variable flow chiller plant design
DESCRIPTION
chiller designTRANSCRIPT
VARIABLE FLOW CHILLER PLANT DESIGN
Julian de BulletJulian de BulletASHRAE Distinguished Lecturer
julian@debullet [email protected] FLOW CHILLER PLANT
DESIGN
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Standard 90.1
Code intended ANSI Code intended, ANSI approved, mandatory language, consensus document
Co-developed with IES
Under continuous maintenance and uses ISCs
On code cycle
Includes both Includes both prescriptive and performance paths
Std 90.1 - Purpose
“ provide minimum requirements ...provide minimum requirements for the energy-efficient design of buildings except low-rise buildings except low rise residential buildings”
Std 90.2 Deals With Low Rise Residential Buildings
Guideline 18 Deals With Advanced Energy Efficient Designs
VARIABLE FLOW CHILLER PLANT DESIGN
4
Chiller Basics
Air, Water Or Evaporatively Cooled
Reciprocating, Scroll, Screw Or Centrifugal Compressors
DX or Flooded EvaporatorsEvaporators
VARIABLE FLOW CHILLER PLANT DESIGN
Cooling Tower Basics
Induced Draft TowerForced Draft Tower
VARIABLE FLOW CHILLER PLANT DESIGN
Load Basics
Chilled Water Coils Transfer Heat From Building Air To Chilled Water
Process Loads Cooling Jackets Cooling Jackets
VARIABLE FLOW CHILLER PLANT DESIGN
HVAC Controls
BACnetAS
H R
E
A ™BACnetE
WebWeb based?based?
OPEN PROTOCOL IS A NORM!
WebWeb--based?based?
VARIABLE FLOW CHILLER PLANT DESIGN
OPEN PROTOCOL IS A NORM!
Basic System
Building Load
Condenser Water Loop
Cooling TowerChill d W t PChilled Water Pump
Chilled Water LoopChillerCondenser Water PumpWater Pump
VARIABLE FLOW CHILLER PLANT DESIGN
Full Load Vs. Annual Load
Chiller58% Chiller
33%Fans43%43%
Design Performance
Tower5%
Fans24%
Pumps13%
Annual Energy Usage
Pumps22%
Tower2%
g gy g
VARIABLE FLOW CHILLER PLANT DESIGN
The Industry ARI Standard
Part Load Analysis (IPLV)Part Load Analysis (IPLV)% Load Old % Hrs New % Hrs
100 17 1100 17 175 39 4250 33 4525 11 12
Systems SolutionSystems Solution
VARIABLE FLOW CHILLER PLANT DESIGN
HVAC HVAC -- Prescriptive Method (6.3) Prescriptive Method (6.3)
HydronicHydronic Systems (6.3.4)!!!!!Systems (6.3.4)!!!!!
Variable Flow Required For Systems Over 10 HP (6.4.3.1)10 HP (6.4.3.1)– Modulate Down To 50%
Exceptions– Where Minimum Flow Is Less Than Flow
Required By Equipment And < 75HP Individual Variable Flow Pumps p
> 100 Feet And 50 hp Motor– 30% Design Wattage At 50% Flow– Controlled As A Function Of Flow Or Pressure
VARIABLE FLOW CHILLER PLANT DESIGN
– Controlled As A Function Of Flow Or Pressure Differential
Why Variable Chilled Water Flow?
Pi i A d P B d O D i Piping And Pumps Based On Design Load Rather Than Connected Load
Lower First Cost
Lower Operating Cost
VARIABLE FLOW CHILLER PLANT DESIGN
Primary/Secondary Design
Primary PumpTyp One Per Chiller
DecouplerBuilding Load2 Way Valves
Condenser Water PumpTyp One Per Chiller
Cooling Tower
Chilled Water Loop
Secondary PumpVariable Flow
Flow Varies With Load
VARIABLE FLOW CHILLER PLANT DESIGN
Primary/Secondary Design
ProsPros Variable Flow Through Secondary Loop Stable Constant Flow through Chillers Stable Constant Flow through Chillers
ConsCons C l it Complexity Low Delta T Syndrome Stepped Primary Flow
(More Pump Work Than Variable Primary Flow)
VARIABLE FLOW CHILLER PLANT DESIGN
Low Delta T-Definition
A Condition Whereby a Low Chilled Water Return Temperature Causes an Temperature Causes an Excessive Amount of Chilled Water to Circulate to Meet System Cooling Loads and System Cooling Loads and Chillers Receiving the Low Temperature CHR CANNOT be pLoaded to Their Design Capacity
VARIABLE FLOW CHILLER PLANT DESIGN
Low Delta T Syndrome
Low Delta T Symptoms And SolutionsLow Delta T Symptoms And Solutions 3 Way Valves
Don’t Use Them
Supply Air Setpoints Lowered Beyond Design Valves Go Wide Open - No Control Ensure Valves Are Tracking
Valves Not Closed When Not Required Ensure Valves Close When AHU Not In Use
All System Components Not Designed For Same Delta T
