Thermal Energy Storage (TES)Tank Design

Presented by

Jim Ford

Business Development Manager

Chicago Bridge & Iron Co.

Why stratified chilled water TES?Can provide energy cost savingsCan provide capital‐cost savingsEnhanced system flexibilityLower supply temperatureDual‐use for fire protection

Flattened thermal and electric load profiles

First, Some BasicsHow Stratification Works

↑ T,  ↓ ρ

Observed in isolated lakes and ponds, water left undisturbed tends to formstratified layers due to gravity  acting on a density gradient

Water Density vs. Temperature

Stratification in TES systems relies on the relationship between densityand temperature to maintain separation between hot and cold fluid

Making Stratification WorkStratified thermal storage can accommodate almost any temperature difference, although the storage volume required is minimized with larger delta‐T

Thermal diffusion between the hot and cold fluid is confined to the interface region called the thermocline

The key to leveraging this phenomenon for thermal storage is creating stratified layers and keeping the stratification intact

Thermal Energy Storage Tank Components

Fill/Drain Overflow

Manhole

Manhole

Lower Diffuser

Center Column

Openings in Center Column: allow flow in/out of tank

Upper Diffuser

Lower DiffuserInlet & outlet

Roof Vent

Discharge and Recharge Flow Schematics

Thermocline

Discharge CycleRecharge Cycle

Chiller

Return from Load

Supply to Load

Recharge Cycle

Hold Cycle

Discharge Cycle

Chiller

Return from Load

Supply to Load

Chiller

Return from Load

Supply to Load

ChillerChiller

Trickle ChargeSystem Shutdown

Chilled Water Storage Cycles

TES Tank Structural Design LimitsLimitation Governed by

Maximum Shell Height Process conditions (pump suction pressure)Soil Conditions (Geotechnical Report)Tank shell thickness considerationsSeismic design, sloshing waveAesthetics

Minimum Shell Height Tank performance/efficiency

Maximum Roof Height ClearancesLocal building codesAesthetics

Maximum Diameter Area available – also consider construction requirements

TES Tank Thermal Design Limits

Design Parameter Range Typical Units

Total Stored Thermal Capacity 1,000 – 160,000 16,250 ton-hrs

Supply & Return Temperature 40– 75 42 / 58 °F

Discharge & Recharge Flow Rate

575 – 33,350300 – 29,000

4,2503,100

gpmtons

Tank Diameter 24 – 224 63 ft

Tank Height 24 – 150 49 ft

Heat Leak Allowance 1 – 2 ~2 % capacity/day

Pressure Drop 0 – 3 ~2 psid

TES Design Standards, Codes, Guides

ASHRAE2005 HVAC Fundamentals Handbook2007 HVAC Applications Handbook, Chapter 34,

Thermal StorageDesign Guide for Cool Thermal storageStandard 150, Method for Testing the Performance of

Cool Storage Systems

TES Design Standards, Codes, Guides

AWWA – American Water Works AssociationD100-05 Welded Steel Tanks for Water StorageD102-06 Painting Steel Water Storage Tanks

ASMEB31.1 – Code for Pressure Piping- Power Piping

NFPA – National Fire Protection AssociationStandard for Water Tanks for Private Water Protection

API – American Petroleum InstituteStandard 650 – Welded Steel Tanks for Oil Storage

TES Tank Design Details to ConsiderAdvantages of taller tanks

•More volumetrically efficient with less volume devoted to:•Thermocline depth•Diffuser depths

•Less Δp between chilled water source and system

Beware of water hammer in the system

Provide an allowance for operating range, commonly 3”,  and thermal expansion

Tank accessories required by the AWWA D100 Standard•Shell and roof manways•Roof vent•Roof access – ladder or stairway•Overflow – capacity based on maximum filling rate, not flow rate in loop

Specify heat gain limit, commonly 2% but is usually more on tanks with small Ton‐hour capacities due to substantially increased insulation thickness

Specify pressure drop measured between inlet and outlet nozzles, commonly <3 psi

TES Tank Instrumentation

Thermowells forTemperature sensors

Roof nozzleFor level gauge/switch

Supply and returnTemperature Sensors, external To tank

Flow meteringis external to tank

District Cooling, St. Paul MN

University of Texas, El Paso

Texas Medical Center, Houston

McCormick Place, Chicago