Design of energy efficient plate heat exchangers using numerical methods

In this study, it is aimed to maintain indoor air quality with heat recovery ventilation in environments where 1 to 4 occupants. For this purpose, the design of a small-capacity (50–200 m³/h) Plate Heat Exchanger (PHE) was targeted to recover the heat exhausted into the atmosphere with stale air in Heating, Ventilation, and Air Conditioning (HVAC) systems. The effects of the PHE's design and operational variables on performance criteria were examined using the Taguchi experimental design and Computational Fluid Dynamics (CFD). The four PHE design parameters investigated were: channel inlet geometry (CIG), average air velocity (u-m/s), channel height (h-mm), and plate size (L-mm). According to the Taguchi method, four sub-levels were determined for each of the design parameters in accordance with the literature. The PHE performance criteria affected by the design variables were selected as thermal power recovered on the fresh air side (Qrec.), sensible thermal effectiveness (ε), total fan power required to maintain flow (Ph,f+s), Electro-Thermal Amplification Ratio (ETAR) and ε×ETAR, which indicate the combined effect of thermal effectiveness and ETAR. Based on Taguchi's "larger-the-better" and "smaller-the-better" categories, the optimal PHE models and their capacities were determined as K-32-10-240 (276 m³/h) for recovered thermal power-Qrec., K-20-10-240 (173 m³/h) for thermal effectiveness-ε, D-20-25-100 (32 m³/h) for both total fan power-Ph,f+s and ETAR, and D-20-25-120 (48 m³/h) for ε×ETAR. In addition, the accuracy of the CFD results was also verified by the analytical methods in the literature. The differences between CFD results and Taguchi predictions for Qrec., ε, Ph,f+s, ETAR, and ε×ETAR were 9.66%, 16.70%, 2.31%, 9.16%, and 14.03%, respectively. The static pressure contours, velocity contours in the flow direction, and temperature contours on the symmetry plane of the fresh channel and temperature contours throughout the plate surface of optimal PHE models were visualized and evaluated using CFD results. In addition, the capacities (volumetric flow rates) of the optimal PHE models and the changes of performance criteria depending on volumetric flow rate were also analyzed.