Mechanical Vapor Compression System Research Articles

Performance analysis of a conventional two-stage indirect evaporative cooler

With the aim of saving a portion of the high-quality energy consumed in mechanical vapor compression systems for air conditioning applications, the present work focuses on utilization of low-quality energy conversion processes due to fluid evaporation. The conventional indirect evaporative cooler is selected based on its preference for further modification compared to a regenerative indirect evaporative cooler. It is configured to be operated with two identical stages in series. This task is achieved by developing a thermodynamic model to analyze the performance of the cooling unit and to indicate the extent of its development compared to the cooler in one stage. Preliminary results show that the best operating condition is when the ratio of primary air to secondary air is 1. The cooling unit produces fairly comfortable air within limited climatic conditions. It delivers air at 26 °C and lower even at climatic temperatures as high as 48 °C, but within a very low relative humidity range. The relative humidity range extends to less than 58% as the outdoor air temperature decreases. At high humidity levels (64 to 80% depending on climate temperature), cool air cannot be obtained at 26 °C, and the cooling unit performance is limited only by what the first stage produces. The average performance of the cooling unit exceeds that of the first stage by 42.6%. Increasing air flow rate leads to an increase in cooling capacity, but it also has a negative impact on supply temperature and effectiveness.

Exergy analysis of hybrid air-conditioning systems with different evaporative-cooling condensers under hot-humid climates

Evaporative cooling (EC) technology can effectively improve the energy efficiency of the mechanical vapor compression (MVC) system by enhancing the heat exchange capacity of its condenser. However, the current evaporative-cooling condenser system is usually only equipped with a single-stage evaporative cooler as the precooling unit, and these designs are mainly suitable for hot-dry conditions. In this study, three hybrid air-conditioning systems with different two-stage evaporative-cooling condenser configurations were proposed, one is single-condenser type and the other two are dual-condenser type, which are used to improve the exergy performance and adaptability of the evaporative condenser system under hot-humid climates. Then, the all systems were modeled via the distributed parametric method and analyzed comparatively based on the exergy method. A suitable exergy reference temperature at air saturation was discussed. Finally, the effect of four key parameters (ambient temperature and relative humidity, outdoor airflow rate and room heat load) was studied. The results showed that under the high temperature, relative humidity or room heat load conditions, the hybrid systems have a low exergy efficiency ratio (EXR) and high exergy efficiency (ηx,OEC). Among them, the newly countercurrent dual-condenser configuration (MVC-TSEC(C)) exhibits the best exergy performance under most hot-humid conditions. Compared to the conventional MVC system, the EXR and ηx,OEC of MVC-TSEC(C) increased by at most 35.0 % and 78.2 %, respectively. Moreover, its components like compressor, condenser and expansion valve have the maximum reduction rates of exergy destruction of 43.5 %, 17.2 % and 55.3 %, respectively.

Energy saving of vacuum-based membrane dehumidification with indirect evaporative cooling in a low sensible-heat-ratio building

In hot and humid climates, dehumidification generally consumes more energy than cooling, and conventional mechanical vapor compression system is not efficient for dehumidification. Vacuum-based membrane dehumidification system have been developed as a more environmentally friendly alternative for dehumidification due to non-refrigerant system and isothermal dehumidification process. In this study, a novel hybrid air conditioning system that combines vacuum-based membrane dehumidification with an indirect evaporative cooler for pre-cooling is proposed to achieve efficient air conditioning in building with low sensible heat ratio. The energy performance of the proposed system is investigated by detailed thermodynamic simulations and compared with conventional variable air volume (VAV) system and indirect evaporative pre-coolers combined VAV system. The simulation results show that when the average sensible heat ratio of the space is 0.73 and the COP of the vacuum-based membrane dehumidifier is 1.0, the proposed system can reduce energy consumption by 16.1 % compared to conventional VAV system and by 6.4 % compared to indirect evaporative pre-cooler combined VAV system during the cooling season. The energy performance of the proposed system is significantly affected by the sensible heat ratio of the building and the energy efficiency of the vacuum-based membrane dehumidifier. When the COP of the vacuum-based membrane dehumidifier reaches 2.0, the proposed system can achieve an energy savings of 48.2 % compared to conventional VAV system.

