EC Directive Research Articles

Cfd-based optimization of Direct evaporative cooling systems for canarian greenhouses in Semi-Arid regions

Direct Evaporative Cooling Systems (DECS) offer a promising solution for mitigating heat stress in greenhouses located in arid and semi-arid regins. To implement DECS efficiently in these regions, it is crucial to understand their impact on greenhouse microclimate parameters. This study investigates the influence of DECS on the microclimate within a canarian greenhouse and identifies key factors affecting their efficiency. Through Computational Fluid Dynamics (CFD) simulations using Ansys, we examined the effects of DECS on temperature, relative humidity, and air velocity within the greenhouse under semi-arid conditions.The results indicate that DECS efficiency is affected by several factors, including fan placement, evaporative pad height, fan spacing, and inlet air fan speed. Higher fan placement cools the upper canopy but increases humidity near the ceiling, whereas lower placement improves temperature uniformity but may require additional humidification. Closer fan spacing results in uneven air velocity, while wider spacing leads to stagnant zones within the greenhouse. Optimal placement of the the evaporative pad is crucial for maximizing the cooling coverage area and minimizes the temperature gradients. Inlet air fan speed also significantly impacts the microclimate, with higher speeds reducing both temperature and humidity. By optimizing these parameters, the DECS system was able to significantly decrease air temperature, increase humidity, and improve air velocity inside the greenhouse. With a pad height of 1.5 m, fans positioned at a height of 2 m, a distance of 6 m between each fan, and an air speed of 1.5 m/s at the entrance – the DECS enhances the local climate. Under these conditions, the mean air temperature drops from 40°C −in greenhouse with natural ventilation- to 21 °C using DECS, while relative humidity increases from 23 % −in greenhouse with natural ventilation- to 67 % using DECS, creating a more favorable environment for plant growth and potentially increasing crop yield and quality. Additionally, energy and environmental analyses show that implementing DECS in Canarian greenhouses, instead of traditional electrical cooling systems, results in substantial energy savings of 123,818.112 kWh/year annually and reduces carbon dioxide emissions by approximately 1.785 tons/year over a 20-year operational lifespan in a semi-arid climate.

Impact of Air Conditioning Type on Outdoor Ozone Intrusion into Homes in a Semi-Arid Climate

Outdoor ozone (O3) is elevated on hot, sunny days when residential air conditioning is used most. We evaluated the impact of direct evaporative coolers (ECs) and vapor-compression air conditioners (ACs) on indoor O3 concentrations in homes (N = 31) in Utah County, Utah, United States of America. Indoor and outdoor O3 concentrations were measured for 24 h at each home using nitrite-impregnated glass-fiber filters. AC homes (n = 16) provided a protective envelope from outdoor O3 pollution. Only one AC home had O3 levels above the limit of detection (LOD). Conversely, EC homes (n = 15) provided minimal protection from outdoor O3. Only one EC home had O3 levels below the LOD. The average indoor O3 concentration in EC homes was 23 ppb (95% CI 20, 25). The indoor-to-outdoor (I/O) ratio for O3 in EC homes was 0.65 (95% CI 0.58, 0.72), while the upper bound for the I/O ratio for AC homes was 0.13 (p < 0.001). Indoor exposure to O3 for residents in EC homes is approximately five times greater than for residents of AC homes. Although ECs offer energy and cost-saving advantages, public health awareness campaigns in O3-prone areas are needed, as well as research into O3 pollution controls for direct ECs such as activated carbon filtration.

