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Suitable
for framing
Maine's Portland
Museum of Art faced unusual humidity concerns as well as other challenges
particular to its two hstoric buildings. By using modern controls and
drawing on creative solutions involving chimneys and transplanted boilers,
the team put the finishing touches on an unobtrusive and museum-quality
system.
By Richard D. Miles, Senior Mechanical Designer, and Clifton W. Greim,
P.E, Partner, Harriman Assocaites
You won't
notice the HVAC components in two newly restored historic buildings that
are part of the Portland Museum of Art in Maine. But that's the point.
Reopened after a two-decade closure, the McLellan House, built in 1801,
and the Lorenzo de Medici Sweat Memorial Galleries, built in 1911, have
HVAC systems that keep people comfortable and the buildings and artwork
safe -- and do it without interfering with either building's historical
integrity.
The two buildings constituted Portland's art museum through most of the
1900s, but were closed to the public in 1980 when construction began for
a new building. Designed by I.M. Pei & Partners, the post-modern Charles
Shipman Payson Building is attached to the Sweat Galleries and the McLellan
House, and opened in 1983.
The plan even then was to restore the historic buildings, forming a three-structure
museum complex that would span three centuries of art and architecture.
That goal was achieved last fall, with the completion of a two-year, $13.5
million restoration of the historic buildings.
Meticulous
restoration
Temperature, humidity factors key to HVAC
design
--work of art
--condensation concerns
--dewpoint analysis
Similar systems
--planned for expansion
--flat-panel radiators
Quiet AHUs
Maintaining critical temperatures
Installation ingenuities
--ducts in fireplaces
--strategically placed shaft
--channels in planks
--reusing plenums
--sensors in ducts
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Meticulous restoration
The restorations of the two buildings were meticulously and sensitively
designed by Ann Beha Architects in Boston. The three-story McLellan House
was originally built for a shipping tycoon and is considered to be an
extraordinary example of Federal-era architecture. It is not only a National
Historic Landmark, but also an official project of Save America's Treasures,
a public-private partnership dedicated to preservation of the nation's
irreplaceable historic and cultural treasures.
Every detail of its restoration was carefully researched, from the selection
of wallpaper and carpeting to the type of nails used. The craftsman who
worked on the architectural millwork even devised tools that could replicate
intricate molding.
The restoration of the galleries that adjoin the McLellan House received
the same careful attention. Margaret Jane Mussey Sweat, the widow of Col.
Lorenzo de Medici Sweat, a former Congressman, bequeathed the McLellan
House, along with money to build the adjoining galleries, to the art society
upon her death in 1908. Designed by architect John Calvin Stevens, the
Beaux-Arts style L.D.M. Sweat Memorial Galleries opened in 1911. The McLellan
House and the Sweat Galleries housed the Portland museum's collection
until 1980.
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Temperature, humidity factors key
to HVAC design
Two basic requirements drove the design of the HVAC systems for the
two buildings: maintaining the temperature and humidity needed to protect
both the buildings and the artwork, and keeping HVAC components out of
view. The challenge of meeting those goals was given to engineers at Harriman
Associates, a full-service architecture and engineering firm with offices
in Auburn and Portland, Maine.
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Work of art The McLellan House is considered
a work of art in itself, and its age and brick-and-mortar construction
necessitated special considerations for climate control. A major concern
was the effect of condensation if insulation were to be installed to provide
energy efficiency. In addition, if artwork were to be displayed, it would
be necessary to maintain relative humidity levels of 40 to 50 percent
in accordance with guidelines established by the American Association
of Museums for accreditation.
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Condensation concerns It was
vital to understand the effects of installing insulation or maintaining
those humidity levels and whether it would cause any deterioration to
the building. Maine's cold weather is part of the problem. The colder
it is outside, the less moisture it takes to cause condensation. That
meant the possibility of high humidity levels, which would move the dewpoint
within the walls. Insulating the walls would cause a higher dewpoint as
well.
The result could be condensation in the walls that could cause enough
pressure as it froze and thawed to deteriorate the face of the brick and
jeopardize the integrity of other parts of the structure
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Dewpoint
analysis That was a consequence that had to be avoided, so a series
of detailed analyses were performed, in which engineers calculated the
dewpoints at various temperature and humidity values.
Based on their findings, no insulation was installed in the McLellan
House, and maintaining a relative humidity of 29 to 30 percent was determined
to be optimum for the integrity of the building structure. This would
be appropriate for interactive computer displays and for visitors to see
how a house of that era would be decorated. It would also facilitate the
display of artwork in protective boxes that provide a microenvironment
that meets the higher levels of temperature andhumidity.