Component innovations for lower cost mechanical vapor compression

Despite significant capital and operating costs, mechanical vapor compression (MVC) remains the preferred technology for challenging brine concentration applications. This work seeks to assess the dependence of MVC costs on feedwater salinity and desired water recovery and to quantify the value of improved component performance or reduced component costs for reducing the levelized cost of water (LCOW) of MVC. We built a cost optimization model coupling thermophysical, heat and mass transfer, and technoeconomic models to optimize and identify low cost MVC system designs as a function of feedwater salinity and water recovery. The LCOW ranges over 3.6 to 6.1 $/m3 for seawater feed salinities of 25–150 g/kg and water recoveries of 40–80 %. We then perform sensitivity analysis on parameter inputs to isolate irreducible costs and determine high value component innovation targets. The LCOW was most sensitive to evaporator material costs and performance, including the overall heat transfer coefficient in the evaporator. Process and material innovations such as polymer-composite evaporator tubes that reduce evaporator costs by 25 % without reducing heat transfer performance by more than 10 % would result in MVC cost reductions of 8 %.

Comparative study on energy-saving performance of single- and two-stage evaporative-cooling condenser systems

The mechanical vapor compression system (MVC) coupled with the evaporative-cooling condenser is an effective method to improve its high temperature adaptability. However, this hybrid systems typically use an evaporative cooler as a single-stage pre-cooling unit of condenser and is mainly designed for hot–dry climates. In this paper, based on conventional evaporative-cooling condenser configuration, three two-stage evaporative-cooling condenser systems (MVC-TSEC(A), MVC-TSEC(B) and MVC-TSEC(C)) were proposed. The MVC-TSEC(A) consists of one condenser and an indirect/direct evaporative-cooler. The MVC-TSEC(B) and MVC-TSEC(C) have two condensers (in series), which are coupled with a two-stage evaporative cooling system. The refrigerant in the MVC-TSEC(C) forms a counter-flow configuration with the outdoor air, while it is concurrent flow in MVC-TSEC(B). Subsequently, the effects of the ambient parameters and outdoor air flowrate on the three two-stage hybrid systems were analyzed comparatively based on detailed numerical models. Finally, the application potential of these hybrid systems was evaluated comprehensively in hot–humid climates. The results showed that the seasonal COP and energy-saving rate for the MVC-TSEC(C) are reached by 4.2–4.7 and 12.7–21.1 %, respectively. Moreover, the static equipment payback period of the three two-stage hybrid systems are 3.8, 3.3 and 3.0 years, respectively.

Comparative study of three hybrid air-conditioning systems based on multiple evaporative coolers and run-around reheating coils

Existing evaporative-cooling hybrid air conditioning systems cannot fully utilize the synergistic energy-saving potential of multiple evaporative-cooling technologies. Moreover, they cannot meet simultaneously the energy-saving requirements of standard mechanical vapor compression (MVC) systems in the terms of fresh air pre-treatment, condenser pre-cooling and supply air reheating. Therefore, in this paper, integrating MVC system with the indirect evaporative cooler, outdoor-air evaporative-cooling unit, and run-around reheating coils, three alternative hybrid systems were proposed to meet the aforementioned three requirements. The three hybrid systems have different outdoor-air unit configurations (single condenser with direct evaporative cooler, dual condenser with direct evaporative cooler, and dual condenser with two-stage evaporative-cooling configuration) and reheat sources (exhaust, outdoor, and mixed air of fresh and return air). Then, the parameter effects and application potentials of the three hybrid systems were analyzed comparatively based on detailed numerical models. The results showed that the third proposed hybrid system (HAC-R3) exhibits the best energy-saving advantages in almost the range of ambient temperature, relative humidity and fresh airflow rate studied. The first proposed hybrid system (HAC-R1) has the simplest outdoor-air side configuration, which is also a good choice in medium–low humidity conditions. In hot-humid summer in southern China, HAC-R3 has the highest average energy-saving rate and seasonal COP of 16.0 % and 7.0 respectively. In addition, HAC-R1 has the lowest static equipment payback period of 3.3 years, slightly lower than that of HAC-R3 (3.4 years).

