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The
of
Steam
CHOS396 R2 (3/05-1M)©2005
ONE-PIPE STEAM SYSTEMS
ONE-PIPE STEAM SYSTEMS
A. HOW ONE-PIPE SYSTEMS WORK
1. Air movement in the system and radiatorsa) Air vent design and operationb) Main vent and riser vent installationc) Air must move out through vent for steam to enter.d) Main and riser vents must work first to provide
steam to all radiators at the same time.
2. Condensate movement in the radiatorsa) Radiator supply valvesb) The condensate must flow back through the same
valve where the steam is enteringc) One-pipe radiator valves cannot be throttled
3. Air vent shut-offa) Float prevents water from escapingb) Vent shuts off when internal element heats up
4. Dimension “A” – condensate movement and return tothe boiler in One-Pipe Systemsa) The lowest steam carrying pipe must be at least 28
inches above the normal boiler water line.
B. SYSTEM CHECKLIST
1. The system piping must provide dry steam—wet steamcauses water hammer, component damage and waterlevel problems.
2. Make sure air vents are working.a) The most important vents are the main and riser vents.b) Make sure they are working and piped to protect
them from water hammer.c) Check the radiator vents.
3. If replacing an old, large boiler, consider the need for aboiler feed system to provide the water storage neededuntil the condensate returns.
4. One-pipe gravity systems cannot be zoned with zone valves.a) When the zone valve closes, the whole pressure of
the boiler pushes back on the returns.b) This requires 30 inches of height over the water level
for every PSI at the boiler.c) Most one-pipe systems will have to be equipped
with drip traps and feed pumps to allow zoning withzone valves.
C. THE NEAR-BOILER PIPING
1. The near boiler piping is the first line of defense for areliable system.a) Correctly installed, the near boiler piping acts as a
moisture separator and boiler water level stabilizer.b) Incorrectly piped or undersized near boiler piping
will cause carryover—the system components maybe damaged and poor heat distribution and noisewill occur.
D. SIZING THE BOILER
1. The boiler output must be large enough to satisfy allconnected radiators.
2. Size the boiler by doing a radiator count, totaling all ofthe connected Square Feet.
3. Select a boiler with a Steam Net Load Rating (in squarefeed of EDR) greater than the total connected radiation.
4. If the boiler is undersized, the radiators furthest awaywill not heat.
5. If the boiler is severely oversized, the steam flow in themains will cause too much pressure drop. The water inthe returns will rise and water hammer can occur.
E. COUNTERFLOW SYSTEMS
1. Basic system piping and operationa) Condensate must flow against the flow of steamb) The boiler header must enter the top of the main on
counterflow systems.
2. Pipe sizing – one pipe counterflow systemsa) Mains are sized one size larger than they would be
for parallel flow piping. This allows room for thecondensate to flow along the bottom of the pipe.
F. PARALLEL FLOW SYSTEMS
1. One pipe parallel flow with wet returna) Operationb) Pipe Sizing
2. One pipe parallel flow with dry returna) Operationb) Pipe Sizing
3. One pipe parallel upflow systema) Operationb) Upfeed Riser and Runout pipingc) Pipe Sizing
4. One pipe parallel downflow systema) Operationb) Downfeed riser pipingc) Pipe Sizing
G. TROUBLESHOOTING
1. Water hammer on start-up
2. Water hammer during mid-cycle
3. Water hammer on shut-down
4. Hammering in the boiler
ONE-PIPE STEAM SYSTEMS
ONE-PIPE STEAM SYSTEMS
1
AIR VENTTYPICAL
Excerpt: “Hoffman Steam Heating Systems”, ITT
Seat
Float
Float Support
2
A. HOW ONE-PIPE SYSTEMS WORK
A. HOW ONE-PIPE SYSTEMS WORK
Figure 1: Air Vent Construction
The float prevents water from escaping. The float can be damaged by water hammer, preventing the ventfrom operating correctly. The thermal element expands when heated to close off the vent.
3
Figure 2: Explanation of Air Vent Ratings
Note that it is important for the boiler cut-out pressure to be lower than the Drop-Out pressure of thevents on the system. Otherwise, they cannot function after the initial cycle. The pressure in the systemwould keep them closed.
A. HOW ONE-PIPE SYSTEMS WORK
4
Figure 3: Selection and Application of Vents
Use adjustable vents when you want proportional venting. The larger the radiator, the larger the ventopening. This way each radiator heats in proportion to its size as intended.
A. HOW ONE-PIPE SYSTEMS WORK
5
A. HOW ONE-PIPE SYSTEMS WORK
Figure 4: Main Vent Installation
You will often find the main vent piped as shown on the right. This allows water hammer at the end ofthe main to slam into the vent. The float will quickly collapse, causing the vent to fail in the closed position.
Pipe the Main Vent as shown on the left. This protects the vent from the hammer at the end of the mainand provides an air cushion against the shock.
If the main vent doesn’t work, the radiator vents must remove the air from the system piping. This willcause the closest radiators to heat first and the furthest radiators may not heat at all when the thermostatshuts down the boiler.
The Main Vent (and Riser Vents) is the heart of a one-pipe system. It must work to provide uniform heatin the building by removing the air from the steam distribution piping. When it works, all the radiatorsreceive steam at the same time.
Wet Return
Water Line
Hartford Loop
Air
Air
Water
MainVent
Air Air
OFF CYCLEVents serve as vacuum breakers. When steamcondenses, it causes a vacuum. The vents let airback in to fill the void.
