High Condensation Resistance of Vinyl Meets Green, Health Care NeedsNovember 30, 2010
Over time, people's tolerance of desert-like interior humidity during the winter has decreased. So, while it may have been normal for one’s parents to wake up with dry throats, people today expect their homes to be more humid. However, higher humidity leads, not surprisingly, to greater and more persistent condensation on windows.
Condensation forms on a surface when the temperature of the object falls below the dew point, the temperature at which airborne moisture (water vapor) turns into a liquid. The amount of water vapor in the air is expressed as relative humidity, defined as the percentage of the actual amount of water vapor present compared to the maximum amount of water vapor the air can hold at a given temperature. Relative humidity is thus temperature dependent. In general, the warmer the air, the more moisture it can hold. So, as the relative humidity increases, the dew point also increases, and condensation will occur at warmer temperatures.
Indoors, when water vapor in the air comes into contact with glass or framing whose surface temperature falls below the dew point, condensation will form. If the dew point is below 32º F, the condensation will be in the form of frost or even ice.
Even when indoor humidity is controlled, interior surfaces of exterior walls and fenestration can, in cold weather, fall below the dew point and encourage condensation. Heat transfer seeks the path of least resistance, so in winter, heat from inside the building will conduct its way through the parts of the window that are the least energy efficient (i.e., most conductive), causing those parts to have lower indoor surface temperatures and thus more likely to generate condensation. The problem then becomes one of keeping the inside surface temperature elevated when outdoor temperatures are frigid, which is the same challenge posed by energy-efficient design, i.e., reducing the amount of heat transfer through the window. Therefore, the same design measures work to improve both, and energy-efficient windows will thus also typically have a high condensation resistance factor (CRF).
Condensation-resistant windows can also mean higher allowable relative humidity indoors (for greater comfort at a lower heat setting and less annoying static electricity in winter) and better clarity of view through the glass.
Condensation is more than mere annoyance or just a comfort issue. The collection of moisture can damage interior surfaces and the indoor environment. In primarily residential venues, the latter can result in moisture-induced mold growth and lead to lawsuits over alleged toxic reactions. In commercial facilities, condensation resistance can rise to the level of being a factor in the building’s purpose and functionality.
In the health care world in particular, green building practices are expanding design visions to emphasize beneficial daylighting, energy efficiency and other key green criteria, while accomplishing the latest sector-specific missions of reducing health care errors; discouraging the spread of infectious agents; improving sound attenuation; increasing patient well-being and enhancing physical security. High-efficiency vinyl windows with high CRF values should be of particular interest to hospitals and other medical facilities because moisture provides fertile ground for growth of potentially dangerous molds and bacteria, and can compromise sensitive diagnostic equipment. Smooth, non-porous surfaces also discourage the collection of dust and the spread of infection and are easy to clean. Windows with vinyl frames and integral blinds, sealed against moisture, dust and mold within insulating glass units, are a good option.
For all these reasons, the green movement, although initially virulently anti-vinyl, is beginning to take a second look at vinyl products, much as occurred in Europe more than a decade ago.