A NEW APPROACH TO NUMERICAL INVESTIGATION OF GFX AND POWER-PIPE DRAIN WATER HEAT RECOVERY (DWHR) SYSTEMS IN BUILDINGS

In this study, a new computational approach is introduced to numerically investigate the thermal characteristics of the vertical GFX and Power-Pipe Drain Water Heat Recovery (DWHR) systems. In a DWHR exchanger, drained warm water from showering passes through a pipe, and it transfers a part of its thermal energy to cold water flowing through a pipe coiled around the vertical one. This computational approach includes three steps: (i) fluid film thickness measurement in the vertical tube using 2D numerical and analytical calculations; (ii) 3D thermal modeling of the heat exchanger (two rings of the GFX exchanger and one ring of the power-pipe exchanger), and finally (iii) generalization of the results into more numbers of rings by using heat exchanger relations. The numerical approaches are based on the finite volume method. This methodology is validated by the experimental works of others and also by using the grid independence study. The main outputs and results include pressure drop in the coiled pipe, thermal effectiveness, and recovered heat energy. One of the important conclusions is that an increase in flow rate decreases the exchanger effectiveness.