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Heating, Ventilating, and Cooling
Historic Buildings: Problems and Recommended Approaches
Sharon C. Park, AIA
The need for modern
mechanical systems is one of the most common reasons to
undertake work on historic buildings. Such work includes
upgrading older mechanical systems, improving the energy
efficiency of existing buildings, installing new heating,
ventilation or air conditioning (HVAC) systems,
or--particularly for museums--installing a climate control
system with humidification and dehumidification capabilities.
Decisions to install new HVAC or climate control systems
often result from concern for occupant health and comfort,
the desire to make older buildings marketable, or the need to
provide specialized environments for operating computers,
storing artifacts, or displaying museum collections.
Unfortunately, occupant comfort and concerns for the objects
within the building are sometimes given greater consideration
than the building itself. In too many cases, applying modern
standards of interior climate comfort to historic buildings
has proven detrimental to historic materials and decorative
finishes.
This Preservation Brief
underscores the importance of careful planning in order to
balance the preservation objectives with interior climate
needs of the building. It is not intended as a technical
guide to calculate tonnage or to size piping or ductwork.
Rather, this Brief identifies some of the problems associated
with installing mechanical systems in historic buildings and
recommends approaches to minimizing the physical and visual
damage associated with installing and maintaining these new
or upgraded systems.
Historic buildings are
not easily adapted to house modern precision mechanical
systems. Careful planning must be provided early on to ensure
that decisions made during the design and installation phases
of a new system are appropriate. Since new mechanical and
other related systems, such as electrical and fire
suppression, can use up to 10% of a building's square footage
and 30%40% of an overall rehabilitation budget, decisions
must be made in a systematic and coordinated manner. The
installation of inappropriate mechanical systems may result
in any or all of the following:
-
large sections of
historic materials are removed to install or house new
systems.
-
historic structural
systems are weakened by carrying the weight of, and
sustaining vibrations from, large equipment.
-
moisture introduced
into the building as part of a new system migrates into
historic materials and causes damage, including
biodegradation, freeze/thaw action, and surface
staining.
-
exterior cladding or
interior finishes are stripped to install new vapor
barriers and insulation.
-
historic finishes,
features, and spaces are altered by dropped ceilings and
boxed chases or by poorly located grilles, registers, and
equipment.
-
systems that are too
large or too small are installed before there is a clearly
planned use or a new tenant.
For historic properties
it is critical to understand what spaces, features, and
finishes are historic in the building, what should be
retained, and what the realistic heating, ventilating, and
cooling needs are for the building, its occupants, and its
contents. A systematic approach, involving preservation
planning, preservation design, and a follow-up program of
monitoring and maintenance, can ensure that new systems are
successfully added--or existing systems are suitably
upgraded--while preserving the historic integrity of the
building.
No set formula exists for
determining what type of mechanical system is best for a
specific building. Each building and its needs must be
evaluated separately. Some buildings will be so significant
that every effort must be made to protect the historic
materials and systems in place with minimal intrusion from
new systems. Some buildings will have museum collections that
need special climate control. In such cases, curatorial needs
must be considered--but not to the ultimate detriment of the
historic building resource. Other buildings will be
rehabilitated for commercial use. For them, a variety of
systems might be acceptable, as long as significant spaces,
features, and finishes are retained.
Most mechanical systems
require upgrading or replacement within 1530 years due to
wear and tear or the availability of improved technology.
Therefore, historic buildings should not be greatly altered
or otherwise sacrificed in an effort to meet short-term
systems objectives.
History of Mechanical
Systems
The history of mechanical
systems in buildings involves a study of inventions and
ingenuity as building owners, architects, and engineers
devised ways to improve the interior climate of their
buildings. Following are highlights in the evolution of
heating, ventilating, and cooling systems in historic
buildings.
Eighteenth Century. Early
heating and ventilation in America relied upon common sense
methods of managing the environment (see figure 1). Builders
purposely sited houses to capture winter sun and prevailing
summer cross breezes; they chose materials that could help
protect the inhabitants from the elements, and took
precautions against precipitation and damaging drainage
patterns. The location and sizes of windows, doors, porches,
and the floor plan itself often evolved to maximize
ventilation. Heating was primarily from fireplaces or stoves
and, therefore, was at the source of delivery. In 1744,
Benjamin Franklin designed his "Pennsylvania stove" with a
fresh air intake in order to maximize the heat radiated into
the room and to minimize annoying smoke.
