AIC Mercer Museum Paper (Mercer5.Txt)


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Recent Planning Experience in Balancing Collection and Building Preservation Needs: Improvements to the Mercer Museum

Presented at 1993 AIC Meeting in Denver

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AIC Mercer Museum Paper (Mercer5.Txt)

  1. 1. This paper was presented at 1993 AIC Meeting in Denver. Mr. Lull's presentation at the 1993 annual meeting also discussed renovations to the Pinkney House at the Kern County Museum in Bakersfield, California. A paper on that project may be found in the Objects Specialty Group Postprints 1991, Volume One, pages 102-107. =============================================================================== Recent Planning Experience in Balancing Collection and Building Preservation ----------------------------------------------------------------------------- Needs: Improvements to the Mercer Museum ---------------------------------------- William P. Lull ABSTRACT The improvement of the collection environment in the Mercer Museum in Doylestown, Pennsylvania, presents several unique challenges. These include an historic solid concrete building; no present heating, cooling or humidity control; an environmentally sensitive collection; little hope of installing a ducted air system; and problems with condensation, high light levels and water leaks. The Museum developed a multi-disciplinary approach under an IMS grant to address these problems. Working independently, the original precept of the consultants at the time of the grant application was to develop a scheme of humidity-controlled heating to reduce high humidity conditions. However, when the consultants met for the on-site meeting after inspection of the building a different approach was developed that would be less intrusive to the building fabric and more consistent with other treatments. The solutions identified included interior window treatments for light and condensation control, improvements to the exterior building details, and improvements to the operable windows and ventilation. Contingencies were developed for modest humidity-controlled heating and increased ventilation in the event that the other treatments proved inadequate to control the high humidity and high temperature problems. 1. INTRODUCTION The main building at the Mercer Museum is an important part of the Museum collection. It no only holds the bulk of Mr. Mercer's original collection but is itself an artifact of early poured-in-place concrete construction. It distinguishes itself as a building originally intended to be a Museum and built in the form of a castle, is an important landmark for the area. The building has problems in the collection environment it provides for the collection. While there are some inherent benefits to the building as an unconditioned space it has some environmental problems, primarily high humidity, high temperatures and water leaks. To address this complex problem the Museum, under the supervision of Mr. Cory Amsler, Curator of Collections, assembled a multi-disciplinary team under an IMS grant. The collection needs were represented by Kory Berrett, Berrett Conservation Studio, the building needs were represented by Dale Frens, Frens and Frens Architects, and the environmental control planning was developed by William Lull, Garrison/Lull.
  2. 2. 2. COLLECTIONS ENVIRONMENT OBSERVATIONS AND EVALUATION This section describes the existing conditions of the collection environment to provide a context for the past environment of the collection, the environmental evaluation, and the need for the improvements. ARCHITECTURAL/GENERAL. The main building at the Mercer Museum is built of poured-in-place concrete. It has an exposed concrete roof with no roof membrane. The windows are mostly fixed sash consisting of cast concrete frames emulating double-hung windows. A few windows are operable wooden frames opened for ventilation. COLLECTIONS DISPLAY AND STORAGE. The collections are stored and displayed in two basic methods. Many of the large pieces are open to the general space where air may freely circulate and where visitors may view the objects from many sides. Most other parts of the collection on display are shown in closed display rooms located around the perimeter of the building. These rooms usually have an exterior exposure, usually with a window, and an interior wall with a window for visitors to view the objects. Some of these rooms are hardly larger than a display case while others are complete rooms. Most storage of the collection is in similar closed rooms away from visitor view. HUMIDITY TOLERANT ENVELOPE. The building is single-glazed and the walls and roof apparently have no cavities or other heterogeneous aspects to their construction; they are simply solid concrete. Since the building is not heated and humidified the classic condensation conditions of a warmed humidified interior exposed to a cold building envelope would not be expected to occur; however, the high thermal mass of the concrete and ready translation of outside conditions to inside apparently allows conditions to occur that lead to condensation on the glass and window frames. HVAC SYSTEM INFRASTRUCTURE. The building has no HVAC distribution infrastructure. The only air handling system in the building is the smoke exhaust system in the south tower which is used for summer ventilation. This is controlled on a subjective basis when the weather is hot by turning on the fan using a timer. There are no other methods for cooling, heating/reheat, humidification, dehumidification, filtration or other tempering of the building environment. The museum complex has hot water heating boilers but these serve other buildings. 3. PROBLEMS The following problems directly relate to the effect of the environment on the collection. They are generally based on the previous collection survey reports by conservators and the on-site discussions of the project team. CONDENSATION STAINING. One of the major problems is condensation on the interior of the concrete frame windows. The Museum staff notes that this "usually occurs when a cool night follows a warm day." It was observed on the sixth floor west windows at the time of the September site visit and is generally characterized by the staff as occurring on the east and west sides of the building. Staining from condensation runoff is apparent at most windows which may be eroding the concrete. In very cold weather the Museum staff reports the condensation can form ice.