For the Sweat Galleries, however, the higher relative humidity of 40 to
50 percent for the display of art could be maintained without damage to
the building itself. Because the building is nearly a hundred years younger
and constructed in a different manner than the McLellan House, it could
handle the effects of dewpoint better. The Sweat Galleries are essentially
a building within a building, with air space between two wall sections,
and dewpoint migration into the air space would not be as damaging as
it would be in the McLellan House.
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Similar systems
Despite the need for different temperature and humidity requirements,
the HVAC systems are similar in the McLellan House and the Sweat Galleries.
Programming differences provide the temperature and humidity levels that
each building needs. Because the two historic buildings are part of a
three-building complex, Harriman Associates analyzed the efficacy of providing
heating and cooling by extending the systems that were in the newer Payson
Building.
A critical part of that decision was the need to make the connections
without interruptions to the climate control in the Payson Building, which
could have adverse effects on the artwork displayed there.
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Planned for expansion Designers
of the Payson Building had planned for an expansion of the hot-water and
chilled-water systems for use in a future restoration of the Sweat Galleries.
The two Wiel-McLain boilers and 250-ton Carrier chiller installed in the
Payson wing boiler plant were large enough to handle the additional load
from the Sweat Galleries. And hot-water and chilled-water lines were run
to a point just outside the Sweat Galleries basement and were valved off
for future connections. All that was needed was to connect new piping
and rebalance and adjust the hot-water and chilled- water flows.
In the McLellan House, two Neca mini-boilers had been installed about
three years ago. Since the current renovation called for an elevator where
the existing boilers were located, they were relocated to a new mechanical
room, and double-walled, insulated breeching was used to make the final
connection.
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Flat-panel radiators The new radiators
in both buildings are made by Panel Radiator Inc., and of a flat, radiant-tube
design that is much less noticeable than the more traditional fin-style
baseboard radiators. In the McLellan House, the radiators are located
under the windows and are configured with three rows of the flat panels,
painted to blend with the decor in each room. The flat perspective fits
in well with the Federal-era architecture. The same configuration is used
for the radiators in the community studio located in the basement of the
Sweat Galleries and is just as compatible with the building's Beaux-Arts
style architecture.
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Quiet
AHU's
The air-handling units (AHUs) in both buildings are manufactured by McQuay,
with a 9,000- cfm-capacity unit in the Sweat Galleries and a 7,000-cfm
capacity unit in the McLellan House. Each has a Herrmidifier humidification
unit mounted within a dedicated module of the AHU. Both units are of a
"blow-through" configuration, with the heating-coil module installed after
the cooling-coil module, allowing reheating during the dehumidification
mode.
The larger Sweat Galleries AHU has a heating capacity of 462Mbh and a
cooling capacity of 360 Mbh. Heating capacity in the McLellan House unit
is 209 Mbh and cooling is 277 Mbh. The humidifier in the Sweat Galleries
has a capacity of 80 lbs/hr of steam, and in the McLellan House, 50 lbs/hr.
A stacked configuration AHU was chosen for the McLellan House to save
footprint space.
The AHUs are also
very quiet. They are double-walled with perforated interior metal sections
that not only act as an insulation barrier, but also provide substantial
acoustic benefit, cutting sound to fan sections and discharge plenums.
"Some noise in the operation of any HVAC system is inevitable," said Kevin
Eames, who has worked in the facilities department of the museum for the
past 20 years and is now facilities director. "But we wanted an environment
that would provide the least disruption to a visitor's enjoyment of the
buildings and the artwork. These units don't detract from that enjoyment.
In fact, the noise they make is hardly noticeable in either building,"
added Eames, who was also the project manager for the museum throughout
the restoration project.
A special effort was made to see that velocities in the duct systems were
kept lower, as an added assist in minimizing air noise.
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Maintaining
critical temperature levels
Variable air-volume
(VAV) boxes are part of the system in the McLellan House, automatically
set to maintain the temperature levels critical to protecting the building.
In the Sweat Galleries, however, more flexibility was needed. While it
was designed to be a constant-volume unit, it is equipped with variable-speed
drives which can be used to manually adjust air flow as needed. It allows
the museum's facilities director to fine tune air flow for any condition
change that may be required.
Ducts in the Sweat Galleries have reheat coils that can be used to further
adjust the temperature in each individual room as required.
