fundamentals of hydronic system design

1

Fundamentals of Hydronic System Design

May 8, 2009ASHRAE Region 6

Chapters Region Conference

Mark HegbergProduct Manager, Danfoss Heating Controls

Agenda

1. “Short Class”1. Very Fundamental

2. You take notes

2. General Class Flow1. Design Problem

2. System Design & Calculation

3. Pump selection

4. Control & System Balance

5. Advanced Concepts

Daniel Bernoulli Bernoulli Equation

Z1

Z2

P2

P1

V1

V2

HL

L2

222

21

12

11 H

ρ

P

2g

Vz

ρ

P

2g

Vz

2

Bernoulli’s Equation...

• Elevation - Potential Energy Of The System, Lifting The Fluid

• Fluid Velocity: Kinetic Energy and Effects of Gravity

• Pressure & Density: Flow Energy Work Done On Surroundings By Fluid

LossHeadH

DensityFluidρ

PressureP

PipeIn Velocity Fluid2g

V

ElevationZ

L

2

Pressure Units

PerfectVacuum

StandardAtmospheric

Pressure

14.7 PSIAor

0 PSIG

0 PSIAor

-? PSIG

DifferenceIn Length

Units:• Inches• Feet• Millimeters• Meters

Liquid Fill• Water• Oil• Mercury

StationarySocket

PressureConnection

BourdonTube

Sector& Pinion

Link

PointerGearHair

Spring

3

Pressure

Or: 0.433 psi / Ft.

• Or Another Way Of Looking At It;

2

2

3 In144Ft1

FtLb.62.34

1'

1'1'

Water62.34 Lb

12"

12"

PSI1Ft2.31

or Ft

InLb.

0.443 2

• A 231 Foot Long Manometer Is Inconvenient for Measuring 100 PSI, and In The Old Days A Common Dense Fluid Was Mercury...

2

2

3 In144Ft1

FtLb.844.87

1'

1'1'

Mercury844.87 Lb

12"

12"

PSI1HgIn2.04

or PSI1

Ft0.17or

FtInLb.

5.87 2

PerfectVacuum

StandardAtmospheric

Pressure

14.7 PSIAor

0 PSIG

0 PSIAor

-? PSIG

≈30 In Hg

4

PerfectVacuum

StandardAtmospheric

Pressure

14.7 PSIAor

0 PSIG

0 PSIAor

-? PSIG

≈30 In Hg

PerfectVacuum

StandardAtmospheric

Pressure

11 PSIA

HgIn21

7PSIHgIn

2.04inLb

11inLb

14.7 22

Pressure

• For this class our reference will be;

Static Pressure

• Static Pressure Is The Elevation

• It’s Created By The Weight Of A Vertical Column Of Water

5

And That Other Unit of Measure? Feet of Head

Feet of Head

• Remember Bernoulli Really Described Energy• Pumps Do "Work" On The Water• Work Is Measured In Ft-Lbs• Water Is Measured In Pounds

LbLb-Ft

Why Use Pump Head?

Water @ 60 F Water @ 200 F Water @ 300 F

Density = 62.34 lbs/cu ft62.34 144 = 0.43 psi/ft2.3 ft / psi30 ft X .43psi/ft =12.9psi12.9 psi X 2.3 ft/psi = 30 ft



92.9 psi 92.3 psi 92.0 psi

80.0 psi 80.0 psi 80.0 psi

P=12.9 P=12.3 P=12.0

Pump Rated For 30 Ft Head @ Flow

6

Review

• Pumps Do The Work: They Add Energy To the Fluid System

– We “Pump” Pounds of Fluid

– Work Measured In Foot-Pounds

– Foot-Pounds of Work Per Pound Fluid Pumped

• Pounds Cancel; We’re Left With Feet or “Head”

• “Density Independent”

• Three Components To Total Head (Work)

– Elevation, Velocity, Pressure

• Work Done on System Components

– Head or Pressure Losses

Design Problem

• Three Story Building

– Four Zones Per Floor

– Each Zone 14 Tons Air Conditioning

– 168 Total Tons

– Evaluate at Constant Entering Air 78½°F DB, 65½°F WB

– 42°F EWT, 16 ½°F ΔT

Develop “Flat” Layout

7

How Does It Work?

SourcePipes

CoilPump

Air Management

• Adds Heat• Rejects Heat• Changes Water

Temperature• BTU/Hour

• Pipes & Coils Provide “Resistance” You Use Energy In Form of Pressure To Move Water

• Air Is In Water, and Goes Into and Comes Out Of Solution As A Function Of Pressure & Temperature

• Pumps Provide Differential Pressure By Converting Electrical Energy To Move Water

Closed Loop Hydronic System Design Method

1. Calculate Facility Load Set Space Design Criteria

Building Code Requirements

ASHRAE Requirements Standard 62.2; Air/Ventilation Requirements

Standard 90.1; Energy

Standard 55; Thermal Comfort

Standard 111; Test & Balance

Guideline 1; Commissioning

Examine Load Requirements Zone Distribution

HVAC Method

Diversity; Do Not Use Diversity When Sizing Pipes & Pumps

System Load

• ASHRAE’s Latest: 1998 “Cooling & Heating Load Calculation Principles” (RP-875) Pedersen, Fisher, Spitler, Liesen

• Air Conditioning Contractors of America

• Manufacturer Load Programs

– System Load

– Block Load

• “Old” Carrier Manual “Engineering Guide for System Design” (1963)

• ASHRAE’s Latest: 1998 “Cooling & Heating Load Calculation Principles” (RP-875) Pedersen, Fisher, Spitler, Liesen

• Air Conditioning Contractors of America

• Manufacturer Load Programs

– System Load

– Block Load

• “Old” Carrier Manual “Engineering Guide for System Design” (1963)

System Impacts

• Heat Transfer Becomes Water Flow

– Over Estimation Causes Over Calculation of Flow

– Energy Efficiency Impacted

– Leads To Bigger Coils & Oversized Control Valves

• Controllability Impacted

• Changes Desired Coil Performance

8

2. Select Heat Transfer Devices Source; Desired System Operating Differential

Temperature Load; Coil that offers required performance at

calculated gain conditions Heating, Cooling & De-Humidification Operating system differential temperature

3. Calculate and “Analyze” System Flows Total System Flow Zone Flow Can the required operating differential temperature

be achieved? Alternative piping and pumping considerations

Closed Loop Hydronic System Design Method Calculate Flow

• Flow

TFlow500Q

)T(TFlb

Btu1GPM

hrmin

60gallb.