Thermal insulation was
rudimentary--often wattle and daub, brick and wood nogging.
The comfort level for occupants was low, but the relatively
small difference between internal and external temperatures
and relative humidity allowed building materials to expand
and contract with the seasons.
Regional styles and
architectural features reflected regional climates. In warm,
dry and sunny climates, thick adobe walls offered shelter
from the sun and kept the inside temperatures cool. Verandas,
courtyards, porches, and high ceilings also reduced the
impact of the sun. Hot and humid climates called for elevated
living floors, louvered grilles and shutters, balconies, and
interior courtyards to help circulate air.
Nineteenth Century. The
industrial revolution provided the technological means for
controlling the environment for the first time (see figure
2). The dual developments of steam energy from coal and
industrial mass production made possible early central
heating systems with distribution of heated air or steam
using metal ducts or pipes. Improvements were made to early
wrought iron boilers and by late century, steam and low
pressure hot water radiator systems were in common use, both
in offices and residences. Some large institutional buildings
heated air in furnaces and distributed it throughout the
building in brick flues with a network of metal pipes
delivering heated air to individual rooms. Residential
designs of the period often used gravity hot air systems
utilizing decorative floor and ceiling grilles.
Ventilation became more
scientific and the introduction of fresh air into buildings
became an important component of heating and cooling.
Improved forced air ventilation became possible in
mid-century with the introduction of power-driven fans.
Architectural features such as porches, awnings, window and
door transoms, large openwork iron roof trusses, roof
monitors, cupolas, skylights and clerestory windows helped to
dissipate heat and provide healthy ventilation.
Cavity wall construction,
popular in masonry structures, improved the insulating
qualities of a building and also provided a natural cavity
for the dissipation of moisture produced on the interior of
the building. In some buildings, cinder chips and broken
masonry filler between structural iron beams and jack arch
floor vaults provided thermal insulation as well as
fireproofing. Mineral wool and cork were new sources of
lightweight insulation and were forerunners of contemporary
batt and blanket insulation.
The technology of the
age, however, was not sufficient to produce "tight"
buildings. There was still only a moderate difference between
internal and external temperatures. This was due, in part, to
the limitations of early insulation, the almost exclusive use
of single glazed windows, and the absence of airtight
construction. The presence of ventilating fans and the
reliance on architectural features, such as operable windows,
cupolas and transoms, allowed sufficient air movement to keep
buildings well ventilated. Building materials could behave in
a fairly traditional way, expanding and contracting with the
seasons.
Twentieth Century. The
twentieth century saw intensive development of new
technologies and the notion of fully integrating mechanical
systems (see figure 3).
Oil and gas
furnaces
developed in the
nineteenth century were improved and made more efficient,
with electricity becoming the critical source of power for
building systems in the latter half of the century. Forced
air heating systems with ducts and registers became popular
for all types of buildings and allowed architects to
experiment with architectural forms free from mechanical
encumbrances. In the 1920s large-scale theaters and
auditoriums introduced central air conditioning, and by
mid-century forced air systems which combined heating and air
conditioning in the same ductwork set a new standard for
comfort and convenience. The combination and coordination of
a variety of systems came together in the post-World War II
high-rise buildings; complex heating and air conditioning
plants, electric elevators, mechanical towers, ventilation
fans, and full service electric lighting were integrated into
the building's design.
The insulating qualities
of building materials improved. Synthetic materials, such as
spun fiberglass batt insulation, were fully developed by
mid-century. Prototypes of insulated thermal glazing and
integral storm window systems were promoted in construction
journals. Caulking to seal out perimeter air around window
and door openings became a standard construction
detail.
The last quarter of the
twentieth century has seen making HVAC systems more energy
efficient and better integrated. The use of vapor barriers to
control moisture migration, thermally efficient windows,
caulking and gaskets, compressed thin wall insulation, has
become standard practice. New integrated systems now combine
interior climate control with fire suppression, lighting, air
filtration, temperature and humidity control, and security
detection. Computers regulate the performance of these
integrated systems based on the time of day, day of the week,
occupancy, and outside ambient temperature.
