Numerical study of the effect of thermal energy storage systems on the energy savings and operation of fresh air heating systems

Abstract To improve indoor air quality and working or living environment, it is a widely recognized and feasible way to introduce outdoor air into the indoor. The utilization of renewable energy can realize the low-carbon and energy-saving operation of introducing fresh air. Therefore, a composite fresh air system is proposed in this paper to introduce energy-saving and low-carbon fresh air into the indoor. It can reduce the energy consumption of fresh air system by renewable energy like solar energy efficiently. It consists of two units coupled in parallel - a thermal energy storage using paraffin as the phase change material (PCM) and a fresh air unit. The fresh air heating process in the composite fresh air system under different system air flow rate is investigated through numerical methods. Numerical results show that when only the thermal energy storage unit operates in the composite fresh air system, although the temperature requirements for fresh air supply cannot be met in the system, the temperature of the outdoor air can still be significantly increased with a maximum of 22 ℃ and an average temperature rise of 4.7 ℃. And when the energy storage unit operates combined with the fresh air unit, the composite fresh air system can meet the requirements of fresh air supply normally when the air flow rate treated by the fresh air unit is greater than or equal to the air flow rate treated by the energy storage unit. Finally, with the bypass of the thermal energy storage unit at an optimal air flow rate of 60 m 3 /h, different energy savings of 7% to 10% can be realized when the system air flow rate varies from 120 m 3 /h to 180 m 3 /h. The research in this work applies the thermal energy storage system to the fresh air heating system appropriately, which not only realizes the efficient use of renewable energy, especially including low-grade energy sources, but also reduces the energy consumption of fresh air system by about 7% to 10%.