8.34Q

ΔTcmQ

EntLvgm

P

Required Water Flow

• 80 GPM / Floor

• 240 GPM Building

gpm2016.5500

12,000)(14q

16.5q50012,000)(14

! Tq500Q

System SyzerThank You! Scott Blackmore & B&G

• Scale 1• Align 16½°F ΔT• 168(,000)• Read Flow

9

20 2020 20 20 20

20 2020 20 20 20

240

240

40

40

40

40

80

80

40

40

40

40

80

80

40

40

40

40

80

80

160 80

160 80

Hydronic Coil Heat Transfer

• Air Side Heat Transfer

Where LMTD is the air-water log mean temperature difference

• Water Side Heat Transfer

Where t is the water temperature rise

q UA LMTD ( ) q=mcp(t2-t1)

2 Pipe Control

T

CM

0%

20%

40%

60%

80%

100%

120%

Alt 1

20°ΔT

Alt 2

60°ΔT

Hot Water Coil Heat TransferPerformance Vs. Water Side ΔT

Hot Water Coil Heat TransferPerformance Vs. Water Side ΔT

% Water Flow

% H

eat

Tran

sfer

HotWaterCoil

75%Design Flow

97.5%Heat

Transfer

90%Design Flow

The coil performance is not linear

The coil performance is not linear

10

Coil Heat Transfer

Perc

enta

ge H

eat T

rans

fer

Percentage Water Flow Rate

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

4 Row Tot

4 Row Sens

4 Row Lat

5 Row Tot

5 Row Sens

5 Row Lat

6 Row Tot

6 Row Sens

6 Row Lat

100%

50%

0%

50%

100%

Total Heat Transfer

Sensible Heat Transfer

Latent Heat Transfer

General Coil Notes

• Traditionally, sensible heat transfer is controlled by throttling flow

• Coil performance tends to be non-linear– More non linear with low water ΔT (6ºF)

– More linear with higher water ΔT (16ºF)

• Coil pressure drop affects– Main & branch pipe sizing

– Control valve operation (valve authority)

– System balance

4. Schematically Design Piping

Select Terminals / Heat Transfer Coils

Component Drops

Note Coil Characteristic for Temperature Drop

Locate Terminals / Heat Transfer Coils

Address Area Fit Constraints

– Size of Unit

– Area of Application

Examine Piping Geography

Develop Pipe Sizing Criteria

Select Control Valve

Examine Valve Authority

General Notes: Air Bind

A B

Supply Main Return Main

3’

1½’

AirWater

• Adequate Operating Differential To Create Flow

11


B

3’

1½’

AirWater

• Adequate Operating Differential To Create Flow


1’ Riser Water Level Displaced By 1’

ΔH A to B = 1’

B


B

3’


ΔH A to B = 5’

B


B

3’


ΔH A to B = 5’

B

Ensure Adequate Differential

High Pressure

Drop

Low Pressure Drop Low Pressure Drop

A

B

Supply Main

Return Main

ΔH

Potential For Air Binding

12

Avoid Ghost Flow Circuits

A

B

Open

Closed

Piping Configuration

• Single Pipe Systems

– Single Load

– Multiple Load

• Two Pipe Systems (Supply & Return)

– Constant Flow Single & Multiple Load

– Variable Flow Single & Multiple Load

• Hybrid Systems

– Bypass Systems

– Primary-Secondary-Tertiary

Single Pipe System

Advantages:

• Simple System!• Less Costly Piping

Disadvantages:

• Simple System!• Zone Temperature Control

Matched Tagged To Source Production

Single Pipe Grid Coil

A

• Depending On “T”Branch Loss

– General Guidance: “B”Length Should Be Twice That of “A”

– High Potential of Air Binding In Grid

– Raising Water Temperature To Compensate Causes Panel Flux To Be Too High

• Guidance: Intertwined Serpentine Coils (Most PexBased Systems Wind Up This Way)

B

13

Closed Loop Circulating System

Definition: Contact With Air At One Location Or Less

Definition: Elevation Differences Do Not Cause Flow

Two Pipe, Direct Return

Two Pipe Distribution System

Supply

Return

Riser (Main)

Riser (Main)

Branch

Old Balancing Technique;

• 2:1- BRPDR 90% design flow at all terminals

• 1:1- 80%

Advantages:

• Water Flow Is Variable– Saves Pump HP

• Water Coil Provides Better Control of Temperature & Humidity

• Temperature To Each Coil Is Constant Per Chiller

Disadvantages:

• Chiller Sees Variable Flow • Flow Through Coil Is

Throttled Creating Variable Return Water Temperature To Chiller

• Must Balance Coil Branches In Relation To Each Other

Two Pipe Variable FlowDistribution System

14

2 Pipe Direct Return Has Unequal Differential Pressures

Hea

d

Distance From Pump0

100%

ΔP2

ΔP3

ΔP1

Two Pipe Constant Flow Distribution System

Supply

Return

T

Advantages:

• Source Sees “Constant” Flow• Water Coil Provides Better

Control of Temperature & Humidity

• Temperature To Coil Is Constant Per Source

Disadvantages:

• Water Flow Is “Constant”• Flow Through Coil Is Throttled

Creating Variable Return Water Temperature To Source

• More Components: Valves• Must Balance Coil Bypass Pipe ΔP

Two Pipe Variable Flow Reverse Return System 2 Pipe Reverse Return Has More Equal Differential Pressures

Hea

d

Distance From Pump0

100%

ΔP1

ΔP2ΔP3

15

Applying Reverse Return

• Loads Should All Be Within 25% Of Each Other

• If Zone Control Is Used, All Branches Should

Be In Similar Zones

• You May Still Have To Balance System

Calculating Friction Head Loss

• hf = Energy Lost Through Friction Expressed As Fluid Feet Of Head, Feet Of Fluid Flowing

• f= Friction Factor

• L= Length Of Pipe

• D= Pipe Diameter

• V= Fluid Average Velocity, Ft/Sec (Flow / Pipe Area)

• g= gravitational constant

h fL

D

V

gf

2

2Darcy-Weisbach Eqn.

5. Size Piping & Calculate Drops Size Pipes In Branches First

2-10 FPS / 1’-4.5’ P Per 100’ (Steel)

Determine Highest Branch Drop & Length Add Coil Drop

Valve Drop Equal To Coil & Pipe or PICV pressure drop

Select Branch To Riser Pressure Drop Ratio

Calculate Mains Divide Worst Branch PD By Ratio, and Then 2 (S&R)

Divide Riser Total Drop By Pipe Length (Target Design Rate)

Examine Target Rate

– Within ASHRAE Guidelines

– Enough Pipe Length vs. TEL Of Fittings

Size Risers

Calculate System & Branch Drops

Design Criteria For Balanced Piping

Examine Pressure Drops Closely For Hydronic Balance

– Branch To Riser Pressure Drop Ratio Helps System Balance In Tolerance

• 4:1 95% Design Flow All Circuits

• 2:1 90% Design Flow

• 1:1 80% Design Flow

• Constant Speed Pump

• Issues

– Equipment Room Piping

– Variable Speed

16

20 2020 20 20 20

20 2020 20 20 20

240

240

40

40

40

40

80

80

40

40

40

40

80

80

40

40

40

40

80

80

160 80

160 80

Sour

ce

100’ 20’ 20’

20’20 20

20 20

240 GPM 40

40 GPM

80 GPM

80

160 80

Sour

ce

100’ 20’ 20’

30’30’

30’

30’ 30’

30’

40 GPM

30’30’ 30’

30’ 30’

40 GPM

40 GPM30’

30’

30’

240 GPM 160 80

100’ 20’ 20’

A

B C 1

2

3

89

5

7

12

46

1011

DE

F

Segment A B C 1-2 2-3 3-4-6 3-5-6 6-7 2-8 8-10-11 8-9-11 11-7 7-12 D E F

Flow

Size

Length

HF Rate

HF Friction Loss

Fittings

Service Valves

Coil

Control Valve

Balance Valve

Source

Total

Path Path Total

A-1-2-3-4-6-7-12-F

A-1-2-3-5-6-7-12-F

A-1-2-8-10-11-7-12-F

A-1-2-8-9-11-7-12-F

A-B-1-2-3-4-6-7-12-E-F

A-B-1-2-3-5-6-7-12-E-F

A-B-1-2-8-10-11-7-12-E-F

A-B-1-2-8-9-11-7-12-E-F

A-B-C-1-2-3-4-6-7-12-D-E-F

A-B-C-1-2-3-5-6-7-12-D-E-F

A-B-C-1-2-8-10-11-7-12-D-E-F

A-B-C-1-2-8-9-11-7-12-D-E-F

Calculate Friction Losses

• Know Length Of Pipe

– Work Darcy-Weisbach Equation

– Use Design Tool

• Count Fittings

– Example: I’m applying stock head loss

– You In Practice: Don’t do this!

