1 INTRODUCTION

Environmental monitoring is used in the field of cultural heritage according to different purposes of conservation. Firstly, the microclimatic monitoring is used to protect work of arts inside large containers such as museums, palaces, and archives (Camuffo et al. 2001, 2002, Brimblecombe et al. 1999, Gysels et al. 2004, Liu et al. 2010). Secondly, the environmental survey is used for monitoring architectural structures hosting heritage such as frescos, graffiti etc. (Bernardi et al. 2000, Becherini et al. 2010, Garcia et al. 2010).

Each type of work of art requires specific climatic conditions of conservation that mainly depend on the typology and physical features of the heritage. In buildings hosting frescos, for example, some very frequent decay forms as the presence of soluble salts and microbiological agents are strongly associated to the internal climatic conditions. Therefore, both in museums and buildings temperature and humidity parameters should be monitored constantly to put in light the risk conditions and establish alert thresholds (Varas et al. 2014).

For this purpose, a pilot activity related to the microclimate monitoring of a church located in Irsina (Basilicata, Southern Italy) has been started. Two monitoring systems are compared, a low cost (LC) system using Arduino and a commercial system (CS) whose technical features are in accordance with to the UNI EN 16242 rule. There is a large amount of potential in using automated tools for environmental monitoring based on these emerging LC hardware platforms, but in order to be truly useful the data they generate should be integrated with the existing systems. The basic idea is to reduce greatly the cost as well as significantly increase the applicability of LC monitoring systems on a large scale.

2 THE CASE STUDY: THE CRYPT OF SAN FRANCESCO D'ASSISI, IRSINA (MATERA)

2.1 Historical information and state of conservation

The Church of San Francesco d' Assisi in Irsina was founded in the early years of the 1100s (Mazzara 1926), the actual façade, instead, dates back to the early 1700s as well as the interior stucco walls. The crypt of San Francesco's church , located under the apse, was made up of a

Low cost strategies for the environmental monitoring of Cultural Heritage: preliminary data from the crypt of St. Francesco d'Assisi's, Irsina (Basilicata, Southern Italy)

M. Sileo, M. Biscione, F.T. Gizzi & N. Masini Institute for Archaeological and Monumental Heritage, Italian Research Council (CNR), Potenza, Italy

M.I. Martinez-Garrido Institute of Geosciences IGEO (CSIC, UCM) and Moncloa Campus of International Excellence (UPM-UCM, CSIC), Madrid, Spain

ABSTRACT: The environmental monitoring system apparently appears to be an easy tool, but it hides some drawbacks such as high purchase and maintenance costs. This implies that the use of technologies to monitor cultural heritage is somewhat limited to analyze sites where the degradation conditions are of particular relevance. With this in mind, the aim of such a research activity is to compare two monitoring systems in relation with the decay problems affecting the paintings of the crypt of St. Francesco d'Assisi's in Irsina (Basilicata, Southern Italy). The first system is a low-cost Arduino wireless platform based on open-source hardware and user friendly software. The second monitoring equipment is a standard commercial product. The basic idea of such a comparison is to attempt to reduce greatly the costs as well as significantly increase the applicability of long-term monitoring systems on a large scale.

quadrangular tower belonging to a Norman castle. The crypt has a rounded arched vault that develops from the long sides. In such areas two large arches, a calotte-vain and an archway with a small door for access are opened respectively into the East side and in the other. The crypt is almost entirely frescoed, the frescos are present on the four walls and on the vault. They were painted between 1370 and 1373 (Nugent 1933) and attributed to workers probable from the Siena school (Mazzara 1926). The historical analysis of archive and bibliographic sources has allowed analyzing the state of conservation and the main restoration interventions that the crypt has undergone since 1926, year of its discovery. Such information is resumed in Table 1. Table 1. State of conservation and restoration interventions on the Frescoes.

1926 Soluble salts on the frescoes, microbiologic agents, moisture, plaster with problems of detachment, dust and neglect

1927 Restoration by Tullio Brizi, consolidation of the plaster and color, cleaning 1969-72 Structural consolidation at vault and external structures of the Crypt 1971 Presence of insects on the frescoes 1977 Deterioration due to moisture and detachment of the plaster 1978-79 Restoration, fixing of crumbling plasters and of paint layer, climatological investigations,

cleaning tests and stratigraphic sections, analysis of the superficial water content, analysis of soluble salts (SSBBAA).

Post earthquake 1980-1981

Minor damages, in the crypt the walls were consolidated by injections of epoxy resins, fixing of paint film, removal of soluble salts from the surface, cleaning of painted surface, grouting the gaps and pictorial integrations (SSBBAA).

