Full Description

An experimental study of condensate formation and runoff was performed by exposing a sheet of glass, cooled at its bottom edge, to an enclosure with a controlled environment. This arrangement mimics the indoor glass surface at the bottom edge of a window when the window is exposed to a cold, outdoor environment. The air in the enclosure was maintained at a constant dry-bulb temperature (Tdb = 22.1C [Tdb = 71.8F]) and constant relative humidity (RH = 30%, 35%, 40%, 45%, or 50%) during individual experiments. It was found that the time until initial runoff, tir , decreased with increasing RH, and tir was sensitive toRHat low RH, but insensitive to RH at high RH. At first, condensate runoff occurred near the bottom of the glass and left one to believe that the remaining condensate was at steady state. But over a 16-hour period, it was found that the condensate runoff front, in every case, progressed upward to include the entire condensate area. The speed of the condensate runoff front increased with RH, and was less sensitive to RH at low RH. Measurement results were used to produce a summary plot showing runoff front position as a function of glass surface temperature and RH. This chart can be used to predict tir and runoff front progression at the bottom edge of any window if the surface temperatureprofile is known.

Citation: ASHRAE Transactions - Volume 120, Part 1, New York, NY