Control strategy of two stage CO2 heat recovery systems in ice rinks.

Heat recovery makes CO2 trans-critical solutions more competitive. The heat recovery can be achieved in one stage or in two stages by using two de-superheaters in serial, because of the CO2 temperature profile. An Engineering Equation Solver (EES) model was developed in order to analyse what are the best operating conditions for an ice rink refrigeration system in 3 different heat recovery scenarios, respecting real de-superheater properties. The scenarios are an one stage which provides water heating from 20 oC to 60 oC, an one stage with 20 oC to 70 oC and a two stage with 20 oC to 70 oC. According to simulated results the refrigeration system can be more efficient if it operates under specific discharge pressure and subcooling. An optimum control strategy has been designed according to each scenario and the heat demand. Results show that the power consumption in the two-stage solution is 10% lower than the one stage scenario from 20 oC to 60 oC. The two-stage solution provides higher quality energy by consuming less electrical power.