Energy systems worldwide are experiencing a transformation spurred by the need to reduce carbon dioxide emissions to prevent climate change impacts. Boosting the proportion of renewable energies that allow the power sector, which is responsible for two-thirds of global emissions, to decarbonize is critical to meeting international energy commitments. And buildings account for one-third of global energy use, with heating and cooling accounting for 60% of that.

On the road to low-carbon, environmentally friendly and energy-efficient buildings, thermal energy storage provides a wide variety of options and advantages for lowering energy consumption and greenhouse gas emissions. Thermal energy storage solutions might operate on principles of thermochemical, latent or sensible energy store and can be used in both active and passive applications in buildings. Active applications allow a reduction in peak load demand by virtue of the stream of stored energy, lowering the needed power requirements of cooling or heating equipment, and also increase system efficiency by changing the operating range (attempting to avoid partial load operations and reducing sporadic input through repeated start/stop). Finally, they also address the timing mismatch between energy supply and demand by increasing the contribution of renewable energy, primarily solar and aero-thermal energy. Passive applications enable buildings to use less energy by increasing thermal inertia, improving thermal comfort and lowering indoor peak temperatures.

Principles of thermal energy storage solutions

As mentioned, thermal energy storage solutions operate on principles of thermochemical, latent or sensible energy storage. Thermochemical heat storage induces a sorption process or bidirectional chemical reaction with the help of a heat source. The large energy density (about 1000 MJ/m3), long-term heat supply and low heat loss are all possible advantages of these storage devices. In latent heat storage solutions, a storage media experiences a phase transition to store or release heat in the storage medium. Most materials suitable for this purpose have a latent heat storage capability of 300 MJ/m3 to 500 MJ/m3.

The last type, sensible heat storage, is extensively used for building applications. This is basically grounded on storing and releasing heat by raising or reducing the temperature of a large thermal capacity-storing medium. Most materials used have a thermal energy storage capacity of around 100 MJ/m3, of which water is the most feasible accessible medium, as at a temperature gradient of 60° C, it has a storage capacity of 250 MJ/m3. However, phase change materials that are used for latent heat storage can hold a greater quantity of heat in a considerably smaller temperature range near the temperature of the phase change when compared with sensible heat storage.

Applications of thermal energy storage solutions

Applications of thermal energy storage solutions can be split into passive and active categories based on their features, varying from high thermal inertia traditional building solutions to innovative thermal energy storage units. Following are some of the examples:

• Thermal energy storage in building components and materials are high thermal inertia elements that increase building thermal performance by dampening thermal oscillations in the interior area. In passive building applications, only latent heat and sensible heat storage are used.

• Thermal mass activation or thermally activated building systems are referred to as utilizing the building construction as a thermal energy storage system via active applications. The functioning mode entails coupling a high-heat-capacity building component to a thermal power source. In these applications, only latent and sensible heat storage systems are used.

• Thermal energy storage parts are made up of enclosed phase change materials that are utilized to improve the environmental performance of systems by freezing the phase change materials for cooling applications through the day, soaking heat gains and preventing heating up. As a result, it functions as an individual cooling system by lowering temperature spikes during the day. Moreover, the applications of these thermal energy storage parts can be divided into two categories: phase change materials used in ventilation systems for individual cooling ventilation, and phase change materials used in solar panels to increase the electrical yield by reducing the global temperature of their surface in contrast to solar panels without them.

• Small-scale thermal energy storage modules are small storage tanks used for heating and cooling purposes that can use latent, sensible or thermochemical storage methods. It enables increased renewable energy consumption (via daily or seasonal storage) or improved heating, ventilation, air conditioning and refrigeration system energy performance.

• Large-scale thermal energy storage modules are referred to as underground thermal energy storage systems or above the ground large-scale water tanks. Solar energy preservation in large-scale buildings or district heating systems is one of their key applications.

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Many technical applications that require the capability to fill the gap among power supply and demand favor the thermal energy storage systems. Such systems can successfully meet energy redistribution requirements for cooling or heating. By utilizing stored thermal energy from thermal energy storage units, peak load demand could be moved to off-peak hours. In comparison to thermochemical and sensible energy stores, the latent functional exhibits good phase transition characteristics in terms of heat storage and release.

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