Application of Climate Data Analysis to Customizing Climate Control Standards for Sustainable Collection Management
Article information
Abstract
In this study, climate data analysis was conducted at two Korean museums to demonstrate its benefits for developing customized climate control standards to preserve artifacts in a sustainable manner. Case studies were conducted at Taean National Maritime Museum and Jungwon National Research Institute of Cultural Heritage where monitoring data were collected over a 7-month period. The results showed that display cases greatly mitigated the risks associated with mold and mechanical deformation: they maintained a consistent relative humidity of 50%–60% while the galleries had a much wider variance of 35%–85%. At Taean National Maritime Museum, the microclimates within the display cases deviated from the climate control standards for the galleries despite artifacts remaining undamaged, which indicates that the standards may need to be reassessed for sustainable collection management. At Jungwon National Research Institute of Cultural Heritage, plastic bags were shown to be an effective strategy for preserving metal artifacts by maintaining the relative humidity below 20% and preventing corrosion. These findings emphasize the need for adopting climate control standards to match the specific context of each museum and demonstrate how a comprehensive climate data analysis can facilitate sustainable collection management for long-term preservation of artifacts.
1. INTRODUCTION
Incorrect climate control can cause physical, chemical, and biological damage to the artifacts within a museum, many of which possess high cultural value. Fluctuations in humidity can cause wooden artifacts to deform by cracking or warping (Gereke et al., 2009; Grottesi et al., 2023; Vici et al., 2006). High temperatures can accelerate hydrolysis and increase the risk of damage to leather and paper-based artifacts (Lu et al., 2009; Małachowska et al., 2021; Vyskočilová et al., 2019). High temperatures and humidity can accelerate the acid degradation of waterlogged wood treated with polyethylene glycol (PEG) (Broda and Hill, 2021; Kim et al., 2021). High humidity can cause metal artifacts to corrode (Morcillo et al., 2015; Watkinson and Lewis, 2004; Watkinson et al., 2019). High temperatures and humidity promote microbial growth that can result in mold on the surface of artifacts (Kula et al., 2022; Passanen et al., 2000).
These risks have led world-renowned museums and cultural heritage research institutes to examine the best climate control practices for conserving their collections of artifacts (Ankersmit and Stappers, 2017; Bickersteth, 2016; Bratasz, 2013; Michalski, 2016). From the 1960s to the early 1990s, a strict climate control standard of 50% ± 5% relative humidity (RH) and 20°C ± 2°C (i.e., the 20/50 rule) was considered ideal (Bickersteth, 2014). However, this standard has several issues. The strictness of this standard made it very difficult for museums to meet (Ankersmit et al., 2018) and, even if a museum was equipped to meet this standard, the electricity consumption and operational costs were enormous. By the mid-1990s, the 20/50 rule began to be questioned. Past records showed that collections were safely preserved with no or minimal damage even when museums deviated from the strict standards (Ankersmit and Stappers, 2017; Bickersteth, 2014; Michalski, 1994). This led conservation researchers to question the necessity of maintaining the strict standards with its associated costs if artifacts remained safe under less strict conditions and resulted in the emergence of sustainable collection management. This concept refers to establishing climate control standards customized to individual museums based on factors such as the building physics, heating–ventilation–air conditioning (HVAC) system performance, artifact material, the sensitivity of artifacts to the climate, and the local outdoor climate (Ankersmit and Stappers, 2017; ASHRAE, 2019; BSI, 2012; Kramer et al., 2016). Sustainable collection management prioritizes passive climate control methods such as using silica gel or airtight packaging rather than active methods such as HVAC operation, which greatly reduces energy consumption and operational costs for museums.
Sustainable collection management has also resulted in a shift in climate control guidelines declared by major organizations. In the UK, the 2009 National Museum Directors’ Conference (NMDC, 2009) announced a set of guidelines for artifact loan conservation aimed at reducing carbon emissions. In 2014, the International Council of Museums Committee for Conservation (ICOM-CC) and the International Institute for Conservation of Historic and Artistic Works (IIC) jointly announced the need to reduce carbon emissions and issued climate control guidelines for sustainable collection management (ICOM-CC, 2014). Recently, countries such as the UK, the USA, the Netherlands, and Australia have either newly established or revised their climate control guidelines to include the concept of sustainable collection management (BSI, 2012; ASHRAE, 2019; Ankersmit and Stappers, 2017; Pagliarino, 2022).