Thermodynamic and economic analysis of an integration system of multi-effect desalination (MED) with ice storage based on a heat pump

In this study, an innovative system that combined a heat pump, multi-effect desalination, and ice storage subsystem is proposed. The heat pump provides both thermal energy and cold energy for the system to achieve desalination and ice generation. The performance of the proposed system is compared with the conventional mechanical vapor compression and air conditioning systems. The thermodynamic, economic, and environmental analysis is also carried out of both proposed and conventional systems. Moreover, the impacts of the different refrigerants, the condensation temperature of the first effect, and the different areas are carried out to evaluate the effects of several vital parameters on the proposed system. Results showed that the specific energy consumption for the proposed and conventional systems is 4.71 kWh/t and 8.94 kWh/t, respectively. For the economic performance, the payback period of the proposed system is 3.85 years, while it is 5.90 years for the conventional system. For the environmental performance, the unit profit CO2 emission is 15.50 kg/$ of the proposed system, which is 7.68% lower than the conventional system (16.79 kg/$). Hence, the proposed system shows higher economic and environmental performance.

Investigation of multi-effect mechanical vapor compression desalination system powered by photovoltaic/thermal, photovoltaic-evacuated tubes, and photovoltaic solar collectors: Techno-economic study

Energy and potable water are two serious necessities for human life all over the world. Solar energy can be used to produce potable water at low cost. Multi-effect mechanical vapor compression desalination system powered by solar energy technology could be a solution of the production of freshwater with high performance and low cost. Techno-economic performance of forward-feed multi-effect mechanical vapor compression desalination system powered by photovoltaic/thermal collectors is investigated. The feasibility of using the electrical and thermal energy of photovoltaic/thermal collectors to directly power the multi-effect mechanical vapor compression system is studied. Performance of the desalination system with photovoltaic/thermal collectors as a power source is assessed and compared to another two systems powered by photovoltaics with evacuated tubes and photovoltaics only. The three proposed systems’ mathematical models are built and solved using MATLAB. The impact of changing effects number, compression ratio, and last effect temperature on systems’ performance is investigated. Results showed that the external preheater enhances the system performance as high-grade electricity is replaced by low-grade heat when increasing the number of effects. Multi-effect mechanical vapor compression could be powered by photovoltaic/thermal collectors at a wide range of compression ratios and number of effects but with a limited range of last effect temperature. Coupling photovoltaic/thermal collectors to multi-effect mechanical vapor compression greatly reduces the required collectors’ surface area in comparison to photovoltaics with evacuated tubes and photovoltaics only with specific collectors’ surface areas of 7.36, 10.65, and 11.98 m2/(m3/day), respectively. The highest performance ratios recorded are 28.42 for photovoltaic/thermal collectors, 16.5 for photovoltaics with evacuated tubes, and 12.96 for photovoltaics only. The lowest unit water costs are 4.15 $/m3 for photovoltaics with evacuated tubes, 4.22 $/m3 for photovoltaic/thermal collectors, and 4.31 $/m3 for photovoltaics. Furthermore, replacing electricity with heat reduces energy storage shares of capital cost from 63% to 48%.

