Static and Dynamic Evaluation Methods for Energy Efficiency in Historical Buildings
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This paper presents the comparative results of energy evaluation of two historical churches. The thermal performance is evaluated by means of static and dynamic computer simulations. The experimental data serve as verification of the thermo-physical parameters of the building envelope components for carrying out energy performance simulations: energy bills, temperature and relative humidity of air. In particular, the simulations are performed using the thermal transmittance values defined by Italian standards, calculated according to the European standard and measured in situ on several ancient buildings with different wall thicknesses and construction techniques. The present study aims to understand which energy audit schemes, more or less evolved, simulate better the real energy performances of the historic buildings and identify the strengths and the limits of each software for static and dynamic energy simulations. The final goal includes the need of intervening on a “particular” type of heritage to optimize the requirements of energy efficiency and effectiveness together with the preservation of their cultural values. An accurate diagnosis is the first step to identify the suitable intervention. Finally, the evaluation of energy retrofit obtained by dynamic simulation permitted to assess the real energy performance improvement and demonstrate that, in some cases, the conservative interventions have a proven effectiveness. INTRODUCTION The energy performance enhancement in existing buildings is an important theme of the European policies on environmental sustainability. The transformation of the on-going energy consumption model towards its conscious management, damage reduction, progressive introduction of renewable energy sources, as a matter of fact, permits to improve the sustainability of the urban environment and reduce the environmental pollution. Energy and environmental programs should be developed starting with a thorough understanding of the behaviour of the historical buildings. This means to recognize the historical transformation of building, its present conditions, material and immaterial values, critical points and issues, and opportunities for the requalification. In this context, the evaluation of energy and environmental performances of the ancient buildings is important to optimize the energy efficiency and the preservation of their cultural values. The relevant issue of compatibility between the permanence of the existing “values” and the new ones related to sustainability can improve the energy performances and its adaptive use. Moreover, the specific study of the historical built heritage is very important to inspire new solutions based on empirical knowledge of the typical pre-industrial world. THERMAL BEHAVIOUR OF ANCIENT BUILDINGS The interventions on historical buildings require a widespread knowledge of history, dimensions, building techniques, structures, materials, and management procedures. Inaccurate understanding of the building characteristics can cause serious physical damage and possible legal claims. It is important to comprehend how modern materials and technical approaches affect the energy performance evaluation of ancient buildings. This theme is not addressed yet sufficiently because of its complexity; in addition there is not an agreement on how to upgrade the general performances, as well as preserve the cultural values. Moreover the current criteria, parameters and the tools of the energy evaluation are thought mainly for modern buildings. The main weakness is related to the lack of suitable information on the building techniques, materials and possible air leakages. An accurate diagnosis is the first step to identify the suitable actions. The perspective of the energy efficiency suggests to investigate the historical building techniques. For this reason, the authors accomplished some experimental measurements to determine the most relevant thermo-physical parameters and the average data of historical walls. The data constitute a wide base for a correct energy audit scheme (Adhikari et al., 2012). Subsequently, the experimental data are used for simulation of the energy performance of two historical churches with static, semidynamic and dynamic tools. The study permits to distinguish the better simulation of the real energy performances of the ancient buildings and to identify the strengths and the potentialities of each software. ENERGY AUDIT SCHEME An Energy audit is a process to evaluate the energy consumption of the building in order to identify the PLEA2013 29th Conference, Sustainable Architecture for a Renewable Future, Munich, Germany 10-12 September 2013 opportunities for retrofit actions. The energy balances are primarily made in order to compare the energy performance of each building. The energy behaviour modelled by the software was compared with the energy consumption estimated from the energy bills. This means to inspect, analyse and survey the energy flow, for reducing energy consumption, improving comfort, health and safety. To carry out the audit, it is necessary to measure the energy performance of the envelope and mechanical plants and collect the management data. Particularly, in this study the following data are collected: location, urban planning, orientation and environmental context; dimensions of the buildings; construction features of the building envelope; efficiency, functioning and maintenance of mechanical and electrical systems; operational data; leakage rate or infiltration of air; monitoring of temperature and relative humidity; energy bills; conservation state of the building. Technological data were estimated using visual testing, heat flowmeter measurements and IR thermography. CASE STUDIES The experimentation was conducted in two historical churches: the Church of the Purification of Santa Maria in Caronno Pertusella and the Santo Stefano Oratory in Lentate sul Seveso. The Purification Church in Caronno Pertusella The Church in Caronno Pertusella, a village in Varese area of northern Italy, was built between 1483 and 1500. Its polygonal apse contains a remarkable series of frescoes by Giovan Paolo Lomazzo and his staff, and an altar piece painted by Bernardino Campi. The building, East-West oriented, has a single nave plant, and one small chapel along the longer sides. The nave has three bays, and each bay has a bricks cross vault as ceiling. The solid masonry is 52 cm thick, and the openings (7 half circle windows) in the upper part of the walls, close to the vaults basis; in the apse there are 2 rectangular windows, as well as in the chapels. The main door is in the façade, but the mostly used entrance is from the southern side. Other two smaller doors are on the northern side, towards the sacristy and the parish building. The heating system consists of a modern gas condensing boiler and radiant floor panels. The thermal power is 19 kW, while the operating temperature is 50/30 °C. During the last restoration (2009-2010), a thermohygrometrical investigation of the masonry was completed. Thermal scanning is served to identify the building techniques and their conditions, those were otherwise not detectable through visual analysis. The results of IR thermography together with the gravimetric tests allowed to localize few areas of rising damp on the northern side due to a leakage from the pipes or a localized accumulation of rain. As an example, the following images show the results of the investigation on the northern chapel (Fig. 1 e 2). In addition, there is also a water infiltration from the roof. Figure 1: The Northern chapel before the restoration Figure 2: Composite of thermograms, showing the texture of the masonry underneath the plaster; emissivity 0.92, T° 12°C, RH 64%, active approach. At last, in the left corner, at the bottom, the surface has a lower temperature due to the evaporation flux occurring there. Gravimetric tests of samples from this surface confirmed that high water content was due to a localized rising damp. Without the application of a thermal stimulation the passive approach allowed the measurement of surface temperature representing the balance condition between the surface and the ambient air. The thermal bridge due to the thinner infilled wall opening is clearly detectable with IRT. During 20092010, the hourly measurements of RH and Air temperature, inside and outside the building, have been carried out. The results show a trend of the air temperatures and RH values with smooth and gradual seasonal variations (Fig. 3 and 4). 0,00 5,00 10,00 15,00 20,00 25,00