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Experimental investigation of energy and exergy performance of a direct evaporative cooler using a new pad type
Abstract
In this paper a comprehensive experimental parametric study on the performance of a new evaporative cooling pad type made of cellulose papers in bee-hive structure is presented. Four different pad sizes of face area 0.335 × 0.390 m² and thicknesses 35, 70, 105, and 140 mm are examined. The tests are carried out in a wind tunnel adapted with the evaporative cooling system. Experiments are conducted to evaluate the cooling pad performance parameters: air temperature drop, air humidity ratio raise, cooling capacity, water evaporation rate, saturation efficiency, pressure drop, energy efficiency, energy efficiency ratio, exergy efficiency and overall exergy efficiency. The effects of the cooling pad thickness and the operating conditions including air velocity, inlet air temperature, water flow rate, water temperature and cooling pad thickness on the performance parameters are investigated. The results show that, the saturation efficiency, exergy efficiency and overall exergy efficiency of the proposed pad enhance with increasing the pad thickness and water flow rate and their highest obtained values are 84%, 92% and 74%, respectively. The maximum pressure drop, temperature drop and cooling capacity obtained for this pad are 46 Pa, 18°C and 6.26 kW, respectively. Moreover, the highest energy efficiency ratio is 281 obtained at 2 m/s air velocity. Finally, new dimensionless experimental correlations for predicting the system performance parameters in terms of various operating conditions and system size are presented.
... The inherent porosity of the bark, being a local material, enables efficient water absorption, resulting in a substantial cooling capacity, particularly when used at higher thicknesses. Nada, Fouda [18] as well as Nada, Elattar [9] demonstrated in their studies that a proposed pad composed of crimped cellulose in the form of hexagonal geometric cells can heighten cooling efficiency. This enhancement is achieved by increasing both the thickness of the evaporative cooling pad and the water mass rate for soaking, leading to higher pad water saturation. ...
... Moreover, as stated by Nada, Fouda [18], the term "energy efficiency (η en )" signifies the ratio of total energies in the air stream entering the evaporative cooler to those in the air stream exiting it. This measure can be employed to gauge the efficiency of the evaporative cooler, and its calculation is as follows: η en =ṁ a,2 h a,1 m a,1 h a,1 +ṁ w,evap h w,v ...
... referring to Martínez, Ruiz [5] as well as Nada, Fouda [18], the exergy efficiency (η ex ) and the overall exergy efficiency (η ex, overall ) can be evaluated using equations (12) and (13), respectively. η ex =ṁ a,2 (ex) 2 m a,1 (ex) 1 +ṁ w,evap (ex) w (12) η ex,overall =ṁ a,2 (ex) 2 m a,1 (ex) 1 +ṁ w,evap (ex) w +Ẇ fan +Ẇ pump (13) Furthermore, the performance of the DEAC with various cooling pads used in the present research was also analyzed using the energy efficiency ratio (EER) as shown below [17,18]: ...
... In the present world, most buildings use AC units that work on the vapour compression (VCR) cycle. They consume high energy and cause environmental hazards (Nada et al. 2019). Therefore, it is imperative to use an energy-efficient system and provide thermal comfort. ...
... The deviations in experimental data lead to uncertain results. Then total uncertainty of the dependent variable expressed in terms of independent variables is given by Equation (5) using the root sum square method (Nada et al. 2019;Doğramacı et al. 2019;Martínez et al. 2018). Uncertainty in cooling effect, ...
... Cooling efficiency (Nada et al. 2019) ...
Current work mainly deals with the design and construction of a
centrifugal humidifier where the humidification and cooling are due to
the soaking of the packing and the dispersion of the water from
packing due to the centrifugal effect. Celdek pad 7090 is used as
humidifying media, and water is used as a working substance.
Experiments are performed by varying the water flow rate (WFR), air
velocity (AV) and rotational packing speed. Performance parameters
such as a difference in dry bulb temperature (DBT), difference in relative
humidity (RH), saturation efficiency, coefficient of performance (COP)
and evaporation rate (ER) are evaluated. Results showed that a water
flow rate of 0.6 litres per minute (L/min), rotor speed of 150 rpm and air
flow rate of 5 m/s gave the maximum performance. The current unit
gave a maximum cooling efficiency, COP and ER equal to 79.23%, 5.24
and 0.90 g/s, respectively. Stationary and dynamic packing conditions
are assessed where it is observed that the performance of dynamic
packing is higher than that of the static case at all operating ranges.
Celdek packing with dynamic conditions can be suitably applied to
handle huge cooling loads, which encourages sustainable energy
sources and reduces environmental pollution by limiting greenhouse
gas emissions.
... In three-stage evaporative cooling, the air is first humidified and cooled indirectly, and then it is made to pass through the cooling coils where it will dehumidify. It is mainly applicable in the monsoon season when the humidity is high [3]. The packing efficiency used for humidification depends on various factors such as material type, thickness, surface area, perforation size, relative humidity, the volume of water, and flow rate. ...
... Results indicated that, with the change in the inlet air velocity, the pressure drop, and the evaporated water increased. Nada et al. [3] studied the cooling pad made of cellulose papers with a bee-hive structure. Four different thicknesses of the packing were selected and studied. ...
... Energy conversion factor or COP is defined as the ratio of total cooling effect to the electrical power consumed by the blower and the motor. It is calculated by using equation (2) [3]. ...
Humidification-dehumidification technology is one of the most economical techniques to fulfill cooling needs. The current work focuses on designing and constructing a novel reciprocating packing humidification system, where four packings are placed in four different slots and operated by a cam follower mechanism. Inlet operating parameters such as air velocity and camshaft rotation are varied to determine the influence on the outlet parameters such as energy conversion rate, energy conversion factor, humidification efficiency, and specific cooling capacity. The reciprocating multistage evaporative cooler performs better than the single-stage cooler with superior values for the performance parameters. With the increase in the camshaft speed, there is a reduction in the energy conversion factor (ECF), humidification efficiency (HE), and evaporation rate (ER). An increase in air velocity increases ER, ECF and decreases HE. The highest humidification efficiency is 72.6%, and the ECF achieved is 2.9, corresponding to an air velocity of 5.6 m/s and a camshaft speed of 10 rpm. Comparison with conventional VCR-based cooling techniques reveals that 7% of energy can be saved using a multistage evaporating cooling device. Sensitivity analysis reveals that the air flow rate is more significant than the camshaft rpm influencing the output responses. Operating parameters have been optimized to attain enhanced performance from the multistage reciprocating cooler. The results indicated that maintaining the air velocity of 5.3–6 m/s and the camshaft speed of 16–18 rpm improves the overall performance of the evaporative cooler with reasonable energy consumption.
... As expected, the literature agrees that the drop in temperature increases when the WBD increases (X. Chen et al., 2018Chen et al., , 2017 (Camargo et al., 2005;Nada et al., 2020Nada et al., , 2019Sheng & Agwu Nnanna, 2012). Because most of the experimental research conducted has not controlled air relative humidity at the inlet airstream, further studies are needed to properly evaluate the effect of the inlet air psychrometric conditions on saturation effectiveness. ...
... A larger WBD would result in increased humidification of the airstream and, consequently, greater temperature drops. Published research also agrees that higher air velocities improve the CC (Do gramacı et al., 2019; Laknizi, Mahdaoui, et al., 2019;Nada et al., 2020Nada et al., , 2019. This demonstrates that its detrimental effect on temperature drop is largely offset by the increase in the airflow rate treated. ...
... However, the larger heat and mass exchanges that are preferred in evaporative cooling processes also result in greater exergy destruction, with the subsequent lower exergetic efficiency. Exergetic efficiency is an appropriate parameter when approaching the study from a wider perspective, including the energy consumed by the pump (almost constant) and fans, through the "overall exergetic efficiency", which was also studied by Nada et al. (2019). This parameter can provide a complete picture of system performance but needs to consider the reduction in the additional air conditioning requirements of conventional systems. ...
Evaporative cooling has a major role to play in fighting climate change and in achieving a low‐carbon economy. As it helps to reduce energy demand for air conditioning, it is gaining attention in terms of improving energy efficiency in buildings. Evaporative cooling from wetted media can enhance water–air contact, thereby improving heat and mass transfer further and avoiding aerosols. Wetted media are commonly called evaporative cooling pads and are widely used in greenhouses, intensive livestock farming, and industrial facilities. However, a deep understanding of evaporative cooling pad performance can enhance their application to indoor occupied spaces such as residential or commercial cooling, or in hybrid air conditioning systems. Most studies analyze pad performance mainly in terms of pressure drop and saturation effectiveness. However, some studies propose alternative cooling efficiency parameters and others provide insights into key aspects such as power requirements and the coefficient of performance, water consumption, risk of water entrainment, material decay, and air quality, as well as the effect of water temperature and salinity, solar radiation, or wind speed. Existing results on these less studied performance issues are reviewed, and we identify the gaps in the literature in addition to highlighting the main challenges encountered, in an effort to guide future researchers in the field and enhance the application of direct evaporative cooling.
This article is categorized under: Energy Efficiency > Systems and Infrastructure
Energy Systems Analysis > Systems and Infrastructure
... Al-Mogbel et al. [30] distinguish "Effectiveness of DEC cooler" from "Effectiveness of IEC cooler". Some authors [10,[31][32][33][34][35][36] define the "cooling efficiency" clarifying that it is the saturation efficiency/effectiveness. Al-Badri and Al-Waaly [37] specify that "the effectiveness of DEC was expressed by the saturation efficiency". ...
... Experimental results from Camargo et al. [61] show that the saturation effectiveness improves for higher DBT, when "more cooling is necessary to propitiate thermal comfort"; however, no information is given about the air humidity. Similarly, Nada et al. [31,42] observe that larger inlet DBT result into also larger humidity increase and consequent temperature drop, cooling capacity and coefficient of performance, as well as into an increase in the saturation effectiveness, but do not provide information on the inlet air humidity during the tests. Sheng and Nnanna [63] also provide experimental results of the saturation effectiveness increase with the DBT, though observe the relevance of air humidity and propose the study of the saturation effectiveness variation in terms of the "humidity ratio increase" (in g/kg). ...
