Test of a device for the active control of environmental humidity in museum display cases

A series of laboratory tests were conducted on a commercial device for active relative humidity control of display cases to assess the ability of the machine to control a medium format museum display case. An extreme museum environment with large relative humidity and temperature fluctuations was simulated and different air leakage rates were produced on a purposely-made display case. The machine was shown to work very effectively for both in humidify and dehumidifying for conditions corresponding to very well sealed to medium sealed. On a very poorly sealed enclosure, the external environmental fluctuation resulted in internal fluctuations but the machine very effectively mitigated these effects. The use of the machine in positive pressure mode and (optional) recirculating mode was shown to be irrelevant to the ability of the machine to control the relative humidity. Positive pressure mode provides a constant flow to remove VOC's from the showcase (which could contribute to artefact degradation.), and to prevent ingress of ambient pollutants.