By Shin Maekawa and Vincent Beltran
It has long been known that the longevity of cultural collections is directly affected by their surrounding environment. Exposure to elevated temperature and relative humidity (RH) can promote chemical aging, and large fluctuations in those parameters can result in mechanical damage to collections. Studies have also shown that microbial growth can significantly increase during long periods of high RH. For museums, libraries, and archives housed in hot and humid regions, the threat from biological infestation is far greater than the risks posed by chemical aging and mechanical damage.
Many cultural institutions in temperate climates have tried various climate control strategies in an attempt to slow the aging of their collections. In addition to reducing the environmental stress, improving the collection environment can limit bacterial and fungal attacks, and if such improvement is combined with the use of integrated pest management programs, problems associated with pest and microbial activities can be avoided without the use of toxic insecticides or fungicides.
In recent years, increasing numbers of cultural institutions located in hot and humid regions have relied on air-conditioning systems to extend the lifetime of their collections, as well as to provide for the comfort of their visitors and staff. The decision to use air-conditioning, however, can lead to a number of problems.
Proper installation of air-conditioning systems requires the reduction of air infiltration into the building and fittings of thermal insulation and vapor retarder film in the wall and floor. For cultural institutions in temperate climates, the typical environmental standard is a temperature of 68°F, plus or minus 2°F (20°C, plus or minus 1°C), and RH at 50 percent, plus or minus 5 percent. For cultural institutions in tropical locations, these conditions may not be practical or even appropriate. Even when preparatory measures have been taken, the installation and operation of air-conditioning systems have repeatedly proven very destructive to the superstructure and interiors of many buildings. Often converted for cultural use, historic structures are particularly susceptible to the loss of much of their original fabric during attempts at air-conditioning installation.
The cost of air-conditioning systems is also significant. The cost of these systems can be prohibitive for cultural institutions, as they are expensive to install, operate, and maintain. Because of the expense of air-conditioning, some institutions have been forced to shut down their systems during off-hours. As a result, museum collections may then be subjected to environmental stresses more severe than those stemming from daily climatic changes.
Combinations of these and other factorssuch as improper design and installationhave resulted in unsatisfactory performance by air-conditioning systems, in turn causing many instances of collection damage. Because of these issues, there has been a compelling need to find alternatives that are robust, economically sustainable, and technologically simple to operate.
Ventilation and Heating for Conservation
In 1993 the GCI initiated a study to examine the efficiency of alternative climate control strategies for the conservation of collections in museums and archives housed in historic buildings, particularly those located in hot and humid regions. This study ultimately led to the GCI's Collections in Hot and Humid Environments project (1997-2002). Among the goals of the project were: (a) to develop a locally sustainable climate-control system that would effectively reduce and stabilize levels of RH to avoid fungal and bacterial infestation, and (b) to provide institutions with a feasible alternative to conventional air-conditioning systems.
The project team first conducted extensive background research and developed a number of findings. In tropical and subtropical climates, the daily variation in temperature can have a range of just 5°C (9°F) during the rainy season, to more than 15°C (27°F) in the dry season. Since moisture content of the air remains fairly constant throughout the day, these temperature fluctuations can produce inverse variations of RH. For example, for a parcel of air at 25°C (77°F) and 80 percent RH, an increase in air temperature of 1°C (1.8°F) will result in an approximately 5 percent reduction in RH. Moreover, temperatures will cool during periods of fog or rain, even in what may seem a persistently hot and humid tropical climate. A similar scenario occurs within buildings as interior areas of higher RH are typically found in its cooler regions because of this inverse relationship between temperature and RH.
Rather than cooling air below its dew-point temperature in an effort to reduce the moisture content, the proposed climate control approach is to raise the temperature in cooler, more humid areas of the structure, thereby lowering RH. The goal is to maintain RH levels at less than 70 percentbelow the threshold RH of 75 percent, above which microbial activity significantly increases.
Heating of a building interior can be achieved through space heaters or through the ventilation of warm, dry outside air into the collection space. Since the natural infiltration of outside air is insufficient, mechanical ventilation is typically necessary. Major alterations to the building, however, can be avoided by mounting ventilators in window and/or door openings. To ensure controlled air movement throughout the affected space, it is necessary to install both supply and exhaust fans and to reorganize shelves and cabinets within the interior space.
After the project completed this background research, a series of laboratory and field experiments was conducted to determine how ventilation could be used to arrest fungal and bacterial activities typically found in cultural collections in hot and humid climates. The project also reviewed practical climate control schemes for museums housed in historic buildings and evaluated the performance of several of these approaches. Findings were then applied to the design and implementation of climate control systems at two historical structures located in hot and humid regions. The two study sites were the multiroom Historic Archive in the historical district of La Laguna on the Spanish island of Tenerife, and Hollybourne Cottage, a large residential building in the Jekyll Island Historic District in the state of Georgia, USA. The efficacy of each climate control design was verified by monitoring of the environment before and after installation.