... He et al. [49] state that it could be counterproductive to use evaporative cooling pads to precool air before natural draft dry cooling towers if outdoor air DBT is below 20 • C, in the case of cellulose pads, and below 24-26 • C for the remaining materials studied. Nada et al. [31] evaluate the DBT in the range 30 • C-50 • C and set the optimal operating conditions at 40 • C. ...
Direct evaporative cooling is widely known for being an energy efficient air conditioning solution for arid and/or semi-arid climates. Commercialized evaporative cooling pads vary in material and construction characteristics, while existing research proposes several alternative wetted media and configurations. The most studied factors on the evaporative cooling pads operation are the air velocity or air mass flow rate, air psychrometric conditions; the pad thickness, its geometric characteristics and configuration, and the water flow rate supplied. The pads performance is commonly characterized through its saturation effectiveness, pressure drop, temperature drop and humidity increase achieved in the treated air, water evaporation and consumption, cooling capacity, coefficient of performance and the heat and mass transfer coefficients. Present work conducts a critical review on the existing experimental and theoretical research on commercial and alternative wetted media, identifies the gaps in the literature, proposes uniform nomenclature and methodologies, and provides a critical view on the optimal operating conditions from wetted-surface evaporative coolers.
... Several studies were conducted on humidification techniques. Nada et al. [1] conducted an experimental study on cellulose pads of four different thicknesses having beehive configurations. Tests were 2. Principle of humidifier unit (methodology) Fig. 1 shows the mechanism of water purifier-humidifier unit. ...
... This cold air is circulated into the space that requires cooling to maintain thermal comfort conditions. Based on this principle, the following expressions are defined to obtain the performance parameters of the system [1]. ...
The present study aimed at fulfilling the necessity of thermal comfort air in a defined space. A novel -humidifier system where the grey/saline water is filtered and used in an evaporative cooling system to fulfil the requirements of thermal comfort air. Water is made to pass through the first stage of packing to filter the contaminated water, and it is filtered again in a humidifier packing section, which then mixes with air to undergo humidification with reduction in its temperature. Experiments were conducted to evaluate, air quality, and system performance. Various humidification parameters such as humidification efficiency, coefficient of performance (COP), change in pressure and specific humidity were determined. Experimental results indicated that, with the rise in the liquid-to-gas ratio, there is a rise in a change in temperature, specific humidity and COP. The system yielded maximum efficiency, pressure drop, COP, specific humidity change, and a temperature drop of 84 %, 270 Pa, 1.85, 1 g/kg and 5.3 ºC respectively. Air quality measurement revealed that departing air offered good thermal comfort without any pollution. Therefore, the innovative system proves beneficial in hot areas that experience significant cooling demands, such as countries in the Middle East, which also face a scarcity of fresh water.
... Nature of Work Packing and flow type Results and Remarks 1. Nada et al. [14] Single stage direct evaporative cooling ...
... It is clearly seen that the performance of the multistage system is better than that of a single stage, as ΔDBT and ΔRH at the exit are higher. Similarly, evaporation rate, humidification effectiveness as well as COP values are noticeably higher than the single stage rotating packing [14][15][16][17]. Consequently, multistage operation can increase the cooler output as a more effective utilisation of water occurs, due to an enhanced interaction between air and water. ...
Evaporative cooling is a passive cooling technique, which is energy efficient, sustainable, and en�vironmentally friendly. The present work deals with the design and construction of a three-stage rotating centrifugal humidifier test rig equipped with a UV filter. Experiments are conducted varying the air velocity and the motor shaft speed. Overall cumulative performances such as DBTratio, RH ratio, humidification effectiveness, coefficient of performance, and evaporation rate are determined with respect to Reynold’s number and stage wise. Measurements of CO2, TotalVolatile Organic Compounds (TVOCs) and formaldehyde are performed at the exit air from the
filter. Results showed maximum evaporation rate, humidification effectiveness, and coefficient ofperformance equal to 0.82 g s−1
, 88.74%, and 6.14, respectively. The cumulative performance
improved for consecutive stages, but stagewise analysis indicated that the first stage gave a maxi�mum performance. Exiting air quality after filtration is improved by 33%, which meets the most exigent standards in terms of the target pollutants.
... Furthermore, the DEC worked properly for different climatic conditions in Morocco. Lastly, Nada et al. [9,22] have analyzed experimentally the geometrical parameters effect on thermal performance and heat transfer process of a new pad in bee-hive structure (cellulose papers) under Egypt weather conditions. Their results revealed that heat and mass transfer coefficients and performance parameters were improved with the increase of air temperature and water flow rate. ...
... Here, Q L is the latent cooling capacity of the DEC; h fg is the specific latent heat of water evaporation; ω a,out is the humidity ratio of outlet air and ω a,in is the humidity ratio of inlet air. Equation (4) below was utilised to determine the energy efficiency ratio [22,48]: ...
This paper presents an experimental investigation of a direct evaporative cooler, DEC, designed and installed in the hot and arid region of Biskra, Algeria. Date palm tree fibers are used as a novel evaporative cooling material. Different performance parameters are experimentally tested to assess the thermal performances of the DEC system. Results show that the cooling capacity, cooling efficiency and total cooling capacity of the pad improve by increasing the pad thickness and air mass flow rate in extreme ambient conditions. Besides, operation duration has no remarkable effect on the DEC performance. The operating parameters (pad thickness, air mass flow rate, ambient conditions, quantity and temperature of water) are the determinant factors to reach the optimum operating conditions of DEC. Finally, a comparison with the usual cooling systems shows that the date palm fibers pad is an effective material compared to the conventional pads in hot and arid zones
... Furthermore, the DEC worked properly for different climatic conditions in Morocco. Lastly, Nada et al. [9,22] have analyzed experimentally the geometrical parameters effect on thermal performance and heat transfer process of a new pad in bee-hive structure (cellulose papers) under Egypt weather conditions. Their results revealed that heat and mass transfer coefficients and performance parameters were improved with the increase of air temperature and water flow rate. ...
... Here, Q L is the latent cooling capacity of the DEC; h fg is the specific latent heat of water evaporation; ω a,out is the humidity ratio of outlet air and ω a,in is the humidity ratio of inlet air. Equation (4) below was utilised to determine the energy efficiency ratio [22,48]: ...
... Furthermore, the DEC worked properly for different climatic conditions in Morocco. Lastly, Nada et al. [9,22] have analyzed experimentally the geometrical parameters effect on thermal performance and heat transfer process of a new pad in bee-hive structure (cellulose papers) under Egypt weather conditions. Their results revealed that heat and mass transfer coefficients and performance parameters were improved with the increase of air temperature and water flow rate. ...
... Here, Q L is the latent cooling capacity of the DEC; h fg is the specific latent heat of water evaporation; ω a,out is the humidity ratio of outlet air and ω a,in is the humidity ratio of inlet air. Equation (4) below was utilised to determine the energy efficiency ratio [22,48]: ...
... The energy consumption in buildings contributes to one-third of the global energy consumption. 49,50 Since the demand for air conditioners is high in hot and arid regions, it results in higher energy consumption triggering the consequences of global warming. 65,66 Emissions of CO 2 and other greenhouse gases from these systems cause climatic disturbances. ...
... Nada et al. 50 conducted an experimental investigation on the new evaporative cooling pad where cellulose pad with beehive con¯guration was used. Four di®erent pad thicknesses were used and examined in a wind tunnel. ...
Heating ventilation air conditioning (HVAC) design mainly deals with moisture and its control. The moisture may be present inside ducts, conditioned spaces, or outdoors. The process of humidification and dehumidification requires equipment for mass and heat transfer, where the transfer of energy and mass takes place at varying concentrations and temperatures. The exchange of mass or heat depends on the type of flow and is conceivably in the form of gas to liquid or liquid–vapor. This paper aims to review the effect of moisture in the buildings and modulate its effect with several humidifying and dehumidifying techniques as sustainable techniques depending upon the external weather conditions to maintain thermal comfort. Various humidification and dehumidification techniques have been discussed with both their merits, limitations, applications and future scope to meet sustainable energy demands.
... Additionally, these researchers thoroughly assessed this system using the Energy Plus program, and they discovered that buildings with this kind of system function better and are more dynamic than those with laboratory mode. Four distinct kinds of pads used in evaporative cooling systems were examined by Nada et al. [18]. The amount of air temperature drop, the amount of air humidity increase, the amount of cooling capacity, the rate of water evaporation over time, and the energy consumed in the total time efficiency were all factors they looked at while testing the cooling pad. ...
The development of life over successive years causes an increasing consumption of energy consumption; the same factor causes people to face energy consumption. The use of fossil fuels for energy supply causes air pollution and environmental degradation factors, which itself causes climate change in the world. Therefore, researchers are looking for ways to optimize energy consumption in the world. One of these ways is to optimize the energy consumption of air conditioners in buildings. For this purpose, this study demonstrates that optimizing the amount of energy consumption of air conditioning systems (ACS) in a residential building helps significantly in reducing the energy consumption of the building. For this purpose, six residential buildings in 4 cities of Iran (Tehran, Shahrekord, Rasht and Bandar Abbas) with different climates have been investigated. For this purpose, 5 design variables of summer clothing insulation level (SCIL), winter clothing insulation level (WCIL), ACS (40 different ACS), cooling thermostat temperature (CTT) and heating thermostat temperature (HTT) have been considered. The objective functions in this study are the cost of installing the air conditioning system (CIACS), the annual cost of bills (ACB) and the predicted percentage of dissatisfied (PPD). The effect of design factors on objective functions has been investigated by Morris's sensitivity analysis. Three Energy Plus, JEPLUS and JEPLUS+EA software are used for optimization. For this purpose, non-dominant sorting genetic algorithm (NSGA-II)-is used for optimization. The optimization results after the calculations showed that Tehran's annual energy consumption has decreased by 81.3%, Rasht by 63.64%, Bandar Abbas by 82.66% and Shahrekord by 77.2%. Also, the PPD for the cities of Tehran, Rasht, Bandar Abbas and Shahrekord improved by 44.42, 50.1, 31.1 and 56.3% respectively.
