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Received 25 October Published 6 March Volume Pages 15— Review by Single-blind. Editor who approved publication: Dr Adolfo Perujo. This cycle is an indirect evaporative cooling—based cycle, which utilizes a smart geometrical configuration for the air distribution. The achievement of this geometry is the high efficiency of the cycle, as it produces cold air of temperature lower than the wet-bulb ambient air temperature.
The heat and mass exchanger is analyzed and described in detail, so the specifications of M-cycle will be clear and understandable. The operation of the standard configuration of M-cycle is studied thereafter and useful conclusions are carried out, about the efficiency and the energy consumption electricity and water. Finally, the energy-saving potential is estimated in conventional cooling systems, in terms of electricity and capital cost, in order to evaluate the financial benefit of M-cycle application: the pay-back period is calculated equal to about 2.
The study is to be a useful tool to anyone interested in energy saving in buildings and in industrial plants, as the operating cost, which is strongly affected by the cooling demand, is significantly reduced by the application of M-cycle. Keywords: M-cycle, evaporative cooling, high efficiency, renewable energy, energy saving, low CO 2 emission. Although conventional air-conditioning systems are widely accepted to be of high energy consumption, they cover a significant part of needs for air-conditioning.
Scientific research focus on improved refrigerants the global warming potential of which is lower than that of restricted R or R or more effective compressors; however, the high operational cost of these units as well as its role in atmospheric pollution cannot significantly be limited. As the dangerous environmental effects of chlorofluorocarbons and greenhouse gases not only as direct emissions, but also as indirect emissions have been reduced, the interest is focused on environment-friendly cooling technologies.
Evaporative air-conditioning is a really promising technology. Whereas conventional systems use chlorofluorocarbon based refrigerants CFCs , evaporative coolers ECs use water. Evaporation technology is simple and functional and has both residential and industrial applications, achieving significant efficiencies in suitable climates hot and dry.
ECs are based on water evaporation and latent heat utilization. When water evaporates and becomes vapor, the heat is removed from the air, resulting in a cooler air temperature. Substantial energy, no chlorofluorocarbon usage, reduced peak demand, reduced CO 2 and power plant emissions, improved indoor air quality, lifecycle, cost effectiveness, easily integrated into built-up systems, and easy to use with direct digital control are the main advantages of ECs. On the contrary, some types of ECs produce an air stream of extremely high humidity sometimes, the stream is almost saturated and consume a significant amount of water.
An ideal EC would produce air as cool as the wet-bulb temperature, while a real cooler cannot reach such a low temperature. Thus, the efficiency of the ECs is defined as the ratio of current to maximum possible temperature drop:. Maisotsenko cycle M-cycle applies an improved design of indirect evaporative cooling. Keeping the humidity ratio of product air constant, it succeeds in decreasing the air temperature down to ambient wet-bulb temperature and close to ambient dew-point dp temperature, by a smart heat and mass transfer procedure.
Paper sheets of a special type, for optimum wetting and mass transfer between them and the air, are used as exchange layers, while the product air which is to cool the air-conditioning spaces is totally protected by moisture of supplying water. M-cycle has been designed to optimize the effectiveness of both stages of evaporation direct evaporation of working stream and heat exchange between streams.
ECs based on M-cycle have been already installed to supply cool air to various applications domestic cooling, commercial and industrial buildings, etc. This paper aims at describing in a simple way the M-cycle operation and utilization and at presenting some useful experimental data, to prove the high efficiency of M-cycle, under Mediterranean climate conditions. Although ECs cannot achieve as low temperature as their users want due to the dew-point temperature restriction , M-cycle is the most effective IEC, the product air of which tends to the outlet air temperature of conventional building air-conditioning systems.
And, as it is a quite new technology about 8 years , its improvement potential in terms of electricity consumption is not negligible. Both working pink lines and product red lines streams use dry channels Figure 1. The working stream passes through the perforations and is driven to the wet channels blue lines, Figure 2. Figure 2 helps in understanding the M-cycle: the working stream, which will evaporate the water, is precooled under constant relative humidity as no mass exchanging takes place along the dry channels.
It enters the wet channels under lower temperature than ambient temperature, and the wet-bulb temperature, which is eliminated at each working channel, is related to the inlet temperature. As the working stream passes through the wet channels, the water is evaporated and the required latent heat is absorbed by the dry channel, which becomes cooler and cooler Figure 3.
In reality, one layer of heat and mass exchanger HMX is show on Figure 4. An M-cycle—based cooled is structured by 40 heat and mass exchanging layers, creating the following apparatus Figure 5. Some auxiliary devices fans and pump are needed to drive the air and the water into the cooler.
Its efficiency is significantly affected by flow rates and ambient conditions and is expressed in wet-bulb terms, in order to indicate the better performance of a Maisotsenko cooler instead of a typical EC. Evaporation in an IEC is caused 1 by the sensible heat of the working stream and 2 by the sensible heat of the product stream. It is clear that, because the two currents do not interact, any water addition will not affect the product stream and its contribution to the increase of the latent heat, which causes evaporation, is linked to the temperature difference of the two streams.