The system fills with air.
The water level in the return finds the same level asthe boiler since there is no pressure difference in thepiping.
AirAir
Air
Burner Off
6
A. HOW ONE-PIPE SYSTEMS WORK
Figure 5: Stand-by Conditions in the System
At the end of each heating cycle, the thermostat shuts off the boiler. With no steam being supplied, thesteam in the system condenses and creates a vacuum. This vacuum causes air to be pulled in through thevents until the system fills with air.
Wet Return
MainVent
Water Line
Hartford Loop
Air
Water
AirAir
Air
Air Air
Steam
Boiler fires.
Water boils in boiler, creating steam. Surface level risesslightly because the steam bubbles displace water.
Pressure pushes air out through Main andRadiator vents.
Water begins to back up in the return riser becauseflow causes pressure drop in piping. So pressure islower at end of piping than at boiler.
Pressure builds in system as steam pushes on the air.
THERMOSTAT CALLS FOR HEAT
7
A. HOW ONE-PIPE SYSTEMS WORK
Figure 6: Call for Heat
The thermostat closes, the boiler fires and the cycle begins.
Wet Return
MainVent(Closed)
Water Line
Hartford LoopWater
AirAir
Air Air
Steam
Steam
When the Main Vent works right it exhausts air quickly from the steam piping. So all branch linesreceive steam at about the same time. This makes heating uniform throughout the building. If themain vent doesn't work, the first radiators get steam first, causing poor heat distribution. The Mainvent closes as steam reaches it.
Radiator vents are smaller. They must vent slowly tomatch the radiation. If they vent too quickly,condensate will back up in the radiator and causewater hammer.
Water backs up higher in the return as the pressuredifference from beginning to end of piping increaseswith flow and condensate begins to form.
The radiator vents continue to vent air as steampushes up toward the radiators.
THE MAIN VENT
8
A. HOW ONE-PIPE SYSTEMS WORK
Figure 7: Importance of the Main Vent
The Main Vent must quickly evacuate all air from the steam piping. This way all branches receive steamat about the same time. And the building will heat evenly.
Wet Return
MainVent
(Closed)
Water Line
Hartford Loop
Steam Steam
Condensate Condensate
Air Air
SteamCondensate
AirAir
Water
Steam
Steam pushes into the radiators. The radiators cool the steam. Steam begins tocondense. The radiators begin to heat up and give off heat to the room as the steamgives off 970 BTU per pound in condensing.
Condensate starts to build up in the bottoms of theradiators and flow out through the radiator valves.
The heavy start-up condensate load adds to thepressure difference, raising the water level in thereturn to its highest point during the heating cycle.
Condensate runs down the branch piping to the main,flowing against the steam coming up the branches.
HEATING BEGINS IN RADIATORS
Boiler water level slightly lower because water hasbeen steamed off and condensate has notreturned yet.
9
A. HOW ONE-PIPE SYSTEMS WORK
Figure 8: Heating Begins in the Radiators
When steam pushes into the radiators it starts to condense and heat the radiators. The radiators begin togive off this heat.
Wet Return
MainVent
(Closed)
Water Line
Hartford Loop
SteamSteam
Condensate Condensate
Air Air
SteamCondensate
VentClosed
VentClosed
Water
Steam
Steam
Steam fills radiators until it reaches the radiator vents.
The radiator vents close when exposed to thesteam temperature.
The riser level drops as the start-up condensateload passes back to the boiler. The steady level isjust enough to overcome the pressure loss throughthe steam piping and return piping.
The boiler continues to fire, providing steam to thesystem, until the thermosat is satisfied.
STEADY STATE HEATING
Boiler water level is lower because of condensateout in the system. In some cases the water levelmay go out of the gauge glass when the boilershuts down. This is because the steam bubblesin the boiler collapse, so the surface level drops.And the condensate has not returned fromthe system.
10
A. HOW ONE-PIPE SYSTEMS WORK
Figure 9: Steady State Heating Conditions
The steam has pushed into the radiators and reached the radiator vents. They shut off when exposed tothe steam temperature. The heating cycle continues until the thermostat shuts off the boiler.
STEAM SYSTEM OPERATION
CYCLE START – AIR IN RADIATORSTEAM AT RADIATOR INLET
11
A. HOW ONE-PIPE SYSTEMS WORK
Figure 10: Radiator at Start of Cycle
Radiator is full of air.
If Main Vent works, all radiators receive steam at the same time.
STEAM SYSTEM OPERATIONAIR VENT ALLOWS AIR TO
BE PUSHED OUT BY THE STEAMCONDENSATE STARTS TO FORM
RADIATOR BEGINS TO BE WARMEDBY CONDENSING STEAM
12
A. HOW ONE-PIPE SYSTEMS WORK
Figure 11: Radiator Begins to Receive Steam
If Radiator Vent works, the steam pressure pushes air out through the vent, allowing steam to enter.Condensate begins to form and roll back through the radiator valve.
STEAM SYSTEM OPERATIONAIR VENT CLOSES
AS STEAM REACHES VENTCONDENSATE LOAD INCREASED
13
A. HOW ONE-PIPE SYSTEMS WORK
Figure 12: Steam Reaches the Air Vent
The vent closes as its element is heated and expanded by the steam temperature.
Excerpt: “Hoffman Steam Heating Systems”, ITT
RADIATOR SUPPLY VALVECANNOT BE USED
TO CONTROL FLOW
Partially closedvalve restrictscondensate
Valve must bekept fully openwhen in use
14
A. HOW ONE-PIPE SYSTEMS WORK
Figure 13: Radiator Supply Valve – One-Pipe Radiators
Do not throttle the valve. This will restrict condensate flow and cause hammer in the radiator.
