Steam Heating System

Facilities ManagementUtilities & Engineering ServicesDuk

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Steam Heating System

DU-101-PP


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STEAM HEATING SYSTEM

PURPOSE The purpose of the Operations and Maintenance Training Program is to

train Operations and Maintenance Technicians in the operation of the Duke University Chiller and Steam Systems.

OBJECTIVES Trainees will demonstrate knowledge of

– Steam Heating System Components– Steam Heating System Components Operation– Steam Heating System Configuration– Steam Heating System Controls and Instrumentation


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PURPOSE The purpose of the Steam Heating System is to provide climate control for

all East Campus, West Campus, and Duke Medical Center buildings.

STEAM HEATING SYSTEM Boilers in the East Campus Steam Plant and the West Campus

Steam Plant supply steam to the Underground Seat and Condensate Distribution System.

The Control Room assures a steady supply of steam to all facilities, bringing boilers online as they are needed and taking boilers offline to accommodate pressure requirements and equipment maintenance.

In the campus buildings, a Pressure Reduction Valve (PRV) Station reduces steam pressure to levels suitable for heating and other services.


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WHY STEAM? Steam is an efficient and easily controlled heat transfer medium. Heat from the boilers is stored in the steam until it is processed in the

building air handlers. Steam transports energy from the boilers to any number of remote

locations with minimal loss of energy. Both steam plants serve a common distribution system, which ensures a

steady supply of steam to all facilities while boilers and other equipment are taken offline:– To provide access for maintenance without interrupting service– To improve equipment life– To enable the most efficient use of resources


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HEAT TRANSFER PRINCIPLES Boilers raise water temperature enough above the boiling point to

produce ‘saturated’ steam. The temperature of latent heat in the saturated steam is maintained until

the steam releases its latent heat into the coils of a heat exchanger.

LATENT HEAT

SATURATED STEAM

CONDENSATE


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Heat naturally flows from a higher temperature level to a lower temperature level. This is known as heat transfer.

The purpose of the distribution system is to convey steam from the boilers to the heat exchange with minimal loss of latent heat along the way.

Pipe walls, condensate film, condensate drops, air film, scaling, and even the insulation on the outside of the pipe all cause some heat loss and condensation. To maintain necessary pressure, the boiler has to work harder.

The effects of these factors on heat transfer can be minimized by:– Drip Leg Stations at regular intervals to remove condensate from the piping.– Monitoring pressure.– Regular maintenance to remove scale and other damage to the pipes.– Conditioning feed water used in the boiler to ensure the steam generated in

the boiler is as pure as possible.


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CONDENSATE RETURN PRINCIPLES Condensate is the byproduct of heat transfer in the Steam Heating System. Condensation forms in distribution piping and heating equipment. As condensation forms in the underground piping, it is separated from the

steam in drip leg stations and returned to the plant where it will be used to preheat feed water.

At a campus building, after steam has condensed and given up its valuable heat in the air handler’s heat exchanger, the hot condensate is pumped back to the boiler before it can cool.

The hot condensate is used to preheat feed water before it enters the boiler, which helps the boiler run efficiently.


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QUESTIONWhy is condensate returned to the plant?

– For disposal– To preheat feed water– To fill the water towers– To absorb steam


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ANSWERTo preheat feed water


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QUESTIONHow does heat flow?

– Lower temperature to higher temperature– Higher temperature to lower temperature– Heat does not flow– Downhill


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ANSWERHigher temperature to lower temperature


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QUESTIONHow is saturated steam made?

– Water is heated enough above the boiling point to produce steam

– Water is heated to boiling– Steam is mixed with hot water– Steam is cooled slowly to remove water


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ANSWERWater is heated enough above the boiling point to produce

steam


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PURPOSE The systems that make up the Steam Heating System work together to

provide a reliable and and efficient heat source for the East and West Campuses and Medical Center.


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SYSTEMS The Duke University Steam Heating System includes the following

equipment and locations:– High Pressure Steam System

• East Campus Steam Plant • West Campus Steam Plant

– Underground Steam and Condensate Distribution System • Steam from the East Campus Steam Plant and West Campus Steam Plant

is fed into the Underground Steam and Condensate Distribution System• Reaches all Duke University facilities

– Medium Pressure and Low Pressure Steam System• Located inside all Campus and Medical Center buildings • Converts high pressure steam to medium pressure steam for services and

low pressure steam for heating.