VARIABLE FLOW CHILLER PLANT DESIGN
Low Delta T Syndrome
Low Delta T Symptoms And Low Delta T Symptoms And Solutions Cont’dSolutions Cont’d
Coils And Valves Not Properly Selected Select Correctly
Coils Piped “Backwards” Coils Must Be Piped So Water Is Counterflow To Air
Improper Tertiary Piping Ensure Tertiary Setpoint Is Above Chilled Water
SetpointSetpoint
Dirty Coils- Clean the Coils
VARIABLE FLOW CHILLER PLANT DESIGN
Low Delta T Syndrome
Low Delta T Retrofit Solutions Cont’dLow Delta T Retrofit Solutions Cont’d
VFD Or Dual Compressor Chillers Excellent Part Load Performance Allows Two Chillers To
Operate More Efficiently Even With Parasitic Losses
Oversize Primary Pumps Oversized Primary Pumps With VFDs Can Over Pump Oversized Primary Pumps With VFDs Can Over Pump
Chillers And Avoid Starting Additional Machines
Variable Primary Flow Variable Primary Flow Easily Accommodates Over Pumping Chillers
VARIABLE FLOW CHILLER PLANT DESIGN
Low Delta T Syndrome
Low Delta T Retrofit Solutions Cont’dLow Delta T Retrofit Solutions Cont’d
Reduce Delta T On Primary Side Larger Pumps And Piping Will Increase Capital Cost Penalty At Full Load
Add Flow Control Valves At Each Coil Ensures Terminal Device Doesn’t Exceed Design Flow Ensures Terminal Device Doesn t Exceed Design Flow Space Cooling Not Satisfied Increase System Pressure Drop Adds Cost Adds Cost
Any More Fixes???yVARIABLE FLOW CHILLER PLANT
DESIGN
Low Delta T SyndromeLow Delta T Retrofit Solutions ?Low Delta T Retrofit Solutions ?
Check Valve InDecoupler
Check Valve Puts Pumps In Series Potentially Over-pump Chiller Can Starve Building Doesn’t Fix Real Problem
VARIABLE FLOW CHILLER PLANT DESIGN
Is it this Simple?
Eliminate De-coupling Lines:
Modern Chillers and Boilers can work with variable flowModern Chillers and Boilers can work with variable flow
Employ Pumps in Series:
Modern DDC controls can Coordinate Series Pumping
Load Flow Control:
Avoid any Overflow by using local Temperature Sensors on the Return Line and Limit the Valve
VARIABLE FLOW CHILLER PLANT DESIGNThe Hartman Company
Variable Primary Flow Design
GeneralGeneral Primary Pump Operates When Chilled Water
Required
Condenser Pump And Tower Operate When Chiller Operates
2 Way Valves 2 Way Valves Diversity To Flow
Works With Single, Series And Parallel Chillers Works With Single, Series And Parallel Chillers
VARIABLE FLOW CHILLER PLANT DESIGN
Variable Primary Flow Design
Bypass LineUsed to Ensure Minimum
Flow Through Chillers
Apply Diversity to FlowUse 2 Way ValvesVFD Primary Pump
Flow Meter
Automatic Isolating Valves
VARIABLE FLOW CHILLER PLANT DESIGN
Variable Primary Flow Design
Design Flowrate Determined by Tube Velocity Minimum 1 5 FPS ( Based On A Reynolds # Of 7500) Minimum 1.5 FPS ( Based On A Reynolds # Of 7500)
Maximum 12 FPS
At Typical Conditions, 6-7 FPS At Typical Conditions, 6 7 FPS
Select Evaporator With More Passes & Higher Pressure Drop
Minimum Flow Typically 50% Or Less Of Design
Bypass Must Be Sized To Maintain Minimum Flow Rate Bypass Must Be Sized To Maintain Minimum Flow Rate Of Largest Chiller
VARIABLE FLOW CHILLER PLANT DESIGN
When to consider VPF ?
When:
•System flow can be reduced by at least 30% of design•System flow can be reduced by at least 30% of design.
•Design affords greater cost savings than a “de-coupled” system.
•Operators will understand how the system works and will run it properly.
•The system can tolerate a modest variation in supply water temperature.y pp y p
•A single chiller is being replaced and the primary flow can be varied.
•Variable Flow can be applied to Parallel as well as Series Flow.
VARIABLE FLOW CHILLER PLANT DESIGN
VPF vs. P/S
450000
500000
300000
350000
400000
200000
250000
300000
kWh
100000
150000
00000
0
50000
Chillers Pumps Towers FansC e s u ps o e s a s
Variable Primary Flow 2 Chiller Primary/Secondary Flow 2 Chiller Parallel FlowVARIABLE FLOW CHILLER PLANT
DESIGN
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VARIABLE FLOW CHILLER PLANT DESIGN