Theoretical investigation of combining cooling tower and cooling coil with direct evaporative cooler

A theoretical study is developed to examine the feasibility of using the cooling tower and the cooling coil with the direct evaporative cooler in the highest summer temperature in Karbala/Iraq. This is due to the inability of the direct evaporative cooler in reducing the outside air temperature and efficiency reduction in the mechanical vapor compression systems despite its high electrical energy consumption at high temperatures. The water in the cooling tower is cooled to a temperature higher than the outdoor wet-bulb temperature by (3.9 ^circ C). The water then passes through the cooling coil where the outdoor air is pre-cooled through it, and the outdoor air temperature decreases by (17 ^circ C) without an increase in humidity. Then the pre-cooled air passes through the direct evaporative cooler where its temperature decreases by (10 ^circ C) and humidity increases. The temperature of the air leaving this combining system is reduced by (27 ^circ C). The results showed that the temperature of the air leaving this combining system is adequate and passes through the comfort zone in the psychrometric chart. The results presented that the cooling tower and the cooling coil alone were unable to reduce the air temperature to reach the comfort zone. A similar observation is noted with the direct evaporative cooler. Therefore, the combining system is considered a more effective alternative to the direct evaporative cooler, and its effectiveness reaches more than 100%. Additionally, it is clean, environmentally friendly, energy efficient, and does not add heat to the surrounding environment in comparison with mechanical vapor compression systems.

Multi-objective optimization with multiple Pareto frontiers applied to a MED desalination system

This article presents the simulation results of a Multi Effect Desalination system coupled to a Mechanical Vapor Compression system. The system is optimized with the Non-dominated Sorting Genetic Algorithm II genetic algorithm by obtaining the optimal results for the desalination plant operating with 8–12 effects, with Forward Feeding and Parallel Cross Feeding. The best results are obtained for two cases: a) For a Multi Effect Desalination system with Parallel Cross Feeding operating with 12 effects, a Top Brine Temperature of 64 °C and a feed water flow rate of 293 kg/s. This configuration presents a Unit Cost of Distilled Water of 1.94 USD/m3 and 128.1 kg/s of fresh water. b) And for a Multi Effect Desalination system with Forward Feeding with 9 effects, a feed water flow rate of 380 kg/s, a Top Brine Temperature of 64 °C, which allows obtaining a Unit Cost of Distilled Water of 1.79 USD/m3. The same system but with 12 effects, a Top Brine Temperature of 72 °C, a feed water flow rate of 380 kg/s allows obtaining a higher water production of 152.3 kg/s, which shows that there is more than one optimal solution for this kind of systems, which depends on the figure to be optimized.

Comprehensive performance of parallel feed MEE-MVC evaporation system

Abstract The mathematical model based on conservation of energy, mass and salinity is established to analyse the comprehensive performance of parallel feed multi-effect evaporation system with mechanical vapor compression (MEE-MVC) system. It is found that the efficiency of the MVC evaporation system gradually improves as the number of evaporator effect increases. However, the optimization trend of specific power consumption (SPC) and coefficient of performance (COP) are declining when the number of evaporator effect exceeds 3, which makes the marginal effect of the efforts made to improve the system gradually weakened. Then, the three-effect MVC evaporation system is taken as the main research subject to investigate comprehensive performance of the system. It was found that the SPC of the system increases with the increase of the total heat transfer temperature difference; on the other hand, the COP decreased significantly with the increase of the total heat transfer temperature difference. Furthermore, increasing the evaporation temperature in the last evaporator as well as compressor efficiency can optimize the energy efficiency of the system. In addition, the compressor efficiency has a greater influence on the SPC when the total heat transfer temperature difference is larger, whereas the compressor efficiency has a greater influence on the COP when the total heat transfer temperature difference is smaller.

