Thermodynamic analysis of a novel tri-generation system based on compressed air energy storage and pneumatic motor

• The proposed system can provide mechanical energy, heat energy and cooling power.
• The exhaust air of pneumatic motor is used as cooling power instead of abandoned.
• A thermodynamic model of the proposed system is constructed and validated.
• The effects of several parameters on system performance are examined.
• The proposed system can improve total energy efficiency of CAES system by 20–30%.

Based on CAES (compressed air energy storage) and PM (pneumatic motor), a novel tri-generation system (heat energy, mechanical energy and cooling power) is proposed in this paper. Both the cheap electricity generated at night and the excess power from undelivered renewable energy due to instability, can be stored as compressed air and hot water by the proposed system. When energy is in great demand, the compressed air stored in this system is released to drive PM to generate mechanical power. The discharged air from PM can be further utilized as valuable cooling power. Compared to conventional CAES systems, the biggest characteristic of the proposed system is that the discharged air usually abandoned is used as cooling power. In order to study the performances of this system, a thermodynamic analysis and an experimental investigation are carried out. The thermodynamic model is validated by the experimental data. Using the validated thermodynamic model, the mechanical energy output, cooling capacity and temperature of discharged air, as well as the efficiency of the system are analyzed. The theoretical analysis indicates that the additional application of discharged air can improve total energy efficiency by 20–30%. Therefore, this system is very worthy of consideration and being popularized.