14-01-2013, 04:10 PM
Boilers
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Introduction
Boilers are pressure vessels designed to heat water or produce steam, which can then be used to provide space heating and/or service water heating to a building. In most commercial building heating applications, the heating source in the boiler is a natural gas fired burner. Oil fired burners and electric resistance heaters can be used as well. Steam is preferred over hot water in some applications, including absorption cooling, kitchens, laundries, sterilizers, and steam driven equipment.
Boilers have several strengths that have made them a common feature of buildings. They have a long life, can achieve efficiencies up to 95% or greater, provide an effective method of heating a building, and in the case of steam systems, require little or no pumping energy. However, fuel costs can be considerable, regular maintenance is required, and if maintenance is delayed, repair can be costly.
Guidance for the construction, operation, and maintenance of boilers is provided primarily by the ASME (American Society of Mechanical Engineers), which produces the following resources:
• Rules for construction of heating boilers, Boiler and Pressure Vessel Code, Section IV-2007
• Recommended rules for the care and operation of heating boilers, Boiler and Pressure Vessel Code, Section VII-2007
Boilers are often one of the largest energy users in a building. For every year a boiler system goes unattended, boiler costs can increase approximately 10% (1). Boiler operation and maintenance is therefore a good place to start when looking for ways to reduce energy use and save money.
Types of Boilers
Boilers are classified into different types based on their working pressure and temperature, fuel type, draft method, size and capacity, and whether they condense the water vapor in the combustion gases. Boilers are also sometimes described by their key components, such as heat exchanger materials or tube design. These other characteristics are discussed in the following section on Key Components of Boilers.
Two primary types of boilers include Firetube and Watertube boilers. In a Firetube boiler, hot gases of combustion flow through a series of tubes surrounded by water.
Fuel Type
In commercial buildings, natural gas is the most common boiler fuel, because it is usually readily available, burns cleanly, and is typically less expensive than oil or electricity. Some boilers are designed to burn more than one fuel (typically natural gas and fuel oil). Dual fuel boilers provide the operator with fuel redundancy in the event of a fuel supply interruption. They also allow the customer to utilize the fuel oil during “peak time” rates for natural gas. In times when the rates for natural gas are greater than the alternate fuel, this can reduce fuel costs by using the cheaper alternate fuel and limiting natural gas use to occur only during “off peak” times.