DYNAMIC THERMAL ANALYSIS OF NEARLY ZERO EMISSION BUILDINGS WITH GEOTHERMAL AND SOLAR PLANTS

At the present day, the need for the reduction of energy consumption is one of the main issues, from the technical, economic and environmental point of view. Buildings are responsible for more than 40% of energy utilization in European countries in 2017 [1]. Thus, actions that increase building energy efficiency are mandatory. Some interventions on the envelope and the internal operating conditions are addressed to the reduction of the heating and cooling loads of the building (i.e. the energy needs). Others pertain directly to the plants that must be properly selected and sized considering, if possible, also the use of renewable energies. In this framework, the present study is devoted to the analysis of energy-efficient buildings, with features aimed to reduce the loads and equipped with efficient plant solutions including innovative ground coupled water-to-water heat pumps and high efficiency air to air heat pump with energy recovery. The first part of the study is devoted to the ground heat exchangers and in particular to the modeling of energy geopiles in which the geothermal heat exchangers are integrated into the foundations of the building. To correctly size a ground heat exchanger (HE) field, in terms of total length, the number of HE and spacing, the ground response is needed and is provided in terms of g–function. A new semi-analytical method is proposed, based on the spatial superposition of a basic analytical solution, namely the single point source solution. This method allows generating ground response function (g-functions) for shapes of the heat exchanger different from classical linear one, as for the case of helix. The method has been validated by comparison with literature analytical solutions and with FEM simulations with Comsol Multiphysics. The second part of the research is devoted to developing a comprehensive model for dynamical energy simulations of a Nearly-Zero-Emission-Building. The model, developed with three different software (Sketch-Up, Openstudio and Energy Plus), represents the Smart Energy Building (SEB) located in the Savona Campus of the University of Genoa. The SEB is a very innovative building for both the envelope (ventilated facades) and the energy systems (i.e. geothermal heat pump and high efficiency air-to-air heat pump with energy recovery). Moreover, it has a complete monitoring system with numerous sensors that provide in real-time numerous thermal and electrical data (temperature, mass flow rates, electrical power, current, etc). All the detailed features of the building have been analyzed: the geometry, the materials, and the internal operating conditions. The climatic conditions of the site where the building is located are considered through a proper weather file. That information allows evaluating, firstly, the heating and cooling loads, which means the energy needs of the building during winter and summer. Then, the thermal plants have been introduced into the model, namely the ground coupled water-to-water heat pump and the air handler associated to a high efficiency air-to-air heat pump with energy recovery. For both the heat pumps, the performance (COP and EER) depends on the load and source-side fluid temperatures. This feature has been carefully implemented in the Energyplus model. The main results from the simulations are zone temperatures and primary energy consumption from the heating and cooling plants. Finally, the PV modules located on the roof of the SEB have been included in the model. The PV field has been analyzed considering electrical power production, cell temperature and solar irradiance received. The SEB is included in the complex and complete monitoring system of the Smart Polygeneration Microgrid of the Savona Campus The validation process of the model with real measurements from the SEB monitoring system would represent an important and original contribution of this study. Unfortunately, a complete analysis is not possible at the moment due to the unavailability of data series about the ventilation system. However, a preliminary comparison between model and measured data has been realized for the electrical production from the PV modules of the roof of the building. In particular, the EnergyPlus model has been updated by inserting a properly modified weather file with the measured values of outdoor air temperature and solar irradiance (global horizontal value). The calculation is done for two sample months (i.e. January and June 2018). The comparison shows a quite good agreement between simulated data trends and measured values, with a discrepancy at peak values. It is not clear if this disagreement is imputable to poor simulation parameter choice or errors in measures acquisition. Future work will be aimed towards completing the validation of the model using the huge amount of data from the monitoring system. Moreover, the model will be used to study the SEB thermal flexibility to different control strategies.