Air Temp and Pressure

Introduction

Boiler air/fuel adjustment is critical to efficient boiler operations. Many boilers are manually adjusted once per year and then left to operate through a wide variation in temperature and barometric weather conditions. The amount of oxygen in the air is directly related to air density and temperature. However, conventional boiler controls are set according to air volume. New boiler controls that adjust air volume according to a continuous oxygen monitoring of the flue gas is one way to maintain correct air/fuel ratios for peak combustion efficiency.

Effects of Air Properties on Oxygen Content

The Table below assumes an initial manual adjustment of 15% excess air, a typical industry practice. As the ambient temperature drops, oxygen content increases; as barometric pressure increases, so does oxygen content for a given volume of air.

Air Temperature	Barometric Pressure	Excess Air Percentage
40F		25.5%
60F		20.2%
80F		15.0% - Initial Setting
100F		9.6%
120F		1.1%
	27 in.	7.0%
	28 in.	11%
	29 in.	15% - Initial Setting
	30 in.	19.%
	31 in.	34.5%

 

More Information

Air Supply

Air Infiltration

Combustion Air Control

Oxygen Control

Flue Gas Analysis

Source: Table Johnston Boiler web site 1/2005; Text Bob Fegan 1/2005;