What is short cycling and why is it important?
A boiler short cycle happens most often when an oversized boiler (Bazooka from the example above) quickly satisfies steam demands, then shuts down until steam is required again. In plants, steam demands can change over time, and many times boilers are installed with the notion that additional steam will be needed in the future. When those additional steam demands never come to fruition, you are left with boiler that is simply too large for your application – the main culprit of short cycling.
According to the U.S. Department of Energy a short cycling boiler is typically 10% to 15% less efficient than a normal boiler operating at low firing rates. Not only is it less efficient, but short cycling also greatly reduces the life of your boiler. Fuel train components take the largest toll when short cycling occurs. If your boiler cycles every five minutes, those components are subject to over 100,000 cycles per year.
Another common cause on hot water boilers for short cycling includes an improper controls strategy and incorrect set points. Reset controls are available that help to regulate feed water temperature as the outdoor temperature changes. It does this by continuously monitoring the temperature differential. This differential helps dictate the boiler’s on/off cycle; if the differential is narrow, the boiler is more subject to short cycling.
Here are a few tips in short cycle prevention:
Maximize multiple boiler operations: The most efficient boilers should be brought on-line as loads increase, while less-efficient units taken off-line first as loads drop off.
Utilize burners with a high turndown ratio
Boiler downsizing: Fuel savings can be achieved by adding a smaller boiler sized to meet average loads at your facility or by re-engineering the plant to consist of multiple smaller boilers. Multiple small boilers offer reliability and flexibility to operators to follow load swings without over-firing and short cycling.
Partner with an expert: Because boiler short cycling is largely dependent upon selecting the correct size for your steam requirements, it is critical to partner with an industry expert to guide you through your selection process. In a similar way, if you required open heart surgery, you wouldn’t go to a general practitioner—you would go to a heart specialist. WARE is that specialist as it relates to boilers. Call Ware today to discuss your steam needs. (800)-228-8861.