STEAM HEATING

STEAM HEATING ) What is Steam Heating a) Steam heat is similar to hot water heat except the latent heat of the steam vapor contains a larger amount of heat 1) 970 btu of latent heat in each pound of water will turn to steam at 212 degrees F. b) Steam is circulated through the system as a vapor to the steam terminal unit, where it is condensed to a liquid & returned to the boiler continue

STEAM HEATING 1) What is Steam Heating c) In a typical 1 pipe system, the boiler is below the terminal heat exchange unit & the steam supply line in pitched upward toward the boiler 1) The condensate returns down the steam line to the boiler by gravity d) In a 2 pipe system the steam vapor line is larger than the liquid condensate return line

STEAM HEATING 2) Boilers & Controls a) Gas & oil fired steam boilers are like hot water boilers 1) Electric steam boilers are typically larger than electric water boilers because of the need for a steam dome b) The low pressure steam boiler has a working pressure of 15 psig or less 1) A quick opening safety relief valve to relieve the pressure is set for 15 psig continue

STEAM HEATING 2) Boilers & Controls c) The steam boiler does not have the liquid head that the hot water boiler has in a tall building 1) When the steam condenses the pressure lowers, The higher pressure steam moves to the lower pressure therefore steam does not require a head pressure like water d) Each boiler must be equipped with a pressure gauge & pressure control for shutting off the boiler when the proper pressure is reached continue

STEAM HEATING 2) Boilers & Controls e) The pressure control & pressure gauge are installed with a trap connector between them and the boiler 1) The trap prevents raw steam from reaching the indicator mechanism a) A bourdon tube is a tube expands with pressure, used in gauges & controls 2) The connector is called a pigtail or a U-Tube a) The pig tail must be installed so that expansion & contraction will not effect the pressure controls 3) A gauge valve should be positioned in the line to allow service to the gauge continue

STEAM HEATING 2) Boilers & Controls f) Each steam system has a boiler vent that allows air to escape the boiler on start up & that breaks the vacuum when the boiler cools the room temperature a) When the boiler cools, the steam inside condenses, The condensation reduces the volume, The boiler pressure would reduce to a vacuum without a vent continue

STEAM HEATING 2) Boilers & Controls g) A gauge glass should be provided with each steam boiler so that the technician can see the boiler water level at a glance a) This glass has valves so that it can be isolated for servicing & in case of breakage b) The gauge glass can be protected by steel rods on the sides of the glass continue

STEAM HEATING 2) Boilers & Controls h) A low water fuel cutoff control is located at the water level to prevent the boiler from overheating a) Water level is critical in a steam boiler because the heat exchanger surface is just below the operating water level b) The low water cutoff is a limit switch which turns off the burner c) The low water cutoff may contain a water makeup switch that operates a solenoid to add water when the float drops d) The low water cutoff is at the water level of the boiler where light floating debris collects, this control should be blown down daily to remove any foreign particles

STEAM HEATING 3) Heating Units & Traps a) Steam terminal units receive steam vapor & condense it while adding heat to the conditioned space 1) A terminal unit can exchange heat to a hot water circuit, a steam radiator, or a forced air coil a) A hot water circuit can be heated with steam by the use of heat exchangers b) The heat exchanger will have pipes which carry steam through a tank of water continue

STEAM HEATING 3) Heating Units & Traps b) Terminal units are rated in square feet of steam 1) One square foot of steam equals 240 btu of heat per hour continue

STEAM HEATING 3) Heating Units & Traps c) There are several types of steam system condensate return methods 1) All methods return condensate to the boiler 2) Many systems have a steam trap at the heat exchanger outlet that creates a liquid seal between the vapor & the liquid parts of the system a) If raw steam is allowed to enter the liquid portion of the system, there will be no pressure difference to encourage steam to flow condensate

STEAM HEATING 3) Heating Units & Traps d) Three types of common steam traps 1) Mechanical 2) Thermostatic 3) Kinetic continue

STEAM HEATING 3) Heating Units & Traps e) The mechanical trap is either a float or an inverted bucket 1) The mechanical trap can have an additional thermostatic feature that vents trapped air to the atmosphere continue

STEAM HEATING 3) Heating Units & Traps f) The thermostatic trap is farther downstream from the terminal unit to allow the condensate to cool and thus attain a lower temperature difference than the saturated steam 1) When the thermostatic element senses condensate, it opens and allows the sub-cooled liquid to move into the condensate main until the element senses hot steam, then the trap closes continue

STEAM HEATING 3) Heating Units & Traps g) The kinetic trap has a moveable disc that allows air & condensate to pass, but not steam. It operates according to the difference between the energy of the moving steam & the energy of the moving air & liquid

STEAM HEATING 3) Heating Units & Traps h) Each trap must be able to move more condensate during a cold start up than during normal operation because a large volume of condensate develops in the cold pipes & coils when steam is first turned into the system i) Each trap has a very small bore through which the condensate passes 1) This bore must be protected with a strainer to prevent pipe scale & other foreign objects from blocking it

STEAM HEATING 4) Residential Type a) Low Pressure Gravity 1) All of the condensate returns to the boiler by its own weight

STEAM HEATING 5) Low Pressure Steam Boiler a) Operates below 15 psi, usually between 0.5 psi to 5 psi b) Low pressure boilers are used in residential heating applications because 1) Safer than high pressure systems 2) Economical 3) Less Service

STEAM HEATING 6) Steam Main a) From the Boiler 1) Minimum size 1.5 inches 2) Maximum run 25 feet b) Horizontal Runs 1) ½ inch to 1 inch pitch towards the boiler return 10 feet run c) Cast iron fittings are used

STEAM HEATING 7) Branches a) From the top of the main at a 45 degree angle 1) Never from side to side because this could create water hammer b) Cast iron fittings are used c) Full size pipe the main and then the branch is reduced d) The pitch is 1 inch per 5 feet of pipe

STEAM HEATING 8) Risers a) Risers are run vertically 1) From the branch or the main to the radiator b) The size of the risers should be no less than 1 inch 1) If the riser is to small it will cause a) Water in the radiator b) Increased friction c) Less circulation

STEAM HEATING 9) Return a) Carries condensate to the boiler b) If the return is horizontal the pitch must be towards the boiler c) Wet return 1) Water in the pipe is higher than the boiler water level d) Dry return 1) Water in the pipe is the same height as the boiler water level

STEAM HEATING 10) Hartford Loop a) Runs from the T on the boiler main to boiler return b) Return line 1) Ties in at the nipple 2 inches below the normal water line c) Keeps water level safe d) Gives longer life to the boiler

STEAM HEATING 11) Steam Piping a) One Pipe 1) Main & return piping are in the same line a) Riser comes off the main b) Condensate returns through the main 2) Size a) Main piping is larger b) Only one valve is used on the radiator 3) Radiators a) The flow end of the radiator is slightly lower