Showing posts with label process cooling. Show all posts
Showing posts with label process cooling. Show all posts

Friday, August 31, 2018

What is a Cooling Tower?

An evaporative cooling tower is heat removal device that uses ordinary water to transfer process waste heat from building and equipment into the atmosphere. All cooling towers operate on the principle of removing heat from water by evaporating a small portion of water that is recirculated through the unit.

The mixing of warm water and cooler air releases latent heat of vaporization, causing a cooling effect to the water.  Cooling towers are a key component of many refrigeration systems and can be found in industries such as chemical processing plants, power plants, steel mills, food processing plants, and many other manufacturing companies where process cooling is required.  Cooling towers are also used to provide comfort cooling for large commercial buildings such as universities, government facilities, airports, schools, hospitals, and hotels.

The video below provides a short review of what cooling towers are and why they are important.

Friday, October 20, 2017

Wet Bulb Temperature and Cooling Tower Performance

corrosion resistant cooling tower induced draft type
Corrosion resistant evaporative cooling tower
Image courtesy Delta Cooling Towers, Inc.
Evaporative cooling towers enable many buildings across the globe to enjoy moderate interior temperatures. They serve as the final heat transfer step that moves heat from the building interior to the surrounding environment. In addition to their extensive application throughout large residential, commercial and industrial HVAC systems, their are numerous process cooling applications that employ evaporative cooling towers as an effective means of heat rejection.

Delta Cooling Towers, Inc. is a globally recognized manufacturer of corrosion resistant cooling towers, air strippers and tanks fabricated of HDPE to provide extended life service. The company posted an article entitled "Understanding Wet Bulb Temperatures And How It Affects Cooling Tower Performance". The original post is on this page of the company website, and all credit for the article goes to them. We share it below also, slightly edited for format on this forum.  From the article...

A cooling tower primarily uses latent heat of vaporization (evaporation) to cool process water. Minor additional cooling is provided by the air because of its temperature increase. Cooling tower selection and performance is based on water flow rate, water inlet temperature, water outlet temperature and ambient wet bulb temperature. Ambient wet bulb temperature and its affect on performance is the subject of this article. Ambient wet bulb temperature is a condition measured by a device called a psychrometer. A psychrometer places a thin film of water on the bulb of thermometer that is twirled in the air. After about a minute, the thermometer will show a reduced temperature. The low point when no additional twirling reduces the temperature is called the wet bulb temperature. The measured wet bulb temperature is a function of relative humidity and ambient air temperature. Wet bulb temperature essentially measures how much water vapor the atmosphere can hold at current weather conditions. A lower wet bulb temperature means the air is drier and can hold more water vapor than it can at a higher wet bulb temperature. For example:
Since cooling tower cells cool water by evaporation, the wet bulb temperature is the critical design variable. An evaporative cooling tower can generally provide cooling water 5° - 7° higher above the current ambient wet bulb condition. That means that if the wet bulb temperature is 78°F, then the cooling tower will most likely provide cooling water between 83° - 85°F, no lower. The same tower cell, on a day when the wet bulb temperature is 68°F, is likely to provide 74° - 76°F cooling water. When selecting 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 during the summer, when air temperatures and humidity is highest. For example, in Indianapolis, Indiana, the design wet bulb temperature is 78°F. Historically Indianapolis can expect less than one 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 lower meaning that a cooling tower cell designed for a 78°F wet bulb will be able to make 65-67°F water for 6,000 hours per year nearly 70% of the year. Most cooling towers are capacity rated at a "standard" wet bulb temperature of 78°F. That means on the days when the wet bulb temperature is 78°F, the tower will produce its stated capacity. In other 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 capacity to produce colder water decreases. Every location has a unique design (worst case) wet bulb temperature that is published by organizations such as ASHRAE and can be obtained easily.

What does it mean when your cooling tower water temperature is higher than the normal 5-7°F above the current wet bulb temperature?

  1. Your cooling load may be larger than the rated capacity of your cooling tower.
  2. Your cooling tower may have lost efficiency
  • Due to scale build up on the tower heat exchange surfaces.
  • Due to loss of air flow across the heat exchange surfaces.
  • Due to improper water flow from clogged nozzles or pump performance
What can you do to improve your tower performance? 

  • Add tower cell capacity
  • Check for the efficiency losses described above
  • Replace the heat exchange surfaces with new clean fill
  • Check for proper airflow
  • Check the water flow is at design
  • Check that nozzles are not clogged or broken

Cooling tower performance is tied to ambient wet bulb conditions. Higher wet bulb temperatures occur in the summer when higher ambient and relative humidity occurs. Initial system design and proper system maintenance is critical to be certain your cooling tower is providing desired cooling.

For more information, or to discuss your own heat transfer challenges, contact a product application specialist. Combine your own knowledge and experience with their application expertise to develop an effective solution.