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HIGH PRESSURE STEAM SYSTEM High Pressure Steam Headers are located in the East Campus Steam Plant

and the West Campus Steam Plant.

EAST CAMPUS STEAM PLANT


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HIGH PRESSURE STEAM HEADER Sensors at the HPS Header send data on the steam to the Control Room.


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EAST CAMPUS STEAM PLANT


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WEST CAMPUS STEAM PLANT


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QUESTIONWhere are HPS Headers located?

– East Campus and West Campus Steam Plants– All steam and chiller plants– Campus and Medical Center buildings– Chiller Plants 1 and 2


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AnswerEast Campus and West Campus Steam Plants


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QUESTIONWhat is the nominal pressure of steam leaving the HPS

Header?– 75 psig– Less than 16 psig– 125 psig– 170 psig


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ANSWER125 psig


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QUESTIONWhich boilers in a Steam Plant supply the High Pressure

Steam Header?– All boilers all the time– Each boiler has its own HPS Header– All boilers that are on line– All boilers that are offline


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ANSWERAll boilers that are on line


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UNDERGROUND STEAM AND CONDENSATE DISTRIBUTION SYSTEM

PURPOSE– The Underground Steam and Condensate Distribution System

conveys high pressure saturated steam to buildings throughout the Duke University Campus and Medical Center

– The nominal steam pressure is 125 psig


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UNDERGROUND STEAM AND CONDENSATE DISTRIBUTION SYSTEM

COMPONENTS– Underground Piping

• The majority of piping is buried.• Steam Vaults (manholes provide access points and junctions for

buried pipes.• There are approximately 35 miles of underground piping.

– Three-pipe design• High Pressure Steam (HPS) supply piping delivers steam to

buildings.• Pumped Condensate (PC) return piping conveys hot

condensate drained from air handlers back to the plant.• High Pressure Condensate (HPC) return piping sends

condensate removed from the High Pressure Steam piping to the plant to be used as make-up feed water.


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COMPONENTS– Tunnels provide access to piping that is not buried

• Tunnels are tall enough to allow personnel to walk upright• Access is provided for maintenance of piping, valves, and

instrumentation• Valves are provided to isolate segments of the system


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COMPONENTS– Steam Vaults (Manholes)

• Steam Vaults are located at no more than 300-foot intervals in underground piping

• HPS Supply side of Steam Vault– 36 inch manhole lid– Drip Leg Station drains and cleans condensate from HPS Supply

• PC Return side of Steam Vault– 24 inch manhole lid– Sump pit provides drainage (with an electric sump pump, when

gravity drainage is not adequate• Junction(s)

– Steam Vaults can contain junctions to connect branches of piping

– HPS Supply and PC Return lines can be joined in a Steam Vault in various configurations

– Not all Steam Vaults contain junctions


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COMPONENTS– Drip Leg Stations

• Drip Pocket drains condensate from steam lines.• Strainer removes dirt and particulates from condensate.

– Steam Entry Pits • Located beneath each Campus and Medical Center building.• HPS Supply enters from the Underground Steam and Condensate

Distribution System.• Steam pressure is reduced at the PRV Station.• Condensate from air handlers drains by gravity into the sump in

the Steam Entry Pit.• Condensate in the sump pit is returned to the Underground Steam

and Condensate Distribution System by the sump pump.


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PIPINGThree Pipe System

– High Pressure Steam (HPS Supply)– High Pressure Condensate (HPC Return)– Pumped Condensate (PC Return)

DRIP LEG STATION

MANHOLE


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THREE PIPE SYSTEMHPS Supply carries steam from the plant to

Campus and Medical Center buildings.

HPS SUPPLY

DRIP LEG STATION

MANHOLE


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THREE PIPE SYSTEMCondensate removed from HSP Supply at the Drip

Leg Station is returned to the Steam Plant in the HPC Return piping.

HPC RETURN

DRIP LEG STATION MANHOLE


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THREE PIPE SYSTEMCondensate from air handlers is pumped from

buildings to the Steam Plant through the PC Return piping

PC RETURN

DRIP LEG STATION

MANHOLE


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QUESTIONWhat are the three pipes in the three pipe design?

