A feasibility study of a tube bundle exchanger with phase change materials: A case study

Abstract

Latent heat thermal storage offers a flexible service to members of a heat district grid as the stored heat can be used to reduce the morning peak demand, limiting the consequences for the production facilities. This work investigates the optimized design of a latent heat thermal storage reactor, integrated in an existing building supplied by district heating, for demand-side management applications. The storage reactor was designed as a tube bundle heat exchanger in which a commercial-grade paraffin was used as the phase change material. The optimized design variables that maximized the use of the Phase Change Material were the tube pitches and the fin heights. The integration of the storage reactor with the energy system required the control and prediction of its state of charge and the power output. These parameters are usually evaluated through 3D numerical dynamic simulations that require a large computational effort, which is beyond the capability of basic microcontroller systems. A simplified parametric model has been used to overcome this issue. A load-tracking algorithm was embedded in an existing building program. The algorithm was able to reduce the thermal power peak by 62 kWh from 6:00 to 9:00 a.m. Decreasing the pitch from 95 mm to 82 mm led to a +34% increase in the use of the PCM. Similar results were obtained when the fin height was increased from 20 mm to 32 mm. The results of this investigation suggest that the proposed model could be applied to similar buildings fed by district heating network systems.