Experimental study of a counter-flow regenerative evaporative cooler

This paper aims to investigate the operational performance and impact factors of a counter-flow regenerative evaporative cooler (REC). This was undertaken through a dedicated experimental process. Temperature, humidity and flow rate of the air flows at the inlet, outlet and exhaust opening of the cooler were tested under various operational conditions, i.e., different inlet air conditions, feed water temperature and evaporation rate were also correspondingly measured. It was found that the wet-bulb effectiveness of the presented cooler ranged from 0.55 to 1.06 with Energy Efficiency Ratio (EER) rated from 2.8 to 15.5. The major experimental results were summarised below: 1) the wet-bulb effectiveness was significantly enhanced through either ways of increasing inlet wet-bulb depression or reducing intake air velocity, or alternatively by increasing working-to-intake air ratio; 2) the cooling capacity and EER of cooler was rapidly increased by means of increasing inlet wet-bulb depression or increasing intake air velocity, or reducing working-to-intake air ratio instead; 3) the effectiveness reduced by less 5% while feed water temperature increased from 18.9 to 23.1°C; 4) apparent acceleration in water evaporation rate was gained from increasing inlet wet-bulb depression or air velocity. The presented cooler showed 31% increase in wet-bulb effectiveness and 40% growth in EER compared to conventional indirect evaporative cooler. The research helped identifying the performance of a new REC with enhanced performance and thus contributed to development of energy efficient air conditioning technologies, which eventually lead to significant energy saving and carbon emissions reduction in air conditioning sector

Investigation of the energy performance of a novel modular solar building envelope

The major challenges for the integration of solar collecting devices into a building envelope are related to the poor aesthetic view of the appearance of buildings in addition to the low efficiency in collection, transportation, and utilization of the solar thermal and electrical energy. To tackle these challenges, a novel design for the integration of solar collecting elements into the building envelope was proposed and discussed. This involves the dedicated modular and multiple-layer combination of the building shielding, insulation, and solar collecting elements. On the basis of the proposed modular structure, the energy performance of the solar envelope was investigated by using the Energy-Plus software. It was found that the solar thermal efficiency of the modular envelope is in the range of 41.78–59.47%, while its electrical efficiency is around 3.51% higher than the envelopes having photovoltaic (PV) alone. The modular solar envelope can increase thermal efficiency by around 8.49% and the electrical efficiency by around 0.31%, compared to the traditional solar photovoltaic/thermal (PV/T) envelopes. Thus, we have created a new envelope solution with enhanced solar efficiency and an improved aesthetic view of the entire building

Energy saving potential of a counter-flow regenerative evaporative cooler for various climates of China: Experiment-based evaluation

© 2017 Recently there has been growing interest in regenerative evaporative coolers (REC), which can reduce the temperature of the supply air to below the wet-bulb of intake air and approach its dew-point. In this paper, we designed, fabricated and experimentally tested a counter-flow REC in laboratory. The REC's core heat and mass exchanger was fabricated using stacked sheets composed of high wicking evaporation (wickability of available materials was measured) and waterproof aluminium materials. The developed REC system has a much higher cooling performance compared to conventional indirect evaporative cooler. However, the decision to use the REC for China buildings depends on a dedicated evaluation of the net energy saved against the capital expended. Such an evaluation requires the hourly-based data on the availability of cooling capacity provided by the REC for various climates. The paper used an experiment-based method to estimate the cooling capacity and energy savings provided by the proposed REC for China's various climates. By using the experimental results and regional hourly-based weather data, the energy saving potential of the REC against an equivalent-sized mechanical air conditioner alone was analysed. The results indicate that, for all selected regions, the REC could reduce 53–100% of cooling load and 13–58% of electrical energy consumption annually

Thermal performance enhancement of a cross-flow-type maisotsenko heat and mass exchanger using various nanofluids

© 2018 by the authors. The incorporation of a Maisotsenko (M) Cycle into an indirect evaporative cooler has led to the achievement of sub-wet bulb temperature without any humidification, thus making it a possible green and sustainable alternative for handling the cooling load of a building. In this work, the thermal performance of a cross-flow heat and mass exchanger (HMX) is enhanced by the addition of nanoparticles in the wet channel because they significantly influence the heat and mass transfer characteristics of the base fluid. A governing model for the temperature and humidity variations of the HMX is numerically simulated. Initial benchmarking is achieved using water properties. Afterward, a comparative study is conducted using aluminum-oxide-, copper-oxide-, and titanium-oxide-based nanofluids. Enhancements of 24.2% in heat flux, 19.24% in wet bulb effectiveness, 7.04% in dew point effectiveness, 29.66% in cooling capacity, and 28.43% in energy efficiency ratio are observed by using alumina-based nanofluid as compared to water in the wet channel of the cross-flow HMX. Furthermore, a particle volume concentration of 1% and a particle diameter of 20nm are recommended for maximum performance

Numerical study of a regenerative counter flow evaporative cooler using alumina nanoparticles in wet channel