An Experimental Investigation on the Performance Analysis of Two-Stage Desert Cooler

The present experimental investigation reports the performance of both the single and two stage direct evaporative cooling systems in composite climatic conditions of Patna, India. A two-stage direct evaporative cooling system has been designed and fabricated. The first stage of the two-stage cooling system utilizes a heat exchanger designed internally to sensibly cool hot and arid ambient air. The effect of varying the frontal air velocity (0.5–9 m/s) and different saline water concentration (5–10%) on the performance of two stage direct evaporative cooler is investigated. The maximum effectiveness of single and two-stage desert cooler is found to be 0.7 and 0.98 at frontal velocity of 2 m/s and 2.5 m/s, respectively. The performance of the two-stage cooler with tap water is found to be 40% higher than the single stage desert cooler. The effectiveness of single and two stage desert coolers with tap water is found to be in the range of 6–11% and 9.3–14% higher compared to the saline water at salt concentrations of 5–10%, respectively. Moreover, increasing salt concentration leads to reduced relative humidity at the cooler exit, with the two-stage cooler exhibiting 28.5% lower relative humidity than single-stage desert cooler.

Developing an experiment-based strong machine learning model for performance prediction and full analysis of Maisotsenko dewpoint evaporative air cooler

Among all direct and indirect water-based evaporative air coolers, Maisotsenko indirect evaporative cooler (MIEC) is the only one which can supply sub wet-bulb air temperature while adding no moisture to the product air. For any given MIEC, four thermal/fluid parameters including dry channel flow rate, wet-to-dry-side air flow ratio, ambient air temperature and ambient relative humidity impact the performance of the MIEC. Sub-wet bulb supply temperature while having maximum cooling capacity happen only for a specific range of the mentioned thermal/fluid parameters. For any ambient condition and dry side air flow, a magic value of air-flow-ratio can maximize the cooling capacity of the cooler. Thousands of data is required to provide a simultaneous multi-aspect analysis of each parameter (while other parameters vary as well) to identify all possible curve behaviors and secrets of this technology. That is why, for the first time in this research, a strong machine learning (ML) model, is developed for MIEC cooler using 625 validated analytical/experimental-based training data (full factorial design). This model is employed to generate around 3600 unseen data to fully clarify the impact of each parameter (on supply temperature, total cooling capacity, useful cooling capacity and wet-bulb effectiveness) while other parameters are variable too. This strategy makes it possible to see all hidden extremum or peak point where the performance of the cooler is maximized or minimized. Interesting results are found in this research. For any ambient condition, there is an extremum point of the air flow ratio at which the total cooling capacity is maximized. The results indicate that as the dry side air flow increases, this extremum value decreases. For instance, under an ambient condition of 18 °C and 9 % relative humidity, the extremum point of the air flow ratio is 0.45 when the dry side air flow is 0.8 L/s and 0.25 when the dry side air flow is 4.8 L/s. In real-world commercial cooler, this can be simply happened by appropriate re-adjusting the dry and wet side fan speeds.

Experimental investigation of earth-air heat exchanger using porous clay vessels for eco-friendly buildings

This study introduces an experimental investigation of a novel direct trend evaporative cooler based on a ground-air heat exchanger (GAHE) using porous clay vessels as an evaporation media under a variety of operational conditions, including air flow rate, inlet air temperature, temperature of inlet water, and in air humidity. The evaluation of the GAHE performance was based on the air-cooling effect, wet-bulb and dew-point efficiencies, energy efficiency ratio, water evaporation rate, specific water evaporation, specific cooling capacity, specific total cost, and CO2 emission rate. The influences of dry-bulb temperature, the incoming air's relative humidity (RH), and six air flow rates ranging from 11 to 25 L/s on the performance are investigated and discussed. Results indicated that increasing the air flow rate leads to an increase in the cooling capacity. Energy efficiency ratio (EER) reaches the highest value of about 25.5 recorded at 3:00 PM with air flow rate = 11 L/s. The lowest EER value is approximately 7.2 when the measured inlet and outlet temperatures are the closest at 7:00 PM, with a flow rate of 25 L/s. Increasing the air flow rate from 11 to 17 L/s increased the wet bulb efficiency, and the airflow rate was inversely proportional to wet-bulb efficiency. The maximum and minimum average dew-point efficiencies are 64% and 58% at 17 L/s and 22 L/s respectively. The water evaporation rate increases by 182.1%, increasing the air flow rate from 11 to 25 L/s.

