large chilled water system design seminar - ashrae · pdf filelarge chilled water system...

Large Chilled Water System Design Seminar

Presented by:Larry Konopacz, Manager of Training & Education

Bell & Gossett Little Red Schoolhouse

This presentation is being brought to you by:

ASHRAE India Chapter and Xylem, Inc.

Saturday, September 21, 2013

The Production Loop

• Chillers• Cooling towers• Free-Cooling &

Waterside Economizer• Thermal Storage• Water Source Heat Pumps

Chilled Water Sources

I Ton Ice =2000 LB;1LB Ice =144 Btu;

1 Ton ice =288,000 Btu

What’s a Ton?

12,000 Btu/h = 500 x gpm x t°F = 1 ton

gpm/ton = 12,000/(500 x t°F)

= 24/t°F

Rule of 24

What Types of Chillers are Available?

• Centrifugal• Rotary screw• Reciprocating• Absorption

Evaporator

Condenser

Compressor

Refrigeration Cycle

Cooling Tower

Condenser

CondenserWater Pump

CompressorMotor

Expansion Device

ChilledWaterPump

High P

ressure Zone

Hot Water Liquid Flow

ReturnWater

Vapor FlowCool Water

SupplyWaterEvaporator

Where is What Used?

• Large chilled water plants - centrifugal• Mid-range size - rotary screw• Smaller chilled water applications -

reciprocating• Inexpensive source of steam or other

energy source - absorption• Combinations of the above

CHILLER Chiller 2

Chiller 1

SupplyReturn Common Pipe

Chiller Piping - Evaporator Side

Supply

Return

CommonPipe

TripleDuty

Chiller 3

Chiller 2

Chiller 1TripleDuty

Typical Piping Method

Supply

Return

CommonPipe

TripleDuty

Chiller 2

TripleDutyChiller 1

Adding Pump Redundancy

Piped forStandbyPumps

Supply

Return

CommonPipe

TripleDuty

Chiller 3

Chiller 2

Chiller 1TripleDuty

Actuated Control Valve

Headered Primary Pumps

Chiller Piping - Condenser Side

Condenser Condenser

Condenser

Cooling Towers

Triple Duty

SRS SRS SRS

TripleDuty

Standby Pump

Condenser

Multi-cell Cooling Tower

Multi-celled Cooling Tower

Cooling Towers

Triple Duty

Condenser

EqualizationLine

Tower Equalization

Cooling Tower Piping Practices

• Fill all sections of pipe to purge air.• Size piping at a minimum of 2 fps to

move free air bubbles to tower.• All piping installed below system purge

level.

System Purge Level

Condenser Water Piping Above Grade

Overhead Piping Concerns

• Piping manifolds can result in low velocities.• Low velocity will allow air to be released.• Air trapped in piping increases head required.• Piping installed above purge level compounds

problem.• Unpurged areas are potential sources of

problems when pumps are turned on.

Elevated Suction Piping Concerns

• Condenser water pump difficult to purge.• At start-up a manual air vent may be required.• During operation air will again accumulate.• Automatic air vent may not work.• If above the basin fill level, the result is

cavitation.

Improper Piping Above Basin Level

System Purge Level

Basin Fill Level

System Purge Level

Multi-tower System, Properly Piped

Tower Piping Observations• At part load reduced velocities in headers may

allow air to be released.• Idle pumps will accumulate air that should be

released prior to starting the pump.• Tower basins should be elevated to ensure

positive pressure under all flow conditions.• Pump casings should be fitted with automatic

air vents.

Condenser Head Pressure Control

With centrifugal chillers a minimum supplywater temperature is needed to:

• Maintain optimum efficiency• Maintain a minimum pressure differential

between condenser and evaporator• Prevent pressure imbalance

Hermetic Compressor Guidelines

• Condenser water temperature > 75 °F.• Establish 75 °F within 15 minutes.• N/O condenser water throttling valve.• Three-way bypass valve can be used.• Constant condenser water flow.• Water temperature control through fan

modulation, or other methods.

Open Compressor Guidelines

• Condenser water temperature > 55 °F.• Three-way bypass valve can be used.• Constant condenser water flow.• Water temperature control through fan

modulation, or other methods.

Water In Water out

Air in Air out

Cooling Towers

Water out

Air in Air in

Water in

Air Out

Induced Draft, Counter-flow Tower

Air Out

Air inAir in

Water out

Water in

Forced Draft, Cross-flow Tower

Temperature Water Flow

Hot water °F

Cold water °F

Wet bulb °F

“L” lb/min of water

ge(“R

” °F)

Heat Load = L x R

Dynamic Relationship of Load, Approach, and Range

Tower Size Relationships

Variables:• Heat Load (Varies Directly)• Range (Varies Inversely)• Approach (Varies Inversely)• Wet-bulb Temperature (Varies Inversely)

Varying any of these variables will affect the size of the tower.

Types of Free-Cooling(Waterside Economizer)

Water out

Air in Air in

Water in

Air Out

Earth Contact Evaporative

Earth Contact Characteristics

• Usually indirect.• Cooling medium and load separated by heat

exchanger.• Stable temperatures.• Water temperature limitations.• Water treatment and pumping costs.• Environmental concerns.

Heat Exchangers

How do they work?• Thin plates are stamped with

a unique chevron pattern and assembled in a frame

• Four holes punched in the plate corners form a continuous tunnel which acts as a distribution manifold for the inlet and outlet of each fluid

How do they work?• Each plate has a gasket that

confines the fluid to the port or to the heat transfer area of the plate

• Units are built to order with a standard 150 psi ASME Code stamped design or to custom designs

LOADCOND

Triple Duty

Sediment RemovalSeparator

Triple Duty

Earth Contact - Summer Cycle

LOADCOND

Triple Duty

Earth Contact - Winter Cycle

Evaporative Characteristics

• Heat rejection device (tower) exists.• As temperature declines, opportunity

arises.• Higher sensible vs. latent loads• Leaving water temperature approaches

42 F.• Freeze protection may be required.

Freeze Protection

• Sump heaters.• Close temperature control.• Accurate water level control.• Prevention of moist air recirculation.• External piping freeze protection.

Evaporative Cooling - Direct

LOADCOND

Triple Duty

Triple DutySediment RemovalSeparator

Single Tower, Summer Cycle

LOADCOND

Triple Duty Triple Duty

* Alternate location of SRS, depending onsystem conditions

NOT RECOMMENDED

Single Tower, Winter Cycle

Evaporative Cooling - Direct

Evaporative Cooling - Indirect

LOADCOND

Triple Duty

Single Tower/GPX, Summer Cycle

Evaporative Cooling - Indirect

LOADCOND

Triple Duty

Single Tower/GPX, Winter Cycle

COND. WATER

CH. WATER

TEMP.DEG. F

EXCHANGERLENGTH

7°F TEMPERATURECROSS

3°F COOLINGAPPROACH

Temperature Cross and Approach

Temperatures are in F Flow is in USGPM

Heat exchanger selection based on max pressure drop of 7 psi

10/3.92=2.55 Approach = 3F

10/4.93=2.03 Approach = 4F

10/5.94=1.69 Approach = 5F

COND. WATER CH. WATER LMTD AREA EXCH. COSTEWT LWT FLOW EWT LWT FLOW DEG F SQ.FT. MODEL INDEX

42 52 1000 57 45 834 3.92 1390 GPX807 1.00

42 52 1000 58 46 834 4.93 1135 GPX807 0.85

42 52 1000 59 47 834 5.94 975 GPX807 0.76

Heat Transfer Area vs Approach

Production Source - Thermal Storage

• Application Criteria• Economics• Storage Media• Storage Technologies• System Configurations

Application Criteria

• High maximum load.• Significant premium for peak demand.• Incentives.• Limited space available.• Limited electrical capacity.• Back-up or redundancy required.

