Actively Managed Thermal Energy Storage
Brian Hampton | Viking Cold Solutions
The objective of integrating a Thermal Energy Storage (TES) system developed by Viking Cold Solutions into a Department of Defense (DoD) installation freezer is to demonstrate the three primary benefits of actively managed TES: reduction of electrical consumption, short and long-term temperature protection for products or food provisions, and increased temperature stability for product safety and food quality. This project will compare the electrical consumption and temperature stability profiles of the demonstration freezer before and after TES is installed. The data will prove the operational benefits of TES and will enable better management of electrical demands on DoD installations, including ones that operating with diesel generation and microgrids, while prioritizing operational capability and safety.
A thermal energy management system is comprised of three main elements:
- Passive, non-circulating TES – Individually sealed plastic bottles (cells) containing water-based environmentally-friendly phase change material (PCM). The cells have been designed and tested to have a service life of 20 years or greater.
- Intelligent Controls – A microprocessor-controlled system which actively measures the temperature conditions inside the freezer and controls refrigeration equipment.
- Remote Monitoring – Outbound data telemetry via a cellular connection for the purposes of remotely monitoring temperature and equipment status which provides alerts and alarms.
The combination of these three elements better manages the electrical consumption of the freezer by utilizing the thermal energy stored in the PCM in lieu of powered refrigeration equipment when desired or required. This stored energy permits electrical load shed or shift while better maintaining specified temperatures. A programmed operating sequence reduces electrical consumption during the hottest period of the day, typically afternoon, when other electrical loads are also at their peak demand and refrigeration is least efficient. Like a battery, the TES must be recharged, so it is recharged when there is less competing demand and the ambient temperature is cooler yielding maximum refrigeration efficiency – generally at night. At all times, and for unplanned shortages or outages, the stored thermal energy protects the product in the freezer if refrigeration is lost, for up to three times longer, thus ensuring safety and reducing spoilage and loss.
When added to an existing freezer, TES provides 20% to 30% greater efficiency with 50% greater temperature stability. TES technology typically has a two to three year simple payback in retrofit applications. In new build applications the cost to make a state of the art freezer 20% to 30% more efficient will cost pennies on the dollar. Depending on the cost of electricity, the TES demonstration which will cost approximately $30,000, would save around $6,000 per year in electrical costs and would have a lifetime net present value of $35,000. Additionally, the value of the backup thermal protection provided by the TES system which protects against mechanical failure or electrical outages and maintains critical supplies of food and product, is too great to be quantified by this demonstration project.