2016 ASHRAE Winter Conference

The energy use-related effects of ultraviolet germicidal irradiation (UVGI) to mitigate biological fouling (biofouling) of a chilled water cooling coil are investigated via a field study. A visibly bio-fouled cooling coil in an air-handling unit serving an operational building in a hot, humid climate is monitored for 5 months to establish a fouled coil baseline. Parameters monitored include air flow rate, airside pressure drop, air temperature and humidity upstream and downstream of the coil, chilled water flow rate, entering and leaving chilled water temperature and waterside pressure drop. A UVGI coil irradiation system is installed on the downstream side of the coil following typical manufacturer guidelines, and the system is then passively monitored over a period of 10 months. An average improvement of 5.2% to 7.9% in coil airside pressure drop, and 11.9% to 12.7% in heat transfer coefficient (both 95% confidence interval) are estimated by comparing data from the baseline and post-irradiation periods. Complexities of the physical phenomena involved, e.g. the effect of both airflow and latent load on airside pressure drop, are taken into account.

The goal of this project was to assess the potential benefits of using a highly-controlled surface wettability to preferentially condense (and therefore locate) water droplets on a heat transfer surface during the early stages of frost growth to affect the thermophysical properties of the frost layer (i.e. density, thermal conductivity, etc.). It was postulated that a thinner, denser frost layer might lead to improved heat conduction (and therefore improved air-side heat tranfer) and longer operational periods before defrosting becomes necessary. The retention of less water on the heat transfer surface following defrosting might also be used to slow frost growth in the subsequent cycle and therefore lengthen the operational cycle. Thus, accompanying this objective was the goal of creating heat transfer surfaces that more completely drain the melted frost layer during an applied defrost cycle.

It has been noticed by many users that whenever a germicidal UV disinfection is performed in a room, there is often a strange odor left behind. It is not ozone, which can be easily identified and measured. It is more like a slightly pungent smell. It's actually easier to acknowledge the smell than to describe it. Until now, no satisfactory scientific explanation about the origin of this peculiar odor has been provided. In this paper, the authors provide a clear explanation of the source of this odor. Evidences show that the root cause seems to be the interaction of UV with airborne dust.