General Overview
The hot water heating (HWH) plant takes input energy (e.g., fuel, electricity, biomass) and generates hot water that is distributed throughout a facility to provide space heating. A HWH boiler may also generate hot water to provide for other loads, 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.
Hot-water Heating Plant Systems and Components
Hot Water Heating Boiler System
The HWH boiler system is the largest energy-consuming system in the hot water heating plant. Hot water is produced primarily through the heat transfer from combustion gases in the combustion chamber to the water. The hot water produced by the system is then transported out to the facility to meet required heating loads or domestic hot water needs. The main components of a HWH boiler system are burner, combustion chamber, heat exchanger, and draft fan and are shown in Figure 2.
Hot Water Loop System
The hot water loop system encompasses the distribution system responsible for moving hot water throughout the building. Components of a typical hot water loop system are primary-only or primary-secondary pumps, piping network and piping insulation and are shown in Figure 3.
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. Figure 4 shows the components for the feedwater system.
Evaluation of Energy Conumption
The total energy consumption of a HWH plant is the sum of the energy consumption of the components of each system. In a HWH plant this includes the fuel usage consumed by the boiler to satisfy the heating load and the electricity required by the burner fan motor, primary and secondary pumps and feedwater pump. Table 1 provides a summary of system component measurements and values needed to quantify the annual energy consumption and operating characteristics of the HWH plant.
|
Plant Quantification |
Values to be Quantified |
Energy Consuming Component |
|
Hot water heating plant fuel consumption (Btu) |
Average hourly fuel consumption (Btuh) |
|
|
Hot water heating plant electricity consumption (kWh) |
|
|
|
Heat load delivered |
Average hourly heat rejected from the hot water loop (Btu/h) |
Terminal Units |
|
Heat recovered |
Average hourly heat delivered to the make-up water (Btu/h) |
Further Reading
- ASHRAE (2020). “ASHRAE Handbook: HVAC Systems and Equipment,” Chapter 32. BOILERS. I-P Edition.