Sizing of the buffer tank in chilled water distribution air-conditioning systems

This article presents a sizing study of the buffer tank in chilled water air-conditioning systems. In order to find out the adequate sizing criteria for buffer tanks in these kind of installations, a review of different manufacturers' guidelines was carried out and it was concluded that there are three main operation parameters affected by the volume of the tank: the ON cycle time, the OFF cycle time, and the number of starts per hour of the chiller compressor. In order to better understand the influence of each parameter, a theoretical analysis was carried out where the impact of the building thermal load in different design criteria was also studied. After a thorough analysis of all the studied criteria, it was concluded that the minimum ON cycle time which is necessary to ensure that the oil returns to the compressor is the most critical criterion. Finally, a design guideline is proposed by the authors in order to determine the minimum volume of the buffer tank, mainly depending on the capacity of the chiller and the temperature deadband of the thermostat control.