By Shin Maekawa and Vincent Beltran
An important tool for preventive conservation is establishing climate control over the environment in which a collection is housed. Reducing relative humidity (RH) and temperature can slow the aging of materials, while decreasing fluctuations in both can limit cycles of swelling and contraction that may lead to the development of fractures. Attack by molds, bacteria, and insects can also be thwarted by minimizing extended periods of humid conditions, which foster microbial growth.
Cultural institutions have generally used conventional air-conditioning or heating, ventilation, and air-conditioning (HVAC) systems as the primary means of climate control. While HVAC systems are capable of moderating the environment for both collection preservation and human comfort, use of typical systems can pose significant obstacles. Excessive capital, operational, and maintenance costs and installation difficulties for historic structures are among the major hurdles.
The Getty Conservation Institute has sought to reduce reliance on conventional air-conditioning systems for collections climate control through the research and application of alternative climate control strategies. Over the last decade, two related GCI projects have investigated climate control alternatives to conventional systems, concentrating on hot and humid regions where microbial activity poses the overwhelming risk to collections.
Alternative Climate Control
Initiated in 1997, the Collections in Hot and Humid Environments project researched and developed an economically sustainable climate control system that can mitigate the risk of biological damage to collections by eliminating prolonged periods of high RH and reducing overall RH levels. The system integrated the use of humidistat-controlled ventilation with either heating or dehumidification, and during several field applications it proved effective and technologically simple.
The subsequent collaborative-based Alternative Climate Controls for Historic Buildings project, begun in 2002, developed case studies that involved local engineers, architects, and contractors in formulating and implementing climate control designs. The case studies (see Conservation, vol. 19, no. 1) included:
- the Valle de Guerra Museum storage facility for the Organismo Autónomo de Museos y Centros del Exemo Cabildo Insular de Tenerife (OAMC) in Tenerife, Spain;
- the storage facility of the Amazonian enthnographic collection of the Emilio Goeldi Museum in Belém, Brazil;
- Hollybourne Cottage in the Jekyll Island National Historic Landmark District in Jekyll Island, Georgia, USA.
Responsibility for system operation, maintenance, and monitoring at each site has been transferred to the respective project partner, and recent results for these case studies have been presented at conferences and in various publications (the GCI maintains an advisory role with each institution). Before transfer, environmental monitoring of the systems verified the successful reduction and stabilization of RH levels to below 70 percent.
The economic benefit of alternative climate control strategies over use of conventional HVAC systems was also confirmed. Compared to a typical HVAC budget, capital costs for each case study were reduced by 75 percent to 90 percent, while savings in operational and maintenance costs ranged from 80 percent to 90 percent.
Comfort and Preservation
The primary objective of these field studies was to establish an appropriate environment for both the collection and building; human comfort was of secondary importance. This hierarchy was due in part to the type of interior space in each case study. The Valle Guerra and Goeldi Museum storage facilities, which house mixed-media collections, receive only limited research and conservation visitation. Hollybourne Cottage, which does not contain a collection, is also the site of only intermittent visitation.
While the ability of the climate control system to establish a safe environment for a collection was confirmed, its capability to provide for human comfort while maintaining this environment remained untested. If the system could also satisfy human comfort levels, the potential application of this low-cost, relatively simple GCI-developed system could be widely expanded. With ten thousand visitors annually, the Casa de Rui Barbosa Museum in Rio de Janeiro, Brazil, provided an ideal venue for testing the applicability of the climate control strategy in a setting where human comfort was an important consideration.
Management and preservation of the Casa de Rui Barbosa Museum are the responsibility of the Fundação Casa de Rui Barbosa (FCRB), a federal public institution connected with the Ministry of Culture. In 2004 the FCRB; the Fundação Vitae Apoio á Cultura, Edução, e Promoção Social; and the GCI established a project with the goal of improving the interior conditions of the museum—particularly in the rooms that make up the library—by addressing human comfort as well as preservation.
Rui Barbosa de Oliveira—a prominent Brazilian humanist, writer, jurist, and statesman who played a major role in the 1891 drafting of the first republican constitution of Brazil—occupied his residence from 1893 until his death in 1923. The following year, the eighteenth-century masonry building was purchased by the government, along with Barbosa's extensive library and archives; in 1930 it was declared the first Brazilian house museum. The Barbosa collection includes artwork, furniture, and several automobiles. However, the library collection—consisting of thirty-seven thousand books covering law, humanities, and culture—is considered the heart of the museum.
Prior to installation of a climate control system, the Casa de Rui Barbosa Museum's building, environment, and collection were assessed to guide development of conservation strategies. The building assessment examined existing structural conditions and modifications to the original design, while the environmental assessment characterized the climate and pollution level of the library and exterior. The collection assessment documented the condition of objects in the library, including books and furniture.
Evaluations of the building and its environment were instrumental in identifying the importance of reinstating the original passive climate architectural features of the building that were currently obstructed. The building assessment clarified the original airflow path in the library space, which vented warm air through the ceiling into the attic and then to the building's exterior via loosely stacked roof tiles. A subsequent roof installation of a synthetic membrane, to guard against heavy rainfall and dust, eliminated this passageway. Similarly, the closure of wall openings in the cellar, to allow for its use as storage and temporary exhibition area, prevented ventilation. The environmental assessment documented the resulting accumulations of heat and moisture in the attic and cellar, respectively. The new climate control system sought to incorporate the spirit of the original design, improving the climate not only in the library but also in the connected problematic spaces of the attic and cellar.
The environmental assessment also detailed the existing climate in the library space, where using window ventilation resulted in large fluctuations in temperature and RH, as well as high levels of pollution and dust. Recommendations called for eliminating window ventilation and installing filtered mechanical ventilation and dehumidification. Although the microenvironment of the library's cabinets, where books are stored behind glass-paneled doors, provided some protection from air pollution and dust, a climate control system could further reduce and stabilize RH, temperature, and dust levels.
