Effects of an ultraviolet coil irradiation system on the airside heat transfer coefficient and low ΔT syndrome in a hot and humid climate

Abstract

Biological fouling (biofouling) on cooling coil surfaces acts as thermal insulation, impeding heat transfer from air to coil surfaces, decreasing airside heat transfer coefficient and degrading coil cooling capacity. It is also a common cause of low ΔT syndrome in chilled water distribution systems. The effects of a commercially available ultraviolet germicidal irradiation system installed in a variable air volume system on the airside heat transfer coefficient, cooling coil capacity, and its potential to mitigate low ΔT syndrome were investigated via a field test. Energy-related measurements including chilled water supply/return temperature, water-/airflow rate and entering/leaving air temperature/relative humidity commenced 4 months before turning on ultraviolet lamps and continued for 10 months after ultraviolet germicidal irradiation intervention. The effects of the ultraviolet germicidal irradiation system were evaluated via a “before ultraviolet” and “after ultraviolet” comparison. After ultraviolet intervention, within the face velocity range of 1.5–3.0 m/s, the airside heat transfer coefficient increased by 11.8%–20.1%, which translated into 8.8%–10.2% increase in the overall enthalpy-based thermal conductance. The coil total cooling capacity and latent cooling capacity increased by 3.3%–3.8% and 4.5%–5.7%, respectively. The chilled water flow rate required to maintain the leaving air temperature set-point decreased by 8.0%–11.9% and the water-side temperature difference increased by 0.4°C–0.6°C.