The dew point is the temperature at which air is saturated with water vapour, which is the gaseous state of water.
When air has reached the dew-point temperature at a particular pressure, the water vapour in the air is in equilibrium with liquid water, meaning water vapour is condensing at the same rate at which liquid water is evaporating.
Below the dew point, liquid water will begin to condense on solid surfaces (such as blades of grass) or around solid particles in the atmosphere (such as dust or salt), forming clouds or fog.
Dew point is closely linked to relative humidity, which is the ratio of the pressure of water vapour in a parcel of air relative to the saturation pressure of water vapour in that same parcel of air at a specific temperature. Relative humidity (RH) is expressed as a percentage.
The relative humidity is 100 percent when the dew point and the temperature are the same. If the temperature drops any further, condensation will result, and liquid water will begin to form.
Compared to relative humidity, dew point is frequently cited as a more accurate way of measuring the humidity and comfort of the air, since it is an absolute measurement (unlike relative humidity).
Most people are comfortable with a dew-point temperature of 16 degrees Celsius or lower. At a higher dew point of, for example, 21 C, most people feel hot or "sticky" because the amount of water vapour in the air slows the evaporation of perspiration and keeps the body from cooling.
Dew point is defined as the temperature at which a given volume of air at a certain atmospheric pressure is saturated with water vapour, causing condensation and the formation of dew. Dew is the condensed water that a person often sees on flowers and grass early in the morning. Dew point varies depending on the amount of water vapour present in the air, with more humid air resulting in a higher dew point than dry air. Furthermore, the higher the relative humidity, the closer the dew point to the current air temperature, with 100% relative humidity meaning that dew point is equivalent to the current temperature.
How does this relate to your cold-store?
Any cold air leaking from your cold-store, whether it be from badly fitting door seals, cold bridging or poor insulation will cause the door, frame or panels to become cold. The warm humid air from a working kitchen will condensate when it comes in contact with the cold section of the cold-room. In the case of a walk-in freezer it may then freeze and ice will start to from.
Here is a link to a handy dew point calculator: http://www.dpcalc.org/