Systems in both buildings are tied into a central direct-digital control
system manufactured by Carrier Corp. and located in the Payson wing of
the museum.Since the system also controls the Payson wing, it makes it
easier for facilities director Eames to make the programming changes and
adjustments needed.
"We already had a Carrier system in the Payson Building, so it made sense
to have continuity among all three buildings. And since I've updated the
systems originally installed in Payson to match the level now in McLellan
and Sweat Galleries, all systems ‘talk' the same language. That makes
it much more efficient to manage the system and to do the programming
changes that are required," said Eames.
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Installation ingenuities
Installing system components in both the McLellan House and the Sweat
Galleries proved challenging. Harriman Associates' engineering designers
looked carefully at all the existing cavities in both buildings that could
be used to hide the components, especially in the McLellan House. The
building has such historical significance that great care was required
to ensure an installation that was unobtrusive and that did not damage
the building's historical integrity.
The lack of space between ceilings and the adjacent floor above in the
McLellan House meant that the more traditional overhead installation of
ducts could not be used, and each floor of the building required a different
solution. On the first floor, the duct work for supply and return air
comes up directly from the basement where the air handlers are located.
However, that could not be done for the second and third floors due to
space constraints.
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Ducts in fireplaces The second-floor
solution was found in the fireplaces that once heated the house. All three
floors of the McLellan House have fireplaces which are connected to chimneys
located on the east and west sides of the building. Engineers saw the
unused fireplace chimneys as an ideal receptacle for the duct work feed
to the second floor, and believed that the fireplace openings would be
an ideal way to bring conditioned air, almost unnoticed, from the basement
to the second floor.
The brick chimney's unevenness and jaggedness could have damaged the vinyl
insulating material on the flexible metal duct work, however. The solution
was to temporarily line the chimney with Tyvek building material first.
Its slippery surface made it possible to snake the duct work in place
without damaging the insulation. Each fireplace was deep enough to be
given a false back that would conceal the duct work. A supply-air grille
integrated into the back of the fireplace, and barely noticeable, sends
conditioned air into the rooms.
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Strategically placed shaft Conditioned
air for three spaces -- a first-floor welcoming area for the public with
interactive displays, a second-floor administrative office, and a meeting
room on the third floor -- arrives through a large shaft that was strategically
placed so it didn't interfere with the use of the building and made efficient
use of space.
A decorative diffuser panel located in a vaulted ceiling in a third-floor
conference room provides an inconspicuous spot for return air. The existing
diffuser panel was meticulously removed and reinstalled by skilled craftsmen
to allow the duct installation.
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Channels in planks Interior walls
in the McLellan House are constructed of vertical planks, 8 inches to
14 inches wide and about 2-1/2-inches thick. Without the space provided
by the more traditional 2-x-4 type of construction, there was little room
to add piping. But engineers were able to use space along the sides of
the fireplaces, and in a few instances, by having channels cut into the
2 1/2-inch planks so that piping could be fit in.
The Sweat Galleries had been constructed when central heating systems
were available, so finding space for duct work and piping was less of
a problem than it was for the McLellan House, while still presenting unique
challenges.
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Reusing plenums The building had been
designed with a gravity heating system. Large, steel plenums with multiple
steam-coil radiators distributed heat by convection up from the basement,
through grates about midway up the walls of the five rooms and vaulted
rotunda making up the galleries. These original plenums were essentially
triangulated, hollow spaces behind the plaster walls on which art was
displayed and provided space for the new duct work and insulation.
However, the modifications required were still difficult because of the
imperfections and unevenness in the interior cavity walls. The original
plaster walls were removed and replaced by drywall over plywood to allow
more flexibility in hanging artwork. Removing the plaster exposed uneven
terra cotta blocking walls, so plywood was cemented to the terra cotta,
and drywall installed over that. And by repositioning the return air grates
near the ceiling, and supply air near the floor, they became less noticeable
and also left more wall space to hang paintings.
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Sensors in ducts Humidity and temperature
sensors are installed in the return air ducts in the galleries, and measurements
sent continually to the computerized direct-digital control system. The
system calculates the average of the readings and uses that to determine
the levels of humidity, cooling, or heating that must be set for the proper
climate control and to avoid rapid temperature and humidity changes which
could damage the artwork on display.
Visitors to the museum praise both the artwork and the sensitive restoration
of the McLellan House and the Sweat Galleries, but few are even aware
of the HVAC system. And that's the way the way it should be.
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Written for Engineered Systems magazine, April 2003
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