Church heating: comparison of different strategies N. Aste*, S. Della Torre*, C. Del Pero*, F. Leonforte*, M. Buzzetti*, R. S. Adhikari*, P. Oliaro* *Dept. of Architecture, Built environment and Construction engineering, Politecnico di Milano, Via Bonardi 9, 20133 Milan (Italy) Abstract - Church heating represents a challenging task because multiple goals have to be fulfilled simultaneously, such as the thermal comfort for the occupants and the optimal internal environmental conditions for the preservation of building components and artworks. In addition, current requirements for environmental and economic sustainability impose to make efforts to minimize the amount of energy needed and the consequent environmental/economic impact. In this context, the present work represents the assessment of the energy, environmental and economic impact of different strategies for church heating, including a novel technology based on the exploitation of renewable energies. The analysis was carried out in a real case-study building, represented by the Basilica di S. Maria di Collemaggio (L' Aquila, Italy), a church of worldwide relevance, currently under restoration. Index Terms - Electric heating; sustainable church heating; friendly heating; cost analysis. 1. INTRODUCTION Heating historical buildings and, in particular, churches, during the winter has different purposes; first of all it aims to ensure an acceptable thermal comfort level to occupants and, secondly, to provide optimal indoor conditions to prevent the deterioration of building components and artworks [1]. However, conservation requirements and energy/running cost saving have hardly been considered while designing heating systems for historic churches. In fact, the low cost of fossil fuels before the 80' in many cases favored the installation of low-efficiency technical systems that currently determines very high specific primary energy consumption (i.e. kWh/m2) and running costs [2,3], even if the churches are commonly heated for few hours in a day/week. In facts, historic churches are typically characterized by very huge air volumes and high thermal mass, and results a significant thermal power and energy demand for heating. In detail, considering the most widespread existing technical systems in churches, it can be stated that two main configurations can be usually found [4]: 1) Central heating, which is a configuration based on a main heat generator (i.e. a gas boiler), a distribution and an emission subsystem, designed to heat the whole church environment; 2) Local heating, which is typically composed by decentralized elements (i.e. infrared heaters) directly placed inside the church and mainly aimed to heat the churchgoers rather than the internal air. 978-l-5090-4682-9/17/$3l.00 ©20 17 IEEE 519 Both the above-mentioned configurations can be coupled with two different operating strategies: • Constant operation, which ensures that during the daytime or the whole opening period of the church the system is fully operated, typically with a thermostat control; • Intermittent operation (on-demand), which implies to switch-on the heating system just in case of particular events such as the celebrations. In this case the control system is a timer. Several research works demonstrated that central heating, specifically with intermittent operation, creates problems in historic churches [5, 6, 7]. In fact, this solution is frequently operated using an all-air system which determines strong fluctuations of air temperature and relative humidity, with consequent negative effects both on comfort and on artworks [8]. In some cases, the internal space is not heated uniformly resulting in sharp contrasts between warm-heated spaces and cold- unheated ones, leading to condensation and mold growth on cold wall surfaces. Under an economic point of view, central heating is often based on outdated natural gas or diesel boilers with low efficiencies, coupled with air blowers, resulting in non-negligible energy costs. In some cases, the operation of central heating could also be all-day-long in order to control the relative humidity and avoid abrupt changes in thermo- hygrometric conditions (conservation heating) but this solution usually implies huge running costs due to the high amount of required thermal energy. On the contrary, local heating, which is more frequently coupled with intermittent operation, typically has a lower/negligible impact on the artworks and ensures competitive running costs [9, 10]. In facts, the variation in air temperature and relative humidity is limited to the areas occupied by churchgoers and usually the heating mechanism is mainly based on irradiation rather than convection, thus involving limited quantity of energy. The typical technical solutions are in fact infrared heaters (powered with natural gas or electricity) or radiant surfaces such as radiant footboards or pew-based heaters. In this sense, the solution developed within the EU project "Friendly Heating" represents a very interesting option for historic churches because it combines good local comfort levels with significant energy savings and