The space requires monitoring of humidity, temperature, and lighting, and measures were taken to ensure the ongoing safety and security of the items. Priorities included provisions for accessioning, cataloging, cleaning, preserving, storing, and displaying artifacts. In general, keeping relative humidity below 50% helps preserve archival items.
Ultimate parameters selected by the archive department included:
- Museum: 68°F and 40% +/- 3% RH, 43°F dewpoint.
- Research space: 68°F +/- 2°F and 40% +/- 3% RH, 43°F dewpoint.
- Archive vault: 67°F +/- 2°F and 43% +/- 3% RH, 43°F dewpoint.
The entire envelope of the archive areas was modified with a 2.5-in.-thick, closed-cell spray foam insulation. Fiberglass batt insulation with an integral vapor barrier was provided for the ceiling cavity and interior walls. A triple-pane, low-E glass window with mechanical shades was provided in the research workroom; doors were equipped with sealing astragals.
Instead of trying to control relative humidity with heat, a gas-fired desiccant dehumidifier with DX cooling was provided, allowing RH to be controlled and held constant year-round. An air-to-air energy exchanger recycles up to 85% of the energy from the conditioned building exhaust. In winter, energy from the exhaust air stream provides free heating; in summer, free cooling.
Particulate filtration is prioritized in the air handler design, including a prefilter, secondary filter, and ULPA filtration. Gaseous filtration was addressed with carbon-type filtration to control sulfur dioxide, nitrogen dioxide, and acetic acid.
The air distribution uses trickle-down displacement ventilation to minimize drafts while providing constant air change in the archive areas at 8 to 10 ACH. Constant minimum outside air was determined to exceed ASHRAE Standard 62.1 and is intended to maintain positive pressurization in the archive areas. The control strategy of dewpoint reset was successfully used to control the desiccant humidifier and duct-mounted humidifiers, precisely maintaining dewpoint at 43°F in the museum, research, and archive vault areas. Clean steam was used for the humidifiers, with water softener and RO water treatment.
Cost effectiveness was improved by minimizing moisture loads with the added vapor barrier, positive air pressurization, and door seals. Choosing a Type 1 silica gel desiccant with natural gas regeneration heat, vs. a low-temperature, glycol air-cooled chiller, avoided a $100,000 building electrical service upgrade and $300,000 in first cost for the chilled water system infrastructure.