Climate Control and
Preservation
Although twentieth
century mechanical systems technology has had a tremendous
impact on making historic buildings comfortable, the
introduction of these new systems in older buildings is not
without problems. The attempt to meet and maintain modern
climate control standards may in fact be damaging to historic
resources. Modern systems are often over-designed to
compensate for inherent inefficiencies of some historic
buildings materials and plan layouts. Energy retrofit
measures, such as installing exterior wall insulation and
vapor barriers or the sealing of operable window and vents,
ultimately affect the performance and can reduce the life of
aging historic materials.
In general, the greater
the differential between the interior and exterior
temperature and humidity levels, the greater the potential
for damage. As natural vapor pressure moves moisture from a
warm area to a colder, dryer area, condensation will occur on
or in building materials in the colder area (see figure 4).
Too little humidity in winter, for example, can dry and crack
historic wooden or painted surfaces. Too much humidity in
winter causes moisture to collect on cold surfaces, such as
windows, or to migrate into walls. As a result, this
condensation deteriorates wooden or metal windows and causes
rotting of walls and wooden structural elements, dampening
insulation and holding moisture against exterior surfaces.
Moisture migration through walls can cause the corrosion of
metal anchors, angles, nails or wire lath, can blister and
peel exterior paint, or can leave efflorescence and salt
deposits on exterior masonry. In cold climates, freeze-thaw
damage can result from excessive moisture in external
walls.
To avoid these types of
damage to a historic building, is important to understand how
building components work together as a system. Methods for
controlling interior temperature and humidity and improving
venation must be considered in any new or upgraded HVAC or
climate control system. While certain energy retrofit
measures will have a positive effect on the overall building,
installing effective vapor barriers in historic walls is
difficult and often results in destruction of significant
historic materials (see figure 5).
Planning the New System
Climate control systems
are generally classified according to the medium used to
condition the temperature: air, water, or a combination of
both (see overview on page 6). The complexity of choices
facing a building owner or manager means that a systematic
approach is critical in determining the most suitable system
for a building, its contents, and its occupants. No matter
which system is installed, a change in the interior climate
will result. This physical change will in turn affect how the
building materials perform. New registers, grilles, cabinets,
or other accessories associated with the new mechanical
system will also visually change the interior (and sometimes
the exterior) appearance of the building. Regardless of the
type or extent of a mechanical system, the owner of a
historic building should know before a system is installed
what it will look like and what problems can be anticipated
during the life of that system. The potential harm to a
building and costs to an owner of selecting the wrong
mechanical system are very great.
The use of a building and
its contents will largely determine the best type of
mechanical system. The historic building materials and
construction technology as well as the size and availability
of secondary spaces within the historic structure will affect
the choice of a system. It may be necessary to investigate a
combination of systems. In each case, the needs of the user,
the needs of the building, and the needs of a collection or
equipment must be considered. It may not be necessary to have
a comprehensive climate control system if climate-sensitive
objects can be accommodated in special areas or
climate-controlled display cases. It may not be necessary to
have central air conditioning in a mild climate if natural
ventilation systems can be improved through the use of
operable windows, awnings, exhaust fans, and other "lowtech"
means. Modern standards for climate control developed for new
construction may not be achievable or desirable for historic
buildings. In each case, the lowest level of intervention
needed to successfully accomplish the job should be
selected.
Before a system is
chosen, the following planning steps are recommended:
1. Determine the use of
the building. The proposed use of the building (museum,
commercial, residential, retail) will influence the type of
system that should be installed. The number of people and
functions to be housed in a building will establish the level
of comfort and service that must be provided. Avoid uses that
require major modifications to significant architectural
spaces. What is the intensity of use of the building:
intermittent or constant use, special events or seasonal
events? Will the use of the building require major new
services such as restaurants, laundries, kitchens, locker
rooms, or other areas that generate moisture that may
exacerbate climate control within the historic space? In the
context of historic preservation, uses that require radical
reconfigurations of historic spaces are inappropriate for the
building.
2. Assemble a qualified
team. This team ideally should consist of a preservation
architect, mechanical engineer, electrical engineer,
structural engineer, and preservation consultants, each
knowledgeable in codes and local requirements. If a special
use (church, museum, art studio) or a collection is involved,
a specialist familiar with the mechanical requirements of
that building type or collection should also be hired.
