RFP-PII_22_Historic_Structure_Report_Attachments_-_Preservation_Brief_24.pdf

PRESERVATION

BRIEFS

Heating, Ventilating, and Cooling Historic Buildings:

Problems and Recommended Approaches

Sharon C. Park, AlA u.s. Department of the Interior National Park Service Cultural Resources

Heritage Preservation Services

The need for modern mechanical systems is one of the most common reasons to undertake work on historic buildings. Such work includes upgrading older me chanical 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. Deci sions to install new HVAC or climate control systems often result from concern for occupant health and com fort, the desire to make older buildings marketable, or the need to provide specialized environments for oper ating computers, storing artifacts, or displaying mu seum collections . Unfortunately, occupant comfort and concerns for the objects within the building are some times 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 ton nage or to size piping or ductwork. Rather, this Brief identifies some of the problems associated with install ing mechanical systems in historic buildings and rec ommends approaches to minimizing the physical and visual damage associated with installing and maintain ing these new or upgraded systems.

Historic buildings are not easily adapted to house modern precision mechanical systems. Careful plan ning must be provided early on to ensure that deci sions 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 boxedchases or by poorly lo cated 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 build ing, 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, preserva tion 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 tl}e 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 sys tems in place with minimal intrusion from new sys tems. Some buildings will have museum collections that need special climate control. In such cases, cura torial needs must be considered-but not to the ulti mate 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 re placement within 15-30 years due to wear and tear or the availability of improved technology. Therefore, his toric buildings should not be greatly altered or other wise 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 own ers, 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 manag ing the environment (see figure 1). Builders purposely sited houses to capture winter sun and prevailing sum mer cross breezes; they chose materials that could help protect the inhabitants from the elements, and took precautions against precipitation and damaging drain age 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 mini mize 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 differ ence 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 pro vided the technological means for controlling the envi ronment 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 introduc-

1. Eighteenth century and later vernacular architecture depended on the siting of the building, deciduous trees, cross ventilation, and the placement of windows and chimneys to maximize winter heating and natural summer cooling. Regional details, as seen in this Virginia house, include external chimneys and a separate summer kitchen to reduce fi re risk and isolate heat in the summer. Photo: NPS Files.

2. Nineteenth century buildings continued to use architectural features such as porches, cupolas, and awnings to make the buildings more comfortable in summer, but heating was greatly improved by hot water or steam radiators .

Photo: NPS Files tion 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 fea tures such as porches, awnings, window and door transoms, large open-work iron roof trusses, roof mon itors, cupolas, skylights and clerestory windows helped to dissipate heat and provide healthy ventilation.

Cavity wall construction, popular in masonry struc tures, 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 fire proofing. Mineral wool and cork were new sources of lightweight insulation and were forerunners of contem porary batt and blanket insulation.

The technology of the age, however, was not suffic ient to produce "tight" buildings. There was still only a moderate difference between internal and external tem peratures. This was due, in part, to the limitations of early insulation, the almost exclusive use of single glazed windows, and the absence of air-tight construc tion. 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 inten sive 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 electric ity becoming the critical source of power for building systems in the latter half of the century. Forced air heat ing systems with ducts and registers became popular for all types of buildings and allowed architects to ex periment 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 heat ing and air conditioning in the same ductwork set a new standard for comfort and convenience. The combi nation and coordination of a variety of systems came together in the post-World War II highrise buildings;

complex heating and air conditioning plants, electric elevators, mechanical towers, ventilation fans, and full service electric lighting were integrated into the build ing's design.

The insulating qualities of building materials im proved. 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 con struction 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 mois ture migration, thermally efficient windows, caulking and gaskets, compressed thin wall insulation, has be come standard practice. New integrated systems now combine interior climate control with fire suppression, lighting, air filtration, temperature and humidity con trol, 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.

3. The circa 1928 Fox Theater in Detroit, designed by C. Howard Crane, was one of the earliest twentieth century buildings to provide air condition ing to its patrons. The early water-cooled system was recently restored.

Commercial and highrise buildings of the twentieth century were able, mostly through electrical power, to provide sophisticated systems that inte grated many building services. Photo: William Kessler and Associates, Arch i tects.

Climate Control and Preservation

Although twentieth century mechanical systems tech nology has had a tremendous impact on making his toric buildings comfortable, the introduction of these new systems in older buildings is not without prob lems. The attempt to meet and maintain modern cli mate 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 humid ity in winter causes moisture to collect on cold sur faces, 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 an chors, angles, nails or wire lath, can blister and peel exterior paint, or can leave efflorescence and salt de posits 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, it is important to understand how building components work together as a system. Methods for controlling interior temperature and humidity and improving ven tilation 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 over all building, installing effective vapor barriers in his toric walls is difficult and often results in destruction of significant historic materials (see figure 5).