– HPS Supply, HPC Return, PC Return– HPS Return, HPC Supply, PC Return– LPS Supply, HPS Supply, PC Return– PC Supply, PRV Return, HPS Supply


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ANSWER35 miles


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QUESTIONApproximately how much piping is in the Underground Steam

and Condensate Distribution System?– 300 feet– 50 miles– 35 miles– 900 yards


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ANSWERHPS Supply, HPC Return, PC Return


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QUESTIONWhat is carried in PC Return piping?

– Condensate from building– Steam from Plant– Condensate from Drip Leg Station– LPS from PRV Station


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ANSWERHPS Supply, HPC Return, PC Return


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TUNNELSProvide easy access to the Underground Steam and

Condensate Distribution System to personnel– Maintaining piping, valves, sensors, and controls– Isolating segments of the system


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UNDERGROUND PIPINGThe majority of piping is buried.Steam Vaults (manholes) provide access and junction points


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STEAM VAULTSHPS supply side of the vault

36 inch Manhole provides access for maintenanceDrip Leg Station drains and cleans condensate from HPS

PC return side of the vault24 inch Manhole provides access for maintenance of

condensate return pipingSump pit provides drainage of condensate lost from the the

system Junction

HPS supply and PC return from various lines can come together in a steam vault


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STEAM HEATING STATION

MANHOLE

HIGH PRESSURE STEAM

DRIP LEG STATION

STEAM VAULT HPS Supply Side

Drip Leg Station 36 inch Manhole for maintenance

access


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MAIN PC RETURN

SUMP PUMP

SUMP

STEAM VAULT PC Return Side

24 inch manhole lid for maintenance access

Sump with Pump

MANHOLE


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MAIN HPS SUPPLY

HPS SUPPLY BRANCH

MAIN PC RETURN

PC RETURN BRANCH

PC MANHOLE

STEAM VAULT Top View of Junction

HPS MANHOLE


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STEAM VAULT DRIP LEG STATION Drip Pocket Strainer Steam Trap HPS SUPPLY

DRIP POCKETISOLATION VALVES

STEAM TRAP STRAINER

BLOWDOWN DRAIN

BLOWDOWN TEST TEE

TO HPC RETURN


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STEAM HEATING STATION

STEAM VAULT DRIP LEG STATION Drip Pocket

– Condensate forming as steam cools can cause water hammer, erosion and scaling of pipe, and pipe and equipment failure

– Condensate drops out of the stream as steam passes over the drip pocket.

DRIP POCKET

HPS SUPPLY

CONDENSATE


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STEAM VAULT DRIP LEG STATION Strainer

Condensate from the drip pocket passes through the strainerFine mesh screen collects dirt and particulates

SCREEN

DRIP POCKET

STRAINER


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STEAM VAULT DRIP LEG STATION Stream Trap

Air and CO2 separate from the condensate and collect in the inverted bucket. When the inverted bucket becomes buoyant, the bucket rises, triggers the valve

above the bucket, and the gases vent out the top of the Steam Trap.

INVERTED BUCKET

STEAM TRAP

VALVE

CONDENSATE FROM STRAINER

TO HPC RETURN


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QUESTIONWhat does a Drip Leg do?

– Removes gases from HPS Supply– Drains and cleans condensate from HPS Supply– Pumps condensate from the Steam Pit Entry– Detects leaks in underground piping


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ANSWERDrains and cleans condensate from HPS Supply


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QUESTIONThe majority of piping is where?

– In tunnels– Buried– Overhead– Underwater


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ANSWERBuried


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QUESTIONHPS supply is connected to HPS Return by what?

– PRV Station– Junction– Drip Leg Station– Steam Vault


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ANSWERDrip Leg Station


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QUESTIONWhat are Steam Vaults also known as?

– Steam Entry Pits– Manholes– Deaerators– Steam Traps


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ANSWERManholes


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QUESTIONWhat does a Steam Trap do?

– Reduces steam pressure– Captures steam for testing– Removes air and CO2 from condensate

– Removes dirt and particles from steam


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ANSWERRemoves air and CO2 from condensate


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QUESTIONWhat does a Steam Vault do?