Team members should be
familiar with the needs of historic buildings and be able to
balance complex factors: the preservation of the historic
architecture (aesthetics and conservation), requirements
imposed by mechanical systems (quantified heating and cooling
loads), building codes (health and safety), tenant
requirements (quality of comfort, ease of operation), access
(maintenance and future replacement), and the overall cost to
the owner.
3. Undertake a condition
assessment of the existing building and its systems. What are
the existing construction materials and mechanical systems?
What condition are they in and are they reusable (see figure
6)? Where are existing chillers, boilers, air handlers, or
cooling towers located? Look at the condition of all other
services that may benefit from being integrated into a new
system, such as electrical and fire suppression systems.
Where can energy efficiency be improved to help downsize any
new equipment added, and which of the historic features, e.g.
shutters, awnings, skylights, can be reused (see figure 7)?
Evaluate air infiltration through the exterior envelope;
monitor the interior for temperature and humidity levels with
hygrothermographs for at least a year. Identify building,
site, or equipment deficiencies or the presence of asbestos
that must be corrected prior to the installation or upgrading
of mechanical systems.
4. Prioritize
architecturally significant spaces, finishes, and features to
be preserved. Significant architectural spaces, finishes and
features should be identified and evaluated at the outset to
ensure their preservation. This includes significant existing
mechanical systems or elements such as hot water radiators
decorative grilles, elaborate switch-plates, and
nonmechanical architectural features such as cupolas,
transoms, or porches. Identify nonsignificant spaces where
mechanical equipment can be placed and secondary spaces where
equipment and distribution runs on both a horizontal and
vertical basis can be located. Appropriate secondary spaces
for housing equipment might include attics, basements,
penthouses, mezzanines, false ceiling or floor cavities,
vertical chases, stair towers, closets, or exterior
below-grade vaults (see figure 8).
5. Become familiar with
local building and fire codes. Owners or their
representatives should meet early and often with local
officials. Legal requirements should be checked; for example,
can existing ductwork be reused or modified with dampers? Is
asbestos abatement required? What are the energy, fire, and
safety codes and standards in place, and how can they be met
while maintaining the historic character of the building? How
are fire separation walls and rated mechanical systems to be
handled between multiple tenants? Is there a requirement for
fresh air intake for stair towers that will affect the
exterior appearance of the building? Many of the health,
energy, and safety code requirements will influence decisions
made for mechanical equipment for climate control. It is
importance to know what they are before the design phase
begins.
6. Evaluate options for
the type and size of systems. A matrix or feasibility studies
should be developed to balance the benefits and drawbacks of
various systems. Factors to consider include heating and/or
cooling, fuel type, distribution system, control devices,
generating equipment and accessories such as filtration, and
humidification. What are the initial installation costs,
projected fuel costs, long-term maintenance, and life-cycle
costs of these components and systems? Are parts of an
existing system being reused and upgraded? The benefits of
added ventilation should not be overlooked (see figure 9).
What are the tradeoffs between one large central system and
multiple smaller systems? Should there be a forced air ducted
system, a two-pipe fan coil system, or a combined water and
air system? What space is available for the equipment and
distribution system? Assess the fire risk levels of various
fuels. Understand the advantages and disadvantages of the
various types of mechanical systems available. Then evaluate
each of these systems in light of the preservation objectives
established during the design phase of planning.
______________________________________________________
Overview of HVAC
Systems
WATER SYSTEMS: Hydronic
radiators, Fan coil, or radiant pipes
Water systems are
generally called hydronic and use a network of pipes to
deliver water to hot water radiators, radiant pipes set in
floors or fan coil cabinets which can give both heating and
cooling. Boilers produce hot water or steam; chillers produce
chilled water for use with fan coil units. Thermostats
control the temperature by zone for radiators and
radiant
floors. Fan coil units
have individual controls. Radiant floors provide quiet, even
heat, but are not common.
Advantages: Piped systems
are generally easier to install in historic buildings because
the pipes are smaller than ductwork.
Disadvantages: There is
the risk, however, of hidden leaks in the wall or burst pipes
in winter if boilers fail. Fan coil condensate pans can
overflow if not properly maintained. Fan coils may be
noisy.
Hydronic Radiators:
Radiators or baseboard radiators are looped together and are
usually set under windows or along perimeter walls. New
boilers and circulating pumps can upgrade older systems. Most
piping was cast iron although copper systems can be used if
separately zoned. Modern cast iron baseboards and copper
fin-tubes are available. Historic radiators can be
reconditioned.