... During their interaction, water evaporates and is absorbed by air, resulting in sensible and latent heat, thereby reducing the air temperature and increasing the humidity content. From the past several years many researchers across the world have suggested various materials and technologies for evaporating cooling (Nada et al., 2019;Do gramacı et al., 2019;Jain & Hindoliya, 2011). ...
Present work aimed at the new approach of determination of the performance parameters of a mixed flow centrifugal dynamic humidifier and the parameters are optimized to yield maximum performance. Input and output parameters were set using the design of experiments and the influence of significant parameters on performance was determined using ANOVA. Input parameters such as air velocity, water flow rate and rotor speed were chosen as input parameters and parameters such as humidification efficiency, coefficient of performance, evaporation rate, and energy consumption were used as performance parameters. The results obtained by the model are compared with the experimental results obtained by the fully constructed centrifugal humidifier. Results indicated that anticipated results agreed with the actual experimental values, with an average error of 4.12%. Maximum performance is obtained for input parameters air flow rate of 0.83 m/s, water flow rate of 0.48 LPM and a rotor speed of 94 rpm. System yielded humidification efficiency, coefficient of performance and energy consumption equal to 62.7%, 5.4, 0.475 g/s and 463.2 Watts, respectively. The confirmation results indicated a good correlation between response surface methodology predicted and experimental results.
... Evaluation of the energy consumption and its comparison with the standard AC system is also paramount. Nada et al. (2019) conducted a study on cellulose pads where pad thickness was varied in the wind tunnel type evaporative cooling system. Air velocity and the inlet temperature was varied. ...
This research is centered around the development and construction of a test apparatus for a counterflow evaporative cooler. The packing material utilized in the testing is coconut coir with wettability values of 300, 400 and 500 m²/m³. The experiments involve varying the air velocity. The study examined performance characteristics, including evaporation rates, cooler efficiency, coefficient of performance (COP) and energy consumption information, in relation to the standard Celdek 7090 packaging. The findings demonstrated that employing a coconut coir with optimal wettability resulted in a cooling efficiency and COP of 53.57% and 1.25, respectively. These values were slightly lower than those achieved with the usual Celdek 7090 packing. Coconut coir, as a biomass-derived material, possesses certain benefits that make it a suitable alternative for filling materials in evaporative cooling processes.
... Fan-pad cooling system design(Nada et al., 2019) ...
This work presents an original and innovative approach by combining greenhouse cooling with artificial intelligence models to ensure food security. The study is divided into two parts: Experimental and theoretical. In the first part, a cooling system was implemented in a tunnel-type agricultural greenhouse and compared to a control system. The cooling system consists of multiple fans powered by two solar panels. Data was collected using an acquisition system (Arduino) over approximately one month. This data, along with external data, was utilized to predict the internal temperature of the greenhouse using back-propagation neural network models. The results obtained demonstrate the reliability of the model based on all tests, as evidenced by the coefficient of determination (R 2) and the mean square error (MSE) for the prediction.
... In another study, S.A. Nada et al. [17] conducted comprehensive experimental parametric research on the bee-hive evaporative cooling pad based on energy and exergy analysis for various operating conditions. They investigated the performance of the evaporative cooling pad, the effects of the cooling pad thickness, and the working conditions on the performance parameters. ...
... Evaporative cooling pads are traditionally used because of their simplicity and low manufacturing cost (Doğramacı and Aydın 2020;Tejero-González and Franco-Salas 2021). Various alternative pad materials have been studied in the evaporative cooling pad field, including fibre pads (Alam et al. 2017;Rawangkul et al. 2008), rigged media pads (Barzegar et al. 2012;Malli et al. 2011;Nada et al. 2019), and packages or fill pads (Doğramacı and Aydın 2020;Gunhan, Demir, and Yagcioglu 2007;Laknizi et al. 2021). Previous studies (Aremu 2013;Chen, Yan, and Min 2019) have attempted to judge the performance of evaporative cooling systems using a Predictive Mean Vote (PMV) model. ...
This study mainly focused on enhancing the water absorption capacity of organic fibers to improve the performance of evaporative cooling pads. The enhancement involved immersing 10 g of Ensete fiber in different volumes of NaOH–water solution (for the cases of 0, 5, 10, and 20% NaOH and the remaining water). Saturation efficiency and predictive mean vote (PMV) were used to quantify performance assessment. The maximum saturation efficiency is 75.66%. The computed PMV for the hourly of 8:00 am through 5:00 pm ranges from –3.17 to –0.70 with much too cool in the early morning at 8:00 am comfortably cool at 9:00 am and 11:00 am and comfortable at 10:00 am, 12:00 am, 1:00 am, 2:00 am, 3:00 pm, 4:00 pm and 5:00 pm. Moreover, from 12:00 pm to 4:00 pm, they remained on the ASHRAE scale of thermal sensations, providing the best alternative to an evaporative cooling pad in the study area and similar air conditions for comfort applications.
... When the flow rate is higher, interaction between air and water will be reduced both in indirect and direct heat exchangers, which reduces ΔDBT in total. The results are similar to that obtained by authors in the published literature [37]. On comparing the total temperature drop, for different cases, nanoparticle added case gives higher ΔDBT than the ...
Indoor comfort has become a necessity in recent times with the advancement of science and technology. The usage of direct type air coolers increases the humidity of the closed room, and this increase in humidity is unfavorable. The present work deals with the study related to the combination of direct and indirect type air cooler to increase the performance. A set of mild steel plates have been arranged to form a cross flow heat exchanger to exchange the heat between cold nanofluid and warm air forms the indirect heat exchanger. Al 2 O 3 -based nanoparticles have been blended with pure water and used in indirect air coolers. Celdek pad 7090 is used as the cooling pad in the direct type of air cooling. Experiments are performed by varying the flow rates of water from 1 to 4 lpm, by varying the air velocities from 3 to 6 ms ⁻¹ , and by varying the concentration of nanoparticles in the water from 0 to 0.2.5%. Performance parameters such as change in temperature, change in Relative humidity (RH), cooling efficiency and coefficient of performance (COP) are determined. It was found that by adding the nanoparticles, the performance of the cooler has been enhanced. Chane in dry bulb temperature (ΔDBT), cooling efficiency increased by 13.1%, 14% as compared to the indirect method without using the nanoparticles and 39.2% and 21% as compared to the only direct type. Similarly, ΔRH reduced by 27% when compared to only direct evaporative cooler. 3 LPM showed the best performance with the highest humidification efficiency and COP of 96% and 5.9, respectively. When the air velocity is increased from 3 to 6 ms ⁻¹ , energy consumption increases by 49%. Combination of indirect–direct techniques with the use of nanofluid has shown the potential of greater reduction in the exit DBT with simultaneously without appreciably increasing the exit RH.
... The authors explained that the enhanced saturation effectiveness resulted from the salt incrustation on the pad, which caused an increase in the air-water contact time. Nada and Fouda [19] proposed a rigid media pad with a beehive structure. Its cooling performance was experimentally examined under various operating conditions (air velocity, inlet air temperature, water flow rate, water temperature, and pad thickness). ...
The present study aimed to investigate an alternative evaporative cooling pad material made from mangosteen peel (MP) waste. Mangosteen peels were used to fill a 150 mm thick mesh container with a packing density of 180 kg/m3. A wind tunnel was constructed and utilized to experimentally evaluate the cooling performance of this organic-waste-based pad under hot and humid conditions (31–34 °C and 55–70% RH). The performance parameters assessed included pressure drop, temperature drop, saturation effectiveness, cooling capacity, and coefficient of performance (COP). The influence of air velocity (0.7, 1.0, 1.4, and 1.8 m/s) on these parameters was also examined. The results revealed that the saturation effectiveness of the MP pad ranged from 53% to 77% within the considered air velocity range. The maximum temperature drop (4.6 °C), saturation effectiveness (77%), cooling capacity (0.6 kW), and COP (3.5) were achieved when the system operated at 1.4 m/s. A comparative study showed that, at this velocity, the MP pad provided performance nearly equivalent to that of the commercial cellulose paper pad, except for the pressure drop. This result affirms the potential of mangosteen peels as a suitable wet medium for evaporative cooling applications.
... Direct evaporative cooling (DEC) system utilize the latent heat of evaporation. The ambient air which is warm interaction with pads that contained water which is at the temperature of wet bulb of the incoming ambient air, released heat [1]. The ambient air goes cool by transferring the heat with water and discharged. ...
Demand of air cooling is on-rise due to global warming and increasing population, especially in developing countries, like Pakistan. One of the challenges of the present time is to meet exponentially growing cooling requirements. In this regard, dew point indirect evaporative cooling (DP-IEC) is proposed which is an energy efficient and low operational cost alternative, for space air cooling especially in the dry and hot climate conditions. For this purpose, several design variant prototypes of the DP-IEC are fabricated through the development of heat and mass exchanger (HMX) which has differ in geometries, working air flow patterns, and efficient materials to ensure the high wettability and low weight to volume ratio. The maximum design thermal capacity of the system is achieved up to 1 Ton at maximum flow rate of air around 250 CFM. The resultant maximum dew point and wet bulb effectiveness are 0.76 and 1.11, respectively. Whereas, the coefficient of performance, energy efficiency ratio, and cooling capacities of different design variant prototypes are achieved up to 16.3, 55.7, and 3.3 kW, respectively. Moreover, the numerical simulation of the DP-IEC is carried out using COMSOL Multiphysics software to ensure the thermal comfort in varying the ambient conditions. The simulated predictions are compared with experimental results of a prototype which shows the maximum deviation around 4.78%. In addition, the DP-IEC is evaluated for reduced the water footprint of the prototype. The water footprint analysis indicates that DP-IEC will be used in a water-scarce country. So, this research work shows that DP-IEC which uses significantly less energy and improved water footprint is suitable for several areas of the world.
... Building sector consumes 32% of the whole world's energy, and the vapor compression system used in AC (air conditioning) consumes about 20% of the energy in buildings. AC unit consumes a lot of energy and causes harm to the environment [1]. The evaporative cooling phenomenon is an alternative method to cool the air, which occurs due to water evaporation and is used alternatively to AC-based systems [2]. ...
