Environmental standards and HVAC decisions are among the most complicated and expensive for historic sites. They often involve the destruction of original building fabric (both at the time of installation and as a result of changes to environmental conditions), the intrusion of modern fixtures, and higher longterm maintenance and utility costs. Recently completed projects at National Trust Historic Sites such as Lyndhurst and Decatur House have clearly shown the failure of modern HVAC projects. As a result, the National Trust for Historic Preservation has launched an initiative to document through case studies a number of unsuccessful recent installations and provide information about new approaches that may be more successful and less expensive. Among the issues addressed will be technology, security, accreditation, building codes, insurance, requirements for collections loans, and balancing the needs of buildings, collections, and visitors. Currently underway are studies at Wilson House and Cliveden, which are attempting a more holistic approach based on the multiple perspectives of architects, engineers, conservators and curators. Initial reports suggest that typical standards adopted by museums (65-70°F and 50±3% RH) are not only very difficult (if not impossible) to achieve in historic buildings, but can also cause irreparable harm to the building (the primary artifact of the site) and result in much higher maintenance and utility expenses (which is not sustainable for most organizations). We’re currently considering much wider tolerances for temperature and emphasizing humidity but much more study will need to be completed. In the meantime, the following resources provide the best thinking about this issue (there are many articles and books on conservation and environmental conditions in museums, but very few for historic sites):
- Jessup, Wendy editor. Conservation in Context: Finding a Balance for the Historic House Museum. Washington, DC: National Trust for Historic Preservation, 1995.
- Kerschner, Richard. “A Practical Approach to Environmental Requirements for Collections in Historic Buildings.” Journal of the American Institute for Conservation 31 (1992): 65-76.
- Stovel, Herb. “The New Orleans Charter: Forging a Strategy to Preserve Historic Structures and Artifacts.” APT Bulletin: The Journal of Preservation Technology 27 (1993): 57-8.
We are soliciting comments from the field, suggestions for case studies, and models for alternatives to traditional HVAC for historic sites, so please post your comments below or contact us at sites@nthp.org.
Historic New England, formerly SPNEA, has been working to assess eight different HVAC systems installed in the 1990s at our sites. We are in the midst of our study but the end result is that all eight systems were over designed and also not capable of achieving 45% RH. In many cases the RH levels today are the same as the RH levels from before the work was started.
Working with our collections staff we are approaching the RH in the houses as a range – between 30 and 60% RH and trying to eliminate the massive fluctuations and the long periods at the extremes but allow basin movement throughout the seasons.
We are downgrading some of the 8 systems to see if we can stabilize the environment with a simpler version of the 1990s systems. We have been experimenting with simplistic systems involving heat and dehumidification in the basement to regulate conditions in the upper floors with some success. We are also experimenting with a number of low tech controls that perform most of the same functions of the sophisticated high end controls.
A lot is going on here at Historic New England on the subject and we would love to share.
Carol Ely provides the following observation from Historic Locust Grove in Louisville, Kentucky:
Attempts at “museum quality” climate control haven’t worked well here. About 8-10 years ago (before I came here) a geothermal system was installed in our 1790s house, at great expense, and with new ductwork and vents run through closets, attics, and cellars, all in the quest to do the right thing in terms of preservation of the building and the collection.
The main fans are in the attic, and, consequently, we just can’t ever balance out the temperature in all levels of the house. The third floor, below the attic, is freezing cold in summer – moisture condenses on the windows – as the system works to cool the lower floors with the constantly-opening front door. The third floor is toasty in winter, as the visitors down below shiver. The system runs almost constantly, and energy cost are very high as we try in vain to maintain a consistent (and in summer, too low, in my opinion) temperature. In addition the west side of the house is always a different temperature from the east side, I think owing to varying levels of efficiency in the placement of the vents and fans.
As a historic structure, we of course lack storm windows, double panes, an enclosed entryway, and other modern changes that would make for efficiency.
There are places where the wallpaper bubbles from the extremes in temperatures near the vents, odd spots of condensation on the floor near some of the vents. So far, this is minor, but might emerge as a problem over time.
