If you have ever looked toward an industrial area and seen a stack emitting steam, you know what a cooling tower looks like. While the public typically thinks that such towers emit pollution, they actually serve a much more benign process: They provide energy-efficient ways of dispersing waste heat from industrial processes.
There are many types of cooling towers, and understanding what they are and how they work is a major endeavor. This Cooling Tower Buying Guide will discuss the popular types of cooling towers, their parts and functions, and what to look for when buying them.
Popular Types of Cooling Towers
Understanding the basics about how cooling towers work isn’t difficult. In industrial operations, these simple seeming stacks pass waste heat generated by industrial processes through some sort of coolant medium (typically water). But while industrial cooling towers may perform much the same task, they actually have a wide array of configurations. There are any number of potential combinations that you may encounter in an industrial water-cooling tower. Below we have listed various ways in which one can categorize a cooling tower, but you should understand that you may encounter cooling towers that combine several of these factors. The most popular types of cooling towers are classified:
- By Tonnage. Specifically, BTU/Hr they can disperse through heat vaporization. The larger the tonnage, the larger the cooling tower will be and the more space it can cool.
- By use. Up to this point, we have discussed cooling towers as though they solely functioned as industrial cooling towers. It’s true that these are the most noticeable water-cooling towers you will encounter, their distinctive silhouettes visible against the horizon. And while industrial cooling towers are incredibly common in the fields of power generation, petrochemical refinement, food production, and many kinds of manufacturing, they aren’t the most common. HVAC cooling towers (heating, ventilation, and air conditioning) remove the heat generated by chillers, and they appear on office buildings and multi-family residences in addition to in industrial contexts.
- By build. Cooling towers come in two basic builds that are decided primarily by their size. Package type cooling towers are smaller devices housed in prefab structures delivered directly to a purchaser. Field erection type are major industrial towers that require the erection of a freestanding, on-site structure.
- Heat transfer methods. In order to cool waste heat to a temperature close to the ambient air, cooling towers must find a way to decrease their temperature. Dry cooling towers work much like a heat-transfer pumps, shunting liquid through a closed-loop system in order to disperse heat. Because these systems don’t use evaporation, they require little liquid to operate. Closed-circuit fluid-cooling towers employ a similar closed-loop system, but they also have a heat exchanger coil that gets sprayed with a separate supply of water. Hybrid cooling towers are closed-circuit systems that can operate either “wet” or “dry.” Open-circuit wet cooling towers allow the cooling liquid, which is usually water, to naturally evaporate as it heats. These are the most popular type of water-cooling tower.
- By air-flow generation methods. Almost all types of cooling towers allow for the movement of air, and some of them do so through natural draft, allowing damp, moist air to rise and cool, dry air to fall into the stack. Fan-assisted natural draft adds a fan to aid the natural draft process. Mechanical draft towers use powerful centrifugal fans or propellers to either pull air up through the tower with a fan at its top (induced draft) or to blow air down into the tower (forced draft).
- By air-to-water flow. Part of the cooling process includes the way in which water and air flow through a tower’s system. Counter-flow towers have air move in the opposite direction from the water, often drawing air from the tower’s bottom while applying water down onto it. In cross-flow towers, water moves vertically while air gets drawn in from the sides, moving perpendicular to the water.
In the following sections, we will contrast these different tower types in more detail.
Heating, ventilation, and air conditioning (HVAC) vs Industrial cooling towers
In addition to their difference in stated purpose, HVAC and industrial cooling towers vary in a number of other ways. Because industrial towers can employ multiple cooling methods, their efficiency can diverge significantly. However, HVAC systems use liquid-cooled chilling, which is typically the most efficient cooling possible. HVAC systems also have a much smaller footprint than the vast majority of industrial towers.
Package vs Field Erection
The type of business you’re operating will entirely determine whether you end up buying cooling towers that are package type or field erections. Because package-type are prefab units directly delivered with heat-resistant materials already installed, they’re intended for use with smaller facilities that don’t require heavy-duty heat dissipation. For major industrial uses in applications such as refining or power generation, field erections are far more common.
Natural draft vs Mechanical draft vs Fan-assisted natural draft
Natural draft evaporative cooling towers see extensive use due to their relatively simple design and ease of operation. They’re commonly used in conjunction with nuclear power generation. Fan-assisted natural draft adds more cooling capability at the cost of slightly more operational cost and required maintenance. Both forced draft and induced draft mechanical systems provide high performance, high compatibility with various facility construction materials, and lots of operational flexibility. However, they are significantly more expensive than natural draft air flow options.
Wet cooling towers or open circuit vs Dry cooling towers vs Fluid cooling towers vs Hybrid cooling towers
Wet cooling towers are among the most popular industrial cooling towers because of their relative simplicity and ease of operation. But when you consider the way in which wet cooling towers work, you start to understand some of their drawbacks. Wet cooling towers and their operation rely on evaporation, and as water vapor disperses into the air, the temperature of the remaining water falls. However, this causes the air’s humidity to increase, which decreases the efficiency of heat dispersal. Wet towers also require large amounts of water and frequent maintenance since rust tends to form.
Dry cooling towers (and related configurations such as hybrid and fluid-cooled towers) don’t have these problems. However, one of their significant downsides is that they’re difficult to scale up for larger sites and can only function efficiently in smaller to medium-sized facilities. When businesses need to disburse truly large amounts of heat, wet cooling tower benefits tend to outweigh their downsides.