Fan Coil Units: Fan coil
systems use terminal cabinets in each room serviced by 2, 3,
or 4 pipes approximately 11/2" each in diameter. A fan blows
air over the coils which are serviced by hot or chilled
water. Each fan coil cabinet can be individually controlled.
Four-pipe fan coils can provide both heating and cooling all
year long. Most piping is steel. Non-cabinet units may be
concealed in closets or custom cabinetry, such as benches,
can be built.
CENTRAL AIR
SYSTEMS
The basic heating,
ventilation and air conditioning (HVAC) system is all-air,
single zone fan driven designed for low, medium or high
pressure distribution. The system is composed of compressor
drives, chillers, condensers, and furnace depending on
whether the air is heated, chilled or both. Condensers,
generally air cooled, are located outside. The ducts are
sheet metal or flexible plastic and can be insulated. Fresh
air can be circulated. Registers can be designed for
ceilings, floors and walls. The system is controlled by
thermostats; one per zone.
Advantages: Ducted
systems offer a high level of control of interior
temperature, humidity, and filtration. Zoned units can be
relatively small and well concealed.
Disadvantages: The damage
from installing a ducted system without adequate space can be
serious for a historic building. Systems need constant
balancing and can be noisy.
Basic HVAC: Most
residential or small commercial systems will consist of a
basic furnace with a cooling coil set in the unit and a
refrigerant compressor or condenser located outside the
building. Heating and cooling ductwork is usually shared. If
sophisticated humidification and dehumidification is added to
the basic HVAC system, a full climate control system results.
This can often double the size of the equipment.
Basic Heat Pump/Air
System: The heat pump is a basic HVAC system as described
above except for the method of generating hot and cold air.
The system operates on the basic
refrigeration cycle where
latent heat is extracted from the ambient air and is used to
evaporate refrigerant vapor under pressure. Functions of the
condenser and evaporator switch when heating is needed. Heat
pumps, somewhat less efficient in cold climates, can be
fitted with electric resistance coil.
COMBINED AIR AND WATER
SYSTEMS
These systems are popular
for restoration work because they combine the ease of
installation for the piped system with the performance and
control of the ducted system. Smaller air handling units, not
unlike fan coils, may be located throughout a building with
service from a central boiler and chiller. In many cases the
water is delivered from a central plant which services a
complex of buildings.
This system overcomes the
disadvantages of a central ducted system where there is not
adequate horizontal or vertical runs for the ductwork. The
equipment, being smaller, may also be quieter and cause less
vibration. If only one air handler is being utilized for the
building, it is possible to house all the equipment in a
vault outside the building and send only conditioned air into
the structure.
Advantages: flexibility
for installation using greater piping runs with shorter
ducted runs; Air handlers can fit into small spaces.
Disadvantages: piping
areas may have undetected leaks; air handlers may be
noisy.
OTHER SYSTEM
COMPONENTS
Non-systems components
should not be overlooked if they can make a building more
comfortable without causing damage to the historic resource
or its collection.
Advantages: components
may provide acceptable levels of comfort without the need for
an entire system.
Disadvantages: Spot
heating, cooling and fluxuations in humidity may harm
sensitive collections or furnishings. If an integrated system
is desirable, components may provide only a temporary
solution.
Portable Air
Conditioning:
Most individual air
conditioners are set in windows or through exterior walls
which can be visually as well as physically damaging to
historic buildings. Newer portable air conditioners are
available which sit in a room and exhaust directly to the
exterior through a small slot created by a raised window
sash.
Fans: Fans should be
considered in most properties to improve ventilation. Fans
can be located in attics, at the top of stairs, or in
individual rooms. In moderate climates, fans may eliminate
the need to install central air systems.
Dehumidifiers: For houses
without central air handling systems, a dehumidifier can
resolve problems in humid climates. Seasonal use of
dehumidifiers can remove moisture from damp basements and
reduce fungal growth.
Heaters: Portable radiant
heaters, such as those with water and glycol, may provide
temporary heat in buildings used infrequently or during
systems breakdowns. Care should be taken not to create a fire
hazard with improperly wired units.