In Korea, only about 50% of museums have conducted a climate data analysis in their buildings (Kim et al., 2023). Such an analysis is essential for sustainable collection management and developing customized climate control standards based on the performance of the overall building, exhibition and storage rooms within the museum, and individual enclosures such as display cases and storage bags. In this study, climate data were collected from two museums to demonstrate the insights that can be gained from climate data analysis and encourage other museums to adopt this practice.
2. MATERIALS AND METHODS
2.1. Taean National Maritime Museum
Figure 1 shows Taean National Maritime Museum, which was established in 2018 and comprises four exhibition halls and three storage rooms with a collection of about 32,000 items. Most of the artifacts are ceramic while the rest are wooden, plant-based, bone-based, or metal. In the storage rooms, the HVAC system runs 24 h every day of the year. In the exhibition halls, the HVAC system only operates during the opening hours (i.e., 09:00–18:00). Climate control depends on the room and the artifacts within. For all rooms, the temperature is maintained at 20°C ± 3°C throughout the year. The RH is set to 55% ± 5% in storage room 1 for organic artifacts; 50% ± 5% in storage room 2 for ceramics and pottery, <50% in storage room 3 for inorganic artifacts, and <20% in cabinets containing metallic artifacts in need of humidity control. The microclimate of the display cases is controlled at 50% RH by Art-Sorb (Fuji Silysia Chemical Ltd., Japan), which is regularly replaced twice a year.
Taean National Maritime Museum: (A) Building, (B) storage room 1, (C) Exhibition hall on the first floor, (D) Exhibition hall on the second floor, (E) Display case on the first floor, and (F) Display case on the second floor.
The study took place over the 7-month period of May– November 2022. The climate data analysis comprised assessing the overall performance of the building and display cases and potential risks. RH and temperature data were collected by dataloggers (Testo 175H1, Germany) at intervals of 1 h from sensors placed to best evaluate the performances of the building, HVAC system, and individual storage and display cases. A display case was selected on each floor, and the cases housed artifacts made from various materials (e.g., iron pot, pine cone, wooden table). The microclimates of the display cases on the first and second floors were compared because the type of display case was identical. A performance index (PI) analysis was conducted to determine if the relative humidity and temperature of each room complied with the standard set by the museum: a temperature of 20°C ± 3°C and a RH within ± 5% of the prescribed level for the material of the housed artifact.
A risk assessment was conducted by following the method described by Martens (2012), which has since been optimized and made accessible by the Jerzy Haber Institute of Catalysis and Surface Chemistry (2020). The risk assessment looked at the risks of biological degradation (i.e., mold), chemical degradation, and mechanical degradation. The risk of mold was assessed by plotting RH and temperature data in a graph including contours at which active mold has been observed (Strang, 2 0 13). T he r isk o f chemical d egradation was assessed by calculating the time-weighted preservation index (TWPI) (Pretzel, 2005). For different combinations of temperature and RH, the rate of decay was calculated and normalized against the standard temperature and RH of 20°C and 50%, respectively. Chemically unstable objects were considered to degrade more slowly than they would at 20°C and 50% RH if TWPI >1 and more quickly if TWPI <1. The risk of mechanical degradation was assessed by analyzing the hygroscopic response to RH fluctuations. The running average of the RH was taken to indicate the RH experienced by the core of a hygroscopic material in an artifact, which could be used to estimate the strain and stress.
2.2. Jungwon National Research Institute of Cultural Heritage
The Jungwon National Research Institute of Cultural Heritage has invested considerable time and resources in maintaining an optimal indoor climate suitable for metallic artifacts in its collection by running a thermo-hygrostat system and performing conservation techniques, but these efforts have not proven highly effective. Earlier studies have shown that, although the RH in the storage room for metallic artifacts had a RH of <40%, these artifacts still required conservation techniques to combat active corrosion (Kim et al., 2023). X-ray diffraction (XRD) analysis revealed the presence of akaganeite in the corroded layer of metallic artifacts, which is a chloride-containing iron oxide–hydroxide mineral. The removal of chlorides from archeological metal is extremely difficult if not impossible (Morcillo et al., 2015; Scheck et al., 2015). Minimizing corrosion requires maintaining a constant low RH. Studies have shown that a RH of >30% accelerates metal corrosion and that akagenite formation should be suppressed by keeping the RH at <20% (BSI, 2012; Watkinson and Lewis, 2004).