Current system focuses on design & construction of a multistage reciprocating evaporative cooling test rig. Four packings that are used will undergo the reciprocating action, powered by the cam follower mechanism maintained at an actual rotation speed. Inlet dry bulb temperature & humidity values are varied to replicate the varying climatic conditions, and the output parameters such as cooling load, evaporation rate (ER), humidification efficiency (HE), coefficient of performance (COP) are obtained. Output results showed that as inlet humidity raises, the performance of system drops. With the rise in the camshaft speed or packing velocity, there is an upsurge in the performance until a cam speed of 10 r/min or packing velocity of 0.083 m/s and with further increases in the value, overall performance drops. The system gave a maximum COP, ER, and HE equal to 3.80, 73.87%, and 0.53 g/kg respectively. A rise in the inlet air temperature yielded a maximum change in dry bulb temperature of 8.2°C. Overall, results indicated that evaporative cooling is more effective in arid climates than the cold and humid climates. Air quality test is performed to measure CO 2 , Total Volatile Organic Compound (TVOC), and Formaldehyde (HCHO), and it is found that humidified air entering the defined space is of excellent quality.
... ECs work by pulling hot, dry outdoor air across a wet evaporative pad typically made from aspen wood shavings, other natural fibers, or corrugated cellulose materials ( Figure 1B). 3,8,10,11 The evaporative pad is kept moist during operation by an electric pump that sends water to distribution troughs at the top of the evaporative pads. As ambient air passes through the wet evaporative pads the water evaporates. ...
Evaporative cooling is an energy efficient form of air conditioning in dry climates that functions by pulling hot, dry outdoor air across a wet evaporative pad. While evaporative coolers can help save energy, they also have the potential to influence human health. Studies have shown residential evaporative coolers may pull outdoor air pollutants into the home or contribute to elevated levels of indoor bioaerosols that may be harmful to health. There is also evidence that evaporative coolers can enable a diverse microbial environment that may confer early‐life immunological protection against the development of allergies and asthma or exacerbate these same hypersensitivities. This review summarizes the current knowledge of bioaerosol and microbiological studies associated with evaporative coolers, focusing on harmful and potentially helpful outcomes from their use. We evaluate the effects of evaporative coolers on indoor bacterial endotoxins, fungal β‐(1 → 3)‐D‐glucans, dust mite antigens, residential microbial communities, and Legionella pneumophila. To our knowledge, this is the first review to summarize and evaluate studies on the influence that evaporative coolers have on the bioaerosol and microbiological profile of homes. This brings to light a gap in the literature on evaporative coolers, which is the lack of data on health effects associated with their use.
... Most buildings use air conditioning systems that operate on vapor compression refrigeration principle. Mechanical refrigeration utilizes a lot of power and is also hazardous to the environment [1]. Therefore, low energy consuming systems such as evaporative cooling units are now used to minimize cost, energy, and pollution. ...
Present work comprises the fabrication of a multistage reciprocating humidifier where four Celdek 7090 pack�ings are arranged at different positions run by a motor connected to a cam follower. Packing dips in the water and comes in contact with air in cross flow direction in a duct. Air velocities and camshaft speeds are varied to evaluate the performance parameters such as outlet dry bulb temperature, outlet specific humidity, evaporation rate, coefficient of performance, cooling effect and humidification efficiency. A theoretical model is constructed to predict the performance of the multistage dynamic humidifier. Stage-wise performance is also determined to analyse the influence of number of stages on the cooler performance. The system gave a maximum evaporation rate, energy conversion factor, humidification efficiency equal to 1.864 g/s, 4.84, and 72.62 %. The predicted performance parameters for various conditions are found to be in agreement with the experimental results. Experimental and empirical results are close to each other with a maximum deviation of 2.1 %, 2.4 %, 8.3 % and
8.5 % for exit air temperature, exit humidity ratio, saturation efficiency and energy conversion factor respec�tively for various tested air flow rates. Stage wise performance revealed that higher number of stages will
drastically deteriorate the performance and simultaneously increase the energy consumption.
... The results showed that for an inlet air with a temperature of 30 o C and relative humidity of 30%, the maximum system exergy efficiency was obtained at about 20%. Martineza et al. [4] and Nada et al. [5] studied the energy and exergy performance of different wet pad materials of evaporative coolers through experiments and found that the exergy efficiency was between 70% and 94% under different pad thicknesses. This research comparatively analyzes the energy and exergy performance of indirect flat evaporative coolers on the basis of a verified numerical model and experimental correlation. ...
External-cooling indirect evaporative coolers with different configurations and working air sources are incomprehensively analyzed and compared so far. This paper investigates the mechanism and theory of operation of indirect flat-panel evaporative coolers based on X-analysis. Then, based on the second law of thermodynamics analysis, the entropy production rate of the flat-plate heat exchanger of the cooler is calculated. As a result of this analysis, the optimal energy efficiency-evaporation efficiency and cooling capacity values are presented in terms of effective parameters in the design.
... Direct evaporative cooling is well known as an energy efficient air conditioning solution [9]. The use of an evaporative cooling approach can save energy, as cold water lowers the condenser temperature and may increase the rate of heat rejection [10,11]. In the recent study [12], the modeling results showed how the use of an evaporative cooler in a 200 m 2 residential house reduced the total energy consumption by 75% compared to traditional air conditioners. ...
Evaporative cooling is widely recognized as an energy efficient and environmentally-friendly air conditioning solution, and it has drawn a lot of market interest in recent years. However, this technology is accompanied by several challenges. For instance, insufficient evaporation due to poor and non-homogenous water distribution of the pre-cooling pad significantly reduces the cooling performance. The aim of the study is to develop a technique for numerical simulation of the distribution of a droplet liquid (water) on the mesh surface of an adiabatic cooler to improve the performance of air conditioning equipment. Modern computer-aided design (CAD)/computational fluid dynamics (CFD) programs were used to solve the issue. For the mathematical modelling of the medium motion, non-stationary Navier–Stokes equations were used. Parameters such as heat, mass transfer, and the efficiency of liquid droplet spraying were determined. The current study presents CAD modelling, conducted in SolidWorks platform, of water distribution on the adiabatic cooling pad’s mesh surface for improving air conditioning equipment performance. This study provides the methodology for computer modeling and numerical calculation of the parameters of adiabatic cooling, such as modelling of water atomization process. The results show that the use of additional metal mesh intended as cooling pads increases the mass transfer coefficient by Sh ≈ 15–40%; heat transfer coefficient Nu increases by ≈20–40%; and the atomization efficiency increases by ≈30–40%. The installation of metal pad mesh allows for equalized uniformity of the water distribution. The results imply that there are more opportunities to optimize the parameters of adiabatic cooling, which should be evaluated in further research on the subject.
... However, it must be taken into consideration that larger pad thickness results in higher pressure drop and, thus, increases operating costs; therefore, the pad thickness must be selected properly to establish a good balance between saturation effectiveness and pressure drop [26][27][28]. Although an increased water flow rate leads to higher saturation effectiveness [29,30], according to study results of various types of cooling pad configurations and materials, once the pad media becomes entirely wetted, the saturation effectiveness does not increase further [31,32]. ...
As the cooling requirement and the energy prices are increasing rapidly across the world, the need to develop highly efficient cooling equipment is rising as well. Adiabatic cooling employs evaporation to pre-cool the air flowing through a closed-loop coil. This study examines various adiabatic evaporative cooling pads in terms of their pre-cooling potential and advantages over currently available technological solutions through isolating three cross-sectional metal cooling pad shapes (W, Z and Z1). The results of the study suggest that the correlation between Δt↓ and RH↑ is somewhat close in all three cases; however, a slightly higher temperature drop is observed when using a W-shaped metal sheet. Pressure drop variability was negligible under current cooling pad configurations and experimental boundary conditions. Further studies focusing on measurement continuity, longevity and boundary conditions’ variability are recommended.
... Building power or energy consumption accounts for 40% of the total energy, and 10% of non-residential buildings are air-conditioned (Nada et al. 2019). HVAC consumes 50% of the building energy in hot and arid climates (Sampath, Kumar, and Reddy 2020). ...
In the present performance parameters is determined for the varied operating conditions using mathematical modelling. Outlet humidity ratio, Dry bulb temperature (DBT), cooling efficiency and cooling effect have been predicted by varying the air velocities, inlet DBT, inlet relative humidity (RH) and pad thickness for three different wettability of Celdek packing. Predicted results revealed that cooling effect, saturation efficiency, ΔDBT and humidity ratio are found to be increasing with the increase in pad thickness and wettability of the material. An increase in the inlet air flow rate and RH resulted in a decrease in ΔDBT, humidity ratio and cooling efficiency. The maximum performance of ΔDBT, ΔRH, saturation efficiency and cooling effects have been observed for Celdek 7090 and are equal to 6°C, 55%, 90% and 7000 Watts for the thickness of 0.3 m, wettability of 630 m2/m3. Wettability of 630 m2/m3 & thickness 0.3 m gave maximum performance.
... Even if energy analysis was made for air conditioning systems, applying the exergy analysis is a more appropriate method. Energy analysis alone is not sufficient in a system [24]. Exergy analysis calculates the reversible work of a thermodynamic process. ...
