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Climate Correlation: Environmental Monitoring at the Library of Congress

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The following is a post by Anna Katherine Overstreet and Alexandra Ptacek, 2022 Junior Fellows, Preservation Directorate. Anna Katherine recently graduated with her undergraduate degree in mathematics from Mississippi State University, and she will be returning in the fall for a graduate degree in statistics. Alexandra is a graduate student of Anthropology and Museum Studies at Arizona State University.

Portrait photos of Junior Fellows
2022 Junior Fellows Anna Katherine Overstreet (right) and Alexandra Ptacek (left).

As Junior Fellows at the Library of Congress (LC) this summer, we analyzed environmental data with the Preservation Research and Testing Division (PRTD) as part of the Preservation: External Climate and Internal Building Climates project. Internal environmental monitoring data was provided by PRTD from office, storage, laboratory, and exhibit spaces in the Thomas Jefferson Building and James Madison Memorial Building. Our goal during the ten-week Junior Fellows Program was to better understand the relationships between external weather conditions and interior microclimates at the Library.

Floor maps of Library’s environmental monitoring sensor location.
Jefferson Building 1st floor map, Jefferson Building 2nd floor map, and Madison Building ground floor map with environmental monitoring sensor location. Data from Gutenberg and Mainz are from older exhibits.

Weather conditions at the Library were obtained from the National Aeronautics and Space Administration (NASA) Langley Research Center (LaRC) Prediction of Worldwide Energy Resource (POWER) Project’s (funded through the NASA Earth Science/Applied Science Program) Hourly 2.0.0 version on 2022/06/06 through their Renewable Energy user community.

The Thomas Jefferson Building was originally constructed in the nineteenth century and provides one example of the challenges facing preservation specialists today. Original structural foundations must undergo modifications to properly manage temperature, humidity, and other conditions to prevent damage to materials within the collection. For example, mold growth can occur in areas with high humidity, and the physical integrity of materials may be stressed under frequent temperature changes.

Levin C. Handy’s 1890 photo showing construction of stone walls of the Thomas Jefferson Building.
Construction of the Thomas Jefferson Building, [Builders at work on the rusticated stone walls of the Library of Congress Thomas Jefferson Building during its construction; U.S. Capitol in the background]. Photo by Levin C. Handy, ca. 1890.

Collection managers and preservation specialists monitor these conditions to ensure the collections are protected from damage and available for future generations. The LC buildings in Washington, DC experience an outside climate that varies between hot, humid summers and cold winters. However, the effects of global warming have brought more intense heat waves, additional rainfall, and greater variations in weather than was present previous years.

Initial findings indicated that outside temperatures have some effect on internal temperatures. For example, temperature readings taken inside the Library, near the Buell Map Exhibit, increase when it’s hotter outside and decrease in colder weather. But we must also take into consideration the effects of HVAC settings, human activities in the spaces, and general building efficiency.

Line plot of external weather and internal temperature of the Abel Buell 1784 map case between 2014 and 2020.
Line plot of external weather and internal temperature of the Abel Buell 1784 map case between 2014 and 2020, data from PRTD and from NASA’s POWER Project’s Hourly 2.0.0 version on 2022/06/06

Anna Katherine Overstreet investigated the relationship of multiple external versus internal climate variables, including temperature, relative humidity, and dew point. The analysis centered on whether the positioning of an internal space, such as on an exterior or interior wall, would affect the relationships between the spaces’ microclimates and the external climate.

Correlation matrix of R-values linking 3 spaces’ temperature, relative humidity, and dew point and identical weather factors, adding barometric pressure.
Correlation matrix describing relationships (correlation) between internal and external climate variables.

As an example, we examined data from a ground floor room in the Madison Building using sensors on one internal wall and one external wall. The temperature data gathered by the internally facing wall sensor was unaffected by the outside temperature, relative humidity, or dew point. This was not the case for the externally facing wall, in which the temperature data was strongly effected by the outside temperature and dew point. The relative humidity data in both areas had very similar correlations with the external temperature, relative humidity, and dew point.

Across the other spaces analyzed in the Madison and Jefferson Buildings, the relationships between interior spaces’ microclimates, especially their temperature and humidity, and the external climate are relatively weak. On the other hand, the relationships tend to be stronger between an external-facing space’s microclimate and the external climate variables, especially regarding temperature and relative humidity. It is interesting to note that barometric pressure and most sensor readings, especially relative humidity, are negatively correlated, meaning the readings move in opposite directions (if one goes up, the other goes down and vice-versa). For example, low barometric pressure outside trends with high interior relative humidity. Barometric pressure fronts are predicted and tracked by many meteorologists, and low barometric pressure is one indication of rainy days. The tracking of these barometric pressure fronts allows a few days’ notice, which could allow collection caretakers to anticipate changes in the internal microclimate conditions, particularly the relative humidity, which could increase in stormy conditions.

Line plots of correlation coefficient as it changes for each hour offset for the data from five indoor spaces.
Line plot of thermal lag with correlation coefficient of outdoor weather conditions and total PRTD data of two Madison Building spaces and three Thomas Jefferson Building exhibit spaces. Data from Gutenberg and Mainz are from older exhibits.

Alexandra Ptacek focused on possible methods to quantify the time lag between external conditions and internal microclimates. This could allow preservation professionals to adjust conditions in spaces proactively rather than reactively after the internal microclimates have already been affected by outside weather conditions. In some public exhibit spaces in the Jefferson Building, we see clear 24-hour cycles, suggesting fluctuations may depend more on other factors such as active business hours and lighting. For example, visitor and staff activities in certain areas may increase the temperature by having more human body heat, possibly decrease the temperature by having more air circulation caused by frequent traffic, or cause other confounding factors such as inadvertent blockage of air vents affecting the efficiency of the HVAC system.

In other areas such as the internal space of G52, PRTD’s scientific wet lab in the Madison Building, findings indicate moderate correlation at 11 hours offset, but additional analysis would be beneficial as this is based on only a few months of data. Alternatively, the previously discussed ground floor room in the Madison Building showed the strongest correlation with a time lag of 25 hours. This means a temperature spike in Washington, D.C. would be expected to correlate with a temperature rise in that particular location of the Madison Building approximately 25 hours later.

We hope that future work will expand into LC’s collection spaces and address questions of data gathering and formatting sustainability to allow for more institutions to address their own climate control concerns. Throughout our time at the library, we have not only gained a better understanding of environmental monitoring methods but also of necessary bureaucratic processes involved in federal employment, Excel software capabilities, and networking opportunities at the LC. Our gratitude for the opportunity to work on this project to the Junior Fellows program, our project mentor, Dr. Andrew Davis, Chief of PRTD Dr. Fenella France, administrative assistant of PRTD Bobbi Hinton, Collections Officer for the Collections Management Division Beatriz Haspo, and all those who have supported this work at LC.

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