Crossflow microsand filtration in cooling tower systems to control fouling in heat exchanger devices

In the context of global warming, there is a growing need for high-performance heat, ventilation and air conditioning systems. Fouling is a challenge, affecting heat exchanger operational and energetic performance. Side stream filtration can be used to improve water quality by reducing particle concentration in the system. The aim of this study was to assess a crossflow microsand filtration unit's efficacy in reducing fouling within an 81-plate heat exchanger, in an in-situ cooling tower circuit. A pilot heat exchanger without filtration was operated under similar conditions. After 3 years of continuous operation, visual inspection of the full-scale heat exchanger plates operating with filtration showed minimal accumulation. Pairs of facing plates (7) were scraped and rinsed to collect total solids accumulated on surfaces. Samples were resuspended and analyzed for solids and metal concentration measurements. Low average values of total volatile solids (45 μg/cm2) and total solids (93 μg/cm2) were indicative of a low biofilm formation. X-ray diffraction revealed the presence of calcite associated to water hardness. Low levels of iron and copper were detected despite slightly corrosive water. In contrast, the pilot heat exchanger exhibited higher deposit accumulation of total volatile solids (90 μg/cm2) and total solids (110 μg/cm2) after only 12 weeks of operation. These findings underscore the role of side stream filtration in reducing particle deposition and biofouling potential in full-scale cooling tower systems. Crossflow microsand filtration is a promising avenue to control fouling in building cooling tower systems, which could contribute in improving the building's energetic performance.

Mots clés

side stream filtration; building energy; HVAC; clogging