General 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 (treated fresh water) and, in steam systems, condensate from the condensate recovery system.
Feedwater System Components
The main components of a boiler feedwater system are one or more feed pumps, and a receiver tank. Feedwater systems may include an economizer and larger systems also can have a deaerator tank. These components are shown in Figure 1.
Pumps and Motors
The feedwater pumps and motors inject 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 will turn on the pumps and feedwater will flow into the boiler.
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.
Feedwater Tank
The feedwater tank is a chamber that receives make-up water and condensate recovered from the condensate recovery system. The makeup water is treated to remove contaminants and its temperature is increased prior to being discharged into the feedwater tank.
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.
Evaluation of Energy Consumption
The primary energy consumption in a feedwater system is the electricity used to run the pump motors. Table 1 provides a summary of system component measurements and values needed to quantify the annual energy consumption and operating characteristics of the feedwater system.
| System Quantification | Values to be Quantified | Energy Consuming Component | Measurements |
| Feedwater pump electricity consumption (kWh) |
|
Pump motor |
|
The primary effect of the economizer is to minimize the fuel usage by recovering heat from the flue stack to pre-heat the feedwater injected into the boiler. Generally, the economizer effect can be reflected in the energy consumption of the overall low pressure steam plant. For more information see the steam plant.
Measurement Locations
The measurement locations for a feedwater water system are shown in Figure 2.
Further Reading
- ASHRAE (2020). “ASHRAE Handbook: HVAC Systems and Equipment,” Chapter 32. Boilers. I-P Edition.
