A real-time algorithm for the determination of R744 systems optimal high pressure

In this paper the optimal energy efficiency and high pressure problem in single stage transcritical carbon dioxide vapour compression units is addressed. A real-time model-based optimisation algorithm for the optimal (or quasi-optimal, close to the optimal) pressure determination is developed as a more efficient and robust solution than literature approximated ones. The problem is solved by a model estimating the system performance and by measuring its boundary conditions. The model is obtained by an on-line artificial neural network identification technique and the optimisation problem is worked out by a particle swarm technique. The proposed algorithm is dynamically tested by simulation, considering the performance of a supply water temperature controlled carbon dioxide heat pump. It appears to successfully approximate the optimal cycle discharge pressure showing an average daily pressure deviation of 0.9 × 105 Pa over a two years simulation period, corresponding to 1.1% increase in the cumulated energy consumption, compared to the optimal pressure solution.

► The optimal energy efficiency and high cycle pressure problem in transcritical carbon dioxide vapour compressor units is addressed.
► A model-based optimisation algorithm for the determination of the optimal pressure value is developed by using combined artificial neural network and particle swarm techniques.
► The algorithm is dynamically tested by simulation, considering a carbon dioxide heat pump water heater.
► The algorithm successfully approximates the optimal cycle pressure discharge values over a two year simulation period.