Charge and discharge strategies for a multi-tank thermal energy storage

This paper presents the results of an experimental study conducted on a multi-tank thermal storage for solar hot water heating applications. The purpose of the study was to investigate the thermal behaviour of the stratified tank system when subjected to constant temperature charging and constant volume hourly draws. The experimental setup consisted of a charge loop to simulate a solar collector input, three commercially available 270 L domestic hot water tanks and three side-arm, natural convection heat exchangers. Tests were performed over 8 h periods for three different plumbing configurations and two different hourly draw volumes. Simulations were conducted using the TRNSYS simulation environment, and the results showed that the TRNSYS model was in good agreement with the experimental results, where the discrepancies between data were found mainly in the regions of high temperature gradients within the storage tanks. Preliminary simulations were also conducted using realistic charge and draw profiles to illustrate the thermal behaviour of the tanks under non-ideal operating conditions.

► A multi-tank system was evaluated under three charge and discharge configurations.
► Constant temperature charging and constant volume draws were performed.
► Charging in series resulted in sequentially stratified tanks.
► Discharging in series resulted in mixing at the bottom of the upstream tanks.
► Discharging in parallel maintained a high degree of stratification in each tank.