The climate data analysis involved determining the effectiveness of using a plastic bag to maintain a low RH, which is conducive to protecting metal objects from corrosion in a passive manner. As shown in Figure 2, a data logger (Testo 175H1, Germany) was vacuum-packed in a polyethylene bag, which reduced the RH to <20%. The bag was placed inside a covered plastic box, which was then placed in a ventilated cabinet. The cabinet was fitted with a fan to create an airflow, which synchronized its microclimate with the climate control of the storage room (RH = 50%).
Experimental setup at the Jungwon National Research Institute of Cultural Heritage.
3. RESULTS
3.1. Taean National Maritime Museum
3.1.1. Data analysis
Figure 3 plots the RH and temperature data of the museum throughout the study period. The RH was relatively constant throughout the study period but stayed at distinct levels in different rooms. The RH in storage rooms 1, 2, and 3 had an average and standard deviation of 64.5% ± 3.0%, 58.7% ± 5.9%, and 49.6% ± 2.9%, respectively. The temperatures were 19.4°C ± 1.5°C, 19.4°C ± 3.3°C, and 20.1°C ± 1.2°C, respectively. The temperatures generally complied with the climate control standards of the museum, but the temperature dropped in storage room 2 during the summer to below 15°C, which is because the RH increased in this room, and the museum decided to adjust the temperature to optimize control over the RH. It proved impossible for the museum to control both the RH and temperature at the same time during the summer, and they decided to prioritize RH control to reduce the risk of mechanical damage from RH fluctuations.
RH and temperature in storage rooms at Taean National Maritime Museum for May–November 2022.
Figure 4 shows the results of the PI analysis for the different rooms and display cases. The RH and temperature requirements were satisfied in storage rooms 1, 2, and 3 for 8.9%, 23.3%, and 55.8%, of the time, respectively. The RH and temperature requirements were not satisfied in the two display cases for almost 100% of the time. However, even though these requirements were not satisfied, regular checks by curators and conservators since the museum opened in 2018 have observed no damage to the artifacts.
PI analysis of the RH and temperature data from Taean National Maritime Museum: (A) Storage room 1, (B) storage room 2, (C) Storage room 3, (D) Exhibition hall on the first floor, (E) Display case on the first floor, and (f) Display case on the second floor. The climate control standard was considered satisfied if the measured data were within the green outlined box. The plots in different seasons are distinguished by color (spring: green, summer: red, fall: yellow).
3.1.2. Risk assessment
Figure 5 shows the risk of mold growth in the museum. The risk was very small in the three storage rooms and in the two display cases. However, the risk was high in the exhibition hall in the summer and early fall although no active mold growth has yet been observed. At high RH, monitoring and regular checks are important to reduce the risk of mold. One potential measure is to use climate control to reduce the RH to <65% in the summer when temperatures are highest.
Risk of mold growth in Taean National Maritime Museum: (A) storage rooms and (B) exhibition halls and display cases. Contours indicate conditions at which active mold has been observed.
Figure 6 shows the risk of chemical degradation. The storage rooms had TWPI values of around 1 except for storage room 1, which houses artifacts made of organic materials in storage 1 and thus are considered chemically unstable. Thus, the risk of chemical degradation was considered significant in storage room 1. The risk was considered low in the other storage rooms owing to their artifacts being made of more stable materials and TWPI values of around 1. The TWPI values were less than 1 for the exhibition hall and display cases, which indicates that chemical degradation is accelerated in these locations. Whether this risk is acceptable depends on the tradeoff between preservation and operational costs.
TWPI distributions in the storage rooms, exhibition hall, and display cases of Taean National Maritime Museum. The bottom and top whiskers indicate the lower extreme (5%) and upper extreme (95%), respectively, of the distribution. The bottom and top of the box indicate the lower quartile (25%) and upper quartile (75%), respectively. The line in the box indicates the median (50%). The number in brackets is the average. TWPI values of <1 indicate a higher risk of chemical degradation.
