The influence of outdoor high temperature environment on human body has attracted people’s attention. Traditional environmental cooling methods are limited to indoors, and the cooling range is limited. In view of the urban high temperature and heat island effect, an efficient and energy-saving outdoor cooling system is urgently needed to improve the urban thermal climate and outdoor environmental quality. The spray cooling technology is a pure physical method with water as the raw material, and absorbs the environmental heat by the principle of evaporation and heat absorption. No harmful substances are produced during the cooling process, and there is no secondary pollution to the environment. The cooling effect is rapid and the human comfort is good. Spray cooling can locally control the temperature of the large environment. The spray cooling system absorbs a large amount of heat from the surrounding environment during the process of vaporization through the water particles emitted into the air, and the principle of evaporative cooling to reduce the temperature of the surrounding environment to achieve the purpose of cooling.
The principle of spray cooling
The spray cooling system uses a high-pressure pump to pressurize the water to 4-7MPa, and then transmits it to a special high-pressure atomizing nozzle through a high-pressure pipeline system to form fine water mist particles that are sprayed into the air, and the mist droplets suspend and diffuse in the air and evaporate continuously. , consumes a lot of heat energy in the air, thereby reducing the temperature of the spray area and achieving the purpose of cooling; at the same time, the fog layer can also absorb, reflect and scatter the sunlight, reducing the intensity of solar radiation in the air and ground below the fog layer , reduce the accumulation of heat on the ground and reduce the ground temperature.
Spray cooling Theoretically, 1m3 of air only needs to absorb the latent heat of evaporation of 2.93g of water to cool 40% of the air isobarically5. It is used for spray cooling in human activity environment, and the fog droplets cannot settle to the ground in large quantities, so as to avoid the inconvenience caused by obvious wetting of pedestrians’ clothing and wetting the ground. Therefore, the spray cooling system is more efficient than the spray or sprinkler irrigation system in traditional agriculture and animal husbandry. Atomization requirements are more stringent.
Spray cooling is suitable for outdoor and semi-outdoor places with good ventilation. It can be used for cooling in public squares, streets, sports venues, playgrounds, factories, outdoor air conditioners, agriculture and animal husbandry and other fields. The cooling effect is obvious and the development prospect is broad. . With the maturity of spray cooling technology, spray cooling is expected to improve the hot outdoor environment in summer to a certain extent, making it possible to adjust the local microclimate in the city.
The role of spray cooling
High-pressure spray systems are mainly used in landscape green spaces, stadiums, theme parks, stage film and television and other fields to create landscape effects. With the development of science and technology, high-pressure spray systems have been increasingly used in the field of outdoor cooling.
The high-pressure spray direct evaporative cooling technology is applied in the field of cooling. It was first used in agricultural production and matured in the World Expo in the United States, Spain, and Japan. Now it has become a more popular outdoor cooling method in the world. The domestic application in the cooling field has been tried since the 1990s, and good application experience has been accumulated. For example, dozens of venues including the China National Pavilion, Saudi Arabia and Brazil Pavilion in the 2010 Shanghai World Expo, the 2011 Xi’an International Horticultural Exposition, Shanghai Oriental Pearl Tower and other tourist queuing areas have installed high-pressure spray cooling systems. These applications have achieved remarkable results.
Spray cooling is to refine water into water mist under a certain pressure and spray it into the air. The water mist inevitably exchanges heat and quality with the air through evaporation. The evaporation process absorbs a large amount of heat from the surrounding air, thereby completing the air cooling process. Cool down. This method utilizes the characteristics of the latent heat of evaporation of water. The key technology of spray cooling is to create ultra-fine water mist particles. The main purpose of this is to increase the surface area of the liquid. The larger the surface area of the droplet, the faster the heat exchange rate with the surrounding air, which ultimately accelerates the evaporation rate of the droplet, so that the hair and floor of the people in the spray area are not wetted. According to the principle analysis of spray cooling technology, the higher the temperature and the lower the relative humidity, the greater the cooling potential of spray cooling technology.
Compared with air conditioners, the biggest advantage of spray cooling is that it reduces carbon dioxide emissions, and the power consumption of spray cooling systems is much lower than that of central air conditioning systems, even lower than the power consumption of ordinary fans. Some literatures have calculated that the carbon emission of the spray cooling system is 0.27g/(m2·), the carbon emission of the air-conditioning system is 7.656g/(m2·), and the carbon emission of the spray cooling system is 3.5 g/(m2·) of the air-conditioning system. %.
In outdoor environments or large space localized environments, ordinary air conditioning systems cannot be used. In these environments, the use of spray cooling systems has obvious cooling effect and energy saving effect. The spray cooling technology and equipment have been successfully applied to the 2008 Beijing Olympic beach volleyball venues, and the cooling effect is obvious (average cooling 3~5). The power distribution load of more than 10,000 square meters of venues is less than 20kW, and the energy saving effect is remarkable.
The function of spray cooling
1. landscaping and moisturizing
Fog can be light and graceful, ethereal and ethereal, and indifferent and vast. It can be a landscape alone, a world of its own, or it can be combined with various elements such as water systems, rockeries, green plants, and lights. Complement each other. Its ever-changing forms and functions will add ink and wash elements to the landscape artistic conception of Chinese gardens. Its unique moisturizing function can better combine the maintenance and growth of plants;
2. Improve the air quality of small environment
After the raw water is professionally treated, and the fog effect generated by the high-pressure microporous impact technology can generate a large number of negative ions known as “air vitamins”, creating an exclusive “forest oxygen bar” in the city, improving air quality, good for physical and mental health;
3. Cool down
The aerosol-like mist molecules can effectively absorb air heat and reduce the local ambient temperature. Its low operating cost and effective cooling effect have been widely used and recognized in the World Expo and many scenic spots, and it has become a public space, community, etc. A new element for outdoor cooling.