High Renewable Energy Sources (RES) share in energy systems entails environmental advantages in its use but drawbacks in its distribution, management and effectiveness. The interconnection between electricity, heat and transport sector seems to be a comprehensive answer. Its actual link is on-going and, currently, involves electricity and heat. Indeed, Power to Heat (P2H) is the strategy of meeting the heating demand by supplying electricity to feed Heat Pump (HP). Their higher efficiency compared to fossil fuel boilers requires a further check in the quality of the heating demand to meet, i.e. the temperature levels. Great part of current building stock calls for High Temperature (HT) Heat which is not affordable by HP maintaining their Coefficient of Performance. To face this issue, RES can be used to produce synthetic fuels for feeding existing energy systems, the so-called Power-to-Gas option. In this way, greening the fuel supply can be seen as the best option for meeting HT heating demand while, Medium and Low Temperature are met by HP. Therefore, two technological scenarios, P2H and its combination with P2G, are presented and assessed in three reference Urban Energy Systems. The authors investigated on the impact of RES share increase from 25% up to 50% in the electricity mix with the objective function of Primary Energy Consumption (PEC). The outcomes of twenty-four energy scenarios, eight for each Reference City were assessed also through the value of delivered Renewable Heat. Finally, the leverage effect of P2G on the system is evaluated in terms of renewable heat contribution.

Cogeneration (CHP) and Heat Pump (HP) are playing a key role in energy systems due to their high efficiency, especially, in energy refurbishment of buildings and industrial processes. This paper explored the opportunity to couple those two well-established technologies for heating purposes. Basically, the coupling entails limitations and constraints consisting of the mismatch between the power sizes of merchandised machines as well as the deriving technical issues. The main aim of this paper is to analyse the coupling procedure to help HVAC specialists in their job. This paper deals with a simple model formulation, based on the First Law of thermodynamics, for CHP/HP systems rating and off-design operations. Indeed, an analytical method was designed along with the definition of a size factor. Then, a graphical method for coupling CHP and HP was presented so as to be an expeditious tool in designing phase. Finally, two numerical applications were illustrated highlighting the energy performance gains and the high level of operation flexibility.

This paper focused on the hydrogen-methane mixtures (H₂NG) implications on end-user devices such as boilers, so as to provide a useful tool for maintenance operators. In detail, according to current standards, H₂NG blends characteristics parameters for boilers combustion efficiency measurement are calculated. Then, the Ostwald chart for each blend is built by the analytical procedure and is plotted. Additionally, the chemical equations as well as the blended gas characteristic values are computed in order to implement them within software library of commercial gas analysers. Indeed, they are commonly based on Ostwald combustion equation for correlating CO, CO₂ and O₂ concentrations. The results can be applied to analyze conventional and widespread domestic boilers fueled with H₂NG addressing all of the technical implications for their performance certification when they are operating also in condensing mode. Air excess and relative humidity are chosen as variables to evaluate their effects on boilers performance. The oxygen concentration ranges from 0% vol. up to 15% vol. The specific heat values drop non-linearly down for each mixture, showing a maximum reduction equal to 9.825%, for H₂NG@30%. A maximum Energy Fraction of Condensation (EFC) enhancement of 0.9% points is noticed for H₂NG@30% vol. While, the highest EFC gain, 4.8% points, occurred at relative humidity of 90% compared to the assumed reference values for calculations.

This paper deals with the potential role of new hybrid CHP systems application providing both electricity and heat which are compatible with the building architectural and landscape limitations. In detail, three different plant layout options for high temperature heat production along with the electricity generation were investigated and compared each other. To do so, conventional natural gas CHPs and back up boiler, two-stage Electric Heat Pumps (EHPs) and trans-critical CO2 electric heat pump (CO2-HP) have been considered as reference technologies to build hybrid systems. In addition, hybrid solar collectors (PV/T) thermal output, along with the recovered low-grade heat from CHP exhaust gas, flowing to the stack, have been used as the CO2-HP low temperature driving source.

This paper deals with the role of Hydrogen enriched Natural Gas (H2NG) in Hybrid Energy Systems for energy refurbishment purposes. In detail, three different plant layout options were investigated. A photovoltaics (PV) array and two-stage electric heat pump (EHP), a hybrid photovoltaic thermal solar collectors combined to gas heat pump (GHP) fuelled with H2NG, and a CHP fuelled with H2NG connected to a two-stage EHP were compared. The required receiving surfaces of PV array were estimated for three different direct normal irradiation (DNI) values in Italy in order to assess how the available roof surface affects the layout choice. A sensitivity analysis was carried out with varying the building power to heat ratio (PTHR) and the hydrogen volumetric fraction in the H2NG mixtures to assess the primary energy consumption (PEC) and renewable energy fraction. When feasible, the PV + EHP shows the best performance in terms of PEC with a solar energy share equal to 65%. In other cases, the PV/T + GHP fuelled with H2NG @30%vol. can be suitable for PTHR higher than 0.2 approximately. Furthermore, the third layout CHP + EHP is not competitive with the other solutions but, it is the best option where no roof surfaces are available for PV or PV/T installation.