thermal energy storage - home page | energy policy … · 2016-06-17 · compact | lightweight |...

Compact | Lightweight | Long Lasting Confidential

Thermal Energy Storage

Said Al-HallajPresented at:

Physics of Sustainable EnergyEnergy Policy Institute, University of Chicago

June 17-18, 2016


Find the Pain: Cooling Commercial Buildings

Consumers pay high prices for consumption and demand charge ($15-24/kW)

Utility companies build new power plants to meet peak demand (< 8 % operation/year)

Higher carbon emissions during peak operation (~0.5 lb CO2/kWh consumed)

>700,000 buildings in US meet this criteria and >300,000 exist in hot areas

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Energy Storage Solutions

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Demand Shift Peak Shaving

Best of two worlds


Current Storage Technologies

Chilled Water Storage

• Sensible Heat Storage: 4.2 x Mass x ΔT

• Water stored in tanks

Ice on Coil

• Latent Heat Storage: 330 kJ/kg x Ice Mass

• External Melt or Internal Melt

Phase Change Materials

• Latent Heat Storage: 150-300 kJ/kg x PCM Mass

• Typically Solid to Liquid

Encapsulated Ice

Latent Heat Storage: 330 kJ/kg x Ice Mass

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Basic Principle of PCM

PCM thermal energy storage (TES) systems store energy as latent heat of fusion

When the temperature of surrounding exceeds the phase transition temperature, the stored latent heat is released isothermally in ideal case

Example: Ice Water (0oC, 330 kJ/kg energy exchange)

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Our Solution: Organic Phase Change Material TES

High Latent Heat organic PCM material (220-280 kJ/kg)

High Thermal Conductivity composite material (10-25 W/m.K)

High temperature operation compared to Ice because of high phase transition temperature (better match with roof top air conditioning units)

Charging duration is shorter and less energy consumption

High discharge rate capability (2-4 times faster than Ice based TES)

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Our solution: Phase Change Composite (PCC)

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SEM images of expanded graphite/wax composite

71x Wax/graphite500x


Ice vs. graphite/wax PCC

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40-60% Copper/Ice

Ice Thermal Conductivity =1.5-2.2 W/m.K

6-8 hours Charge/Discharge Duration

15-25% Copper/PCC

PCC Thermal Conductivity =10-22 W/m.K

1-2 hours Charge/Discharge Duration

100 kWh Ice TESsold by Ice Energy


How it Works

1. 2.

1. 2. 3.Existing air conditioner

runs at night when

electricity is cheap

to charge the battery.

PCC TES Unit

becomes fully

charged with

“cooling power”.

PCC TES Unit discharges to

provide cooling to small

commercial buildings during the

day when electricity prices are

high.

Smart Control System IntegratesBuilding, Weather, AC Unit and TES Unit

AC Unit

TES UnitCommercialBuilding


TES Prototype System Assembly – 4.2 kWh*

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PCC Slab + Copper Serpentine

*Prototype unit validated by DNV-GL and achieved >90% efficiency


Thermal Imaging during Discharge

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100% Charged0 min 20 min 1.5 hrs 2.5 hrs

80% Discharged 3.25 hrs

“Cold Energy” is gradually released from top slabs to bottom slabs during discharge


Case Study

Building: Small quick service restaurant building

Compare Ice and PCM Composite TES systems

Compare Cooling Strategies

Compare Economics

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Peak Shifting Strategy

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A 30 ton-hr Ice TES and 24 ton-hr PCC/TES integrated with existing A/C system and compared separately

Peak energy consumption is drastically reduced

System oversized for low-summer days, hence lots of potential to reduce system size


Peak Shaving Strategy

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A 14 ton-hr PCC TES was added to existing A/C system

Peak Shaving strategy also results in significant savings

Economics were in favor of smaller system


System designed for peak shaving.

COGS includes material, labor and

installation costs.

PCC-TES Unit Economics

• Retrofit savings for building $1,269 year.

• Payback period in 2.6 years with incentives.

• 30 – 50% ROI depending on cost of capital.

50 kWh Peak Shaving Unit* Building Owner Savings

Unit Revenue $10,000

COGS $6,500

Gross Margin 35%

Gross Profit $3,500

Chiller Savings $2,000

Rebates $5,316

Yearly Electricity Savings $1,269

ROI Simple Payback

30-50% 2.61 years

* A 50 kWhr prototype is currently under development in collaboration with National Renewable Energy Laboratory (NREL) as part of a Wells-Fargo funded Innovation Program (IN2)


Conclusions

Robust thermal energy storage systems are very promising technologies that have great potential in commercial buildings applications

TES is a thermal battery that can be designed to completely shift cooling load or partial load shift. This is similar to a hybrid battery or an electric battery vehicle

TES brings in significant savings to all stakeholders involved – consumer, power generator, grid operators

TES reduces carbon emissions by operating the existing HVAC system more efficiently

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Questions

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Thank you Mike Pintar (Booth School of Business) and Siddique Khatib (AllCell R&D Director)

thermal energy storage - home page | energy policy … · 2016-06-17 · compact | lightweight |...

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