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

Created by the HVAC&R Center at University of Wisconsin-Madison

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

Created by the HVAC&R Center at University of Wisconsin-Madison

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

Created by the HVAC&R Center at University of Wisconsin-Madison

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

Created by the HVAC&R Center at University of Wisconsin-Madison

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)

Created by the HVAC&R Center at University of Wisconsin-Madison

• Chilled water

• Ice harvesting

• Ice on coil

• Encapsulated Ice

• Eutectics

Phase ChangePhase Change

Sensible ChangeSensible Change

Storage System TypesStorage System Types

Created by the HVAC&R Center at University of Wisconsin-Madison

ThermoclineCharge Discharge

BuildingLoad

Chiller

40°F

60°F

Stratified Chilled Water StorageStratified Chilled Water Storage

Created by the HVAC&R Center at University of Wisconsin-Madison

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

Created by the HVAC&R Center at University of Wisconsin-Madison

Ice HarvesterIce Harvester

Return

Supply

Refrigeratedparallel plates

Created by the HVAC&R Center at University of Wisconsin-Madison

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

Created by the HVAC&R Center at University of Wisconsin-Madison

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

Created by the HVAC&R Center at University of Wisconsin-Madison

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

Created by the HVAC&R Center at University of Wisconsin-Madison

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

Created by the HVAC&R Center at University of Wisconsin-Madison

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