The Abbey Newsletter

Volume 18, Number 7
Nov 1994

Further Comments on Climate Control Guidelines

by William P. Lull
Garrison/Lull Inc., Princeton Junction, NJ

The following commentary is based on a letter that Mr. Lull sent in August to Museum News, which had requested his thoughts on the CAL press release.

I would like to offer the following facts and observations regarding the Smithsonian Conservation Analytical Laboratory (CAL) press release [reprinted in the August-September issue of the Abbey Newsletter]. Being neither a conservator nor a conservation scientist, I am reluctant to comment on the results of conservation research. However, when I saw the press release statements on safe environmental set points and museum buildings systems, I felt a response was necessary to help clarify some issues. After discussing this with many conservators, curators, conservation scientists and archivists over the past few days, I have also found a general interpretation of the press release not consistent with the CAL research I have seen presented.

In discussing the press release with Marion Mecklenburg, David Erhardt and the CAL Director, Lambertus van Zelst, it is hard to draw the same sweeping conclusions that others drew from the press release. Their position on the press release issues I discussed with them is closer to that held by others in the conservation community. Dr. Mecklenburg noted that the "new" criteria should not be applied without the advice and possible moderation of conservation professionals.

The press release is misleading in two important respects. First, the description of the research conclusions does not accurately represent the generally accepted results of the research. Second, the observations on buildings systems are limited to the Smithsonian experience and not generally applicable to typical museums.

Mechanical vs. Chemical Degradation

From the two CAL papers I have seen presented at AIC, and from discussion with others, the emphasis of the CAL research highlighted in the press release is on how material samples mechanically tolerate temperature and humidity changes. The primary conclusion that might be drawn from their research is that test materials are not mechanically as sensitive to fluctuations in conditions as some believe. However, CAL's fluctuation research does not address the kinetics of the materials--how they deteriorate chemically over time with temperature and humidity conditions.

The press release implies, if it does not state directly, that prolonged conditions within the very broad range of conditions suggested (35%-65% RH, 52°-88° F) is safe. Paragraph 6 of the press release plainly states that objects "may be safely stored or placed on exhibit" under these conditions. This also implies that conditions may be maintained at the extremes of these ranges. Paragraph 14 apparently opens the door for any environmental conditions: the "low end" prevents some damage and "at higher values . . . physical damage is minimized." This is simply not the case for many if not most collections, and is not necessarily supported by the research. Field observations correlating object damage with humidity problems are overwhelming. Two papers that I coauthored and presented at AIC (1,2) document several such problems from unstable humidity.

While some materials in almost any collection can tolerate extremes, the conditions in a museum must be maintained for the most sensitive objects, unless they are housed under separate conditions. In fact, one CAL paper clearly notes that paper-based materials will have a dramatically longer life, three to five times as long, if the humidity is kept at an average of 30% rather than 50%, a far cry from conditions freely floating to highs of 65%. Moreover, research at the Library of Congress suggests that paper exposed to humidity cycling between 40% and 60% RH will deteriorate as if it were held constantly at the more damaging 60% level.

In summary, CAL research plays an important part as another piece in the puzzle of understanding how objects behave and how their life under museum, library and archival care can be extended. However, the acceptable conclusions do not support the sweeping changes suggested in the press release. A reduced humidity set point in winter has been a viable, published and exercised option for decades. Where appropriate, it is common to consider and use this option for modern projects. Furthermore, acceptance of fluctuations has always been a practical necessity for many institutions. However, the broad relaxation of temperature and humidity criteria suggested in the press release is a policy not endorsed by most, including those who are familiar with the CAL research.

Building Systems and Costs

The sensational aspect of the press release is the reference to saving millions of dollars on building systems costs in museums. This estimate is not the result of research but is only speculation. My discussions with the CAL research staff indicate they do not have a broad knowledge of environmental control in buildings and HVAC systems; their observations are limited to their encounters with Smithsonian staff in regard to a few Smithsonian projects. No part of their formal research even touches on building systems. This does not mean that such research has not been done: it has been done to some extent by the Getty Conservation Institute. However, the CAL observations on building systems are apparently speculation from an inadequate information base.

The press release makes claims for annual operating cost savings using their "new" criteria. If they are suggesting that humidity levels should be allowed to fluctuate, as is suggested in the research they have presented at AIC, then this has already been simulated to some extent by research at the Getty (3). This showed that if humidity is allowed to vary by ±5% instead of ±2%, then annual HVAC operating costs would be reduced by just less than 2%; if allowed to vary by ±7% instead of ±2%, the savings would be just less than 3%. This is hardly a major change when HVAC energy costs may only be half of the total energy bill. Considering a museum's total annual energy costs, the savings at ±7% RH might come to just over 1% of the total. For all the museums in the United States, this might total as much as a million dollars, but only because of the number of museums involved. These same museums could realize greater savings from the use of tinted glazing or reduced lamp wattages while actually reducing environmental risk to the collection.