Storage Media

• Chilled Water• Ice Harvesting• External/Internal Ice Melt

Pressure sustainingand check valve

StorageWarmCool

Variable volumedistributionpump

Constant volumeprimary pump

Chiller

Stratified Chilled Water System

30 40 50 60 70

Bottom -20

Depth of tank, ft

Temperature, °F

Thermocline

Temperature Stratification

StorageWarm

Chiller

Distributionpump

Primary pump

Transfer PumpDirectioncontrolvalves

Use of Pressure Sustaining Valves

StorageWarm

Variable volumeprimarypump

Chiller

Heat Exchanger

Variable volumesecondarypump

Incorporating Heat Exchangers

Section1

Section2

Section3

Section4

Ice harvesterchiller

Chilled water pump

Ice waterrecirculationpump

Ice Harvesting System

Charging ModeDischarging Mode

External Melt Ice Storage

WaterIceCold glycol Warm glycol

Charging Mode Discharging Mode

Encapsulated Ice StorageCharge and Discharge Modes

Time of Day

Cooling load (met by storage)

ChargingStorage

Chiller meets load directly

Chiller on

Chiller off

Full Storage Strategy

Time of Day

Cooling load(met by storage)

ChargingStorage

Cooling load(met by chiller)

Chiller runs continuously

Partial Storage - Load Leveling

Time of Day

(met by storage)ChargingStorage

ChargingStorage

(met by chiller)

Cooling load

Reduced on-peak demand

Partial Storage - Demand Limiting

Production Source - Water Source Heatpumps

• Growing market segment• System temperature range 40 - 90 °F• Energy added below 40 °F (heat)• Heat removed above 90 °F (cooling

tower)

Air Coil(Evaporator)

CoolAir Compressor

Reversing Valve

Capillary

Air Conditioner Cooling

Air Coil(Condenser)

WarmAir

Reversing Valve

Capillary

Air Conditioner Heating

Water Coil(Evaporator)

Water Coil(Condenser)

System Water Supply

Return

Compressor

RefrigerantLoop

Heat Pump Cycles - Water Source

Design Considerations

• Use slow closing two-way valves for each zone

• Good system balance required• Use staged c/s or v/s pumps• Use with cooling towers and GPX• Use with closed circuit cooling towers

Water SourceHeat Pump

BufferTank

( Optional )

Compression Tank

GasketedPlate HeatExchanger

CoolingTower

Heat Pump-Water Source Schematic

Closed Circuit CoolerHeat Rejecter

Water SourceHeat Pump

BufferTank

( Optional )

Compression Tank

Heat Pump-Water Source Schematic

Comments?Questions?

Observations?

Variable Volume Distribution

Variable flow through coil Constant flow through system

Three Way Valve

Variable flow through coil Variable flow through system

Two Way Valve

Three-Way Valve Systems

• Low return temperatures• Balance problems• Increased flow at part load• Extra chillers to provide flow at low t• Chillers operate at high kW/ton

CHILLER

Two-Way Valve System with Chiller BypassA

We want:a. variable volume, to save pumping

costs at part load,b. constant flow through the chiller to

protect it.

A Solutiona. constant flow primary system for the chillersb. variable flow secondary system for the load

A Problem

CHILLER

Return

Primary-SecondaryCommon Pipe

SupplyPrimary Loop

Production

Secondary LoopDistribution

Primary-Secondary Terms

Fundamental Idea

SecondaryPump

Tee“A”Primary

Tee“B”

Low pressure drop in the “common pipe”

Primary-Secondary Pumping

The idea is based on:

– Conservation of Mass

– Conservation of Energy

50 GPM100 GPM

50 GPM

Law of the Tee: Diversion

40 GPM60 GPM

100 GPM

Law of the Tee: Mixing

No Secondary Flow

100 GPM @ 45°F

SecondaryPump

A B100 GPM @ 45°F 100 GPM @ 45°F

PrimaryPump

Primary = Secondary

100 GPM @ 45°F0 GPM

Pump On

100 GPM @ 45°F 100 GPM @ 55°F

100 GPM @ 55°F

Primary > Secondary

Pump On

Mixing at Tee B

100 GPM @ 45°F

50 GPM @ 45°F

100 GPM @ 50°F

50 GPM @ 55°F

50 GPM @ 45°F

Pump On

Mixing at Tee A

100 GPM @ 45°F 100 GPM @ 55°F100 GPM @55F

200 GPM @ 50°F 200 GPM @ 55°F

Primary < Secondary

Two-way Valve

Control Valve in Secondary

Primary-Secondary Pumping

CHILLER

Return

Primary-SecondaryCommon

SupplyPrimary Loop

Production

Secondary LoopDistribution

Common Pipe Design Criteria

• Use the flow of the largest chiller– Chiller staging at half of this flow is

common• Head loss in common <1 1/2 ft

– Distribution pipe size is often used where reductions would be inconvenient

• Three pipe diameters between tees– Excessive length increases total head loss

• Low velocities in system piping

Return

Supply

PumpController

SecondaryConstant Speed

Common

Chiller 3

Chiller 2

Chiller 1

Design of the Common Pipe

10 dia.

Common Pipe Configurations

F1 F2 F3

Control ValvesClosing

Control ValvesOpening

Secondary System Curve

From Loads

Common

To Loads

Production

Secondary Pumps1500 gpm each

Distribution

Chiller 2, off

Chiller 1, on

1500 gpmeach

Typical System

Common -- No Flow

SecondaryPumps

1500 15000

CHWS Temp45oF

CHWR Temp55oF

ECW Temp55oF

Chiller 2, off

Chiller 1, on

Production = Distribution

Common -- 500

SecondaryPumps

1500 20000

CHWS Temp47.5oF

CHWR Temp55oF

ECW Temp55oF

Mixing (1500 @ 45) + (500 @ 55)

Chiller 2, off

Chiller 1, on

Distribution > Production

>1500 GPM

ReturnCommon

Supply

>1500 GPM

>1500 GPM@ 47.5oF

>1500 GPM@ 55oF

Be Careful!

Chiller 2, off

Chiller 1, on

Check Valve in Common?

StepFunction

LinearFunction

Return

Primary/SecondaryCommon

Supply

Production

Distribution

Chiller 3

Chiller 2

Chiller 1

What can we do?

0-10 30-40 60-70 90-1000

0-10 30-40 60-70 90-100

% Load

Typical Load Profile

Chiller 2, 60%

Chiller 1, 40%

% Load

% Time

100755025

Chiller 1

Chiller 2

Multiple Chillers

What else can we do?Reset Supply Temperature

• Lower chiller set point when mixing occurs to maintain a constant temperature to the system.– Allows us to mix colder water and maintain supply

temperature to secondary. (coils)• Expect increases in cost of chiller operation at

lower set point: 1-3% per degree of reset.• Adds to control complexity.• Delays start of the next chiller.

Common -- 900

SecondaryPumps

15002100

CHWS Temp45oF

CHWR Temp55oF

ECW Temp52oF

Mixing (2100 @ 55) + (900 @ 45)

(Flow in GPM)

P/S Chiller Bridge - Front Loaded Common

Chiller1, on

Chiller 2, on

Production > Distribution

“Loading” a Chiller

• A chiller is a heat transfer device. Like most equipment, it is most efficient at full load.

