JAIC 1994, Volume 33, Number 2, Article 11 (pp. 199 to 210)
JAIC online
Journal of the American Institute for Conservation
JAIC 1994, Volume 33, Number 2, Article 11 (pp. 199 to 210)




This article demonstrates a technique for analyzing the heat and moisture performance of a building envelope assembly. The technique is based on classical methods but extends the amount of information both put in and extracted. It combines standard psychrometrics with information from known references regarding the moisture contents of materials. The technique contains some allowance for convective and transient effects, and it provides an indication of material moisture contents and potential for damage. The technique also allows acceptable hygrothermal ranges and permissible hygrothermal shocks for artifacts to be described visually.

Humidity settings for the indoor air of museums are discussed. The only current guideline for winter performance is that running window condensation indicates excessive humidity. During the summer, achieving proper balance between lowering the air temperature and removing humidity requires a certain sophistication of system design and operation. Humidity control that overrides temperature control during periods of extreme outdoor conditions is recommended.

Building instrumentation is discussed and the advantages of digital recording of data are highlighted. The clustering of data points on a psychrometric chart is described, using the psychrometric analysis above as a guide. The relationship between the clustering of indoor conditions and stresses on the building enveloped are portrayed on the psychrometric chart, but they are not analyzed in detail.

All of the above assumes that the only moisture contributions to the museum air are those accounted for by human use and mechanical provision. However, many buildings have leaky roofs and foundations that seep groundwater from the surrounding soil. Humidity control is not possible in buildings with leaky roofs or foundations. Correcting these defects must have first priority.

Copyright 1994 American Institute for Conservation of Historic and Artistic Works