Toledo and Price

Introduction

The environment plays a major role in material deterioration, and buildings are the first shield against it. In the humid tropics, strong solar radiation and heat gains, coupled with a naturally high air moisture content, may make internal environments unbearable both for human beings and materials. Apart from discomfort, these "green-house" conditions may promote biodeterioration. Mould growth, in particular, is a threat in still or enclosed spaces.

It is true that hot and humid conditions help accelerate material decay (Thomson 1986), but it is also true that museum objects acclimatise to local prevailing conditions, and that it may be better to have internal stable conditions, regardless of figures, than variable ones (Michalski 1993). But how high and harmful to museum objects are natural levels of humidity and temperature in the humid tropics indoors? How even (or unstable) is the climate (both external and internal), and on what grounds?

To remedy these conditions, small Brazilian museums, often housed in historic buildings, are often naturally ventilated and lit. In hot and humid regions, buildings can be open to benefit from ventilation, because the climate is mild and allows for it, internal conditions being almost the same as those external. In the humid tropics, it is well acknowledged, both in traditional and contemporary architecture, that shading and ventilation are key points to control and improve internal climate conditions (Givoni 1994).

Only a few museums are air conditioned in Brazil, mainly the large and national ones. In the case of Northeast Brazil, the misuse of these systems is notorious, since the institutions often operate their plants solely for the visitors' comfort. They are switched on during working hours, and switched off at the end of the day. Which of the two attitudes is the most damaging to museum collections? Nobody knows yet, for little is known about hot and humid museums.

To know more about hot and humid museums, a case study was set up in the coast of Northeast Brazil, and the two types of internal environment control were examined. Firstly, the degree of environment stability was assessed in three local museums. This paper thus looks at internal climate fluctuation, and discusses each building's performance in safeguarding museum collections.

The tropical climate and museum buildings

Recife and Olinda are situated 8° below the equator, the former being approximately 7 m above sea level, and the latter 50 m. A hot and humid, but fairly mild and stable, climate dominates this region of Brazil. The mean air temperature and relative humidity figures are 26° C and 79% RH (National Institute of Meteorology 1996). The climate presents two seasons: a wet and cooler season, from May to August, and a dry and hotter one, from September to April.

Not only to have an overall view of hot and humid museums, but also to evaluate architectural changes, in concept and detailing, covering both period of construction and type of environmental control, three museum buildings were chosen as a small but representative sample. Two are naturally ventilated historic buildings from the 18th and 19th centuries, and the third, a modern air-conditioned one, from the 1960s.

To measure air temperature (T) and relative humidity (RH), three pairs of loggers were placed in each building, as follows: one outdoors (in a shielded place), one in the centre of a room, and one inside a display case, so that usual museum environments could be observed. In the case of the 18th century building, which exhibits only easel paintings, the space between the picture and the wall was monitored as the third and smallest microclimate.

Considering the relative steadiness of the climate, the loggers were programmed for hourly readings. As a first treatment for collected data, weekly maximum and minimum levels of air temperature and relative humidity were identified for each building, and then compared through tables and graphs, according to Oreszczyn (Oreszczyn, et al. 1994), and are the main reference for this paper.

The first building to consider is the 18th century edifice that houses the Museum of Contemporary Art of Pernambuco - MAC. This building was a religious prison during the Brazilian colonial period. Its construction dates from 1765. It is a simple yet imposing two-storey building on a hill in Olinda. Its fabric, made of brick and sandstone, is quite thick (about 1 m). The building is covered by a thin pitched roof made of wood and burnt clay tiles. It has a large area of windows provided with security bars that remain open day and night. This listed building was restored in 1966 to become a museum. Most of its collections are paintings on canvas, hung directly on the walls (Figure 1).

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Figure 1: The Museum of Contemporary Art of Pernambuco's main facade.

The interior of the oldest museum building is the most humid and variable of the three, presenting not only the highest RH figures, but also the largest RH daily ranges. Not only relative humidity but also temperature figures vary following those of the exterior. Figures taken from the three spots measured are quite similar, showing that, despite its large thermal inertia, the building does not have much buffering ability against climate. On the contrary, the interior of the building seems to retain detrimental conditions longer, and very often internal conditions are worse than those found outdoors. Apart from this, its thin roof brings a great deal of climatic instability, at least to the first floor, since it allows daily gains and losses of heat and moisture to the exterior.