• To “load” a chiller means:– Supply it with its rated flow of water– Insure that water is warm enough to permit

removal of rated Btu without freezing the water

Chiller Performance Curve1.1

20 30 40 50 60 70 80 90 10010

per Ton

Percent Load

0-10 30-40 60-70 90-1000

0-10 30-40 60-70 90-100

% Load

Typical Load Profile

Chiller 2, 60%

Chiller 1, 40%% Load

% Time

100755025

Chiller 1

Chiller 2

60/40 Chiller Split to Help Minimize Low Part Load Operation

% Load

% Time

100755025Chiller 1

orChiller 2

Chiller 3

Chiller 1and

Chiller 2

Chiller 1 or Chiller 2and

Chiller 3

Chiller 2, 40%

Chiller 1, 40%

Chiller 3, 60%

Three Unequally Sized Chillers

% Load

Approaching Flow = Load

% Load

% Flow

100755025

Ch 1Ch 2 Ch 3 Ch 4

Ch 1 Ch 2 Ch 3

Ch 1 Ch 2

Applying a Variable Speed Chiller

From loads

Common

To Loads

Chiller 3

Chiller 2

Chiller 1

Back Loaded Common

Common0 Flow

SecondaryPumps

CHWS Temp45oF

CHWR Temp55oF

Chiller 2, off

Chiller 1, on

15001500

Production = Distribution

Common500 gpm

SecondaryPumps1500

1500 20000

CHWS Temp47.5oF

CHWR Temp55oF

Mixing (1500 @ 45) + (500 @ 55)

Chiller 1, on

Chiller 2, off

Distribution > Production

Common900

SecondaryPumps1500

1500 GPM@ 49oF

CHWS Temp45oF

CHWR Temp55oF

Mixing (900 @ 45) + (600 @ 55)

900 600

900 GPM@ 45oF

600 GPM@ 55oF

1500 GPM@ 55oF

Chiller 2, on

Chiller 1, on

Production > Distribution

Return

Supply

PumpController

SecondaryPumps

Chiller 3

Chiller 2

Free Cooling

Maximize Free Cooling

Return

Supply

PumpController

SecondaryPumps

Chiller 3

Chiller 2

Chiller 1

Primary-Secondary System

25 50 75 100

Design Coil Flow%

Primary Pumps = V/V

Secondary Pumps +

Constant Flow Primary Pumps, only

Pump Horsepower Comparison

2012 ASHRAE Handbook - HVAC Systems and Equipment, p 44.11

% Flow

0 10 1009080706050403020

BaseDesignHP %

% Full Load(Design) HP

Pump Over-headed by 150%Constant Flow, C/S Pump(3 Way Valve)

Constant Flow, C/S Pump(3 Way Valve)

C/S Pump(2 Way Valve)

Pump Head Matchedto System @Design Flow

Constant vs Variable Volume

0 1000 2000 3000 4000 5000 6000 7000 8000 9000

Pipe Length, Feet

Yearly Operating C

ost x $1000

c/s @ 1.0

c/s @ 1.25

c/s @ 1.50

c/s @ 2.0

Impact of Piping Length and Overheading

Always Size the Pump to the System!

But...• Uncertainties

– Coils– Control valves– Primary data

• Lead times

Dealing With an Overheaded Pump

• Throttle at the discharge valve– Limits on the valve

• Flow balance & trim pump impeller– Required by ASHRAE/IES 90.1

Additional Concerns

• Pump Protection at minimum flow

• Chiller Staging and De-staging instrumentation.

Pump Protection

Minimum recommended flow from ESP Plus = 900 gpm

Bypass Options1. Establish a minimum flow equal to or greater than

the minimum required to protect the pump.2. Install a bypass at the end of the mains with a

balance valve to set minimum flow.3. Install a bypass at ends of zones.4. In retrofits, leave a three way valve at the end of the

system.5. Use P or flow sensing to open pump bypass only

when needed.6. V/S pumps are not as big a problem because of

lower head at reduced flow.

System Bypass Options

Return

Supply

PumpController

SecondaryConstant Speed

PrimarySecondaryCommon

Chiller 3

Chiller 2

Chiller 1

From Loads

Common

To LoadsProduction

Secondary/Pumps

Distribution

Chiller 2, off

Chiller 1, on

FSTS-S

TS-RTP-R

Chiller Staging Instrumentation

Common Pipe Flow Indication

From LoadsCommon

To Loads

Production

Secondary/Pumps

Distribution

Chiller 2

Chiller 1 Flow

Switches

Comments?Questions?

Observations?

Large Chilled Water Design SeminarVariable Speed Pumping

Why variable speed?

1. When should I use it?2. How does it work?3. What about variable primary flow?

Typical operating load profile

2% 3%5%

5%3% 2%

Bell & Gossett 70V1970s

Adjustable Frequency Drives

• Rectifier section– converts AC to DC– several varieties available

• Inverter section– forms a synthetic sine wave– several varieties available– maintains a controlled frequency/voltage ratio

• Requires an automatic control system• Adds to the initial cost of the system

Affinity Laws

1. Capacity varies as the RPM change ratio:

FLOW 2 = FLOW 1 ( SPEED 2 / SPEED 1)

2. Head varies as the square of the RPM change ratio:

HEAD 2 = HEAD 1 (SPEED 2 / SPEED 1)2

3. Brake horsepower varies as the cube of the RPM change ratio:

BHP 2 = BHP 1 (SPEED 2 / SPEED 1)3

Affinity Laws for Centrifugal Pumps

0 10 20 30 40 50 60 70 80 90 100

Flow/Speed, Percent

FlowHeadHorsepower

Theoretical Savings

% Design Flow

Pump Curves 100% Speed

40%30%

FlowBHP

10 20 30 40 50 60 70 80 90 1000

HP Draw

Design

P Sensor/Transmitter25 Ft. Head

Required Differential Pressure

System Curve& V/S Control System

piping headloss curve

Distribution

Overall system curve

0200 400 600 800 1000 1200 1400 16000

Set Point25 FT Differential Head Maintained Across Load

(Set Point)

Effect of Constant* Set Point

piping headloss curve

Distribution

Overall system curve

0200 400 600 800 1000 1200 1400 16000

Control curve Set point,25 FT

As the valve closes, the pump slows down

*What’s Constant?

Q1Q2Flow, Q (gpm)

Head, H (feet)

PumpInitial Speed

Decrease in Heat Load Results in Troom < T set pointCauses Two Way Valves to Throttle Flow

Control Curve

Pipe, FittingFriction Loss

Q1Q2Flow, Q (gpm)

Head, H (feet)

Pump Curve

Control Curve

Decrease in Pump Speed Reduces Flow, Reduces Error

Speed 1

Speed 2

Pipe, FittingFriction Loss

System Operation on Control Curve at Lower Speed

Q1Flow, Q (gpm)

Head(ft) Pipe, Fitting

Friction Loss

Control CurveSpeed 1

Final Speed C

Return

CHILLER

Supply

Variable Head Loss

Constant Head Loss

PumpController

Adjustable Freqy. Drives

Variable vs Constant Head Loss

Percent D

esign BH

% Flow

0 10 1009080706050403020

100 C/S, Constant Flow System Pump Head Matched toSystem at Design Flow

C/S, Variable FlowV/S, 0% Variable Hd Loss, 100% Constant Hd

V/S, 25% Variable Hd Loss, 75% Constant Hd

Variable Head Loss Ratio

Variable Head Ratio w/ Overheading

0 10 1009080706050403020

BaseDesignHP %

% Full Load(Design) HP

Pump O’Headed by 150%Constant Flow, C/S Pump(3 Way Valve)

Constant Flow, C/S Pump

(3 Way Valve)

C/S Pump(2 Way Valve)

Pump HD Matchedto System @Design Flow

* 25/75 Means:25 % Variable HD Loss75 % Constant HD Loss

0100 200 300 400 500 600 700 800 900 10000

40 %30 %

80 %85 %80 %70 %60 %50 %

% Speed Curves

Constant Efficiency Curve

% EfficiencyH

V/S Curves

0100 200 300 400 500 600 700 800 900 10000

40 %30 %

80 %85 %80 %70 %60 %50 %

% Speed Curves

% EfficiencyH

Efficiency Changes

Minimum Drive Speed120

0100 200 300 400 500 600 700 800 900 10000

40 %30 %

80 %85 %80 %70 %60 %50 %

% Speed Curves

% Efficiency

Return

CHILLER

Supply

Variable Head Loss

Constant Differential Head Loss

PumpController

Multiple Pump System Staging

Control Curve

Pump 1

Pumps 1 & 2 Pumps 1, 2 & 3

1770 RPM

600 RPM 900 RPM1150 RPM

1450 RPM

Parallel V/S Operation

Set Point (Input Signal)

Technologic™ Pump

Controller

Adjustable Frequency

Drive (Controlled Device)

SystemSensor/ Transmitter

3f , 60 Hz Power (Control Agent)

