What is Thermal Energy Storage?

Thermal energy storage (TES) is an important energy management technology that allows excess thermal energy to be stored and reused when needed. This technology can employ various storage methods depending on different application scenarios and requirements, including water-based, ice-based, cryogenic storage, and thermosilicon technology. Thermal energy storage not only balances energy supply and demand and improves energy efficiency but also promotes the widespread application of renewable energy.

Definition of Thermal Energy Storage

Thermal energy storage (TES) refers to the cooling or heating of a storage medium. Storage media include liquids such as water or solid materials such as rock. Thermal energy storage technology is a key energy management solution that can store and release thermal energy on different timescales, thereby improving energy efficiency and promoting the integration of renewable energy.

Characteristics of Thermal Energy Storage

It can store temporarily unused or excess thermal energy through a certain medium for reuse when needed; it can improve energy efficiency, especially in solar energy utilization, industrial waste heat collection, and air conditioning waste heat recovery, showing broad application prospects. Currently, there are three main methods: sensible heat storage, phase change heat storage, and thermochemical reaction heat storage.

As an important solution for heat management utilizing waste heat and renewable energy, TES technology has attracted much attention from researchers, who have focused on its potential for integration into heat pumps. TES systems can store excess heat energy during periods of high availability and utilize it during periods of low availability.

Reduce operating costs

Taking the energy storage interconnected heat pump as an example, it is an innovative system form developed on the basis of air source heat pump and water source heat pump. The system introduces a phase change energy storage device and uses the unique properties of heat storage materials to assist the heat pump in heating. Through the energy storage module, the air source heat pump and water source heat pump can be effectively combined, which broadens the original usage conditions of the two and thus builds a reliable and stable heating system. In the heating radiator renovation project of a residential community in Northwest China, the nighttime temperature of the coldest month in the area is between -5℃ and -15℃, and the traditional air source heat pump is difficult to operate normally under this condition. However, the actual operation survey shows that compared with the conventional air source heat pump, the energy storage interconnected heat pump can reduce investment by 32%, the power distribution power is reduced by 29%, and the operating energy consumption is reduced by 21%, which is very significant in terms of energy saving.

Balancing supply and demand

The large-scale energy storage air source heat pump water heater is a typical case. It uses two phase change energy storage devices to provide hot water to users while also providing free cooling. Furthermore, by storing energy at night, the system achieves peak shaving and valley filling of electricity, effectively solving the drawbacks of the air source heat pump hot water supply mode. However, the system structure is relatively complex. To meet the needs of end users, a balance between heating and cooling capacity must be achieved, and end users often have different needs for these two. Therefore, it is necessary to scientifically and rationally design the capacity of the phase change energy storage devices on both sides to achieve a dynamic balance between supply and demand.

Improving the coefficient of performance and shortening the heating time The integration of thermoelectric heat pumps (TeHPs) with heat storage tanks is a successful example. The TeHP units with integrated heat storage tanks achieve a higher coefficient of performance (COP), with the COP of the system with heat storage tanks reaching 1.97. far higher than the 1.58 of the system without heat storage tanks. From a long-term perspective, a higher COP is expected to bring energy savings and a more sustainable heating solution. In addition, the integration of heat storage tanks also significantly shortens the time required to heat the test chamber space. Through heat storage, the time required to heat the test chamber is reduced by 18 minutes, and the required temperature can be reached quickly [4]. Improving thermal energy utilization efficiency

The combination of TES and heat pumps has shown great advantages. With the help of efficient energy storage media such as phase change materials (PCM), more thermal energy can be stored in a limited space, thereby improving the overall performance of the heat pump system. For example, Wu et al. used PCM composite material (75% paraffin + 25% expanded graphite) in an air source heat pump system, which increased the thermal conductivity to 4-5 W/m²K and improved the system efficiency by 3.6%[5].

Solving the problem of time allocation by peak shaving

PCM thermal storage units have the ability to store heat and can provide heat support for the continuous operation of heat pumps (HP). When the heat source is insufficient or unstable, it can play a buffering role. Moreover, the integration of PCM and HP can prevent the equipment from starting and stopping frequently through thermal management, anti-frost and other measures, and improve the stability of COP and HP. For example, a large-scale energy storage air source heat pump water heater unit can improve the system operating conditions by realizing peak shaving and defrosting through energy storage, and can also provide free cooling in summer and transitional seasons.

Providing Demand Flexibility The combination of heat pumps and thermal energy storage brings demand flexibility to home and district heating systems. For example, Hlanze et al. achieved a 27.1% reduction in electricity costs through a time-of-use pricing strategy, strongly demonstrating the economic benefits of TES. In the field of solar-assisted heat pumps (SAHP), Youssef et al. [8] designed a dual-source system that improved COP by 14% in cloudy weather; Plytaria et al. combined a floor radiant heating system with PCM to reduce power consumption by 40%. For air source heat pumps (ASHP), Li et al.'s pool heating system achieved flexible thermal energy scheduling with the help of PCM thermal storage units, and Du et al.'s experiments showed that its operating cost could be reduced to 15.1% of that of traditional electric heating methods. The Heat Storage Performance Tester provides standardized procedures and controls for radiation heat conditions, offering repetitive measurements of the heat storage and thermal transfer properties of protective fabric materials. Through measurement, the material's characteristics and rating can be quickly identified, and the likelihood of burn-in is predicted using the instrument's integrated burn model.

Thermal Energy Storage (TES) technology, with its diverse storage methods and significant application advantages, occupies an increasingly important position in energy management. From reducing operating costs and balancing supply and demand to improving coefficient of performance and thermal efficiency, and further to peak shaving and providing demand flexibility, the integration of TES with systems such as heat pumps demonstrates enormous potential and value. The emergence of the Heat Storage Performance Tester provides a standardized means to accurately assess the heat storage and heat transfer characteristics of protective fabric materials, further promoting the refined application and development of heat storage technology in various fields. It is foreseeable that with continuous technological innovation and improvement, heat storage technology will play an even more crucial role in the process of energy efficiency and sustainable development.