MNHS is proud to have received our second NEH grant for energy efficient cold storage (press release)! This NEH Sustaining Cultural Heritage Implementation Grant will allow us to implement the recommendations from our interdisciplinary study on energy efficient cold storage. In 2012, NEH awarded a Sustaining Cultural Heritage Planning grant to the Minnesota Historical Society (MNHS) to conduct an interdisciplinary study that balanced issues of long-term preservation for film materials. These issues included preservation metrics, potential energy use, cost for maintenance, as well as investment cost for any recommended system or building upgrades. At the conclusion of the study in 2014, the interdisciplinary team reduced the broader set of options into a cohesive set of recommendations that include building improvements and specific upgrades of equipment. When implemented, these recommendations would produce a colder and drier environment that helps preserve film materials longer while concurrently reducing the energy required to sustain that environment.
Cold storage is challenging in that it significantly increases the lifespan of specific types of materials, primarily film materials. However, cold storage spaces are difficult to maintain at cold and dry conditions and they typically utilize a lot more energy. The History Center’s vast collections includes three cold storage rooms that currently stores audio-visual collections film, magnetic media, and microfilms. The three spaces are maintained at 62°F (+/- 2°F) and 36% relative humidity (+/- 3%). While this is significantly cooler than the other collections storage spaces, there are various industry standards that recommend different ranges of conditions, most of which are colder than our current setpoints. For example, the International Standards Organization (ISO) recommends 36°F and 20-30% relative humidity for nitrate-based photographic film, which is well outside of the rule-of-thumb set-point. Even with similar media, such as other photographic film, you will find a range of materials. Depending on the film, polyester or acetate requires different conditions, and even color or black-and-white film have recommended ranges from 14°F to 70°F and 20% to 50% relative humidity. 
Agreement on the setpoints is one aspect of the study that really benefited from our interdisciplinary process. The group initially described the temperature and relative humidity need as “as cold as we can get.” However, for mechanical engineers, this isn’t specific enough for a design. In theory, a huge industrial system can get us any temperature or humidity level we want. The challenge is maintaining such a space and paying for the extremely high energy costs. In particular, our cold storage spaces aren’t designed for the ideal temperatures. The space is two levels below ground, and contains three rooms operated at the same conditions from the same Air Handler Unit (AHU-5). Room 105.7 holds most of the audio-visual film and the KSTP collection; Room B-151 holds microfilm; and Room B-152 holds primarily photographic negatives. Just to maintain current conditions of about 60°F and 40% in these three rooms, a separate 250-ton chiller is dedicated to providing super-cooled water to meet the temperature set-point. The combined energy consumption of the chiller, as well as the other environmental control components such as the air handler, fans, and pumps, use about 500,000 kilowatt-hour per year during the cooling season. At our current rate of $0.085 per kilowatt-hour, the MHS pays about $40,000 a year for 4-6 months of the summer to support these space conditions that are sub-optimal for the particular materials contained within it.
This second grant will allow us to implement a separate desiccant dehumidification system, additional insulation of the walls, and potentially installing a freezer room for particularly sensitive film materials. In the reconfiguration, we will also explore the use of capturing waste heat from the desiccant and the freezer, variable speed drives, and reconfigured outdoor air intakes that will reduce special media filtration systems. In all, the bundle of strategies will help MNHS increase the film collections Preservation Index (PI), Image Permanence Institute’s measure of the “decay rate of vulnerable organic materials” in different temperature and relative humidity conditions, while also decreasing energy use and operating costs. The study estimated an increase to the PI by 2-4 times from 100 years to a range of 200 - 400 years allowing for seasonal fluctuations. Further, a subset of critical film material will increase its PI from 100 years to 900 years. In addition to improving the long-range preservation for film collections, there is also an anticipated savings of $16,600 in energy costs per year as compared to baseline adaptations of the existing system.
In this second phase of the project, we will implement and test the results of the study, as well as continue the collaborative process with a range of staff from collections, conservation, facilities, risk management, and sustainability, and external experts in museum sustainability, archival architecture, film preservation, and building mechanical systems. In addition, one of the significant challenges of the project is the design and planning for temporary storage, applicable moving logistics, and access during the construction period. The team will be planning the temporary storage logistics for a construction period of winter 2018-2019. Stay tuned to the blog for project updates!
 Adelstein, P.Z. IPI Media Storage Quick Reference, 2nd edition. Image Permanence Institute, Rochester, NY. 2009.