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A novel energy index to assess plants capable of producing electricity from a renewable source is introduced in this paper. This index allows to evaluate the bidirectional energy flows on the external power grid, due the electricity exported to the grid from a renewable-based system and the electricity imported from the grid, in comparison to the electricity demand of a building. In this paper, attention is focused on a solar photovoltaic (PV) system satisfying the energy demands of an office building. Electricity from the solar PV system is partly used to operate a ground source heat pump to meet space heating and cooling demands, and partly used for other electrical loads. An energy, economic and environmental impact analysis of the proposed system is also reported. A sensitivity analysis varying the photovoltaic system capacity (2.5–10.0 kW) and the battery storage size (3.2–9.6 kWh) is also carried out. A saving in terms of primary energy and a carbon dioxide emission reduction can be obtained by a renewable-based system compared to a conventional one consisting of a natural gas fuelled boiler for space heating, an electric chiller for space cooling and the national power grid for electricity demand.

In this paper four different air conditioning systems designed for a building located in Naples, are investigated. The first plant is based on distributed energy conversion systems: twelve boilers and twelve chillers. In the second solution the space heating demand is satisfied by a centralised boiler while the cooling load is met by a centralised chiller. The third option consists of a trigeneration plant. The fourth configuration is composed by an electric heat pump satisfying space heating and cooling and a centralised boiler used for domestic needs. Dynamic simulations have been carried out to compare the energy and environmental performance of the centralised systems with those achieved by the distributed one. Besides, as further loads, for the third option, two electric vehicles charged by the cogenerated electricity surplus are compared to diesel cars. The results show that the best energy and environmental performance are achieved by the cogenerator-based system, with a primary energy demand of 120.6 MWh/y and equivalent dioxide carbon emissions of 25.2 t/y in the configuration without vehicles. This result is also confirmed with electric and diesel vehicles. The energy competitiveness of the plant with the electric heat pump is achieved only in a scenario with a high penetration of renewable energy sources.

The reduction of buildings energy demand represents one of the main goals in developed countries in order to achieve a sustainable future. In Italy a significant number of public administration offices are located in historical buildings, especially in small provincial towns. In this paper the analysis of the energy and environmental effects deriving from the plant renovation of the Palazzo San Giorgio, the building offices of the municipality of Campobasso (Southern Italy), is carried out. The simulation model of the building-plant system has been implemented with the TRNSYS software using data collected in the survey campaign. It has been calibrated on the basis of the billed electricity and gas consumption and then, further used to evaluate the reduction of the building primary energy demands and CO2 emissions deriving from some non-invasive energy refurbishment measures: led lighting, thermostatic valves, cogeneration system and photovoltaic plant. The latter was considered in two variants: the first one provides a system completely integrated into the roof, the second one high efficiency non-integrated panels. The interventions have been evaluated both individually and combined. A primary energy saving of about 47% and a reduction in CO2 emissions of 73% are obtained with the best combined renovation action.

In this paper two solar electric-driven air conditioning systems are compared and analyzed from an energy and environmental point of view. Both systems satisfy the electricity, space heating and cooling needs of an existing multi-purpose, multi-story building that is simulated with TRNSYS 17. The first one, considered as reference system, is based on a centralized electric heat pump coupled with a conventional photovoltaic plant installed 10 years ago. The second one, hereinafter proposed system, has a hybrid configuration, consisting of a ground-source heat pump, a low temperature thermal network and a series of electric heat pumps, one per apartment. In addition, the plant is connected to a high-performance commercial photovoltaic system equipped with a solar tracking system to the panels. Five different solutions realized with vertical, two horizontal orientations, polar and two-axis trackers are taken into account and compared with the standard fixed configuration. The last hybrid configuration can be seen as an upgrade of an existing decentralized air conditioning system in which the local electric heat pumps are converted in water-to-water devices that interact with the thermal grid representing the heat source/sink for them. In both solar electric heating and cooling plants the photovoltaic system is installed on the building roof and it produces electricity to feed the heat pumps and end-users. The electricity surplus or the load not covered by solar field is fed to/taken from power grid. The energy and environmental analyses have been performed by considering both average annual and monthly values of power grid efficiency and CO2 emission factor for electricity. By comparing reference system and proposed one equipped with a two-axis tracker system a primary fossil energy saving of 101.67% is achieved in summer period and 28.10% in winter period. These percentages are the highest values recorded, even if, for all configurations the energy analysis rewards the proposed system. The results of environmental analysis demonstrate that the reference system has the worst performances compared to proposed system with all solar tracker systems selected guarantying positive values for avoided carbon dioxide index up to 45.86%.