Study on the leakage in water-injected twin-screw steam compressor

Steam compressor shows great energy-saving potential in mechanical vapor compression and high-temperature heat pump systems. However, leakage remains a huge problem for compressor performance improvement and design optimization. In this article, a thermodynamic model with detailed leakage flow model was developed for the working process in water-injected twin-screw compressor. Altogether, leakage in different paths and heat and mass transfer between injected liquid and compressed vapor were considered. Compared with experimental results, the accuracy of predicted efficiency is within ± 5% for all tested operating conditions. In the validated model, leakage flow in five leakage paths and their effects on compressor efficiency was investigated. Results indicate that leakage can reduce volumetric efficiency by up to 50.2%, while the injected water liquid vaporization can improve volumetric efficiency by 7.9% at 5000 r·min−1. The leakage through contact line (CL), tip sealing (TS) line, and discharge end face (DE) show the most important impact on compressor efficiency, while the leakage through blow hole (BH) and suction end face (SE) has little impact on compressor efficiency. Compared with zero leakage under certain conditions, the reduction of volumetric efficiency caused by CL, TS line, and DE can reach up to 22.4%, 20.4%, and 12.7%, respectively. Reducing clearances of the above three leakage paths can efficiently improve the performance of steam compressor, especially for CL.

Comprehensive test of ultra-efficient air conditioner with smart evaporative cooling ventilation and photovoltaic

Going by current usage trends, the use of room air conditioners will increase by three times by 2050. Therefore, it is necessary to investigate an ultra-efficient air conditioner with extremely low operating energy consumption to realize the goal of climate change, especially in the (sub) tropical area. In this paper, an ultra-efficient air conditioner with smart evaporative cooling ventilation and photovoltaic is proposed, which is composed of a highly efficient air conditioner, a fresh air ventilator with evaporative cooling, an evaporative condenser, and a photovoltaic. The mechanical vapor compression system adopts a gas-injected vapor compression cycle with relay cooling, which adapts to extremely high temperatures and harsh environments. Fresh air ventilation, water usage, and indoor temperature/humidity control strategies are also proposed. In the 31-day field test, the independent ventilator operation hours accounted for approximately 38.4% of the total test period. The electricity savings reached 89.8% as the indoor temperature and humidity satisfied all requirements. Through a typical 10-day lab-simulated year-round performance test, the calculated annual power consumption of the ultra-efficient air conditioner was 746.2 kWh, which was 82.8% lower than that of the baseline prototype. Based on the Indian Seasonal Energy Efficiency Ratio test, the calculated results revealed a consumption of 8.43 kWh/kWh, an improvement of approximately 140.7%. The comprehensive electricity-saving rate was 84.1%. The developed prototype won the global cooling prize since it will counterbalance the booming of residential cooling demand in the future, demonstrating a reliable route for energy savings for room air conditioners.

Development of biomass based-activated carbon for adsorption dehumidification

Desiccant dehumidification systems can be utilized for decoupling moisture removal duty from the conventional mechanical vapor compression systems. Dehumidification using desiccant dehumidifiers is expected to exhibit a better energy efficiency. However, the high energy needed in the regeneration process limits its applicability. To realize the full potential of this technology, it is necessary to develop materials that can be regenerated using heat sources under 70 °C. In this study, activated carbons (ACs) derived from waste biomass were developed as desiccant materials. The ability of activated carbon (AC) to remove the moisture was controlled by carefully preparing the material to achieve the right operation window for optimum moisture sorption processes. The porous and surface characteristics of the newly-prepared AC were analyzed and compared with those of silica gel. The adsorption isotherm measurements were conducted, and the data were fitted with Henry–Sips and Do–Do isotherm models. The current ACs exhibit an excellent water adsorption capacity (up to 0.41 g/g). The efficacy of the ACs for dehumidification applications was assessed using the weather data from several regions of Indonesia, from North Sumatera to Papua. The results revealed that under the studied conditions, the new desiccant material showed a better dehumidification capacity than silica gel. Moreover, the reported AC can be regenerated using temperatures as low as 40 °C, which is readily available from waste heat, including the heat rejection from the condenser of an air-conditioning unit.

