Maintaining Ice-on-Coil & Stratified Chilled-Water Thermal Energy Storage (TES) Plants

Optimizing Off-Peak Ice Build & Peak Load Shifting for Southern California Facilities

Direct Engineering Summary

Maintaining Ice-on-Coil and Stratified Chilled-Water Thermal Energy Storage (TES) plants involves precise control of chiller operation at 26°F glycol temperatures during off-peak hours for ice production, and meticulous management of blending valves and heat exchangers to deliver 44°F chilled water during peak demand. This strategy leverages Southern California's time-of-use utility rates, significantly reducing operational costs. Western Mechanical, Inc., with CSLB #618138 and UA Local 250 journeymen, specializes in these complex systems, ensuring optimal performance and energy savings. Contact us at (661) 251-0111 for expert service.

Maintaining Ice-on-Coil & Stratified Chilled-Water Thermal Energy Storage (TES) Plants - Western Mechanical, Inc. CSLB #618138

Engineering Tolerances & Governing Standards

Parameter	Specification	Standard
Ice Build Glycol Temperature	26°F (–3.3°C) +/- 0.5°F	ASHRAE 90.1, Title 24 Part 6
Chilled Water Supply Temperature	44°F (6.7°C) +/- 1.0°F	ASHRAE 170, HCAI PIN 70
Thermal Storage Efficiency	85% minimum (charge/discharge)	ISO 50001, CEC Guidelines
Glycol Concentration (Ethylene/Propylene)	30-40% by volume	ASTM D1177, Manufacturer Specs
Peak Demand Load Shift	4 PM - 9 PM utility window	SCE/PG&E Time-of-Use Tariffs

Precision Control for Off-Peak Ice Production

The core thermodynamic principle of Ice-on-Coil TES systems relies on utilizing chillers to produce low-temperature glycol, typically around 26°F, during off-peak electrical demand periods. This super-cooled glycol circulates through coils submerged in water, freezing it into ice. The latent heat of fusion of water (144 Btu/lb) makes ice an incredibly dense energy storage medium. Critical to this process is maintaining precise glycol temperature and flow rates to maximize ice production efficiency without risking chiller damage or inefficient operation. This night-time operation leverages significantly lower utility rates, particularly in Southern California's tiered time-of-use structures.

Maintaining the integrity and efficiency of the ice-building phase requires meticulous attention to refrigerant charge, glycol system cleanliness, and chiller control logic. Any deviation in glycol concentration or the presence of air in the system can drastically reduce heat transfer efficiency, leading to incomplete ice formation or excessive chiller run times. Western Mechanical, Inc. UA Local 250 journeymen are adept at calibrating these complex control sequences, ensuring chillers operate at their optimal coefficient of performance (COP) during the ice-build cycle, thus maximizing energy savings and extending equipment lifespan.

Stratified Chilled-Water TES & Blending Valve Management

Stratified chilled-water TES tanks operate on the principle of density differences between cold and warm water. Chilled water, typically 38-40°F, is introduced at the bottom of a large, insulated tank, pushing warmer return water (around 55-60°F) upwards. During discharge, the cold water is drawn from the bottom, and warm return water is introduced at the top, maintaining distinct thermal layers. The thermocline, the boundary between cold and warm water, is crucial for efficiency. Proper diffuser design and minimal turbulence are essential to prevent mixing and preserve the thermal stratification, ensuring maximum usable storage capacity.

The discharge phase, occurring during peak demand hours (e.g., 4 PM to 9 PM), requires sophisticated blending valve control. For Ice-on-Coil systems, the ice melt water, often below the desired supply temperature, is blended with warmer return water to achieve a precise 44°F supply. Similarly, for stratified tanks, blending valves ensure the facility receives a consistent temperature. Improper valve calibration or control logic can lead to temperature fluctuations, reduced comfort, or inefficient use of stored energy. Our technicians ensure these critical components are precisely tuned for seamless peak load shifting and optimal system performance.

Heat Exchanger Care & Lifecycle ROI

Heat exchangers are fundamental to both Ice-on-Coil and stratified TES systems. In Ice-on-Coil, the evaporator coils within the ice tank are specialized heat exchangers. In stratified systems, external plate-and-frame heat exchangers may be used to isolate the primary chiller loop from the storage tank loop, or to provide free cooling when ambient conditions allow. Maintaining optimal heat transfer across these surfaces is paramount. Fouling from scale, corrosion, or biological growth (especially in open-loop cooling tower systems feeding the chillers) can severely degrade performance, requiring higher energy input to achieve desired temperatures.

Regular inspection, cleaning, and chemical treatment of heat exchangers are critical to sustaining the high efficiency and long-term ROI of TES plants. In the Southern California climate, hard water and airborne contaminants necessitate proactive maintenance strategies. By minimizing fouling and ensuring proper fluid dynamics, Western Mechanical, Inc. helps facilities maximize the energy cost savings derived from peak load shifting, extending the operational life of expensive chiller and TES tank assets, and ensuring compliance with local energy efficiency standards like Title 24 Part 6.

UA Local 250 Certified Field Diagnostic & Commissioning Protocol

Verify glycol concentration using a refractometer, maintaining 30-40% by volume for freeze protection and optimal heat transfer.
Monitor chiller evaporator approach temperature during ice-build; deviations indicate fouling or refrigerant issues.
Inspect TES tank diffusers for damage or obstructions, ensuring proper thermal stratification in chilled-water systems.
Calibrate blending valves to maintain a consistent 44°F chilled water supply temperature during discharge, verifying with NIST-traceable thermometers.
Perform eddy current testing on chiller condenser tubes and inspect heat exchanger plates for fouling or pitting, scheduling cleaning as needed.

Facility Director & Chief Engineer FAQs

What is the ideal glycol temperature for ice building in TES systems?

The ideal glycol temperature for ice building in an Ice-on-Coil TES system is typically 26°F (-3.3°C). This temperature allows for efficient freezing of water around the coils while minimizing the risk of chiller operational issues. Precise control is crucial for optimal energy storage.

How do TES systems shift peak electrical loads?

TES systems shift peak electrical loads by operating chillers during off-peak hours (e.g., overnight) when electricity is cheaper, to create ice or super-cool water. This stored thermal energy is then used to cool the building during expensive peak demand periods (e.g., 4 PM-9 PM), reducing reliance on grid power during high-cost windows.

What maintenance is critical for stratified chilled-water tanks?

Critical maintenance for stratified chilled-water tanks includes regular inspection of internal diffusers for integrity, monitoring the thermocline stability, and ensuring the tank remains sealed and insulated. Preventing mixing of hot and cold layers is paramount for maintaining storage efficiency and delivering consistent supply temperatures.

Why is heat exchanger cleaning important for TES plant efficiency?

Heat exchanger cleaning is vital for TES plant efficiency because fouling (scale, biological growth) on heat transfer surfaces significantly reduces their ability to exchange heat. This forces chillers to work harder, consuming more energy and increasing operational costs, directly impacting the ROI of the TES investment.

Acton Headquarters & 24/7 Southern California Dispatch

Western Mechanical, Inc. • 2210 Soledad Canyon Road, Suite O, Acton, CA 93510 • Primary Phone: (661) 251-0111 • 24/7 Toll-Free: (800) 585-5085 • CSLB #618138 (C-20, C-38, C-4)