• Determine Branch & Riser Losses

– Coils, Specialty Devices

– Trying To Get Rough Cut for Control & Balance Valves

17

Copper Pipe Friction Loss

Volumetric Flow Rate, GPM

Hea

d L

oss

Due

To

Fric

tion

, Ft.

Per 1

00 F

t. Pi

pe

Friction Loss Charts

• Published by ASHRAE & Hydraulic Institute

• D/W Eqn.

Add 15%!Add 15%!

Scale 2 Pipe SizingScale 3 Velocity Check

2”

3¼

18

2”

3.6

Pipe Sizes½”-2”

Fitting Loss PictogramFitting Pressure Loss

• Variety of Fitting Loss Methodologies

Accuracy Varies Widely

Elbow Equivalents (Least Accurate)

Total Equivalent Length

“K” Factor (Current ASHRAE Recommendation)

Hf = KV2

2g

19

Fitting Pressure Loss How Do Fitting Drops Stack Up?

2” 90° Steel Elbow (K=1)

• 1961 H/I TEL 8.5’

• ASHRAE - H/I “K” Factor

• ASHRAE RP-968– (Rahmeyer); K Factor varies

widely as a function of velocity

>11

FPS

TEL “K”

% TEL hfOver“K”

Rahmeyer “K”

GPM K2

% K hfOverK2 hf

.04

.07

.11

.15

.20

.26

.33

.391.9

1520253035404550

116

<3F

PS

hf hf

.505

.535

.535

.543

.552

.561.57

.626.71

.03

.03

.09

.13

.17

.23

.29

.351.91

261272418151515100

98-1851565755534541

SEGMENT A B C 1-2 2-3 3-4-6 3-5-6 6-7 2-8 8-10-11 8-9-11 11-7 7-12 D E FFlow 240 160 80 80 40 20 20 40 40 20 20 40 80 80 160 240Size 4" 3" 2.5" 2.5 1.5 1.25 1.25 1.5 1.5 1.25 1.25 1.5 2.5 2.5" 3" 4"

Length 100' 20' 20' 30 30 60 60 30 30 60 60 30 30 20' 20' 100'HF Rate 3 5.5 4.5 4.5 12.5 9 9 12.5 12.5 9 9 12.5 4.5 4.5 5.5 3

Friction Loss 3 1.1 0.9 1.35 3.75 5.4 5.4 3.75 3.75 5.4 5.4 3.75 1.35 0.9 1.1 3Fittings 2 2 2 2 2 2 2 2 2 2 2 2

Service Valves 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2Coil 17 17 17 17

Control ValveBalance Valve

Source 30Total 5 3.1 2.9 3.35 7.75 26.4 26.4 7.75 7.75 26.4 26.4 7.75 5.35 4.9 5.1 37

PATHTOTAL

A-1-2-3-4-6-7-12-F 5 3.35 7.75 26.4 7.75 5.35 37 92.6A-1-2-3-5-6-7-12-F 5 3.35 7.75 26.4 7.75 5.35 37 92.6

A-1-2-8-10-11-7-12-F 5 3.35 7.75 26.4 7.75 5.35 37 92.6A-1-2-8-9-11-7-12-F 5 3.35 7.75 26.4 7.75 5.35 37 92.6

A-B-1-2-3-4-6-7-12-E-F 5 3.1 3.35 7.75 26.4 7.75 5.35 5.1 37 100.8A-B-1-2-3-5-6-7-12-E-F 5 3.1 3.35 7.75 26.4 7.75 5.35 5.1 37 100.8

A-B-1-2-8-10-11-7-12-E-F 5 3.1 3.35 7.75 26.4 7.75 5.35 5.1 37 100.8A-B-1-2-8-9-11-7-12-E-F 5 3.1 3.35 7.75 26.4 7.75 5.35 5.1 37 100.8

A-B-C-1-2-3-4-6-7-12-D-E-F 5 3.1 2.9 3.35 7.75 26.4 7.75 5.35 4.9 5.1 37 108.6A-B-C-1-2-3-5-6-7-12-D-E-F 5 3.1 2.9 3.35 7.75 26.4 7.75 5.35 4.9 5.1 37 108.6

A-B-C-1-2-8-10-11-7-12-D-E-F 5 3.1 2.9 3.35 7.75 26.4 7.75 5.35 4.9 5.1 37 108.6A-B-C-1-2-8-9-11-7-12-D-E-F 5 3.1 2.9 3.35 7.75 26.4 7.75 5.35 4.9 5.1 37 108.6

• Organize through spreadsheet Moving Towards Pump Selection…

• Friction Losses Unaccounted for;

– Control Valve

• Need to understand “controls”

– Balance Valve

• Need to understand “balance”

– Suction Diffuser

• Should understand pumps

– Pump Discharge Valve(s)

• Should understand pumps and systems

20

Room Air Re-circulated

BlowerCoil

Add Valves

Automated Control

Unit Heater

Hot Water

Heated Room Controller

Control Signal

Actuator

Automated Control

The controller output signal acts in a proportional manner to the difference in the actual from the desired temperature

adding what is lost

The controller output signal acts in a proportional manner to the difference in the actual from the desired temperature

adding what is lost

Energy is lost proportionally to

the outside temperature

q = UA(Ti-TO)

Energy is lost proportionally to

the outside temperature

q = UA(Ti-TO)

CoilBlowerProcess

ManipulateWaterFlow

Disturbances

ControlTemperature

Theory

• Solar• Change Weather• People

Heat Gains

21

CoilBlowerProcess

ManipulateWaterFlow

Disturbances

ControlTemperature

Theory

Heat Gains

Water FlowAir Flow

• Unaccounted for Changes In Differential Head

• Friction Head Loss Distribution

• Pressure Control Dynamics

A Fairly Simple Concept...