EVALUACIÓN DEL POTENCIAL DE UN SISTEMA HÍBRIDO INTERCAMBIADOR TIERRA-AIRE Y ENFRIAMIENTO EVAPORATIVO

These days, everyone is concerned with conserving energy. Among the existing heating and cooling technologies to reduce energy consumption in buildings are the Earth-to-Air Heat Exchangers (EAHE). These systems can be combined with evaporative cooling, either direct or indirect, to improve the global performance. In the literature, hybrid solutions with direct evaporative cooling systems at the exit of EAHEs are proposed for indoor cooling. Due to limitations of indoor RH, most applications focus on greenhouses. Moreover, existing works target hot and arid climates. This work targets both indirect evaporative cooling (IEC) and direct evaporative cooling (DEC) to be combined with an EAHE installed at a near Zero Energy Building. The supplied relative humidity is analyzed to evaluate its feasibility for occupied spaces. The performance and energy savings achievable are studied through simulation using TRNSYS software.

Enhancing the Efficiency of Air Conditioning Systems in High-Temperature Climates Through Direct Evaporative Cooling

Enhancing the Efficiency of Air Conditioning Systems in High-Temperature Climates Through Direct Evaporative Cooling

Determination of Performance of Different Pad Materials and Energy Consumption Values of Direct Evaporative Cooler

The purpose of this study is to determine the performances of luffa and greenhouse shading netting (which can be used as alternatives to commercial cellulose pads, that are popular for cooling greenhouses), the contribution of external shading to the evaporative cooling performance, and the energy consumption of the direct evaporative cooler. In this experiment, eight different applications were evaluated: natural ventilation (NV), natural ventilation combined with external shading net (NV + ESN), cellulose pad (CP), cellulose pad combined with external shading net (CP + ESN), luffa pad (LP), luffa pad combined with external shading net (LP + ESN), shading net pad (SNP), and shading net pad combined with external shading net (SNP + ESN). The cooling efficiencies of CP, CP + ESN, LP, LP + ESN, SNP, and SNP + ESN were found to be 37.6%, 45.0%, 38.9%, 41.2%, 24.4%, 29.1%, respectively. Moreover, their cooling capacities were 2.6 kW, 3.0 kW, 2.8 kW, 3.0 kW, 1.7 kW, 2.0 kW, respectively. The system water consumption values were 2.9, 3.1, 2.8, 3.2, 2.4, 2.4 l h−1, respectively. The performance coefficients of the system were determined to be 10.2, 12.1, 11.3, 11.9, 6.6, 7.8. The system’s electricity consumption per unit area was 0.15 kWh m−2. As a result of the study, it was determined that commercially used cellulose pads have advantages over luffa and shading net materials. However, luffa pads can be a good alternative to cellulose pads, considering their local availability, initial cost, cooling efficiency, and capacity.

Performance evaluation of an indirect-direct evaporative cooler using biomass-based packing material

ABSTRACT To overcome the drawbacks of a single-stage evaporative cooler, an indirect-direct type evaporative cooler was proposed and fabricated. An alternative arrangement of mild steel plates wherein unmixed heat transfer occurs between air and water to form an indirect evaporative cooler. This is followed by a packing arrangement made of biomass-based coconut coir that forms a direct evaporative cooler. Experiments were conducted by varying the air and water flow rates, and the performance of the coconut coir was compared with that of a commercially available celdek packing. Experimental results indicated that a combination of an indirect-direct evaporative cooler helped cool air without an appreciable increase in air-specific humidity. The performance of the coconut coir is slightly lower than that of the Celdek coir in terms of the drop in DBT and wet-bulb effectiveness. A maximum wet bulb effectiveness of 0.78 and 0.63 was achieved for the celdek and coconut coir packings, respectively. The maximum performance was attained at an air velocity of 6 m/s and a water flow rate of 3 LPM. Owing to the different advantages of coconut coir over celdek packings, it is recommended to use coconut coir as an alternative packing in indirect-direct evaporative coolers.

