Passive and active humidity control for museums and display cases: materials, systems, and multi-level integration

Museum collections are vulnerable not only to persistently high or low relative humidity (RH), but also to repeated RH fluctuations that drive dimensional deformation, cracking, corrosion, salt migration, and biological deterioration. This review synthesizes passive and active humidity-control technologies for museums, with particular emphasis on display-case microclimates and their coupling with room-level environments. A two-dimensional classification framework is established in which the spatial scales of building/room, display case, and material/object are distinguished from the primary control functions of humidity buffering, dehumidification, humidification, and auxiliary support. Passive technologies are evaluated in terms of sorption isotherms, applicable RH ranges, cabinet airtightness, buffering capacity, regeneration, and integration into enclosure panels and linings. Active display-case systems based on vapor compression, thermoelectric cooling, Stirling cooling, and diffusion-absorption refrigeration are compared with respect to response speed, control accuracy, energy demand, noise, vibration, and maintenance. The available evidence shows that passive buffering is most effective in well-sealed cases subject to moderate disturbances, whereas active bidirectional regulation is required for strict targets, frequent opening, or large external loads. The most promising route is therefore a multi-level hybrid strategy combining room-level background control, enclosure airtightness, cabinet-level active correction, material-level buffering, and risk-informed monitoring and predictive control. Remaining challenges include sensor drift, cabinet leakage identification, model calibration, sorbent aging, standardized testing, and life-cycle assessment.