1 INTRODUCTION

The focus of this paper is the effect of indoor climate control on the museum building envelope. The climate control system includes all of the equipment providing heating, humidification, cooling, and dehumidification. Managing humidity in a building requires before all else that there be no roof leaks and no entry of liquid water through the building foundation.

Some terms should be defined at the outset:

• the “building envelope” comprises the roof, wall, and window systems in a building, separating the indoors from the outdoors
• “psychrometrics” is the science of air-water relations
• “hygrothermal” properties of materials describe the response of materials to temperature and humidity effects

Many museums are in older buildings. Indeed, one of the first uses often considered in adaptive use of historic property is as a museum. Typically, the original building envelope was designed to work compatibly with the original climate control system. It is correct to assume that a changed climate control system will have an effect on the envelope unforeseen by the original designer. Only proper study can reveal the likelihood of damage to the envelope. To the chagrin of many conservators and museum administrators, many new systems have been found to perform undependably, produce erratic and nonuniform conditions, and have unwelcome effects on the building envelope. To determine why some systems succeed and others fail requires a critical review of the standard methods of envelope analysis.

This paper presents a new method of portraying some of the temperature and humidity information that is readily found in building science literature. It illustrates the use of the psychrometric chart as a base of information on temperature and humidity. Additional information can be then added as graphic overlays regarding moisture content of materials, damage conditions, convection and transient (time-dependent) effects. The method of compiling and illustrating the effects not the analytic methods presented here is innovative.