A cooling tower primarily uses latent heat of vaporization (evaporation) to cool process water. Minor extra cooling is supplied by the air because of its temperature improve.
Cooling tower selection and efficiency is predicated on water circulation price, water inlet temperature, water outlet temperature and ambient wet bulb temperature.
Ambient wet bulb temperature and its affect on efficiency is the topic of this text.
Ambient wet bulb temperature is a situation measured by a device referred to as a psychrometer. A psychrometer places a thin film of water on the bulb of a thermometer that is twirled in the air. After a few minute, the thermometer will show a decreased temperature. The low point when no extra twirling reduces the temperature known as the wet bulb temperature.
The measured wet bulb temperature is a operate of relative humidity and ambient air temperature. Wet bulb temperature primarily measures how a lot water vapor the atmosphere can hold at current weather conditions. A lower wet bulb temperature means the air is drier and may hold more water vapor than it will probably at a higher wet bulb temperature.
When deciding on a cooling tower cell, the highest or the design wet bulb temperature your geographical area will encounter must be used. Highest wet bulb temperatures occur in the course of the summer, when air temperatures and humidity are highest.
Again by instance, in Indianapolis, Indiana the design wet bulb temperature is 78°F. Historically Indianapolis can anticipate less than 1 hour per year that the conditions exceed a 78°F wet bulb. Typically 6,000 hours a year will have a wet bulb of 60°F or decrease that means that a cooling tower cell designed for a 78°F wet bulb will be capable of make 65° – 67°F water for six,000 hours per yr … practically 70% of the yr.
Most cooling towers are capability rated at a “commonplace” wet bulb temperature of 78°F. Which means on the times when the wet bulb temperature is 78°F, the tower will produce its stated capability. In different words, a tower rated to produce 135 tons of cooling will produce 135 tons of cooling at a 78°F wet bulb temperature. At a higher wet bulb temperature, the tower cell capability decreases.
Each location has a singular design (worst case) wet bulb temperature that’s revealed by organizations comparable to ASHRAE and might be obtained easily. You possibly can view Wet Bulb Temperatures for an inventory of sample cities (opens new window : PDF file : 20K).
So, what does it mean when your cooling tower water temperature is higher than the conventional 5° – 7°F above the present wet bulb temperature?
Cooling tower performance is expounded to ambient wet bulb circumstances. Higher wet bulb temperatures happen in the summer when increased ambient and relative humidity happens. Preliminary system design and correct system maintenance is essential to make sure your cooling tower cell is providing correct cooling.