Combined heat and power generation traditionally allows for higher energy performance than separate production of heat and electricity. However, the significant increase of the renewable energy sources contribution in electricity production has spatially and temporally modified the context in which polygeneration systems operate and the energy and environmental profitability of these technologies could be undetermined. In such a situation it seems interesting to investigate the influence of the power grid efficiency variation on the polygeneration systems performance. For this purpose energy and environmental performance of a proposed system based on combined production are compared to those achieved by a conventional system based on separate production. The primary energy demand of conventional and proposed systems due to electricity depends on the efficiency of the national electric energy system features. In this paper, this efficiency is considered to be time-varying (hour-by-hour) and it is further taken into account that the electric system efficiency changes in different regions of the same Country. According to Italian day ahead market of electricity the national territory is divided in 6 zones; two of them (Centre-North zone and Centre-South zone) will be specifically considered and compared hereinafter. The differences that arise in results are also assessed with respect to the case in which national and local average efficiency is taken into account. The environmental analysis is performed considering the average and the time-varying Italian and local electricity emission factors. The results have highlighted that the cogeneration system feasibility depends upon the variability of these factors. Indeed, referring to thermoelectric-based power grid efficiency, only in Centre-North zone is more energetically convenient to produce heat and power by separate production systems. The environmental analysis outcomes have showed the same trend of energy analysis results in all the considered zones underlining that the evolution towards sustainability in Smart Grids requires an integrated approach.

Electric air-conditioning systems driven by electricity from a wind turbine can be defined as wind electric and cooling systems according to the definition of solar-activated air-conditioners. They can potentially contribute to reduce primary energy demand and CO2 emission in the civil sector. In this paper, mini wind turbines are considered coupled with a ground source heat pump in order to serve an office building for air-conditioning and supply the electricity surplus for the pure electric load of the user. Different plant configurations are considered. First of all, assessments with two kinds of wind turbines (5&ndash, 5.5 kW), vertical and horizontal axis, are performed, also considering the coupling with one and two identical wind generators. Secondly, to better use on-site electricity, a parametric study is proposed taking into account different battery storage system sizes (3.2&ndash, 9.6 kWh). Finally, the plant is simulated in two locations: Naples and Cagliari. Simulation results demonstrate that the source availability mainly affects the system performance. In Cagliari, the primary energy reduction per kWh of final energy demand (for pure electric load, space heating, and cooling) is equal to 1.24, 54.8% more than in Naples. In addition, the storage system limits the interaction with the power grid, lowering the exported electricity from about 50% to about 27% for Naples and from 63% to 50% for Cagliari. The fraction of the load met by renewable energy accounts for up to 25% for Naples and 48% for Cagliari.

In this paper a polygeneration system based on compression/absorption heat pump (CAHP) is analyzed. This innovative heat pump is contemporary activated by both thermal and electric energy, ensuring more flexibility with respect to a traditional absorption heat pump and allowing to optimize the mix of energy vectors that feeds the system. Moreover this kind of absorption system can overcome some typical disadvantages of the traditional absorption heat pump, such as the limited range in terms of operating temperatures, as well as the quite low pressure and temperature lift achievable between evaporator and condenser. The integration of a compression/absorption heat pump with cogenerator or renewable energy technologies, such as solar thermal collectors, allows to reduce the fossil fuel use. The energy performance could be optimized varying the compression ratio of the compressor. In particular increasing this parameter it is possible to reduce the heat source temperature and so to optimize the system performance that depends on the heat source temperature. Hereinafter the performance of a small scale polygeneration system based on a CAHP is analyzed considering the installation in Naples, southern Italy. A microcogenerator, fuelled by natural gas, provides both thermal and electric energy to the CAHP in order to deliver cooling energy, besides heat and electricity.

In this paper a solar electric heating and cooling system consisting of a photovoltaic plant and an air handling unit equipped with desiccant wheel is analysed. The dehumidification of process air supplied to a conditioned room is achieved by means of the desiccant wheel that is filled with a hygroscopic material instead of throughout a cooling dehumidification as it happens in standard air handling units. The desiccant wheel regeneration, for a continuous operation, is obtained by using the electricity available from the solar plant in an electric heater. Dynamic simulation have been carried out to compare this innovative system with a conventional one for a year of operation, considering that it serves a university classroom of 63.5 m2 located in Benevento. Primary energy saving and equivalent CO2 emission reduction are estimated as a function of photovoltaic plant peak power and panels tilt angle. The proposed solution demonstrates to be very interesting for an energy and environmental point of view, reaching maximum energy saving and emission reduction over 79%. Optionally four different tracking systems were simulate for solar field. The two-axis tracker achieves the best energy and environmental performance but it has the worst behaviour considering the interaction with the power grid.