A significant portion of energy consumption is due to energy consumption in buildings. Heating, cooling, and air conditioning systems have the largest share in this energy consumption. Evaporative cooling systems, which have the advantage of being economical, zero pollution, and easy maintenance are preferred to reduce energy consumption in buildings. These systems are used in many areas such as greenhouses, broiler houses, and warehouses. In this study, analyzes of exergy, sustainability, and cooling efficiency in four different situations of a ground source direct evaporative cooling system were made. The system was studied in four different cases. While the highest exergy efficiency was obtained in case 3 with 20.83%, the exergy efficiencies in other cases were obtained as 16.83%, 17.49%, and 18.36%, respectively. In addition, the highest specific exergy loss was determined as 100.51 J/kg in case 2, while it was calculated as 73.08 J/kg, 80.23 J/kg, and 73.05 J/kg for the other cases, respectively. It is seen that the sustainability values are in parallel with the exergy efficiency when the evaporative cooling system is examined for four different cases. The sustainability values were determined as 1.20 for case 1, 1.21 for case 2, 1.26 for case 3, and 1.22 for case 4. It is determined that the exergy efficiency gives precise information about the usability and sustainability of the system when these situations are evaluated. The exergetic improvement potential (EIP) was determined as 0.061 for case 1, 0.082 for case 2, 0.063 for case 3, and 0.059 for case 4, respectively. Although the highest exergy efficiency is obtained in case 3, it has a higher recovery potential than case 1 and case 4. In addition, cooling efficiencies for four different cases were obtained as 33.70%, 34.81%, 41.69%, and 36.95%, respectively. The temperature differences between the room and ambient temperatures were determined as 1.45 °C, 1.21 °C, 1.6 °C, and 1.48 °C for each case, respectively.
... In hot and humid climates, Heating ventilation and air conditioning (HVAC) units consume 50% of the building energy and according to the survey, energy consumption in buildings and residential buildings have increased to 40% worldwide in recent years and 6% of the energy is utilized by using air conditioning (AC) unit in the household [1]. This led to global warming and increased cooling demands, and it is predicted that these demands will further increase in the next few years [2]. ...
Excessive energy consumption has led to environmental problems and climate change. Cooling of the building is the key reason for energy consumption in hot regions. Due to the consistent sunlight intensity and high temperatures, the use of cooling units are inevitable. Single stage humidifiers are widely used which provided evaporative cooling consistently. Present work focuses on designing and fabricating a novel multistage reciprocating humidifier operated by a cam follower mechanism. Four packings are operating at four different positions in dynamic conditions. A theoretical model has been constructed to predict the thermal performance parameters using commercially available celdek packing 7090, 5090, honeycomb and corrugated. Theoretically predicted results agree with the experimental results with a maximum deviation of 2.1%., 4.8% and 8.6% for DBT, humidity ratio and saturation efficiency. Variation of the results is studied stage wise, and its change in performance is analyzed. Simulated results indicated that celdek 7090 outperformed the others in terms of change in dry bulb temperature, humidity ratio and saturation efficiency by 0.6%, 0.8% and 1.2% for the airflow rate of 5.6 m/s, respectively. Increasing the pad thickness showed improvement in the drop in dry bulb temperature, increased humidity ratio, and saturation efficiency. It is recommended to use zig-zag celdek 7090 type with 15 cm thickness in a multistage cooler to obtain the best performance for cooling applications in buildings with less cost.
... They found energy production numbers a useful indicator to optimize the cooler. Nada et al. (2019) did exergetic analysis of the DEC with four different pad thicknesses. The exrgetic performance improves with an increase in the pad thickness and water flow rate. ...
The ambient condition varies drastically in the composite climate and the direct evaporative cooling is effective in the dry months; whereas, the regenerative evaporative cooling is effective in the humid months. Hence, seasonal change of the cooling device is needed for effective cooling. In this situation, a dual-mode evaporative cooler (a two-in-one device) is an intelligent choice, which operates in direct mode in the dry months and regenerative mode in the humid months. Hence, this novel evaporative cooler is fabricated in this study and experimental exergy, economic, and sustainability analyses are performed to check the acceptability. Effects of various operating parameters on the performance are experimented in both (indirect and direct) modes of operation. The exergy destruction, exergy efficiency, sustainability index, and specific total cost of the developed device are estimated in both modes of operation. It is found that the exergy efficiency and sustainability of the regenerative mode are higher while the specific total cost of the direct mode is lower. The developed device is more economical in both operating modes as compared to the conventional air conditioner.
... All systems are chosen to operate under the same conditions as far as possible to compare the measured performance parameters of the humidification materials tested in the literature fairly. Table 3 shows that the studied hollow fiber membrane humidifier had a substantially higher value of humidity ratio increase than other types of humidifying pads tested in the literature [14,[36][37][38][39][40][41]. Moreover, the hollow fiber membrane humidifier is more efficient in humidifying the volcanic tuff (value of 80.17%) than the volcanic tuff (value of 81.98%), and coarse pumice in the literature [39] stones (value of 87.37%) is slightly low. ...
Implementation of heating, ventilation, and air conditioning units in buildings for space cooling represents a passive method for achieving thermal comfort and reducing power consumption. This paper introduces solar energy assisted in-direct evaporative cooling system with a novel multi-passage dry channel. The main objectives are to evaluate exergy variations, sustainability, and total cooling cost based on the inlet conditions for four modes: A, B, C, D (without evaporative cooling, with evaporative cooling, preheating, and preheating with humidification). This comparative study explores thermal performance enhancement of an indirect evaporative cooling system across four operational modes. Mainly, the exergy outlet values increase significantly by 77.39%, while exergy destruction decreases by 54.86%. Both energetic and exergetic coefficient of performances witness remarkable enhancements, with energetic Coefficient of Performance (COP) rising by 321.32%. Exergy efficiency experiences a notable enhancement of 29.974%, and sustainability index shows a consistent upward trend, with a 119.34% increase observed in Mode D compared from Mode A. Entropy generation decreases significantly, indicating improved system efficiency. Total capital cost per unit of cooling capacity decreases notably, highlighting cost savings. These findings underscore the effectiveness of incorporating preheating and humidification processes in optimizing indirect evaporative cooling system performance, emphasizing both exergy efficiency and cost-effectiveness.
The application of nozzle-assisted spray cooling to proton exchange membrane fuel cell (PEMFC) stack radiators has shown superior performance when compared with conventional air-cooled radiators. However, challenges remain with regard to high power consumption. This study experimentally optimized a low-pressure compact drizzling module coupled with a stack radiator as an alternative spray cooling strategy. The effects of the distance between the drizzling module and the radiator (30–90 mm) were examined, along with the influence of the spray flow rate/temperature, air velocity/temperature, and coolant flow rate on the thermal performance. The results showed that among the operating variables, the impact of the drizzling distance decreased with an increase in air velocity. Moreover, the drizzling performance was significantly influenced by the spray flow rate and air velocity, with minimal impact from the coolant-side variables. Optimal thermal performance was achieved at a distance of 50 mm and spray flow rate of 0.4 LPM, resulting in a 142 % improvement in heat rejection compared to an air-cooled radiator and a 132 % increase in the air-side pressure drop. Additionally, heat rejection only decreased by 7.3 % as the spray temperature increased from 40 °C to 70 °C. Two novel empirical correlations were developed, predicting heat transfer improvement and air-side heat transfer coefficient with over 85 % accuracy. These findings underscore the potential of drizzling cooling for stack radiators in fuel-cell vehicles, while the empirical correlations offer valuable insights for the development of spray-cooled radiators for next-generation electric vehicles.
Global use of energy-inefficient mechanical vapor-compression air conditioning (AC) is increasing dramatically for home cooling. Direct evaporative coolers (EC) offer substantial energy savings, and may provide a sustainable alternative to AC for homes in hot, dry climates. One drawback of ECs is the potential for infiltration of outdoor air pollution into homes. Prior studies on this topic are limited by small sample sizes and a lack of comparison homes. In this study, we used aerosol photometers to sample indoor and outdoor fine particulate matter (PM2.5) from 16 homes with AC and 14 homes with EC in Utah County, Utah (USA) between July 2022 and August 2023. We observed a significantly larger infiltration factor (Fin) of outdoor PM2.5 in EC vs. AC homes (0.39 vs. 0.12, p = 0.026) during summer. Fin significantly increased during a wildfire smoke event that occurred during the study. During the wildfire event, EC homes offered little to no protection from outdoor PM2.5 (Fin = 0.96, 95% confidence interval (CI) 0.85, 1.07), while AC homes offered significant protection (Fin = 0.23, 95% CI 0.15, 0.32). We recommend additional research focused on cooling pad design for the dual benefits of cooling efficiency and particle filtration.
Conventional air‐conditioned storage systems are more energy intensive which requires a consistent supply of electricity. Apart from this, it is costly and not suitable in remote areas where electricity is almost inaccessible. Therefore, the present study aimed to test the performance and feasibility of an integrated earth air heat exchanger and direct evaporative cooling system for storage of fruits and vegetables. The effects of air velocity (4–6 m/s), water flow rate (0.032–0.096 kg/s), and thickness of the cooling pad (50–150 mm) with corresponding responses were investigated in order to develop response surface methodology (RSM) and artificial neural network (ANN) models and compared them to predict temperature drop and humidity rise. Using RSM model, the optimum values for maximum temperature drop (16.80°C) and humidity rise (70.85%) within a range of input variables were found to be 4 m/s air velocity, 0.065 kg/s water flow rate, and 150 mm thickness of the cooling pad. For predicting the temperature drop and humidity rise, the higher (0.992 and 0.998) lower MAE (0.045 and 0.064), RMSE (0.187 and 0.266), and values (0.028 and 0.001) were observed in the ANN model. The developed ANN model was better than RSM models, and the model prediction was in good agreement with experiment values within the range of ±5% uncertainty. The results of this study indicate that the proposed cooling system can be successfully applied to store horticultural commodities.
Practical Application
Introduced hybrid cooling technique is low‐cost and eco‐friendly, and can be commercially used for on‐farm storage of fruits and vegetables to enhance their shelf life. The system is helpful for smallholder farmers/retailers to maintain the quality of the commodity during storage, minimize post‐harvest losses, and fetch good market value for the commodity.
Evaporative cooling phenomenon yields a cooling and humidification process widely used in AC applications to maintain thermal comfort in the space. Present work deals with the design & construction of a dynamic hu�midifier that operates on the centrifugal action principle. Celdek pad is positioned inside a frame that holds the
water effectively and later dispersed in the air. Heat & mass transfer mathematical model is constructed and parameters such as evaporation rate, cooling efficiency, cooling effect, coefficient of performance, specific hu�midity at the exit and exit temperatures are determined and validated with empirical values. Maximum Hu�midification efficiency of 82%, cooling effect of 3061 W and rate of evaporation of 0.82 g/s have been noticed from the experiments. Both Experimental and theoretical results agree with a maximum deviation of 8%. Also, it is found that packing in dynamic action gave maximum humidification performance compared to the stationary type except for coefficient of performance. Motor shaft speed of 150–160 rpm and the air velocity of 6.5 to 7 m/s yielded optimum results.