The Climate Control System
The climate control system implemented at Casa de Rui Barbosa is similar in concept to previous case study installations. In the library, maintaining an appropriate environment of less than 65 percent RH—below the RH threshold for microbial growth—relies on humidistat-controlled ventilation and dehumidification. The presence of humid interior air and the availability of exterior air with low RH trigger the ventilation mode (operation of supply and exhaust ventilators or fans). The dehumidification mode (carried out by a small air-conditioning split unit with a reheat coil) reduces interior RH levels when this arid exterior reservoir is unavailable.
Addressing human comfort while still meeting preservation needs, however, involved additional considerations for the climate control system. Indoor fresh air requirements typically call for a rate of seven to eight liters per second per person to limit buildup of carbon dioxide, moisture, and body odor. Although the ventilation mode provided adequate fresh air to the building's interior, the use of the dehumidification mode alone could not. Thus, a hybrid mode was introduced that triggered dehumidification and ventilation simultaneously—but only during visiting hours. This continuous movement of a large volume of air through the climate-controlled space also promotes a cooling sensation of the skin surface by increasing transpiration, thereby enhancing human comfort.
Although not capable of the level of temperature control provided by conventional air-conditioning, the climate control system at Casa de Rui Barbosa did reduce maximum temperatures. Generally set at 32°C for unoccupied spaces—a typical summer daytime temperature in the region—peak interior temperature at Casa de Rui Barbosa was lowered to 28°C in an effort to improve human comfort. This reduced set point also protects against condensation within the building and ductwork, as it remains above peak dew point temperatures recorded on the most humid days in Rio de Janeiro.
The design of the Casa de Rui Barbosa system differs dramatically from those implemented in previous case studies. Located in the cellar away from public view, the supply ventilator and dehumidification units are connected to the library space by ductwork to diffuser grills on the library floor; the diffusers deliver the conditioned air into the room with minimal vertical air velocity. Once supplied, the conditioned air is either returned to the dehumidifier via floor grills or exhausted to the exterior through the ceiling and attic by a fan positioned in a duct leading to the attic skylight. Mechanical ventilation is also provided in the cellar through restored wall openings fitted with filters. A programmable logic control unit controls return and exhaust air, as well as ventilation and dehumidification, by comparing RH and temperature conditions for the exterior and library.
In October 2006 an initial trial of the Casa de Rui Barbosa system conducted on a typical spring day—air temperature of 27°C and 80 percent RH—successfully produced a stable library environment of 25°C and 62 percent RH. System performance will be monitored for the next year to assess its effectiveness during a range of outside environmental conditions.
The long-term success of the Casa de Rui Barbosa system will represent a significant advance in the Alternative Climate Controls for Historic Buildings project. As evidenced by installations at storage and noncollection spaces, the GCI-developed climate control system can produce an environment that minimizes risk for collections in a manner that, relative to conventional HVAC systems, is low in cost, is easy to use and modify, and requires little maintenance. The Casa de Rui Barbosa installation furthers this research by providing for human comfort within the boundaries of an appropriate environment for collections. The ability of the alternative climate control system to address the environments of both visited and nonvisited spaces will greatly broaden its potential use.
Dissemination and Collaboration
The Casa de Rui Barbosa climate control system represents the fourth and final case study of the Alternative Climate Controls for Historic Buildings project. While results have been disseminated in numerous presentations and publications, the GCI also plans to mark the closure of the five-year project by consolidating the research from all case studies into a comprehensive publication that will elucidate the concepts behind the climate control approach and provide details on the design, installation, and operation of each case study.
The development of new and important avenues of environmental research will depend largely on a critical evaluation of the current status of heritage climate control. To further this process, the GCI and OAMC organized the Experts Roundtable on Sustainable Climate Management Strategies in April 2007 in Tenerife. This multidisciplinary forum convened an international gathering of experts in heritage preservation whose discussion focused on recent approaches to environmental management in a broad range of contexts, including results from the GCI's Alternative Climate Controls for Historic Buildings project. It is hoped that this meeting will stimulate development of collaboration to further the accessibility of climate control strategies to the cultural community.
Shin Maekawa is a senior scientist and Vincent Beltran is an assistant scientist with the GCI's Science department.
Environmental Management in China's Forbidden City
Because of its expertise in researching and developing alternative climate control systems, the GCI is assisting with a climate control system for Emperor Qianlong's Lodge of Retirement, an eighteenth-century compound in the Forbidden City palace in Beijing. Part of a larger effort spearheaded by the World Monuments Fund to restore the Qianlong Garden complex, this initial system will serve as a model to guide the environmental management of similar structures in the Forbidden City.
In May 2006 Shin Maekawa of the GCI and Ernest Conrad of Landmark Facilities Group were invited to develop a concept and specifications for a climate system that could be installed in the Lodge of Retirement's theater structure. Unique due to its merging of Western influence and Chinese aesthetic, the interior decorations of the theater, including trompe l'oeil murals, have deteriorated, partly because of exposure to extreme levels of relative humidity (RH) and temperature.
The new climate control system combines particulate filtration and dehumidification. Both strategies will be utilized during most of the year to reduce dust levels and limit peak interior RH to below 60 percent, protecting materials from fungal attack. Internal temperature will also be restricted to a maximum of 27°C to provide human comfort. Winter operation, however, will employ only air filtration, allowing interior RH and temperature to drift toward minimum values of 30 percent and below 0°C. This method avoids the potential for condensation that a more active climate control system might exhibit when attempting to heat and humidify air.
The Architectural Design and Research Institute at Tsinghua University carried out local fabrication and installation of the climate control system during March 2007.