• We control for comfort as indicated by temperature

– Humidity Control “Implied” By Coil Selection

• Various levels of implementation

– Economic Criteria

– Process Criteria

– Paradigm Criteria

Proportional Control

KSP +

MV -

e KeOutputSignal

“Control Theory”

Outp

ut

0-1

0 V

DC

SP

t0-10 VDC

Control Signal

Room Controller

Actuated Valve


Room Controller

Actuated Valve

y

Outp

ut

0-1

0 V

DC

SP

t

eError

e - Error

Linear

Resp

onse

0-10 VDCControl Signal

22


Outp

ut

0-1

0 V

DC

SP

t0-10 VDC

Control Signal

Room Controller

Actuated Valve

y

y

(y-yi)=K(t-ti)y = Valve Positionyi = Initial Valve Positiont = Temperatureti = Initial TemperatureK = Constant (gain)

Traditional 2 Way Valve Temperature Control

• Controller controls because response is predictable

• Variable coil flow

• Variable system flow

• “Why” variable speed pumping can be used

T

CM

Valve Characteristic

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0% 20% 40% 60% 80% 100%

% Valve Lift

% B

ran

ch

Flo

w

Quick Opening

Linear

Equal Percentage

• ASHRAE Research (RP-5) Boiled It Down To This

– Just About Every HVAC Text On Valves Uses This Type of Figure

– The Coil Gain (Proportional Band) Isn’t the Same As The Controllers… Why We Use An Equal Percentage Valve

Source: ASHRAE Handbook

Coil Characteristic Valve CharacteristicControlledRelationship

Gain

Gai

nGain

Gain

23

Linear Stem Valves (Globe)

To Select Properly;

• Required Flow Rate (GPM)

• Select Differential Pressure– Magnitude Depends On;

• Control; Open-Closed/Modulating

• Hydraulic Design Philosophy; Balanced, Unbalanced, Branch & Riser Pressure Drops

• Pump Control; Constant vs. Variable Speed

• Required Valve Authority

– Consider Characteristic Requirement

Coil

Controllability ~ Constants

• Constant Differential Pressure Keeps Predictable Flow Characteristic

TC Valve Throttle In

Here 90% Time

1%

8%

Adjustment

0

25

50

75

100

0 25 50 75 100

PO

SIT

ION

OF

CO

NTRO

LLED

DEVIC

E%

OF

STRO

KE

CONTROLLED VARIABLE% OF CONTROLLER SCALE

0% 10% 100%THROTTLING %Proportional Action • Two Position

Room

Tem

per

atu

reVal

ve P

ositio

n Open

SetPoint

24

Proportional Action • Proportional Positioning

Room

Tem

per

atu

reVal

ve P

ositio

n Open

SetPointOffset

Closed

Valve Description

• Many terms describe valves

• Flow Coefficient

– CV

– Rangeability

Control Valve Integration

0

25

50

75

100

0 25 50 75 100

% O

F FL

OW

% OF VALVESTROKE

EQUAL PERCENTAGE CHARACTERISTIC

y

Flow Coefficient

SG

ΔPCq V

25

Flow Coefficient

SG

ΔPCq V

)t500(tqQ lvgent Heat Transfer

FlowWater = 1

Units = PSI

Calculate DesiredLive with Available

Rangeability

• With & W/O Actuator

• Without Actuator, 30:1

• With Actuator, 100+:1

• Globe Valves “De-Facto”Standard

• Ball Valve…

FlowMinFlowMax

0%

20%

40%

60%

80%

100%

0% 20% 40% 60% 80% 100% 120% 140%

MaximumValve Stroke

Coil Characteristic

Eq%

Cha

ract

eris

tic

50%

Aut

hori

ty

Cont

rol C

hara

cter

istic

The Goal; Make the red line straight and 100% to 100%Authority

• Valve authority affects controllability

• The Controller cannot control properly = PMIN / PMAX

PENT

PLVG

PMINPMAX

Supp

ly

Retu

rn

26

Valve Authority

Constant Flow Coefficient Pipe Coil Service Valves Balancing Valves

Variable: Control Valve

Supply

Ret

urn

CV2 CV2CV1

2V2

2V1

V2V1VSYS

CC

CCC

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0% 20% 40% 60% 80% 100%

% Valve Lift

% B

ran

ch

Flo

w

Valve Specification• Modified Equal Percentage Valve• Globe Pattern• 2” Size• 30:1 Rangeability

Valve Specification• Modified Equal Percentage Valve• Globe Pattern• 2” Size• 30:1 Rangeability

β=

1.0

β=

.50

β=

.3β=

.1

Valve Characteristic and Authority

Selection

• Required Flow Rate (GPM)

• Select Differential Pressure

– Magnitude Depends On;

• Control; Open-Closed/Modulating

• Hydraulic Design Philosophy; Balanced, Unbalanced, Branch & Riser Pressure Drops

• Pump Control; Constant vs. Variable Speed

• Required Valve Authority

– Consider Characteristic Requirement

• Solve Algebraically

Hea

d

Distance From Pump0

100%

ΔP1+ΔP2 ΔP2 ΔP3

Understand Hydraulics

ΔP1

ΔP2

27

Balance Valve

• Temperature Control Valves– Electronically Actuated

– Characteristic for control

• Temperature Control Valves Require Balancing Valves– “Static”; “Circuit Setter”: Constant

speed flat curve pumping systems with “low” head loss distribution systems

– “Dynamic” or Automatic Flow Limiting; Variable Speed Variable Flow Pumping Systems

Static Balancing Valve

Dynamic Balancing Valve Cartridge

Considering Our Example

Balance:

– Farthest Circuit (Highest Head Loss) 108.6’

– Middle Circuit; 100.8’ – About 8’ required to balance

– Closest Circuit; 92.6’ – About 16’ required to balance

Control Valve:

– 50% Authority means 108’ (47 psi) selection pressure drop! A 216 foot head pump!!

Options:

– ?


Length 100' 20' 20' 30 30 60 60 30 30 60 60 30 30 20' 20' 100'HF Rate 3 5.5 4.5 4.5 12.5 9 9 12.5 12.5 9 9 12.5 4.5 4.5 5.5 3




Source 30Total 5 3.1 2.9 3.35 7.75 26.4 26.4 7.75 7.75 26.4 26.4 7.75 5.35 4.9 5.1 37

PATHTOTAL

A-1-2-3-4-6-7-12-F 5 3.35 7.75 26.4 7.75 5.35 37 92.6A-1-2-3-5-6-7-12-F 5 3.35 7.75 26.4 7.75 5.35 37 92.6

A-1-2-8-10-11-7-12-F 5 3.35 7.75 26.4 7.75 5.35 37 92.6A-1-2-8-9-11-7-12-F 5 3.35 7.75 26.4 7.75 5.35 37 92.6

A-B-1-2-3-4-6-7-12-E-F 5 3.1 3.35 7.75 26.4 7.75 5.35 5.1 37 100.8A-B-1-2-3-5-6-7-12-E-F 5 3.1 3.35 7.75 26.4 7.75 5.35 5.1 37 100.8

A-B-1-2-8-10-11-7-12-E-F 5 3.1 3.35 7.75 26.4 7.75 5.35 5.1 37 100.8A-B-1-2-8-9-11-7-12-E-F 5 3.1 3.35 7.75 26.4 7.75 5.35 5.1 37 100.8

A-B-C-1-2-3-4-6-7-12-D-E-F 5 3.1 2.9 3.35 7.75 26.4 7.75 5.35 4.9 5.1 37 108.6A-B-C-1-2-3-5-6-7-12-D-E-F 5 3.1 2.9 3.35 7.75 26.4 7.75 5.35 4.9 5.1 37 108.6

A-B-C-1-2-8-10-11-7-12-D-E-F 5 3.1 2.9 3.35 7.75 26.4 7.75 5.35 4.9 5.1 37 108.6A-B-C-1-2-8-9-11-7-12-D-E-F 5 3.1 2.9 3.35 7.75 26.4 7.75 5.35 4.9 5.1 37 108.6

• Actually calculate and show all fittings and losses…SEGMENT A B C 1-2 2-3 3-4-6 3-5-6 6-7 2-8 8-10-11 8-9-11 11-7 7-12 D E F

