Misting System and Fogging System

The terms of misting system and fog system are generally used interchangeably. In some instances, the term fog system may be used to describe a system that is designed for special effects. However, simply say, a misting system and a fog system are simply two different terms used to describe the same thing.

The cooling systems components supplied from RELAB are based on pressure range less than 1000 psi/70 bar, so we often call them for same system. But the two systems also have a bit difference. 

1.Cooling Systems:

Techniques of cooling can be organized into several categories, including pad and fan, misting, and fog. Each utilizes the evaporative cooling process to reduce air temperature, as well as, fan ventilation for exchanging the moist air with dry outside air. The effectiveness of each system is highly dependent on the ambient air-water vapor properties. Low air humidity will increase the cooling capacity of the evaporative system, while higher humidity will decrease cooling.

In addition, cooling effectiveness is dependent on the nozzle design and system operating pressure, which directly influences evaporation of the droplet due to the droplet size delivered from the nozzle. Water quality is important for the long-term effectiveness and required maintenance of evaporative cooling systems.

2. Misting System:

The mist systems are mostly used for contact cooling, usually for the purpose of humidification for propagation. The nozzles are distributed within a pipe network uniformly throughout the area to be cooled or humidified. The pipe network is the distribution system from the pump or water source to the nozzles. It may be located at bench top level for direct application to the plant, or it may be located overhead at the gutter level to provide increased humidity throughout the greenhouse. A filter is necessary to reduce the amount of particles that may block the nozzles.

The required components for a misting system include tubing, specialty misting system nozzles, and a water supply. Additional components may be required for a specialty use of the misting system or to improve its performance.

The most effective method of improving the performance of a misting system that only utilizes line pressure is to add a high pressure pump. By increasing the pressure of the misting system to 600~1000 psi, the misting systems performance can be improved by up to 300%. 

The nozzle spacing is approximately 3.3 m2 (36 ft2) per nozzle. Timing of the misting periods, frequency and duration must be controlled to prevent excessive wetting and subsequent over-watering of the crops below. An example is 15 seconds every 2 - 3 minutes.
 

3.Fogging System:

The fogging system for evaporative cooling is similar in many respects to a traditional misting system. But sometimes people prefer to say: it operates at a much higher pressure (1000 - 2000psi) and with very low volume nozzles (4.5L/hr).
The low volume, high pressure fog consists of tiny water droplets which can evaporate more readily than the larger droplets from mist systems.

The increased surface area to volume ratio improves the rate of vaporization. If designed and installed properly, no water droplets will contact the crop or floor of the greenhouse below. System operating effectiveness is greatly improved over misting systems.

High quality water and filtration systems are extremely important to reduce the problem of clogging nozzles.
The uniformity of air temperatures within the greenhouse with the fog system with distributed nozzles is significantly improved compared to the pad and fan system.