3f, Variable Frequency Variable Voltage

Feedback Signal

Controlled Variable

Set Point +/- error

Variable Speed Pumping Equipment

The Controlled Variable Determines the Type of Sensor

Pressure

Differential Pressure

Differential Temperature

••••• •••••

Pump Controller

Temperature

4-20 ma

signal

Technologic™ Pump

Controller

Feedback Signal

Controlled Variable

Set Point +/- error

Technologic™ Pump Controller

• Controls pumps and drives– Accept set point, analyze sensor input– PID function– Pump staging– Pump alternation

• Recognize and react to component failure• Provide message display• Central management system link• Safeguard system

PID Control

• Eliminates offset from set point• Allows for timely speed change• Handles large, sudden disturbances• Prevents oscillation and over-damping

Technologic™ Pump

Controller

Feedback Signal

Controlled Variable

Set Point +/- error

Adjustable Frequency Drive

Constant Voltage & Frequency

Rectifier Section

Direct Current

Inverter Section

Variable Voltage & Frequency

Pump Motor

Some important issues: Rectifier and Inverter Design Drive Efficiency RFI and EMI Noise Audible Noise Size and CostManual drive bypass

0 20 40 60 80 100

Design Speed, %

Currently AvailableAFDsTypical Older AFDs

Other Types

Typical Efficiency RangeVariable Speed Drives

Pump and Motor

The Pump

• Minimum Flow• Minimum Speed• “Inverter Duty”

Motors• Motor Couplers

Maintaining Minimum Flow120110

010 20 30 40 50 60 70 80 90 1000

% Flow

d100 % Speed

30% Speed

EPDM couplers on variable-speed pumps

Failed Hytrel Coupler from a Variable Speed Pump

Variable Flow Through

The Evaporator

Return

CHILLER

Supply

Variable Head Loss

Constant Differential Head Loss

PumpController

Primary-Secondary System

Primary-Secondary

• Common Practice.

• Why?

– Protection.

• Nuisance shutdowns.

• Freezing.

• Costly downtime.

Variable Primary Flow

AFD AFD AFD

CHILLER

Flow Meter, option

ModulatingValve

Two-position Control Valves

Sensor

Controller

P SensorD

What’s different?• Primary pumps only • Flow meters or p sensors at each

chiller.• Two-position isolation valves at each

chiller• Minimum flow bypass with a modulating

control valve.• “Smarter” controller.

Alternative #1

• Minimum Flow Bypass at Chillers–Minimum Chiller Flow

–Minimum Pump flow

• Ganged Pumps

DPSENSOR

FLOW METER

DPSENSOR

AFD AFD AFD

SIGNALS TO TECH

SIGNAL TO TECH

NOTE:ALL SENSOR SIGNALS WIRED TO TECHNOLOGIC 5500

BYPASS: FOR SYSTEMS WITH EXTENDED LIGHT LOADS/WEEKEND SHUTDOWNS. SET BALANCE VALVE FOR LOW FLOW TO REDUCE THERMAL STRATIFICATION AND ALLOW QUICK START UP AFTER SHUT DOWN.

SIGNALS TO TECH

FLOWMETER/TRANSMITTER

TEMPERATURE SENSOR

ISOLATION VALVE

CHECK VALVE

CHILLER CHILLER CHILLER

SUPPLY

RETURN

TDV TDV TDV

Monitoring Chiller Flow

P sensors - Technologic controller ensures the chiller is in proper working condition by monitoring each working chiller’s differential pressure. Flow through the chiller is calculated using the values defined in the user setup.

Flow sensors - Technologic controller ensures the chiller is in proper working condition by monitoring each working chiller’s flow rate.

Technologic 5500

• Initial programming is crucial.

• Must use accurate data from the chiller manufacturer.

• Start-up coordination should include the BMS too.

Technologic 5500 Control Variables

1. Monitor zone differential pressure sensors, compare actual values to the required set points.

• Pump speed is modulated to maintain set point.

• Pump staging will occur as required to meet set point.

Control sequence is exactly as described earlier.

Technologic 5500 Control Variables2. Determine if the minimum flow requirements are being met for all working chillers.

Prevents freeze-up or chiller low-flow trips

If chiller flow is too low, controller opens minimum flow bypass valve in programmed increments. Size the valve for system p.

“Requests” de-staging action from the chiller control system or BMS.

Allows for operator intervention, decision making.

Required by code in some areas.

Ganged pumps allow operation of two chillers with one pump.

Technologic 5500 Control Variables3. Monitors chiller flow rate to prevent operation above the maximum flow for the chillers and the pumps.

Excess chiller flow generates a request to stage on an additional chiller. Minimum flow bypass valve is closed.

Operator or BMS intervention required.

Ganged pumps allow operation of one chiller, two pumps.

Optional system flow meter provides end-of-curve protection for the pumps

Alternative #2

• Bypass at End of System

• Minimum chiller flow

• Minimum pump flow

• Ganged Pumps

DPSENSOR

FLOW METER

DPSENSOR

DPSENSOR DP

SENSORDP

SENSOR

AFD AFD AFD

SIGNALS TO TECH

SIGNAL TO TECH

SIGNALS TO TECH

TEMPERATURE SENSOR

ISOLATION VALVE

CHECK VALVE

SUPPLY

RETURN

TDV TDV TDV

CHILLER CHILLERCHILLER

Alternative #2

• Minimum flow bypass valve is controlled to protect both the pumps and the chillers.– Pump requires >25% BEP flow– Minimum flow of largest chiller

• Size the bypass valve using the zone p.

• Best for systems with extended light loads or weekend shut-down.

Alternative #3

• Primary pumps piped directly to chillers.

• More common in retrofit systems.

• Easier for applying un-equally sized chillers in parallel.

DPSENSOR

FLOW METER

DPSENSOR

AFD AFD AFD

SIGNALS TO TECH

SIGNAL TO TECH

BYPASS: FOR SYSTEMS WITH EXTENDED LIGHT LOADS/WEEKEND SHUTDOWNS. SET BALANCE VALVE FOR LOW FLOW TO REDUCE THERMAL STRATIFICATION AND ALLOW QUICK START UP AFTER SHUT DOWN.

SIGNALS TO TECH

TEMPERATURE SENSOR

CHECK VALVE

ISOLATION VALVE

TDV TDV TDV

CHILLER CHILLER CHILLER

SUPPLY

RETURN

Pump Selection• Equal size pumps.

– Redundancy.– Parts.– Maintenance.

• Unequal size pumps.– Control issues.– Flow issues.– Premature failure, large pump at low flow.

Chiller Selection

• Equal size chillers.– Redundancy.– Parts.– Maintenance.

• Unequal size chillers.– Control issues.– Flow issues– Additional equipment.

• Size bypass for minimum flow of largest chiller.– Minimum building load?

• Size bypass modulating valve– for system p, if it’s installed near the chillers– for zone p, if it’s out in the system.

• Program the controller with the chiller p set points for minimum and maximum chiller flow.– Verify with chiller manufacturer.

• Sequence chillers based on p or temperature sensors.

• Use accurate, calibrated flow meter or p sensors at each evaporator

• Allow for operator training.– Initial– On-going

Consider this design if:• System flow can be reduced by 30%.

• System can tolerate modest changes in water

temperature.

• Operators are well trained.

• Demonstrates a greater cost savings.

• High proportion of operating hours at:

– Part load.

– Full load with low entering condenser water.

Turn-down Ratio• Chiller manufacturers publish 3 - 11 fps

evaporator velocity range (typically).• You may have to increase your

“acceptable head loss” targets, use more pump head.

• Nominal base of 7 fps desirable.• Variation of 1 to 2 fps.• Work with the manufacturer.

Rate of Change*Maximum rate of flow change, % design flow per minute

Source Vapor Compression Absorption

#1 4-12 **

#2 20-30 2-5

#3 ** 30

#4 2 **

#5 ** 1.67

*Table 2-2ARTI-21CR/611-20070-01, 2004, Bahnfleth & Peyer** Information not provided

Do not use if:

• Supply temperature is critical.

• Three-way valves are used throughout.

