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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
Large Chilled Water System Design Seminar
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
Low P
ressure Zone
Load
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
Pumps
Cooling Towers
Triple Duty
SRS SRS SRS
TripleDuty
Standby Pump
Condenser
Condenser
Condenser
Multi-cell Cooling Tower
SRS
Multi-celled Cooling Tower
Cooling Towers
Triple Duty
Condenser
Condenser
Condenser
EqualizationLine
SRS
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
SRS
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
SRS
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
“L” lb/min of water
Load
Ran
ge(“R
” °F)
Ap
proa
ch(°
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
EVAP
Triple Duty
Sediment RemovalSeparator
Triple Duty
TOWER
HEAT
EXCH
GPX
Earth Contact - Summer Cycle
LOADCOND
EVAP
Triple Duty
Sediment RemovalSeparator
Triple Duty
TOWER
HEAT
EXCH
GPX
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
EVAP
Triple Duty
Triple DutySediment RemovalSeparator
TOWER
Single Tower, Summer Cycle
LOADCOND
EVAP
Triple Duty Triple Duty
Sediment RemovalSeparator
TOWER
* Alternate location of SRS, depending onsystem conditions
NOT RECOMMENDED
Single Tower, Winter Cycle
Evaporative Cooling - Direct
Evaporative Cooling - Indirect
LOADCOND
EVAP
Triple Duty
Sediment RemovalSeparator
Triple Duty
TOWER
HEAT
EXCH
GPX
Single Tower/GPX, Summer Cycle
Evaporative Cooling - Indirect
LOADCOND
EVAP
Triple Duty
Sediment RemovalSeparator
Triple Duty
TOWER
HEAT
EXCH
GPX
Single Tower/GPX, Winter Cycle
COND. WATER
CH. WATER
TEMP.DEG. F
EXCHANGERLENGTH
57=
42=
45=
52=
7°F TEMPERATURECROSS
3°F COOLINGAPPROACH
T1
t2
t1
T2
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
T
Vent
Load
Pressure sustainingand check valve
StorageWarmCool
Variable volumedistributionpump
Constant volumeprimary pump
Chiller
Stratified Chilled Water System
30 40 50 60 70
-5
-10
-15
Bottom -20
Top 0
Depth of tank, ft
Temperature, °F
Thermocline
Temperature Stratification
Vent
Pressure sustainingand check valve
StorageWarm
Cool
Constant volumeprimary pump
Chiller
Distributionpump
Primary pump
Load
Transfer PumpDirectioncontrolvalves
Use of Pressure Sustaining Valves
Load
T
Vent
Pressure sustainingand check valve
StorageWarm
Cool
Variable volumeprimarypump
Constant volumeprimary pump
Chiller
T
Heat Exchanger
Variable volumesecondarypump
Incorporating Heat Exchangers
Section1
Section2
Section3
Section4
Ice harvesterchiller
Load
Chilled water pump
Ice waterrecirculationpump
Ice Harvesting System
Charging ModeDischarging Mode
External Melt Ice Storage
Ice
WaterIceCold glycol Warm glycol
Charging Mode Discharging Mode
Encapsulated Ice StorageCharge and Discharge Modes
Tons
Time of Day
Cooling load (met by storage)
ChargingStorage
ChargingStorage
Chiller meets load directly
Chiller on
Chiller off
Full Storage Strategy
Tons
Time of Day
Cooling load(met by storage)
ChargingStorage
ChargingStorage
Cooling load(met by chiller)
Chiller runs continuously
Partial Storage - Load Leveling
Tons
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
Water SourceHeat Pump
Water SourceHeat Pump
Water SourceHeat Pump
Water SourceHeat Pump
Water SourceHeat Pump
Water SourceHeat Pump
Water SourceHeat Pump
Water SourceHeat Pump
BufferTank
( Optional )
Compression Tank
GasketedPlate HeatExchanger
CoolingTower
Heat Pump-Water Source Schematic
Closed Circuit CoolerHeat Rejecter
Water SourceHeat Pump
Water SourceHeat Pump
Water SourceHeat Pump
Water SourceHeat Pump
Water SourceHeat Pump
Water SourceHeat Pump
Water SourceHeat Pump
Water SourceHeat Pump
Water SourceHeat Pump
BufferTank
( Optional )
Compression Tank
Heat Pump-Water Source Schematic
Comments?Questions?
