The misting cooling system uses the principle of water mist evaporation to absorb heat to achieve a cooling effect. The higher the temperature and the lower the relative humidity, the greater the cooling potential of the misting cooling system technology. It is worth noting that misting cooling systems have been widely used.In the hot summer, the existing outdoor thermal environment is not enough to meet human needs for outdoor thermal comfort. To overcome the discomfort caused to the human body by the outdoor thermal environment, misting cooling systems have become the focus of people’s attention.
A series of effective improvement measures have been proposed to alleviate the adverse effects of urban heat islands and local overheating in cities, including retroreflective materials, green vegetation, cool roofs, etc. Although these technical measures have shown a specific cooling effect, passive cooling The rapid cooling effect for a specific area is slight, the significance is low, and the transient benefit is not apparent enough.
However, a misting cooling system has been proposed as a promising active cooling technology unlike passive measures. To verify the outdoor cooling effect of the outdoor misting system in summer and ensure that the outdoor misting system can effectively improve the outdoor thermal environment and enhance human thermal comfort.
A dry and hot environment will have a better cooling effect than a hot and humid environment. Due to the increase in indoor relative humidity, rising cooling systems are generally not used in traditional residences. However, some notable buildings, including livestock and poultry houses, greenhouses, outdoor structures, etc., still use misting cooling methods. In these unique buildings, suitable air temperature and humidity are two crucial environmental parameters for the healthy growth of livestock, poultry, and plants.
The harsh high-temperature environment causes a sharp decline in the survival rate of animals and poultry, and the livestock and poultry houses have poor thermal insulation performance and low air tightness. The application of traditional air conditioning requires high energy consumption. Therefore, a misting cooling system has become an effective means to improve the thermal environment of livestock and poultry houses.
How does Misting Cooling System Improve the Thermal Environment?
Misters are tested for cooling to improve the comfort of urban public spaces. Experiments have proven that misters can reduce the temperature by 8.2°C and increase the average humidity by 7%, maximizing the subject’s satisfaction in the misters’ environment.In addition, it uses solar energy plus fuzzy logic to control misters to improve misters’ efficiency and reduce power intelligently. The experimental results show that the outdoor misting system can reduce the air temperature by 6.14℃-7.5℃ and control the average relative humidity at 51.2%. -67.5%, providing an effective strategy for intelligent control in high-humidity areas
Then, 24 nozzles were installed above the school rooftop, and the equipment was operated for a week. The results showed that the misters could reduce the temperature at 2.2m and 1.1m above the ground by 7.4°C, and the relative humidity increase was controlled below 13%. Through experiments, the cooling characteristics of water mist in a long and narrow space were studied, and it was concluded that as the water flow increases, the local temperature drops by 10-14°C.
We established an outdoor misting system in the atrium. Experiments show that the outdoor misting system can reduce the temperature of the lower surface of the lighting roof glass by 5-5.6℃, reduce the temperature difference between the upper space and the bottom space by 3.2-4.1℃, and increase the relative humidity by 9-16%.
In the misters environment, the temperature dropped by 2.9±1.2°C. In the misters’ mode with a fan, the temperature further dropped by 3.6±1.4°C, the relative humidity increased by 15.9±4.7%, the overall average human temperature dropped by 0.53°C, and the skin temperature dropped by 1.10°C. The head drop is the most significant and has sound effects regarding thermal sensation and comfort. When mister equipment is operated in residential areas, experiments show that when the wind speed is less than 3.3 m/s, a cooling effect of an average temperature drop of 3°C can be achieved within a mister’s radius of 3m.
Misting systems were installed on the air conditioner’s roof, balcony, and outdoor unit. The results showed that the misting system reduced the temperature by 60% and the energy consumption by 80%. A misting cooling system was installed on the air conditioner’s outdoor unit. The results showed that the outdoor misting system reduced the temperature by 2-5°C, significantly reducing the air conditioner’s energy consumption. Provides a reference for the temperature range of outdoor misting systems.
Secondly, experimental methods were used to establish the correlation between environmental parameters and cooling effects on the inner and outer surfaces of the roof. The results showed that the external surface temperature dropped by 4.8-19.5°C, and the internal surface temperature dropped by 0.2-4.9°C. Although the misting system has a significant cooling effect on the roof, the shading product is not apparent. The potential reasons are related factors such as the small thickness of the mist layer and wind interference.