• Existing controls are old, inaccurate.

• Operators are unlikely to operate the

system as designed.

Supply Water Temperature

• Dependant on :– System volume.– Rate of flow change.

• Application specific.• Consider thermal storage

Operator Ability

• Within operator’s ability?.– Commercial buildings may not have well

qualified operators.• Training is mandatory.

– Initial– Periodic, in view of operator turnover.

Start-Up & Shut-down• In systems that start-up and shut-down, it

may be advisable to anticipate, and avoid, rapid changes in flow as control valves all tend to act together.

• Control system, BMS, manual procedures.

• Use slow opening/closing valves at the chiller, 60-90 seconds.(?)

Controls Complexity

• Additional controls for the chillers • Additional controls the pumps. • Pumps operate on flow, temperature, and P.

• Chiller P.

Sensor Calibration

• Multiple sensors control:– Flow.– Temperature.– Delta p

• Maintenance.• Calibration.

Summary• Evaluate all the options.

• Read some articles:– Variable Primary Flow CHW: Potential Benefits and Application Issues

by Bahnfleth and Peyer. Pennsylvania State University, ARTI-

21CR/611-20070-01

– Chilled Water System for University Campus by Stephen W. Duda, PE,

ASHRAE Journal May, 2006

• Another tool for the toolbox.

Comments?Questions?

Observations?

Primary-Secondary-Tertiary Pumping Systems

CHILLER

Zone A

Zone B

Zone C

Variable Speed Pump

Primary-Secondary-Tertiary

CHILLER

Zone AZone B Zone C

DP Controller

WRONG !

Direct Pumped Zones

WRONG !

Zone A Zone BZone C

Automatic Flow ControlValve

Hard set valve

CHILLER

Constant Demand Zones

CHILLER

Zone A

Zone B

Zone C

Variable Speed Pump

Primary-Secondary-Tertiary

RIGHT !

Three Different Buildings• “A” has coils selected for 44°F.• “B” has coils selected for 45°F.• “C” has coils selected for 46°F.

• Therefore, the supply water temperature must be at least 44°F for “A”.

• But what about “B” and “C”?

CHILLER

Zone A

Zone B

Zone C

Optional Variable Speed Pump

Primary-Secondary-Tertiarycan be even more useful

LoadMV

Load MV

Common T2

ChilledWaterReturn

PumpedChilledWaterSupply

TertiaryZonePump

T2 T3 T4

Temperature Sensor Locations

½” Circuit Setter

LoadMV

Load MV

CommonT2

ChilledWaterReturn

TertiaryZonePump

Tertiary Bridge

LoadMV

Load MV

Common T2

ChilledWaterReturn

TertiaryZonePump

T2 T3 T4

Temperature Sensor Locations

1. Permits operating at highest allowable zone temperature

2. Maximizes coil flow rate, good film coefficients

3. Maximizes flow rate through each control valve

4. Ensures good humidity control

5. Minimizes the amount of coil reheat

ADVANTAGES

1. Temperature of return water is unknown

2. Temperature of return water to chiller may be too high

3. Will not recognize increased supply water temperature

DISADVANTAGES

LoadMV

Load MV

Common T2

ChilledWaterReturn

TertiaryZonePump

T1 T2 T3 T4

T2 Operation

1. Maintains chilled water return temperature at setpoint

2. Will not overload the chiller

ADVANTAGES

1. No control of zone supply water temperature

2. Could lose humidity control

DISADVANTAGES

LoadMV

Load MV

Common T2

ChilledWaterReturn

TertiaryZonePump

T1 T2 T3 T4

T3 Operation

1. There are no perceived advantages at this location

ADVANTAGES

1. Little, if any, valve modulation unless it is set to close on sensing supply temperature lower than permissible in the zone

DISADVANTAGES

LoadMV

Load MV

Common T2

ChilledWaterReturn

TertiaryZonePump

T1 T2 T3 T4

T4 Operation

1. Maximizes coil flow rate

2. Ensures good humidity control

ADVANTAGES

1. Temperature of return water is unknown

2. Temperature of return water to chiller may be too high

DISADVANTAGES

No single sensor location satisfies all design criteria

SO........

LoadMV

Load MV

Common T2

ChilledWaterReturn

TertiaryZonePump

T2 T3T1

Applying Zone Valve Controller

1. Temperature control to the zone (T1 sensing).2. If T1 is satisfied, return water temperature to the chiller

plant (T2 sensing).3. Monitor secondary chilled water supply temperature

(T3 sensing) for temperature increase due to secondaryreturn water recirculation or temperature decrease due tochiller leaving water temperature reset.

4. Reference point for automatic reset and T (T2 - T3) control (T3 sensing).

Control Algorithm

So what…?

• Satisfy zone cooling requirement at the maximum possible supply temperature

• Minimize secondary flow rate

• Optimize return water temperature

Chiller P

Secondary Pumps

TertiaryPump

3-way Valve Application

Problems

• Bypass returns cold water to chillers, reduces system t.

• Linear valve characteristics can cause increased flow at part load.

• Balancing required in bypass pipe and coil-to-coil.

• High cost per ton at the chiller.

CommonT2

Load MV

T2T1 T3

FlowMeter

SmallBy-Pass

Secondary Supply

Secondary Return

3-way Valve System

T2 T2T2 T2

FlowMeter

T3Common

T3CommonCommon

Zone SupplyTemperature

Chiller SupplyTemperature

TerminalUnit Control

TerminalUnit Balance

Zone BiasControl Valve

Rolairtrol

Zone(Tertiary)

ReturnWater

Temperature

Zone 3Zone 1 Zone 2 Zone 4

Common

3D Valves

Distribution(Secondary)

T1T1 T1T1

Chiller

Multi-zone Application

• Individual building temperature control• Static pressure isolation• Return water temperature control• Btu/hr totalization• Outdoor temperature reset• Independent operation

District Cooling Application

• Independent pressure control

• HVAC fluid isolation

District Cooling Application with GPX

T2 T2T2 T2

FlowMeter

T3Common

T3CommonCommon

Zone SupplyTemperature

Chiller SupplyTemperature

TerminalUnit Control

TerminalUnit Balance

ZoneBalanceValve

Zone BiasControl Valve

Rolairtrol

Zone(Tertiary)

ReturnWater

Temperature

Zone 3Zone 1 Zone 2 Zone 4

3D Valves

T1T1 T1T1

Chiller

VPF Application

Comments?Questions?

Observations?

Primary-Secondary Zone Pumping Systems

CHILLER

Return

Supply

Zone A Zone B Zone C

Primary-Secondary Zone Pumping

Shared Piping

CHILLER

Return

Supply

Shared Pipe

CHILLER

Return

Supply

Shared Pipe

Shared Piping

CHILLER

Return

Supply

1500 gpm 1500 gpm (1500 gpm)

Current = 1500Future = 3000

Future Zone C

Flow :

Present and Future Piping

Return

Supply

(1500 gpm) (1500 gpm)

A1 A2 A3

B1 B2 B3

Pressure drop:A to A1+B to B1Present = 20.8’*Future = 45.2’

1500 gpm @ 80’

Zone A

4500 gpm*

Zone A Requirements

Table 9-1 Zone A calculations

Zone A (A to A1 + B to B1) Future Flow @ 4500 gpm Present Flow @ 3000 gpmPipe Size 14” 14”Pressure Drop - ft / 100 ft 2.26 1.04Equivalent Length(supply & return) 1000 ft x 2 = 2000 ft 1000 ft x 2 = 2000 ftPressure drop 45.2 ft 20.8 ftZone pressure drop 80 ft 80 ftTotal pressure drop 125.2 ft 100.8 ftPump Selection @ 1500 gpm 1510-6G @ 56.4 hp = 75 hp* 1510-6G @ 45.8 hp = 60 hp*

Note: 15 hp additional for future requirements* Nominal horsepower motor for NOL pump

Zone A Calculations

Return

Supply

1500 gpm @ 80’ (1500 gpm)