Observations?
Large Chilled Water System Design Seminar
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
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
CHILLER
CHILLER
Return
Primary-SecondaryCommon Pipe
SupplyPrimary Loop
Production
Secondary LoopDistribution
Primary-Secondary Terms
Fundamental Idea
SecondaryPump
Tee“A”Primary
Pump
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
Off
A B100 GPM @ 45°F 100 GPM @ 45°F
PrimaryPump
Primary = Secondary
100 GPM @ 45°F0 GPM
Pump On
A B
100 GPM @ 45°F 100 GPM @ 55°F
100 GPM @ 55°F
Primary > Secondary
Pump On
A B
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
A B
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
CHILLER
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
Pumps
Common
Chiller 3
Chiller 2
Chiller 1
Design of the Common Pipe
10 dia.
Common Pipe Configurations
A B
C D
Head
F1 F2 F3
H1H2
H3
Flow
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
45F
Typical System
Common -- No Flow
SecondaryPumps
1500
1500
1500 15000
CHWS Temp45oF
CHWR Temp55oF
ECW Temp55oF
1500
Chiller 2, off
Chiller 1, on
Production = Distribution
Common -- 500
SecondaryPumps
1500
2000
1500 20000
CHWS Temp47.5oF
CHWR Temp55oF
ECW Temp55oF
Mixing (1500 @ 45) + (500 @ 55)
Chiller 2, off
Chiller 1, on
2000
Distribution > Production
>1500 GPM
ReturnCommon
Supply
>1500 GPM
0 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
5
10
15
20
25
30
0-10 30-40 60-70 90-100
% T
ime
% Load
Typical Load Profile
Chiller 2, 60%
Chiller 1, 40%
% Load
% Time
100
80
60
40
20
100755025
Chiller 1
Chiller 2
1
1 2 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
3000
2100
15002100
1500
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
1.0
0.9
0.8
0.7
0.6
0.5
KW
per Ton
Percent Load
0-10 30-40 60-70 90-1000
5
10
15
20
25
30
0-10 30-40 60-70 90-100
% T
ime
% Load
Typical Load Profile
Chiller 2, 60%
Chiller 1, 40%% Load
% Time
100
80
60
40
20
100755025
Chiller 1
Chiller 2
1
1 2 2
60/40 Chiller Split to Help Minimize Low Part Load Operation
% Load
% Time
100
80
60
40
20
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
Time
Approaching Flow = Load
% Load
% Flow
100755025
100
75
50
25
Ch 1Ch 2 Ch 3 Ch 4
Ch 1 Ch 2 Ch 3
Ch 1 Ch 2
Ch 1
Applying a Variable Speed Chiller
From loads
Common
To Loads
Chiller 3
Chiller 2
Chiller 1
Back Loaded Common
Common0 Flow
SecondaryPumps
1500
CHWS Temp45oF
CHWR Temp55oF
Chiller 2, off
Chiller 1, on
1500
1500
15001500
Production = Distribution
Common500 gpm
SecondaryPumps1500
2000
1500 20000
CHWS Temp47.5oF
CHWR Temp55oF
500
Mixing (1500 @ 45) + (500 @ 55)
500
Chiller 1, on
Chiller 2, off
Distribution > Production
Common900
SecondaryPumps1500
2100
1500
2100
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
Primary-SecondaryCommon
Chiller 3
Chiller 2
Free Cooling
Maximize Free Cooling
Return
Supply
PumpController
SecondaryPumps
Primary-SecondaryCommon
Chiller 3
Chiller 2
Chiller 1
Primary-Secondary System
BHP
125
100
75
50
25
150
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
90
80
70
60
50
40
30
20
10
0 10 1009080706050403020
100
110
120
130
140
150
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
50
100
150
200
250
300
350
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.