Next generation air conditioner for sustainable cooling solutions

Generally in summer, air conditioning systems are essential for improving the human comfort and productivity. The mechanical vapor compression system (VCS) is probably the most used system. However, the refrigerant used in VCS is harmful to the environment and the initial cost is high. So, the aim of this study is to introduce a sustainable, energy-efficient and climate-friendly air conditioning system in which there is no refrigerant. The proposed system is the integration of two modules i.e., Direct evaporative cooling (DEC) module and vacuum-assisted isothermal membrane-based air dehumidification (VIMAD) module, where the DEC module will cool and humidify the entering air stream and then this cool and humidified air will enter into the VIMAD module and the air will get dehumidified. Finally, the output will be cool and dehumidified air at the exit of the system. In this paper, the proposed system is explained. Moreover, the basic principle of the DEC, the background of DEC and the basic principle of the VIMAD system, background on the types of membrane materials that can be used in VIMAD are explained. Also, the effects of various parameters on the performance of the DEC and VIMAD are presented.

Energy/exergy analysis of solar driven mechanical vapor compression desalination system with nano-filtration pretreatment

The performance of the mechanical vapor compression desalination system is limited due to the required vacuum pressure and associated high temperature scaling problem. Thus, a new solar driven mechanical vapor compression desalination plant with nano-filtration pretreatment operating at atmospheric pressure is developed for a production of 500 m3/day. The electrical and thermal energies of the new system are generated using the integration of solar photovoltaic modules and parabolic trough collectors. To evaluate the performance of the new system, energy/exergy analysis is performed by employing a MATLAB package and a Graphical User Interface (GUI) tool. Also, an economic evaluation for the plant's direct, indirect, and unit product costs ($/m3) is presented. The predicted results are validated with the available measurements. The effects of different design parameters such as feed water temperature, distilled and brine water temperature difference, salt rejection and recovery ratio on plant performance are investigated. The proposed plant's exergy efficiency is found to vary from 14.59 to 20% consistently with design parameters. The enhancement in exergy efficiency is estimated to be 153.7%, 56.3%, 32.63% and 27% compared with Multi-Effect evaporation mechanical and conventional vapor compression, forward feed multi-effect mechanical vapor compression and reverse osmosis systems, respectively. The salt rejection and recovery ratio are found to be the most significant parameters to enhance the plant exergy efficiency. Furthermore, the photovoltaic unit has a significant effect on exergy destruction of the plant with a percentage of 85.79%. The parabolic trough collectors also have high exergy destruction of about 69.53%. The economic analysis reveals that the unit water price for the proposed plant is equal to 1.54 $/m3. Therefore, the developed solar-NF-MVC system suits small scale units for remote communities.

Analysing the transport phenomena of novel dew-point evaporative coolers with different flow configurations considering condensation

This paper entails a study on the transport phenomena of a novel dew-point evaporative cooler with counter-flow closed-loop configuration, a potential alternative to the conventional mechanical vapor compression system. In contrast to the conventional indirect evaporative cooler and the regenerative indirect evaporative cooler, the proposed novel dew-point evaporative cooler is capable of achieving the simultaneous goals of pre-cooling, energy recovery and dehumidification. The novel dew-point evaporative cooler is classified as either type 1 or type 2 based on the relative flow direction between the water and the supply air. A two-dimensional computational fluid dynamics model is judiciously developed and employed to conduct a comparative study which evaluates the performance of the conventional indirect evaporative cooler vis-a-vis both novel type 1 and novel type 2 configurations. Experimental data is then employed to validate the predictive accuracy of the mathematical model. The distributions of both temperature and humidity ratio are plotted for a typical case of the novel cooler incorporating both flow configurations and considering the effects of moisture condensation. Additionally, the impacts made by key parameters on the cooling performance under condensation state are analyzed by using three evaluation indexes, namely, latent efficiency, wet-bulb efficiency, and enlargement coefficient. By regulating several operating parameters, the variations of the three evaluation indexes are plotted via the proposed numerical model. Key results from this study revealed that the novel type 1 flow configuration is capable of achieving the highest latent and wet-bulb efficiencies, and enlargement coefficient. It is also observed that the relative flow direction between the water and the supply air exerts a stronger influence on the cooler performance compared to the changes of the water mass flow rate.