The second is the 19th century building that houses the State Museum of Pernambuco - MEP. This building was originally a villa, a single-storey dwelling of an eclectic taste, which belonged to a wealthy Portuguese family during the Brazilian imperial period. The second storey was added in the beginning of the 20th century. In the 1940s it was refurbished to become a museum. It is located in Recife's city centre, where traffic is heavy and air pollution may be a cause of concern. It is provided with a veranda on its western facade. This high-ceilinged building is a medium-weight construction whose walls are made of plain burnt bricks about 40 cm thick. It also has a large area of doors and windows, most of which are open during the day and closed at night. This is a historical-ethnographic museum exhibiting a variety of objects, ranging from archaeological pieces, paintings, and furniture, to native people's artefacts (Figure 2).

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Figure 2: The State Museum of Pernambuco's main facade.

The interior of the 19th century building is the most stable of the three. Apart from being hotter and drier than the first one, it has a great ability to buffer external conditions. It is able to dampen both external air temperature and relative humidity fluctuations, and this can be due to two factors. The combination of a veranda covering external walls might be an answer. The existence of cross ventilation during the day, and the maintenance of the building closed and hot during the night, might be another answer.

The third is the 20th century building that houses the Museum of Man of Northeast - MHN of Joaquim Nabuco Foundation. This is a purpose-built museum building, and winner of a local competition in the 1960s. This two-storey building was originally naturally ventilated, and provided all over with upper openings facing prevailing winds. In the beginning of the 1980s it was incorporated by Joaquim Nabuco Foundation and refurbished to house a larger collection. It was then sealed and air-conditioned. It is an exemplar of the Brazilian modern architecture, adapted to local climate conditions, with screened walls, patio, and an open lobby. The building can be considered a light-weight one, due to its double hollow brick walls, about 30 cm thick. It is an anthropological museum, exhibiting sugar-making related objects, north-eastern cultural objects, and arts and crafts (Figure 3).

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Figure 3: The Museum of Man of Northeast's main facade.

The interior of the 20th century building is the driest of the three. Because it is sealed, it remains dry even when the machines are switched off. Also because of an interrupted run of the air-conditioning plants, internal T figures and fluctuation are opposite, and as large as, those of the outside; the RH fluctuation equals that of naturally ventilated museums, showing much lower figures though.

When comparing the museums' locations, the 20th century building's site is the most humid at 85% RH, the 19th century building's is the driest at 55% RH, and the 18th century building's falls in-between at 75% RH. External T figures remain quite alike. Inside the museums, though, the highest RH fluctuation is presented by the 18th century museum building (about 30 percentage points), while the lowest is presented by the 19th century one (about 15 percentage points). The 20th century building is in-between (about 20 percentage points). For indoor air temperature, the 20th century building presents the highest fluctuation (about 10° C), and the 19th century building, the lowest one (about 2.5° C). The 18th century building fluctuates 3.5° C on average (Figure 4).

Temperature graph

Figure 4: Weekly maximum and minimum fluctuations for each museum building.

Conclusion

The results so far reveal the 19th century museum's interior as the most stable of the three, since it presents the lowest RH and T swings, and it is worth noting that these conditions are maintained in spite of the building being naturally ventilated. Its veranda, coupled with its opening regime, may contribute to this satisfactory situation. On the other hand, the 18th century building, being also naturally ventilated, is the most problematic, presenting both high climatic figures and high daily fluctuations. Its thermal inertia coupled with its opening regime may contribute to this detrimental situation.

Computer packages to simulate real and ideal environments have been increasingly produced and used to validate environmental data and to assert assumptions for existing or purpose-designed buildings. Some of them, available at the Bartlett School of Graduate Studies, University College London, are being used in the current stage of this research, in an attempt to evaluate some passive methods of museum environment control, such as roof insulation, window screening and shading, and wall treatment. The results are to provide the basis for guidelines for controlling the museum environment in the humid tropics.

Acknowledgements

This PhD research has been sponsored by Fundação Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES, Brazilian Government, and made possible thanks to Yuri Amorim, who was responsible for data collection in Brazil.

References

Givoni, B. 1994. Passive and Low Energy Cooling of Buildings. New York: Reinhold.

Michalski, S. 1993. "Relative humidity: a discussion of correct and incorrect values." In:, Pre-prints of the ICOM 10th Triennial Meeting, Washington DC, USA. Washington D.C.: ICOM.

National Institute of Meteorology - 3° DISME. 1996. Registros Climatológicos Diários de Superfície 1995/1996.

Oreszczyn, T., Cassar, M., and Fernandez, K. 1994. "Comparative study of air-conditioned and non air-conditioned museums." In: Preventive Conservation - Practice, Theory and Research: Pre-prints of the IIC Congress, Ottawa, Canada. Ottawa: ICOM.

Thomson, G. 1986. The Museum Environment. Oxford: Butterworth-Heinemann.