introduction to cool thermal storage
TRANSCRIPT
Created by the HVAC&R Center at University of Wisconsin-Madison
Introduction to Cool Introduction to Cool Thermal StorageThermal Storage
A short explanation of the “why’s” and “how’s” to storing cold energy
Data found in this presentation is from Design Guide for Cool Thermal Storage, ASHRAE
Created by the HVAC&R Center at University of Wisconsin-Madison
Benefits of Cool Benefits of Cool StorageStorage
• Reduces electrical demand
• Can reduce energy consumption
• Increases load factor (end-use & utility)
• Potential to reduce first cost
• Lowers operating cost
• Flexible cooling system, i.e. cold air
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Operating StrategiesOperating Strategies
•Full Storage
- Daily
- Weekly
- Other
•Partial Storage
- Load leveling
- Demand limiting
Created by the HVAC&R Center at University of Wisconsin-Madison
Full Storage StrategyFull Storage Strategy
Base load
Lights
Cooling
Fans, etc
Base load
Lights
Fans, etc
Cooling
Time
kW
500
1000
1500Non-Storage Storage
DEK
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Full StorageFull Storage
Attractive for high demand structuresAttractive for short on-peak periods
+ Maximum peak kW reduction+ Simple control+ Can use existing equipment
- Larger storage volume required- Requires precise system sizing
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Partial StoragePartial Storage
+ Minimizes refrigeration plant size
+ Minimizes storage size
- Does not minimize peak demand
(Load leveling)
Load
Time
discharge
charge charge
Chiller capacity
DEK
load metby chiller
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Peak Demand Limit
Cooling PowerBuilding Power
Time (hr)
2 4 6 8 10 12 14 16 18 20 22 24
0.2
0.4
0.6
0.8
1.0
Pow
er D
eman
d (k
W)
Partial StoragePartial Storage(Demand Limiting)(Demand Limiting)
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• Chilled water
• Ice harvesting
• Ice on coil
• Encapsulated Ice
• Eutectics
Phase ChangePhase Change
Sensible ChangeSensible Change
Storage System TypesStorage System Types
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ThermoclineCharge Discharge
BuildingLoad
Chiller
40°F
60°F
Stratified Chilled Water StorageStratified Chilled Water Storage
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Stratified Chilled Water StorageStratified Chilled Water Storage
+ Uses standard chillers+ Efficient operation+ Economical for large systems+ Reliable+ Simple+ Fire protection use
$ Tank Costs: $28 - $43/ton-hr(based on a 14,000 Ton-hr tank)
$ Tank interface: $70-$470/ton(pumps, valves, controls, etc.)
$ Chiller reduction: $250/ton
- Low energy density- Potential space constraints- Maximum water density @ 39F
Advantages
Disadvantages
Costs
Performance
0.60-0.65 kW/ton
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Ice HarvesterIce Harvester
Return
Supply
Refrigeratedparallel plates
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Ice HarvesterIce Harvester
+ Capable of high discharge rate+ Can be used as a chiller+ Separate production & storage+ Allows for cold air distribution
$ Tank Costs: $20 - $25/ton-hr(based on a 14,000 Ton-hr tank)
$ Tank interface: $70-$470/ton(pumps, valves, controls, etc.)
$ Ice Maker: $1200/ton
- Complex system- High maintenance costs- Defrost losses & cycling- High refrigeration unit cost
Advantages
Disadvantages
Costs
Performance
1.0-1.1 kW/ton
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Ice Ice -- On On -- CoilCoil
Brine IceWater
Static Ice Systems
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Ice Ice -- On On -- CoilCoil
+ Modular+ Simple static design+ Reliable+ Allows for cold air distribution
$ Tank Costs: $60/ton-hr(190 nominal Ton-hr tank)
$ Chiller reduction: $450/ton
- Uses a secondary fluid- Requires chiller w/LWT ~24F
Advantages
Disadvantages
Costs
Performance
0.85-1.0 kW/ton
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IceIce--OnOn--Pipe (Refrigerant Based)Pipe (Refrigerant Based)
+ Modular+ Allows for cold air distribution
$ Tank Costs: $90/ton-hr
- High refrigerant charge- Operates at low suction temps.- Energy efficiency f(ice thick)
Advantages
Disadvantages
Costs
Performance
0.95-1.2 kW/ton
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Encapsulated IceEncapsulated Ice
+ Static design+ Reliable+ Allows for cold air distribution
$ Tank Costs: $50-70/ton-hr$ Chiller reduction: $450/ton
- Performance depends on tank- Uses a secondary fluid- Requires chiller w/LWT ~24F- Open hydronic system
Advantages
Disadvantages
Costs
Performance
0.85-1.2 kW/ton
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Eutectic SystemsEutectic Systems
+ Uses convetional chillers+ Requires less storage vs. water+ Water used for charge/discharge
$ Tank Costs: $100-150/ton-hr$ Chiller reduction: $250/ton
- Discharge temperature is high- Poor dehumdification- Requires more storage vs. ice- Potential for system corrosion
Advantages
Disadvantages
Costs
Performance
0.6-0.7 kW/ton
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How Can TES Reduce kWh?How Can TES Reduce kWh?
•Ambient temperature relief at night to improve chiller performance
•Avoids severe penalties for part load chiller operation
•Including cold air reduces pump and fan power
•Increase the use of free cooling and heat recovery