______________________________________________________
Designing the new
system
In designing a system, it
is important to anticipate how it will be installed, how
damage to historic materials can be minimized, and how
visible the new mechanical system will be within the restored
or rehabilitated spaces (see figure 10 af). Mechanical
equipment space needs are often overwhelming; in some cases,
it may be advantageous to look for locations outside of the
building, including ground vaults, to house some of the
equipment but only if it there is no adverse impact to the
historic landscape or adjacent archeological resources.
Various means for reducing the heating and cooling loads (and
thereby the size of the equipment) should be investigated.
This might mean reducing slightly the comfort levels of the
interior, increasing the number of climate control zones, or
improving the energy efficiency of the building.
The following activities
are suggested during the design phase of the new
system:
1. Establish specific
criteria for the new or upgraded mechanical system. New
systems should be installed with a minimum of damage to the
resource and should be visually compatible with the
architecture of the building. They should be installed in a
way that is easy to service, maintain, and upgrade in the
future. There should be safety and backup monitors in place
if buildings have collections, computer rooms, storage vaults
or special conditions that need monitoring. The new systems
should work within the structural limits of the historic
building. They should produce no undue vibration, no undue
noise, no dust or mold, and no excess moisture that could
damage the historic building materials. If any equipment is
to be located outside of the building, there should be no
impact to the historic appearance of building or site, and
there should be no impact on archeological resources.
2. Prioritize the
requirements for the new climate control system. The use of
the building will determine the level of interior comfort and
climate control. Sometimes, various temperature zones may
safely be created within a historic building. This zoned
approach may be appropriate for buildings with specialized
collections storage, for buildings with mixed uses, or for
large buildings with different external exposures, occupancy
patterns, and delivery schedules for controlled air. Special
archives, storage vaults or computer rooms may need a
completely different climate
control from the rest of
the building. Determine temperature and humidity levels for
occupants and collections and ventilation requirements
between differing zones. Establish if the system is to run 24
hours a day or only during operating or business hours.
Determine what controls are optimum (manual, computer, preset
automatic, or other). The size and location of the equipment
to handle these different situations will ultimately affect
the design of the overall
system as well.
3. Minimize the impact of
the new HVAC on the existing architecture. Design criteria
for the new system should be based on the type of
architecture of the historic resource. Consideration should
be given as to whether or not the delivery system is visible
or hidden. Utilitarian and industrial spaces may be capable
of accepting a more visible and functional system. More
formal, ornate spaces which may be part of an interpretive
program may require a less visible or disguised system. A
ducted system should be installed without ripping into or
boxing out large sections of floors, walls, or ceilings. A
wet pipe system should be installed so that hidden leaks will
not damage important decorative finishes. In each case, not
only the type of system (air, water, combination), but its
distribution (duct, pipe) and delivery appearance (grilles,
cabinets, or registers) must be evaluated. It may be
necessary to use a combination of different systems in order
to preserve the historic building. Existing chases should be
reused whenever possible.
4. Balance quantitative
requirements and preservation objectives. The ideal system
may not be achievable for each historic resource due to cost,
space limitations, code requirements, or other factors beyond
the owner's control. However, significant historic spaces,
finishes, and features can be preserved in almost every case,
even given these limitations. For example, if some ceiling
areas must be slightly lowered to accommodate ductwork or
piping, these should be in secondary areas away from
decorative ceilings or tall windows. If modern fan coil
terminal units are to be visible in historic spaces,
consideration should be given to custom designing the
cabinets or to using smaller units in more locations to
diminish their impact. If grilles and registers are to be
located in significant spaces, they should be designed to
work within the geometry or placement of decorative elements.
All new elements, such as ducts, registers, pipe-runs, and
mechanical equipment should be installed in a reversible
manner to be removed in the future without further damage to
the building (see fig 11).
Systems Performance
and Maintenance
Once the system is
installed, it will require routine maintenance and balancing
to ensure that the proper performance levels are achieved. In
some cases, extremely sophisticated, computerized systems
have been developed to control interior climates, but these
still need monitoring by trained staff. If collection
exhibits and archival storage are important to the resource,
the climate control system will require constant monitoring
and tuning. Backup systems are also needed to prevent damage
when the main system is not working. The owner, manager, or
chief of maintenance should be aware of all aspects of the
new climate control system and have a plan of action before
it is installed.
