Evaluating energy-saving potential in micro-cold storage units integrated with phase change material

One of the challenges for the commercialization of PCM-based cold storage systems is their ability to absorb load fluctuations, the ability for quick charge and discharge, as well as the potential for energy saving by reducing the compressor running time. The present work describes the possibilities for energy conservation through the experimental integration of latent thermal energy storage in an electricity-driven cold storage unit. A portable cold storage unit with a net volume of 1 m3 (35 l) was retrofitted with a PCM-based heat exchanger unit. The unit was designed to maintain the temperature inside the storage space at 9–10 °C for 1 h using an organic phase change material. The PCM-based heat exchange surface embedding was created to consider the maximum surface exposure area and minimum thickness to reduce the charging (freezing) and discharging (melting) periods. Experiments were carried out with and without PCM to observe the backup time given by the PCM unit, the frequency of on–off compressor cycles, and the potential for energy and economic savings. Based on a six-hr trial at a set temperature of 9 °C, it was found that the designed heat exchanger unit provided a stable temperature for 55 min on compressor shut down at an average ambient temperature of 35° C, thus validating the design. The compressor on–off cycles are reduced from 6 to 1 per hour, compressor on time is reduced by 31%, and an energy saving of about 40% is obtained with PCM integration. The energy savings per kg of PCM is about 5.5% which is the highest reported for cold storage in the literature to date.