Boilers

Overview

Boilers consume large amounts of energy performing a very wide range of work. When considering their energy usage and efficiency improvement potential, they must first be grouped into a few categories such as ‘Steam’ or ‘Hot Water’ and then further grouped by boiler design. If the boiler is more than about 10 years old, there are likely several things that can be done to improve its efficiency. If the boiler is more than about 30 years old, depending on its size, it may be a candidate for replacement or major modification. Large boilers, over 100 hp, can typically be economically retrofitted with things like a new high efficiency burner and advanced controls. Smaller boilers are typically more economical to replace with a new boiler with all the new energy efficiency features built into them.

Energy Efficiency

To understand what energy efficiency measures are possible for a boiler, it must first be known if the boiler is steam or hot water and what/how the boiler is currently controlled. Many boiler efficiency improvements are made as retrofits to existing controls that do things like more precisely measure and control the amount of fuel and air that enters the burner. Other measures are add-on items such a flue stack economizer. Still other options work remote of the boiler, such as a blow-down heat recovery system.

It is also important to understand the significant difference in the efficiency ratings that can be applied to a boiler. For example, Combustion Efficiency refers to the instantaneous efficiency of the burner at converting natural gas fuel and oxygen into heat. Then that heat must get into the water and that heated water/steam must get to the point of use. A boiler rarely runs at peak-on all the time; there is almost always cycling, where the boiler operates at part loads. These and many more factors can make it a challenge to estimate the savings potential from taking action until a fair amount of data and knowledge about the boiler is gathered and analyzed.

Many boiler retrofit measures individually may only save 1 or 2 percent. However, if the boiler is big and runs many hours, that can be a significant amount of energy saved. Other measures like economizers when properly applied, may save as much as 10% of total boiler energy usage and return a payback in only a few months.

More Information

For the most comprehensive energy efficiency information available about Boilers, Steam and Distribution Systems, please visit our Boiler Consortium web site atwww.cleanboiler.org and click on ‘Boiler Efficiency Improvement Guide.