A1 A2 A3

B1 B2 B3

Pressure drop: Zone BAtoA1+ BtoB1 + A1toA2 + B1toB2Present =20.8’ 9.0’*Future = 45.2’ 33.4’

1500 gpm @ 80’

4500 gpm* 3000 gpm*

Zone B Requirements

Table 9-2 Zone B calculations

Zone B(A1to A2+B1 to B2) Future Flow @ 3000 gpm Present Flow @ 1500 gpmPipe Size 12” 12”Pressure Drop - ft / 100 ft 1.67 0.45Equivalent Length(supply & return) 1000 ft x 2 = 2000 ft 1000 ft x 2 = 2000 ftPressure drop 33.4 ft 9.0 ftPrevious pressure drop 45.2 ft 20.8 ftZone pressure drop 80 ft 80 ftTotal pressure drop 158.6 ft 109.8 ftPump Selection @ 1500 gpm 1510-6G @ 71.4 hp = 100 hp* 1510-6G @ 49.6 hp = 60 hp*

Note: 40 additional hp required for future requirements* Nominal horsepower motor for NOL pump

Zone B Calculations

Return

Supply

1500 gpm @ 80’

A1 A2 A3

B1 B2 B3

Pressure drop: Zone CAtoA1+ BtoB1 + A1toA2 + B1toB2 + A2toA3+ B2toB3Present = 45.2’ + 33.4’ + 21.4’Future = Present

1500 gpm @ 80’ 1500 gpm @ 80’

4500 gpm 3000 gpm 1500 gpm

Zone C Requirements

Zone C (A2 to A3 + B2 to B3) Future Flow @ 1500 gpm Present Flow @ 0 gpmPipe Size 10”Pressure Drop - ft / 100 ft 1.07Equivalent Length(supply & return) 1000 ft x 2 = 2000 ftPressure drop 21.4 ftPrevious pressure drop(A to A2, B to B2)

78.6 ft

Zone pressure drop 80 ftTotal pressure drop 180.0 ftPump Selection @ 1500 gpm 1510-6G @ 82.7 hp = 125 hp*; Note: 50 hp more

than Zone A

Zone C Calculations

Zone Pumping SummaryPresent Requirement Future Requirement

Summary Duty Pump Standby Pump Duty Pump Standby PumpZone A 1 @ 75 hp 1 @ 75 hp 1 @ 75 hp 1 @ 75 hpZone B 1 @ 100 hp 1 @ 100 hp 1 @ 100 hp 1 @ 100 hpZone C 1 @ 125 hp 1 @ 125 hp

2 @ 175 hp 2 @ 175 hp 3 @ 300 hp 3 @ 300 hpTotal 4 @ 350 hp 6 @ 600 hp

* Nominal horsepower motor for NOL pump

Zone Pump A

Zone Pump B

Zone Pump C

Friction LossSupply Header

Friction LossReturn Header

LoadFriction

Pressure Diagram - Zone Pumped System

Return

Supply

PumpController

Chiller 3

Chiller 2

Chiller 1

3000 GPM 1500 GPM

3000 GPM1500 GPM

1500 GPM 1500 GPM

BB1 B2

(1500 GPM)

Primary-Secondary Equivalent

Primary-Secondary pressure drop calculation:

Pipe Segment Pressure DropPresent, feet

Pipe Segment Pressure DropFuture, feet

A to A1 + B to B1 20.8 A to A1 + B to B1 45.2A1 to A2 + B1 to B2 9.0 A1 to A2 + B1 to B2 33.4A2 to A3 + B2 to B3 DNA A2 to A3 + B2 to B3 21.4Zone B 80.0 Zone C 80.0Total 109.8 Total 180

P-S Calculations

Distribution pump selection:

Present = 3000 gpm @ 109.8 feet, increase impeller to 13.5” for future head requirements:2 @ VSCS 8x10x17L @ 111.0 hp 125 NOL1 @ VSCS 8x10x17L @ 111.0 hp 125 NOL, standby

Total 3 Pumps 375 NOL, Total

Future = 4500 gpm @ 180 feet:3 @ VSCS 8x10x17L @ 114.4 hp 375 NOL1 @ VSCS 8x10x17L @ 114.4 hp 125 NOL

Total 4 Pumps 500 NOL

P-S Calculations

Comparison

• Zone Pumping– Present

• 350 hp

– Future• 600 hp

• P/S Pumping– Present

• 375 hp

– Future• 500 hp

Primary-Secondary Zone Pumping Cautions

• Excessive initial horsepower

• Initial equipment investment

• Future considerations

• Reduced Horsepower

Comments?Questions?

Observations?

Variable Speed Sensor Selection and Location

Return

Supply

PumpController

DifferentialPressureSensorC

hiller 3

Chiller 2

Chiller 1

Direct Return Piped System

Return

Supply

PumpControllerAFDs

Chiller 3

Chiller 2

Chiller 1

WRONG!SinglePointPressure Sensor

Single Point Pressure Sensor

Head, FT

0200 400 600 800 1000 1200 1400 16000

Flow, gpm

1750 RPM(Maximum rpm)

1480 RPM(Minimum rpm)

Constant PressureDesign PointShut-off head

Control Curve Using Single Point Pressure Sensor

Single Point Pressure Sensor in a CHW System

• A rise in the average water temperature results in a net expansion of the water.

• This “net expansion” volume flows into the compression tank, raising the system pressure.

• The pump slows down.

What if?

Return

CHILLER

Supply

PumpController

P Sensor hereZone A Zone B Zone C

Sensor Across Mains At Pump

• What’s the set point?– It’s the greatest branch and distribution

piping head loss calculated at design flow. In other words…design head.

• What will the flow be in each zone?– Determined by the zone path CV

Head, FT

0200 400 600 800 1000 1200 1400 16000

Flow, gpm

Maximum rpm

Minimum rpm

Design Point

Differential Pressure Sensorat the Pump

Variable Head Loss Ratio

Percent D

esign BH

% Flow

0 10 1009080706050403020

100 C/S, Constant Flow System Pump Head Matched toSystem at Design Flow

C/S, Variable FlowV/S, 0% Variable Hd Loss, 100% Constant Hd

25’ Head

Coil or Valve?

Return

Supply

Variable Head Loss

Constant Head Loss

PumpController

DifferentialPressureSensorC

hiller 3

Chiller 2

Chiller 1

Maximizing Variable Head Loss

CHILLER

CHILLER Pump

Controller

DP Sensor

Zone 120 ft

Zone 220 ft

A B C D

Control Area

P AB+EF20FT

P Zone 120FT

P BC+DE20FT

P Zone 220FT

TDH = P AB + EF + BC + DE + P ZONE 2 = 60 FT

Pressure Drops in Piping (Table 11-1)

Control Area Calculation

What pump head is required at:zero flow?full flow?less than full flow?

Table 11-2 Control Area CalculationFlow

Zone 1Flow

Zone 2FrictionLoss

FrictionLoss

Zone 1

PZone 1

FrictionLoss

Zone 2

PZone 2

0 gpm 600 gpm 5 0 40 20 20 20 45300 gpm 300 gpm 5 5 25 5 20 20 30600 gpm 0 gpm 5 20 20 0 0 20 25

0 gpm 0 gpm 0 0 20 0 0 20 20600 gpm 600 gpm 20 20 40 20 20 20 60

0 100 300 500 600 900 1100 1200Flow, gpm

Head, FT

Lower LimitUpper LimitSingle Point

Control Area

So What...?• Staging pumps in a closed loop HVAC

system by flow alone may not work because of different head requirements for a given flow.

• “Wire to water” pump efficiency calculations at part load depend heavily on the assumptions made about the nature and shape of the control curve.

Single Sensor, Including Balance Valve Pressure Drop

Zone 125 ft

Zone 220 ft

AB (50)

E (10)F

What do you mean...?

• The head loss across the coil and the wide open valve in zone 1 is 25 feet at full flow.

• If that’s true, then we need to add an extra 15 feet of head loss in the balance valve to insure adequate flow out to Zone 2 when the Zone 1 valve is wide open.

