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 savings Can provide capital‐cost savings Enhanced system flexibility Lower supply temperature Dual‐use for fire protection Flattened thermal and electric load profiles
First, Some Basics How Stratification Works Observed in isolated lakes and ponds, water left undisturbed tends to form stratified layers due to gravity acting on a density gradient
↑ T, ↓ ρ
Water Density vs. Temperature Stratification in TES systems relies on the relationship between density and temperature to maintain separation between hot and cold fluid
Making Stratification Work Stratified 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 Manhole
Roof Vent
Upper Diffuser Center Column
Openings in Center Column: allow flow in/out of tank
Manhole Inlet & outlet Lower Diffuser Fill/Drain
Lower Diffuser Overflow
Discharge and Recharge Flow Schematics
Thermocline
Recharge Cycle
Discharge Cycle
Chilled Water Storage Cycles Return from Load
Recharge Cycle Chiller
Supply to Load
Return from Load
Hold System Trickle Cycle Shutdown Charge Chiller
Supply to Load
Return from Load
Discharge Cycle Chiller
Supply to Load
TES Tank Structural Design Limits Limitation
Governed by
Maximum Shell Height
Process conditions (pump suction pressure) Soil Conditions (Geotechnical Report) Tank shell thickness considerations Seismic design, sloshing wave Aesthetics
Minimum Shell Height
Tank performance/efficiency
Maximum Roof Height
Clearances Local building codes Aesthetics
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 – 33,350 300 – 29,000
4,250 3,100
gpm tons
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 ASHRAE 2005 HVAC Fundamentals Handbook 2007 HVAC Applications Handbook, Chapter 34, Thermal Storage Design Guide for Cool Thermal storage Standard 150, Method for Testing the Performance of Cool Storage Systems
TES Design Standards, Codes, Guides AWWA – American Water Works Association D100-05 Welded Steel Tanks for Water Storage D102-06 Painting Steel Water Storage Tanks ASME B31.1 – Code for Pressure Piping- Power Piping NFPA – National Fire Protection Association Standard for Water Tanks for Private Water Protection API – American Petroleum Institute Standard 650 – Welded Steel Tanks for Oil Storage
TES Tank Design Details to Consider ¾Advantages of taller tanks •More volumetrically efficient with less volume devoted to: •Thermocline depth •Diffuser depths •Less Δp between chilled water source and system ¾Beware of water hammer in the system ¾Provide an allowance for operating range, commonly 3”, and thermal expansion ¾Tank 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 ¾Specify heat gain limit, commonly 2% but is usually more on tanks with small Ton‐hour capacities due to substantially increased insulation thickness ¾Specify pressure drop measured between inlet and outlet nozzles, commonly <3 psi
TES Tank Instrumentation Roof nozzle For level gauge/ switch
Supply and return Temperature Sensors, external To tank
Flow metering is external to tank
Thermowells for Temperature sensors
District Cooling, St. Paul MN
University of Texas, El Paso
Texas Medical Center, Houston
McCormick Place, Chicago
