## 1 Introduction
Active PCM-TES systems (underfloor heating, PCM ceiling slabs and other systems) and passive PCM-TES systems (PCM slab walls, PCM shutters, PCM building blocks, air heating systems, underfloor heating, ceiling slabs, etc.) have high potential to reduce the heating load in buildings [4; 6; 7; 8; 9; 10]. The use of PCMs in cooling, heating and power generation is divided into four temperature ranges: For the low temperature range (\(-20\)\({}^{\circ}\)C to \(5\)\({}^{\circ}\)C), mainly organic compounds are used as PCMs. For the medium-low temperature range (\(5\)\({}^{\circ}\)C to \(40\)\({}^{\circ}\)C), mainly organic compounds and salt hydrates are used. For the medium temperature range (\(40\)\({}^{\circ}\)C to \(80\)\({}^{\circ}\)C), mainly organic PCMs such as paraffin and fatty acids are used. Finally, for the high temperature range (\(80\)\({}^{\circ}\)C to \(200\)\({}^{\circ}\)C), salt hydrates have long dominated the TES sector due to their durability and economic advantages, while organic PCMs are seldom used in this temperature range [11]. Cool thermal energy storage (CTES) currently represents a significant area of application for industrial refrigeration, such as process cooling, food preservation and building air conditioning systems. One of the possibilities is the application of a phase change in which the temperature range can be appropriately adjusted for proper and efficient operation of the cooling system. For air conditioning and refrigeration (cold storage), temperatures between \(5\) and \(15\)\({}^{\circ}\)C are optimal for heat storage, but at lower temperatures, latent heat storage materials are more efficient than sensible heat storage materials (such as water). CTES can have an important role in peak load management and addressing the problem of the interruption of power supply from renewable energy sources, especially when CTES is integrated into district cooling systems [12; 13]. PCMs can be integrated into free cooling systems, passive building heating and cooling systems, and evaporative and radiant cooling systems to improve indoor thermal comfort and reduce energy consumption. With systems integrated into PCMs, energy cost savings of up to 50% can be achieved compared to traditional options, with the fastest payback of approximately 6 years [14; 15; 16]. For space cooling, a suitable general-purpose cooling medium is water with a temperature of 5-12 \({}^{\circ}\)C. The reasons for its significant application are mainly associated with its high specific heat capacity, simple equipment, low cost and unpretentious technical requirements. However, the accumulation of cold in water as a liquid has one significant drawback, namely the range of the temperature interval, which, in many cases, is only a few degrees. Many applications in the industrial and food sectors require temperatures up to 8 \({}^{\circ}\)C, and others such as refrigeration and air-conditioning require systems up to 15 or 18 \({}^{\circ}\)C, and this significantly limits the amount of accumulated cold (energy extracted from the water); the lower limit is, in practice, a temperature above 4 \({}^{\circ}\)C that occurs due to pressure changes associated with the water anomaly. Other problems arising from the above include the low energy storage density, the large volume of the water storage tanks and the difficulties in storing and treating the cold. However, the use of PCM for CTES purposes is still limited due to its low thermal conductivity. As a result, extensive research has been carried out to improve its thermal performance by adding nanomaterials, microencapsulating and stabilizing its form. In addition to scientific research papers, there are review articles on CTES using PCMs [17]. Currently, there is extensive research on TES systems for heat and cold storage in renewable-energy-based systems [18; 19; 20].