At the same time, the misting system can improve thermal comfort and produce a better overall thermal sensation. The cooling range of outdoor air (including skin) is mainly controlled within the scope of 1.0-9.0℃. In addition, the general growth range of relative humidity is between 5.3% and 29.3%, primarily related to the local climate. The misting cooling system significantly improves the outdoor thermal environment.
Effect of Equipment Performance on Cooling Misters Effect
Outdoor misters led to some important conclusions regarding outdoor and indoor thermal environments. At the same time, research was conducted on improving the operating performance of cooling misters from both internal and external aspects. Internal factors mainly include misters equipment such as nozzle type, nozzle water pressure, nozzle diameter, droplet size, nozzle height, angle, etc. External factors include environmental factors such as air temperature, relative humidity, wind speed, and solar radiation.
Also Reference: What range can the 65Ft (20M) Patio Misting System cool?
Cooling misters have been widely studied to improve outdoor thermal environments and air quality, and some critical conclusions have been reached. Some people have also studied the influencing factors that restrict the cooling performance of outdoor misters, which mainly include the equipment’s internal characteristics and the environment’s external factors. Elements. The research on the internal factors that affect the equipment itself primarily focuses on the control factors of the nozzle itself, including nozzle type, water pressure, nozzle diameter, droplet size, nozzle height, angle, etc. In contrast, the research on the external factors that affect the equipment mainly focuses on air temperature and relative humidity. , wind speed, solar radiation, and other environmental factors
Nozzle Diameter and Nozzle Type
The nozzle design not only determines the average size of the sprayed droplets but also affects the cooling efficiency of misters. On the one hand, small-diameter nozzles matched with high-pressure pumps are usually preferred, while smaller-diameter droplets can be produced with pneumatic nozzles driven by high-pressure air. In addition to pneumatic nozzle systems, there are also hydraulic nozzle systems. The difference between the two is that the latter uses less energy, but the trade-off is that larger droplets evaporate more slowly and are more likely to create a wet feeling.Also Reference:Instructions for Use of Misting Nozzles
On the other hand, when the angle and flow rate of the hollow cone nozzle and the full cone nozzle are the same, the latter has a more considerable throwing distance, can improve the cooling efficiency, and has a good and uniform misters effect. The main factor affecting heat transfer is the misters’ mass flow rate. As the water pressure increases, the mass flow rate increases, the heat transfer performance increases, and the spray effect will also change. For research on cooling misters water pressure,
Nozzle Water Pressure
The direct evaporative cooling technology that combines the high-pressure misting system with the low-pressure misting system makes up for the shortcomings of the high-pressure misting system and the short contact time with the air, increases the time and area of heat exchange between droplets and philosophy, and thereby improves the cooling efficiency. We did a numerical simulation experiment on the effect of pressure on the impact of a misting cooling system. The experimental results show that as the pressure increases, the liquid film thickness shows an overall thinning trend, the atomization effect is enhanced, and the heat transfer capacity of misters is improved.
Comparing the high-pressure system with the low-pressure system in a naturally ventilated greenhouse, the results show that the high-pressure system’s cooling efficiency and average evaporation efficiency are higher than those of the low-pressure system. Therefore, when the water flow rate is fixed, the higher pressure is more efficient. Smaller nozzles produce more cooling.
In addition to the water pressure of the nozzle, the height at which the nozzle is set and the direction of the nozzle also affect the spray effect. Under the same operating conditions, the gravity angle affects heat transfer performance. When the gravity angle is 30° or 120°, the heat transfer effect is the best, and when the gravity angle is 180°, the heat transfer effect is the worst.
Through experiments, it was concluded that when the movement trajectory of the sprayed droplets is a parabola, the heat exchange of the droplets in the air is more complete; that is, the cooling effect is better when the nozzle is tilted than when the nozzle is vertically downward.
Regarding the setting of the nozzle height, in the previous experiment, it was proved that as the droplet landing distance increases, the cooling effect gradually decreases, and the experimental results show that the spray system can reduce the temperature within 1 meter from the nozzle by 6-12°C. The temperature drops by 1.5-4℃ within 3 meters from the nozzle and by 0.5-1.5℃ within 7 meters from the nozzle.