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5. The installation of vapor retarders in walls of historic buildings in an effort to contain interior moisture can cause serious damage to historic finishes as shown here. In this example, all the wall plaster and lath have been stripped in preparation for a vapor barrier prior to replastering, Con trolling interior temperature and relative humidity can be more effective than adding insulation and vapor barriers to historic perimeter walls. Photo:

Ernest A. Conrad, P.E.

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C. Moisture Condensation in Walls

4. Mechanical heating and cooling systems change the interior climate of a building, Moisture in the air will dissipate from the warmer area of a building to the colder area and can cause serious deterioration of historic materials. Condensation can form if the dew point occurs within the building wall, particularly one that has been insulated (see a and b), Even when vapor retarders are installed (c), any non-continuous areas will provide spaces for moisture to pass. Wall Section Drawings: NPS files

Planning the New System

Climate control systems are generally classified accord ing to the medium used to condition the tem~erature:

air, water, or a combination of both (see overvIew on page 6). The complexity of choices facinp a buildinp owner or manager means that a systematic approach IS critical in determining the most suitable system for a building, its contents, and its occup~nts. ~o m~tter .

which system is installed, a change m the mtenor ch mate 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 me chanical system, the owner of a historic buildi~g .

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 build~g and costs to an owner of selecting the wrong mecham-cal 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 combina tion of systems. In each case, the needs of the u~er, the needs of the building, and the needs of a collectIon or equipment must be considered. It may not be neces- .

sary to have a comprehensive climate control sy'stem if climate-sensitive objects can be accommodated m spe cial 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, ex haust fans, and other "low-tech" means. Modern standards for climate control developed for new con struction may not be achievable or desir~ble for ?istoric buildings. In each case, the lowest level of mterventlOn 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 arc~it~ctural spaces. What is the intensity of u~e of the buildmg:

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 inappro priate for the building.

2. Assemble a qualified team. This team ideally should consist of a preservation architect, mechanical engineer, electrical engineer, structural engine~r, and preservation consultants, each knowledgeable m codes and local requirements. If a special use (church, mu-seum, 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 fac tors: the preservation of the historic architecture (aes thetics and conservation), requirements imposed by mechanical systems (quantified heating and cooling loads), building codes (health and safety), ten.ant re quirements (quality of comfort, ease of operatIon), ac cess (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 con struction materials and mechanical systems? What con dition 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 suppres sion systems. Where can energy efficiency be improved to help downsize any new equipment added, an?

which of the historic features, e.g. shutters, awnmgs, skylights, can be reused (see. figure 7)? Evaluat~ air infiltration through the extenor envelope; momtor the interior for temperature and humidity levels with hy grothermographs for at least a year. Identify building, site, or equipment deficiencies or the presence of .as bestos that must be corrected prior to the installation or upgrading of mechanical systems.

6. A condition assessment during the planning stage would identify this round radiator in a small oval-shaped vestibule as a significant element of the historic heating system. In upgrading the mechanical system, the radiator should be retained. Photo: Michael C. Henry, P.E. , AlA.

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 conden sate 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 up grade older systems. Most piping was cast iron although cop per systems can be used if separately zoned. Modern cast iron baseboards and copper fin-tubes are available. Historic radia tors can be reconditioned.

cast iron baseboard cast iron radiator

Fan Coil Units: Fan coil systems use terminal cabinets in each room serviced by 2, 3, or 4 pipes approximately 1-1/2" 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 ben ches, can be built.

return piping Fan coil unit

CENTRAL AIR SYSTEMS

The basic heating, ventilation and air conditioning (HVAC) sys tem is all-air, single zone fan driven designed for low, medium or high pressure distribution. The system is composed of com pressor drives, chillers, condensers, and furnace depending on whether the air is heated, chilled or both. Condensers, gen erally air cooled, are located outside. The ducts are sheet metal or flexible plastic and can be insulated. Fresh air can be circu lated. 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.

supply

Heating furnace with cooling coil

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.

Cooling cycle compressor refrigerant flow he.li" ~ ,',"po .. lo.

expansion valve cycle reverses for heating

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 han dling 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 I a complex of buildings.

This system overcomes the disadvantages of a central ducted ;

system where there is not adequate horizontal or vertical runs I for the ductwork. The equipment, being smaller, may also be

I quieter and cause less vibration. If only one air handler is being utilized for the building, it is possible to house all the equip-ment 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.

Water-serviced Air Handlers:

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t) return air o fresh air intake

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~~~~~~cooling coil ~ humidifier foi1 I Conditioned ~, ~ Air handler space ~n

(J return air

Chiller In

Fresh air intake

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 hu midity may harm sensitive collections or furnishings. If an inte grated 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 dam aging 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.