6
System Bypass Options
Return
Supply
PumpController
SecondaryConstant Speed
Pumps
PrimarySecondaryCommon
Chiller 3
Chiller 2
Chiller 1
2
5
3
From Loads
Common
To LoadsProduction
Secondary/Pumps
Distribution
Chiller 2, off
Chiller 1, on
FP
FSTS-S
TS-RTP-R
TP-S
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%
15%
20%
30%
15%
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
1020
3040
50
6070
8090
100
0 10 20 30 40 50 60 70 80 90 100
Flow/Speed, Percent
Perc
ent
FlowHeadHorsepower
Theoretical Savings
% H
ead
% B
HP
% Design Flow
120
110
100
90
80
50
40
30
20
10
70
60
120
110
100
90
80
50
40
30
20
10
70
60
0 0
Pump Curves 100% Speed
90%
80%
70%
60%
50%
40%30%
Head
FlowBHP
10 20 30 40 50 60 70 80 90 1000
HP Draw
Design
Head
P Sensor/Transmitter25 Ft. Head
Required Differential Pressure
System Curve& V/S Control System
Flow
piping headloss curve
Distribution
Pum
p TDH
Overall system curve
Hea
d 80
60
40
20
110
0200 400 600 800 1000 1200 1400 16000
100
Set Point25 FT Differential Head Maintained Across Load
(Set Point)
Effect of Constant* Set Point
piping headloss curve
Distribution
Pum
p TDH
Overall system curve
Head
80
60
40
20
110
0200 400 600 800 1000 1200 1400 16000
Flow
100
Control curve Set point,25 FT
As the valve closes, the pump slows down
*What’s Constant?
AB
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
AB
Q1Q2Flow, Q (gpm)
Head, H (feet)
Pump Curve
Control Curve
Decrease in Pump Speed Reduces Flow, Reduces Error
Speed 1
Speed 2
C
Q3
Pipe, FittingFriction Loss
System Operation on Control Curve at Lower Speed
AB
Q1Flow, Q (gpm)
Head(ft) Pipe, Fitting
Friction Loss
Control CurveSpeed 1
Final Speed C
Q4
Return
CHILLER
CHILLER
CHILLER
Supply
Variable Head Loss
Constant Head Loss
PumpController
Adjustable Freqy. Drives
Variable vs Constant Head Loss
Percent D
esign BH
P
% Flow
90
80
70
60
50
40
30
20
10
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
V/S, 50% Variable Hd Loss, 50% Constant Hd
V/S, 75% Variable Hd Loss, 25% Constant Hd
V/S, 100% Variable Hd Loss, 0% Constant Hd
Base
Variable Head Loss Ratio
Variable Head Ratio w/ Overheading
90
80
70
60
50
40
30
20
10
0 10 1009080706050403020
100
110
120
130
140
150
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
120
110
100
90
80
50
40
30
20
10
70
60
0100 200 300 400 500 600 700 800 900 10000
100 %
90 %
80 %
70 %
60 %
50%
40 %30 %
80 %85 %80 %70 %60 %50 %
85 %
% Speed Curves
Constant Efficiency Curve
% EfficiencyH
ead,
Fee
t
GPM
V/S Curves
120
110
100
90
80
50
40
30
20
10
70
60
0100 200 300 400 500 600 700 800 900 10000
100 %
90 %
80 %
70 %
60 %
50%
40 %30 %
80 %85 %80 %70 %60 %50 %
85 %
% Speed Curves
Constant Efficiency Curve
% EfficiencyH
ead,
Fee
t
GPM
Efficiency Changes
Minimum Drive Speed120
110
100
90
80
50
40
30
20
10
70
60
0100 200 300 400 500 600 700 800 900 10000
100 %
90 %
80 %
70 %
60 %
50%
40 %30 %
80 %85 %80 %70 %60 %50 %
85 %
% Speed Curves
Constant Efficiency Curve
% Efficiency
Hea
d, F
eet
GPM
Return
CHILLER
CHILLER
CHILLER
Supply
Variable Head Loss
Constant Differential Head Loss
PumpController
Adjustable Freqy. Drives
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
Flow
••••• •••••
Pump Controller
Temperature
4-20 ma
signal
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
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
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
Adjustable Frequency Drive
Constant Voltage & Frequency
Power
Rectifier Section
Direct Current
Inverter Section
Variable Voltage & Frequency
Power
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
120
0 20 40 60 80 100
Design Speed, %
Effic
ienc
y, %
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
100
90
80
50
40
30
20
10
70
60
010 20 30 40 50 60 70 80 90 1000
% Flow
Hea
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
CHILLER
CHILLER
Supply
Variable Head Loss
Constant Differential Head Loss
PumpController
Adjustable Freqy. Drives
Primary-Secondary System
Primary-Secondary
• Common Practice.
