Journal Article

Tunable Thermal Energy Storage to Enable Decarbonization of Space Conditioning in Commercial Buildings

Sweeney, Micah, Over, Molly K, Grieve, M. James, Dyall, Alexander K

2024

Overview

Large amounts of energy storage will be needed to manage renewable-intensive grids and to decarbonize buildings and transportation. Thermal Energy Storage (TES) has the potential to lower first cost while improving round-trip efficiency, safety, and durability compared to lithium batteries. Heating and cooling of buildings consumes 20% of global energy and drives peak electric loads, especially during extreme hot or cold weather. TES can shift heating and cooling loads to off-peak or renewable-intensive periods, thereby reducing grid stress and energy costs during peak periods and supporting renewable integration (by reducing electric consumption during periods when renewable supply is low, and increasing electric consumption when renewable supply is surplus to real-time needs). Integrating TES with heat pumps or chillers can improve efficiency by 20-30% by shifting operation into the heat pump or chiller's optimal efficiency range, and to the optimal time of day based on outdoor temperature (e.g. running the heat pump at night when it is cooler outside and storing cooling for use the next afternoon). In addition to this efficiency benefit, off-peak electricity is often half the price of peak electricity, and load flexibility is a significant benefit to electric utilities in meeting targets for very high reliability and resiliency. This paper reports on early testing of a novel, tunable TES system which uses proprietary materials to store heat and/or cooling at a range of adjustable temperatures optimal for space conditioning in buildings. For example, one can: (a) store heat in winter retuned to store cooling in summer, for 4-seasons markets, as a direct retrofit for chiller/boiler hydronic systems changing to heat pumps, and (b) store cooling in humid weather, at the low temperature required for dehumidification, retuned to store cooling in dry weather, at a more efficient, higher temperature. Tunability significantly reduces the required footprint compared to systems that use non-tunable materials, and provides flexibility to pursue peak load shifting, efficiency improvement, waste heat recovery or enhanced renewable integration as HVAC loads and electricity prices vary. Tunable TES can be applied to large building, campus and district energy applications, and can be used with air-source, ground-source or hybrid heat pump architectures. This paper will report on a recent collaboration between a pre-commercial start-up company and a research organization, where capacity (energy) and rate (power) were measured for stored cooling at 43[degrees]F (6[degrees]C) and stored heat at 150[degrees]F (65.5[degrees]C) at a meaningful lab scale. The research organization provided third-party measurement and verification to validate performance.

• Publisher: American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc. (ASHRAE),American Society of Heating, Refrigeration and Air Conditioning Engineers, Inc
• Subject: Air conditioning / Alternative energy sources / Batteries / Buildings / Chillers / Climate / Cold weather / Cold weather construction / Commercial buildings / Comparative analysis / Conditioning / Cooling / Cooling loads / Cooling systems / Dehumidification / Efficiency / Electric utilities / Electrical loads / Electricity / Electricity consumption / Electricity pricing / Energy consumption / Energy costs / Energy industry / Energy storage / Flexibility / Force and energy / Heat exchangers / Heat pumps / Heat storage / Heating / HVAC / Ice / Load shifting / Low temperature / Materials recovery / Peak load / Performance evaluation / Reliability / Research centers / Retrofitting / Stress (Psychology) / Stress management / Summer / Temperature / Thermal energy / Waste heat recovery / Winter