• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.1
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• pp.88-98
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• 2016

The Korean summer is hot and humid, and air-conditioners consume considerable amounts of electricity. In such cases, the simultaneous use of indirect evaporative coolers may help reduce the sensible heat and save electricity. In this study, heat transfer and pressure drop characteristics of indirect or regenerative evaporative coolers made from plastic/paper are investigated. The results showed that heat and mass transfer model based on the ${\epsilon}-NTU$ method predicted the indirect evaporation efficiencies, cooling capacities and pressure drops adequately. Both for indirect or regenerative evaporative cooler, the indirect evaporation efficiency increased with increasing dry channel inlet temperature or relative humidity. The indirect evaporation efficiency of the regenerative evaporative cooler was larger than that of the indirect evaporative cooler.

• Proceedings of the SAREK Conference
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• 2006.06a
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• pp.743-748
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• 2006

Ren et al. analyzed the performance of the indirect evaporative cooler according to the direction of the flow considering evaporation water flow and wetness. However the effect of NTU of each channel on the performance of the indirect evaporative cooler according to the direction of the flow was not analyzed exactly. In this study the effect of the direction of the flow on the Indirect evaporative cooling performance changing NTU of each channel are investigated theoretically. The cooling process of the indirect evaporative cooler by flow direction is modeled into a set of linear differential equations and solved to obtain the exact solutions to the temperatures of the hot fluid, the moist air, and evaporation water. Based on the exact solution in the case of different NTU of each channel, we study the change of the distribution of the temperature according to each flow direction and at the same time analyze the effect of the flow direction on the cooling performance.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.9
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• pp.714-721
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• 2006

In evaporative cooling applications, the evaporation water is supplied usually sufficiently larger than the amount evaporated to enlarge contact surface between the water and the air. Especially in indirect evaporative coolers, however, if the evaporation water flow rate is excessively large, the evaporative cooling effect is not used for heat absorption from the hot fluid but spent to the sensible cooling of the evaporation water itself. This would result in a decrease in the cooling performance of the indirect evaporative cooler. In this study, the effects of the evaporation water flow rate on the cooling performance are investigated theoretically. The cooling process in an indirect evaporative cooler is modeled into a set of linear differential equations and solved to obtain the exact solutions to the temperatures of the hot fluid, the moist air, and the evaporation water. Based on the exact solutions, it is analyzed how much the cooling performance is affected by the evaporation water flow rate. The results show that the decrease in the cooling effectiveness is substantial even for a small flow rate of the evaporation water and the relative decrease is more serious for a high-performance evaporative cooler.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.27 no.9
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• pp.475-483
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• 2015

In Korea, a typically hot and humid summer means that air-conditioners consume a large quantity of electricity; accordingly, the simultaneous usage of an indirect evaporative cooler may reduce the sensible-heat level and save the amount of electricity that is consumed. In this study, the heat-transfer and pressure-drop characteristics of an indirect evaporative cooler made of paper/plastic film were investigated under both dry and wet conditions; for the purpose of comparison, an indirect evaporative cooler made of plastic film was also tested. Our results show that the indirect evaporative efficiencies under a wet condition are greater than those under a dry condition, and the efficiencies of the paper/plastic sample (109% to 138%) are greater than those (67% to 89%) of the plastic sample; in addition, the wet-surface, indirect evaporative efficiencies of the paper/plastic sample are 32% to 36% greater than those of the plastic sample. Further, the wet-surface pressure drops of the paper/plastic sample are 13% to 23% larger than those of the plastic sample, and this might have been caused by the surface roughness of the samples. A rigorous heat-transfer analysis revealed that, for the plastic sample, 30% to 37% of the wet channels remained dry, whereas all of the channels were wet for the paper/plastic sample.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.23 no.1
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• pp.8-15
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• 2011

Cooling load reduction was analysed of a ventilation system adopting a regenerative evaporative cooler. The regenerative evaporative cooler is a kind of indirect evaporative cooler which cools the air down to its inlet dewpoint temperature in principle without change in the humidity ratio. The regenerative evaporative cooler was found able to cool the ventilation air to $18{\sim}21^{\circ}C$ when the outdoor condition ranges $25{\sim}35^{\circ}C$ and 0.01~0.02 kg/kg. When the outdoor humidity ratio is lower than 0.018 kg/kg, the regenerative evaporative cooler was found to provide cooling performance enough to compensate the ventilation load completely and to supply additional cooling as well. Energy simulation during the summer was carried out for a typical office building with the ventilation system using the regenerative evaporative cooler. The results showed that the seasonal cooling load can be reduced by about 40% by applying the regenerative evaporative cooler as a ventilation conditioner. The reduction was found to increase as the outdoor temperature increases and the outdoor humidity ratio decreases.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.1
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• pp.21-28
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• 2017