28" A
Note: Return line loss includes safety factor
DIMENSION "A"GRAVITY RETURN
SYSTEMS
15
A. HOW ONE-PIPE SYSTEMS WORK
Figure 14: Gravity Return Systems – Dimension “A”
The only way water can be pushed back into the boiler is for the return water to raise to a height highenough to overcome the line losses and the difference in pressure between the boiler and the end of themain. Allow 28 inches as shown for most existing gravity systems.
DIMENSION "A"GRAVITY RETURN
SYSTEMS
Steam PipingPressure Drop
Wet ReturnPressure Drop
Wet Return PressureDrop Safety Factor
Overall SafetyFactor
Start-up CondensateAllowance
Over 100 MBH Under 100 MBH
14"
4"
2"
–
8"
28"
3.5"
3.5"
–
7"
–
14"TOTALS
System Size
16
A. HOW ONE-PIPE SYSTEMS WORK
Figure 15: Dimension “A” – Adding Up the Drops
Most gravity systems were piped for a 1/2 psig (14 inches) drop through the main. If the drop is higher,increase the 28" minimum. If the pipe insulation has been removed and not replaced, increase the 8"start-up condensate allowance.
⌧ THE SYSTEM
1. The system must provide dry steam for performanceand system component life.
2. Wet steam will cause water hammer, resulting in damageto vent valves or anything else in the way.
3. Water carryover to the system will cause the boiler waterlevel to drop too quickly. This will cause overfilling andflooding.
⌧ CHECK DIMENSION “A”
4. Make sure the lowest steam carrying pipe (or dry return)is at least 28 inches above the normal boiler water line.If the piping pressure drop is more than 1/2 psig,increase this minimum as needed.
5. Dimension “A” may have been correct at one time, butit could have changed if the piping was modified overthe years.
6. The new boiler water line may not be the same as theold boiler. If the new water line is higher, be very carefulthat you still have the 28 inches minimum to any steamcarrying pipe or dry return.
⌧ CHECK ALL AIR VENTS
7. Make sure all main and riser vents and all radiator ventsare working.
8. Make sure the main vent is piped correctly.
⌧ COMPARE NEW BOILER TO OLD
9. If you are replacing an old, large boiler, you may needto install a boiler feed system to provide the storageneeded.a) The old, large boilers had more water content. So
they could steam longer before they needed wateradded.
b) New, high efficiency boilers don’t have as muchwater content. So they can usually only steam forabout 15 minutes before they drop to the low waterpoint.
c) A boiler feed system tank holds enough water toallow a long time for condensate to come back. Itcan supply water to the boiler when needed whilethe condensate makes its rounds in the system.
⌧ BE CAREFUL WHEN ZONING
10. Gravity return systems usually don’t have enough heightfrom the boiler to the lowest steam carrying pipe toprovide 30 inches for every psi pressure at the boiler.a) One-pipe systems should operate around 2 psig at
the boiler. This would be 60 inches (5 feet) ofpressure applied on the returns when a zone valve isclosed.
11. If you are installing zone valves, you will probably haveto also install a boiler feed system or condensatereceiver system and install drip traps on the main andreturn risers. The system will no longer be gravity return.
⌧ CHECK THE SYSTEM HISTORY
12. Ask the owner and maintenance personnel about anyproblems the system had before. This will give you agood lead on repairs or replacements that may beneeded.
⌧ CHECK ALL THE PIPING
13. Make sure the wet returns are not plugged or leaking. Ifthere are signs that the old boiler used a lot of make-upwater it could be that the wet return is leaking. Replacethe wet returns.
14. Make sure all pipes are sloped in the right direction. Ifthey are pitched the wrong way or sagging, hammer willoccur.
15. If additional heated space has been added to thebuilding, make sure the pipes are large enough for theconnected radiation.
17
B. SYSTEM CHECKLIST
B. SYSTEM CHECKLIST
DIMENSION "B"GRAVITY RETURN
SYSTEMS
Boiler pressure acts on water in returns
Water Line
Pressure = 0 when valve closes
30" per PSIat Boiler
Zone Valve
Returns
Steam Supplies
B
18
B. SYSTEM CHECKLIST
Figure 16: Dimension “B” – Result of Zone Valve or Trap on Gravity System
When the zone valve closes, all of the boiler pressure pushes back on the returns. This raises the waterlevel in the returns above the boiler water level 30 inches for every psi pressure at the boiler. This will usually require the addition of drip traps and a feed system.
2" SkimConnection
SteamSupply
Offset Header Required to Prevent Damageto Boiler From Expansion of Header
NEAR-BOILER PIPING
Return
19
C. THE NEAR-BOILER PIPING
Figure 17: Typical Near-Boiler Piping
C. THE NEAR-BOILER PIPING
1. Follow the boiler manufacturer’s guidelines on near-boiler piping and pipe sizing.
2. Pay special attention to the number and location ofrisers off of the boiler.
3. Too few risers or risers in the wrong locations can causea sloped water line in the boiler and/or heavy carryoverto the system.a) Sloped water line can actually result in dry firing
some sections of the boiler and result in severedamage.
HEADER CONNECTIONSFOR MULTIPLE BOILER RISERS
RIGHT
EQU
ALI
ZER
WRONGEQ
UA
LIZE
R
Water separates fromthe steam when it turnsup into the take-off.
