Air-Tight

Air Change Rate can be taken as a measurement of the air-tightness of a showcase. The Air Change Rate is the amount of inside air that leaks (without being forced by mechanical means) out of the case and is therefore exchanged with ambient air over a defined period of time.

An Air Change Rate of 1/10 per day means that a showcase will have exchanged 10% of it's internal air with ambient air over a 24 hour period, or in other words - the case "may" exchange all of it's internal air with ambient air every 10 days.

Realistic values for modern showcases are Air Exchange Rates of 1/5 to 1/6 per day - which is also the recommended range for the use of our devices. It might be possible to use miniClima Constant Humidity Devices on showcases with higher Air Exchange Rates than 20%, but the user should be aware that a lot of the work carried out by the device will be lost to the environment.

It is not possible, though, to give a difinitive answer to the question of when the point is reached where the use of the CHD becomes useless. Too many factors (and their interactions) play an eminent role in humidity regulation, e.g. the ambient conditions or the tightness against the diffusion of moisture vapour, called "steam-tightness", which is discussed below.

It is possible that a showcase may be constructed extremely air-tight, but because of materials used, it is not "steam-tight" and may therefore be unsuitable for humidity control using a CHD.

Steam-Tight

Unlike the air-tightness, where exchange of air as a whole is the problem, the steam-tightness refers to the sealing of the showcase material against diffusion or permeance of moisture vapour. Brick or stone, and most woods do have a humble steam-tightnesses; metal foils, glass and some synthetic plastics provide better values.

Without wanting to restrict the use of certain materials when using our equipment, it is essential to know (as it is with air-tightness) that the more a showcase meets the criteria of being designed steam-tight, the sooner and more likely one will end up with a working system. Once a (case-specific) value is exceeded, all efforts to control the humidity level will become fruitless.