Experimental investigation on operating strategies of a cooling system combined phase change cold storage with evaporation for data centers

Introducing phase change cold storage extends the application range of direct evaporative cooling technology for data centers, enabling year-round free cooling in certain regions. However, research on the collaborative optimization of direct evaporation module layout and spray flow prediction to enhance the energy-saving performance of the coupled system is still limited. This study experimentally investigated the thermal performance of two combined systems incorporating direct evaporative cooling at the front and middle of the phase change segment. Subsequently, a sensitivity analysis on the middle system was carried out to investigate main factors, i.e., inlet temperature and humidity, spray flow rate, and wind speed, leading to the development of a spray flow prediction model. The results show that: (i) Under conditions of 32 °C, 40 % relative humidity, and 1.6 m/s wind speed, both systems keep outlet air below 27 °C and 80 % relative humidity, with the middle system delivering the highest energy efficiency ratio. (ii) Under conditions of 32 °C inlet temperature and 0.08 L/min spray flow, the air supply requirement will not be satisfied if the inlet relative humidity exceeds 45 % or the wind speed exceeds 2 m/s. (iii) The outlet temperature correlates quadratically with the inlet temperature and linearly with other parameters; the outlet relative humidity correlates linearly with the inlet humidity and quadratically with the others. (iv) The middle system reduces pump energy consumption by more than 75 % and water consumption by 8 %–25 %, compared with the traditional direct evaporative cooling system.