Water pools under thetake-off, causing heavycarryover to the system.
20
C. THE NEAR-BOILER PIPING
Figure 18: Correct Piping of Steam Take-Off from Boiler Header
SIZE
TH
E BO
ILER
TO H
AN
DLE
TH
E RA
DIA
TIO
N
Height 1 Column 2 Column 3 Column 4 Column 5 Column14" 4.0017" 4.0018" 2.25 3.00 5.0020" 1.50 2.00 5.0022" 3.00 4.00 6.0023" 1.67 2.3326" 2.00 2.67 3.75 5.0032" 2.50 3.33 4.50 6.5038" 3.00 4.00 5.00 8.0044" 10.0045" 5.00 6.00
RATING – Square Feet per SectionCOLUMN RADIATION
RATING – Square Feet per SectionTUBULAR RADIATION
Height 3 Tube 4 Tube 5 Tube 6 Tube 7 Tube14" 2.6717" 3.2520" 1.75 2.25 2.67 3.00 3.6723" 2.00 2.50 3.00 3.5026" 2.33 2.75 3.50 4.00 4.7532" 3.00 3.50 4.33 5.00 5.5038" 3.50 4.25 5.00 6.00 6.75
RADIANT CONVECTORWidth Height
Square FeetPer Section
5" 20" 2.257 1/2" 20" 3.40
CAST IRON BASEBOARDWidth Height
Square FeetPer Linear Foot
2 1/2" 10" 3.40
21
D. SIZING THE BOILER
Figure 19: Select a Boiler with a Net Load Rating Greater Than the Total Connected Radiation
D. SIZING THE BOILER
Pitch up1" per 10 ft
Water Line
MainVent
A
Maximum Header Length 100 ft
Steam main feeds steam to system and condensate back to boiler. Condensate flowsagainst the steam in the main.
The main pitches upward away from the boiler twice as much as a parallel flowsystem.
The boiler header must enter the top of the main, unlike parallel flowsystems, where the main feeds off the top of the boiler header.
Note that Dimension “A” is at the lowest point ofthe steam main as shown. But Dimension “A”doesn't have to be 28 inches for counterflowsystems. There is almost no pressure drop from theboiler to the point of condensate return. The onlyloss is the piping loss for the condensate.
No return riser is used since the condensate feeds back to the equalizer pipe.No Hartford Loop is needed since the return is above the water line.
ONE-PIPE COUNTERFLOW SYSTEM
Steam
Condensate
22
E. COUNTERFLOW SYSTEMS
Figure 20: Schematic Piping – Typical Counterflow System in Operation
E. COUNTERFLOW SYSTEMS
PIPE SIZING – ONE-PIPECOUNTERFLOW SYSTEMS
STEAM SUPPLY SIZING - ONE PIPE COUNTERFLOW MAINPITCHED MINIMUM 1 INCH PER 10 FEET
Pipe Size Square Ft EDR Btu/Hr Net Pounds/Hr2 1/2" 386 92,640 97
3" 635 152,400 1594" 1,163 279,120 2915" 2,457 589,680 6146" 4,546 1,091,040 1,137
Note: Pipe capacities based on recommended increase one pipe size for counterflow one-pipe mains
RUNOUT SIZING FOR RUNOUTS UNDER 8 FEET(ADD ONE PIPE SIZE FOR LONGER RUNOUTS
Pipe Size Square Ft EDR Btu/Hr Net Pounds/Hr1" 28 6,720 7
1 1/4" 64 15,360 161 1/2" 64 15,360 16
2" 92 22,080 232 1/2" 168 40,320 42
3" 260 62,400 65
RADIATOR SUPPLY VALVES AND VERTICAL CONNECTORSPipe Size Square Ft EDR Btu/Hr Net Pounds/Hr
1" 28 6,720 71 1/4" 64 15,360 161 1/2" 92 22,080 23
2" 168 40,320 42
BOILER EQUALIZER CONNECTIONPipe Size Square Ft EDR Btu/Hr Net Pounds/Hr
1 1/2" 900 216,000 2252 1/2" 6,400 1,536,000 1,600
)
23
E. COUNTERFLOW SYSTEMS
Figure 21: Minimum Pipe Sizes – One-Pipe Counterflow Systems
Use this chart to compare the size of existing piping and to determine sizing of lines for added zones andbranches.
Steam main feeds steam to system and condensate to Return.Condensate flows with the steam in the main.
The main pitches downward away from the boiler atleast 1 inch per 20 feet.
Dimension “A” must be 28 inches for mostsystems. Check the main and return sizes againstthe chart to be sure this is enough.
The return riser feeds condensate to the wetreturn.
