Energetic macroscopic representation of a mechanical compression-assisted hybrid thermochemical cycle exploiting low grade heat for cold applications

This paper describes an original model based on The Energetic Macroscopic Representation (EMR) to develop a control structure of an innovative compression-assisted hybrid thermochemical cooler driven by low-grade thermal energy. Hybrid thermochemical cooler with mechanical compression have a wider operating temperature range than conventional thermochemical processes. This makes it possible to exploit lower grade heat sources and/or produce cold at lower temperatures. In addition, the ability to control compressor speed increases thermochemical process controllability to respond to load or source variations. Nodal modeling of each process component is developed according to the EMR formalism. A parametric identification and validation of this process model is then carried out using experimental data. The deviation from the experimental data is lower than 1 bar for the reactor, condenser and evaporator pressure, lower than 0.1 for the reaction advancement and lower than 2 degrees C for the reactor wall temperature. The EMR model is then inverted to obtain a process control law for maintaining a cold room at-18 degrees C. Despite the variation in cooling demand from a minimum of 100 W to a maximum of 700 W, the compressor's control structure was able to regulate its speed of rotation to maintain the cold room temperature at-18 +/- 0.5 degrees C for 24 h.