The first cooling tower was designed during the Industrial Revolution and is used to extract heat from industrial, power and HVAC processes. If you asked the question “how to design a cooling tower” in the late 1800’s, the answer would be quite a bit different than the answer in 2012.
Today we have evolved substantially with improved knowledge around energy efficiency, water conservation, reduced emissions and overall environmental impact, worker safety, improved reliability, and aesthetics. Nevertheless, today’s conventional cooling tower basic design has many similarities to the design of a cooling tower over 100 years ago. This can easily be seen on the brochures of many leading manufacturers showcasing:
- Large top mounted fans operating in the hot, corrosive exhaust air stream exposed to the elements that can lead to devastating results to the process when they fail
- Ladders and handrails to routinely access mechanical equipment 15’-30‘ or higher above ground level
- Drift rates of .002% and greater with open air inlet louvers allowing significant chemically treated water to escape and land on adjacent ground, cars, equipment, buildings and humans
- Large unsightly stagnant water basins exposing basin water to the sun and natural elements allowing harmful breeding such as Legionnaires’ Disease
- Corrosive materials of construction such as galvanized metal that can leach harmful elements into the circulating water and deteriorate quickly
- Distribution systems with a single operating point that require entire cells to be turned off during off-peak operating conditions, which is the majority of the time, for optimal performance
- Distribution systems that can clog easily requiring maintenance personnel to routinely enter the tower box for maintenance
How To Design A Cooling Tower
Many manufacturers have put an adhesive bandage on the conventional cooling tower design problem by offering an option to address the design flaw that most concerns each specific prospective customer. For example, a forced-draft design is offered when there are concerns of drift and top-mounted fans. A stainless steel or FRP design is offered when corrosion or long life expectancy is a concern. Basin sweepers are offered when concerns of stagnant basins arise.
Many of these options help reduce the concern. Unfortunately, they often do not always address the entire problem that is your primary concern (ex. SS basins when most of the structure is still galvanized) or create other unfavorable impacts (ex. having to maintain belts with many forced draft designs). Take care when designing your next cooling tower project to ensure your concerns are adequately addressed. If your only concern is initial cost, you will likely end up with a cooling tower that comes with many of the same design limitations of technology that was in play 100 years ago. If you seek out the latest technology available that addresses each of the design flaws listed above, you will likely find a relatively quick return on your additional investment and sleep much better if cooling tower operation is your concern. Think about “how to design a cooling tower” not only for 2012, but for the anticipated useful life of your next cooling tower. After all, you will live with the cooling tower and its corresponding energy efficiency, water consumption, environmental impact, safety, reliability and aesthetics for the life of the cooling tower.
Forced draft cooling tower installations are becoming increasingly more popular. Cooling tower technology allows for a fan to be mounted on the top or bottom of a cooling tower. Cooling towers with top mounted fans are called “induced draft” cooling towers and cooling towers with bottom mounted fans are called “forced draft” cooling towers.
Forced Draft Cooling Tower
Induced draft cooling towers frequently employ a fan, coupling, gear box, drive shaft and motor at the top of the cooling tower. This equipment is used to induce air from the bottom air inlet louvers up through the fill media. This location accelerates wear and tear of the equipment because it is exposed to the elements (sun, rain, snow, etc.), and is positioned in the hot, corrosive exhaust airstream. This makes the mechanical equipment difficult, expensive, time-intensive and dangerous to maintain.
Forced draft cooling towers have the mechanical equipment at the bottom of the tower. This location allows the equipment to operate in the cool, dry intake airstream protected from the elements. This location makes the equipment accessible from ground level so it is easy, inexpensive, less time consuming and much safer to repair while enjoying substantially increased life expectancy of the mechanical equipment.
Cooling tower Legionella is an ever increasing concern, especially in many HVAC scenarios such as hospital cooling towers, university cooling towers, and other like applications where the cooling tower exists among a large population. There are six events that must ensue in order for a Legionellosis case to occur: (1) An environmental reservoir must exist; (2) multiplication to high cell counts must occur; (3) there must be a mechanism to disseminate bacteria; (4) the disseminated strain must be virulent; (5) infection must occur at susceptible site on a host; and (6) the host must be susceptible.
Being reservoirs of water and dust, all cooling towers can potentially harbor Legionella sp. bacteria thereby satisfying event (1). Events (4) through (6) are beyond the control of cooling tower manufacturers and operators. Thus we have events (2) and (3) in which to exert a protective influence. The environmentally friendly and operator friendly design of the Tower Tech Modular Cooling Tower™, especially when combined with a judiciously administered and monitored biocidal treatment regimen, effectively addresses events (2) and (3).
Learn more about how to avoid cooling tower Legionella by visiting our white paper: http://www.towertechinc.com/documents/Legionella_Control_White_Paper_05072004.pdf
FRP cooling tower structures have become increasingly more popular over the past 20 years. Historically, galvanized metal for small to mid-sized applications and wood for mid to large-sized applications had the dominant role in cooling tower structures. Due to environmental, aesthetic, dependability and life expectancy concerns, many users have turned to alternate materials of cooling tower construction such as FRP.
FRP Cooling Tower
Galvanized metal and wood structures have posed serious environmental concerns due to the harmful chemicals that can leech out into the cooling tower blow down. The corrosive nature of the materials can become unsightly, require maintenance and repair, and result in reduced life expectancy of the cooling tower.
FRP cooling tower structures are not corrosive and therefore improve environmental friendliness and aesthetics while significantly improving life expectancy with little to no maintenance required. FRP cooling towers include hand laid up, injection molded and pultruded methods of construction. Hand laid up is less popular due to the difficulty of getting consistent fiber distribution, which can result in fiber bloom and degradation concerns. Injection molded FRP is popular for keeping a low price with smaller HVAC applications. Pultruded FRP is the material of choice for mid and large size applications due to the structural integrity of the structure.
Most pultruded FPR cooling towers will have an initial investment 30% greater than that of galvanized metal or wood. However, the benefits to the environment, lack of required maintenance, improved aesthetics and dependability, and significantly improved life expectancy offer a solid ROI.