level control is a relatively more important issue for package type cooling towers. Field erected type Facilities such as power plants, steel processing plants, petroleum refineries, or petrochemical plants usually install field erected type cooling towers due to their greater capacity for heat rejection. Field erected towers are usually much larger in size compared to the package type cooling towers. A typical field erected cooling tower has a pultruded fiber-reinforced plastic (FRP) structure, FRP cladding, a mechanical unit for air draft, and a drift eliminator. Heat transfer methods With respect to the heat transfer mechanism employed, the main types are: wet cooling towers or evaporative cooling towers operate on the principle of evaporative cooling. The working coolant (usually water) is the evaporated fluid, and is exposed to the elements. closed circuit cooling towers (also called fluid coolers) pass the working coolant through a large heat exchanger, usually a radiator, upon which clean water is sprayed and a fan-induced draft applied. The resulting heat transfer performance is close to that of a wet cooling tower, with the advantage of protecting the working fluid from environmental exposure and contamination. adiabatic cooling towers spray water into the incoming air or onto a cardboard pad to cool the air before it passes over an air-cooled heat exchanger. Adiabatic cooling towers use less water than other cooling towers but do not cool the fluid as close to the wet bulb temperature. Most adiabatic cooling towers are also hybrid cooling towers. dry cooling towers (or dry coolers) are closed circuit cooling towers which operate by heat transfer through a heat exchanger that separates the working coolant from ambient air, such as in a radiator, utilizing convective heat transfer. They do not use evaporation. hybrid cooling towers are closed circuit cooling towers that can switch between wet or adiabatic and dry operation. This helps balance water and energy savings across a variety of weather conditions. Some hybrid cooling towers can switch between dry, wet, and adiabatic modes. In a wet cooling tower (or open circuit cooling tower), the warm water can be cooled to a temperature lower than the ambient air dry-bulb temperature, if the air is relatively dry (see dew point and psychrometrics). As ambient air is drawn past a flow of water, a small portion of the water evaporates, and the energy required to evaporate that portion of the water is taken from the remaining