This website requires certain cookies to work and uses other cookies to help you have the best experience. By visiting this website, certain cookies have already been set, which you may delete and block. By closing this message or continuing to use our site, you agree to the use of cookies. Visit our updated privacy and cookie policy to learn more.
This Website Uses Cookies
By closing this message or continuing to use our site, you agree to our cookie policy. Learn More
This website requires certain cookies to work and uses other cookies to help you have the best experience. By visiting this website, certain cookies have already been set, which you may delete and block. By closing this message or continuing to use our site, you agree to the use of cookies. Visit our updated privacy and cookie policy to learn more.
Process Cooling logo
search
cart
facebook twitter linkedin youtube
  • Sign In
  • Create Account
  • Sign Out
  • My Account
Process Cooling logo
  • Home
  • Magazine
    • Current Issue
    • Digital Editions
    • Archives
    • News
    • Products
    • Columns
    • Commentary
    • Web Exclusives
  • Multimedia
    • Podcasts
    • eNewsletter
    • PC Mobile App
    • Photo Galleries
    • Videos
    • Webinars
  • Technology
    • Air Cooling
    • Ammonia Refrigeration
    • Cryogenic Systems
    • Equipment Cooling
    • Flow Control/Monitoring
    • Heat Transfer
    • Industrial Gases
    • Leak Detection
    • Temperature Control/Sensing
    • Water Cooling
    • Water Treatment
  • Equipment
    • Chillers
    • Compressors/Condensers
    • Cooling Towers
    • Enclosure Cooling
    • Fans & Blowers
    • Filtration
    • Heat Exchangers/Coils
    • Pumping
    • Refrigeration Systems
    • Valves & Piping
  • Design/Build
  • Industry Focus
    • All Process Industries
    • Beverages & Breweries
    • Chemicals/Petrochemicals
    • Cosmetics & Fragrances
    • Dairy Foods
    • Electronics
    • Food Processing
    • Pharmaceuticals
    • Power Plants
    • Plastics
    • Soaps/Cleaners
  • Resources
    • Events
    • Classifieds
    • Custom Content & Marketing Services
    • Market Research
    • Store
    • White Papers
  • Directories
    • Buyers Guide
    • Cooling Capabilities
    • Take a Tour
    • Heat Transfer Fluids
  • Contact
    • Advertise
    • Contact Us
  • Subscribe
    • Print Edition Subscription
    • Digital Edition Subscription
    • eNewsletters
    • Online Registration
    • Customer Service
Home » Control Algorithms

Control Algorithms

October 1, 2008
Reprints
No Comments

The control algorithm can have a far-reaching effect on system stability, accuracy and cost. Four common temperature control algorithms are on-off, proportional, proportional with integral and derivative (PID), and heuristic.

On-Off Control
On-off control turns cooling fully on (or off) exactly at the setpoint temperature. This is the simplest and often the most accurate type of control algorithm. As long as thermal lag in a system is modest and cooling capacity is approximately matched to the load, it is hard to beat on-off control.

Proportional Control
Proportional control modulates the amount of cooling in some way so that cooling is applied gradually as the temperature approaches setpoint, and it does not reach its full capacity until the temperature exceeds the setpoint by a predetermined amount. The range of temperature from where cooling is first applied to where it is fully on is called the proportional bandwidth. This range is usually centered on the setpoint.

Proportional control is the first step toward a more sophisticated control algorithm and often is used when a system is difficult to control due to a longer thermal lag time or mismatched cooling capacity. It can add stability by preventing large oscillations in temperature, but the increased stability comes at the cost of accuracy, as the controlled temperature can settle anywhere within the bandwidth, depending on the load conditions.

PID Control
PID control starts with a proportional control algorithm and adds corrections based on the integrated difference between the actual and setpoint temperature (the “I” or integral term) as well as the rate of rise of load temperature (the “D” or derivative term). The added terms correct for the tendency of plain proportional control to settle anywhere within the bandwidth and exhibit small oscillations. However, some effort is needed to “tune” the parameters, and a longer overall time is required to reach setpoint.

Heuristic Control
Heuristic control throws away any “cookbook” approach to control type and employs whatever method appears necessary to achieve adequate control of a particular system. It can be thought of as mechanizing what a smart, quick human might do if they were reading the process temperature and had their hand on a cooling amount knob. Heuristic control often uses a combination of on-off and proportional load switching mixed together in a complex timing sequence.

Before choosing an algorithm, you should discuss the options with your equipment vendor. For some processes, a simple control type, such as on-off, might provide the best performance, while a more sophisticated (and more expensive) control, such as PID, might spoil a well-designed thermal system by mistuning. Heeding a vendor’s advice on this selection can result in substantial cost and performance advantages.

Links

  • Thermalogic Corp.
  • Web-Exclusive Sidebar:
    A Common Cooling Control Pitfall
  • Related Article:
    Keep Your Cool

Subscribe to Process Cooling

Related Articles

A Common Cooling Control Pitfall

Norish Ltd. Solves Warehousing Control Issues

Improved Control Yields Better Seals and Fasteners

Debris Control Reduces Downtime at Automotive Plant

You must login or register in order to post a comment.

Report Abusive Comment

Subscribe For Free!
  • Print Edition Subscriptions
  • Digital Edition Subscriptions
  • eNewsletters
  • Online Registration
  • Subscription Customer Service

More Videos

Popular Stories

hybrid cooler

Hybrid Cooling Saves Water, Reduces Energy Use

descaling cooling towers

Cleaning Scale from Cooling Tower Systems

News_900

Partnership Focused on Industrial Refrigeration

112719-eurovent

Opting for Evaporative Cooling Will Reduce Carbon Dioxide Emissions, Says Report

112719-towers

Planned Cooling Tower Demolition Sparks Community Protest

CoolingCapabilities_360


Events

January 1, 2030

Webinar Sponsorship Information

For webinar sponsorship information, visit www.bnpevents.com/webinars or email webinars@bnpmedia.com.

View All Submit An Event

Poll

What Do You Look For in a Process Cooling Equipment Supplier?

Let’s talk purchasing: When specifying and purchasing industrial process cooling equipment, what about an equipment supplier is the most important to you?
View Results Poll Archive

Products

Refrigeration Systems and Applications, 3rd Edition

Refrigeration Systems and Applications, 3rd Edition

See More Products

events_360

Process Cooling Magazine

Process Cooling November/December 2019

2019 November/December

Check out the November/December 2019 edition of Process Cooling: Tackling tower scale, hybrid cooling, energy conservation, paper mills and plastic towers and much more!
View More Create Account
  • Resources
    • Manufacturing Group
    • List Rental
    • Contributor Guidelines
    • Web Exclusives
    • Product of the Month
    • Partners
    • Manufacturers Photo Gallery
    • Polls
    • Survey and Sample
  • Want More
    • Connect
    • Privacy Policy

Copyright ©2019. All Rights Reserved BNP Media.

Design, CMS, Hosting & Web Development :: ePublishing