1995 Presence of moisture and condensation, worrying static-cracking situation 1996 Restoration, protection of painted facades with alchilalcossi hydrophobic silanes at

osmotic penetration, consolidation of the plaster, closure of injuries cleaning of painted surfaces, color fixing, removal of multiple layers of carbonate soluble salts. Work suspended in April 1997 for structural interventions.

2004 Fissures and cracks in the walls, the risk of swelling of the pictorial film

In particular, in the last century, the crypt frescos have been restored many times, as decay problems were never adequately solved at the origin. At present, the problems affecting the frescos are grouped into three categories:

1. the presence of biological materials that extend locally such as dark patina on the walls of the frescos at various levels on the arches and lunettes on the east wall and discontinuously on the south and north walls; 2. the presence of salts such as crystalline superficial veils or a powdery appearance whitish in color on most of the frescos; 3. the presence of cracks on the plaster on the walls and in several points appear to have caused the detachment of the plaster from the substrate. The diffusion of decay forms is such as to compromise a long-term preservation of a good part of the fresco. The aim of microclimatic monitoring is to identify the causes of presence of biological materials and salts (such as the presence of condensation or infiltration of water) and to propose a long-term solution for a correct conservation of the frescos.

3 EXPERIMENTAL APPARATUS AND METHODOLOGY

The main thermo-hygrometric parameters inside the Crypt were investigated in order to study the microclimatic conditions in which the frescos have been preserved. The monitoring started in September 2013 with the installation of the commercial system (CS) and will continue for one year. In November 2013 the low-cost system (LC) was also installed so the comparison of the data discussed in this work includes the period from November to February. Anyway, the period investigated is not representative of the general microclimatic conditions of the site under study because it includes only the 2013/2014 winter, with no intermediate season (spring) when

the condensation phenomena are more probable. In order to understand the conservation conditions of the frescos, the condensation phenomenon was monitored on the walls using the measured values of the thermo-hygrometric parameters.

The experimental apparatus is composed of two microclimatic monitoring systems, a commercial system (CS) and a low-cost system (LC) designed and realized with free hardware and software. The instrumental characteristics of the CS and LC sensors are reported in Table 2. Table 2. Instrumental characteristics of the sensors of the CS and LC systems.

Parameters Measure

range Accuracy Repeatability

Time of acquisition

Time of data transmission

CS Temperature

sensor -40/+ 60 °C +/- 0.1 °C +/- 0.1 °C 5 minutes 12 hours

LC Temperature

sensor -55/+125 °C

+/-0.3 °C (-10/+30°C)

+/-0.3 °C 5 minutes In real time

CS Humidity

sensor 0/100%

+/-0.8% (10-80%)

>0.5% 5 minutes 12 hours

LC Humidity

sensor 0/100%

+/-2% (-40/80%)

+/- 1% 5 minutes In real time

The thermo-hygrometric parameters are measured in seven different portions of the Crypt;

CS and LC sensors are placed in each area, so it is always possible to compare data from the two types of monitoring systems. The detection of air temperature and humidity is carried out in two places, one outside the building on the north side (Fig. 1G) and the other at the center of the crypt at a height of about 2.5 meters (Fig. 1A).

Figure 1. The Frescos of the Cript of San Francesco D’Assisi, Irsina and the schematic sensors localization of the monitoring systems.

The other five measurement positions are located on the south wall at two heights, 1.5 (B) and 2.5 (C) meters above the floor on the frescoed surfaces affected by the presence of biological materials and cracks, others are located on the east wall inside the two SE (D) and NE (E) lunettes, where salts, biological materials and cracks are likely to be found, the last sensor is

located on the north wall (F) at a height of about 2.5 meters where biological materials, salts and cracks are present.

The data from external thermo-higrometric conditions and rainfall are made available by Alsia (Agenzia Lucana di Sviluppo e di Innovazione in Agricoltura - Regione Basilicata) from S. Maria D'Irsi weather station.

4 PRELIMINARY RESULTS

4.1 Microclimatic analysis

The microclimatic monitoring started in September 2013 with the installation of the CS system. The LC system was installed in November, so the preliminary data analyzed in this work are related to four months from November 2013 until the end of February 2014. The monitoring involved 6 servings in the Crypt. In particular, in position A the temperature and the humidity of the air have been analyzed, while in positions B, C, D, E and F the surface temperature and the air humidity in proximity of the surfaces were monitored (Fig. 1). Indoor data were correlated with those of the external weather station in Santa Maria d'Irsi, made available by 'Alsia. Following are reported the results of these correlations.

The air temperature inside the Crypt followed the thermal trends of the external air in the whole monitoring period. Nevertheless the amplitude of the daily thermal cycles of the internal air was generally lower than the external one because of the wall thermal inertia of the crypt. This was also the responsible for the many hour delay between the air temperature highest and lowest values inside and outside the Crypt (Fig. 2) (Martínez-Garrido et al. 2014). CS and LC temperature are completely overlapped, small differences are on the order of +/-0,5 °C on the average.