Cross-flow vs Counter-flow
Counter-flow designs have multiple advantages from a design standpoint, such as greater operational reliability and higher efficiency. However, they require powerful pumps, which boost expenses, and generate a great deal of noise. Cross-flow towers cost less to install and operate, but they’re also less reliable. In cold weather, they tend to freeze, and dirt accumulates more easily.
Cooling Tower Parts and Functions
When considering buyer cooling towers for sale, it helps to know not only the most popular tower types, but also the parts that may comprise them. Common cooling tower parts (and their concomitant functions) include the following:
- Fill: This material encourages evaporation in wet cooling towers by increasing the contact between the cooling liquid and their air. They include a substance intended to disturb the liquid (splash fill) and material that encourages the liquid to spread itself thinly (film fill).
- Distribution System: A means of moving the water to disperse heat. This can include a basin lined with nozzles that uses gravity to draw liquid down through a tower (cross-flow).
- Drift Eliminators: Baffles that help minimize steam from escaping from the tower into the surrounding environment.
- Louvers: These devices shield water-storage containers from direct sunlight, preventing algae growth.
- Casing: This material surrounds the vast majority of the tower’s components and serves a protective function.
- Fan, Motor, Driveshaft, and Speed Reducer: Some cooling towers employ fans and their associated hardware in order to move air throughout the system.
- Fan Stack: Combined of a cylinder, air inlet, and diffuser, a fan stack minimizes noise and helps the fan work more efficiently.
- Fan Deck: A flat section at the top of a cooling tower, the fan deck is often designed as a maintenance space where employees can inspect a tower’s hardware.
- Valves: Valves have multiple uses throughout a cooling tower and can ensure the even distribution of liquid, control liquid entering or leaving the tower, or setting a flow rate.
- Collection Basin: These containers collect water at the bottom of the tower after it has cooled.
- Distribution Basin: Often part of a distribution system in cross-flow towers, these containers hold hot water before it is dispersed through spray nozzles.
- Tower Structural Frame: This is usually a steel frame that supports the tower, allows the construction of access ladders, and facilitates the installation of wind restraints and vibration mounts.
Factors Affecting Performance
A cooling tower’s performance can be evaluated by several common factors, such as:
- Wet-Bulb Temperature: The typical temperature as measured by a thermometer is called the dry-bulb temperature because it doesn’t account for humidity. When you factor humidity in, the measurement is called wet-bulb temperature, and the greater the amount of humidity, the less evaporation can occur.
- Cooling Range and Approach: The cooling tower’s approach is defined as the difference between the cold water in the system and the wet-bulb temperature, and the range is the difference between the temperature of the water entering the tower and the temperature as it exits. These are important diagnostic tools for operators, because a lower approach indicates greater efficiency, while a lower range indicates less efficiency.
- Consumer Heat Load: This absolute measurement indicates how much heat the tower can remove from a unit of water.
Applications of Cooling Towers
Cooling towers have many different applications, and following are some of the areas where you’ll find them employed:
- Power generation
- Heating, Ventilation, and Air Conditioning (HVAC)
- Thermal power stations
- Food processing
- Chemical production
- Natural gas processing
- Oil refining and other petrochemical processes
- Semiconductor manufacturing
- Hospitality industries
- Medical facilities
- Large retailers
Cooling Tower Benefits
Facilities that employ cooling towers can realize multiple benefits, such as:
- Extended equipment life
- A reduction in manual maintenance requirements
- Improvements in operating efficiency
- Lowering the risk of bacterial contamination
- A reduction in system down-time
- Water savings
- A decrease in chemical costs
What to look for when buying Cooling Towers
When buying cooling towers used or new, you ought to keep a number of important considerations in mind. To ensure that you purchase a cooling tower that works for your specific context, pay attention to the following tips:
- Make sure to calculate heat load, approach, range, and wet bulb temperature prior to purchasing so that you don’t buy an undersized tower.
- If your tower will be in direct sunlight, ensure that it is coated with a UV-protecting substance to prevent degrading.
- Wet towers should use galvanized steel for internal components to discourage rust.
- Wet towers benefit from high-density polyethylene (HDPE) components that eliminate the need for harsh, algae-killing biocides that can damage the tower.
- For towers that use fans, ensuring that the fan remains balanced when active and inactive increases equipment life and decreases noise.
- For high-capacity towers, ensure that they have installed ladders for maintenance access.
- Towers can emit significant noise pollution, and sound-dampening technology can reduce it appreciably.
- Are parts easily available for your particular model of tower?
- Does your wet tower come with eliminators or drip catchers, which can significantly decrease drift?
Cooling Towers Parts & Accessories
Virtually every cooling tower part and accessory available helps maintain a tower’s original function or offers necessary replacement parts. Some of these include:
- Cooling Tower Fills
- Cooling Tower Nozzle
- Drift Eliminator
- Air Inlet Louver
- Cooling Tower Sprinkler Head
- Mist Eliminator
- Cooling Tower Motor
- Cooling Tower Fan
If you’re considering purchasing cooling towers and their associated equipment, see what Surplus Record has available. Search for “cooling towers” at the top of Surplus Record’s website to see the available selection.