  3. 3. COLLECTION SPOTTING. Collection objects kept near the windows show surface spotting and staining which is apparently due to condensation at the windows. PARTICULATE CONTAMINATION. As noted by previous project conservators there is a clear level of particulate contamination a portion of which is suspected as coming from the exposed interior concrete surfaces. The particulate observed in the collection areas at the was generally lightweight with some soot. The lightweight matter was suspected as coming from the collection or the museum visitors. Analysis of samples was performed to determine how much of the particulate is from the concrete structure itself. The 23 December 1992 analysis by Dr. George Segan Wheeler concluded "the particulates derive primarily from the cement which is probably degrading by infiltration of water from the exterior." That report indicates that most of the particles were in the size of 4 to 80 microns with 20 to 30 microns average, with the fibers also noted as "probably from the cement." HUMIDITY CONDITIONS. Mr. Berrett identified a problem with occasional high humidity conditions in winter and problems with occasional humidity excursions of over 20% RH in all seasons. The open windows are suspected as allowing outside weather conditions to be rapidly transmitted into the building. BROKEN/LEAKY OPERABLE SASHES. Several of the operable windows are broken or their sashes do not seal well. This allows in the infiltration of moist air and some water when it rains since these are casement windows. RAIN LEAKS. There are several isolated places noted by the staff where rain leaks into the building. This not only poses a long-term threat to the building but increases the internal high humidity problems. TEMPERATURE CONDITIONS. Mr. Berrett noted that summer high temperatures were most problematic on the fifth and sixth floors in the areas with poor ventilation. The ventilation is currently limited to the operable windows. LIGHT EXPOSURE. Mr. Berrett identified light exposure problems from the several windows. 4. TEAM APPROACH Working independently, the original precept of the consultants at the time of the grant application was to develop a scheme of humidity-controlled heating to reduce high humidity conditions, using a temporary mock-up of the heating scheme as a test. However, when the consultants met for the on-site meeting after inspection of the building a different approach was developed. Mr. Berrett's priorities for improving the environment were listed along with Mr. Frens' planned treatments for preservation of the building and Mr. Lull's possible environmental control treatments. Priority was placed on: a) isolating the interior environment from exterior humidity extremes, b) controlling condensation, c) ventilating for high temperatures at the upper floors, d) controlling particulates, and e) reducing daylit light levels. Mr. Frens was able to offer several passive treatments he would otherwise suggest for preservation of the building that could lead to improvements for
  4. 4. the interior environment, including treatment of the building envelope to address water leaks and rebuilding of the operable windows used for ventilation. Mr. Lull helped the team identify the limitations of the existing structure for supporting not only a conventional HVAC system but even a humidity-controlled heating system to reach all the spaces; virtually any ducted air system would be physically, historically and aesthetically intrusive and yet would be required to provide air to condition the closed display rooms, called "glazed alcoves" by Mr. Mercer, which are key to the museum display program. Window condensation was addressed through planned secondary interior glazing to prevent the interior moisture from reaching the cold panes of glass. This also provided the opportunity for using tinted glazing to reduce light levels and glare for the collection on display. Improved ventilation would be provided to address the heat gain at the upper floors. Since the performance of many of these improvements could not be readily quantified backup plans were developed for dealing with high temperatures and high humidity. If temperatures were still too high an increased ventilation scheme was developed. If humidity levels were still too high in cool weather humidity-controlled heating can be provided through the use of the original tunnel under the main floor which many speculate was intended by Mr. Mercer for steam heating pipes . The important aspects of the plan were the use of treatments that were otherwise indicated for preservation of the building, and the selection of passive techniques which would not require any permanent intrusion or modification to the building. No major energy costs would be incurred allowing the improvements to have a minimum impact on the museum's operating budget. The contingency of using central humidity-controlled heating, while having a possible significant energy cost, was confined to a tunnel which would again cause no changes to the building's historic fabric and any leaks from the new system could not reach collection areas. DISQUALIFIED TREATMENTS. The following possible treatments to address the humidity and particulate problems were identified but disqualified by the project team. In many cases, as indicted, (*) this was due to a requirement for installation of a ducted air system. 1. DEHUMIDIFICATION.* High humidity could be reduced in summer through the use of a central dehumidification system. Mr. Lull pointed out that local dehumidifiers in rooms might require additional electric power distribution within the building, and that responsible use of them would require provision of a condensate pumping and removal system. He pointed out that they would also increase and decentralize the fire risk in the building and would have a significant energy cost. 2. FILTRATION.* The smaller air borne particulates could be filtered out of the air through the use of a central filtration system. Mr. Lull indicated that this would have had a significant increase in annual energy costs. 3. AIR-CONDITIONING.* High temperatures could be addressed through conventional cooling which might also serve some or all of the dehumidification functions. Mr. Lull indicated that this would have had a dramatic increase in annual energy costs. 4. CLEANING OF CONCRETE. The interior exposed surfaces of concrete could
