Field measurement and modeling of UVC cooling coil irradiation for heating, ventilating, and air conditioning energy use reduction (RP-1738)—Part 1: Field measurements

Abstract

Wet cooling coil surfaces can provide opportunities for microorganism growth. This biological fouling (biofouling) increases airside pressure drop and decreases airside heat transfer coefficient. Ultraviolet germicidal irradiation is one method to eliminate biofouling. The current article reports field measurements of changes in pressure drop and heat-transfer characteristics of fouled coils treated with ultraviolet germicidal irradiation designed for surface disinfection. Ultraviolet germicidal irradiation systems were installed in operating air-handling units with visibly fouled cooling coils at sites in Tampa, Florida and University Park, Pennsylvania. Pressure drop data were controlled for airflow and latent load, and overall heat-transfer coefficient data were controlled for heat exchanger entering conditions. Analysis of Tampa site data showed an initial mean 22.70% to 22.72% decrease (µ ± 2σ) in airside pressure drop and a mean 13.2% to 13.6% (µ ± 2σ) increase in overall heat-transfer coefficient. Longer-term improvement was 14.6% for the airside pressure drop and 15.7% for overall heat-transfer coefficient, though the decrease in pressure drop improvement was not able to be explained. The University Park, Pennsylvania site, cleaned by unaware maintenance personnel before data collection, had an initial mean 10.3% pressure drop improvement and 57.7% overall heat-transfer coefficient improvement, followed by a long-term 0% pressure drop improvement and 36.7% overall heat-transfer coefficient improvement.