Energy retrofit in cultural heritage: a choice-driven process for 20th century historic buildings

Many studies identify the energy retrofit of historic buildings as the current challenge of research. In fact, along with the numerous issues related to energy improvement of building stocks, when energy enhancement is applied to cultural heritage, a plethora of other aspects need also to be addressed. They concern conservation targets, restoration rules, preservation of building aesthetic, historic and social values. These goals may seem to contradict the purpose of updating the heritage to today’s energy standards. Indeed, this is a very controversial matter, and it is extremely difficult to find the equilibrium between the energy efficiency and the respect of the heritage in all its facets. Any design step is a hard choice, balancing goals and constraints pulling towards two opposite directions: conservation versus innovation. The aim of this research is to develop a methodology for strongly supporting the energy efficiency process in heritage buildings. The focus is on weighted, well-balanced choices. The strategy developed, called a five-step choice-driven process, organizes all the choices to be made into a logical sequence, and allows to ponder pro and cons during each stage. The method involves the historic and architectural analysis of the building, the assessment of its energy consumption, the design of several energy improvement scenarios, the economic valuation of the proposed interventions under a life cycle cost perspective, as well as the quantification of conservation criteria and indoor environmental quality. An analytic hierarchy process allows to compare and rank the design alternatives, leading to identify the one embodying the best equilibrium between the multiple targets considered. A Monte Carlo simulation, finally, allows for uncertainty in the process, defining the risk quantification. The methodology developed is applied and tested on the case study of Italian 20th century-built heritage. The results achieved are quite significant since they demonstrate how important it is to deepen the collaboration between conservation and energy-economic assessments, involving methods which help dealing with scenario analysis, multi-criteria choices, uncertainty and risk. The process is innovative as it considers a comprehensive holistic point of view, and it combines in synergy different disciplines.