JAIC 1994, Volume 33, Number 2, Article 12 (pp. 211 to 220)
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Journal of the American Institute for Conservation
JAIC 1994, Volume 33, Number 2, Article 12 (pp. 211 to 220)




The variety of climate control systems among the sites is problematic. Some sites still have the mechanical heating systems that were in place when the state acquired them; others have complete heating, ventilating, and air conditioning (HVAC) systems that have created new problems.

The comprehensive HVAC systems introduced in the 1970s were intended to achieve the environmental standards of that era. These large mechanical systems were installed outside of the historic house, with underground pipes to carry glycol-water mixtures inside to air handlers and exchange units. One drawback of these systems, aside from the subsoil disturbance of archaeological evidence required for their installation, is the costly outside expertise required for repair or adjustments. Despite contractual arrangements, these experts are not available when crisis strikes. More important, there is increasing evidence that these systems cannot effectively maintain adequate relative humidity (RH) levels for collections without damaging the historic structure itself. Furthermore, experience from the past 10 years indicates that such systems do not even maintain good conditions for collections; indeed, at times they provide conditions that can be destructive. Monitoring at sites with 1970s systems has shown that RH levels are excesively high in summer and low in winter, just as they are in sites without modern systems.

Efforts in environmental management now include the creation of controlled local environments. When the entire heating system failed at Senate House, Kingston, in December 1992, furniture was grouped in the center of the rooms and covered with blankets to slow environmental shifts. This technique proved fairly successful. During this two-week period, outside temperatures fluctuated widely. Internal changes were effectively moderated by the masonry walls and the blankets. Although the coverings were light (averaging one blanket thick), they slowed the environmental response time by several hours and prevented rapid, injurious variations in RH. Unfortunately, the lessons learned from such experiences are only slowly realized, but each episode produces worthwhile data. Since the value of overall HVAC systems is limited, future efforts to regulate interior climate will concentrate on humidistatic controls.

Attempts to monitor interior environments throughout the system have been inconsistent. Hygrothermographs frequently are neglected because staff members are busy. Even when the instruments have been maintained, years of data often have been collected without being analyzed. Beginning in 1994 the bureau will phase in the use of electronic loggers, and the responsibility for their maintenance will shift to the conservators. The loggers are set to record the temperature and relative humidity every 30 minutes for 6 months. The accumulated data can then be extracted in the format desired—daily, weekly, monthly, etc. Hygrothermographs will continue to be used on site so daily conditions can be observed.

Another significant environmental concern for historic houses is lighting. Some houses are fitted with ultraviolet-filtering films, storm windows, and interior shutters; others have no light barriers at all. In many cases period documentation dictates where objects should be placed; these decisions frequently clash with good conservation practice. The only solution may be to minimize the intrusion of light with UV filters, drapes, rotational displays, or covers. While only sparse records of monitoring and adjusting light levels exist, it is clear that past attempts to control light levels failed to reconcile conservation standards with the needs of period interpretations.

Monitoring shows that some forms of ultraviolet filters applied even 10 years ago are still effective. Unfortunately, there is a temptation among site staff to believe that UV filters eliminate all potential for damage by light. Education of site staff and monitoring of light levels by consevators will be necessary to maintain awareness of the threat posed by all types of light. Environmental management remains one of the most important yet perplexing issues conservators contend with in historic houses. One approach under consideration is to hire a roving conservator who would, among other duties, be responsible for environmental monitoring.

Copyright � 1994 American Institute for Conservation of Historic and Artistic Works