Boiler
Understand how the boiler works. Explore component overviews, measurements, and additional resources.
Overview
A boiler system provides hot water or steam to distribute the heating load within a facility. Heat is transferred from the combustion chamber to water until the set point temperature for hot water, the boiling point for steam, or beyond the boiling point superheated steam.
Components
Heat Exchanger
The heat exchanger in boiler systems facilitates heat transfer from the fuel combustion chamber to the water without direct contact. Non-condensing boilers typically have a single heat exchanger chamber, while condensing boilers include a secondary heat exchanger to increase the heat transfer area and improve efficiency.
Burner
The primary function of the burner is to deliver fuel and air, mix them in the correct proportions, provide an ignition source, and ensure efficient combustion. Burners can be designed for a single fuel or configured to operate on multiple fuels. Burner controls play a crucial role in the overall efficiency of the boiler system. Depending on the system, the firing rate may be constant, variable in discrete stages, or fully variable.
Draft Fan (Burner Fan Motor)
Mechanical draft boilers usually have a draft fan that creates the required pressure difference. It is driven by a motor to provide oxygen to the combustion chamber for adequate combustion.
Draft fans can be:
Combustion Chamber
The combustion chamber is where the fuel is burned. It houses the burners and is designed to support extremely high temperatures.
How do I…
Assess System Energy Usage
The primary energy consumption of a boiler system is the fuel that is used to drive the combustion reaction to heat the water. Its key energy-consuming components include the burner and, if present, the draft fan. The primary energy source is typically liquid fuel or natural gas, though electricity may also be used to power the draft fan.
Quantify Fuel Usage (Btu)
Determine the total amount of fuel used by the boiler to heat the water.
Equipment to Measure
Burner
What to Measure:
- Average hourly fuel usage of the boiler (gal/h)
- Total operating hours of the burner motor (h)
- Average hourly outdoor air temperature (°F)
Quantify Electricity Usage (kWh)
Determine the total amount of electricity used to operate the motors.
Equipment to Measure
Burner Fan Motor
What to Measure:
- Average hourly true RMS power draw of the burner fan motor (kW)
- Total operating hours of the burner motor (h)
Measurement Locations
Further Reading
ASHRAE (2014). “ASHRAE Guideline 14-2014 – Measurement of Energy, Demand, and Water Savings.” Annex A.
ASHRAE (2020). “ASHRAE Handbook: HVAC Systems and Equipment,” Chapter 11. STEAM SYSTEMS. I-P Edition.
ASHRAE (2020). “ASHRAE Handbook: HVAC Systems and Equipment,” Chapter 21. FANS. I-P Edition.