Experimental and numerical assessment of thermal energy storage unit with PCM integrated to air source heat pump for enhancement of load shifting

• Experimental and numerical study on TES unit integrated with ASHP. • Full latent heat utilization was unachievable without heat transfer enhancement. • Using PCM improved ASHP performance by 18.5% and load shifting by up to 10.1%. • Increasing effective thermal conductivity of PCM led to 23.5% higher heating time. • Load shifting increases up to 82.3% when PCM uses 100% of latent heat stored. Within the present work, experimental and numerical assessment of a thermal energy storage (TES) unit integrated to air source heat pump (ASHP) were conducted. The TES unit consists of a water tank and additional tubes inside, which are filled with TES material, namely pure water or phase change material (PCM). In the experimental work, lauric acid was used as PCM and the results were compared to the case of using water as TES material. The experiments were conducted for four different heating loads ranging from 3.1 to 12 kW. Besides, a numerical model was established based on experimental data. In the numerical simulations, four different PCMs including the lauric acid used in the experiments were considered, and their thermal performances were numerically evaluated and compared to that of water as a TES material. According to the experimental data obtained and analyzed, using PCM reduced the heating time from 1.6 % to 16.1 %. Nevertheless, the ASHP performance was improved by 18.5 % using lauric acid. Relatedly, the load shifting index ( LSI ) was enhanced by up to 10.1 %. Numerical simulations revealed that using appropriate PCM can result in 3.6 % longer heating time and can increase LSI from 64.9 % to 68.9 %, compared to water. Besides, increasing effective thermal conductivity of PCM can allow using 100 % of the latent heat stored, resulting in an enhancement of 23.5 % in heating time and an improvement of LSI from 68.9 % to 82.3 %.