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.
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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 CO2 emission Introduction 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.
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 CO2 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.
There are two basic categories of EC: direct and indirect. According to the first configuration, the water evaporates into the air to be cooled; as a result, the product air is cold and wet. A typical direct EC DEC consists of a box with voluminous humidification blocks, a water pump, and a water distribution system. The fan draws in warm and dry ambient air through the wet blocks, cooling it. The latent heat of the air is used to evaporate the water.
Evaporation cools the air while increasing its moisture content or relative humidity. No heat is added or taken out of the air; thus, it is an adiabatic process of constant enthalpy. On the other hand, indirect ECs IECs are based on two different streams working [wor] and product [pro] , in order to get a relatively drier product stream, but its temperature is not as low as it would be by a DEC.
A heat exchange layer is used between the working airstream and the supply airstream, because the ambient wet-bulb wb temperature is theoretically the minimum achievable temperature of a conventional evaporative system. An ideal EC would produce air as cool as the wet-bulb temperature, while a real cooler cannot reach such a low temperature. 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. 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 1 Dry channels configuration.
Figure 2 Wet channels configuration. 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. Figure 3 Heat and mass exchanging. Figure 4 Heat and mass exchanger layer configuration. 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.
Figure 5 Maisotsenko-cycle cooler configuration. The basic principle of the M-cycle is that the temperature difference between the stream is higher than in a typical IEC.
As it always happens in IECs, the humidity ratio of the product stream is kept constant along the cooler. The working stream, of mass flow M, also enters the cooler at the upper level and is driven through dry channels at this level.
As it meets the perforations, an amount of this is led to the lower level, which is always wet. Due to the contact of the working air with the wet surface of the channels at the lower level, the evaporation of the water takes place and the working stream is cooled. This cooling absorbs heat from the working stream while it is at the upper level which is consequently precooled, so being cooler than the ambient air, it is driven to the heat exchanging zone and from the product stream, while they are both in the zone of heat exchanging.
At this zone the product air is cooled and the working stream is exhausted, almost saturated, and cooler than the ambient air. Theoretically, the minimum possible temperature of state is the ambient air dew point; however, generally this state is between the ambient air wet bulb and the dew point.
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. M-cycle cooler performance 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 entire air passes through this duct.
Secondary resistor: a resistor of 1, W power is used for assistance in air preheating. Due to its position, this resistor heats the whole air, before splitting the streams. Air flow regulators: the air flow of each stream is independently controlled. Contrary to the fan, whose speed control refers to the entire quantity of air, here there are two regulators one for each stream.
Main resistors: each of the two main resistors of 1, W was placed in the interior of the duct of each stream. The halt of electricity has been secured in case the fan is disabled, so as to avoid any superheating of the resistors. Exhaust stream duct: in order to stop the wet air suction by the main suction duct and exchanger malfunction , the highly humidified working stream is rejected in the atmosphere fairly away from the main air duct entrance.
The hotwire was placed in the center of each air duct, so as to measure the maximum velocity. The measurement procedure results are shown in Table 1. The correlation of the ambient temperature with the heat available for evaporation is also clear: below For this reason, the specific water consumption was defined, which is equal to the amount of water the evaporation of which can produce 1 kWhc.
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.
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. In this chapter, a commercial cooler based on M-cycle is compared to a conventional one of the same cooling capacity: evaporative cooler conventional cooler As the electricity cost is about 0.
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. Conclusion 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.
Disclosure The authors report no conflicts of interest in this work.
Maisotsenko cycle: technology overview and energy-saving potential in cooling systems
Registered: Abstract The Maisotsenko Cycle M-Cycle is a thermodynamic conception which captures energy from the air by utilizing the psychrometric renewable energy available from the latent heat of water evaporating into the air. The cycle is well-known in the air-conditioning AC field due to its potential of dew-point evaporative cooling. However, its applicability has been recently expanded in several energy recovery applications. Therefore, the present study provides the overview of M-Cycle and its application in various heating, ventilation, and air-conditioning HVAC systems; cooling systems; and gas turbine power cycles. Principle and features of the M-Cycle are discussed in comparison with conventional evaporative cooling, and consequently the thermodynamic limitation of the cycle is highlighted. It is reported that the standalone M-Cycle AC MAC system can achieve the AC load efficiently when the ambient air humidity is not so high regardless of ambient air temperature.
Overview of the Maisotsenko cycle – A way towards dew point evaporative cooling