Wet Return
MainVent
Water Line
Hartford Loop
Steam
CondensateCondensate
SteamCondensate
RadiatorVent
RadiatorVent
Water
Steam
Steam
ONE-PIPE PARALLEL SYSTEMwith WET RETURN
Pitch down1" per 20 ft
A
24
F. PARALLEL FLOW SYSTEMS
Figure 22: Schematic Piping – One-Pipe Parallel Flow System with Wet Return
F. PARALLEL FLOW SYSTEMS
PIPE SIZING – ONE-PIPEPARALLEL FLOW SYSTEM
WITH WET RETURN
RADIATOR RUNOUT SIZING FOR RUNOUTS UNDER 8 FEET(ADD ONE PIPE SIZE FOR LONGER RUNOUTS
Pipe Size Square Ft EDR Btu/Hr Net Pounds/Hr1" 28 6,720 7
1 1/4" 64 15,360 161 1/2" 64 15,360 16
2" 92 22,080 232 1/2" 168 40,320 42
3" 260 62,400 65
RADIATOR SUPPLY VALVES AND VERTICAL CONNECTORSPipe Size Square Ft EDR Btu/Hr Net Pounds/Hr
1" 28 6,720 71 1/4" 64 15,360 161 1/2" 92 22,080 23
2" 168 40,320 42
W ET RETURN SIZINGPipe Size Square Ft EDR Btu/Hr Net Pounds/Hr
1" 700 168,000 1751 1/4" 1,200 288,000 3001 1/2" 1,900 456,000 475
2" 4,000 960,000 1,000
BOILER EQUALIZER CONNECTIONPipe Size Square Ft EDR Btu/Hr Net Pounds/Hr
1 1/2" 900 216,000 2252 1/2" 6,400 1,536,000 1,600
STEAM SUPPLY SIZING - ONE PIPE PARALLEL FLOW MAINPITCHED MINIMUM 1/2 INCH PER 10 FEET
Pipe Size Square Ft EDR Btu/Hr Net Pounds/Hr2" 386 92,640 97
2 1/2" 635 152,400 1593" 1,163 279,120 2914" 2,457 589,680 6145" 4,546 1,091,040 1,1376" 7,642 1,834,080 1,911
)
25
F. PARALLEL FLOW SYSTEMS
Figure 23: Minimum Pipe Sizes – One-Pipe Parallel Flow System with Wet Return
Use this chart to compare the size of existing piping and to determine sizing of lines for added zones andbranches.
Steam main feeds steam to system and condensate to Return.Condensate flows with the steam in the main.
The main and dry return pitch downward away fromthe boiler at least 1 inch per 20 feet.
Dimension “A” must be 28 inches for mostsystems. Check the main and return sizes againstthe chart to be sure this is enough.
The dry return feeds condensate to the return riser.Locate the Main Vent near the end of the dry return.
Wet Return
Dry Return
MainVent
Water Line
Steam
CondensateCondensate
SteamCondensate
RadiatorVent
RadiatorVent
Water
Steam
Steam
ONE-PIPE PARALLEL SYSTEMwith DRY RETURN
Pitch down1" per 20 ft
A
Hartford Loop
26
F. PARALLEL FLOW SYSTEMS
Figure 24: Schematic Piping – One-Pipe Parallel Flow System with Dry Return
PIPE SIZING – ONE-PIPEPARALLEL FLOW SYSTEM
WITH DRY RETURN
R A D IA T O R R U N O U T S IZ IN G F O R R U N O U T S U N D E R 8 F E E T(A D D O N E P IP E S IZ E F O R L O N G E R R U N O U T S
P ip e S iz e S q u a re F t E D R B tu / H r N e t P o u n d s / H r1 " 2 8 6 ,7 2 0 7
1 1 / 4 " 6 4 1 5 ,3 6 0 1 61 1 / 2 " 6 4 1 5 ,3 6 0 1 6
2 " 9 2 2 2 ,0 8 0 2 32 1 / 2 " 1 6 8 4 0 ,3 2 0 4 2
3 " 2 6 0 6 2 ,4 0 0 6 5
R A D IA T O R S U P P L Y V A L V E S A N D V E R T IC A L C O N N E C T O R SP ip e S iz e S q u a re F t E D R B tu / H r N e t P o u n d s / H r
1 " 2 8 6 ,7 2 0 71 1 / 4 " 6 4 1 5 ,3 6 0 1 61 1 / 2 " 9 2 2 2 ,0 8 0 2 3
2 " 1 6 8 4 0 ,3 2 0 4 2
D R Y R E T U R N S IZ IN GP ip e S iz e S q u a re F t E D R B tu / H r N e t P o u n d s / H r
1 " 3 2 0 7 6 ,8 0 0 8 01 1 / 4 " 6 7 2 1 6 1 ,2 8 0 1 6 81 1 / 2 " 1 ,0 6 0 2 5 4 ,4 0 0 2 6 5
2 " 2 ,3 0 0 5 5 2 ,0 0 0 5 7 5
W E T R E T U R N S IZ IN GP ip e S iz e S q u a re F t E D R B tu / H r N e t P o u n d s / H r
1 " 7 0 0 1 6 8 ,0 0 0 1 7 51 1 / 4 " 1 ,2 0 0 2 8 8 ,0 0 0 3 0 01 1 / 2 " 1 ,9 0 0 4 5 6 ,0 0 0 4 7 5
2 " 4 ,0 0 0 9 6 0 ,0 0 0 1 ,0 0 0
B O IL E R E Q U A L IZ E R C O N N E C T IO NP ip e S iz e S q u a re F t E D R B tu / H r N e t P o u n d s / H r
1 1 / 2 " 9 0 0 2 1 6 ,0 0 0 2 2 52 1 / 2 " 6 ,4 0 0 1 ,5 3 6 ,0 0 0 1 ,6 0 0
S TEA M S U PPLY S IZ IN G - O N E PIPE PA R A LLEL FLO W M A INPITC H ED M IN IM U M 1/2 IN C H PER 10 FEET
Pipe S ize S quare Ft ED R B tu/H r N et Pounds/H r2" 386 92 ,640 97
2 1/2" 635 152 ,400 1593" 1 ,163 279 ,120 2914" 2 ,457 589 ,680 6145" 4 ,546 1 ,091 ,040 1 ,1376" 7 ,642 1 ,834 ,080 1 ,911
)
27
F. PARALLEL FLOW SYSTEMS
Figure 25: Minimum Pipe Sizes – One-Pipe Parallel Flow System with Dry Return
Use this chart to compare the size of existing piping and to determine sizing of lines for added zones andbranches.