Regular training sessions
on operating, monitoring, and maintaining the new system
should be held for both curatorial and building maintenance
staff. If there are curatorial reasons to maintain constant
temperature or humidity levels, only individuals thoroughly
trained in how the HVAC systems operates should be able to
adjust thermostats. Ill-informed and haphazard attempts to
adjust comfort levels, or to save energy over weekends and
holidays, can cause great damage.
______________________________________________________
HVAC Do's and Don'ts
DO's:
-
Use shutters, operable
windows, porches, curtains, awnings, shade trees and other
historically appropriate nonmechanical features of
historic buildings to reduce the heating and cooling
loads. Consider adding sensitively designed storm windows
to existing historic windows.
-
Retain or upgrade
existing mechanical systems whenever possible: for
example, reuse radiator systems with new boilers, upgrade
ventilation within the building, install proper
thermostats or humidistats.
-
Improve energy
efficiency of existing buildings by installing insulation
in attics and basements. Add insulation and vapor barriers
to exterior walls only when it can be done without further
damage to the resource.
-
In major spaces,
retain decorative elements of the historic system whenever
possible. This includes switch-plates, grilles and
radiators. Be creative in adapting these features to work
within the new or upgraded system.
-
Use space in existing
chases, closets or shafts for new distribution
systems.
-
Design climate control
systems that are compatible with the architecture of the
building: hidden system for formal spaces, more exposed
systems possible in industrial or secondary spaces. In
formal areas, avoid standard commercial registers and use
custom slot registers or other less intrusive
grilles.
-
Size the system to
work within the physical constraints of the building. Use
multi-zoned smaller units in conjunction with existing
vertical shafts, such as stacked closets, or consider
locating equipment in vaults underground, if
possible.
-
Provide adequate
ventilation to the mechanical rooms as well as to the
entire building. Selectively install air intake grilles in
less visible basement, attic, or rear areas.
-
Maintain appropriate
temperature and humidity levels to meet requirements
without accelerating the deterioration of the historic
building materials. Set up regular monitoring
schedules.
-
Design the system for
maintenance access and for future systems
replacement.
-
For highly significant
buildings, install safety monitors and backup features,
such as double pans, moisture detectors, lined chases, and
battery packs to avoid or detect leaks and other damage
from system failures.
-
Have a regular
maintenance program to extend equipment life and to ensure
proper performance.
-
Train staff to monitor
the operation of equipment and to act knowledgeably in
emergencies or breakdowns.
-
Have an emergency plan
for both the building and any curatorial collections in
case of serious malfunctions or breakdowns.
DON'TS:
-
Don't install a new
system if you don't need it.
-
Don't switch to a new
type of system (e.g. forced air) unless there is
sufficient space for the new system or an appropriate
place to put it.
-
Don't over-design a
new system. Don't add air conditioning or climate control
if they are not absolutely necessary.
-
Don't cut exterior
historic building walls to add through-wall heating and
air conditioning units. These are visually disfiguring,
they destroy historic fabric, and condensation runoff from
such units can further damage historic materials.
-
Don't damage historic
finishes, mask historic features, or alter historic spaces
when installing new systems.
-
Don't drop ceilings or
bulkheads across window openings.
-
Don't remove
repairable historic windows or replace them with
inappropriately designed thermal windows.
-
Don't seal operable
windows, unless part of a museum where air pollutants and
dust are being controlled.
-
Don't place
condensers, solar panels, chimney stacks, vents or other
equipment on visible portions of roofs or at significant
locations on the site.
-
Don't overload the
building structure with the weight of new equipment,
particularly in the attic.
-
Don't place stress on
historic building materials through the vibrations of the
new equipment.
-
Don't allow
condensation on windows or within walls to rot or spall
adjacent historic building materials.
______________________________________________________
Maintenance staff should
learn how to operate, monitor, and maintain the mechanical
equipment. They must know where the maintenance manuals are
kept. Routine maintenance schedules must be developed for
changing and cleaning filters, vents, and condensate pans to
control fungus, mold, and other organisms that are dangerous
to health. Such growths can harm both inhabitants and
equipment. (In piped systems, for example, molds in
condensate pans can block drainage lines and cause an
overflow to leak onto finished surfaces). Maintenance staff
should also be able to monitor the appropriate gauges, dials,
and thermographs. Staff must be trained to intervene in
emergencies, to know where the master controls are, and whom
to call in an emergency. As new personnel are hired, they
will also require maintenance training.
