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FULL-COLOR TRAINING GUIDE SERIES The of Steam ONE-PIPE STEAM SYSTEMS

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FULL-COLOR TRAINING GUIDE SERIESFULL-COLOR TRAINING GUIDE SERIES

Price $20.00Price $20.00Price $20.00

The

of

Steam

CHOS396 R2 (3/05-1M)©2005

ONE-PIPE STEAM SYSTEMS

ONE-PIPE STEAM SYSTEMS

ONE-PIPE STEAM SYSTEMSPIPING AND

TROUBLESHOOTING

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.

36

G. TROUBLESHOOTING

Figure 34: How Water Hammer Occurs

G. TROUBLESHOOTING

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

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CHOS396 R2 (12/10-1M)©2010

ONE-PIPE STEAM SYSTEMS

ONE-PIPE STEAM SYSTEMS