The Best Design for a Direct Evaporative Cooling System Based on Pressure Drop at Desired Saturation Efficiency: A Cost–Benefit Optimization

The Best Design for a Direct Evaporative Cooling System Based on Pressure Drop at Desired Saturation Efficiency: A Cost–Benefit Optimization

Experimental study on exhaust internal circulation desiccant wheel evaporative cooling chiller

Evaporative cooling chillers reduce the water temperature by absorbing heat during the evaporation of water without the need for compressor assistance or refrigerants. It is an energy-saving and environmentally friendly cooling technology but it needs necessary improvements in the applicable environmental area and refrigeration performance due to ambient air wet-bulb temperature limitations. To obtain chilled water below the dew-point temperature of the ambient air, an exhaust internal circulation desiccant wheel evaporative cooling chiller is proposed and experimentally investigated. A combination of a heat pipe exchanger, a desiccant wheel, an air cooler and an air heater are applied to reduce the wet-bulb temperature of the ambient air before it passes through the direct evaporative cooler. At the same time, the low-temperature and low-humidity exhaust air from the direct evaporative cooler is used to circulate to improve chiller performance. The experimental results show that the average chilled water temperature of the proposed chiller is 10.2 ℃ lower than that of the direct evaporative cooling chiller under five typical environmental conditions. The wet-bulb efficiency of the proposed chiller is the highest at high temperatures and high humidities (36 ℃ and 80% RH), which is 6 times greater than that of direct evaporative cooling chillers. Therefore, the proposed chiller expands the application range of evaporative cooling technology, which is especially suitable for humid areas with low-grade heat utilization such as solar energy.

An experimental investigation on the novel hybrid indirect direct evaporative cooling system

The Evaporative Cooling Technology has revived in the past few decades owing to the gradual shift of economies towards investing in sustainable cooling systems which has led to many governments defining sustainability targets in reducing GHG emissions and achieving climate neutrality with many EU countries aiming to reach net zero emissions by 2050. The major contribution towards GHGs are the conventional air conditioning systems which incorporate energy intensive compressor units and refrigerants as working fluids. A great deal of research has been done on the Evaporative Cooling Technology particularly, the DEC – Direct Evaporative Cooling systems due to their cost-effectiveness, design simplicity and feasibility. The present study proposes a HIDEC – Hybrid Indirect Direct Evaporative Cooling System as an alternative to the conventional vapor compression systems which is unique considering its compact and two in one design incorporating both Indirect and Direct Cooling Channels in a single system. The HIDEC Experimental System is developed passing through the stages of fabrication and design, followed by realtime testing in the hot and humid, and hot and dry sub tropical climatic conditions of Islamabad. The HIDEC Experimental System when operated in Dual Hybrid Mode provides a substantial supply air temperature drop to 24.8 °C with a maximum achievable COP of 35.2 and Cooling Capacity of 16.8 kW. The overall wet bulb effectiveness of the system elevates to 85%, whereas the dew point effectiveness reaches a maximum of 80%.

Energy, exergy, economic, exergo and enviro-economic analysis of solar powered humidification dehumidification desalination system: An experimental investigation

A solar-powered humidification dehumidification (SPHDH) desalination system presents an economically viable thermal desalination approach for satisfying the requirement of freshwater. The traditional solar air heater and saline water as the cooling fluid in the condenser, impose restrictions on the SPHDH system’s performance and lifespan. The present study involves a solar air heater, humidifier (packed bed type), and heat exchanger coupled with a direct evaporative cooler to develop a SPHDH desalination system. The collector employed in this study consists of double-end open evacuated tubes, while the cooling medium utilized is ambient air. Moreover, in the context of a humidifier, two distinct packing materials, specifically cellulose and aspen pads are employed in order to examine the impact of the packing material on the system. The performance evaluation is conducted through the energy, exergy, GOR, effectiveness, economic, exergo, and enviro-economic assessments. The findings indicate that the cellulose pad exhibits superior performance when compared to the aspen pad. This is due to lower air flow resistance and a greater contact surface area. The system’s highest mean energy and exergy efficiency is obtained with cellulose pads, i.e., 31.2 % and 5.10 %, respectively. Moreover, the cellulose pads have shown to achieve a maximum production of 3.12 kg/m2/day at a cost of 0.038 $/kg. The exergo-economic values based on energy and exergy are 14.76 kWh/$ and 2.56 kWh/$, respectively.