In addition to regular
cyclical maintenance, thorough inspections should be
undertaken from time to time to evaluate the continued
performance of the climate control system. As the system
ages, parts are likely to fail, and signs of trouble may
appear. Inadequately ventilated areas may smell musty. Wall
surfaces may show staining, wet patches, bubbling or other
signs of moisture damage. Routine tests for air quality,
humidity, and temperature should indicate if the system is
performing properly. If there is damage as a result of the
new system, it should be repaired immediately and then
closely monitored to ensure complete repair.
Equipment must be
accessible for maintenance and should be visible for easy
inspection. Moreover, since mechanical systems last only 1530
years, the system itself must be "reversible." That is, the
system must be installed in such a way that later removal
will not damage the building. In addition to servicing, the
backup monitors that signal malfunctioning equipment must be
routinely checked, adjusted, and maintained. Checklists
should be developed to ensure that all aspects of routine
maintenance are completed and that data is reported to the
building manager.
Conclusion
The successful
integration of new systems in historic buildings can be
challenging. Meeting modern HVAC requirements for human
comfort or installing controlled climates for museum
collections or for the operation of complex computer
equipment can result in both visual and physical damage to
historic resources. Owners of historic buildings must be
aware that the final result will involve balancing multiple
needs; no perfect heating, ventilating, and air conditioning
system exists. In undertaking changes to historic buildings,
it is best to have the advice and input of trained
professionals who can:
-
assess the condition
of the historic building,
-
evaluate the
significant elements that should be preserved or
reused,
-
prioritize the
preservation objectives,
-
understand the impact
of new interior climate conditions on historic
materials
-
integrate preservation
with mechanical and code requirements,
-
maximize the
advantages of various new or upgraded mechanical
systems,
-
understand the visual
and physical impact of various installations,
-
identify maintenance
and monitoring requirements for new or upgraded systems,
and
-
plan for the future
removal or replacement of the system.
Too often the presumed
climate needs of the occupants or collections can be
detrimental to the long-term preservation of the building.
With a careful balance between the preservation needs of the
building and the interior temperature and humidity needs of
the occupants, a successful project can result.
Bibliography
Banham, Reyner. The
Architecture of the Well-Tempered Environment. London: The
Architectural Press, 1969.
Burns, John A., AIA.
Energy Conserving Features Inherent in Older Homes
Washington: U.S. Department of Housing and Urban Development
and U.S. Department of the Interior, 1982.
Cowan, Henry J. Science
and Building; Structural and Environmental Design in the
Nineteenth and Twentieth Centuries. New York: John Wiley
& Sons, 1978.
Ferguson, Eugene S. "An
Historical Sketch of Central Heating: 1800-1860," in Building
Early America (Charles Peterson, editor) Philadelphia:
Chilton Book Co., 1976.
Fitch, James Marston.
American Building; The Environmental Forces That Shape It.
Boston: Houghton-Mifflin Co., 1972.
Giedion, Siegfried.
Mechanization Takes Command; a Contribution to Anonymous
History. New York: Oxford University Press, 1948.
Merritt, Frederick S.
Building Engineering and Systems Design. New York: Van
Nostrand Reinhold Co, 1979.
Smith, Baird M.
Preservation Briefs 3: Conserving Energy in Historic
Buildings. Washington, DC: U.S. Department of the Interior,
1978.
Turberg, Edward. A
History of American Building Technology. Durham: Durham
Technical Institute, 1981.
Acknowledgements
The author gratefully
acknowledges the invaluable assistance of Michael C. Henry,
P.E., AIA, in the development and technical editing of this
Preservation Brief. Technical review was also provided by
Ernest A. Conrad, P.E. Thanks is also given to staff members
of the National Park Service Cultural Resources Programs,
including Tom Keohan and Catherine Colby, Rocky Mountain
Region; Michael Crowe, Western Region; Mark Chavez, Midwest
Region; Randall J. Biallas, AIA, Chief, Park Historic
Architecture Division, and George A. Thorsen, Historical
Architect, Denver Service Center. Special thanks is also
given to Michael J. Auer of Technical Preservation Services
for his editorial assistance in preparing this paper and Tim
Buehner for his assistance with the illustrations.
Washington, D.C. October,
1991
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