A heating plant refers to a steam or hot water heating system that serves a number of outlying buildings. It is specified by the type of equipment used. The equipment consists of the boiler; pumps; valves; the piping of the steam-water system; and the storage, handling and feed equipment of the fuel system. The key components of a heating plant include operating conditions, type of boilers, and source of fuel.
Heating plants are common among older university campuses, rural or off-grid industrial sites and military complexes. Often these facilities are co-located with electric municipal or industrial utilities. Shared usage is common between processing plants that use high-pressure steam and then forward the low-pressure steam to a hospital or college to utilize the heat rather than discharge it to the environment via a cooling tower or cooling ponds. The space that houses a small boiler within the basement of single building is usually referred to as the boiler room, as opposed to a heating plant.
The capacity and operating pressure and temperature are key design questions determined by the anticipated heat load. To avoid complete outage, a heating plant usually has two or three boilers. Steam pressures are usually limited to less than 150 psig (1035 kPa). A typical operating range is from 100 to 125 psig (690 to 862 kPa), but the most economical design will consider the higher cost of a higher pressure system versus the operating load required to heat the buildings.
A water-tube design is often used for boilers employed in heating plants. In this design, hot gases from the combustion of the fuel pass over steam-generating tubes in which water from the feedwater drum is heated to boiling. The steam rises to a steam separation drum where condensed water flows by gravity through large tubes called downcomers back to the feedwater drum to preheat that input. Additional energy is added to the steam by heating it above its boiling point by drawing steam from the steam separation drum back through the hot gas chamber one more time.
The boiler can be fueled from a variety of sources, including gas, coal, or other fossil fuel. Many renewable resources are used as well, including geothermal heat, wood, municipal waste or agricultural biomass. The energy source is selected based on availability, cost, and heat load requirements. When a high-energy fuel source is present and the heat load is relatively low, cogeneration of electricity is possible from a sidestream of steam passing through a turbine. A heating plant that is using a waste steam line from a high-pressure steam source may use a reboiler to boost the heating value of the incoming steam or may simply consist of the distribution system.