Less attention and analysis have been given to cooling indirect evaporative coolers with different configurations and working air sources so far. This paper investigates the mechanism and theory of operation of indirect flat-panel evaporative coolers based on X-analysis. Then, based on the second law of thermodynamics analysis, the entropy production rate of the flat-plate heat exchanger of the cooler is calculated. As a result of this analysis, the optimal energy efficiency-evaporation efficiency and cooling capacity values are presented in terms of effective parameters in the design. It was concluded that dew point effectiveness and COP of the proposed system change monotonously with inlet mass flow rate, temperature and humidity ratio of primary air, respectively. The dew point effectiveness also varies monotonously with the mass flow rate ratio of secondary air to primary air. However, there exists an optimal mass flow rate ratio resulting in a maximum COP.
Present work involves designing and fabricating the three-stage humidifier test rig where three Celdek 7090 packings are arranged vertically at equidistance, forming a multistage humidifier. Water flow rate and airflow rates are regulated to obtain required humidification under both single pad and three pad configuration. Output variables like coefficient of performance, evaporation rate, cooling effect, cooling efficiency and pressure drop are determined. Results indicated that three stage packing gave high performance compared to the single stage. Change in temperature, change in humidity, saturation efficiency & coefficient of performance values are 6.5°C, 44%, 80% and 2.1 respectively, are the maximum values noticed for the multistage humidifier. The study indicated that with the increase in rate of water flow, there is an rise in performance parameters till a water flow rate of 0.6 liters per minute, and after this value, performance deteriorates. Even though multistage performs better than a single stage, as the number of stages increased, the stage-wise performance declines.
This paper examines experimentally the performance of direct evaporative cooling system for the hot and dry climate of Vidarbha region (Wardha, Maharashtra, INDIA, 20.75° N, 78.60° E). The evaporative cooling system of larger capacity has been designed for effective cooling of classrooms and laboratory spaces of Bajaj Institute of Technology, an engineering institution located at Wardha District. The cooling structures existing in the literature might not be appropriate for this weather condition. Keeping in view this problem, an evaporative cooling section is fabricated using newly developed porous-cellulose material, structured in the form of a honeycomb, to meet the comfort necessities of hot and dry ambience. The evaporative cooling systems of capacity 6000 CFM have been commissioned in the cooler chambers associated with the amenities described above. Experiments have been conducted in the summer months to examine the saturation efficiency of the system, for various test situations in the amenities. In order to reduce the penetration of sound into the conditioning rooms, the effect of Nitrile rubber sheets was also examined. The direct evaporative cooling system exhibited a saturation efficiency ranging from 45.0% to 68.0% for the different test situations in amenities. The provision of Nitrile rubber inside the walls of cooler chamber could reduce the sound intensity by about 18.8%.
In this paper, an experimental analysis of the refrigeration effect of the evaporative cellulose cooling pads was investigated. The experimental test was performed with the air velocity ranging from 0.5 m/s to 4 m/s, the water temperature ranged from 8–10 ℃ and the temperature and humidity of ambient ranged from 28–30 ℃ and 65–75%, respectively. The temperature of chilled water temperature, temperature, and humidity of the inlet air, and the ratio of water-air flow rate have a strong influence on the performance of the cooling pad. A correlation was also developed to predict the cooling capacity of the cooling pad, which shows good agreement with the experimental data.KeywordsCooling padEvaporative coolingPorous foamGreen buildingHVAC
Evaporative cooling is a natural, environment-friendly, and economical method of air-conditioning involving minimal energy consumption. However, the wider dependency on the climatic condition, lower cooling capacity, lesser effectiveness, excess humidification, etc., limits the evaporative coolers' global acceptance. Therefore, multi-staging of evaporative coolers or hybridization with any conventional direct expansion system is recognised as a solution for building air-conditioning. Accordingly, a three-stage cooling test rig comprising indirect and direct evaporative coolers followed by a direct expansion system is indigenously developed and efficacy of seven single to multi/hybrid modes is experimentally evaluated. Rigorous experiments are conducted during the entire summer of Hyderabad, India, from April to July of 2019 by operating the test rig from 20th to 26th of each month from 8:00 AM to 8:00 PM with an interval of one hour. Based on the acquired experimental data, energy, exergy, heat transfer and environmental analyses are carried out. The three-stage cooling combination exhibits the highest wet-bulb effectiveness reaching a maximum of 300% with the lowest supply air temperature of 16 °C. Multi-staging provides an average sensible cooling load reduction ranging from 15.21% to 65.04% on the direct expansion cooling system. Moreover, the two-stage indirect-direct evaporative cooler exhibits excellent exergy efficiency with sufficient cooling capacity reaching 90%. The DEC-DX, IEC-DEC and IEC-DEC-DX cooling combinations exhibit superior SEER magnitudes over entire cooling season indicating effectiveness of evaporative pre-cooling.
In this study, a direct evaporative pad cooling system to be used for a poultry house is simulated under the climate conditions of six Moroccan cities. The objective is to optimize the parameters affecting the performance of the system for each city. The thermodynamic properties of humid air are extracted from the open source program CoolProp, and a computer program is used to perform a parametric study in order to find the impacts of the pad thickness and the frontal velocity on system's performance. Simulations have been conducted on cellulosic pad cooling and obtained results show that the system has the potential to lower the outdoor temperature during the hottest period with a coefficient of performance higher than 80, while the average rate of water consumption is higher than 3.3kg per hour.
This paper demonstrates the thermodynamic performance analysis of direct evaporative cooling system by increasing sides of cooling media. In this paper, a different configuration of cooling media has been developed for determining the behaviour pattern of the direct evaporative cooling system based on performance characteristics using Aspen fibers media. The effect of inlet air temperature, humidity and mass flow rate of air has been discussed in detail by using the different configuration of cooling media. The result indicates that the saturation efficiency is approximately same for entire developed top flow and ordinary lateral flow configurations excluding triangle top flow configuration. The highest saturation efficiency were observed for triangle configuration 97% for case-I. Maximum saturation efficiency of the triangular configuration of an evaporative cooling system was found to be 97%, 88%, nil and 89% for case-I, case-II, case-III and case-IV respectively, over ordinary and other top flow DEC system.
This paper presents an experimental study to enhance the performance of a small air condition (A/C) system by mean of direct evaporative cooling method. A setup of cooling system is designed to simulate extremely hot weather where the dry bulb temperature (DBT) reaches the vicinity of 55 ◦C which represents the highest possible weather temperature that was recorded during summer. The proposed design utilizing an evaporative cooling cycle where the air flows over wet pads before it goes through the condenser. Four different parameters are considered to be studied, namely coefficient of performance (COP), energy saving, cooling capacity and the compressor auto-shut down in very high weather temperature. The results showed significant enhancement to the entire A/C system performance where the refrigeration capacity is increased in the range of 5% to 7.5% and there is 0.12A to 0.16A electrical current reduction for each temperature degree reduction. Moreover, and the compressor continued working even with a voltage drop of 16% (185 V instead of 220 V) which can help overcoming a serious problem that middle east countries (such Iraq) suffer during summer.
Evaporative cooling systems are a widely used technique in Mediterranean greenhouses. In this study, the cellulose evaporative cooling pads most commonly used in this region were tested in the laboratory using a new methodology in a wind tunnel to determine the water flow on the pad and air flow through it, as well as the water consumption and pressure drop caused by each pad as a function of air speed. Greater water flow increased the pressure drop, but the main effect on performance was caused by modifying the air flow through the pad. We recommend a range of air speeds through the pad of 1 to 1.5 m s' 1, at which the pressure drop was between 3.9 and 11.25 Pa, depending on the type of pad and the water flow applied. On the other hand, saturation efficiency ranged between 64% and 70%, while the amount of evaporated water varied between 1.8 and 2.62 kg h -1 K -1 per square meter of pad area. © 2010 American Society of Agricultural and Biological Engineers.
The aim of this study is to determine the relationship that is found among the velocity of the air passing through the pad, the obtained decrease at the temperature of the air passing the pad and the cooling efficiency at the cellulose based evaporative cooling pad, and be of help to the people who designed and operate these systems. In this study, cellulose based evaporative cooling pad (CELdek R 7060-15, Munters AB, Kista, Sweden) was used and the tests conducted were completed at 2 periods. Air velocities were determined as 0.5, 1.0 and 1.5 ms -1 at the first period, and 0.75, 1.25 and 1.75 ms -1 at the second period. The water flow rate at the air velocities, chosen for both periods, was selected as 4 Lmin -1 m -2 . As a result of the research, it was determined that it was not possible to make a mathematical connection among velocities of the air passing through the pad, obtained decrease at the temperature of the air passing the pad and the cooling efficiency. However, it can be said that the most appropriate air velocity for the pad used in the test should be higher than 0.5 ms -1 and lower than 1.5 ms -1 .
It is favorable to increase the energy efficiency of an air-cooled chiller with an efficient, reliable and cost-effective method. Coupling a direct evaporative cooler with an air-cooled condenser seems to be a feasible solution to this problem. To maximize the energy saving potential of an evaporative air-cooled chiller (EACC), which composes of an evaporative air cooler and a conventional air-cooled chiller, a mathematical model was developed and a new index, increase of seasonal energy efficiency ratio (ISEER), was proposed to evaluate the energy saving potential of the evaporative air-cooled chiller. The energy saving potential of EACC was simulated by using the hourly weather data for four typical cities in China. The impacts of various factors on the energy saving potential were analyzed and it was found that there exists an optimal pad thickness which maximizes the energy saving. The optimal pad thickness varies with climatic condition and face velocity. Optimization results of the pad thickness in 31 main cities in China are presented. The maximum energy saving potential of EACC in China is between 2.4% and 14.0% depending on the climatic condition. It is necessary to determine optimal values for the design parameters according to different climatic condition for maximum energy saving.
