HVAC Boiler Efficiency
HVAC Boiler Efficiency
Studies have shown time and time again, that most facilities with a boiler, waste large amounts of fuel. With fuel rates on the rise, it is becoming even more important that boilers operate at peak efficiency. It is too often the case that boiler operators are concerned only with the fact that the boiler merely runs - placing little regard on its efficiency. Nevertheless, try to consider different options, to increase your boiler’s efficiency.
Does My Boiler Need Replacing?
Boiler replacement is usually is done when:
- poorly functioning equipment needs to be improved
- there is an expansion of an existing facility
- there is a construction of a new facility
Boiler repair or tune-up is usually done when:
- there is need for a small amount of added boiler capacity
- there is a small building or equipment addition
Factors to Consider
Condition of the equipment – Do boiler tubes have leaks? What have the water treatment practices been like in the past?
Energy – What are the operating hours, what is the size of the boiler compared to its load?
Reliability – How important is the boiler exactly? What is it used for? Is there a back-up?
Maintenance costs – how much will it be to repair?
Repair interim – can the building withstand the downtime required to replace the boiler?
Satellite boilers and water heaters – You can eliminate most distribution-system losses by installing equipment near the load. Doing this, you must consider potential venting issues and the availability of natural gas service.
Building requirements for steam - Does the building only use steam to generate hot water? If so, it id cost-effective to replace steam boilers with high-efficiency hot-water boilers in order to improve system efficiency, and reduce operating and maintenance costs.
Efficiency and Boiler Design
Boiler design has the biggest impact on the system’s overall efficiency and maintenance costs. The initial cost is a small portion of investment in a boiler. Energy costs usually take up 70-80 percent of the annual operating cost of boiler systems and 30-50 percent of the life-cycle cost.
Since a boiler’s capital cost is a major component of its life-cycle cost, deferred maintenance that shortens equipment life hurts the bottom line. A typical boiler uses many times the initial capital expenditure in fuel annually, so to maximize the boiler investment, managers need to specify the most efficient boiler for the application.
replacement options:
- converting steam to hot-water boiler system
- use non-condensing type boilers and water heaters
- use condensing type boilers and water heaters
Nevertheless, an efficiency increase of 11-15 percent is possible when comparing condensing equipment with non-condensing equipment. Managers can easily address the creation of sulfuric acid in flue gases by using stainless steel for flue piping and by collecting and draining condensate. This can result in efficiencies of greater than 95 percent.
Efficiency and “On/Off” Cycling
The less boilers cycle on and off, the more efficient they are. Because of this, modular boiler installations are becoming more common, compared with the traditional option of installing one large boiler with a 100% redundant back-up boiler.
Boilers generally have very bad efficiencies at low loads. The reason installations of multiple packaged boilers can operate more efficiently, is that they are better able to match the current load with boiler capacity, and due to this, cycle on and off less often.
Cost-Effective Details
Modern boilers include the following burner features:
- electronic control systems that monitor flue-gas components and adjust fuel and air as needed
- re-circulated flue gases, that ensure optimal combustion with minimal excess air
- highly improved turndown ratios to improve efficiency at less than peak load
- forced draft burners, instead of atmospheric burners
Dual-Fuel Choices
Dual fuel burners often are a realistic option for facilities that can use an alternate fuel, such as oil, during short periods that a gas utility is under peak demand. The result is lower annual interruptible gas rates. Backup fuel also might be provided to ensure boiler operation in the event of a problem with the gas system. Fuel oil fires at higher efficiencies than natural gas, because it has less water vapor during combustion, but this equipment typically is more costly to operate.
New and Retrofit Applications That Improve Efficiency
- Install Burners equipped with digital-combustion management, to automatically adjust excess air and fuel for precise control.
- retrofit existing boilers with new burners and controls.
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