Application of the comparative methodology for the definition of individual building elements energy requirements in Italy

Directive 2010/31/EU establishes that Member States must ensure that minimum energy performance requirements for buildings as well as for individual building elements are set with a view to achieve cost-optimal levels. The comparative methodology is here applied to two reference buildings; different energy efficiency measures are considered one at a time in order to find the optimality in terms of costs/benefits; results are then discussed. The definition of the individual building elements refurbishment cost/benefits effectiveness wants to address building administrations to define suitable energy requirements as well as economic incentives, as to promote the energy consumption reduction according to EU requirements

Cost-optimal approach to transform the public buildings into nZEBs: an European cross-country comparison

A cross-country comparison of the RePublic_ZEB project results is presented. The paper reports on the energy efficiency measures and on the options considered for the refurbishment of the public buildings taken as representative of the building stock in the countries involved in the project. The nZEB solutions are compared in terms of adopted energy efficiency measures; moreover, the nZEBs are quantitatively defined through a set of energy, economic and environmental parameters. The paper aims at giving an overview on the meaning of nZEB in the European context, and on its energy and economic feasibility for real public existing buildings

Livelli ottimali di costo per i requisiti di prestazione energetica degli edifici

L'articolo presenta la metodologia per l'analisi comparativa messa a punto ed applicata ad edifici di riferimento su scala nazionale con il proposito di determinare livelli ottimali di costo da utilizzare come metro per la formulazione di prescrizioni energetiche in ambito edilizi

On the refurbishment of the public building stock toward the nearly zero-energy target: two Italian case studies

The study presents some results of the on-going European Project, RePublic_ZEB, on the refurbishment of the public building stock towards nearly Zero Energy Building (nZEB). The work is focused on the application of the nZEB requirements to two existing public buildings representative of the 1960s in Northern Italy. Many packages of energy efficiency measures that comply with nZEB requirements are identified and evaluated. The aim is to promote energy efficient but also cost-effective solutions for the Italian building stock refurbishment. The results are presented in terms of “package of measures”, energy consumption, global costs, actualized pay-back period and CO2 emission

The Rebound Effect after the Energy Refurbishment of Residential Buildings towards High Performances

In the last decades, governments worldwide have promoted energy efficiency improvements in order to reduce the building energy consumptions and CO2 emissions. In many geographical contexts, the largest and most cost-effective energy saving potential is in the existing housing stock renovation. For this reason, many energy efficiency policies are focused on the energy refurbishment of the existing buildings. Though the energy consumption of buildings is supposed to decrease after a retrofit, several studies show that the energy performance does not increase as much as it would be expected and that a significant gap between the estimated and the real energy savings - called rebound effect - occurs. This deviation can partly depend on the model used for the energy performance evaluation, but changes in the occupants’ behavior after a thermal retrofit of an existing dwelling are also revealed. The present paper examines the influences of occupant behavior on the energy savings for some retrofitted Italian residential representative buildings. Some typical use patterns are defined according to statistics of the national census of population and dwellings and the expectations of the building occupants are specified before and after the retrofit. The main objective is to investigate the elasticity of the energy consumption in function of the occupancy parameters before and after the application of high energy efficiency improvements. The analysis is carried out by means of a simplified energy performance assessment model. The outcomes of this study consist in defining synthetic indicators for the quantitative assessment of the rebound effect

Energy cost and discount rate influence on the optimal packages of energy efficiency measures.

