RANDOLPH, N.J. — What's a cooling tower? A cooling tower is a simple device used by many dry cleaners to cool their dry cleaning machines (DCM).
Cooling towers are a relatively inexpensive and dependable means of removing heat from DCMs. There are other ways to cool your equipment, but if you are paying for electricity and water, a cooling tower is often the most economical.
Cooling towers use the outside air to cool water which is circulated through the DCM’s refrigeration heat exchangers, Still condensers and/or solvent coolers.
In an evaporative cooling tower, some of the water being cooled evaporates into a moving air stream. When water evaporates, it removes lots of heat from the rest of the water. Each one pound of water that is evaporated removes approximately 1,000 BTUs from the system.
Water lost through evaporation is replaced by what is called “makeup” (city water). Removing heat by evaporation is highly efficient. That’s why you can cool a large amount of water with only a small amount of evaporation.
A “cooling tower system” might seem complicated, but it’s not.
An electric pump takes the water from the storage tank and pushes it through the coils in the DCM. The water picks up heat from the coils and then flows out of the DCM and up to the cooling tower.
It goes up to the top of the cooling tower and flows through the tower from top to bottom. The water is cooled. Cool water then drains out of the bottom of the tower through a large pipe down to a storage tank where the pump starts the cycle over again. (See the diagram.)
Depending on the size of the tower, this water flow can be 75-300 gallons per minute (GPM). Most of the water is reused at 93%. How great is that!
The key to tower performance is rapid water flow. A cooling tower doesn’t drop the water temperature as much as a refrigeration unit, so the higher flow makes up the difference.
HOW COOLING TOWERS WORK
For small applications such as dry cleaners, the most commonly used towers are mushroom-shaped assemblies housing evaporative cooling tower with distribution arms (also called “sprinkler arms”).
Warmed water is pumped to the tower inlet. The water flows through the inside of the standpipe and is distributed through the sprinkler arms, located above the fill. (See the diagram.)
The bottom of the sprinkler arms have a series of holes that are pointed on a slight angle. The water is forced out of the holes and the reactive force causes the arms to rotate. In this way, the water is distributed evenly into a thick maze of corrugated plastic called “the fill.”
Many towers put sails or blades on top of the sprinkler arms to help rotate the arms using the air flow from the fan. At the same time, a large fan, located at the top of the tower, pulls large volumes of air (10k-20k cubic feet per minute) into the tower and out the top.
The air enters the tower through a screened cylinder which wraps around the circumference of the tower just up from the bottom (inlet louver). The Dry air in (as shown) goes through the fill from the bottom to the top. The heat is transferred to the air.
HOW IS THE COOLING TOWER MAINTAINED?
Cooling towers should be installed and maintained in accordance with the operator’s manual provided by the manufacturer.
Because the tower is outside and air is being pulled into the tower and out the top, air contaminants (dust, dirt, leaves and insects) can accumulate on the inlet louvers and/or inside the tower. In addition, because the tower is exposed to heat and sunlight, bacteria can grow on inside surfaces of the tower.
It is recommended that, at least twice a year, the tower and storage tank be cleaned and disinfected. The cleaning should include removal of the fan and power washing all internal surfaces of the tower and storage tank, with all the cleaning water and debris drained to the sewer.
In addition, the sprinkler arms should be inspected and cleaned inside and out and repaired if required. All interior surfaces should be thoroughly inspected.
It is recommended that spare parts be on hand before cleaning. The spare parts should include replacement inlet louvers, replacement spindle, washer and support wires for the sprinkler arm, and a bottom drain filter, as a minimum.
Check back Thursday for the conclusion.
Have a question or comment? E-mail our editor Dave Davis at [email protected].