A FUNDAMENTAL PERSPECTIVE on CHILLED WATER...
Transcript of A FUNDAMENTAL PERSPECTIVE on CHILLED WATER...
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A FUNDAMENTAL PERSPECTIVEon
CHILLED WATER SYSTEMS
Wm J. CoadCoad Engineering Enterprises
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Fundamental Parameter
Performance
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Examples of Other Parameters
FinancialCost (Investment)Operating CostMaintenance & RepairEnergy
ReliabilityServiceabilityEnergy ConsumptionPower consumption
EnvironmentalRefrigerantsWater UseChemicals
FlexibilityExpandabilityAdaptability
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1. Single Cooling Coil for Human Comfort (HC)
2. Multiple Coils (HC), Simultaneous Loading
3. Multiple Coils (HC), Non-simultaneous Loading
4. Multiple Coils, Some HC, Some Process Loads
5. Process Loads, Similar Requirements
6. Process Loads, Dissimilar Requirements
7. Any Combination of the Above
Nature of Loads
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First Law
Heat Capacity Equationq = mC Δt Btu/hr
For Chilled WaterQ = GPM (500)(tr-ts) Btu/hr
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Energy Flow DiagramFor Load System
Load
Water Flow InX gpm @ t
Water Flow OutX gpm @ t
Load Heat Inq
BoundaryS
R
L
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Independent Variable qL
Dependent VariablesGPM
tStR
qL = GPM (500) (tR-tS)
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To Obtain Maximum Humidity Control~ Constant tS
To Obtain Maximum Chiller Benefit~ Constant tR
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Energy Flow DiagramFor Source System
Source
Water Flow OutX gpm @ t
Water Flow InX gpm @ t
Plant Energy Inq
Boundary S
R
P
RejectedHeat Out
q = q + qL PR
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LoadSource(Plant)
CustomerSupplier
Flow: X gpm @ t
Flow: X gpm @ tR
S
tt
tR
R
S
is the highest temperature in the system
PlantEnergy In
q
LoadHeat In
qP L
RejectedHeat Out
q = q +qR P L
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qL = GPM (500) (tR-tS)
If Load wants constant tS
Plant wants constant tR
Only option is to vary the GPM
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Load Control Options
COIL1
COIL2
X gpm @ tX gpm @ t
X gpm @ t
X gpm @ t
X gpm @ t
X gpm @ t
S S
R R
X < X
q = GPM 500 (t -t ) q = GPM 500 (t -t )
Variable Flow in LoadVariable Flow in SystemConstant t and t
Variable Flow in LoadConstant Flow in SystemConstant tVariable t
variable variable
R
R
1
R SR S
1 R
1
11
SS
S
S R S
R
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COIL1
COIL2
S S
R RVariable Flow, Constant t
Variable Flow, Constant t
Constant Flow LoadsVariable Flow System
SmallBypass
Pumped Tertiary System
ConstantFlowLoads(Variable t )
S
S
R
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COIL1
COIL2
S S
R RVariable Flow, Constant t
Variable Flow, Constant t
Multiple Variable Flow Loads
SmallBypass
Pumped Tertiary System
VariableFlowLoads(Constant t )
S
S
R
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Distributed Pumping
Variable GPM, Constant t
Variable GPM, Constant t
Constant orVariable GPM
Multiple LoadOptions
R
SS S
RR
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1. The water entering the chillers can never be warmer than the water entering the plant.
2. The water entering the plant can never be warmer than the weighted average leaving the loads.
3. The load on the plant is equal to the product of the flow leaving the plant, the Δt and the appropriate constant.
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Single Chiller Plant
Chiller
S
R
Constant Flow, Constant t
Variable tR
S
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Chiller1
Chiller2
Load
Multiple Chiller PlantParallel Chillers
Constant Flow, Variable t
Constant Flow, Variable t
ConstantFlow
S
R
S
R
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Chiller2
Chiller1
Load
Multiple Chiller PlantSeries Chillers
Constant Flow, Constant t
Constant Flow, Variable t
ConstantFlow
R
S
R
S
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Chiller1
Chiller2
Load2
Load1
Other Multiple Chiller Plants (1)Constant or Variable GPMConstant or Variable t
Variable t Constant t
BypassValve
R R
S
Y
S
R
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Chiller1
Chiller2
Load2
Load1
Other Multiple Chiller Plants (2)Constant or Variable GPMConstant or Variable t
Variable t Constant t
BypassValve2 Position
ChillerValves
S
R RYR
S
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Chiller1
Chiller2
Load2
Load1
Multiple Chiller PlantCompound Piping Equal Unloading
Variable GPMConstant t
Variable GPMVariable t
Variable GPMConstant t
Constant GPMConstant t
Constant GPMVariable t
S
R
S
S
R
R R
B
A
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Chiller1
Chiller2
Load2
Load1
Multiple Chiller PlantCompound Piping Sequence Unloading
Variable GPMConstant t
Variable GPMConstant t
S
R
R
S
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1. Identify the types of loads to be served.
2. Design the load connections to receive water at the temperature(s) supplied from the plant and return water at the temperature required by the plant.
3. Design the plant to operate in harmony with the load requirements.
4. Keep all design concepts and algorithms as simple and understandable as possible.
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The dynamics of the load and the source are intrinsically interdependent, thermally and hydraulically, and the failure of any component to perform as designed cannot be accommodated by adding complexity to the other components.