NET ZERO ENERGY BUILDINGS: AN ITALIAN CASE STUDY. ANALYSIS OF THE ENERGY BALANCE AND RETROFIT HYPOTHESIS IN ORDER TO REACH THE NET ZERO ENERGY TARGET.

In the last years the concept of Net Zero Energy Building (NZEB) has been developing and spreading in the scientific community. The work presented in this thesis has been largely developed in the context of the International Energy Agency (IEA) joint Programme Solar Heating and Cooling (SHC) Task40 and Energy Conservation in Buildings and Community Systems (ECBCS) Annex52: Towards Net Zero Energy Solar Buildings. It is known that the energy consumption in Europe for residential and commercial buildings is around 40 % of the total production. It is then extremely important to optimize both the implementation of energy efficiency measures and the usage of renewable resources that can be harvested on site. When energy efficiency measures are successfully combined with on-site renewable energy sources, and the energy consumption is equal (or nearly) to the energy production, then the output achieved can be referred to as ―near net zero energy ―or ―net zero-energy building‖. In Chapter 2 a description of the main typologies of NZEB is carried out, revealing that the most important ones are the following: site-ZEB and source-ZEB depending on where the energy balance is calculated. After a brief description of the NZEB most common definitions and classifications many examples have been examined, analyzing their features in relation to the climate in which they are, in order to show different solutions and approaches to the problem of reaching net zero energy balances (Chapter 3). In this thesis an Italian case-study has been examined: the Leaf House (LH) located in Ancona, Italy. The Leaf House is one of the best case studies of the IEA/SHC/ECBS/Task 40 Programme, in terms of thermo-physical characteristics of the building envelope, thermal plant, building automation system and energy monitoring. In Chapter 5 the Leaf House case-study is described in detail as well as the model implemented into the TRNSYS software (Chapter 6), reproducing the energy production system, the thermal features of the building and comparing simulated with monitored data. Particular attention has to be paid to the Leaf House monitoring system, which allows the assessment of the building energy balance.A careful analysis of monitored data brings to search some improving strategies to reach the zero energy target. After the simulation of the real building systems (through the software TRNSYS-Chapter 6), several scenarios have been investigated to improve energy performances of the building. Moreover the implemented model has been properly calibrated. The study proposes a detailed analysis of the case-study in order to show the possible energy savings that an NZEB can achieve in comparison with a non-net zero energy building. The re-design options are then proposed and the results evaluated by TRNSYS are described in detail. The monitored situation shows an energy consumption of 37 MWh for the year 2009; although around 6 MWh are wasted in the monitoring equipment the energy production is lower than this value. A simple solution, to reach the NZEB status is moving towards a higher production: e.g. the substitution of the PV panels with higher efficient others. In this way the energy balance reaches ―zero‖ during the year. Nevertheless the problem can be solved otherwise, reducing the energy needs. In this direction, the Geothermal Heat Pump and its energy needs have been analyzed in detail. It has been verified that the COP of the machine is way lower than the declared 4.6 and that an effective 4.6 COP could lead to significant energy savings. The idea of reaching higher efficiencies led to the proposal of a different plant scheme with the exclusion of a heat exchanger to reduce as much as possible energy losses. While it is possible to obtain the NZEB status simply making a substitution of the PV panels, the investigation on further energy savings has been continued. Finally the Italian case study allow to identify the strategies to improve the energy performances of the a Near Net Zero Energy building to reach the NZEB target. It represents also an Italian reference for others who wish to build NZEBs in the Italian context. At last two annexes to this work are shown, the first shows objectives and activities of the Task 40 ECBS Programme while the second shows the Building description file created into TRNBUILD environment, in order to describe the Leaf House building envelope features.