The use of Maisotsenko Cycle (M-Cycle) has enhanced the domain of evaporative cooling technologies to sub-wet bulb temperature cooling while ensuring moisture control. Several studies have demonstrated the use of cross-flow heat & mass exchanger (HMX) offers higher cooling capacity; however, it has lower cooling effectiveness and Energy Efficiency Ratio (EER). In contrast, a counter-flow (HMX) offers high cooling effectiveness with lower cooling capacity. In this paper, the performance of counter-flow HMX is enhanced by addition of alumina nanoparticles in feed water due to enhanced heat and mass transfer characteristics of nanofluids compared to original base fluid. Here, a mathematical model is formulated by incorporating the nanofluids in a selected control volume. The developed model is solved numerically on a discretized HMX length. Initially, the model is benchmarked against previously published results using water as base fluid. A comparison between HMX performance using water and alumina nanofluid is performed in terms of Performance Enhancement Ratio (PER). PER indicates 1-18% increase in cooling effectiveness, 18-43% increase in cooling capacity and 9-19% increase in EER by using alumina in water when working air temperature is increased from 20°C to 45°C. Similarly, an increase in PER is also observed by changing air velocity. Increase of 41% is observed in cooling capacity and 18% increase in EER is observed by changing particle volume fraction from 0 to 2 percent. This research identifies ways to reduce the carbon emissions of a building by increasing the energy efficiency of existing evaporative cooling technology using nanofluids

Investigation and Evaluation of Winter Indoor Air Quality of Primary Schools in Severe Cold Weather Areas of China

The indoor air quality (IAQ) in classrooms has attracted more and more attention. Unfortunately, there is limited information relating to IAQ in the primary schools in severe cold weather areas of China. In this study, a field investigation on the IAQ of a primary school of Shenyang in northeast China was carried out by physical measurements and questionnaire surveys. The carbon dioxide (CO2) concentration in selected classrooms was continuously measured for a week, and the corresponding ventilation rate was calculated. Meanwhile, the perceptions of the IAQ, the purpose and the comfort degree of window opening have also been recorded from 106 pupils, aged 9−12. The results indicate the ventilation rate is considerably inadequate in about 99% of the class time due to the low frequency of window opening. The average daily CO2 concentration in these classrooms is 1510−3863 ppm, which is far higher than the recommended value of 1000 ppm. Most pupils understand that the purpose of opening windows in winter is to improve air quality. However, there are big differences between the measurement results and subjective judgments of indoor air quality. Contrary to the high measured CO2 concentration, around 70% pupils consider the air fresh, and only 3.7% pupils are dissatisfied and even very dissatisfied with IAQ in their classroom. It is necessary to change the existing manual window opening mode, because the pupils’ subjective judgment affects the window opening behavior

Numerical study of a M-cycle cross-flow heat exchanger for indirect evaporative cooling

In this paper, numerical analyses of the thermal performance of an indirect evaporative air cooler incorporating a M-cycle cross-flow heat exchanger has been carried out. The numerical model was established from solving the coupled governing equations for heat and mass transfer between the product and working air, using the finite-element method. The model was developed using the EES (Engineering Equation Solver) environment and validated by published experimental data. Correlation between the cooling (wet-bulb) effectiveness, system COP and a number of air flow/exchanger parameters was developed. It is found that lower channel air velocity, lower inlet air relative humidity, and higher working-to-product air ratio yielded higher cooling effectiveness. The recommended average air velocities in dry and wet channels should not be greater than 1.77 m/s and 0.7 m/s, respectively. The optimum flow ratio of working-to-product air for this cooler is 50%. The channel geometric sizes, i.e. channel length and height, also impose significant impact to system performance. Longer channel length and smaller channel height contribute to increase of the system cooling effectiveness but lead to reduced system COP. The recommend channel height is 4 mm and the dimensionless channel length, i.e., ratio of the channel length to height, should be in the range 100 to 300. Numerical study results indicated that this new type of M-cycle heat and mass exchanger can achieve 16.7% higher cooling effectiveness compared with the conventional cross-flow heat and mass exchanger for the indirect evaporative cooler. The model of this kind is new and not yet reported in literatures. The results of the study help with design and performance analyses of such a new type of indirect evaporative air cooler, and in further, help increasing market rating of the technology within building air conditioning sector, which is currently dominated by the conventional compression refrigeration technology

Evaluation Strategies on the Thermal Environmental Effectiveness of Street Canyon Clusters: A Case Study of Harbin, China

Urban overheating significantly affects people’s physical and mental health. The addition of street trees is an essential, economical, and effective means by which to mitigate urban heat and optimize the overall thermal environment. Focusing on typical street canyon clusters in Harbin, China, landscape morphology was quantified by streetscape interface measurements (sky view factor, tree view factor, and building view factor). Through ENVI-met simulations, the correlation mechanism between streetscape interface measurements and thermal environment was evaluated, and optimization methods for assessing the thermal environment of urban streets were proposed. The results revealed: (1) The thermal environment optimization efficiency of general street canyon types was greatest when street tree spacing was 12 m. At present, the smaller spacing has not been simulated and may yield better thermal environment results. The average decrease in temperature (Ta), relative humidity (RH) and mean radiant temperature (MRT) was 0.78%, 2.23%, and 30.20%, respectively. (2) Specific street canyon types should adopt precise control strategies of streetscape interface according to their types to achieve the optimal balance between thermal environment optimization and cost. (3) Streetscape interface measurements and thermal environment indexes show quadratic correlation characteristics, and are critical points for further investigation. The conclusions are more specific than previous research findings, which are of great significance for decreasing the urban heat island effect at the block scale, improving residents’ physical and mental health, and improving the urban environment quality