We monitor the humidity levels, which swing widely but stay mainly in the broadest acceptable zone. However, there seems to be nothing I can do to influence the system to correctly humidify or dehumidify when the situation calls for it. You can see the spikes in the humidity monitors on days with high attendance, simply because the door is open frequently. So how do we ameliorate the extremes? Not clear to me.
When the system was installed, our preservation consultant warned that unless the house basement was included in the envelope of climate control, it wouldn’t work; and including the basement was logistically nearly impossible and was not attempted. In the summer we run portable fans in the basement to keep the air moving, but there’s no evidence that it helps much.
So all in all, it’s not a disaster, but it’s not effective and is very expensive to run. That’s my take on it, somewhat subjective. I wasn’t here when the system was designed, and my own lack of understanding of HVAC engineering frustrates me, so if more appropriate technical information will be helpful to your research, I can certainly look up the specs and talk with those more knowledgeable. By the way, this lack of staff technical knowledge of systems is probably part of the problem for other small sites, not just us. I don’t have an in-house person with HVAC experience who can maintain, adjust, recommend, and handle problems that arise.
Thanks for looking into this issue.
Numerous professionals in the conservation, engineering and architectural fields have advocated rethinking the requirements for tight environmental controls for collections in historic buildings. Most recently, this rethinking has been has been driven by energy costs, by the impact of tight control on carbon-fuel consumption and greenhouse emissions, and by a better understanding of collections risks from conservation science.
The competing objectives for stewardship of a specific heritage building and its collections, while being environmentally responsible (in the large sense), will necessarily be resolved on a case-by-case basis through collaboration of informed stakeholders and professionals, taking into account the financial and technological capabilities of the responsible institution. The solution will be the best fit for that specific case, rather than prescriptive templates or formulae.
These complex issues have been explored at several recent conferences, and much of the content is readily available on the web:
• Experts Roundtable on Sustainable Climate Management Strategies, sponsored by the Getty Conservation Institute, Tenerife, Spain, April 2007.
(http://www.getty.edu/conservation/science/climate/climate_experts_roundtable.html)
• From Gray Areas to Green Areas: Developing Sustainable Practices in Preservation Environments sponsored by the Kilgarlin Center of the University of Texas, November 2007, Austin TX, November 2007.
(http://www.ischool.utexas.edu/kilgarlin/gaga/proceedings.html)
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• Climate Change and Museum Collections, sponsored by the Internation Instotute for Conservation of Art and Historic Artifacts, London, UK, September 2008.
(http://www.iiconservation.org/docs/IIC_climate_change_transcript.pdf)
Chapter 21: Museums Libraries and Archives of the Applications Handbook of the American Society of Heating, Air Conditioning and Refrigeration Engineers (ASHRAE) is very helpful in setting realistic and achievable expectation for interior environmental control, and is based on the implications of building/envelope type and climate. Unfortunately it is not available on the web, but a discussion of its application for historic buildings can be found at (http://www.ccaha.org/uploads/media/60213dd7cba6f6fc2d64c9cfd9b84222.pdf) . Chapter 21 is now being updated by an ASHRAE Technical Committee.
Lastly, the “cost of control” of environments in historic house museums is addressed in an interesting thesis, A Comparison of the Efficacy and Costs of Different Approaches to Climate Management in Historic Buildings and Museums, by David Artigas, a graduate student at the University of Pennsylvania, and can be found at (http://repository.upenn.edu/hp_theses/63/ ) .
Happy reading!
Michael C. Henry, PE, AIA
Watson & Henry Associates, Bridgeton, NJ
Adjunct Professor of Architecture, Historic Preservation
University of Pennsylvania, Philadelphia
The Unico System is an ideal HVAC solution for historic renovation where retaining the original architechtural integrity is desired.
The Unico System is installed in homes and historic locations throughout the United States and in a Cornerstone Partner with The National Trust for Historic Preservation. We have completed projects in the Mark Twain House, Booker T. Washington’s house, Lincoln’s Cottage, and most recently the Harry S. Truman Little White House. Vistitors to the home neither see or hear the HVAC system unless they are searching for it, and there is now a uniform temperature throughout the house to better preserve and protect the historic artifacts and furnishings that are a part of Harry S. Truman’s Little White House.
For more informatio on the Unico System visit our website at http://www.unicosystem.com.