Steam and Hydronic Heating Systems

Conduction

Transfer of heat between objects that are touching.

Convection

Movement of heat from hot to cold in air or liquids.

Radiation

Transfer of heat by electromagnetic waves through space.

Steam Heating System

The boiler is located in a central plant and the steam is distributed to individual buildings of campus complexes or utility districts.

Hydronic Heating System

Hydronic heating systems consist of a boiler, fittings, accessories, hot water supply system, circulating pump, terminal devices, controls, and hot water return system.

Types of Hydronic Boilers

Steel boilers are usually welded together to form a single unit with a specific output rating.

Cast Iron Boilers

Cast iron (sectional) boilers consist of hollow sections that are bolted together, and by adding or removing sections to the boiler a required output rating is achieved.

Fire Tubes

Fire tubes hold the hot products of combustion, which heat the water that surrounds the fire tubes.

Water Tubes

Water tubes hold water heated by the hot products of combustion, which surround the water tubes.

Electric Boilers

An electric boiler is a boiler that uses heat produced by resistance heating elements to produce steam or heat water directly.

Safety Valve

The capacity of a safety valve is the amount of steam in pounds per hour (lb/hr) that the safety valve is capable of venting at rated pressure.

Safety Relief Valve

A safety relief valve is a valve on a hot water boiler that prevents excessive pressure from building up during a malfunction and is rated in Btu relieved per hour (Btu/hr).

In-Line Water Pressure-Temperature Gauge

A pressure-temperature gauge measures the pressure and temperature of boiler water at the point on the boiler where the gauge is located.

Aquastat Boiler Water Monitor

An Aquastat senses the temperature of boiler water and cycles the burners as necessary to maintain the boiler water temperature at the setpoint.

Feedwater System

The feedwater system must supply sufficient water at the proper temperature and pressure to maintain a normal operating water level (NOWL).

Normal Operating Water Level (NOWL)

Without a proper NOWL, the boiler will not maintain a proper or safe pressure or temperature.

Check Valves

Check valves allow boiler water to flow in only one direction.

Condensate Return Tank

The condensate return tank collects condensate from the terminal heating units to be returned back to the boiler.

Discharge Flow Rate

The discharge flow rate of a centrifugal feedwater pump is dependent on impeller size and speed, with the pressure rating of the pump being dependent on the number of stages.

Centrifugal Pump

A centrifugal pump contains a rotating impeller inside a cast iron or steel housing.

Pipe Mounted Circulating Pumps

Pipe mounted circulating pumps are small pumps (0 gpm to 100 gpm) that are installed in the piping of a hydronic system.

Floor Mounted Circulating Pumps

Floor mounted circulating pumps are large pumps (over 100 gpm) that must have the system piping run to the pump.

Expansion Bends

Expansion bends in steam lines allow movement created by expansion and contraction without causing damage to the steam header or branch lines.

Steam Traps

Steam traps operate automatically and are located throughout the steam system after each device where steam is used or heat is released.

Steam Strainers

Steam strainers located before steam traps must be routinely cleaned to ensure efficient removal of foreign matter from steam.

Hydronic Heating Systems

All components, piping, and terminal devices of hydronic heating systems operate while full of water. Water expands as it is heated.

Expansion Tank

An expansion tank is a device that is partially filled with air and acts as a cushion as water in the system expands.

Pressure-Reducing Valve (PRV)

A pressure-reducing valve (PRV) reduces the pressure of the makeup water to between 12 psi and 18 psi so that the boiler can use the water, or it controls the pressure of the hot water in the heating system.

Flow Control Valves

Flow control valves regulate the flow (amount) of water in a hydronic heating system.

One-Pipe Hydronic Piping System

One pipe is used to supply and return boiler water in one-pipe hydronic piping systems.

Two-Pipe Hydronic Piping System

Two separate pipes are used to supply and return boiler water in two-pipe hydronic piping systems. Most common.

Three-Pipe Hydronic Piping System

A three-pipe hydronic piping system uses two supply pipes and one return pipe.

Four-Pipe Hydronic Piping System

A four-pipe hydronic piping system uses supply and return heating piping and supply and return cooling piping. Basically 2 separate 2-pipe systems.

Radiant Heating Devices

Radiant heating devices use hot water to heat a surface to a temperature high enough for heat to flow from the surface.

Convection Heating Devices

Convection heating devices contain hot water coils that heat air as the air flows over the hot water coils.

Baseboard Convectors

Baseboard convectors are smaller than cabinet convectors and use a section of finned tube to transfer heat.

Forced Convection Heaters

Forced convection heaters contain blowers that move air. Very similar to radiant heaters but include a blower fan.

Zone Valves

Zone valves regulate the flow of water in a control zone or terminal device of a building. Controlled by the BMS.

Low-Temperature Limit Control (Freeze Stat)

A low-temperature limit control (freeze stat) is used on terminal devices that use outdoor air for ventilation to protect the devices from freezing when outdoor air temperature drops below 32°F, because water in the coil of the terminal unit may freeze.

Programmable Thermostat

The standard features of a programmable thermostat are multiple day and night setpoints for heating and cooling, deadband settings, and override capabilities.

Boiler Room Log

Most boiler manufacturers recommend that a boiler room log or record be maintained, recording daily, weekly, and monthly maintenance activities.

Boiler Inspections

Boiler Inspections made by state boiler inspector prior to occupancy of a building. Division of the State Fire Marshal's office.