Flow 240 160 80 80 40 20 20 40 40 20 20 40 80 80 160 240Size 4" 3" 2.5" 2.5 2 1.5 1.5 2 2 1.5 1.5 2 2.5 2.5" 3" 4"

Length 100' 20' 20' 30 30 60 60 30 30 60 60 30 30 20' 20' 100'HF Rate 3 5.5 4.5 4.5 3.25 3.75 3.75 3.25 3.25 3.75 3.75 3.25 4.5 4.5 5.5 3

Friction Loss 3 1.1 0.9 1.35 0.98 2.25 2.25 0.98 0.98 2.25 2.25 0.98 1.35 0.9 1.1 3Fittings

Service Valves

Coil 17 17 17 17Control ValveBalance Valve

Source 30Total 3 1.1 0.9 1.35 0.98 19.3 19.3 0.98 0.98 19.25 19.25 0.98 1.35 0.9 1.1 33

PATHTOTAL

A-1-2-3-4-6-7-12-F 3 1.35 0.98 19.3 0.98 1.35 33 59.9A-1-2-3-5-6-7-12-F 3 1.35 0.98 19.3 0.98 1.35 33 59.9

A-1-2-8-10-11-7-12-F 3 1.35 0.98 19.25 0.98 1.35 33 59.9A-1-2-8-9-11-7-12-F 3 1.35 0.98 19.25 0.98 1.35 33 59.9

A-B-1-2-3-4-6-7-12-E-F 3 1.1 1.35 0.98 19.3 0.98 1.35 1.1 33 62.1A-B-1-2-3-5-6-7-12-E-F 3 1.1 1.35 0.98 19.3 0.98 1.35 1.1 33 62.1

A-B-1-2-8-10-11-7-12-E-F 3 1.1 1.35 0.98 19.25 0.98 1.35 1.1 33 62.1A-B-1-2-8-9-11-7-12-E-F 3 1.1 1.35 0.98 19.25 0.98 1.35 1.1 33 62.1

A-B-C-1-2-3-4-6-7-12-D-E-F 3 1.1 2.9 1.35 0.98 19.3 0.98 1.35 0.9 1.1 33 65.9A-B-C-1-2-3-5-6-7-12-D-E-F 3 1.1 2.9 1.35 0.98 19.3 0.98 1.35 0.9 1.1 33 65.9

A-B-C-1-2-8-10-11-7-12-D-E-F 3 1.1 2.9 1.35 0.98 19.25 0.98 1.35 0.9 1.1 33 65.9A-B-C-1-2-8-9-11-7-12-D-E-F 3 1.1 2.9 1.35 0.98 19.25 0.98 1.35 0.9 1.1 33 65.9

• Upsize pipe; Ignore fitting & service valve losses• 40% Reduction in head• Why did we do this…

28

Control Valve

• We reduced head loss to 66’

• We want 50% Authority, so size valve for ____

– 66’ (28.6 PSI)

74.3C

2.3166

202.3166

CGPM20

! PCq

V

V

V

66’

3.75

System Syzer: Scale Five

Control Valve Selection

• Which one do you believe?

• Required CV = 3.75• Pipe Size = 1½”• Rules of Thumb

– One pipe size smaller– 5 PSI; CV = 9

Control Valve Selection

There is an awful lot that goes into understanding valve selection

– One valve isn’t necessarily better than another

– Long discussion on hydraulics

Remember we reduced pump head 40% only to have to double it for the control valve

– 108 Feet to 66 Feet to 132 Feet; Net result 24 foot increase

– Skipping a long introduction; Apply dynamic pressure compensating control valves (i.e. “PICV”) tp reduce required head losses, and factor back in estimates for fittings and service devices

• Selected on flow requirement

29

Pressure Independent Control Valves

Pressure Independent Control Valves

• Pressure is kept constant across temperature control orifice by modulating pressure regulator

Two Integrated Valves One Body

• Selection by flow rate

– 1½” valve has maximum flow of 44 GPM

• Differential pressure

– 2-5 PSI design head loss

– 2-50 PSI operating differential

• TC Valve always has 100% authority

– Integrated pressure regulator maintains set pressure

• May be easily adjustable

• Eliminates need for extraneous balancing valves

M

P1 P3P2

P1 P2 P3

Technology Changes…

• Problem is head loss

– Head loss is required for (standard) valves to work

• Still, “old” design guidance is good

– Proven

– Essential element was to drive down head loss i.e. make the system more energy efficient through larger pipe sizes…

– We can easily get to 110 feet, can also upsize main piping

• 240 GPM @ 110 -120 Ft.

• Pick a pump

30

What is a centrifugal pump?• Three Basic Components Motor

(Driver)

Volute Impeller

• Other Components Based On Design

Base

Coupler

Centrifugal Pumps

Volute

Impeller

Seal

Pump ShaftBearings

End Suction Pump

• Single Suction Impeller

• Broad Range of Flow

• HVAC Workhorse

Base Mounted

Close Coupled

End Suction Pump

Bell & Gossett Series 1510Bell & Gossett Series 1510

31

Line Mounted Pump Small Circulators…”Boosters”

• Concept of pumped HVAC goes back to 1920’s

• Transition from gravity hot water heating to forced circulation

• “Boosters”; industry workhorse until ’80s

• ≈ 100 GPM, 40 Ft.Bell & Gossett Series 100Bell & Gossett Series 100

Wet Rotor Circulator Pumps Range In Size Greatly!

5 GPM 15,000 GPM

Circulator

Double Suction Impeller

32

Why So Many Pumps?

•Function of Flow, Head, Speed, Impeller Profile, Force

•Application

– HVAC

– Wells

– Irrigation

– De-watering

– etc.

Bernoulli’s Theorem

a

b

P

WZ

V

g

P

WZ

V

ga

aa b

bb

2 2

2 2

The total head of a fluid at “a” is equal to the total head at “b”, provided that there’s no loss due to friction or work, and no gain due to the

application of work.

Impeller Pump Impeller

33

Single Suction Impeller Impeller and volute

End Suction Pump; Single Suction Impeller

Gauge TapsGauge Taps

DrainDrain

SealSeal

BearingBearing

Slinger Ring

Slinger Ring

SuctionSuction

DischargeDischarge

ShaftShaft

Typical Impellers

Single Suction Double Suction

34

Impeller DynamicsVR

VT

VS

Vanes

Rota

tion

VT = Tangential Velocity

VR = Radial Velocity

VS = Vector SumFullSize

Impeller

Impeller Dynamics

VR

VT

VS

80%

80%

12 80%QQ

Rota

tion

VT = Tangential Velocity

VR = Radial Velocity

VS = Vector SumTrimmedImpeller

Impeller Types

• Open

• Semi-open

• Closed

- Single suction

- Double suction

• Non-clogging

• Axial flow

• Mixed flow

Seals

Shaft

ProcessFluid

Leakage

Environment VesselWall

35

Typical Mechanical Seal

• Normal to HVAC Pump Construction

– Circulating fluid flushes and cools faces

– “2” Seals

– Many seal materials based on application

Pump Seal Detail

Ceramic Seal InsertGraphite Seal Ring

Compression Ring

Impeller

Retainer (Sec Seal)

Gasket

Rotary Assy

Stationary Assembly

Secondary Seal (Seal Bellows)

Seal Lubrication– Separate surfaces

– Prevent contact of high surface points

– Reduce friction / heat

– Carry away the heat that is generated

Separation

Lubricant

Heat

StationaryCeramic

RotatingGraphite

Seal Cavity

36

Suction Piping Detail

5 dia.

