Airing Out the Library
July 01, 2001

By Staff
Appeared in California Libraries

Most of us have an appreciation for the written word and the buildings that house them. Often, books themselves dictate the need for special temperature and humidity conditions in libraries. Appropriate environments help reduce the deterioration rate of stored materials, be they books, film or tape, and provide health and comfort for the occupants using the space. Providing for the stability of that environment can often be as critical as the protection of the materials within that environment. As with any other building type, the building architecture of a library is integral in maintaining the appropriate indoor environment, so this is where we begin.

Reducing the Loads
The envelope of any building provides the means to shelter those inside from the weather outside. This is no different for a library. Libraries usually have windows and skylights, providing natural light, passive heat and views of the outdoors. The building envelope must be optimized to provide all of the above, and to reduce the direct solar gain and thermal transmission that adds to the air conditioning load and can be harmful to the materials stored and used within the library. This is accomplished in an integrated fashion by careful analysis of glazing performance and exterior shading devices. The envelope in general, and the window and skylight performance in particular, play an integral part in bringing in appropriate levels of natural light. During the heating season, materials located near exterior walls can be damaged by condensation formation due to the moisture differences between the indoor and outdoor environments. Appropriate consideration of thermal insulation and vapor barriers in the envelope construction can help to minimize this effect. Spectrally selective glass will allow appropriate levels of visible natural light to be brought in to the space while minimizing the heat generating solar gain brought into the space. Consideration of where this occurs is also important as short-wave (direct beam solar) radiation can be particularly damaging to materials.

Now that we have brought in natural light, let's make sure we can improve the energy performance of the building by allowing the high-efficiency artificial lights to be dimmed or shut off, automatically. Dimming or switching off lights whenever possible saves the electrical energy of the lights, but also reduces the air conditioning load (and potentially reduces the overall size of the air conditioning equipment) required to offset the heat gain of the lights.

Technology continues to evolve and impact the design of our libraries. Heat gain from computer equipment continues to decrease as efficiency increases, but the number of workstations or laptop hoteling locations increases with time. The design team should be aware of the current ASHRAE (American Society of Heating Refrigeration and Air Conditioning Engineers) research regarding the measured heat gain due to typical computer equipment. This research indicates that the heat rejection from today's computer equipment is significantly less than engineers typically design for.

With the envelope and internal loads reduced and optimized, there may be opportunities to use passive systems to condition the indoor environment.

Passive Conditioning and the Indoor Environment
In evaluating the appropriateness for passive conditioning in a library, the designers need to consider indoor air requirements and the capability of the local climate to meet these needs. Generally speaking, libraries have two groups of requirements. The first falls in to a general category of health and safety for building occupants as listed in ASHRAE Standard 55 (Thermal Environmental Conditions for Human Occupancy) and ASHRAE Standard 62 (Ventilation for Acceptable Indoor Air Quality). The second group of requirements pertains to special collections. In terms of both health and safety and collections requirements, it can be useful to label spaces in three ways, as shown in Table 1.

High Internal Sources of Contaminants (Dirty)
Low Internal Source of Contaminants (Clean)
Non-public access
  • Conservation laboratories, museum workshops (VOCs, fumes, dusts)
  • "Wet" collections (alcohol evaporation from poorly sealed jars in natural history collections)
  • Photographic collections ("vinegar syndrome" produces acetic acid vapors)
  • Most storage areas, vaults, library stacks
Public access
  • Display of conservation work in progress (unusual and temporary)
  • Galleries, reading rooms
Non-public access
  • Smoking offices (unusual)
  • Offices (non-smoking)
Public access
  • Cafeterias, rest rooms, spaces where smoking is permitted
  • Public spaces without food preparation or smoking

Table 1 Classification of Rooms for Museums and Libraries
(1999 ASHRAE Applications Handbook)

Most libraries have some precision control allowing for short-term temperature and relative humidity fluctuations of +/- 9°F and +/- 10% relative humidity, and allow for some seasonal fluctuations. Special collections and archival rooms are more precisely conditioned and closely controlled. The ASHRAE Applications Handbook provides guidance for these conditions.

Assuming outdoor climate conditions are appropriate, many portions of a library can use natural ventilation as the primary means of air conditioning the building for many hours each year. Careful consideration must be given to the location of inlets and outlets designed into the building envelope to insure that proper air movement occurs and occupied areas do not become stagnant. Outdoor noise sources, outdoor air quality, pest control issues, and security issues also require due consideration when assessing the locations of openings into the building, and whether natural ventilation is appropriate. The natural ventilation concept integrates very well with the natural lighting scheme.

Exposing thermal mass to the occupied space helps to dampen the daytime temperature swings and maintains a relatively stable indoor environment. The exposed thermal mass strategy is also extremely effective in combination with a night ventilation strategy, whereby the heat of the envelope and internal loads is absorbed and stored in the thermal mass, is radiated back to the space in the evening when the building is more lightly occupied or unoccupied, and exhausted from the building. The thermal mass is then cool and ready to absorb more heat energy the following morning.

Appropriate and Optimal Air Distribution Systems
The natural ventilation conditioning strategy is typically augmented by a mechanical system to offset the peak heating and cooling loads that occur during the summer and winter seasons. This is known as a mixed-mode ventilation system, and can be operated automatically throughout the year using magnetic switches in windows (to shut down or throttle back mechanical systems when windows are open) or using a seasonal switchover schedule. It is pointless incorporating a natural ventilation scheme if it is not integrally controlled with the mechanical system as the Library will essentially be air conditioning the outdoors at great operational expense.

Libraries typically utilize all-air systems to minimize any potential damage caused by leakage from water pipes or steam pipes. How that air is delivered to the space is another matter. More and more libraries are utilizing under floor air distribution or low-level displacement ventilation systems to provide the comfort cooling directly to the occupied zone. Displacement ventilation uses the natural buoyancy of the heat in the space to pull cool air from the floor level, through the occupied zone, and out of the space at high level. Air is delivered at floor level at a temperature in the range of 62°F to 68°F to prevent drafts, rather than the more conventional 54°F to 58°F for overhead air distribution. The elevated supply temperature means that less mechanical cooling is required, saving capital and operational costs, and 100 percent outside air (free cooling) can be delivered to the space for more hours throughout the year, improving the indoor air quality of the building (assuming acceptable outside air quality) and providing a more healthy environment for the building users.

Another consideration is the level of filtration of the air delivered to the spaces, and this is largely dependent upon whether archival documents are being stored or displayed. Archival areas typically require higher quality environments with close control of temperature and relative humidity, and may not be appropriate areas for natural ventilation.

Renewable Power Systems, Anyone?
Now that we have made a very energy efficient building, incorporated passive systems where appropriate and optimized our active systems, we need to determine how we are powering these efficient active systems. They are significantly smaller and more energy efficient than conventional systems, and there may be an opportunity to use renewable or near-renewable resources and on-site power generation to drive them. Installations of wind power, solar photo-voltaics, fuel cells and micro-turbines are now much more common than even five years ago, and there are federal, state and utility incentives available to help offset increased capital costs.

Better Jump on This Bandwagon!
The process and technologies used to achieve a high performance library are certainly not revolutionary. Today's design and construction industry is too often driven by capital cost and schedule, without due consideration of a building's true life cycle costs and the health and comfort of the building's users. The integrated design process of reducing a building's loads, incorporating passive systems, optimizing active systems and utilizing renewable resources is a true team effort involving owners, architects, engineers, occupants, contractors, etc. The process may take a little longer and require slightly higher design fees, but the resulting sustainable, high performance, healthy building will pay back year after year.