The Commission Delegated Regulation No. 244/2012 supplementing Directive 2010/31/EU on the comparative methodology framework for calculating cost-optimal levels of minimum energy performance requirements enforces Member States to perform an analysis to determine the sensitivity of the calculation outcomes to changes in the energy price developments and the discount rates, as well as other parameters which are expected to have a significant impact on the outcome of the calculations. In Italy the cost optimal methodology has been performed by using a simulation tool enforced on a quasi-steady state numerical model (UNI/TS 11300) while the cost optimisation procedure is based on a sequential search-optimisation technique considering discrete options, as introduced in a previous work. Packages of energy efficiency measures giving optimal EP levels have been found for different buildings and climatic conditions. Results show that the optimal solutions are strongly influenced by energy costs of the different energy wares, and this can affect the suitable technical solutions for refurbishment. The present work is focused on the definition of different economic scenarios. The aim is to assess a wide economic framework as to determine the influence of the energy cost and discount rate on the costs/benefits analysis and how cost optimal solutions can change according to these trends. Different energy cost variations are considered for electricity and natural gas, which are the most used energy carriers in Italy. The economic framework is applied to four Italian reference buildings to emphasize its influence when different building uses and climatic boundary conditions are considered. Discrepancies in results are then discussed

The Energy Performance Assessment of nZEBs: Limitations of the Quasi-Steady State Approach

The European Directive 2010/31/EU on the energy performance of buildings (EPBD recast) establishes the target of nearly Zero Energy Buildings (nZEB) for all new buildings and major renovations of existing buildings by the end of 2020. This paper investigates the accuracy of the quasi-steady state method, according to the Italian technical specification UNI/TS 11300, in predicting high performance buildings’ energy consumptions. Both the terms of the building energy balance and the simplified dynamic parameters are assessed by comparing the simplified model with dynamic numerical analysis. The two calculation models are applied to some real low energy buildings, which are representative of the Italian building stock. The envelope U-values are assumed as complying with Italian official nZEB requirements. Weather data from some Italian locations, two inertial mass configurations and different system operating chedules are considered. The comparison between the dynamic and static calculations for low energy buildings’ energy performance assessment reveals some discrepancies: the quasi- teady state model generally overestimates the energy need for space heating and underestimates the energy need for space cooling; the gaps are bigger among various Italian locations and inertial mass configurations than among different system operating schedules. The reasons of this gap are discussed in the paper. It is highlighted that in some particular cases the national regulations should introduce the dynamic numerical analysis as reference calculation model

Assessment of cost-optimal energy performance requirements for the Italian residential building stock

Directive 2010/31/EU establishes that Member States must ensure that minimum energy performance requirements for buildings are set with a view to achieve cost-optimal levels. The paper presents a methodology for identifying the cost-optimal levels for the Italian residential building stock, following the Guidelines accompanying the Commission Delegated Regulation No. 244/2012. The methodology is applied to a reference building of the IEE-TABULA project and considering different energy efficiency measures. The energy performance and the global cost calculations are performed according to UNI/TS 11300 and EN 15459, respectively. A new cost optimisation procedure based on a sequential search-optimisation technique considering discrete options is applied

Energy performance characterisation of vented opaque envelope through simplified methodologies

Opaque vented façades are innovative and widely-used technological systems adopted both in new constructions and in building renovations. According to European Directive 2010/31/EU (EPBD recast) on the energy performance of buildings, each Member State should give priority to passive cooling techniques in order to enhance building performance during the summer period. For this purpose opaque vented envelope could be an appropriate technological solution to reduce the summer peak loads and the energy consumption. Although the EPBD recast has submitted the development of calculation methods for the energy performance evaluation to the European Committee of Standardisation (CEN), there is a lack in European Standards on the calculation of non conventional building envelope performance, including vented façades. The object of the present work is the thermal performance characterization of vented vertical opaque enclosures in real conditions of use, through simplified parameters. Starting from EN ISO 6946 and EN ISO 13786, new equivalent thermal parameters are defined, such as the equivalent steady state thermal transmittance, the equivalent periodical thermal transmittance and the time shift. Equivalent parameters are obtained by evaluating surface inside face conduction in the opaque components, under stabilized periodic external conditions, for the summer design day. An equivalent outside temperature is used, which considers both the convective and the radiative thermal exchanges (solar and infrared waves), for different boundary conditions (orientation). The tool used for calculations is based on the conduction transfer function - CTF - method, as implemented in the thermal dynamic simulation program Energy Plus. Through a sensitivity analysis, different opaque enclosures are analyzed, varying the design parameters such as the thickness, the height and the length of the vented cavit