Diffuser passages: Passageways within a centrifugal compressor that convert kinetic energy into static pressure. The passageways start out small and increase in size.

Economizer: Heat exchange device incorporated to increase overall efficiencies. Economizers can be found on both chillers and boilers though they operate differently.

Flue gas: Combustion gases from the burning of a fuel within a boiler.

Flue gas recirculation: Diverting some of the flue gas exiting the furnace of a boiler back into the combustion chamber to reduce emissions.

HHV: Stands for Higher Heating Value.

Inlet vanes: Device used within a centrifugal compressor to control flow by pre-swirling the refrigerant.

Impeller: Rotating component within a centrifugal compressor that draws in refrigerant and accelerates it.

LHV: Stands for Lower Heating Value.

MBTUH: Sometime referred to as MMBTUH, is a measure for the rate of heat transfer commonly used in boiler applications. 1 MBTUH is equal to 1,000,000 Btu/h.

Mud drum: Lower drum on a water tube boiler where the feedwater will enter.

No. 2 Fuel Oil: One of the fuel options used for combustion in boilers. Also can be referred to as a diesel fuel oil or a distillate fuel oil.

Pressure Relief Valve: An inline device on a pipe used to reduce the pressure of a fluid to a desired level.

Risers and Downcomers: Tubes connecting the steam drum and mud drum on a water tube boiler.

Spud Burner: A device used to bring in fuel to a furnace.

Steam Drum: Upper drum on a water tube boiler where the saturated steam exits.

Steam Traps: Devices inline with a steam pipe that will only allow condensate to pass.

Ton: Measure of energy transfer. A ton is often used for performance ratings of refrigeration systems. 1 ton equals 12,000 Btu/h.

Volute: Chamber on the outskirts of a centrifugal compressor where the compressed vapor is collected.