To evaluate the performance of an M-cycle—based device, a HMX of a nominal cooling capacity of 0. Figure 6 Experimental rig. Notes : A, main suction duct; B, fan; C, secondary resistor; D, splitter; E, air flow regulators; F, main resistors; G, stream ducts; H, exhaust stream duct. The hotwire was placed in the center of each air duct, so as to measure the maximum velocity. The correlation of the ambient temperature with the heat available for evaporation is also clear: below Usually, the evaporating cooler manufacturers give a typical value of hourly water consumption; however, this value does not take into account the cooler efficiency.
For this reason, the specific water consumption was defined, which is equal to the amount of water the evaporation of which can produce 1 kWh c. Using the experimental data, it is concluded that the specific water consumption tends to reduce as the ambient temperature increases due to a higher increase of the cooling capacity, varying between 2.
The increased amount of heat inserted in the cooler, when the ambient air is hotter, reinforces the evaporation phenomenon, as already mentioned, resulting in higher temperature drops through the cooler. The efficiency of the cooler is directly affected, as the higher the temperature, the more effective the cooler. Two cases of limited mass flow were examined. If the working stream flow is limited, the weakening of the evaporation so the temperature drop in the product stream is lower works as an obstacle to the cooling capacity, but not as much as a limited product stream flow does.
So, if we aim to minimize water consumption, the lowering of the working stream mass flow is the best solution the cooler consumes less than 1. There is no doubt about the effect of the reduction of the product stream flow on the improvement of the cooler efficiency.
On the contrary, it is shown how disastrous a reduction of the working stream flow can be because the poor evaporation makes the cooler inefficient for significant temperature drops. Even then, in this case, the efficiency is comparable to that of DECs, even without producing humid air like these and almost double the efficiency of typical indirect evaporative systems.
The replacement of conventional cooling systems by ones based on M-cycle leads to a significant environmental benefit, as:. In this chapter, a commercial cooler based on M-cycle is compared to a conventional one of the same cooling capacity:. As the electricity cost is about 0. Ignoring the rates of return, it is clear that at about 6, hours of operation Figure 7 , the increased cost of installation of an EC balances the increased cost of operation of an conventional cooler.
Thus, the payback period of an EC, compared to a conventional one, is about 2. Figure 7 Operational cost of evaporative cooler and of a conventional cooler. In this paper, a cooler utilizing the M-cycle is analyzed; the aim was the production of dry and cool air with low electricity consumption only a simple axial fan of W consumes electricity and improvements of the cooler characteristics efficiency and water consumption.
The efficiency does not depend on the ambient conditions, but the product stream temperature, which is to be driven to the cooled space, is strongly affected by the humidity of the region where the cooler is installed. The specific water consumption of the cooler under normal mode varies under common ambient conditions between 2.
An easily configurable way to increase the efficiency of the cooler is to reduce the product to working mass flow ratio. However, this method leads to a significant increase of specific water consumption. It was also important to understand the energy-saving potential of an EC, based on M-cycle. As a conclusion, M-cycle can satisfy the cooling demand of most Greek cities and it is also expected to do at other Mediterranean regions of similar ambient conditions , without consuming high amounts of electricity and water.
At humid climates, the cycle could not be recommended, as both product air temperature and hourly consumption are rather high. Gillan L, Maisotsenko V. Maisotsenko open cycle used for gas turbine power generation. Thermodynamic performance assessment of a novel air cooling cycle. Int J Refrig. Hasan A. Indirect evaporative cooling of air to a sub wet-bulb temperature.
Appl Therm Eng. Bruno F. On-site experimental testing of a novel dew point evaporative cooler. Energy Build. Riangvilaikul B, Kumar S. An experimental study of novel dew-point evaporative cooling system. Anisimov S, Pandelidis D. Numerical study of perforated indirect evaporative air cooler. Int J Energy Clean Environ. Modelling of indirect evaporative air coolers. Int J Heat Mass Transf. Comparative study of the performance of the M-cycle counter-flow and cross-flow heat exchangers for indirect evaporative cooling.
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The Maisotsenko Cooling cycle combines the thermodynamic processes of heat exchange and evaporative cooling in a unique indirect evaporative cooler resulting in product temperatures that approach the dew point temperature not the wet bulb temperature of the working gas. This cycle utilizes the enthalpy difference of a gas, such as air, at its dew point temperature and the same gas saturated at a higher temperature. This enthalpy difference or potential energy is used to reject the heat from the product. Consider the cooling gas to be air and the liquid to be water; the Maisotsenko Cycle allows the product fluid to be cooled in temperature ideally to the dew point temperature of the incoming air. This is due to the precooling of the air before passing it into the heat-rejection stream where water is evaporated. For purposes of this paper, the product fluid is air.
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