1. Pipe supported2. Length of suction

piping allows even impeller loading

RIGHT WRONG

1. Pipe weight hangs on pump flange.

2. Short suction pipe results in uneven impeller loading.

Why 5 Diameters?

Suction Diffusers Suction Diffusers

37

Construction

Orifice Cylinder Full-LengthStraightening Vanes

EPDM O-RingBronze Start-Up Strainer

Installation

Suction Diffuser

ToPumpTo

Pump

FromSystemFrom

System

SupportFoot

SupportFootStraightening

VanesStraightening

Vanes

AccessRequired

Pump Curve

38

Curve Construction

Tota

l Hea

d In

Fee

t

Capacity In US Gallons Per Minute

1

2

3

4

Water Horsepower Input

Tota

l Hea

d In

Fee

t


Hor

sep

ower

Inp

ut

Head Capacity

Water H.P.Input

Water horsepower

WHP=Flow x Head x SG÷3960

BHP and WHP

Tota

l Hea

d In

Fee

t


Hor

sep

ower

Inp

ut

Head Capacity

WHP

B.H.P. InputTo Shaft

H.P. LostTo Friction

& Recirc.

39

Brake Horsepower

BHP =Flow X Head x Sp. Gr.

3960 x ηPump x ηMotor

BHP Horsepower provided at the motor shaft

Flow GPM through the pump

Head feet of head developed by the pump

ηPump efficiency of the pump at the operating point

3960 constant required to provide consistent units

Where:

Pump Efficiency

HP

HPpump Brake

Waterη

Sources Of Inefficiency

• Bearing friction

• Seal

• Fluid friction

• Recirculation

• Shock losses

Pump Efficiency Curve

Tota

l Hea

d In

Fee

t


Effic

ienc

y

Head Capacity

Efficiency

MaximumEfficiency

At This Point

40

Multiple Impeller Curves

Tota

l Hea

d In

Fee

t


Efficiency Curves

Higher RPM Pumps

Tota

l Hea

d In

Fee

t


Efficiency Curves

Speed Effects

Tota

l Hea

d In

Fee

t


1100 RPM 1700 RPM 3500 RPM

Pump Impeller vs. Horsepower

Tota

l Hea

d In

Fee

t


15 HP

10 HP

7.5 HP5 HP

9½"

8¾

8"

7¼"

41

3 HP2 HP

Non-Overloading Motor Selection

Non-Overloading Motor Selection

Speed vs. Horsepower

Tota

l Hea

d In

Fee

t


15 HP1750 RPM

10 HP

7.5 HP5 HP

9½"

Net Positive Suction Head Required Why Worry About Cavitation?

• Noise

• Performance

• Damage

• To What?

– Pipes

– Valves

– Pumps

42

What’s Going On?

1 2

3

4

5

1 2 3 4 5

Entr

ance

Los

s

Fric

tion

Loss

Hyd

raul

ic S

hock

(Tur

bule

nce)

Pres

sure

Incr

ease

From

Impe

ller

Pres

sure

Pump Curve

NPSHRNPSHR

20

10

0

NPSHRNPSHR

Minimum Head Required To Prevent Cavitation

Minimum Head Required To Prevent Cavitation

NPSHRNPSHR

Hydraulic Institute Standards

• ANSI/HI 9.6.1 (1998)

• NPSHR

– NPSHR Of A Pump Is The NPSH That Will Cause The Total Head (First Stage Head For Multi-Stage Pumps) To Be Reduced 3%, Due To Flow Blockage From Cavitation Vapor In The Impeller Vanes

NPSHRNPSHR

NPSHRNPSHR

20

10

0

3% HeadDeviation& InducedCavitation

3% HeadDeviation& InducedCavitation

43

• Cavitation Does Not Start At NPSHR

• The Starting Point Of Cavitation Is Referred To As Incipient Cavitation

– Incipient Cavitation Can Be From 2 to 20 Times the 3% NPSHR Value

– Magnitude Depends On Pump Design

NPSH Margin Recommendations

• Cooling Towers– Low Energy 1.3 or 3 Feet Whichever Is Greater

– High Energy 1.5 or 5 Feet Whichever Is Greater

• General Industry– Low Energy 1.1 or 2 Feet Whichever Is Greater


• Building Services– Low Energy 1.1 or 2 Feet Whichever Is Greater


NPSHANPSHR

Issues

• Extra Margin May Be Required To Account For Pump Wear

• Suction Piping

– In General >5 Diameters LONG Radius Elbow

– >8 Diameters Short Radius Elbow

– Manifolds

D2 D2L2

L2

L1

D1

D2/D1 L1 L2

≥0.3 ≥2D1 ≥5D2

≥0.3 ≥2D1 ≥5D2

Avoiding The Issue

• Choose The Right Pump

– Avoid Pump Curve Extremes

Design Flow

Flow

Hea

dH

ead

44

Shape of The Curve

Tota

l Hea

d In

Fee

t


Steep Curve

Flat Curve

BEP

Affinity Laws

11

22 Q

DD

Q

11

22 Q

RR

Q

1

2

1

22 H

DD

H

1

3

1

22 P

DD

P

1

2

1

22 H

RR

H

1

3

1

22 P

RR

P

GPM Capacity Ft. Head Brake H.P.

Dia

met

erSp

eed

Q = FlowD = Imp. Diam.

H = Head P= PowerR = Speed

Pump Selection for Best Operation

Hig

h Te

mp

erat

ure

Rise

Low

Flo

w C

avita

tion

Low

Bea

ring

& S

eal L

ife

Red

uced

Impe

ller L

ife

Suct

ion

Reci

rcul

atio

nBE

P

Cav

itati

on

Low

Bea

ring

&Se

al L

ife

Dis

char

ge R

ecirc

ulat

ion

% Flow

% H

ead

% R

elia

bili

ty

η x 0.92

η x 0.53

η x 0.1

η

Good Practice-30% to +15%

Better Practice-20% to +10%

Best Practice-10% to +5%

Of BEP

CharacteristicLife ~ MTBF

Why is Pump Requirement 240 GPM @ 120 Feet?

• Pump Energy Is Absorbed By System

• How Much?

– Pump Is Putting Energy In That Meets The Specific Flow And Head That System Will Take

– What Will The System Take… As Much As Pump Will Give!

• The Flow In The System Is A Balance Of The Pump Capacity and The System Capacity

• We Need To Understand Pumps and Systems

45


AB

f

2b

bb

P

2a

aa h

gV

ZWP

Eg

VZ

WP

22

f

2a

2b

abab

P hg

Vg

VZZ

WP

WP

E

22


AB

f

2b

bb

P

2a

aa h

gV

ZWP

Eg

VZ

WP

22

fP hE

Calculated Pump Requirement

• Add All Terminal Flows

– Total All Branch Flows In GPM

• Select Greatest Hydraulic Pressure Loss Circuit

– Branch Loss + Shared Riser Piping; 66 Feet of Head

– Pressure Independent Control Valve; 11 Feet

– Total Head Loss 110 - 119 Feet if we worry about fittings, service valves, etc.

