A Proposal for New Microclimate Indexes for the Evaluation of Indoor Air Quality in Museums

Abstract

A correct artwork preservation requires strict values of several microclimate parameters, in particular temperature, humidity, and light. In existing museums, the evaluation of the effectiveness of current building plant systems and management is essential to avoid artwork deterioration. In this work, we propose the use of five simple performance indexes that use monitored data to estimate the suitability of the whole museum system in the maintenance of benchmark values of temperature, humidity, and light. The new indexes also take into account microclimate daily span and spatial homogeneity, which can represent a criticality in the preservative process. We apply these new indexes to the results of a monitoring campaign in Palazzo Blu, a museum in Pisa, which lasted for almost four months during a temporary exhibition on Toulouse-Lautrec works. The indexes show a mainly acceptable instantaneous microclimate, but HVAC (Heating, Ventilating and Air Conditioning) system improvement is necessary to avoid high thermo-hygrometric daily span. This methodology is useful for the identification of microclimate criticalities and can help the cooperation between conservation experts and professionals giving hints to improve museum internal microclimate. In case ofalready optimal microclimate, these indexes can be useful in more complex analyses, including simulations of possible retrofit actions, keeping microclimate suitability as a constraint.Keywords: indoor microclimate quality index; museum; monitoring campaign; HVAC system On Microclimate for Artwork PreservationArtworks need strict microclimate conditions to be preserved. Each typology of artwork (e.g., paper, frescoes, paintings, stones) needs specific microclimate conditions for their preservation; in general, typical environmental parameters to be controlled are:• maximum daily and seasonal temperature difference ( • C);• mean relative humidity (%);• maximum daily and seasonal relative humidity difference (%);• maximum allowed illuminance (lx).For each type of artwork, standards suggest suitable microclimate intervals [1][2][3]; in some cases, however, if the artifact has been acclimatized to a particular historical climate environment, it is preferable to maintain these conditions instead of standard intervals, to avoid climatic shocks of the artwork [4,5]. Technical standard UNI 10829 [1] lists acceptable values for illuminance and optimal and acceptable ranges for temperature and relative humidity (in some cases, it is not possible to achieve, at the same time, visitor comfort and correct conditions for artwork preservation [6]). The presence of dust and gaseous pollutants and microbial and UV radiations can also threaten artwork integrity [7][8][9].

A procedure for identifying chemical and biological risks for books in historic libraries based on microclimate analysis

“…Daily Span Index (DSI) [38], which identifies the percentage of days in which the maximum values of temperature and relative humidity span do not exceed the allowed limits; Spatial Homogeneity Index (SHI) [38], which identifies the percentage of time in which microclimate is sufficiently homogeneous in the defined volume, according to the allowed spatial variations:…”

Data of temperature and relative humidity in a historic library in Portugal

“…They show some additional analyses of indoor microclimate in the Baroque Library of the University of Coimbra, Portugal. In the library, temperature and relative humidity were gathered during a 6-month monitoring campaign in several points of the rooms, to verify if the internal microclimate would lead to damage and deterioration of the 40 thousands old and rare books that are hosted inside [2] , [3] . The Library has a total volume of 7,000 m 3 and an area of about 1,250 m 2 distributed along three floors (the Noble floor, the Intermediate Floor, and the Academic Prison).…”

Preservational Climate Conditioning for Artworks on Paper

“…The variable presence of visitors and employees can cause significant and sudden changes of the environmental conditions; so the reaction of the HVAC system must be extremely quick in order to restore the design values of the thermal-hygrometric conditions for the conservation [4]. For example, Schito, et al have tracked the changes of air temperature and RH during the operating hours of the museum and noticed that there is an increase in the air temperature of almost 6°C and RH 15% during the busiest working hours [9]. These are worrying results, having in mind that monthly variations of RH should not exceed 5%.…”