• Why?
– Protection.
• Nuisance shutdowns.
• Freezing.
• Costly downtime.
Variable Primary Flow
AFD AFD AFD
CHILLER
CHILLER
CHILLER
Flow Meter, option
ModulatingValve
Two-position Control Valves
DP
Sensor
Controller
DP
Sen
sor D
P SensorD
P S
enso
r
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
DPSENSOR
DPSENSOR
DPSENSOR
AFD AFD AFD
SIGNALS TO TECH
SIGNAL TO TECH
SIGNAL 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.
T
T
FFF
SIGNALS TO TECH
SIGNALS TO TECH
F
T
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.
OR
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
SIGNAL TO TECH
SIGNAL TO TECH
NOTE:ALL SENSOR SIGNALS WIRED TO TECHNOLOGIC 5500
T
T
FFF
SIGNALS TO TECH
SIGNALS TO TECH
F
T
FLOWMETER/TRANSMITTER
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
DPSENSOR
DPSENSOR
DPSENSOR
AFD AFD AFD
SIGNALS TO TECH
SIGNAL TO TECH
SIGNAL 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.
T
T
FFF
SIGNALS TO TECH
SIGNALS TO TECH
F
T
FLOWMETER/TRANSMITTER
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.
Design Considerations
• 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.
Design Considerations
• 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?
Large Chilled Water System Design Seminar
Primary-Secondary-Tertiary Pumping Systems
CHILLER
CHILLER
Zone A
Zone B
Zone C
Variable Speed Pump
Primary-Secondary-Tertiary
CHILLER
CHILLER
Zone AZone B Zone C
DP Controller
WRONG !
Direct Pumped Zones
WRONG !
Zone A Zone BZone C
Automatic Flow ControlValve
T
Hard set valve
CHILLER
CHILLER
Constant Demand Zones
CHILLER
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
CHILLER
Zone A
Zone B
Zone C
Optional Variable Speed Pump
Primary-Secondary-Tertiarycan be even more useful
?
T3
T1
LoadMV
Load MV
Load MV
Common T2
T4
ChilledWaterReturn
PumpedChilledWaterSupply
TertiaryZonePump
T2 T3 T4
Temperature Sensor Locations
T1
½” Circuit Setter
T3
T1
LoadMV
Load MV
Load MV
CommonT2
T4
ChilledWaterReturn
PumpedChilledWaterSupply
TertiaryZonePump
Tertiary Bridge
Tertiary Bridge
T3
T1
LoadMV
Load MV
Load MV
Common T2
T4
ChilledWaterReturn
PumpedChilledWaterSupply
TertiaryZonePump
T2 T3 T4
Temperature Sensor Locations
T1
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
T3
T1
LoadMV
Load MV
Load MV
Common T2
T4
ChilledWaterReturn
PumpedChilledWaterSupply
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
3. Will not recognize increased supply water temperature
DISADVANTAGES
T3
T1
LoadMV
Load MV
Load MV
Common T2
T4
ChilledWaterReturn
PumpedChilledWaterSupply
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
T3
T1
LoadMV
Load MV
Load MV
Common T2
T4
ChilledWaterReturn
PumpedChilledWaterSupply
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
3. Will not recognize increased supply water temperature
DISADVANTAGES
No single sensor location satisfies all design criteria
SO........
T3
T1
LoadMV
Load MV
Load MV
Common T2
ChilledWaterReturn
PumpedChilledWaterSupply
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
lant
Secondary Pumps
TertiaryPump
TertiaryPump
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.