• Pump Requirement Is Required Flow @ Required Head; 240 GPM @ 120 Feet of head

46

5¾”

• “2½AB” Operating Point

– 240 GPM @ 120 Ft

– η = 74%

– 10 HP @ Design

– 15 HP Motor for NOL

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

0 50 100 150 200 250 300 350 400 450 500

Plot Your Pump Curve… Analyze System Flow & Head Relationship

• Q1 = Know (design) Flow

• Q2 = Final Flow

• h1 = Know (design) Head

• h2 = Final Head

1

2

2

1

2

hh

QQ

47

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

0 50 100 150 200 250 300 350 400 450 500

1

2

2

1

2

h

h

Q

Q

Draw System Curve

00960

3612063160

120220155250

HeadFlow

Pumps in Parallel

System Head

1/2 system flow

1/2 system flow

• Size pump piping for total flow• Select pumps for ½ design flow and full head

Specification

• 1400 Total GPM• 72.5 Ft. Head• 2 Pumps In Parallel• 4 BC Pump

Specification

• 1400 Total GPM• 72.5 Ft. Head• 2 Pumps In Parallel• 4 BC Pump

0

10

20

30

40

50

60

70

80

90

100

0 100200

300400

500600

700800

9001000

11001200

48

0

10

20

30

40

50

60

70

80

90

100

0 100200

300400

500600

700800

9001000

11001200

550≈ GPM

0

10

20

30

40

50

60

70

80

90

100

0 100200

300400

500600

700800

9001000

11001200

13001400

15001600

17001800

19002000

21002200

0

10

20

30

40

50

60

70

80

90

100

0 100200

300400

500600

700800

9001000

11001200

13001400

15001600

17001800

19002000

21002200

0

10

20

30

40

50

60

70

80

90

100

0 100200

300400

500600

700800

9001000

11001200

850 GPM

49

0

10

20

30

40

50

60

70

80

90

100

0 100200

300400

500600

700800

9001000

11001200

13001400

15001600

17001800

19002000

21002200 0

10

20

30

40

50

60

70

80

90

100

0 100200

300400

500600

700800

9001000

11001200

13001400

15001600

17001800

19002000

21002200

0

10

20

30

40

50

60

70

80

90

100

0 100200

300400

500600

700800

9001000

11001200

13001400

15001600

17001800

19002000

21002200

Head72.5'@GPM1400

PointFixedhh

QQ

CurveSystem

1

2

1

2

2

0

10

20

30

40

50

60

70

80

90

100

0 100200

300400

500600

700800

9001000

11001200

13001400

15001600

17001800

19002000

21002200

Design Point1400 @ 72.5’

Each PumpOperates At700 @ 72.5’

One PumpOperates To1050 @ 72.5’

And Is OnCurve

50

0

10

20

30

40

50

60

70

80

90

100

0 100200

300400

500600

700800

9001000

11001200

13001400

15001600

17001800

19002000

21002200

10 HP

15 HP

20 HP

Check Pump Horsepower Operating Points

0

10

20

30

40

50

60

70

80

90

100

0 100200

300400

500600

700800

9001000

11001200

13001400

15001600

17001800

19002000

21002200

Design Point1400 @ 72.5’

Parallel Pumping

• Selection– One Half Design Flow At Design Head

– Two Equally Sized Pumps

– PUMP CONTROLLER

• Technique– Safety: System Curve Intersects Both Curves At

Design Condition

• Benefit– Instead of 2 full sized pumps, 2 half size

– Staging; Most of year is with one pump not two

Problem

51

195 GPM 81% Design210 GPM

• 1 Pump: 87% Design Flow

Discussion

• Same pump, different size impellers depending on accuracy of calculation

• 80%+ design flow on one pump operation, reasonable efficiency 66%

• 7.5 BHP

• Backup pump with low hours

Primary-Secondary System Allows Separation of Equipment Losses

52

What Is Primary Secondary?What Is Primary Secondary?

• Method Of Breaking Systems Into Smaller More Manageable Sub-Systems

• Hydraulically and Thermodynamically Isolates One System From Other

• Instead Of One Large Pump Two (or more) Small Pumps

Primary Secondary Issue

• Coordination of Primary & Secondary Flows

– Causes Mixing

– Mixing Point Moves

• Returning to Source, Poor ΔT

• Returning to Field, Reduced Heat Transfer Performance & Increased System Flow

• Traditional VSVF Systems; “Low Delta T”

– Move Towards VSVF Primary & Secondary


Length 100' 20' 20' 30 30 60 60 30 30 60 60 30 30 20' 20' 100'HF Rate 3 5.5 4.5 4.5 12.5 9 9 12.5 12.5 9 9 12.5 4.5 4.5 5.5 3




Source 30Total 5 3.1 2.9 3.35 7.75 26.4 26.4 7.75 7.75 26.4 26.4 7.75 5.35 4.9 5.1 37

PATHTOTAL

A-1-2-3-4-6-7-12-F 5 3.35 7.75 26.4 7.75 5.35 37 92.6A-1-2-3-5-6-7-12-F 5 3.35 7.75 26.4 7.75 5.35 37 92.6

A-1-2-8-10-11-7-12-F 5 3.35 7.75 26.4 7.75 5.35 37 92.6A-1-2-8-9-11-7-12-F 5 3.35 7.75 26.4 7.75 5.35 37 92.6

A-B-1-2-3-4-6-7-12-E-F 5 3.1 3.35 7.75 26.4 7.75 5.35 5.1 37 100.8A-B-1-2-3-5-6-7-12-E-F 5 3.1 3.35 7.75 26.4 7.75 5.35 5.1 37 100.8

A-B-1-2-8-10-11-7-12-E-F 5 3.1 3.35 7.75 26.4 7.75 5.35 5.1 37 100.8A-B-1-2-8-9-11-7-12-E-F 5 3.1 3.35 7.75 26.4 7.75 5.35 5.1 37 100.8

A-B-C-1-2-3-4-6-7-12-D-E-F 5 3.1 2.9 3.35 7.75 26.4 7.75 5.35 4.9 5.1 37 108.6A-B-C-1-2-3-5-6-7-12-D-E-F 5 3.1 2.9 3.35 7.75 26.4 7.75 5.35 4.9 5.1 37 108.6

A-B-C-1-2-8-10-11-7-12-D-E-F 5 3.1 2.9 3.35 7.75 26.4 7.75 5.35 4.9 5.1 37 108.6A-B-C-1-2-8-9-11-7-12-D-E-F 5 3.1 2.9 3.35 7.75 26.4 7.75 5.35 4.9 5.1 37 108.6

• Two pumps– Source 240 GPM @ 30 Ft.– Load 240 GPM @ 90 Ft.