– Holds steam until it is needed– Provides access to underground piping– Serves as an entry point for HPS Supply into a building– Removes steam from condensate lines


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ANSWERProvides access to underground piping


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LOW PRESSURE AND MEDIUM PRESSURE STEAM SYSTEM– Steam Pit Entry is the vault beneath each building where HPS Supply

enters the building and PC Return leaves.– The PRV Station in each building reduces high pressure steam (125

psig) to medium pressure steam\ (75 to 16 psig, and medium pressure steam to low pressure steam (less than 16 psig).

– Medium pressure steam is used for building services washing hot water, and other services).

– Low pressure steam is used by air handlers to heat the building.– Condensate from the air handlers flows to the sump pit by gravity. The

condensate pump sends condensate to the plan through the PC Return piping.


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STEAM PIT ENTRY– Entry point for Buildings– Maintenance access– Drip Leg removes

condensate– Condensate Pump

returns condensate to Steam Plant

CONDENSATE PUMP

DRIP LEG


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PRV Station Reduces pressure in buildings in two stages

– HPS Supply to Medium Pressure Steam (MPS) for services– MPS to Low Pressure Steam (LPS) for heating

HPS FROM STEAM PLANT

MPS TO SERVICES

LPS TO HEATING

PRV


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PRV STATIONPRV

– PRV uses adjustable spring and diaphragm design to reduce steam pressure.

– The PRVs in the first stage of the PRV Station reduce steam pressure from 125 psig (HPS) to 75 to 16 psig (MPS)

– The PRVs in the second stage of the PRV Station reduce steam pressure from 75 to 16 psig to less than 16 psig (LPS).


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QUESTIONWhat does a PVR Station do?

– Reduces pressure so steam can be used for services and heating – Pumps condensate from the air handlers– Increases steam pressure so steam can reach the most remote air

handlers– Converts steam to hot condensate


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ANSWERReduces pressure so steam can be used for services

and heating


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QUESTIONWhat is LPS used for?

– Reducing pressure from HPS Supply– Heating– Hot water– Pumping condensate back to the plant


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ANSWERHeating


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QUESTIONWhich of these is MPS used for?

– Reducing pressure from HPS Supply– Heating– Hot water– Pumping condensate back to the plant


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ANSWERHot water


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QUESTIONWhat does a PRV do?

– Reduces voltage to the condensate pumps– Reduces steam pressure– Converts condensate to steam– Removes air and CO2 from steam


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ANSWERReduces steam pressure


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STEAM HEATING SYSTEM CONFIGURATION AND PROCESS FLOW


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HPS HEADERS, EAST AND WEST STEAM PLANTS Steam from boilers is regulated in HPS Header Header supplies HPS to Underground Steam and Condensate Distribution

System Steam pressure exiting plant is 125 psig

HPS HEADER

BOILERS

UNDERGROUND PIPING


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STEAM VAULT HPS steam enters Steam Vault Condensate drains into Drip Pocket Steam Trap removes air and CO2

Strainer removes dirt and particulates

STEAM VAULT

DRIP LEG STATION

STEAM TRAP


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STEAM ENTRY PIT HPS enters Campus and Medical Center buildings at Steam Entry Pit Drip Leg removes condensate

STEAM ENTRY PIT

DRIP LEG


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PRV STATION HPS is reduced to MPS, 75 to 16 psig MPS is reduces to LPS, less than 16 psig LPS is sent to the building heating system

PRV STATION

75-16 psig

> 16 psig

125 psig


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STEAM ENTRY PIT Condensate from heat heating goes to the Condensate Pump Condensate is returned to the Steam Plant


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QUESTIONWhat is the function of the Steam Pit Entry?

– Where HPS Supply enters a building– Entrance to Steam Vault– Contains the LPS Station– Contains air handlers


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ANSWERWhere HPS Supply enters a building


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QUESTIONSteam from boilers enters the distribution system where?

– PRV Station– HPS Header– Steam Pit Entry– Steam Vault


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ANSWERHPS Header


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QUESTIONWhat is the pressure of low pressure steam?

– Below 16 psig– 16 psig– 75 psig– 24 psig


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ANSWERBelow 16 psig


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QUESTION In what part does the Drip Leg Station collect condensate

from HPS Supply?– The Drip Leg Station does not collect condensate– Steam Trap– Strainer– Drip Pocket


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ANSWERDrip Pocket


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QUESTIONWhat does the strainer do?