Evaporative cooling strategy using cooling pad material made from stove wicks in walk-up flat in the humid tropical climate of Surabaya

Generally, the thermal conditions in simple flats for rent are still not within a comfortable range. There is no implementation of artificial ventilation (Air Conditioner) with adjustable air temperature, so passive strategies still need to be pursued. In this case, the strategy pursued is Direct Evaporative Cooling (DEC) system with cooling pads made from stove wicks. Experimental methods were conducted in one of the apartment buildings in Surabaya, namely Indrapura Walk-up Flat. The research results indicate that at relatively high outdoor air temperatures from 12:00 to 15:00 local time, ranging from 27.9 to 32oC, the implementation of DEC was able to reduce the air temperature by 1.94-2.08oC

A numerical study of cucurbit cultivation in a greenhouse under direct solar radiation and equipped with a direct evaporative cooler in summer season

The performance of direct evaporative cooler to meet cooling demand of a greenhouse in Tehran in the hottest months of the year as well as water and electricity consumption were numerically studied. The suitable values of air change per hour (ACH) was also obtained for cultivation of tomato, cucumber, eggplant and bell peppers. The k-Ԑ Realizable Turbulence and Discrete Ordinates (DO) models was used for simulating the airflow and estimating radiative heat transfer, respectively. The results showed that an ACH of 10 is proper for tomato cultivation. When the ambient temperature is maximal, an ACH of 15 can be used for cucumber cultivation. However, ACH cannot be kept constant, and ACHs of ≤10 should be utilized when the ambient temperature decreases. For eggplants, it is better to use an ACH 20 at hot hours and an ACH of 10 when the temperature declines. For the bell pepper plant, 20 and 10 ACHs are suitable for day and night hours, respectively. Moreover, the maximum daily water consumed in the greenhouse happens in August and equals 222 lit/day for 20 Air Changes per Hour (ACH). The minimum daily water is consumed in July, equaling 106 lit/day for an ACH of 10. In the present study, the electricity rate consumed in the greenhouse equals 127W when ACH = 20, i.e., the consumed electric energy is 3 kWh for the entire system in a 24-h interval.

Infiltration of Outdoor PM2.5 Pollution into Homes with Evaporative Coolers in Utah County

Global use of energy-inefficient mechanical vapor-compression air conditioning (AC) is increasing dramatically for home cooling. Direct evaporative coolers (EC) offer substantial energy savings, and may provide a sustainable alternative to AC for homes in hot, dry climates. One drawback of ECs is the potential for infiltration of outdoor air pollution into homes. Prior studies on this topic are limited by small sample sizes and a lack of comparison homes. In this study, we used aerosol photometers to sample indoor and outdoor fine particulate matter (PM2.5) from 16 homes with AC and 14 homes with EC in Utah County, Utah (USA) between July 2022 and August 2023. We observed a significantly larger infiltration factor (Fin) of outdoor PM2.5 in EC vs. AC homes (0.39 vs. 0.12, p = 0.026) during summer. Fin significantly increased during a wildfire smoke event that occurred during the study. During the wildfire event, EC homes offered little to no protection from outdoor PM2.5 (Fin = 0.96, 95% confidence interval (CI) 0.85, 1.07), while AC homes offered significant protection (Fin = 0.23, 95% CI 0.15, 0.32). We recommend additional research focused on cooling pad design for the dual benefits of cooling efficiency and particle filtration.