Figure 7 shows the risk of mechanical degradation caused by a large RH fluctuation of 35%–85% in the exhibition hall on the first floor. Studies have indicated that objects with a low risk of mechanical degradation can tolerate RH fluctuations of up to ± 20% RH (ASHARE, 2019; Erhardt and Mecklenburg, 1994; Martens, 2012; Michalski, 2000). Regarding the fact that the ship replica in the exhibition hall represents an object with low risk of mechanical degradation, its 4cm wooden deck showed warping. Thus, proper measures such as installing a door or air curtain might be considered in order to mitigate the mechanical risk caused by the huge RH fluctuation.
RH fluctuations (blue line) in the exhibition hall on the first floor of Taean National Maritime Museum and the response times for the wooden ship replica in the exhibition hall. The response times after 1 week (orange line) and 1 month (gray line) were taken to represent the RH experienced by the wooden deck covering the ship and the wooden hull, respectively.
Figure 8A shows the RH fluctuations inside the display case on the first floor. The RH inside the display case remained at 50%–60%, which is a much smaller variation than that of the exhibition hall. In this environment, thin wooden objects such as wooden tags can be safely exhibited without the risk of mechanical degradation. These results indicate that the buffer effect was most obvious during the summer (June–September). Figure 8B shows that the absolute humidity (AH) was consistently lower inside the display case than in the exhibition hall (dark blue line). On September 21, the AH inside the display case shifted toward that of the exhibition hall, which can be attributed to the display case being opened. In the fall, the AH in the exhibition hall closely matched the outdoor AH, which indicates a high rate of air exchange between the indoor and outside environments. This matches the practices of the museum, which actively allows air to be exchanged in the fall to reduce the RH in the exhibition hall.
Fluctuations in humidity in the exhibition hall and display case on the first floor of Taean National Maritime Museum: (A) RH and (B) AH.
3.2. Jungwon National Research Institute of Cultural Heritage
Figure 9 shows the results of the experiment at Jungwon National Research Institute of Cultural Heritage. The plastic bag was effective at maintaining the RH below 20% (Figure 9A), but the AH increased over time because of the presence of leaks (Figure 9B). The stable RH inside the bag despite the leaks can be attributed to the increase in temperature during the study period. These results indicate that the plastic bag and vacuum packing are effective measures for maintaining a low RH locally to protect metal artifacts. The effectiveness of the plastic bag for local climate control can be further optimized by improving the seal to increase airtightness, adding silica gel as an extra moisture absorbent, and using a second bag to reduce the air exchange rate.
Effectiveness of local climate control measures using a plastic bag and vacuum packing: (A) RH and (B) AH.
4. DISCUSSION AND CONCLUSIONS
This study aimed to demonstrate the importance of monitoring climate data in museums and how climate data analysis can be used to identify risks and facilitate sustainable collection management. For Taean National Maritime Museum, a risk assessment was performed to analyze the risks of biological, chemical, and mechanical degradation. Museums can tailor their climate control standards based on such an analysis to defend against the highest risks. The results showed that the actual conditions did not match the museum’s standards for climate control, but the lack of deterioration of the artifacts indicate that these standards should be closely reviewed and adjusted to be more realistic. Display cases were confirmed to be effective at protecting susceptible objects with a much more stable RH than the exhibition hall. Their effectiveness can be further improved by increasing their airtightness and adding moisture absorbents. The experiment on local climate control at Jungwon National Research Institute of Cultural Heritage showed that vacuum packing can effectively maintain the RH in a plastic bag below 20%, which can be used to protect metallic artifacts from corrosion. The effectiveness of this measure can be improved by increasing the airtightness of the seals and adding a moisture absorbent such as silica gel.
Passive climate control strategies are beneficial for reducing the maintenance costs and carbon footprints of museums while still protecting their collections. The two case studies showed how monitoring and analyzing climate data can help museums gain more insight into the environmental conditions that their artifacts are actually exposed to and their effects. The results are expected to facilitate sustainable collection management and to help museums develop customized climate control standards based on local climate conditions in their exhibition halls, storage rooms and display cases as well as the materials their collections are made from.