Performance of a new discharging scheme for water pit thermal energy storage system integrated heat pump

Water pit thermal energy storage (PTES) for using waste heat in non-heating season has emerged in district heating due to its low cost and high thermal storage density. In current applications of PTES, when the heating temperature cannot be met, PTES is used as the heat source for heat pumps, despite still possessing direct heating capacity in combine heating. For this reason, a new three–stage discharging scheme for PTES is proposed, which contain single heating and combine heating to achieve higher heating performance. The TRNSYS model and the developed thermocline dynamic locating method were validated with past experimental data and were further applied to explore the disturbance effects of discharging operations on PTES. The results show that compared with the two–stage discharging scheme, the three–stage discharging scheme improves heating exergy by 7.93 %, and the number of complete mixings in PTES decreased once. The minimum storage temperature of 9.36 °C is obtained, and the heat storage capacity is increased by 18.15 %. Additionally, for one million m 3 of PTES, using the cost–volume curve instead of fixed cost reduces the payback period by 35.65 %. Considering both the cost–volume curve and carbon trading , the payback period drops to 4.04 years. • A three–stage discharging scheme for water pit thermal energy storage improves heating exergy by 7.93 %. • A thermocline dynamic locating method is developed based on temperature curve. • The PTES disturbances by discharging operations is observed based on thermocline behavior.