Maximizing CO2 Heat Pump Systems Performance via Extremum Seeking Control

In this paper, the energy efficient control of carbon dioxide heat pump systems is discussed from an experimental point of view. The performance of this kind of systems strongly depends on the operating conditions and in particular on the cycle high pressure. Because of the limited knowledge of certain system parameters and the difficulty of developing and implementing effective models, the problem of determining the optimal value for the cycle high pressure that leads to the maximum system performance is here faced by means of a model-free approach. Specifically, an Extremum Seeking Control (ESC) scheme, which can search for the unknown or slowly varying optimum input with respect to a certain performance index, is adopted. In particular, a variable water flow rate heat pump unit was considered. In this scenario, the performances of the ESC were compared with those provided by other methods available in literature (e.g. Liao's model). Experimental tests show that the ESC scheme guarantees better performance.