Set Point, Zone 1, 40 ft

Flow Zone 1 Flow Zone 2 Friction Loss

Friction Loss

Head Required

Zone 2Setpoint -

Friction Loss

0 gpm 600 gpm 5 20 20 0

300 gpm 300 gpm 5 5 5 30

600 gpm 0 gpm 5 0 0 40

Excess head means wasted energy

CHILLER

CHILLER Pump

Controller

DP Sensor

Zone 1 Zone 2

A B C D

Sensor Location

Single Sensor in Zone 2

FlowZone 1

FlowZone 2

Friction LossAB+EF

Friction LossZone 1

Friction LossBC+DE

P Zone1,Available

P Avail -Friction Loss

Zone 1 0 gpm 600 gpm 5 0 20 40 40300 gpm 300 gpm 5 6.25 5 25 13.75600 gpm 0 gpm 5 25 0 20 - 5

Zone 1 requires 600 gpm at 25 ftZone 2 requires 600 gpm at 20 ft

Inadequate head for Zone 1

Sensor in Zone 1

Flow Zone 1 Flow Zone 2 Friction LossAB+EF

Friction LossBC+DE

Head RequiredZone 2

Setpoint -Friction Loss

0 gpm 600 gpm 5 20 20 5300 gpm 300 gpm 5 5 5 20600 gpm 0 gpm 5 0 0 25

Zone 1 requires 600 gpm at 25 ftZone 2 requires 600 gpm at 20 ft

Inadequate flow in Zone 2

What can we do...?In this system:• Single sensor in Zone 2 at 20 ft fails to

provide adequate flow only when – load in Zone 2 < 50% and – load in Zone 1 > 75%

• Is this a predictable, recurring situation?– manual adjustment– programming

• Add a second sensor

Return

CHILLER

Supply

PumpController

DP Sensors

Applying Multiple Sensors

Use Multiple Sensors?• Load

– Similarity– Priority– Diversity

• One building or several• Redundancy• First cost vs operating cost

The “Active Zone”• Zone set points do not have to be the

same.• Technologic™ pump controller scans all

zones often, comparing process variable to set point in each case.

• Pumps are controlled to satisfy the worst case.

• What happens to the rest of the zones?

Effect of Sensor Location

Zone 1 Zone 2

Multiple sensors, set point across Zone 1, = 25 FT and setpoint across Zone 2 = 20 FT, (Table 11-6)FlowZone

FlowZone

Friction LossAB+EF

MinimumReq’d

P Zone 1,

PZone1

Available

Friction LossBC+DE

MinimumReq’d

P Zone2

PZone 2

Available 0 600 5 0 40 20 20 20300 300 5 6.25 25 5 5 20600 0 5 25 25 0 0 25

Multiple Sensors & Setpoints

Row 1. Sensor 2 is controlling, Zone 1 is over pumped.Row 3. Sensor 1 is controlling, Zone 2 is over pumped.Total pump head required:

row 1 45 ftrow 2 30 ftrow 3 30 ft

CHILLER

Return

Supply

Reverse Return Piped System

Reverse Return Systems• If all the circuits are the “same length”,

will the pump still change speed?• Suppose a coil with a high p

requirement and another with a lower p requirement are served by the same reverse return piping system. OK?

• If the coils are serving different sides of the building, could we have a problem?

CHILLER

Return

Zone A Zone CZone B

Tertiary Piped System

CHILLER

Return

Supply

Zone Piped System

Summary• Give priority to the needs of the branch.• The rule of sensor location is simple and easy

to apply: – If you have to use a single sensor, put it across

the critical branch.– What’s the “critical branch”?– It’s the same one that determined the pump head.

• As we’ve seen, the analysis is more important than the “rule”.

Comments?Questions?

Observations?

Achieving Hydronic System Balance

Systems Approach

Source

Air ManagementDistribution

Verification

Control

Philosophy

Systems Approach

• All components work together as “team”– Components interact and work as well as we

understand them

• A collection of mismatched components will not perform as expected

• Owner, engineer, architect, contractor, and operators are part of the system too!

Hydronic Balancing

• We worry about balance because:– Load calculations are approximate– Piping circuitry analysis is approximate– Control valve selection is approximate– Approximations will lead to underflow and

overflow situations• Results of overflow or underflow

– Design Dt cannot be achieved– Supply temperature controller hunts (?)– Sequence of operation can be upset.

For example:

• Published by ASHRAE & Hydraulic Institute

• Darcy-WeisbachEquation.

Add 15%!

• It’s test, adjust & balance• Test: The system, now built, is verified in

operation to perform to the expected level.– What do we measure?

• temperature, flow, pressure drop, energy consumption….

– What do we test with?– Can we test with what is installed?– Can we obtain accurate readings?

What Is Balancing?

• What level of adjustment, and for what purpose?– Create comfort conditions– Minimize energy consumption– Prevent equipment damage

• How do we adjust?

Adjust: tested in operation, the system is found lacking and needs fine tuning.

Adjust

Balance

• Balance is often interpreted to mean ±10% of design flow.

• This generalization may or may not yield satisfactory heat transfer required for comfort conditions

Redefining Balance

• Evaluate System Operation– If the goal is occupant comfort, then heat

transfer becomes the key concern.– We control heat transfer as a sensible

temperature control process between controller, control valve and coil

– Analysis should account for interaction of all key components, and how they affect the rest of the system

Balanced Hydronic Systems

• All terminals receive enough flow to produce satisfactory heat transfer (97.5% - 102.5%)

• At design conditions, all terminals receive satisfactory flow with the pump in a specified range of operation

• Under temperature control modulation to match load, circuit flow does not exceed design flow accuracy

Chilled Water Coil Flow vs. Heat Transfer

0% 20% 40% 60% 80% 100% 120% 140% 160% 180% 200%0

45Total

Sensible

Latent

• 30”H X 46”W •10 FPI / 4 Row •30 GPM / 10°∆T •85° DB/ 71° WB Ent •45° EWT •15 Circuits •3/8” Tube •4000 CFM •Nominal 10 Ton Rating

% Flow

de ∆

Chilled Water Coil Flow vs. Emission

• 30”H X 46”W •10 FPI / 4 Row •30 GPM / 10°∆T •85° DB/ 71° WB Ent •45° EWT •15 Circuits •3/8” Tube •4000 CFM •Nominal 10 Ton Rating

80% 100%

10097%

Flow Tolerance – 97% Design HT

4050607080

100120140160180200220240

0 2 4 6 8 10 12 14 16 18 20 22 24

±5% ±10% ±15% ±20%

Suggested Flow Tolerance (%)

-0 / +10%

ling6°16°

Balancing, The Obvious Answer

• Maximum branch flows need to be controlled• Balancing valves are one solution• Pressure independent flow control is another

method• “Systems” perspective needs to be

maintained; pipe, valves, calculations.

Pressure Dependent Balancing Valve

0 50 100 150 200 250

Flow (USGPM)

Pressure Dependent Balancing Valve

Cartridge

Orifice is sized for the design flow

Pressure Independent Flow Limiting Valve

Cartridge Operation

Flow Flow

P1 is lowCartridge Opens

P1 - P2 = Constant

P1 is highCartridge Closes

P1 - P2 = Constant

P1 P2 P1 P2

Differential Pressure in PSI

FixedOrifice

Control Range

Design Flow AccuracyRange

Externally adjustable flow limiting balance valves

½” – 2” sizes available

.18 to 45.46 GPM

Externally adjustable flow limiting balance valve and a modulating control valve

½” – 2” sizes available

.13 to 37 GPM

Pressure Independent Control Valves

It’s more than just “balancing valves”

• Piping system decisions:– Usually have a choice between two size pipes

– Varied methods of pipe head loss calculation

• Have to account for safety factors, aging

• Control valve selection: may not get the exact flow coefficient you need.

• Have to have a way to validate (test) and make adjustments (branch & system)

• It takes some judgment and experience.

Design Criteria For Piping

ASHRAE recommends:• Velocity

– General 4 -10 fps– Mechanical rm. 6 -15 fps

• Maximum velocity– 1500 hr/yr 15 fps– 3000 hr/yr 13 fps– 6000 hr/yr 10 fps

• Pressure drop– 1.0 to 4.0 ft / 100 ft.

