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knowledge center: glossary

Boiler — A closed vessel, tank or furnace, where heat produced from the combustion of fuels such as natural gas or fuel oil is used to generate hot water or steam for applications ranging from building space heating, electric power production or industrial process heat. Some boilers can be as large as a 20-story building.

British Thermal Unit (BTU) — The standard measure of heat energy. It takes one Btu to raise the temperature of one pound of water by one degree Fahrenheit. For example, it takes about 2,000 Btus to make a pot of coffee. One Btu is equivalent to 252 calories, 778 foot-pounds, 1055 joules, and 0.293 watt-hours.

Chiller — A piece of equipment for removing heat from a gas or liquid stream for air conditioning and cooling purposes. It cools water, usually to between 40 and 50 degrees Fahrenheit for eventual use in commercial HVAC (heating, ventilating, and air conditioning) systems. The main purpose of commercial HVAC systems is to provide the people working inside buildings with "conditioned" air so that they will have a comfortable and safe work environment. "Conditioned" air means that air is clean and odor-free, and the temperature, humidity, and movement of the air are within certain comfort ranges.

Cogeneration — The use of what would be waste heat (hot stack- exhaust gasses) in an electric generating facility (power plant) that would come from the boiler or a gas turbine to produce steam for heating, hot water or air conditioning.

Combined-Cycle Power Plant — A power plant that uses two thermodynamic cycles to achieve higher overall system efficiency; e.g.: the heat from an electric generator gas-fired combustion turbine is used to generate steam to operate a steam turbine to generate additional electricity for distribution to customers.

Condensate — The liquid resulting when water vapor contacts a cool surface; also the liquid resulting when a vaporized working fluid (such as a refrigerant) is cooled. It's the water that remains when all the energy has been used up.

Condensation — The process by which water in the air changes from a vapor to a liquid due to a change in temperature or pressure; occurs when water vapor reaches its dew point (condensation point). It is the beads of water that appear on the outside of a cold glass of liquid.

District Heating/Cooling — A system in which steam or hot or chilled water is piped from a central boiler plant or electric power/heating plant to a cluster of buildings for space heating, hot water or air-conditioning.

Evaporation — The conversion of a liquid to a vapor (gas), usually by means of adding heat.

Heat Exchanger — A piece of equipment used to transfer heat from one fluid (liquid or gas) to another or when two different types of liquid (water and oil) need to be heated. For example, when steam is used to heat air for space heating.

Main — A large pipe that carries the steam, gas or water from the power plant.

Pound of Steam — One pound of water (weight) in vapor phase; it is NOT steam pressure, which is expressed as pounds per square inch (psi).

Service Line — The pipe that delivers steam, gas or water from the main to the customer.

Steam — Water in vapor form; used as the working fluid in steam turbines and heating systems.

Steam Boiler — A type of furnace in which fuel is burned and the heat is used to produce steam.

Steam Turbine — A piece of equipment that converts high-pressure steam, produced in a boiler, into mechanical energy by rotating blades in a cylinder (like a child's pinwheel toy.) The turbine then turns a generator shaft to produce electricity. It may also be used to turn a compression shaft to run a chiller in an air-conditioning system.

Steam Uses — Steam has many uses including space heating; hot water; air conditioning, sterilization of medical equipment in hospitals; humidization of art works in museums; steam tables in restaurants; laundry and dry cleaning in dry cleaning stores; etc.

Trap — A piece of equipment that removes unwanted water from the steam system; it is NOT to be confused with a sink or sewage trap.

Water Hammer — When condensate is not removed effectively from steam pipes, water hammer can result. It usually causes banging noises in the pipes and can be severe enough to destroy equipment.

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