Boiler Water Line
Wet Return
HartfordLoop
RiserDripped
Riser NotDripped
RiserDrip
DirtPocket
Give good pitchto long feeds
RadiatorVent
RadiatorVent
RadiatorVent
MainVent
MainVent
MainVent
SupplyMain
Steam main feeds steam to Upfeed Risers and Branches. Main and dripped risers feed condensate toreturns.
The main pitches downward away from the boiler at least 1 inch per 20 feet. Note that dripped riserconnections pitch down from the main. Undripped riser connections pitch upward from the main.
Dimension “A” must be 28 inches for most systems. Check the main and return sizes against the chart tobe sure this is enough. The lowest steam carrying pipe, either a main or a riser or branch line, determinesthe smallest Dimension “A”.
Provide a Main Vent at the top of each riserand at the end of the steam main.
ONE-PIPE PARALLEL UPFEED SYSTEM
A
A
28
F. PARALLEL FLOW SYSTEMS
Figure 26: Schematic Piping – One-Pipe Parallel Upfeed System
Steam feeds up the risers to the radiation. Condensate flows down the risers to the main or to drip legs asshown.
29
F. PARALLEL FLOW SYSTEMS
Figure 27: Minimum Pipe Sizes – One-Pipe Parallel Upfeed System
Use this chart to compare the size of existing piping and to determine sizing of lines for added zones andbranches.
UP-FEED RISER SIZINGPipe Size Square Ft EDR Btu/Hr Net Pounds/Hr
1" 45 10,800 111 1/4" 98 23,520 251 1/2" 152 36,480 38
2" 288 69,120 722 1/2" 484 116,160 121
3" 800 192,000 2004" 1,520 364,800 380
UP-FEED RISER DRIP SIZING
Riser Size Drip to Wet ReturnDrip to Dry Return(With Loop Seal)
1" 3/4" 3/4"1 1/4" 3/4" 3/4"1 1/2" 3/4" 1"
2" 1" 1"2 1/2" 1" 1"
3" 1" 1"
WET RETURN SIZINGPipe Size Square Ft EDR Btu/Hr Net Pounds/Hr
1" 700 168,000 1751 1/4" 1,200 288,000 3001 1/2" 1,900 456,000 475
2" 4,000 960,000 1,000
DRY RETURN SIZINGPipe Size Square Ft EDR Btu/Hr Net Pounds/Hr
1" 320 76,800 801 1/4" 672 161,280 1681 1/2" 1,060 254,400 265
2" 2,300 552,000 575
RADIATOR SUPPLY VALVES AND VERTICAL CONNECTORSPipe Size Square Ft EDR Btu/Hr Net Pounds/Hr
1" 28 6,720 71 1/4" 64 15,360 161 1/2" 92 22,080 23
2" 168 40,320 42
BOILER EQUALIZER CONNECTIONPipe Size Square Ft EDR Btu/Hr Net 672Pounds/Hr
1 1/2" 900 216,000 2252 1/2" 6,400 1,536,000 1,600
PIPE SIZING – ONE-PIPEPARALLEL UP-FLOW SYSTEM
STEAM SUPPLY SIZING - ONE PIPE PARALLEL FLOW MAINPITCHED MINIMUM 1/2 INCH PER 10 FEET
Pipe Size Square Ft EDR Btu/Hr Net Pounds/Hr2" 386 92,640 97
2 1/2" 635 152,400 1593" 1,163 279,120 2914" 2,457 589,680 6145" 4,546 1,091,040 1,1376" 7,642 1,834,080 1,911
UPFEED RISER RUNOUT SIZING WHEN RISER IS DRIPPED
RUNOUT SLOPED DOWN 1/2" PER 10 FTPipe Size Square Ft EDR Btu/Hr Net Pounds/Hr
1" 68 16,320 171 1/4" 144 34,560 361 1/2" 224 53,760 56
2" 432 103,680 1082 1/2" 696 167,040 174
UPFEED RISER RUNOUT SIZINGWHEN RISER IS NOT DRIPPED
RUNOUT SLOPED UP 1/2" PER 10 FTPipe Size Square Ft EDR Btu/Hr Net Pounds/Hr
1" 28 6,720 71 1/4" 55 13,200 141 1/2" 81 19,440 20
2" 165 39,600 412 1/2" 260 62,400 65
RADIATOR RUNOUT SIZING FOR RUNOUTS UNDER 8 FEET(ADD ONE PIPE SIZE FOR LONGER RUNOUTS)
Pipe Size Square Ft EDR Btu/Hr Net Pounds/Hr1" 28 6,720 7
1 1/4" 64 15,360 161 1/2" 64 15,360 16
2" 92 22,080 232 1/2" 168 40,320 42
3" 260 62,400 65
Up-Feed Riser
3 Ft ApproximatelySteam Main
Pitch 1/2" per Foot&
Increase Pipe One Size
UP-FEED RUNOUTWHEN NOT DRIPPED
One size larger than riser
30
F. PARALLEL FLOW SYSTEMS
Figure 28: Upfeed Riser and Runout When Not Dripped
UP-FEED RISERWITH DRIP LINE
Wet Return
Elevation End View
Up-Feed Riser
Steam Main
Pitch 1/2" per 10 ft
31
F. PARALLEL FLOW SYSTEMS
Figure 29: Upfeed Riser Connection When Dripped to Wet Return
UP-FEED BRANCHCONNECTION (NOT DRIPPED)
Elevation End View
Up-Feed Riser
Steam Main
Pitch 1/2" per 10 ft
32
F. PARALLEL FLOW SYSTEMS
Figure 30: Upfeed Branch Connection When Not Dripped
Elevation End View
Steam Main
Down-Feed Riser
Pitch 1/2" per 10 ft
RUNOUT TODOWN-FEED RISER
33
F. PARALLEL FLOW SYSTEMS
Figure 31: Downfeed Riser Connection to Steam Main
Boiler Water Line
Wet Return
HartfordLoop
RiserDripped
RiserDrip
DirtPocket
Give good pitchto long feeds
RadiatorVent
RadiatorVent
RadiatorVent
MainVent
MainVent
MainVent
MainVent
ExpressSteam Supply
Riser
Express Steam Riser feeds top floor steam main. Steam main feeds steam to Downfeed Risers andBranches. Main and dripped risers feed condensate to returns.