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(Air conditioner)

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.

exhaust fan

Dehumidifiers: For houses without central air handling sys tems, a dehumidifier can resolve problems in humid climates.

Seasonal use of dehumidifiers can remove moisture from damp basements and reduce fungal growth.

portable unit ~ (dehom;difie,) lA

Heaters: Portable radiant heaters, such as those with water and glycol, may provide temporary heat in buildings used infre quently or during systems breakdowns. Care should be taken not to create a fire hazard with improperly wired units.

portable heater electric baseboard

Compiled by Sharon C. Park. Sketches adapted from Architectural Graphic Standards with permission from John Wiley and Sons.

4. Prioritize architecturally significant spaces, fin ishes, and features to be preserved. Significant archi tectural spaces, finishes and features should be identified and evaluated at the outset to ensure their preservation. This includes significant existing mechan ical systems or elements such as hot water radiators, decorative grilles, elaborate switchplates, and non mechanical architectural features such as cupolas, tran soms, or porches. Identify non-significant spaces where mechanical equipment can be placed and sec ondary 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, mezza nines, 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 abate ment 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 build ing? How are fire separation walls and rated mechani cal 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 require ments 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 hu midification. What are the initial installation costs, pro jected fuel costs, long-term maintenance, and life-cycle

7. Operable skylights and grilles that can be adapted for return air should be identified as part of the planning phase for new or upgraded mechanical systems. Photo: Dianne Pierce, NPS files.

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 trade-offs between one large central system and multiple smaller systems?

Should there be a forced air ducted system, a 2-pipe fan coil system, or a combined water and air system?

What space is available for the equipment and distribu tion 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.

8. In considering options for new systems, existing spaces should be evalu ated for their ability to house new equipment. This sketch shows several areas where new mechanical equipment could be located to avoid damaging significant spaces. Sketch: NPS files

9. Improving ventilation through traditional means should not be overlooked in planning new or upgraded HVAC systems. In mild climates, good exhaust fans can often eliminate the need for air conditioning or can reduce equip ment size by reducing cooling loads. Photo: Ernest A . Conrad, P.E.

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 a-f). 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 re sources. 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 back-up monitors in place if buildings have col lections, 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 archeo logical 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. Some times, 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. Spe cial archives, storage vaults or computer rooms may need a completely different climate control from the rest of the building. Determine temperature and hu midity levels for occupants and collections and ventila tion requirements between differing zones. Establish if the system is to run 24 hours a day or only during op erating or business hours. Determine what controls are optimum (manual, computer, preset automatic, or other) . The size and location of the equipment to han dle 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 sys tem 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 interpre tive 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 in stalled 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 pre serve the historic building. Existing chases should be reused whenever possible.

4. Balance quantitative requirements and preserva tion 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 ceil ing areas must be slightly lowered to accommodate ductwork or piping, these should be in secondary ar eas away from decorative ceilings or tall windows. If modern fan coil terminal units are to be visible in his toric 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 regis ters 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 re moved 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, ex tremely 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. Back-up systems are also needed to pre vent 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 sys tem 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 at tempts to adjust comfort levels, or to save energy over weekends and holidays, can cause great damage.

10. The following photographs illustrate recent preservation projects where careful planning and design retained the historic character of the resources.

before after

a. Before and after of a circa 1900 school entrance. The radiators have been replaced with a two-pipe fan coil system built into bench seats . The ceiling was preserved and no exposed elements were required to add air conditioning. Piping runs are under the benches and there was no damage to the masonry walls. Photos: Notter Finegold + Alexander Inc. and Lautman Photography, Washington.

historic after

d. Auditors Buildings, Washington, D.C. This upper floor workspace had been modified over the years with dropped ceilings and partitions. In the recent restoration, the open plan workspace was restored, the false ceiling was removed, and the fireproof construction was exposed. A vari able air volume (VA V) system using round double shell exposed ductwork is in keeping with the industrial character of the architectural space.

Photo: Kenneth Wyner Photography, courtesy of Notter Finegold + Alexander Inc. Before view provided by Notter Finegold + Alexander/Mariani.

b. Central air conditioning was installed in the corridors of this circa 1900 school building by adding an air handler over the entrance from a vestibule.

The custom-designed slot registers provide linear diffusers without detracting from the architecture of the space. Photo: Lautman Photography courtesy of Notter Finegold + Alexander Inc.

e. Town Hall, Andover, MA. The upstairs auditorium was restored and new mechanical systems were installed. Perimeter baseboard radiation provides heat and air handlers, located in the attic space provide air conditioning. The cast iron ceiling grille was adapted for return air and the supply registers were installed in a symmetrical and regular manner to minimize impact on the historic ceiling. Photo: David Hewitt/Anne Garrison for Ann Beha Associates.

c. Conference room, Auditors Building, Washington, D.C. The historic steam radiators were retained for heating. The cast iron ceiling register was retained as a decorative element, but made inoperable to meet fire codes.