If the cooling effect at the height of 2.8m is used as a benchmark when the nozzle height is 3.3m, the cooling effect decreases by 0.1-0.5℃, and when the nozzle height is 2.3m, the cooling effect increases by 0.1-0.7℃. A misting cooling system was established, verifying that the optimal mister’s height location is the place with the most significant heat transfer coefficient. This test proved that as the height of the nozzle increases, both the evaporation amount and the evaporation rate increase significantly.
Droplet Diameter Size
Different droplet diameters will also lead to different misters. Tests confirmed that smaller droplet sizes and lower airflow rates lead to better cooling and that local ambient humidity has a greater cooling effect than temperature. If the pressure swirl nozzle is studied, it is believed that the droplet impact Weber number decreases monotonically, and it is obtained that as the distance increases, the average size of the droplets first decreases and then increases. The misters cone generated by the pressure swirl nozzle is: The conclusion that hollow becomes full cone.
The test results show that the larger the diameter of the droplet, the longer the life of the droplet and the greater the falling distance. Taking 6m as the limit distance, it is verified that a droplet with a diameter of 150μm will fall under the selected specific circumstances (still atmosphere). ideal case of free fall) can evaporate completely. If we conduct a systematic parameter analysis of the evaporative cooling of the outdoor misting system, the results show that the outdoor misting system has better cooling performance for a wider droplet distribution. It can be seen that the smaller droplet size can better absorb the surrounding heat and accelerate the evaporation process, thus improving the misting cooling efficiency.
Finally, it is worth noting that an experimental study on the initial water temperature, if we think that the difference in water temperature will cause changes in flow rate, the test results show that although increasing the initial water temperature will increase the evaporation rate of misters, it will also reduce the evaporation rate of the nozzles. Its own lifespan, and the cooling effect is not ideal.
The main influence of the nozzle equipment parameters on the spray effect is summarized. In summary, the design of the nozzle equipment has a certain impact on the misters effect. The appropriate nozzle height, larger water pressure, smaller nozzle diameter, and the sprayed water The denser the fog, the better the cooling effect.
However, this is only a judgment under ideal conditions and does not apply to all experimental environments, mainly because the system is also affected by the environment , so it is impossible to draw up the optimal cooling configuration in a specific mode. It needs to be analyzed and treated specifically according to the local experimental environment, and the optimal solution for outdoor misting system design suitable for local climate conditions should be matched as much as possible.
How to Improve The Efficiency of Cooling Misters
In high-humidity areas, water evaporates slowly in outdoor misters, making it difficult to achieve an effective cooling effect. Therefore, adding some easily evaporated liquids to the water can improve the phase change heat absorption capacity, accelerate the heat absorption process from liquid to gaseous state, and thereby improve the performance of cooling misters. Effect,
The factors of the outdoor environment are more complex. The mist droplets often cannot accurately land on the surface of the human body to achieve cooling, or a large number of mist droplets are concentrated in one place, causing an uncomfortable feeling of humidity. To address this problem, we added fans and cooperated with outdoor misters to form a Misting fans can accurately land misters at fixed points, allowing misters to absorb heat and cool down while sending mist droplets to their destination. In a country like Singapore with high temperatures and high relative humidity all year round,
The misting fans system can be turned on only when the test performance temperature set value reaches 29.2°C. This ambient temperature set value is affected by the environment and climate zone, and requires specific analysis based on the climate zone and meteorological environment of the region.If air misters are used to analyze the amount of misters and the cooling effect, the wind is used to drive the droplets to move to farther areas to achieve the effect of accelerating droplet evaporation and cooling. At the same time, increasing the water flow under misting fans will enhance the cooling effect, and with time As the wind speed increases, the range covered by misters increases, further expanding the cooling area.
The continuous operation of cooling misters will not only damage the life of the machine and increase power consumption, but also affect the thermal comfort of the human body due to the continuous accumulation of relative humidity. Therefore, cooling misters require a suitable control system. Feasibility and economic benefits of using fixed misting cooling system and mobile misting cooling system.
The results show that the fixed misting cooling system has good economic benefits in terms of construction cost, operation cost, maintenance cost, etc. It is the future development trend to use renewable energy to continuously supply the power required for the equipment of the misting cooling system.