Vapor Barrier Problem
A problem with a room's vapor barrier exists when condensation occurs through pinhole-size openings in a room's envelope (walls and ceilings). If a hole exists in a vapor barrier, any vapor pressure difference between the inside and the outside forces vapor through the hole. This differential vapor pressure can be significant, especially in the summer months.
For example, when:
1. The outside conditions are 90-degrees F with 50% relative humidity; the vapor pressure equals 0.75 inches Hg.
2. The inside conditions are 45-degrees F with 85% relative humidity; the vapor pressure equals 0.25 inches Hg.
Thus, the vapor pressure difference from the outside to the inside is 0.50 inches Hg. This pressure is equal to 6.8 inches of water standing on a ceiling in the room!
Solution: Seal these holes so vapor does not enter the room, thus preventing condensation when the vapor reaches the cold space.
The holes must be sealed on the warm side (the vapor barrier side) with a true vapor barrier product.
Another solution to reduce the effect of vapor leaks in the ceiling (assuming the holes cannot be sealed properly) is to reduce the vapor pressure above the ceiling.
Installing air conditioning or dehumidification equipment above the ceiling lowers the vapor pressure differential, which helps reduce the effective differential, but it does not change the fact that holes still exist in the vapor barrier. This "solution" simply slows the rate of vapor passing through the holes.
Ventilation Problem
Condensation can occur when humid air is drawn into a room through openings (such as doors), and condenses when it reaches the colder room. This condensation can form as moisture on the walls and ceiling, or as fog in the room.
Solution: Prevent air from entering the room in an uncontrolled manner. In order to accomplish this, the air flow in the entire facility must be accounted for by investigating the air flow balance. Many times, the air flow in the problem room alone is investigated. However, each point of exhaust and supply from the facility must be accounted for to ensure that the building is in proper balance.
Each area within the facility must also be evaluated to determine the desired air flows between adjacent spaces. The determination of where the air should be flowing within the spaces depends on the food-safety objectives as well as other considerations.
Humidity Problem
Condensation can occur when moisture is produced in the room by equipment or open-product cooling. The moisture evaporated from the product or released by the process raises the room's relative humidity, thus creating air (vapor) that is prone to condense.
Solution: If the problem is caused by open-product cooling, then dehumidifying the room with a desiccant dryer or ventilation with outside air may solve the problem. Product quality must be considered when taking this approach, so as not to affect the moisture content of the product.
If equipment exhaust is venting to the room, then providing an exhaust hood, or otherwise venting the equipment to the outside, should solve the problem. Remember that any air exhausted from the room must be balanced with air from some other source. (See ventilation problem above.)
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