Transient performance analysis and investigation of three proposed solar powered humidification–dehumidification (HDH) water desalination systems: single stage (SS), double stages (DS) and modified double stages (MDS) systems are presented for hot and humid cities. Open/closed modes of operations of the systems are also investigated. A parametric study of the hourly and daily systems performance is presented at various operating parameters. The results reveal that: (i) inserting solar collectors in HDH systems for air and water heating substantially enhances the system's performance; (ii) the fresh water productivity of all systems at open mode of operation increases with increasing the outdoor air temperature and humidity; (iv) at low outdoor humidity, the system's performance at closed mode of operation is higher than those at open mode of operation and the opposite is true at high outdoor humidity; (v) comparing between the three systems, MDS system (open mode) can produce fresh water of 350 kg/day with GORday of 1.63 and its fresh water productivity enhances with 86.7% and 34% than SS and DS systems, respectively; and (vi) using control system, the performance of the proposed systems can be maximized by changing between the open/closed mode of operations according to the outdoor conditions.
Energy consumption by human enhanced activities has led to distinctive environmental problems; in particular, climate change and global warming. In hot regions, the main reason for energy consumption comes from the cooling of many buildings. The intensity and duration of the sunshine in hot regions have a direct relation with the usage of cooling systems. The aim of this paper is to study the performance of eucalyptus fibre pads which can be used as a new material for the evaporative cooling process in order to reduce the energy consumption caused by cooling loads. A wind tunnel is used to investigate the performance of evaporative cooling by eucalyptus fibres. This paper also analyses the behaviour of the eucalyptus fibres under different conditions. From the measurement of one material sample, it was found that the maximum reduction of air temperature was between 11.3 °C and 6.6 °C, while the maximum cooling efficiency was in the range of 71% and 49% at 0.1 and 0.6 m/s air velocities respectively. Corresponding cooling capacities were also calculated as 108 W and 409 W indicating a directly proportional relation between air velocity and cooling performance.
This paper experimentally studies the thermal and fluid-dynamic behaviour of a new type of evaporative pad made from a high-density polyethylene mesh. Three different pad sizes with dimensions of 492 × 712 mm and thicknesses of 80, 160, and 250 mm are tested. The experiments are conducted in a subsonic wind tunnel adapted to recirculate water on the pads by a pump-driven circuit. A complete set of tests are carried out in which the cooling pad operating parameters such as air flow velocity, water flow rate and pad thickness are varied. As a result, the values of the following characteristic variables of the cooling pad are obtained: saturation efficiency, energy efficiency, exergy efficiency, pressure drop, humidity ratio variation, air temperature variation and amount of evaporated water. The results show that the maximum saturation efficiency of this type of pad is 80.5% and the maximum pressure drop in the air flow is less than 17 Pa. In addition, it is established that the behaviour of exergy efficiency is opposite to the expected function of the evaporative pad and varies from 70% to 94% with decrease in pad thickness. Finally, a new overall exergy efficiency is proposed in this study to optimize the operating conditions of the evaporative pad in air conditioning applications.
This paper presents a numerical model for a compact direct-contact cross-flow air/water heat exchanger where evaporating water cools down an air stream, and where an innovatively designed metallic direct evaporative pad enhances air-water interaction. The numerical model implements energy and mass conservation equations of humid air and water in a one-dimensional geometry by applying correlations for heat and mass transfer coefficients. The system of ordinary differential equations is solved by central-finite discretisation using Matlab. The effective hydraulic diameter is isolated as the only unknown model parameter, and is determined by a parameter estimation using experimental data available from a producer of such a direct evaporative pad. The numerical model is able to predict the air outlet temperature, with an maximal error of 1.33 % compared to experimental data for different inlet temperature and humidity values. Humid air properties inside and at the outlet of the direct evaporative pad, the pad effectiveness and the water consumption can be evaluated by the presented model. The use of the numerical model is demonstrated with examples analysing the impact on heat exchanger effectiveness of a changed geometry (design analysis) and of varying air inlet conditions for a given geometry (operational analysis).
Mass, energy, entropy, and exergy balances and exergy efficiency relations are developed for common air-conditioningprocesses that include simple heating and cooling, heating with humidification, cooling with dehumidification, evaporative cooling, and adiabatic mixing of airstreams. An illustrative example of a heating process with humidification is considered and the effects of air temperature and relative humidity at the inlet and exit, the temperature of steam used for humidification, and the dead state properties of exergy efficiency and exergy destruction are investigated. The results indicate that processes with low exergy efficiency and high exergy destruction have significant potential for improving performance. A parametric investigation shows that exergy efficiency and exergy destruction are very sensitive to air properties and dead state conditions. It is seen that the use of exergy in assessing HVAC&R systems can be highly advantageous, leading to technical advantages such as improved efficiency as well as environmental improvements through reduced emissions and economic benefits. Many of the benefits of applying exergy analysis are not necessarily attainable via energy methods.
A procedure for testing evaporative cooling pads was developed to relate efficiency, face air velocity, and static pressure drop across the pads. This article outlines the test procedure; describes how pad performance is affected by pad angle, pad thickness, and initial aging; analyzes the accuracy of the test method; and compares test results with those of previous researchers. Many experimental cross-corrugated cellulose pads of varying design were tested, including three designs currently on the market (10 cm (4 in.) 45°-45°, 15 cm (6 in.) 45°-45°, and 15 cm (6 in.) 30°-30°).
This paper presents an experimental investigation of the Coefficient of Performance (COP)’s augmentation of an air conditioning system utilizing an evaporative cooling condenser. The experimental facility consisted of four major components, which are, the compressor, the evaporator, the thermal expansion valve, and the condenser. An evaporative cooling unit was located upstream from the condenser. Thermal parameters, such as relative humidity, dry bulb temperature, and wet bulb temperature were measured to evaluate the effect of in-direct evaporative cooling on the system's COP. The results indicated an inverse relation between the condenser inlet dry bulb temperature and the COP. The changes in specific enthalpy of the air across the evaporative cooled condenser were due to latent heat transfer and sensible heat exchanges, whereas the specific enthalpy changes for the conventional condenser were primarily caused by sensible heat exchanges. By using the evaporative cooling condenser to pre-cool the air, the saturation temperature drop through the condenser increased from 2.4 °C to 6.6 °C. It also resulted in an increase of the mass flow rate of refrigerant that went into the evaporator. This mass increase of liquid entering the evaporator consequently resulted in the increase of COP from 6.1% to 18%. A power reduction up to 14.3% on the compressor was also achieved. The result reveals the relation between water consumption and compressor energy saving regarding to their costs. Although greater power reductions were fulfilled at higher dry bulb temperatures, in this circumstance, the cost-optimal applicable temperature is around 33.1 °C.
This paper presents a study on the performance of the evaporative cooling process in air washers with the use of mass balances, energy and exergy equations. Usually, the performance of these devices is described in terms of their saturation effectiveness based on energy analysis. This method, however, is inappropriate to identify the main sources of irreversibility within the process. It is also unsuitable to give the optimum conditions for operating the system with a proper use of energy resources. Thus, an exergy analysis was developed to complement the energy analysis of the process. A mathematical model based on mass and energy balances was used to determine the water and air properties in the washer. The influence of the humidity and temperature of the air and water at the inlet, the washer length in the saturation effectiveness, and the second law efficiency was investigated. The results showed that the best condition of the intake air for obtaining thermal comfort does not coincide with the best condition for the thermodynamic performance of the system. The energy and exergy analyses were carried out simultaneously to generate the conditions required for optimum performance with minimal exergy depletion.
A cross-flow direct evaporative cooler, in which the wet durable honeycomb paper constitutes as the packing material, is investigated. The system is expected to act as both humidifier and evaporative cooler to create a comfortable indoor environment in arid regions. A mathematical model, including the governing equations of liquid film and gas phases as well as the interface conditions, has been developed. The interface temperature of falling film has been predicted and discussed in detail. Analysis results indicate that there exists an optimum length of the air channel, which results in the lowest temperature, and the system performance can be further improved by optimizing the operation parameters, such as the mass flow rates of feed water and process air, as well as the different dimensions of the honeycomb paper.
A special test setup is designed to evaluate the performance of three natural fibers to be used as wetted pads in evaporative cooling. The chosen fibers are date palm fibers (stem), jute and luffa. As a reference, a widely used commercial wetted pad is chosen. The performance criteria include cooling efficiency, material performance and cooling efficiency degradation. The results show that the average cooling efficiency is highest for jute at 62.1%, compared to 55.1% for luffa fibers, 49.9% for the reference commercial pad and 38.9% for date palm fiber. Material performance tests comprise salt deposition and bio-degradation (mold forming). Jute has the least salt deposition followed by palm and luffa fibers. The commercial type has the highest salt deposits. The highest resistance to mold forming is offered by luffa followed by palm fibers. The commercial type and jute have very poor performance. The results of the cooling efficiency degradation indicate that luffa has an overall advantage over the other fibers. Palm fibers and the commercial type have a significant reduction in the cooling efficiency, while jute has the highest deterioration. The total results indicate that luffa has an overall advantage over the other fibers. However, if the jute surface can be treated to offer higher mold resistance characteristics, it would provide the best alternative.
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 100cm 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 1m 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.
Increasing the coefficient of performance of air conditioner with air-cooled condenser is a challenging problem especially in area with very hot weather conditions. Application of evaporatively cooled air condenser instead of air-cooled condenser is proposed in this paper as an efficient way to solve the problem. An evaporative cooler was built and coupled to the existing air-cooled condenser of a split-air-conditioner in order to measure its effect on the cycle performance under various ambient air temperatures up to 49 °C. Experimental results show that application of evaporatively cooled air condenser has significant effect on the performance improvement of the cycle and the rate of improvement is increased as ambient air temperature increases. It is also found that by using evaporatively cooled air condenser in hot weather conditions, the power consumption can be reduced up to 20% and the coefficient of performance can be improved around 50%. More improvements can be expected if a more efficient evaporative cooler is used.