Primary Secondary Layout

53

Further Definition

• Primary: 240 GPM@ 58 Ft. 4.7 BHP

Further Definition

• Three Secondary Pumps (Floor Zones) 80 GPM@53 Ft

Discussion

• Horsepower 10.25

– 3 x 1.85

– 1 x 4.7

• Smaller pumps less expensive, but maybe not in total

• Easier expansion, simpler management

– May offer operating benefit to non-variable flow source

Implied Control

• Controllability ~ Constants

•Water Flow: Keep System Differential Pressure Constant

–Old Paradigm: Apply Constant Speed Flat Curve Pumps

–Adjust All Hydronic Loops To Same Friction Loss

54

Horsepower Is Reduced

5 HP

3 HP

Variable Speed Pumping

• Controllability ~ Constants– Water Flow: Keep System

Differential Pressure Constant

• New Paradigm: Variable Speed Pumps – System Differential Changes

In Reaction To Valve Position

– Control Valve Requires the Same Control Influence as Previously, But Lower Differential Heads Bring Out Selection Mistakes

Variable Speed Pump Paradox Solved, Energy Saved

5 HP

¼ HP

Hea

d Red

uced

80%

+

Speed = 100%

Speed = 37%

Variable Speed Pump Application

• Ideal “Engineering” form of hydronic control; Energy Saving

– Coils operate 80% year with 50% of flow or less

– 50% flow ≈ 12.5% Brake Horsepower

• In our problem, we would probably go with 2 pumps in parallel at ½ Flow and full head

• Review and understand Balancing & Controls

55

Typical Variable Speed Setup

Path P3

Path P1

Path P2

Power

SpeedDrive

Differential Pressure Sensor

PumpControl

Varia

ble

Hea

d

Variable H

ead

Controlled Head(Constant)

Example

Path P3

Path P2

Differential Pressure Sensor

20 20

202020

100

100

200

20

BV

0

BV

?

A

B

C

F

E

D

Path With Design Head

100

100

Flow

100206020Balanced

6020402020Head

E-FBVB-EA-BPath 2

1002020202020Head

E-FD-EC-DB-CA-BPath 3

Both Valves 50%

50

50

Flow

?5?5Head

100206020Balanced

6020402020Design

E-FBVB-EA-BPath 2

40552055Head

1002020202020Design

E-FD-EC-DB-CA-BPath 3

56

Paradigm Change

• System Curve Implies 1 Flow, 1 Head• Variable Speed Does Not Follow; Why?

0

50

0

100

100

Path 3

2000

4010050

30100100

701000

100200100

TDHFlowPath 2

1

2

2

1

2

h

h

Q

Q

Evaluate Using Flow Coefficient

Path P3

Path P2

20 20

202020

100

100

20

BV

0

BV

40

A

B

C

F

E

D 3420/2.31

100C

tCoefficienFlow P3

V

19.660/2.31

100C

tCoefficienFlow P2

V

Control Area

0

10

20

30

40

50

60

70

80

90

100

0 50 100 150 200

Balancing Implication

• This Is The Classic (ASHRAE) Balancing Argument– “Balancing ruins the control valve”

• Excess Balancing Valve Drop Causes Skewed Flow Performance– “Must use high performance valve”– “I don’t like the “extra” pressure drop you have to use for a flow

limiter…”• No; 80% wrong

– 80% Fallacy• Balance provides functionality when all TC valves are open• TC Valve control does not recognize changes in system differential

pressure• Flow limiters don’t add extra pressure drop when properly applied

– 20% Right?• Static balance does skew improperly sequenced VSVF pump systems

• This is a control set point problem, not a balance problem

57

Set Point = 20 Ft

B

C

D

E

F

G

b

c

d

e

f

g

0.7

0

CV

1

CV

2

CV

3

CV

4

CV

5

CV

6

0.7

0

1.38 1.38

1.16 1.16

1.58 1.58

1.5 1.5

A a

0 0 0

7.1 7.1 5.7

5.9 5.9 9.5

5.4 5.4 13

5.1 5.1 16.3

4.9 4.9 19.6

01000

2X 4 =0

8452000

2X 4 =0.7

845+7713000

2X 4 =1.16

23504000

2X 4 =1.38

30645000

2X 4 =1.5

37676000

2X 4 =1.58

845

771

735

714

701

3767

3767 GPM @ 32.7’Flow (USGPM)

Hea

d (F

eet)

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

0.0 1000.0 2000.0 3000.0 4000.0 5000.0 6000.0

Inner Valves Close Head

Outer Valves CLose

System Curve

Valve 1 Closed

Valve 6 & 5 Closed

Valve 1-3 Closed

Valve 6 Closed

Valve 6-4 Closed

Valve 1 & 2 Closed

Plot of Valve & Head Combinations

In VSVF Hydronic Systems of Any Type

• Control valves will change system flow greater than the control valve selection

• This can effect control system stability in

– Chiller staging

– Pump staging

– Other circuits temperature control

• There’s more to it than just the valve!


0

10

20

30

40

50

60

70

80

90

100

0 100 200 300 400 500 600 700 800 900 1000

n=100%

n=90%

n=80%

n=60%n=50%

n=70%

n=30%n=40%

The idea of Variable Speed Pumping is to have even speed transition proportional to changes in head and flow

58


0

10

20

30

40

50

60

70

80

90

100

0 100 200 300 400 500 600 700 800 900 1000

ΔP

Normal pump control often uses a controlled differential pressure across one or more branches that indicate changes in building load (implication)


0

10

20

30

40

50

60

70

80

90

100

0 100 200 300 400 500 600 700 800 900 1000

ΔP ~ Gain

However, pump and system curve intersection should be steep enough so that a change in flow rate actually yields a change in differential head significant enough to get the control algorithm to modify pump speed in a reasonable increment


0

10

20

30

40

50

60

70

80

90

100

0 100 200 300 400 500 600 700

Valve ΔPChangesRadically The old “flat curve” pump characteristic

could hurt system performance, the pump speed controller could easily jump from full speed to much less (100% to 40%) causing improper control throughout all affected but non connected loops (Chillers, towers, pump stage, etc.). Remember: the valve controller always thinks it has a predictable characteristic because of constant ΔP across it.

“Traditional” Balance Valves

• Static: Circuit Setter

• Dynamic: Griswold, Circuit Sentry

Just Provide Maximum Flow Protection

– Static Valves Proportionally Balance; Only Have 75% Pump All Valves Get 75% (Constant Speed Pumps, Not Variable Speed)

– Dynamics Clip Excess Flows & Lose Balance Effects When Required (Variable Speed Pumps)

59

Variable Speed Pump Paradox Solved, Energy Saved

5 HP

¼ HP

Hea

d Red

uced

80%

+

Speed = 100%

Speed = 37%

Variable Speed Pump Paradox

• Big Energy Savings

– Coil; Little Flow… Lots of Heat Transfer

– Hydraulics; Change Pump Speed, Change Valve and Heat Transfer Predictability… Lose Control

• PIC Valves; Can Stop Over Flow and Maintain 100% Valve Authority, 100% Control Predictability

PIC Valves with Flow Setting

• Lift & Turn To Percentage of Rated Flow

• Lack traditional proportionality of static balance, although the “control valve” can now control and provide such…impossible with standard ATC valves

• Provide majority of system required features and benefits

Summary/Tips• Load analysis

– Tip: If you have to apply a diversity factor do not factor it into pump or pipe sizing.

• Flow– Overflowing coils does not add appreciable heat transfer…it takes surface

area. Slightly oversize the coil and then operate at a lower temperature.

• Pipe– You only install it once. Spend the money on larger pipe to reduce head

loss. Be very judicious in applying any diversity when sizing pipe.

• Pumps– Often cost more to run in one year than they cost to install.– No head, no flow. – Learn more; study up on variable speed pump application.

• Controls– Modulate coils and use VS pumps. Carefully coordinate control valve and

spend the extra cash to apply pressure independent control valves

60

Just About Quittin’ Time!

• There’s a lot more to know!– We didn’t cover air and pressure management

– Many variations on systems and materials

– Practice lots!

• We did not cover Open Systems (Cooling Towers)

• Most of our discussion is applicable to all system designs– Keep sense of relativity

A difference to be a difference must be a big enough difference to make a difference!

…Gil Carlson