Figure 2. T min/med/max outside (°C), CS_T and LC_T air temperature from center of crypt (°C), Rainfall (mm of rain).

The air average temperature level inside the crypt was generally higher than outside, indeed during the night the air temperature inside did not decrease as much as outside, because of the stone inertia, so, notwithstanding the little dimension of the crypt, a gradual accumulation of thermal energy was observed, resulting in a thermal level inside the crypt higher than the outside. Relative humidity (RH) was very variable inside the crypt (Fig.3), assuming in the whole period values between 38 and 88% (CS) and until 92 % (LC) , with daily excursions of 20%, thus generating great stress on the frescoed surfaces. This variability is caused from the external RH, and depends directly on rainfall and inversely on temperature (Fig. 3). There are some differences from CS and LC relative humidity, generally LC_RH is 5% higher starting from December (Fig.4).

Figure 3. Relative humidity of air from center of crypt compared with outside. RH min/mean/max outside (%), CS_RH and LC_RH (%), Rainfall (mm of rain).

Figure 4. Thermo-hygrometric conditions from center of the crypt (LC and CS), Rainfall (mm of rain).

The exchange inside/outside is very high, in fact RH trend are directly correlated to rainfall data and inversely to thermal air data (Fig. 4). This behavior is typical of an opened environment, where the main heat and humidity transfer processes are regulated by outside conditions.

The mix ratio (CS_MR and LC_MR curve in Fig. 5) between measurements at the center of the room and near to the walls (an example is also reported in figure 5 (data from North Wall, TN) shows relatively higher values in the month of November 2013 while these values are lower in the subsequent period. In order to identify water vapor condensation on the fresco surface, the theoretical curve of the dew-point (DP) temperature was calculated on all walls by using the formula suggested by Camuffo (1983) and by the UNI EN 16242 (2013), an example from the North wall is shown in figure 5. The data show that the contact temperature of the surfaces monitored is always greater than dew point temperature on all the walls investigated (Fig. 5, Data from North Wall). In particular, the dew point spread decreases during the winter (December to February), but the temperatures are 2 °C higher than the dew point theoretical curve (Fig .5 on 02/12/2013). This does not exclude that in the spring months this difference may be canceled resulting in the formation of condensation on the walls. the microclimatic monitoring in the following months will provide further explanations.

Figure 5. CS_T N and LC_TN are the temperatures on the North wall (°C); CS_DP and LC_DP are dew point curves (°C); CS_MR and LC_MR are mix ratio curves.

4.2 Reliability of the two monitoring systems

The comparison between the two monitoring systems, commercial (CS) and low-cost (LC), was carried out by assessing their hardware and software reliability, acquisition and transmission, data security, as well as the reliability of the data collected. With regard to hardware systems, both systems use wifi data loggers with differences in the type of power supply and consumption, in fact CS uses 4 x 1.5 V alkaline batteries that need to be replaced every 2 months (1 month in winter). The LC system using data loggers is powered with long-life lithium batteries, which allow sampling for over 5 months consecutively. As regards data transmission, in CS the data stored by data loggers are sent to the web platform every 12 hours, but if UMTS signal decreases, the data are stored in the system and they are sent during the next connection; such strategy is adopted to preserve data logger battery life. In LC the data collected are sent in real time in a wireless way to the acquisition system, which sends them in real time to a web platform where an instant view of the measured parameters is possible. This solution, however, has some limitations, in fact when the UMTS signal decreases, data are not sent successfully from the central unit, and this brings about a lack of data due to the lack of additional memory in data loggers, which is a configuration to reduce costs. the Lack of data is, however, a problem affecting both systems during the period monitored. Indeed for CS the sampling problems of data were recorded in particular for one of the humidity sensors that after about two months showed a drift of the results. Other problems have been the disconnections that affected two of the data loggers several times due to the missing wi-fi signal, thus generating different periods of non-sampling. On the other hand, LC system, in spite of being affected by the UMTS signal fluctuations, shows only an occasional loss of data. Regarding the reliability of the data, LC and CS systems show quite similar temperature and humidity data for the period under review, there are small variations depending on the slightly different placements of LC and CS sensors in each area of the Crypt (Fig. 4). These results validate the low-cost system for the study of microclimate and also for the connection to automatic systems to control humidity and temperature.

5 CONCLUSIONS

Environmental monitoring is highly infeasible due to high costs. Therefore, we have analyzed comparatively two monitoring systems, the low-cost Arduino equipment and the standard commercial one. This approach has been tested to monitor the thermo-hygrometric conditions of the crypt of St. Francesco d'Assisi's in Irsina (Basilicata, Southern Italy).