  5. 5. be cleaned to remove any particulates present on the surface. Mr. Lull suggested a HEPA-rated vacuum be used to assure all particulates were caught. The preponderance of the project team felt that the dust analysis indicated this was not necessary as a formal project and could be addressed as a general staff activity with normal vacuums. 5. MAIN ROOF MEMBRANE. If the patching and/or sealants used in the repair of leaks proves ineffective in making the main roof weather tight then a roof membrane might be needed, although this would not be historically accurate. This might cause a problem with condensation on the underside of the new membrane depending on outside temperatures, inside temperature records and conditions for balanced vapor flow to avoid condensation. Mr. Frens indicated that the roof problems related primarily to edge and boundary conditions and not to water penetration of the roof itself so a membrane would be of little benefit. * This option generally requires a ducted air system or piping system. With the preponderance of the collection located in closed or semi-closed rooms a ducted air system would require duct penetrations through the poured concrete walls and floors and an exposed duct system in the building. Options based on all-water piped systems were similarly discarded since they still required penetrations of the concrete and brought with them a great risk from leaky and frozen pipes, and would pose an unmanageable maintenance burden from the many small terminal devices to be maintained. Each of these could also be expected to have significant energy costs, not only for the fans to move the air but the operating costs for heating, dehumidification and cooling. 5. CONSERVATION ENVIRONMENT IMPROVEMENTS The following improvement plan was developed to address as many of the problems as possible. They may have a significant cost and should generally be designed by an architect and/or engineer. They are the improvements that were developed with the project consultants to strike a balance between improved environmental conditions, minimum impact on the structure of the building and reasonable owning and operating cost implications for the Museum. 1. CLEANING IMPROVEMENT. To deal with the particulate problem the preponderance of the project team felt that the use of conventional vacuum cleaning would be appropriate and that no special filtration would be required since no particulates were found at the level that would require a HEPA vacuum. For convenience in cleaning the collection the vacuum should be the type that attaches to the waist with a belt. 2. REMOVE GLASS PANELS AND UNDERCUT DOORS. To promote air flow in the various closed exhibit rooms the project team agreed with Mr. Berrett's suggestion that one or more panels of glass be removed and that the doors be undercut. This should be carefully done so that security of the contents is preserved and might involve the use of heavy security screens where necessary. 3. ACRYLIC PANELS FOR WINDOW CONDENSATION. The fixed-sash windows with condensation problems should be considered for interior-applied secondary glazing with acrylic panels. To be effective the panels need to seal against the interior air reaching the original exterior window
  6. 6. glass. Since condensation apparently forms on the thin window frame mullions and muntins the panel should preferably span the window, applied to the thicker part of the wall. As reported by Mr. Berrett, to reduce light level and glare the panels should be tinted. (See later discussion of acrylic panel tests.) 4. REPAIR ENVELOPE LEAKS. The water leaks at various areas should be repaired. This should include patching window problems, miscellaneous wall conditions, a roof membrane for the balcony, and other conditions determined by the restoration architect. 5. RENOVATED OPERABLE SASHES. The current operable sashes are often broken, inoperative or ineffective in keeping rain out. The restoration architect should consider redetailing the windows for more effective seals and replacement of casement and sliding sash windows with awning windows for better protection from rain ingress. All non-fixed sashes should be made operable for current or future ventilation requirements. (See next item.) 6. BETTER VENTILATION OF SUMMER HEAT GAIN AND HUMIDITY. The ventilation system should be improved in its ability to address high temperature and high humidity conditions. This would involve improving the ventilation air discharge, thermostatic/humidistatic control of the ventilation, and motorized damper operation of the renovated window sashes. CONTINGENCY IMPROVEMENTS. These improvements are contingency improvements in the event that the main improvements prove ineffective in meeting project goals. These have not been identified as part of the main improvements because they have a significant capital or operating cost, or are more intrusive to the building fabric. 1. CENTRAL HUMIDITY-CONTROLLED HEATING. If the main improvements do not provide sufficient control over high humidity conditions when the temperature is low outside then humidity-controlled heating might be used. While a ducted air distribution system might be too intrusive on the historic structure, the building might be centrally heated with steam, glycol/water or hot water piping located in the service tunnel located below the floor in the main level. This area could be easily served by piping running to a heat source to the north or south, and would present little risk to the collection from leaks since it is below collection levels. To enhance the heating effect the existing floor grille might need to be opened up and additional grilles might need to be added. Improvements to the tunnel might be necessary to improve cleanliness, maintenance access and discourage pest ingress. The control of such a system would need to avoid rapid temperature changes and might need to seek a backward-averaged humidity level, rather than be particularly responsive to acute conditions. This option would have significant energy use implications. 2. IMPROVED CENTRAL VENTILATION. If the renovated windows and automatic controls still prove inadequate for removal of summer heat (when outside conditions are favorable) then further improvements should be considered in the following order: a. ADD EXHAUST FAN TO ALTERNATE TOWER. The other tower could be equipped with a ventilation system similar to the existing system
