cooling and indirect evaporative cooling system

This study investigates the performance of a hybrid passive cooling system that combines a hydronic radiative cooling (RC) panel integrated with a cross-flow dew-point indirect evaporative cooler DPIEC equipped with a closed cycle water reclamation using air-water harvesting (AWH) system. The study was performed on a typical residential house located in the hot and mostly dry climate of Kuwait. The house hourly cooling load was calculated using the transient simulation software TRNSYS. A mathematical model integrating the hydronic RC panel and the DPIEC models was developed and simulated to predict the system operation over the cooling season. The integrated hybrid system’s performance was compared with two systems: i) the DPIEC unit standalone, and ii) the conventional cooling system, while focusing on the role of the RC system.It was found that the use of the RC panel’s power during nighttime and daytime reduced the water consumption of the DPIEC unit by an average of 44.2% in comparison to that of a DPIEC unit operating alone during the cooling season. Moreover, a significant reduction of 53.4% in the electrical energy consumption was achieved by hybrid system compared to a typical AC system during the entire cooling season in Kuwait.

Energy-saving potential of dedicated outdoor-air system assisted by vacuum-based membrane dehumidifier

The proposed research presents a dedicated outdoor-air system (DOAS) integrated with a vacuumbased membrane dehumidifier (VMD). The primary objective of this study was to evaluate the energy-saving potential of the proposed VMD–DOAS combination. VMD–DOAS comprised a membrane-energy exchanger (MEE), dew-point indirect evaporative cooler (DP-IEC), and VMD. VMD possessed a characteristic by virtue of which the dehumidification process was isothermal; i.e., no temperature change was observed during the VMD process. While VMD served to control the dry-air supply, the required target temperature (i.e., 17 °C) was maintained via DP-IEC operation. The remaining sensible heat of the conditioned zone was controlled by the ceiling radiant cooling panel (CRCP). The load of the conditioned zone was driven by TRANSYS 18, and an engineering equation solver (EES) was used for evaluating the energy-saving potential of the proposed system with CRCP by comparing it against the variable-air-volume (VAV) system. Results of this study demonstrated that the proposed DOAS with CRCP consumed 37% less operating energy compared to the VAV system. This observed energy-saving potential of the proposed system was driven by reducing the dehumidification load and subsequent energy recovery by MEE.

Comparative study of the conventional types of heat and mass exchangers to achieve the best design of dew point evaporative coolers at diverse climatic conditions

The objective of this research is a comparative analysis of various kinds of heat and mass exchangers of dew point indirect evaporative cooler. Considering three key performance parameters of an evaporative cooler, namely life-cycle cost, annual water consumption and the annual average of the coefficient of performance as objective functions, the best design of two popular types of the dew-point evaporative cooler (counter-regenerative and cross configurations) for employing in small-scale residential buildings was found through a multi-objective optimization approach. Both operational and geometric characteristics of the coolers were selected as the design (decision) variables while proper constraints such as thermal comfort were imposed. Afterward, between the optimized counter-regenerative and cross configurations, the foremost one was selected for representative cities of four diverse groups within the Köppen-Geiger climate classification system. It was found that in very hot and dry areas, the counter-regenerative configuration was the ideal choice while in other investigated climates, using cross configuration was a better alternative. Moreover, the results showed that in comparison to the base case conditions by using the best-optimized configurations, 64.4, 86.4, and 1039.0% improvements in life-cycle cost, the annual water consumption, and the annual average of the coefficient of performance were achieved, respectively.