2 FM quick reads on boiler controls
1. Three Boiler Control Upgrades Can Improve Energy Efficiency
Today's tip comes from James Piper, contributing editor for Building Operating Management and Maintenance Solutions magazines:
When specifying boiler controls it is important to understand that operating efficiency is only one consideration. The boiler control system must be able to meet the facility's peak heating load while operating efficiently under part-load conditions. Typical controls that facility managers should consider when upgrading existing boilers include the following:
1. Flue-gas trim. One of the best indicators of a boiler's combustion efficiency is the flue-gas composition. Trim controls constantly monitor the temperature and the chemical composition of the flue gas, making changes to the combustion controls to limit the quantity of excess air brought into the boiler. While all boilers require some excess air for complete combustion, natural-gas-fired boilers can operate effectively with as little as 3 percent excess air. Boiler efficiency increases approximately 1 percent for each 15 percent decrease in excess air provided to the boiler. With most boilers operating at 10 percent or more excess air, the annual energy savings from flue-gas trim controls is significant.
2. Automatic blowdown. To limit the quantity of deposits that can accumulate in a steam boiler, technicians can bleed off part of the boiler's water, typically on a continuous basis. The boiler wastes energy if the blowdown rate is too high, and the concentration of solids in the water becomes too high if the blowdown rate is too low. Automatic blowdown controls regulate the quantity of water that technicians bleed from the system based on the actual level of contaminants.
3. Sequencing. Many facilities operate more than one boiler at a time, depending on the load. This frequently results in more boiler capacity than is actually needed. Since the operating efficiency of a boiler is highest when it is operating at or near full load, this practice can waste a significant amount of energy. Automatic sequencing controls examine the load conditions and determine the boiler or combination of boilers that will meet that load most efficiently.
2. Boiler Control Upgrades Plus Regular Maintenance Can Improve Energy Efficiency
Today's tip comes from James Piper, contributing editor for Building Operating Management and Maintenance Solutions magazines: Focus on boiler controls to reduce energy use.
New boiler controls can provide major gains in energy efficiency, performance, and safety at a much lower cost than replacing boilers. Older-generation boiler controls used mechanical linkages. With age and use, linkages wear and go out of adjustment, reducing the unit's efficiency. Older-generation controls also suffer from offset, which occurs when the system operates close to, but not exactly at, the desired setting.
Today's boiler controls incorporate microprocessors, solid-state sensors, and independent servo motors, which give managers accurate and reliable operation, eliminating problems such as offset.
When evaluating control options, it is important to remember boiler controls perform three basic functions: combustion control; water-level control; and flame safeguarding. If a facility uses multiple boilers, the control system must perform a fourth function: sequencing. Facility managers must factor all of these issues into their control decisions. Three types of boiler controls to consider upgrading are flue gas trim, sequencing and automatic blowdown.
Getting the proper controls installed is only the first step in achieving efficient and reliable boiler operation. To keep things operating that way over the life of the system, technicians must properly maintain controls. But the importance of proper maintenance goes far beyond efficiency and reliability issues. It also incorporates safe boiler operation.
Technicians must keep logs for boiler operations, recording operating parameters frequently enough to identify trends. Equally important, they must review those logs regularly to actually detect the trends.
At least once each month, technicians must test a boiler's safety equipment, such as the safety-relief valve, water-level control, and low-water fuel cutoff, according to the boiler manufacturer's recommendations. Larger boilers require more frequent testing.
They also should test all controls for proper operation and calibration at least once annually, and they should inspect, clean, and lubricate mechanical linkages according to manufacturer directions.