Indirect evaporative cooling, which utilizes a cooling effect obtained by the evaporation of water, is energy-effective compared to the conventional vapor compression method. It is also eco-friendly, due to the non-usage of CFC refrigerant. In this study, three indirect evaporative cooler samples of the cross flow type(size: $300mm{\times}300mm{\times}300mm$, channel pitch: $5mm{\times}5mm$, $5mm{\times}7mm$, $7mm{\times}7mm$) were made using plastic/paper composites. Tests were conducted to measure indirect evaporative efficiencies and pressure drops. Results showed that the efficiency was the highest for the $5mm{\times}5mm$ sample, owing to the largest surface area. The saved electrical energy was also the greatest for that sample. The pressure drop of the wet channel was larger than that of the dry channel as expected. A theoretical model was proposed, which underestimated both the indirect evaporation efficiency and the pressure drop.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.11
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• pp.732-739
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• 2016

In Korea, the summer is hot and humid, and much electricity is consumed for air conditioning. Thus, the simultaneous usage of an indirect evaporative cooler and a common air conditioner could reduce the sensible heat and save electricity. This study developed a U-type cross-counter flow indirect evaporative cooler (IEC) made of plastic and paper. The efficiencies were compared with those of a cross-flow IEC. The specimen was $500mm{\times}500mm{\times}1000mm$. the results show that the indirect evaporation efficiencies of the cross-counter flow sample were 6-21% higher than those of the cross-flow sample. The pressure drops of the cross-counter sample were 51-66% higher. Thermal analysis based on the -NTU method predicted the experimental data within 10%. The electrical energy saved by the use of the cross-counter flow IEC was larger than that of the counter flow IEC, and the difference increases with the velocity. However, the the cross-counter IEC is two times larger than the cross-flow IEC, which may increase the material cost and water usage.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.20 no.7
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• pp.462-469
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• 2008

A regenerative evaporative cooler has been fabricated and tested for the evaluation of cooling performance. The regenerative evaporative cooler is a kind of indirect evaporative cooler comprised of multiple pairs of dry and wet channels. The air flowing through the dry channels is cooled without any change in the humidity and at the outlet of the dry channel a part of air is redirected to the wet channel where the evaporative cooling takes place. The regenerative evaporative cooler fabricated in this study consists of the multiple pairs of finned channels in counterflow arrangement. The fins and heat transfer plates were made of aluminum and brazed for good thermal connection. Thin porous layer coating was applied to the internal surface of the wet channel to improve surface wettability. The regenerative evaporative cooler was placed in a climate chamber and tested at various operation condition. The cooling performance is found greatly influenced by the evaporation water flow rate. To improve the cooling performance, the evaporation water flow rate needs to be minimized as far as the even distribution of the evaporation water is secured. At the inlet condition of $32^{\circ}C$ and 50%RH, the outlet temperature was measured at $22^{\circ}C$ which is well below the inlet wet-bulb temperature of $23.7^{\circ}C$.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.12
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• pp.8165-8175
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• 2015

In Korea, summer is hot and humid, and air-conditioners consume lots of electricity. In such case, simultaneous usage of indirect evaporative cooler may reduce the sensible heat and save the electricity. In this study, heat transfer and pressure drop characteristics of indirect evaporative cooler made of aluminum, plastic, plastic/paper are investigated both under dry or wet condition. Results show that indirect evaporation efficiencies of the plastic/paper sample (38.5% ~ 51.4%) are approximately the same as those of the aluminum sample (41.9% ~ 47.5%), and are larger than those of the plastic sample (29.0% ~ 37.4%). This suggests that the plastic/paper sample could be a good substitute to the aluminum sample. However, the pressure drops across the paper channel are 92% ~ 106% larger than those across the aluminum channel. The heat transfer coefficients of the paper channel under dry condition are 15% ~ 44% larger than those of the plastic channel. The increases are 185% ~ 203% for the aluminum channel. The pressure drops of the paper channel are 34% ~ 48% larger than those of the plastic channel and 93% ~ 106% larger than those of the aluminum channel. Rigorous heat transfer analysis reveals that, for the plastic sample, 30% ~ 37% of the wet channels remain dry, whereas all the channels are wet for plastic/paper sample. For aluminum sample, the ratio is 17% ~ 23%.

• Proceedings of the SAREK Conference
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• 2005.06a
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• pp.102-102
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• 2005