  7. 7. except better suited for continuous duty. It should make full use of the available window areas for exhaust louvers and should use a fan capable of greater air flows at lower noise levels. b. REPLACE EXISTING FAN SYSTEM. The existing fan system could be replaced with a fan capable of greater air flows at lower noise levels. This option would have significant energy use implications. 3. LOCAL FANS IN CLOSED AREAS. If the other improvements prove inadequate to address condensation or mold problems in the closed exhibit alcoves then fans might be used in them to increase air flow. With the fans would come some additional energy use, additional maintenance, and added risk of fire. 4. LOCAL HUMIDITY-CONTROLLED HEATING. Similar to the central system, this would be the use of electric heaters in in the closed exhibit alcoves with humidistats used for control in addition to thermostats. With the heaters would come significant additional energy use, additional maintenance, added risk of fire, and possibly the need to install additional electric service to the rooms where it is used. 5. RECIRCULATED AIR. Mr. Berrett felt strongly that a central recirculated air system be considered for destratification and improved air turnover in the collection spaces for more even conditions and to suppress mold growth. The application of this may ultimately be limited by the available shaft space for vertical ducts inside the building. Creating additional vertical shaft space is possible and options might include an added exterior chase, an interior shaft created by penetrating a vertical series of galleries, or a new exterior tower that might house the shaft and new HVAC equipment. This option would have a significant energy use implication, particularly if high velocity/high pressure air distribution was required. A major advantage would be that such a system might offer the opportunities for filtration, and for heating, cooling and dehumidification at significant additional energy use. 6. INTERIOR CONCRETE SEALANT. A concrete sealant might be applied that could help reduce the generation of particulates while also reducing the infiltration of water vapor into the building from the concrete. Mr. Frens indicated that it would be hard to find an effective sealant that: a) would not change the appearance of the concrete, b) could be easily reversed, c) that had a proven track record of performance, and d) that would not need to be reapplied after a period of time, such as 10 years, to renew its efficacy. The preponderance of the project team felt that treatment of the concrete was not necessary to control the particulate problem, which was attributed primarily to housekeeping, and was otherwise an option of last resort. ACRYLIC PANELS. A test of the possible treatment of the windows with acrylic panels was performed by Mr. Frens. The panels were effective at reducing light and UV levels while having very little impact to the appearance of the building from the outside. The reduction of light transmission was generally not noticed from the inside. There was a problem with condensation within the cavity created by the application of the panel. Although different panel types were tried including an application of a panel with holes, each was plagued by moisture formation within the cavity
  8. 8. between the glazing surfaces. Two additional treatment option tests were identified to prevent both surface and cavity condensation. a. SEALED CONCRETE. The whole-window treatment might be tried again but this time a strippable sealant, as suggested by Mr. Frens, might be used on the exposed concrete to inhibit moisture migration into the cavity between the glazing elements. b. SINGLE-PANE PANELS. To reduce the exposure of concrete in the cavity between the glazing elements the acrylic panels could be applied to each window pane instead of the whole window. To eliminate the exposure of concrete the acrylic panels could be applied with a glazing tape that would at once seal the concrete at the edge of the window pane and hold the acrylic panel in place. This treatment test should include summer conditions to be sure there will be no "popping-off" effect, expansion damage or other problems due to dimensional change in the acrylic panel as it warms and cools. To help avoid this the new acrylic panel should be under-sized sufficiently to allow for expansion. This approach has the advantage of having a minimum impact on the appearance of the window and can provide the same tinting or UV protection as the large panels. It also avoids reworking some parts the window frame edge condition that Mr. Frens indicated would be required to support the whole-window treatment. The single-pane treatment has the disadvantage of not providing as large a sealed air space so the thermal benefit for controlling condensation may be limited, and they may have a higher cost due to greater labor in fitting and installation. This treatment will also not protect the window muntins and mullions from condensation. The results of these tests should identify the final details for condensation control at the windows. William P. Lull is a graduate of the Building Technology program at MIT, a principal and senior conservation environment consultant at Garrison/Lull Inc., and is Adjunct Associate Professor of Building Technology at New York University. He has formerly worked as a designer and project manager for architects, engineers and government agencies. Mr. Lull has been an invited lecturer for many groups and author for several publications. He has consulted on collection environments in many museums, libraries, archives and historic structures in the US and throughout the world.