The preliminary results obtained by comparing the data recorded from the two systems show almost the same trend in temperature and humidity values in the different positions of the crypt. This preliminary result seems to confirm the suitability of the low-cost system as a valuable tool for monitoring the indoor environment. However, these deductions should be confirmed by long-term monitoring analysis which will be carried out during the next months.

ACKNOWLEDGEMENTS The Authors thank Basilicata Region for supporting this activity in the framework of the Project “PRO_CULT” (Advanced methodological approaches and technologies for Protection and Security of Cultural Heritage) financed by Regional Operational Programme ERDF 2007/201. The Authors thank Superintendence for Architectural Heritage and Landscape of Basilicata, Matera and also the Arcidiocesi Matera-Irsina. M.I. Martínez-Garrido participation was supported by a Moncloa Campus of International Excellence (UPM-UCM,CSIC) International Program for Attracting Talent fellowship.

REFERENCES Becherini, F., Bernardi, A. & Frassoldati, E. 2010. Microclimate inside a semi-confined environment:

Valuation of suitability for the conservation of heritage materials. Journal of Cultural Heritage 11: 471-476.

Bernardi, A., Todorov, V. & Hiristova, J. 2000. Microclimatic analysis in St. Stephan’s church, Nessebar, Bulgaria after interventions for the conservation of frescoes. Journal of Cultural Heritage 1: 281-286.

Brimblecombe, P., Blades, N., Camuffo, D., Sturaro, G., Valentino, A., Gysels, K., Van Grieken, R., Busse, H.J., Wieser, M., Kim, O. & Ulrych, U. 1999. The indoor environment of a modern museum building, the Sainsbury Centre for Visual Arts. Norwich, UK. Indoor Air 9: 146-164.

Camuffo, D. 1983. Indoor dynamic climatology: Investigations on the interactions between walls and indoor environment. Atmospheric Environment 17(9): 1803-1809.

Camuffo, D., Van Grieken, R., Busse, H-J., Sturaro, G., Valentino, A. Bernardi, A., Blades, N., Shooter, D., Gysels, K., Deutsch, F., Wieser, M., Kim, O. &Ulrych, U. 2001. Environmental monitoring in four European museums. Atmospheric Environment 35(S1): S127-S140.

Camuffo, D., Bernardi, A., Sturaro, G. & Valentino, A. 2002. The microclimate inside the Pollaiolo and Botticelli rooms in the Uffizi Gallery. Florence. Journal of Cultural Heritage 3: 155-161.

Garcia-Diego, F.J. & Zarzo, M. 2010. Microclimate monitoring by multivariate statistical control: The renaissance frescoes of the Cathedral of Valencia (Spain). Journal of Cultural Heritage 1: 339-344.

Gysels, K., Delalieux, F., Deutsch, F., Van Grieken, R., Camuffo, D., Bernardi, A., Sturaro, G., Busse, H.J. & Wieser, M. 2004. Indoor environment and conservation in the Royal Museum of Fine Arts, Antwerp, Belgium. Journal of Cultural Heritage 5: 221-230.

Liu, B., Chen, X., Fang, D., Perrone, A., Pispas, S. & Vainos, N.A. 2010. Environmental monitoring by thin film nanocomposite sensors for cultural heritage preservation. Journal of Alloys and Compounds 504S: S405-S409.

Martínez-Garrido, M.I., Aparicio, S., Fort, R. Anaya, JJ. & Izquierdo, M.A.G. 2014. Effect on solar radiation and humidity on the inner core of walls in historic building. Construction and Building Materials 51: 383-394.

Mazzara, M.S. 1926. Le pitture Quattrocentesche e Francescane di Irsina in Lucania. Reggio di Calabria: Soprintendenza per le antichità e l'arte del Bruzio e della Lucania.

Nugent, M. 1933. Affreschi del ‘300 nella Cripta di San Francesco ad Irsina. Bergamo: Istituto Italiano d'Arti Grafiche.

SSBBAA, Soprintendenza per i beni architettonici e paesaggistici della Basilicata. Relazione: Irsina (MT) - Chiesa di S.Francesco D'Assisi - affreschi della Cripta. Matera, 09/09/2004.

UNI EN 16242:2013. Conservazione dei beni culturali - Procedure e strumenti per misurare l’umidità dell’aria e gli scambi di vapore tra l’aria e i beni culturali.

Varas-Muriel, M.J., Martínez-Garrido, M.I. & Fort, R., 2014. Monitoring the thermal–hygrometric conditions induced by traditional heating systems in a historic Spanish church (12th–16th C). Energy and Building Journal 75: 119-132.