How to Evaluate Low Excess Air Controls for Packaged Boilers

Abstract

There are many types of excess-air trim systems available today in what manufacturers view as a boom market catalyzed by inflated oil prices. For the small boiler owner, determining whether low-excess-air (LEA) firing can be cost-justified and what type of system would be appropriate is a difficult decision requiring a great deal of thought and engineering judgment. And since no two excess-air trim systems are exactly alike in control philosophy, it is very important to select the one that best suits your particular boiler and payback requirements. Prudent engineers generally recommend an in depth evaluation of boiler and controls before specification. The starting point for any evaluation should be an analysis of existing heat transfer characteristics within your boiler so that a reliable estimate of the efficiency gain from LEA firing can be determined. Recall that heat transfer takes place in three main areas of the boiler-the radiant section, convection bank, and heat recovery equipment (economizers and air heaters). LEA firing alters the normal heat transfer distribution among these three areas.