These studies demonstrated a remarkable ability to dramatically improve interior environments using ventilation and heating strategies that, relative to air-conditioning, were significantly less expensive and much simpler to install, operate, and maintain. The results of this research were presented at multiple conferencesincluding the 2003 ICOM-CC meeting in Rio de Janeiroand described in articles in several publications. Among these are Restaurator (vol. 19, 1998), Management of Environmental Quality: An International Journal (vol. 14, no. 3, 2003), and IAQ 2001Moisture, Microbes, and Health Effects, a postconference publication of the American Society of Heating Refrigeration Air-conditioning Engineers.
Alternative Climate Control Project
Following the successes of these two experimental trials, in 2002 the GCI initiated a follow-up project, Alternative Climate Controls for Historic Buildings, to develop case studies with past and present project partners interested in expanding their use of humidistat-controlled ventilation and heating to other facilities. These additional installations have been supported by local resourcesincluding the hiring of local engineers, architects, and contractors and the purchase of equipment. The GCI's follow-up project provides technical support during the design and installation of these new climate control systems, as well as performance monitoring and suggestions for further improvements. Presently, GCI staff members are working at two museum storage facilities and are continuing system monitoring and improvement at Hollybourne Cottage.
The Valle de Guerra museum storage facility for the Autonomous Entity of Museums and Centers of the Island Government of Tenerife, Spain, is housed on the second floor of a contemporary four-story concrete building located on a northeast hillside of the island. The mixed-media collection at this facility includes pottery, baskets, wooden and metal tools, textiles, and modern machines. Occupying approximately 440 square meters with a three-meter ceiling, this storage space is divided into five rooms and contains windows only on two adjacent walls.
The climate control system at Valle de Guerra, installed in August 2002, consists of supply and exhaust fans and convective heaters that are controlled by interior and exterior humidistats. Because it was not possible to install additional windows to promote cross ventilation, filtered supply air is taken from windows along the northwest wall and ducted to the southeast end of the space, where it is released. Exhaust ventilators are mounted on existing windows along the northeast wall. Monitored since installation, the climate in the storage facility initially maintained an RH environment of between 50 percent and 75 percent and displayed a significant humidity variation between rooms. Minor modifications to the facility's climate control design now produce a narrower RH range of 55 percent to 65 percent throughout the year.
The storage facility for the Amazonian Ethnographic collection of the Emilio Goeldi Museum in Belém, Brazil, is the second site of current work. Located on a research campus outside of the city, the facility encompasses part of a contemporary single-story brick building previously used as office space. This facility is approximately 271 square meters with a 3.5-meter-high ceiling, and it houses a collection that includes woods, feathers, animal skins and bones, vegetal seeds and fibers, textiles, and some metals. Due to limited available space, a compact shelving system was also installed. The creation of potentially harmful microclimates within the shelving was avoided through the use of perforated side panels and open-slot drawers.
The climate control system at the Goeldi Museum storage facility, funded by the Vitae Foundation, was installed in July 2003 and is composed of supply and exhaust fans, recirculation fans, and dehumidifiers. The use of dehumidification at this site replaces the heating component and increases the energy efficiency of the system. Humidistats are located at the center of the storage facility and outside the structure control system operation. Positioned outside the building wall, supply fans transfer filtered air into the space through ducts and distribute it along the collect air via floor ducts along the east and west walls. Several portable dehumidifiers are positioned along its walls and connected to permanent drains within the room. Although outside dew-point temperature typically ranges from 25°C to 27°C, the climate of the storage space has been maintained between 65 percent and 70 percent RH at temperatures of 32°C to 33°C.
Since its installation in June 2000, the climate control system at Hollybourne Cottage on Jekyll Island, Georgia, has undergone multiple phases of refinement. In its fifth phase since May 2003, the current climate control configuration consists of humidistat-controlled heaters, supply and exhaust fans, and dehumidifiers. In addition, steps have been taken to address human comfort issues and improve the system's energy efficiency. This climate control system has remained remarkably maintenance free during its four years of operation.
The GCI will prepare detailed reports on the design, installation, and operation of each site's climate control system for both conference presentation and journal publication. The GCI also plans to consolidate the information produced by this research into a comprehensive publication that will be part of the Institute's Research in Conservation book series. The publicationwhich will be designed for general use by the museum communitywill describe the concepts behind this approach to climate control and provide details regarding the case studies that grew out of the initial research.
Shin Maekawa is a senior scientist and Vincent Beltran is an assistant scientist with the GCI's Science department.