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The development of heat pump technology in the tertiary sector can lead to a reduction in greenhouse emissions and enhanced exploitation of renewable energy sources, including solar energy. The present paper investigates the potentiality of an energy system equipped with photovoltaic thermal (PV) hybrid solar collectors, a storage tanks for the heat source and a heat pump for the space heating of a small office located in three different European cities. The behaviour of the heat pump according to the heat taken from the photovoltaic panels and stored in the tank has been analysed. An energy analysis was performed according to the efficiency of the heat pump and then the thermodynamic parameters of the system were evaluated. The analytical model of each subsystem of the thermal plant was developed in Matlab where hourly simulation during the period of heating season were performed. Therefore, a comparison between the results obtained for Rome, Milan and Cracow provided the heating energy demand covering rate for each of the cities in different subsystem efficiency conditions. When thermal and electrical efficiency of PVT are set respectively to 0.6 and 0.15 and the efficiency of storage unit heat exchanger is considered equal to 0.9 the heating demand covered for Rome is 70%, for Milan is 62%, while for Cracow is 47%. Those values show a good potential for supporting heat-pump based PV-T heating systems. • A novel combined PV-T heat pump system for supporting building heating is proposed. • A mathematical model of the system is developed. • The system performance is studied for three different locations: Cracow, Milan and Rome. • The system heating efficiency is the highest in Rome, while the lowest in Cracow. [ABSTRACT FROM AUTHOR]

In this paper, a novel gas-liquid compressed air energy storage prototype, installed in the laboratory of DIAEE Department of Sapienza University of Rome, is studied. Similar to the Compressed-Air Energy Storage (CAES), the Gas-Liquid Energy Storage (GLES) technology is based on gas compression/expansion, where the liquid-piston compression and expansion are utilized. This paper reports on the experimental performance of the first GLES prototype and presents the results from a validated mathematical model. The results show that the proposed system has a high energy efficiency (indicated) over 90%, and then to achieve high values of round trip efficiency (RTE), it is important to improve and optimize the efficiency of the auxiliaries (Motor/Pump and Turbine/Generator). Two different Test, with two different speed of charging phase were done. From the results of the experimental measurements done with the prototype built in the laboratory of the DIAEE Department of Sapienza University of Rome, it can be seen that for slow compression the RTE of the system is around 72%, instead for the fast compression phase, the RTE is around 70%. A mathematical model was implemented and tested with the experimental measurements. From results it can be seen a good agreement between the experimental and numerical analysis, with a maximum error in the Test B (slow compression) equal to 2.5% and 1% respectively for charging and discharging phase. From the parametric analysis it can be seen that only the volume of the tank and the pressure ratio are needed to predict the round trip efficiency of the system. • A novel prototype of an energy storage system (CEAS) where the air is compressed by liquid is presented. • Energy storage (compression) achieved via liquid piston with hydraulic pump. • Energy recovery (expansion) achieved passing liquid through hydraulic turbine. • A validated mathematical model of the system is presented. • Experimental and simulated system performance are presented. [ABSTRACT FROM AUTHOR]

Radiative cooling allows to cool down surfaces in a renewable way. It can be combined with solar collection functionality to produce heat and cold in a single device known as Radiative Collector and Emitter (RCE). In this paper we propose to combine a RCE with compression heat pumps to improve its performance, producing both heat and cold. Two combined systems are studied: a peak load shifting configuration where radiative cooling and cold production for demand occur simultaneously, and a decoupled configuration with an intermediate tank. The research numerically simulates both systems in different cities and climates, and compares them to a reference system based on a conventional heat pump. The results reveal and improvement of the performance in both configurations: a greater performance of the heat pump is found in the intermediate tank configuration; but after considering the electrical consumptions of all components of the system, peak load shifting configurations exhibit the best performance in most of the cities. Denver, Lleida and Rome – cities with dry climate and moderate cooling requirements – are the top cities with the greatest improvement of the performance. In the solar heating mode, the facilities show an underutilization of the collection field. • Two combinations of radiative cooling and water-water heat pump are analyzed. • The two systems supply cooling and DHW demands in a single-family house. • Simulations of combined heat pump and radiative collector and emitter are performed. • An improvement of the COP of the heat pump in combined systems is obtained. • Electricity savings up to 33% in combined systems are achieved. [ABSTRACT FROM AUTHOR]

The present paper presents a methodology to effectively address the evaluation of building energy retrofitting projects in a highly uncertain context. Buildings are modelled in terms of archetypes which are characterized by specific features, e.g., U-values, heating plant typology, surface to volume ratio, etc. By using the Monte Carlo approach, the proposed method can address the influence of more than thirty important parameters on the final result in terms of energy savings, Net Present Value and other indices aimed to quantify the level of risk associated to complex energy efficiency interventions, e.g., energy saving at risk. The methodology is tested on a case study related to a building built in the '60s and located in Rome, Italy. However, the method is applicable irrespectively of the location, climatic conditions, and typology of the building. Results highlight that a retrofitting intervention consisting in wall insulation has a risk to be unprofitable equal to 47%. This can be ascribed to the mild climatic conditions of the location. • The Monte Carlo approach for analysing energy efficiency interventions in buildings is proposed. • Metrics are introduced for estimating the technical and financial risk of the interventions. • The proposed approach is relevant for any retrofitting project where high level of uncertainty is expected. [ABSTRACT FROM AUTHOR]