T1MV
CommonT2
T3
Load
Load MV
Load MV
T2T1 T3
FlowMeter
SmallBy-Pass
Secondary Supply
Secondary Return
3-way Valve System
T2 T2T2 T2
FlowMeter
T3Common
T3CommonCommon
T3
Zone SupplyTemperature
Chiller SupplyTemperature
TerminalUnit Control
Valve
TerminalUnit Balance
Valve
]e
Zone BiasControl Valve
Rolairtrol
Zone(Tertiary)
Pump
ReturnWater
Temperature
Zone 3Zone 1 Zone 2 Zone 4
Common
3D Valves
Distribution(Secondary)
Pumps
T1T1 T1T1
T3
Chiller
Chiller
Chiller
GPX
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
T3
Zone SupplyTemperature
Chiller SupplyTemperature
TerminalUnit Control
Valve
TerminalUnit Balance
Valve
ZoneBalanceValve
Zone BiasControl Valve
Rolairtrol
Zone(Tertiary)
Pump
ReturnWater
Temperature
Zone 3Zone 1 Zone 2 Zone 4
3D Valves
T1T1 T1T1
T3
Chiller
Chiller
Chiller
GPX
VPF Application
Comments?Questions?
Observations?
Large Chilled Water System Design Seminar
Primary-Secondary Zone Pumping Systems
CHILLER
CHILLER
Return
Supply
Zone A Zone B Zone C
Primary-Secondary Zone Pumping
Shared Piping
CHILLER
CHILLER
Return
Supply
Zone A Zone B Zone C
Shared Pipe
CHILLER
CHILLER
Return
Supply
Zone A Zone B Zone C
Shared Pipe
Shared Piping
CHILLER
CHILLER
Return
Supply
Zone A Zone B Zone C
1500 gpm 1500 gpm (1500 gpm)
Current = 1500Future = 3000
Current = 0Future = 1500
Current = 3000Future = 4500
Future Zone C
Flow :
Present and Future Piping
Return
Supply
Zone A Zone B Zone C
(1500 gpm) (1500 gpm)
A1 A2 A3
B1 B2 B3
Pressure drop:A to A1+B to B1Present = 20.8’*Future = 45.2’
A
B
1500 gpm @ 80’
Zone A
4500 gpm*
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
Zone A Zone B Zone C
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’
A
B
1500 gpm @ 80’
4500 gpm* 3000 gpm*
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
Zone A Zone B Zone C
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
A
B
1500 gpm @ 80’ 1500 gpm @ 80’
4500 gpm 3000 gpm 1500 gpm
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
0 0
Zone Pump A
Zone Pump B
Zone Pump C
Friction LossSupply Header
Friction LossReturn Header
LoadFriction
Loss
Pressure Diagram - Zone Pumped System
Return
Supply
PumpController
AFDs
Chiller 3
Chiller 2
Chiller 1
3000 GPM 1500 GPM
3000 GPM1500 GPM
1500 GPM 1500 GPM
A
A1 A2
BB1 B2
A3
(1500 GPM)
B3
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?
Large Chilled Water System Design Seminar
Variable Speed Sensor Selection and Location
Return
Supply
PumpController
AFDs
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
90
80
50
40
30
20
10
70
60
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
CHILLER
CHILLER
Supply
PumpController
P Sensor hereZone A Zone B Zone C
AFDs
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
90
80
50
40
30
20
10
70
60
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
P
% Flow
90
80
70
60
50
40
30
20
10
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
V/S, 50% Variable Hd Loss, 50% Constant Hd
V/S, 75% Variable Hd Loss, 25% Constant Hd
V/S, 100% Variable Hd Loss, 0% Constant Hd
Base
25’ Head
Coil or Valve?
P
Return
Supply
Variable Head Loss
Constant Head Loss
PumpController
AFDs
DifferentialPressureSensorC
hiller 3
Chiller 2
Chiller 1
Maximizing Variable Head Loss
CHILLER
CHILLER
CHILLER Pump
Controller
DP Sensor
Zone 120 ft
Zone 220 ft
AFDs
A B C D
EF
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
AB+EF
FrictionLoss
Zone 1
PZone 1
FrictionLoss
BC+DE
FrictionLoss
Zone 2
PZone 2
TDH
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
10
20
30
40
50
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
C
D
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
AB+EF
Friction Loss
BC+DE
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
CHILLER Pump
Controller
DP Sensor
Zone 1 Zone 2
AFDs
A B C D
EF
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
CHILLER
CHILLER
Supply
PumpController
DP Sensors
Zone A Zone B Zone C
AFDs
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
AB
EF
C
D
OR
Multiple sensors, set point across Zone 1, = 25 FT and setpoint across Zone 2 = 20 FT, (Table 11-6)FlowZone
1
FlowZone
2
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
CHILLER
Return
Zone A Zone CZone B
Tertiary Piped System
CHILLER
CHILLER
Return
Supply
Zone A Zone B Zone C
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?