A review of recent advances in indirect evaporative cooling technology

Indirect evaporative cooler with dew point cooling has great potential to replace the conventional mechanical vapor compression system in air conditioning industry. In this paper, a detailed review has been conducted on recent developments in the indirect evaporative cooling (IEC) systems as well as their associated design parameters and operating conditions for higher cooling effectiveness and cooling capacity. The current review also consolidates the design and performance of various indirect evaporative cooling systems (such as classical indirect evaporative cooler, regenerative, dew point cooler, and Maisotsenko cycle based cooler). Furthermore, integration of these indirect evaporative cooling systems with other cycles is elaborated. In addition, the thermal management potential of the indirect evaporative coolers in various applications is highlighted. It is found that major design parameters include system configuration, inlet airflow conditions, channel geometry, and evaporative material. It is also found that counter-flow arrangement with higher inlet air temperature, lower inlet air humidity, smaller channel height, smaller inlet air velocity, higher channel length, and higher working to intake air ratio, triangular shape of channel with fabric evaporative material yields higher cooling effectiveness and efficiency. This review indicates that the IEC systems could be a potential replacement for the conventional vapor compression cycle based cooling systems in buildings and other applications.

Energy and exergy performance comparison of conventional, dew point and new external-cooling indirect evaporative coolers

External-cooling indirect evaporative cooling is an effective energy saving technology, where air–water finned coils are linked with packed cooling tower by water pipes. However, external-cooling indirect evaporative coolers with different configurations and working air sources are incomprehensively analyzed and compared. This study presented an energy and exergy analysis of five external-cooling indirect evaporative coolers, including conventional configuration, dew point configuration, newly patented dew point configuration, and energy recovery forms of the first two. In order to analyze the evaporative cooler and its hybrid system combined with mechanical vapor compression system, the numerical model and experimental correlation are used. The effect of four selected parameters (ambient temperature, ambient humidity ratio, total number of transfer units and fresh air flowrate), and the summer energy saving potential in three different cities are studied. The analysis results show that the new dew point configuration has the best performance under the conditions of high temperature, high humidity, and high fresh air flowrate. This new dew point cooler’s hybrid system achieves the best energy saving rate in humid and arid climates, between 19.1% and 48.5% compared with the pure mechanical vapor compression system. In this study, the advantages and disadvantages of presented designs are established and their application potential under different climates is estimated.

Development of an evaporative cooler system applied to the air conditioning of urban buses

Air conditioning for buses is an important incentive tool for the public transport, since it offers comfort to passengers and stimulates the use of this kind of transport which is fundamental to improve urban mobility. Currently, air conditioning equipment for buses is the mechanical vapor compression (MVC) type. However, this kind of system has two main disadvantages: the high financial cost and power consumption by the vehicle engine. The purpose of this study is to develop an evaporative cooler for buses, which is a simple, environmental friendly, low-cost solution that does not use engine power for its operation. The first step was the design and construction of the prototype. The following step was to evaluate the built prototype through performing experimental tests. The prototype presented a saturation efficiency of approximately 70%, airflow rate of 421.5 m³/h and energy consumption of 98.4 W. After determining the prototype technical characteristics, the evaporative cooling system was developed for an urban bus, seeking to meet the air renewal required by ANSI/ASHRAE standard 62.1 and to promote the passenger’s thermal comfort as specified by ISO 7730 and ANSI/ASHRAE Standard 55. The thermal comfort provided by the new cooling system was evaluated through the PMV-PPD indexes. A value of 0.35 was obtained for the PMV index and the PPD index obtained a value of 7, indicating that approximately 93% of the passengers will be satisfied regarding their thermal comfort for the established environmental conditions. The evaporative cooling system had a total energy consumption of approximately 0.4 kW, which represents only 5% of the energy that would be consumed by a MVC system. Therefore, the evaporative cooling performance depends on the climatic conditions of the environment, especially humidity. However, when applied in favorable conditions (low humidity), the evaporative cooling system proved to be a viable solution to replace the MVC systems in buses air-conditioning application, where its main advantage is its positive cost-benefit and energy savings. http://dx.doi.org/10.18226/23185279.v8iss1p46