Hot-Water Heating Plant
Understand how the hot water heating plant turns fuel, electricity, or biomass into hot water for space heating, domestic use, and process heat. Explore system overviews, measurement steps, and additional resources.
Overview
The hot water heating (HWH) plant takes input energy (e.g., fuel, electricity, biomass) and generates hot water, which is distributed throughout a facility to provide space heating. An HWH boiler may also generate hot water to provide for other demands, such as domestic hot water or process heat. A hot water heating plant consists of a hot water heating boiler, a feedwater system,and a hot water heating loop.
Systems
Hot Water Heating Boiler
A boiler system is the largest energy-consuming part of a plant. It heats water by transferring energy from combustion gases, then distributes it to meet space heating or domestic hot water needs.
Feedwater System
The feedwater system provides treated make-up water and returned hot water from the hot water loop. Feedwater requires proper treatment to remove pollutants and preserve the efficiency of the boiler.
Hot Water Loop
The hot water loop system encompasses the distribution system responsible for moving hot water throughout the building.
How do I…
Assess Plant Energy Usage
The hot water heating plant’s total energy usage includes the fuel used by the boiler(s) and the electricity used by the burner fan motor, as well as the primary, secondary, and feedwater pumps.
Quantify Fuel Usage (Btu)
Determine the amount of fuel needed to satisfy the building’s heating load.
Equipment to Measure
What to Measure:
- Average hourly fuel usage by the boiler (gal/h for fuel oil or propane, ccf/h for natural gas)
- Average hourly outdoor air temperature (°F)
Measurement Locations
Quantify Electricity Usage (kWh)
Determine the amount of electricity needed to run the boiler and circulate the water.
Equipment to Measure
What to Measure:
- Average hourly true RMS power (kW) of the burner fan motor.
What to Measure:
- Average hourly true RMS power (kW) of the feedwater pump motor.
What to Measure:
- Average hourly true RMS power (kW) of the primary pump motor.
- Average hourly true RMS power (kW) of the secondary pump motor (if present).
- Total operating time (hours) of the pump motors.
- Average hourly outdoor air temperature (°F).
Measurement Locations
Assess Plant Performance
The performance of a hot water heating plant can be characterized by the heat load delivered to terminal units and the quantity of heat recovered (if a heat exchanger is present).
Quantify Heat Load Delivered (Btu)
Average hourly heat rejected from the hot water loop via terminal units.
Equipment to Measure
Hot Water Loop
What to Measure:
- Average hourly flow rate (gpm) of hot water in the loop
- Average hourly temperature (°F) of hot water entering the terminal unit
- Average hourly temperature (°F) of hot water leaving the terminal unit
Quantify Heat Recovered (Btu)
Average hourly heat delivered to the make-up water.
Equipment to Measure
Heat exchanger
What to Measure:
- Average hourly flow rate (gpm) of feedwater
- Average hourly temperature (°F) of water entering the heat exchanger
- Average hourly temperature (°F)of water leaving the heat exchanger
Further Reading
- ASHRAE (2020). “ASHRAE Handbook: HVAC Systems and Equipment,” Chapter 32. BOILERS. I-P Edition.