Large Chilled Water System Design Seminar
Achieving Hydronic System Balance
Systems Approach
M
Load
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%
0% 20% 40% 60% 80% 100% 120% 140% 160% 180% 200%0
5
10
15
20
25
30
35
40
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
% H
eat E
mis
sion
% Flow
Wat
ersi
de ∆
T (°
F)
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%
10
20
30
40
50
60
70
80
90
10097%
Flow Tolerance – 97% Design HT
260
4050607080
100120140160180200220240
0 2 4 6 8 10 12 14 16 18 20 22 24
±5% ±10% ±15% ±20%
Sup
ply
Wat
er T
empe
ratu
re °
F
Suggested Flow Tolerance (%)
-0 / +10%
Hea
ting
Coo
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
20
40
60
80
100
120
140
0 50 100 150 200 250
Flow (USGPM)
Hea
d (F
eet)
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
Flow
in G
PM
Differential Pressure in PSI
FixedOrifice
Control Range
Design Flow AccuracyRange
Pressure Independent Flow Limiting Valve
Externally adjustable flow limiting balance valves
½” – 2” sizes available
.18 to 45.46 GPM
Pressure Independent Flow Limiting Valve
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
2½
3
4
5
6
8
10
12Maximum Velocity for Pipes
over 12 in. Size
120
180
350
410
740
1200
1800
2500
8.5 fps
180
270
530
620
1100
1800
2700
3800
13.0 fps
85
140
260
310
570
900
1300
1900
6.5 fps
130
210
400
470
860
1400
2000
2900
9.5 fps
68
110
210
250
440
700
1000
1500
5.0 fps
110
170
320
370
680
1100
1600
2300
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
Operating Hours/Year
Nominal Pipe Size, in. Other
(GPM)
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
Operating 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
421
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
ead
Distance From Pump0
100%Pump head constant
Improved β
Branch:Riser Pressure Drop RatioH
ead
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
340
287
253
229
211
196
20
28
36
44
52
60
1000
1000
1000
1000
1000
1000
1
2
3
4
5
6
BranchAvailable
∆PBranchFlow
Total 6000@68’
CV
CV
CV
CV
CV
CV
1
2
3
4
5
6
A
B
C
D
E
F
G
b
c
d
e
f
g
a
4
4
4
4
4
4
4
4
4
4
4
4
10 10 0
Set Point = 20 Ft
8
16
24
32
40
Branch = 20’Risers = 48’Ratio = 0.4
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
Inner Valves Close HeadOuter Valves CLoseSystem Curve
Head ControlMin 2
1
212
QQhh
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
Out Valves Close HeadInner Valves CloseSystem Curve
CV
CV
CV
CV
CV
CV
1
2
3
4
5
6
A
B
C
D
E
F
G
b
c
d
e
f
g
a
.83
.83
.83
.83
.83
.83
.83
.83
.83
.83
.83
.83
10 10 0
6000 @ 30
Plot of Valve & Head Combinations 6000 GPM @ 30’ 2:1 Branch Riser Pressure Drop Ratio (BRPDR)
1.7
3.4
5.1
6.8
8.5
2:1 BRPDR
2’
1234566000 GPM@88 Ft Hd
10’
10’
40’ 32’ 24’ 16’ 8’ 0’
10’10’10’10’10’
10’10’10’10’10’VFD
20’
4’ 4’ 4’ 4’ 4’F’ E’ D’ C’ B’ A’2’
4’ 4’ 4’ 4’ 4’F E D C B A4’
1
23
These Must Be Balanced!
Variable Primary Flow System
Control Area for Variable Flow-Variable Speed Primary Distribution System
0.0
20.0
40.0
60.0
80.0
100.0
120.0
0 1000 2000 3000 4000 5000 6000 7000Flow (GPM)
Hea
d (F
eet)
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!