Saturday, April 29, 2017

Dual Application for Cooling Tower

Plastic cooling tower air stripper
Plastic cooling tower assembly
Courtesy Delta Cooling Towers
Cooling towers are readily identified by their ubiquitous presence in large commercial cooling systems. They are an effective means of rejecting heat from from a centralized liquid system. The general operating principle of a cooling tower involves a thermal and mass transfer from the cooling water to the surrounding air. The water is distributed by a number of means throughout the cooling tower fill, drastically expanding the surface area of the water. Air from the surrounding atmosphere is moved across the water surface. Assuming that the air is within the performance range of the cooling tower, the resulting evaporation of a portion of the water cools the liquid water remaining behind.

There are other applications for cooling towers, and Delta Cooling Towers, Inc., described one in a March 2017 news post. The application centered around a municipality with two challenges in providing potable water to residents. The water was being sourced from very deep wells and, without treatment, had an unacceptably high delivery temperature. Additionally, the sourced groundwater exhibited unacceptable levels of radon and hydrogen sulfide, naturally occurring gaseous contaminants that required level reductions to render the water suitable for human consumption and use.

Air strippers, equipment that aerates the water, are a common means of reducing the gaseous contaminant levels. In this case, though, there was the additional challenge of reducing the water temperature. All needed to be accomplished at process flow rates commensurate with the size of the municipal water demand.
A solution that solved both issues arose with the use of a cooling tower selected to provide sufficient aeration for gaseous contaminant reduction and cooling of the water to acceptable levels.
You can access the entire case history by reaching out to a product specialist, with whom you should share your own liquid processing challenges. Combining your process knowledge and experience with the product application expertise of knowledgeable professionals will produce effective solutions.

Tuesday, January 19, 2016

Delta Cooling Towers - News Update

AHR Expo announcement for Delta Cooling Towers
Delta Cooling Towers
Exhibiting at AHR Expo 2016
Delta Cooling Towers manufactures corrosion resistant cooling towers for commercial and industrial applications where these product features are important:
  • Seamless double wall engineered plastic (HDPE) shell
  • Corrosion proof construction
  • Direct drive fan system
  • Totally enclosed VFD rated motors
  • Factory assembled for simple installation
  • 20 Year shell warranty
  • PVC water distribution system with non-clog large orifice removable nozzles
  • High efficiency PVC fill
  • Made in the USA
Mountain States Engineering and Controls (MSEC) represents the manufacturer in Colorado, Wyoming, and Montana You can visit the Delta Cooling Towers booth at AHR Expo January 25 - 27 in Orlando, Florida. 

Corrosion resistant cooling tower for HVAC or industrial cooling
HDPE Cooling Tower
Courtesy Delta Cooling Towers

Monday, October 5, 2015

Cooling Tower Corrosion Resistance - It's Easy

Corrosion resistant cooling tower installation
Corrosion resistant cooling tower
Courtesy Delta Cooling Towers
Machinery that will be continuously bathed in a spray of water throughout its operating life is certainly a good candidate for some corrosion protection. Locate this equipment outdoors, perhaps in a coastal area, and the potential to gain benefits from a corrosion resistant installation are more than clear.

Cooling towers fit my previous description admirably, and their scope of application makes them an essential element of facility operation. Every unit is exposed to combined effects of variable water chemistry, constant saturation at elevated temperatures, and aeration. Some cooling towers also are impacted by potentially harmful agents in the process water and various airborne pollutants, including sulfur oxides and acid rain.

For those not entirely familiar with how a cooling tower works, here are the very basics. Cooling towers transfer an amount of heat from one or more water-cooled machines or systems to outdoor air. Heated water from the water cooled systems enters the cooling tower, distributes over a heat transfer surface (sometimes called the fill), and is cooled by an induced air flow that is forced through the fill. The flowing air causes a portion of the water to evaporate, removing heat and lowering the temperature of the water. The cooled water is collected in a basin and returned to the system to repeat the heat transfer cycle.

Traditionally, cooling towers were fabricated of metal because of its structural strength and ability to be formed using readily available fabricating means. Differing metals were employed, at basic to premium price points, to provide increased levels of resistance to the ever present corroding nature of water and weather. Many cooling towers built today employ the same, or similar, materials and methods used decades ago. There is, and has been for quite some time now, a modern alternative to metal cooling tower construction that provides substantially increased levels of corrosion resistance at a competitive price point.

Delta Cooling Towers, Inc. manufactures cooling towers using structural and other plastics, enabling them to provide a 20 year warranty covering the basic structure of the unit. The product line provides capacity and performance range to cover almost any requirement. If you are in the business of specifying heat rejection equipment for your own facility, or one of your client's, you should get more detailed information about this equipment. Have a discussion about your application requirements, and concerns about operational longevity, with a product specialist. Good decisions come from combining the knowledge and experience of many.

As a quick reference, included below is a list of materials used in the construction of the Delta Cooling Towers unit. A quick glance by anyone familiar with the corrosion susceptibility of metals used in tower construction will see that the superior performance of the plastic materials should be given serious consideration on a cooling tower project.