The main pitches downward away from the boiler at least 1 inch per 20 feet. Note that dripped riserconnections pitch down from the main. Undripped riser connections pitch upward from the main.
Dimension “A” must be 28 inches for most systems. Check the main and return sizes against the chart to be surethis is enough. The lowest steam carrying pipe, either a main or a riser or branch line, determines the smallestDimension “A”.
Provide a Main Vent at the top of each riser and just above the lowest branch oneach of the Downfeed Risers.
ONE-PIPE PARALLEL DOWNFEED SYSTEM
A A
A
34
F. PARALLEL FLOW SYSTEMS
Figure 32: Schematic Piping – One-Pipe Parallel Downfeed System
The main advantage of this system is that the condensate flows in the same direction as the steam in all ofthe downfeed risers.
PIPE SIZING – ONE-PIPEPARALLEL FLOW DOWN FEED SYSTEM
S T E A M S U P P L Y S I Z I N G - O N E P I P E P A R A L L E L F L O W M A I NP I T C H E D M I N I M U M 1 / 2 I N C H P E R 1 0 F E E T
P i p e S i z e S q u a r e F t E D R B t u / H r N e t P o u n d s / H r2 " 3 8 6 9 2 , 6 4 0 9 7
2 1 / 2 " 6 3 5 1 5 2 , 4 0 0 1 5 93 " 1 , 1 6 3 2 7 9 , 1 2 0 2 9 14 " 2 , 4 5 7 5 8 9 , 6 8 0 6 1 45 " 4 , 5 4 6 1 , 0 9 1 , 0 4 0 1 , 1 3 76 " 7 , 6 4 2 1 , 8 3 4 , 0 8 0 1 , 9 1 1
E X P R E S S R I S E R S I Z I N G - P A R A L L E L D O W N F E E D S Y S T E MP i p e S i z e S q u a r e F t E D R B t u / H r N e t P o u n d s / H r
2 1 / 2 " 6 3 6 1 5 2 , 6 4 0 1 5 93 " 1 , 1 2 8 2 7 0 , 7 2 0 2 8 2
3 1 / 2 " 1 , 5 4 8 3 7 1 , 5 2 0 3 8 74 " 2 , 0 4 4 4 9 0 , 5 6 0 5 1 15 " 4 , 2 0 0 1 , 0 0 8 , 0 0 0 1 , 0 5 06 " 7 , 2 0 0 1 , 7 2 8 , 0 0 0 1 , 8 0 08 " 1 5 , 0 0 0 3 , 6 0 0 , 0 0 0 3 , 7 5 0
D O W N - F E E D R I S E R S & B R A N C H E S T O D O W N F E E D R I S E R SP i p e S i z e S q u a r e F t E D R B t u / H r N e t P o u n d s / H r
1 " 6 8 1 6 , 3 2 0 1 71 1 / 4 " 1 4 4 3 4 , 5 6 0 3 61 1 / 2 " 2 2 4 5 3 , 7 6 0 5 6
2 " 4 3 2 1 0 3 , 6 8 0 1 0 82 1 / 2 " 6 9 6 1 6 7 , 0 4 0 1 7 4
3 " 1 , 2 7 2 3 0 5 , 2 8 0 3 1 83 1 / 2 " 1 , 8 4 8 4 4 3 , 5 2 0 4 6 2
4 " 2 , 5 6 0 6 1 4 , 4 0 0 6 4 0
R A D I A T O R R U N O U T S I Z I N G F O R R U N O U T S U N D E R 8 F E E T( A D D O N E P I P E S I Z E F O R L O N G E R R U N O U T S
P i p e S i z e S q u a r e F t E D R B t u / H r N e t P o u n d s / H r1 " 2 8 6 , 7 2 0 7
1 1 / 4 " 6 4 1 5 , 3 6 0 1 61 1 / 2 " 6 4 1 5 , 3 6 0 1 6
2 " 9 2 2 2 , 0 8 0 2 32 1 / 2 " 1 6 8 4 0 , 3 2 0 4 2
3 " 2 6 0 6 2 , 4 0 0 6 5W E T R E T U R N S I Z I N G
P i p e S i z e S q u a r e F t E D R B t u / H r N e t P o u n d s / H r1 " 7 0 0 1 6 8 , 0 0 0 1 7 5
1 1 / 4 " 1 , 2 0 0 2 8 8 , 0 0 0 3 0 01 1 / 2 " 1 , 9 0 0 4 5 6 , 0 0 0 4 7 5
2 " 4 , 0 0 0 9 6 0 , 0 0 0 1 , 0 0 0
R A D I A T O R S U P P L Y V A L V E S A N D V E R T I C A L C O N N E C T O R SP i p e S i z e S q u a r e F t E D R B t u / H r N e t P o u n d s / H r
1 " 2 8 6 , 7 2 0 71 1 / 4 " 6 4 1 5 , 3 6 0 1 61 1 / 2 " 9 2 2 2 , 0 8 0 2 3
2 " 1 6 8 4 0 , 3 2 0 4 2
B O I L E R E Q U A L I Z E R C O N N E C T I O NP i p e S i z e S q u a r e F t E D R B t u / H r N e t P o u n d s / H r
1 1 / 2 " 9 0 0 2 1 6 , 0 0 0 2 2 52 1 / 2 " 6 , 4 0 0 1 , 5 3 6 , 0 0 0 1 , 6 0 0
)
35
F. PARALLEL FLOW SYSTEMS
Figure 33: Minimum Pipe Sizes – One-Pipe Parallel Downfeed System
Use this chart to compare the size of existing piping and to determine sizing of lines for added zones andbranches.