What is "Precision Heating and Cooling Equipment"?

The press release makes claims for construction cost savings. It perpetuates the myth that some sort of special, obscure, "precision" type of system is required for humidity control at 50% RH that is not required with relaxed criteria.

The press release states, "Up to 50 percent of construction costs for new museums and archival storage facilities may go toward highly specialized heating and cooling systems." The 50% is misleading; it is based on two Smithsonian projects. Neither is typical or representative of most museums and archives. For the vast majority of museum and archives projects, all mechanical and electrical systems in a new building account for about 30% of total project construction costs. The HVAC systems themselves account for only about 20% of total new construction costs, although they make up a higher percentage in renovations. Fifty percent is easily twice the typical fraction of the cost.

Good environmental control does not require special or extraordinary equipment: it consists mostly of avoiding common mistakes in equipment selection, location and installation. Except for unusual challenges that may be posed architecturally, an HVAC system for good humidity control around 70°F and 50% RH is quite simple: a modulating pressurized steam manifold humidifier, a cooling coil sufficiently cold to provide the needed dew point, a reheat coil, and a good control system. We regularly find these in buildings dating to the 1930s. What part can we delete, based on the CAL research? CAL scientists could not endorse 70% RH for the extended periods typical for systems without reheat or with a too-warm cooling coil. A humidifier is required to reach even 30% RH at comfortable working temperatures in temperate winters. At most one might downsize the steam boiler if 30% RH is the winter set point instead of 50% RH. The marginal cost in a slightly smaller boiler might be a few thousand dollars on a $5 to $10 million project.

The "remedy" to fluctuations is proper adjustment of controls and not the introduction of any expensive or complicated piece of equipment. Provided appropriate decisions are made, stable conditions for collections are neither unusual nor extremely expensive.

Compared to most other types of buildings, there are greater expenditures for museums and archives to provide the essential HVAC elements (humidifier, reheat, cold cooling coil). Most of the "extra" capital is spent in providing equipment that will work reliably for more than a year or two, and do so at reasonable cost. When construction cost cuts lead to the selection of short-life equipment, or equipment too expensive to operate, then the project is left without basic humidity control after only a few years.

The press release states that "making use of conventional equipment avoids the structural damage that might result from installing precision heating and cooling systems." This is inaccurate and misleading, and shows the poor quality of the information in the press release. "Conventional equipment" for humidification, by any sense of the words, will, if effective, pose a risk to a building envelope that is intolerant of humidified conditions in winter. The informed reader can likely determine that the press release is really trying to address the risk of condensation damage to intolerant buildings when a humidity level of 50% is maintained in winter. What they are trying to say is that reduced humidity in winter can be a valuable option to consider, but again, this is not new information.

Museum, library and archives directors, as a rule, are neither scientists nor engineers. They are not equipped to deal with the details of research and building systems. They rely on others to interpret these issues. The press release suggests that capital and operating cost savings would accrue if things are changed according to their research. My main concern is that the press release will be used to relax environmental conditions in existing systems with good performance, and mandate unwise cost reductions for new or renovated systems. The well-meaning director, incapable of assessing the details but needing to conserve precious resources, might interpret the press release as cause to require a cut in capital costs for new building projects, to mandate a cut in operating costs for his current building systems, or to abandon important environmental improvement plans. These actions may be taken without regard for the actual environment that will result. Deletions consistent with the impression left from the press release, though not consistent with the CAL research, may result in collections being exposed to prolonged winter humidities below 25% RH, and prolonged summer humidities between 60% and 80%, conditions the CAL researchers would not endorse. Mechanical systems so compromised can require expensive retrofits to provide or restore essential elements (humidifiers, reheat, cold cooling coils) that cost less when installed initially.


1. "The Conservation Environment at the W.H. Mathers Museum: A Long-Term Path to Success," paper presented at the AIC annual meeting, 1990, by William P. Lull , Conservator, W.H. Mathers Museum.

2. "Humidity and the New Carriage Museum at the Museums at Stony Brook," paper presented at the AIC annual meeting, 1990, by William P. Lull; Merri Ferrell, Curator of Carriages, Museums at Stony Brook; and Linda E. Merk, Conservator at Fine Objects Conservation Inc.

3. "Energy Impact of Various Inside Air Temperatures and Humidities in a Museum when Located in Five U.S. Cities," ASHRAE Paper 3390, by J.M. Ayres, PE; H. Lau, Ph.D., PE; and J.C. Haiad, all with Ayres Ezer Lau, Inc., Los Angeles. ASHRAE Transactions, 1990, pt. 2; p. 100-111. (As an ASHRAE paper, it had to pass jury review before it was given.)

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