Photo: Kenneth Wyner Photography courtesy of Notter Finegold + Alexan der Inc.

f. Homewood, Baltimore, MD. This elegant circa 1806 residence is now a house museum. The registers for the forced air ducted system seen behind the table legs, are grained to blend with the historic baseboards. The HVAC system uses a water/air system where chilled water and steam heat are converted to conditioned air. Photo: Courtesy Homewood Museum, Johns Hopkins University.

HVAC Do's and Don'ts

DO's:

• Use shutters, operable windows, porches, curtains, awnings, shade trees and other historically appro priate non-mechanical 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 switchplates, 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 sys tem for formal spaces, more exposed systems possi ble 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 con straints of the building. Use multi-zoned smaller units in conjunction with existing vertical shafts, such as stacked closets, or consider locating equip ment 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 moni tors 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 mal functions 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 sys tem or an appropriate place to put it.

• Don't over-design a new system. Don't add air con ditioning or climate control if they are not abso lutely 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 fea tures, or alter historic spaces when installing new systems.

• Don't drop ceilings or bulkheads across window openings.

• Don't remove repairable historic windows or re place them with inappropriately designed thermal windows.

• Don't seal operable windows, unless part of a mu seum where air pollutants and dust are being controlled.

• Don't place condensers, solar panels, chimney stacks, vents or other equipment on visible por tions 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, mon Itor, 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 ex ~mple, molds in condensate pans can block drainage lmes and cause an overflow to leak onto finished sur faces). 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 ad~ition to regular cyclical maintenance, thorough mspectIons should be undertaken from time to time to evaluate the continued performance of the climate con trol s):,stem. As the system ages, parts are likely to fail, and SIgns of trouble may appear. Inadequately venti lat~d. areas may smell musty. Wall surfaces may show stammg, wet patches, bubbling or other signs of mois ture damage. Routine tests for air quality, humidity, and temperature should indicate if the system is per forming properly. If there is damage as a result of the new system, it should be repaired immediately and then c~osely monitored to ensure complete repair.

EqUIpment must be accessible for maintenance and should be visible for easy inspection. Moreover, since ~echanical systems last only 15-30 years, the system ~tself mu~t be "reversible." That is, the system must be mstalled m such a way that later removal will not dam age t~e building. In addition to servicing, the back-up momto~s that signal malfunctioning equipment must be routmely checked, adjusted, and maintained.

Checklists should be developed to ensure that all as pects. of routine maintenance are completed and that data IS reported to the building manager.

a

Conclusion

The successful integration of new systems in historic buil~ings can be challenging. Meeting modern HVAC requrrem.ents for human comfort or installing con tr~lled clImates for museum collections or for the oper atIon 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, ventila~ing, and air conditioning sys tem eXIsts. In undertakmg changes to historic build ings, 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 th<if should be preserved or reused, prioritize the preservation objectives, understand the impact of new interior climate condi tions 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 occu pants or collections can be detrimental to the long-term preservation of the building. With a careful balance ?etw:en the preservation needs of the building and the mtenor temperature and humidity needs of the occu pants, a successful project can result.

11. Durin$ the restoration of this 1806 National Historic Landmark (photo a), a new climate control system was installed. The architects removed all the earli ~; m~c7anlca~~1ulp7ent fr0 b m l the house and Installed new equipment in a 30' x 40' concrete vault located underground 150 feet from the house itself (photo . n y con I lOne air IS own Into the house reusing much of the circa 1930s ductwork. Photos: Thomas C. Jester.

Bibliography

Banham, Reyner. The Architecture of the Well-Tempered Environment.

London: The Architectural Press, 1969.

Burns, John A., AlA. Energy Conserving Features Inherent in Older Homes. Washington: US. Department of Housing and Urban Devel opment and US. 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) Philadel phia: 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: US. Department of the Interior, 1978.

Turberg, Edward. A History of American Building Technology. Durham:

Durham Technical Institute, 1981.

cover photo: This historic coal boiler continues in use after its conversion to an oil-fired boiler. Photo: NPS files

Acknowledgements

The author gratefully acknowledges the invaluable assistance of Michael C. Henry, P.E., AlA, 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, induding Tom Keohan and Catherine Colby, Rocky Mountain Region; Michael Crowe, Western Region; Mark Chavez, Midwest Region; Randall J.

Biallas, AlA, Chief, Park Historic Architecture Division, and George A. Thorsen, Historical Architect, Denver Service Center.