Experimental and numerical study of PCM storage integrated with HVAC system for energy flexibility

This paper presents both experimental and numerical studies of PCM storage integrated with an HVAC system. The experiments focus on PCM storage in 3 different sizes, and study the temperature change in the PCM storage during the charge and discharge period, the impact of the PCM quantity on the charge and discharge rates of the PCM storage and the impact of the discharge air temperature and airflow rate on the discharge rate. The main conclusions are that the temperature effectiveness of the PCM storage depends more on the PCM quantity than the discharge inlet air temperature and airflow rate. The air path in the PCM storage should not be too long to achieve the longer PCM activation in time. The storage with 36 pieces of PCM plates and latent storage capacity of 5.23 MJ can be charged/discharged fast, with high and stable outlet air temperature (above 28 °C for 3 h), especially during the discharge period. The most promising configuration of the experimental study was chosen for a numerical study the energy flexibility of the HVAC system without PCM and with PCM. A model of the PCM storage integrated with an HVAC system is built with EnergyPlus and validated by experimental data. The study concluded that the HVAC heating setpoint control based on the electricity price without PCM storage has limited cost-saving potential due to the high electricity transmission and tax cost. The PCM storage integrated with an HVAC system can reduce the energy cost by 7 % while obtaining a similar indoor thermal comfort level compared to the HVAC heating setpoint control without PCM storage. The payback time of HVAC with PCM is seven years compared to HVAC system without PCM. The cost reduction of energy flexibility of the system is relatively limited because the electricity transmission cost and electricity tax account for 80% of the total electricity cost in Denmark.