Experimental study on energy-saving effect of alternate temperature system with cold storage unit

Alternate temperature systems with variable cooling load are commonly found in many applications, such as environmental tests. In this paper, we incorporate an ice-cold storage unit (i.e., a new design degree of freedom) into an alternate temperature system, and present an experimental study on the energy-saving effect of the design with cold storage. The cold storage energy comes from a part of the refrigerant bypass loss. Two lab-scale prototypes were developed and the work consumption of the system with cold storage was compared to that without cold storage. The experiment shows that the incorporation of the cold storage unit significantly reduces the energy consumption. Under the specified nominal design conditions, the compressor consumes 5.32 kWh/period energy for the design without cold storage, while it consumes only 3.77 kWh/period energy for the design with cold storage due to less compressor operating time. Compared with the design without cold storage, the energy consumption reduction ratio (α) of the design with cold storage reaches approximately 24.7%. When the heat capacity of the load increases, e.g., from 6.84 kJ/℃ to 20.66 kJ/℃, the energy-saving effect of the design with cold storage becomes weaker, e.g., α decreasing from 24.7% to 20.8% accordingly. For extremely low heat generation in the load, the energy-saving effect of the design with cold storage diminishes. The effects of the fan’s operating frequency and the cold-water temperature are also analyzed. Further design improvement is suggested. This work emphasizes the value of the incorporation of cold storage (i.e., adding more design degrees of freedom) for alternate temperature systems which reduces the heat transfer difference and the entropy generation.