Distribution of temperature, moisture and organic acids in storage facilities with heritage collections

The preservation of heritage collections in storage largely depends on the air quality conditions. Uncontrolled airflow transports unconditioned air into the building. Lowering the air exchange rate in unoccupied storage facilities is therefore essential to ensure acceptable climate conditions for the preservation of collections, while at the same time reducing the energy use for climate control. The concern is, however, that a restricted airflow can create uneven microclimates within a room, with thermal stratification as well as accumulation of indoor generated pollutants, which may accelerate the deterioration of the collections. This paper examines the air distribution within one storage building with a heating, ventilation and air-conditioning (HVAC) system, and in two rooms in another storage with semi-passive climate control. A sensor grid was established in each room in order to map the distribution of temperature, relative humidity (RH) and volatile organic acids determined as the sum of acetic and formic acid concentration. This study demonstrated that both tested ventilation forms upheld
an acceptable climate performance with appropriate temperature and moisture distributions and without air pockets producing problematic microclimates. However, organic acids accumulated in concentrations up to 134 μg m3 in parts of one storage room with semi-passive climate control. Whether to install a HVAC system with gaseous air filtration to remove organic acids will ultimately depend on the threshold level that caretakers are willing to accept.