Feedwater System
Understand how the feedwater system works. Explore component overviews, measurements, and additional resources.
Overview
The feedwater system usually receives condensate recovered from the condensate recovery system and make-up water (treated fresh water). It maintains water levels in the boiler, extending its lifespan.
Feedwater systems supply fresh water to hot water or steam boilers to make up for losses from boiler blowdown, steam traps, hot water use, or other losses. The feedwater system receives inputs of make-up water and, in steam systems, condensate from the condensate recovery system.
Components
Feedwater Pumps and Motors
The feedwater pump and motor injects the feedwater stored in the feedwater tank into the boiler. The pumps and motors are driven by a feedwater controller that monitors the water level of the boiler and the water contaminant levels. When the controller receives the signal, it turns on the pumps and feedwater flows into the boiler.
Feedwater pumps can be:
Economizer
An economizer, or flue gas heat recovery unit, is a heat exchanger that is installed on the stack of a boiler to recover heat from combustion gases discharged through the stack and otherwise would be wasted. The primary effect of the economizer is to reduce fuel consumption by recovering heat from the flue stack to preheat the feedwater before it enters the boiler. This heat recovery improves efficiency and can be reflected in the overall energy consumption of the low-pressure steam plant.
Feedwater Tank
A feedwater tank is a chamber that receives makeup water and condensate recovered from condensate recovery system. The makeup water is treated to remove contaminants and its temperature is increased prior to being discharged into the feedwater tank.
Piping Network
The piping network for a feedwater system can serve one or multiple boilers for a hot water or steam plant where each boiler has its own feedwater valve. The feedwater valve opens and closes based on the boiler controller signal.
How do I…
Assess System Energy Usage
The primary energy consumption in a feedwater system is the electricity used to run the pump motors.
Quantify Electricity Usage (kWh)
Determine the total amount of electricity used to operate the pump motors.
Equipment to Measure
What to Measure:
- Average hourly true RMS power draw (kW) of the pump motor.
- Total operating time (hours) of the pump.
What to Measure:
- Average hourly true RMS power draw (kW) of the pump motor.
- Total operating time (hours) of the pump.
Measurement Locations
Further Reading
ASHRAE (2020). “ASHRAE Handbook: HVAC Systems and Equipment,” Chapter 32. Boilers. I-P Edition.