Balancing Stewardship and Sustainable Practice

How can you make significant reductions in energy use and still provide a preservation environment for collections in your care? Providing a tightly controlled storage climate is costly and energy-intensive. Because of concern about climate change, as well as for budgetary reasons, collecting institutions are actively searching for ways to responsibly lower energy consumption. Individuals responsible for collection stewardship need to be involved in these activities. They should be prepared to make informed decisions based on current research, reliable data, and a factual understanding of the relationship between environment and material decay. They need specific guidelines and methods for avoiding risks to collections while taking advantage of opportunities for sustainability.

The place to begin is with the evolution of ideas relating to managing the environment in libraries, archives, and museums.  A number of generally accepted ideas—that environments should be steady and unwavering, that room temperature and 50% RH are ideal, and that short-term fluctuations matter more than long-term trends—are now regarded by preservation scientists as outmoded and counterproductive. The persistence of this overly simplistic model limits the ability to consider new approaches that factor in sustainability and global environmental responsibility. Even the greenest of buildings can’t make 'flat lining' at 70oF and 50% RH sustainable.

A close reading of the literature of conservation will reveal that the creators of the unwavering 70/50 recommendations regarded their suggestions as provisional pending closer study. The evolution away from such simple ideas and toward a more modern view is based on preservation research done over the last twenty years.  Advances in research in chemical kinetics, biology and material science allow for a more nuanced understanding of how the environment influences collection materials. The scientific facts of material deterioration do not support the simple 'one-size-fits-all' philosophy of environmental management. Modern thinking holds that all environments are compromises among various agencies of decay, depending on the nature of the collection and prevailing conditions. 

Research done at the Smithsonian’s Museum Conservation Institute established that extremes of dryness and dampness pose the greatest risk of physical damage. That statement contains one of the most significant differences between old thinking and new thinking. We’re now concerned much more with what poses the greatest threat (identifying the circumstances we need to avoid) than with articulating an ideal.

Through years of research on topics including accelerated aging, moisture and temperature equilibration, and the impact of cycling, the Image Permanence Institute and the Library of Congress, among others, confirmed that the speed controls on natural aging are the temperature and humidity in the storage environment. They are always present, have the broadest effect on the largest number of items in the collection, and act as enablers (or inhibitors) of damage caused by other factors such as light or pollutants.

The majority of outdoor climates experience a warm summer and a cool or cold winter. As the temperature varies throughout the year so does the amount of moisture in the air, which is represented by the dew point. Rising summer temperatures mean that the air holds more moisture. In summer, the air is too warm and has too high a dew point (moisture content).  A control scheme that only concerns itself with maintaining a steady temperature at about 70oF ignores the fact that for months on end the indoor RH will be sky high, risking mold, metal corrosion, mechanical damage and a high rate of natural aging. 

In winter, the opposite happens. The outdoor air is cold and therefore has very little moisture content. Heating that air to 70oF when it contains so little moisture will cause a dangerously low indoor RH, leading to mechanical damage for many objects.  In addition, a steady 70oF is too warm to prevent a rapid rate of natural aging in many organic materials.  Heating less will actually help to bring the RH out of the dangerously dry zone.

So what is the sustainable solution? The best way to balance stewardship and sustainable practice is to work toward an optimal balance of preservation quality, energy cost, and consumption of fossil fuels. The major barrier to achieving this is the lack of understanding on the part of both preservation and facilities staffs of what variations in environment are tolerable and which are detrimental to collections. A better understanding of what recent preservation research has shown can help as you negotiate changes in the storage environment.

The new model for environmental management might be formulated this way: 

  • The extremes of RH—too dry, too damp—are the most threatening to long term collection preservation, especially if they are prolonged for the several weeks that most collection objects require to fully feel the effect. Controlling these extremes is essential.
  • The ‘spikes’ that matter most are the big seasonal hump and trough of RH during periods of summer dampness and winter dryness. Most short-term events are insignificant so don't waste resources dealing with them.
  • During the summer, when dew points are high, keep the temperatures as low as you can without causing the RH to be more than 60%. The goal is to dehumidify as much as possible to enable a combination of both cool temperature and moderate RH.
  • In the winter, when dew points are low, raise the RH through humidification. Failing that, cool the space or heat it less to raise the RH. Your goal once again is to attain the lowest temperature setting you can mange while maintaining RH between about 20% and 60%.
  • Forget about maintaining a constant temperature—the objects don't need it. Avoid the extremes – high temperatures increase the rate of natural aging, lead to excessive dryness and cost extra energy to provide. Cold temperatures (below 40oF) can cause brittleness in some materials and freezing can destabilize some organic materials.

We consider this more holistic approach sustainable in that it allows for an adjustable allocation of resources, and reasonable limits on both harm to collections and to the environment.

A word of caution – from the engineer's point of view, raising the chilled water temperature is a good way to save money and reduce energy use. In many system designs, this will mean a higher dew point. This is an area where preservation is affected negatively.  A low dew point temperature allows better control of the RH as you lower the temperature allowing you to achieve the cool and dry environment that is best for preservation of organic material.

There is certainly much more to know about the effect that energy-saving strategies may have on long-term preservation. How much outside air is necessary? Can the amount of sub-cooling and reheating be reduced? What happens if we shut down fans or turn off lights? What about night-time or weekend setbacks in temperature? As noted elsewhere in this issue of Climate Notes, IPI has received an IMLS grant to study the effect of AHU shutdowns during unoccupied hours, and has applied to NEH for another to do research on the effect of night and weekend setbacks in temperature or RH.