Consider:• Branch to riser pressure

drops should be 2:1 or greater

• Direct return circuits in variable speed / variable flow hydronic circuits require much more attention to detail and control sequence

CHAPTER 6HEATING, VENTILATING, AND AIR CONDITIONING

SECTION 6.5Prescriptive Path

12Maximum Velocity for Pipes

over 12 in. Size

8.5 fps

13.0 fps

6.5 fps

9.5 fps

5.0 fps

7.5 fps

TABLE 6.5.4.5 Piping System Design Maximum Flow Rate in GPM

Operating Hours/Year

Nominal Pipe Size, in. Other Variable Flow/Variable Speed Other Variable Flow/

Variable Speed Other Variable Flow/Variable Speed

<2000 Hours/Year <2000 and <4400 Hours/Year >4400 Hours/Year

ASHRAE 90.1-2010

Piping System Design Maximum Flow Rate –Friction Loss Rate Comparison

Friction Loss Rate

Velocity

Nominal Pipe Size, in. Other

Friction Loss Rate (Ft/100 Ft)

VariableSpeed(GPM)

FrictionLoss Rate

(Ft / 100 Ft)Other(GPM)

Friction Loss Rate

(Ft / 100 Ft)

VariableSpeed(GPM)

Friction Loss Rate

(Ft / 100 Ft)Other(GPM)

Friction Loss Rate

(Ft / 100 Ft)

VariableSpeed(GPM)

Friction Loss Rate

(Ft / 100 Ft)2 1/2 120 10.01 180 21.78 85 5.2 130 11.66 68 3.42 110 8.48

3 180 7.26 270 15.78 140 4.5 210 9.74 110 2.86 170 6.514 350 6.55 530 14.56 260 3.72 400 8.46 210 2.48 320 5.525 410 2.84 620 6.25 310 1.67 470 3.68 250 1.12 370 2.346 740 3.47 1100 7.44 570 2.11 860 4.63 440 1.3 680 2.968 1200 2.2 1800 4.79 900 1.27 1400 2.95 700 0.79 1100 1.8610 1800 1.52 2700 3.3 1300 0.82 2000 1.86 1000 0.5 1600 1.2112 2500 1.18 3800 2.63 1900 0.7 2900 1.57 1500 0.45 2300 1.01

>4400 Hours/Year<2000 Hours/Year<2000 and <4400

Hours/Year

Nominal Pipe Size, in. Other

(GPM)Velocity (ft/sec)

VariableSpeed(GPM)

Velocity (ft/sec)

Other(GPM)

Velocity (ft/sec)

VariableSpeed(GPM)

Velocity (ft/sec)

Other(GPM)

Velocity (ft/sec)

VariableSpeed(GPM)

Velocity (ft/sec)

2 1/2 120 8.04 180 12.06 85 5.69 130 8.71 68 4.56 110 7.373 180 7.81 270 11.72 140 6.08 210 9.12 110 4.78 170 7.384 350 8.82 530 13.36 260 6.55 400 10.08 210 5.29 320 8.075 410 6.57 620 9.94 310 4.97 470 7.53 250 4.01 370 5.936 740 8.22 1100 12.22 570 6.33 860 9.55 440 4.89 680 7.558 1200 7.7 1800 11.55 900 5.78 1400 8.98 700 4.49 1100 7.0610 1800 7.32 2700 10.98 1300 5.29 2000 8.13 1000 4.07 1600 6.5112 2500 7.17 3800 10.89 1900 5.45 2900 8.31 1500 4.3 2300 6.59

<2000 Hours/Year<2000 and <4400

Hours/Year >4400 Hours/Year

SYSTEM SYZER– Flow/Pressure Drop

ASHRAE 90.1 max pipe size information

Estimated annual energy cost based

on pipe sizeNote that cost is based on a constant load – it is independent of the info in ASHRAE frame

959080

% Design FlowIn End Circuit

Ratio, Branch ToDistribution

• And it falls off much more below 1:1

Branch to Riser Pressure Drop Ratio

Branch:Riser Pressure Drop RatioH

Distance From Pump0

100%Pump head constant

Improved β

Branch:Riser Pressure Drop RatioH

Distance From Pump0

100% β constantReduced pump head

Issue: System Curve

• When we have many path’s, we have manysystem curves depending upon which valves are open.

• In VS/VF systems, the pump flow changes as the control valves modulate. The pump speed adjusts to those changes.

Flow (USGPM)

Pipe Size

Friction Loss

(Feet)

Velocity (FPS)

Reynolds Number

Flow TypeFriction Factor

5000 12 4.48 14.34 1172764 Transition 0.01414 2.77 11.86 1066660 Transition 0.013916 1.41 9.08 933291 Transition 0.013818 0.78 7.17 829403 Transition 0.013820 0.45 5.77 743901 Transition 0.013824 0.18 3.99 618839 Transition 0.0138

5500 14 3.33 13.04 1173326 Transition 0.013816 1.7 9.99 1026626 Transition 0.013718 0.94 7.89 912343 Transition 0.013620 0.54 6.35 818292 Transition 0.013624 0.22 4.39 680723 Transition 0.0137

6000 14 3.94 14.23 1279992 Transition 0.013716 2.01 10.89 1119949 Transition 0.013618 1.11 8.61 995283 Transition 0.013520 0.64 6.92 892682 Transition 0.013524 0.26 4.79 742607 Transition 0.0136

A much larger system

Balanced Flow

CoefficientCV

BranchAvailable

∆PBranchFlow

Total 6000@68’

10 10 0

Set Point = 20 Ft

Branch = 20’Risers = 48’Ratio = 0.4

Flow (USGPM)

0.0 1000.0 2000.0 3000.0 4000.0 5000.0 6000

Inner Valves Close HeadOuter Valves CLoseSystem Curve

Head ControlMin 2

Flow (USGPM)

0.0 1000.0 2000.0 3000.0 4000.0 5000.0 6000.0

Out Valves Close HeadInner Valves CloseSystem Curve

10 10 0

6000 @ 30

Plot of Valve & Head Combinations 6000 GPM @ 30’ 2:1 Branch Riser Pressure Drop Ratio (BRPDR)

2:1 BRPDR

1234566000 GPM@88 Ft Hd

40’ 32’ 24’ 16’ 8’ 0’

10’10’10’10’10’

10’10’10’10’10’VFD

4’ 4’ 4’ 4’ 4’F’ E’ D’ C’ B’ A’2’

4’ 4’ 4’ 4’ 4’F E D C B A4’

These Must Be Balanced!

Variable Primary Flow System

Control Area for Variable Flow-Variable Speed Primary Distribution System

0 1000 2000 3000 4000 5000 6000 7000Flow (GPM)

System CurveInboardOutboard

Valve 6 Closed

Valve 6 & 5Closed

Valve 6,5,4ClosedValve 6,5,4,3

Closed

Valve 6,5,4,3,2 Closed

Valve 1 Closed

Valve 1,2 Closed

Valve 1,2,3 Closed

Valve 1,2,3,4 Closed

Valve 1,2,3,4,5 Closed

All Open

All Closed

Thoughts On Selection

• Coil pressure drop dominates system controllability.

• Control valve selection with β = 0.5• Balancing valves: provide trim…

– Use as much PD as possible in control valves– Absorb the rest at the balancing valve.

• Use independent flow measurement– Triple Duty Valve– Pump– Circuit Setters

Summary: Why Test & Balance?

• Load calculations can be inaccurate causing excess flow

• Pipe and fitting predicted losses will vary from actual performance– Aging factors / fouling will actually occur many years in

the future– Safety factors result in pump over-heading, improper

pump selection and over flow.• Control valve sizing is not exact.• Systems are not built as designed.

Additional Resources

• http://www.bellgossett.com– Resources & Tools

– XylemKnowsH2o

• http://mediasite.xyleminc.com• Our Representative in your area.

Questions?Thanks for Attending!

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