TROUBLESHOOTINGWATER HAMMER ON START-UP
TROUBLESHOOTINGWATER HAMMER ON START-UP
LOOK FOR SAGS IN STEAM MAINAND DRY RETURN PIPING, WHEREWATER CAN POCKET.
LOOK FOR CONCENTRIC REDUCERWHICH WOULD CAUSE WATER TOPOCKET.
CHECK FOR LONG STEAM MAINSWITH NO DRIP LINES.
CHECK DIMENSION "A". IF THEBOILER WATER LEVEL IS TOO HIGH,DRY RETURNS MAY NOW BE WET.
37
G. TROUBLESHOOTING
Figure 35: Troubleshooting Water Hammer Which Occurs Shortly After Start-up
TROUBLESHOOTINGWATER HAMMER IN MID-CYCLE
TROUBLESHOOTINGWATER HAMMER IN MID-CYCLE
WET RETURN LINES MAY BECLOGGED, CAUSING CONDENSATETO BACK UP INTO STEAM PIPING.
DIRTY BOILER WATER OR WRONGNEAR-BOILER PIPING COULD BECAUSING WET STEAM.
THE BOILER MAY BE OVERSIZED OROVERFIRED. THIS CAUSES TOOMUCH PRESSURE DROP IN MAIN, SOCONDENSATE BACKS UP IN RISER.
38
G. TROUBLESHOOTING
Figure 36: Troubleshooting Water Hammer Which Occurs During Mid-Cycle
TROUBLESHOOTINGWATER HAMMER IN MID-CYCLE
TROUBLESHOOTINGWATER HAMMER IN MID-CYCLE
CHECK THE HARTFORD LOOP. THENIPPLE MAY BE TOO LONG. ONLYUSE A CLOSE NIPPLE.
MAKE SURE THE STEAM PIPING ISINSULATED. IF INSULATION HASBEEN REMOVED, TOO MUCH PIPINGCONDENSATE WILL RESULT ANDCAUSE CONDENSATE TO BUILD UPIN THE PIPING.
HartfordLoop
Use closenipple only
RADIATOR VENTS MAY BE TOOQUICK. THIS CAUSES CONDENSATETO POOL AND BLOCK SUPPLY.
39
G. TROUBLESHOOTING
Figure 37: Troubleshooting Water Hammer Which Occurs During Mid-Cycle
TROUBLESHOOTINGWATER HAMMER ON SHUTDOWN
TROUBLESHOOTINGWATER HAMMER ON SHUTDOWN
CHECK THE HARTFORD LOOP. THENIPPLE MAY BE TOO CLOSE TO THEBOILER WATER LEVEL. IT MUST BE2 TO 4 INCHES BELOW.
MAKE SURE THE STEAM PIPING ISINSULATED. IF BOILER ROOM PIPINGINSULATION HAS BEEN REMOVED,BUT SYSTEM PIPING INSULATIONREMAINS, A VACUUM WILL OCCURIN THE BOILER ROOM PIPING ONSHUTDOWN, CAUSING WATERLEVEL TO BOUNCE.
HartfordLoop
Top of Nipple2 to 4" BelowBoiler Water Line
40
G. TROUBLESHOOTING
Figure 38: Troubleshooting Water Hammer Which Occurs On Shut-Down
TROUBLESHOOTINGHAMMERING IN THE BOILER
TROUBLESHOOTINGHAMMERING IN THE BOILER
CHECK FOR FLAME IMPINGEMENTON THE LEGS OF WET BASEBOILERS. THIS CAUSES STEAMPOCKETS TO FORM. THE STEAMCOLLAPSES AND CAUSES HAMMER.
CHECK THE BOILER FOR SEDIMENTACCUMULATION. SEDIMENT IN THELEGS OR BOTTOM OF THE BOILERCAN SLOW CIRCULATION ANDCAUSE HAMMER.
OVERSIZED TANKLESS COILS CANCAUSE THE BOILER WATER LEVELTO COLLAPSE DURING HIGHPOTABLE WATER FLOW. THIS CANCAUSE HAMMERING.
SteamPocket
41
G. TROUBLESHOOTING
Figure 39: Troubleshooting Hammering in the Boiler