This paper presents performance analysis of two new evaporative cooling pad materials. Now-a-days evaporative cooling pads are commonly made from aspen and khus fibers. These two materials along with new materials namely coconut fibers and palash fibers have been tested in a laboratory using suitably fabricated test set up. Air flow rate was kept constant. Evaporative cooling effectiveness was obtained and compared with that of aspen and khus pads. The effectiveness of pad with palash fibers was found to be 13.2% and 26.31% more than that of aspen and khus pads respectively. Whereas effectiveness of coconut fibers was found to be 8.15% more than that of khus and comparable with that of aspen pad. Khus pad offers lowest pressure drop where as aspen pad (most commonly used) offers highest pressure drop among the four materials tested. The proposed new material (palash) offers pressure drop lower than that of the aspen pad. Because of better performance, lower costs and easy availability of coconut and palash fibers, their use as wetted media may enhance the scope of using these materials in domestic and commercial evaporative cooling systems for sustainable development.
This paper reports a performance analysis for a new sustainable engineering application to beneficially reuse an abundant agricultural waste, coconut coir (Cocos nucifera), in evaporative cooling pads. Two small coconut coir pads of different configurations were fabricated and tested using a laboratory‐scale experimental arrangement. The air supply velocity was controlled and varied between 1.88 and 2.79 m s−1. Heat and mass transfer coefficients, evaporative cooling efficiency and pressure drop across the two types of coconut coir pad were analysed and compared with those of a commercial rigid media paper pad. Results show that the cooling efficiency of the manufactured coconut coir evaporative cooling pad was fairly good (about 50%) and close to that of the commercial paper pad (about 47%). The average pressure drop across the two coconut coir pads was 1.5 and 5.1 Pa respectively. Correlations for heat and mass transfer coefficients expressed using Nusselt and Sherwood numbers are also reported. In addition, the cooling potential of the coconut coir pads was analysed using the average climatic conditions of the central region in Thailand throughout the year. The analysis showed that the air temperature leaving the coconut coir pad varied from 23 to 28°C. Commercial development appears feasible given the coconut coir pad's good performance, lower cost and its availability throughout the country.
In this paper heat and mass transfer, process in direct evaporative cooler is discussed. A simplified mathematical model is developed to describe the heat and mass transfer between air and water in a direct evaporative cooler. The model consists of the governing equations with their boundary conditions and some associated algebraic equations. The related latent heat of water evaporation is taken as a heat source in the energy equation, and the mass of evaporated water is treated as a mass source in the mass equation. The study presents a comparison of the computed results with that of experimental results for the same evaporative cooler. A good agreement between the calculated and experimental results is achieved. The influences of the inlet frontal air velocity, pad thickness, inlet air dry-bulb temperature on the cooling efficiency of the evaporative cooler are calculated and analyzed. The predicted results show validity of simple mathematical model to design the direct evaporative cooler, and that the direct evaporative cooler with high performance pad material may be well applied for air conditioning systems.
The heat and mass transfer between air and water film in the direct evaporative cooler is theoretically analyzed in present paper. A simplified cooling efficiency correlation is proposed based on the energy balance analysis of air. The correlation may be applied to the water-drip cross-flow direct evaporative cooler, in which the wet special durable papers with different wave angles form the air channel. The Influences of the air frontal velocity and the thickness of pad module on the cooling efficiency of a direct evaporative cooler are discussed. An optimum frontal velocity of 2.5 m/s is recommended to decide the frontal area of pad module in the given air flow. The simplified correlation of cooling efficiency is validated by the test results of a direct evaporative cooler.
In this study, the performance of rigid media evaporative cooler, equipped with corrugated papers as a wetted medium, was mathematically modeled. The governing equations of air were solved using finite difference analysis and Projection algorithm. Saturation efficiency and pressure drop as functions of air velocity and media depth were calculated. Effects of corrugation shape, mean plate space, Reynolds number and Prandtl number were also considered. Analysis of the results showed that efficiency improves with decreasing velocity and increasing depth of media. Pressure drop increases with increase of both velocity and media depth. In addition, efficiency becomes approximately independent of velocity with increasing depth to a certain value. Results obtained were compared with those of channel flow and showed that, corrugating one side of the channel at high velocity can improve efficiency by 40%.
Air-cooled chillers traditionally operate under head pressure control via staging constant-speed condenser fans. This causes a significant drop in their coefficient of performance (COP) at part load or low outdoor temperatures. This paper describes how the COP of these chillers can be improved by a new condenser design, using evaporative pre-coolers and variable-speed fans. A thermodynamic model for an air-cooled screw-chiller was developed, within which the condenser component considers empirical equations showing the effectiveness of an evaporative pre-cooler in lowering the outdoor temperature in the heat-rejection process. The condenser component also contains an algorithm to determine the number and speed of the condenser fans staged at any given set point of condensing temperature. It is found that the chiller’s COP can be maximized by adjusting the set point based on any given chiller load and wet-bulb temperature of the outdoor air. A 5.6–113.4% increase in chiller COP can be achieved from the new condenser design and condenser fan operation. This provides important insights into how to develop more energy-efficient air-cooled chillers.
It is no longer acceptable, in most circles, to present experimental results without describing the uncertainties involved. Besides its obvious role in publishing, uncertainty analysis provides the experimenter a rational way of evaluating the significance of the scatter on repeated trials. This can be a powerful tool in locating the source of trouble in a misbehaving experiment. To the user of the data, a statement (by the experimenter) of the range within which the results of the present experiment might have fallen by chance alone is of great help in deciding whether the present data agree with past results or differ from them. These benefits can be realized only if both the experimenter and the reader understand what an uncertainty analysis is, what it can do (and cannot do), and how to interpret its results.This paper begins with a general description of the sources of errors in engineering measurements and the relationship between error and uncertainty. Then the path of an uncertainty analysis is traced from its first step, identifying the intended true value of a measurement, through the quantitative estimation of the individual errors, to the end objective—the interpretation and reporting of the results. The basic mathematics of both single-sample and multiple-sample analysis are presented, as well as a technique for numerically executing uncertainty analyses when computerized data interpretation is involved.The material presented in this paper covers the method of describing the uncertainties in an engineering experiment and the necessary background material.
The objective of this study was to evaluate the suitability of pumice stones, volcanic tuff and greenhouse shading net as alternative pad materials to the widely used and commercial one called CELdek. For this purpose, the tests were carried out at four levels of air velocity (0·6, 1·0, 1·3 and 1·6 m s−1) four levels of water flow rate (1·0, 1·25, 1·5 and 1·75 l min−1) and three levels of pad thickness (50, 100 and 150 mm). The tests were made at 30±1 °C and 40±1% relative humidity air conditions. The temperature of water flow was kept constant at 25±2 °C during the tests. According to the results of this study, it can be stated that the volcanic tuff pads are good alternatives to the CELdek pads at 0·6 m s−1 air velocity.
A compact wind tunnel was developed to simulate evaporative cooling pad–fan systems and to provide direct measurement of system performance. Two alternative materials including one made of coarse fabric PVC sponge mesh 2.5 mm diameter in pinhole and one made of fine fabric PVC sponge mesh in 7.5 mm diameter pinhole were tested as pads in wind tunnel experiment. We have experimentally examined the effects of air velocity, water flow rate, static pressure drop across pad, and pad thickness on evaporative cooling efficiency. Pad face velocities and associated static pressure drops that allow a pad–fan system works were measured. The dimensionless working equations of heat and mass transfer coefficients through various thickness of alternative pad media could be obtained through curve fitting technique based on the measurements. For coarse PVC sponge mesh, hH/hM=1.33ρaCPaLe2/3(Les/Le)1/4; whereas for fine fabric PVC sponge mesh, hH/hM=2.76ρaCPaLe2/3(Les/Le)1/4 were hH is heat transfer coefficient, hM is mass transfer coefficient, ρa is air density, CPa is specific heat of air, Le is Lewis number, and Les is Lewis number at water temperature. Under a system setting of water flow rate, pad thickness of 150 mm, and air velocities ranged from 0.75 to , the cooling efficiencies for coarse fabric PVC sponge varied from 81.75 to 84.48%, whereas 76.68 to 91.64% for fine fabric PVC sponge. Results of this study will be used to determine operating protocols for future tests investigating criteria.
High ambient temperature has a negative effect on silk production. During heat stress, penalties to the efficient performance, production, reproduction, feed conversion, health and welfare of the animals can be severe. This research was aimed at investigating the feasibility of using direct evaporative cooling to improve the indoor air conditions in a silkworm rearing house. To this end, a silkworm rearing house of 32 m2 floor area was fabricated and tested at Mahasarakham University. A cooling pad measuring 1·8 m by 3·6 m was placed on the north wall and a fan on the south wall. Experiments were performed through two seasons, namely: winter (November–December 2003) and summer (March–April 2004). Various operating airflow rates were considered to assess cooling performance and energy efficiency ratio (EER) of the evaporative cooling system. The results showed indoor dry bulb temperature drops of 6–13 °C could be achieved parallel with a 30–40% rise in relative humidity. The EER tends to be very high because the system consumes only fan and water pumping power. The economic analysis indicates that the payback period of the evaporative cooling system is about 2·5 years. Therefore, the direct evaporative cooling method demonstrates significant potential for silkworm rearing house cooling.
A simplified mathematical model is developed to describe the heat and moisture transfer between water and air in a direct evaporative cooler. The mass of evaporated water is treated as a mass source of air flow, and the related latent heat of water evaporation is taken as a heat source in the energy equation. The momentum caused by water evaporation is taken into account in the momentum equations. The effective air viscosity and diffusion coefficient are decided experimentally. The models and methods are validated by comparing the numerical results with those of experiment for the same evaporative cooler. The influences of the inlet frontal air velocity, pad thickness, inlet air dry-bulb and wet-bulb temperatures on the cooling efficiency of the evaporative cooler are calculated and analyzed.The cooling effects of the direct evaporative cooler are predicted for use in four different regions in northwest China using the present numerical method and local weather data for air conditioning design. The predicted results show the direct evaporative cooler with high performance pad material may be well applied for air conditioning with reasonable choices for the inlet frontal velocity and pad thickness.
A comparison between a conventional heat pump system and one incorporating heat recovery/evaporative cooling
- Saman