Energy, exergy, environmental, and economic (4E’s) analysis of a solar driven humidification-dehumidification desalination system: An experimental investigation

A solar-driven humidification-dehumidification (SDH-DH) desalination system has shown to be a highly efficient and viable solution to meet the freshwater needs of a community. However, the solar air heater based on flat plate collector, imposes constraints on their efficiency. The current work focuses on the development of an SDH-DH desalination system. This system is comprised of a solar air heater that utilizes a double-ends open evacuated tube collector, a humidifier equipped with cellulose pad packing material, and a dehumidifier based on a direct evaporative cooler. The current SDH-DH desalination system is operated in two modes, namely open loop and closed loop, at four distinct process air flow rates. The system's performance indices are evaluated based on energy, exergy, environmental and economic analysis. The solar air heater is capable of generating hot air at an approximate average temperature of 100 °C, while maintaining an airflow rate of 150 kg/h. This enhances the efficiency of the humidifier, resulting in a freshwater production rate of about 2.43 L/m2/day at a cost of 0.027 $/L. Moreover, the use of an evaporative cooler-based dehumidifier effectively mitigates the issue of fouling that arises during the condensation process. The system achieved the maximum mean energy efficiency of 25.39 % and exergy efficiency of 4.59 % in a closed loop configuration, with an air flow rate of 150 kg/h. The total CO2 reduction amounts to 119.08 tons during the designated duration.

Experimental and analytical study of the energy and exergy performance for different evaporative pads in hot and dry climate

In this work, effects of using different evaporative cooling pads (ECPs) on the energetic and exergetic efficiency of a direct evaporative air cooler (DEAC) have been theoretically and experimentally investigated. Three types of ECPs were used, i.e., honeycomb cellulose cooler pad (HCCP), shading-cloth cooler pad (SCCP), and aspen wood wool cooler pad (AWWCP). For SCCP and AWWCP, a 3-cm pad thickness was used, while for the HCCP, three different values of pad thickness were used, i.e., 3, 5, and 7 cm. Tests were carried out using air velocities of 8, 14, and 19 m/s, measured at the DEAC outlet. Engineering equation solver (EES) used for performing the required calculations of the various parameters affecting the thermal performance of the DEAC, i.e., dry bulb temperature at exit (Tdbo), relative humidity at exit (RHo), mass of water evaporated, saturation efficiency, energetic efficiency (ηen), exergetic efficiency (ηex), and the overall exergetic efficiency (ηexoverall). Results showed the great effectiveness of HCCP compared to the other studied types. HCCP showed the highest energetic efficiency reached 103 % for 3 cm thickness of the ECP, and the highest exergetic efficiency of about 19 %. All with the highest temperature difference, achieving 10.3 °C.

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).

Thermo-economic assessment of air conditioner utilizing direct evaporative cooling: A comprehensive analysis

As concerns regarding energy consumption and environmental impact continue to grow, the need for efficient and sustainable cooling technologies becomes increasingly significant. Among various alternatives, direct evaporative cooling (DEC) has emerged as a promising solution due to its energy-efficient operation and low environmental footprint. This paper aims to provide a comprehensive thermo-economic assessment of a 5.25 kW capacity split air conditioner (SAC) integrated with direct evaporative cooling, focusing on evaluating its performance, energy consumption, coefficient of performance(COP), and economic viability. A numerical model is developed to determine the reduction in the condenser inlet air temperature due to direct evaporative cooling. The ambient temperature (30–45 ⁰C), relative humidity (20–80 %), and evaporator temperature (3–12 ⁰C) are taken as the design variables. Box–Behnken design (BBD) technique of response surface methodology is applied for multi-objective optimization. The COP, total cost rate (TCR), and total exergy destruction (E˙D,t) are set as the objective functions. Cooling capacity, life period, operation time, interest rate, maintenance factor, and electricity cost are taken as constants. The thermoeconomic optimization evolved maximized COP enhancement of 68.94 %, and reduction in TCR and ED,t by 26.12 % and 57.23 %, respectively. The water consumption to energy saving ratio varies from 5.5 to 9.8 L/kWh for different months of the cooling season. The thermoeconomic performance and sustainability of DECSAC is observed to significantly improve compared to conventional SAC specifically in hot-dry climates. The simple payback of the proposed system ranges between 1.21 to 2.99 years depending upon the operating conditions.