– Removes air and CO2 from condensate– Removes LPS from HPS Supply– Removes dirt and particulates from condensates– Removes latent energy from HPS Supply


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ANSWERRemoves dirt and particulates from condensate


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OPERATIONS MONITORING– Operation of the Steam Heating System at Duke University is

monitored through the Control Room, at West Campus Chilled Water Plant #2.

– The Digital Control System (DCS) provides operators with information on system operation and control over system parameters.


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PLANT ROUNDS– During an Operator’s routine shift, Rounds are accomplished to record

key information and visually assess Steam Heating System operation, as well as other systems in the Steam Plants.

– Each Steam Plant has a Round Sheet to be filled out by the Operator.– Each plant has different requirements for plant rounds.– The information is recorded, not only for the current status, but also

to record system trends.


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WEST PLANT– The following is recorded, during operator rounds, for the West Plant, at 0800,

1600, 2000, and 0400 hours:• Steam header PSI• DA steam PSI/water temperature• Steam flow, drum PSI, and gas/fuel Oil PSI to Boilers 1, 2, 3, 6• Steam flow, drum PSI, fuel oil PSI to BLR, and atomizing steam for boilers 4

and 5• City water PSI• C/W booster pump online, and pump outlet PSI• Softeners online• FWP online, and discharge PSI• Plaint air PSI• Air storage tank PSI


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WEST PLANT– The following is recorded, during operator rounds, for the West Plant, at 0800,

1600, 2000, and 0400 hours:• Air compressor online, PSI, and temp• Generator (volts/temp)• Condensate pumps online, and discharge PSI• Tunnel condensate pumps leaking• Cond economizer rounds• Fan status, pump online, water level, flue gas temp in/out, makeup temp

to V01, makeup temp to HA-02, condensate temp leaving HA-01• Glycol system• Pump online, inlet/outlet PSI, glycol inlet/outlet temp, CHW inlet/outlet

temp• Chemical pumps rounds (day shift only)• Softeners rounds (day shift only)• Fuel oil/SPCC rounds day shift only


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EAST PLANT– The following is recorded, during operator rounds, once on dayshift, and once on

nightshift:• Deaerators• Pressure, steam temp, water temp, PC bypass closed• Heating water pumps• Suction/discharge PSI• HP steam to DA• Top/bottom PSI• Steam letdown• Top/bottom PSI, SF#1 breaker on/off• Rooftop• Breakers• Operating Floor• Leak detector, NG/propane valve, HRS inlet/outlet water temp, HRS drain

water temp, HRS soft water inlet/outlet PSI, blowoff tank outlet temp• Rooftop


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EAST PLANT– The following is recorded, during operator rounds, once on dayshift, and once

on nightshift:• Breakers• Basement area• Steam header PSI, city water inlet PSI, city water PSI after strainer, vacuum

skid sight glass, pumps 5-8, booster pumps 1 and 2, HP drip station, fire water system, sump pump station, AHU-1 breaker

• Fan room• SF-2-SF-4 breakers: valves open, AHU-2 breakers: valves open• Outside building• Condensate tank levels, natural gas piping, propane skid, vaporizer,

emergency generator, propane unloading area• Night Shift Only: Softeners online, GMPs, polishers online, boiler 1-15,

chemical pump, softeners, and brine tank


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EXAMPLE WEST PLANT ROUNDS SHEET (front and back)


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EXAMPLE EAST PLANT ROUNDS SHEET (front and back)


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TYPICAL PROBLEMS ASSOCIATED WITH THE STEAM HEATING SYSTEM– Clogged Strainer

• Most likely cause is mesh strainer is full of debris.– Failed Steam Trap

• Most likely cause is failure or clogging of vent.– Flooding of Steam Vault or Steam Entry Pit

• Most likely cause is sump pump has failed or drain is clogged.

– Failed PRV• Most likely cause is clogged valve, degraded diaphragm, or spring

requires adjustment


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QUESTIONWhere does Operations Monitoring take place?

– Control Room in each steam plant– Control Room in West Campus Steam Plant– Control Room in Chiller Plant #2– Control Room in Chiller Plant #1


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ANSWERControl Room in Chiller Plant #2

Documents

Steam Heating System