The paper investigates the introduction of a solar heating and cooling system in an office building characterized by low energy demand with respect to the current national building stock and located in Southern Italy. Dynamic simulations are carried out in order to evaluate the thermo-economic performance of the analyzed system considering different solar panel technologies (flat plate and evacuated tube), tilt angles (10–70°), collecting areas (30–60 m 2 ), hot and cold storage sizes, reference emission factors, electricity and natural gas unitary prices. To satisfy cooling demand a small scale adsorption chiller activated by thermal energy available from solar collectors is considered. The solar heating and cooling system demonstrated primary energy saving and equivalent dioxide carbon emission reduction higher than 23% in comparison to the reference conventional system. The results show that the solar energy system will be competitive when the electricity and natural gas prices will be high and strong government incentives will be provided.

Desiccant-based air handling units can provide significant operational advantages and can use solar energy as the main heat source. Hereinafter a plant equipped with a silica-gel desiccant wheel is analyzed for two Italian locations (Benevento and Milano). A parametric study involving collectors types, surfaces, tilt angles and installation site has been performed. The proposed system has been compared with a conventional HVAC unit, through dynamic simulations. In terms of energy and environmental analysis, solar desiccant systems should always be preferred to conventional ones, even when the solar thermal energy surplus is fully dissipated. A maximum primary energy saving of about 10% and 20% with flat plat and evacuated tube collectors, respectively, occurs in both locations. The savings increase up to about 58% and 72% in Benevento and 43% and 58% in Milano, when the solar heat excess is completely used for further energy demands. One observes that systems with evacuated tube collectors are preferable where the available space for the solar field is small, instead with larger surfaces flat plate collectors are advantaged. In terms of economic analysis, the shortest payback periods are 6 and 8 years for Benevento and Milano, respectively.

Urban heat island affects cities climate and results in higher air temperature with respect to the surrounding rural zones. Anthropogenic heat released by human activities exacerbates this phenomenon which impacts on environmental and energy fields. Air conditioning is commonly used to achieve comfort indoor conditions in the warmer urban climate but it is also one of the serious cause of the urban heat islands. The heat rejected by the condensers of air conditioning systems, increases the air temperature next to the buildings in which they are installed. In this paper a system consisting of a ground-source heat pump, a low temperature thermal network and a series of electric heat pumps, is analysed. The thermal grid is the heat source/sink for the water to water electric heat pumps that are installed at each end-user of a multi-purpose six floors building located in Naples (Southern of Italy). In cooling mode the condenser heat is discarded in the ground by the ground source heat pump that operates between the lower temperature thermal grid and the borefield. In the heating period the thermal network is heated by the ground source heat pump, that draws energy from the ground. The models simulating the energy conversion systems, the low temperature thermal network and the building, are implemented in the dynamic simulation software TRNSYS 17. A first advantage of the proposed configuration is the avoided interaction with the outside air and the corresponding mitigation of the urban heat island phenomenon. A second one is the higher coefficient of performance of the water to water electric heat pumps, operating with a lower temperature gap with respect to the case in which the electric heat pumps interact with the outside air. Furthermore, the interaction with thermal grid allows high seasonal performance due to the low fluctuation of the temperature with respect to the air. Finally this energy efficient system could be simply installed not only in the new buildings, but also in refurbishments. The proposed system is compared with a conventional one installed in each dwelling consisting of an air to water air conditioner for cooling operation and a boiler for heating. Interesting global and local environmental advantages are obtained.

In this paper, three alternative layouts (scenarios) of an innovative solar-assisted hybrid desiccant-based air handling unit (AHU) are investigated through dynamic simulations. Performance is evaluated with respect to a reference system and compared to those of the innovative plant without modifications. For each scenario, different collector types, surfaces and tilt angles are considered. The effect of the solar thermal energy surplus exploitation for other low-temperature uses is also investigated. The first alternative scenario consists of the recovery of the heat rejected by the condenser of the chiller to pre-heat the regeneration air. The second scenario considers the pre-heating of regeneration air with the warmer regeneration air exiting the desiccant wheel (DW). The last scenario provides pre-cooling of the process air before entering the DW. Results reveal that the plants with evacuated solar collectors (SC) can ensure primary energy savings (15%–24%) and avoid equivalent CO2 emissions (14%–22%), about 10 percentage points more than those with flat-plate collectors, when the solar thermal energy is used only for air conditioning and the collectors have the best tilt angle. If all of the solar thermal energy is considered, the best results with evacuated tube collectors are approximately 73% in terms of primary energy saving, 71% in terms of avoided equivalent CO2 emissions and a payback period of six years.

A hybrid solar-assisted trigeneration system is analyzed in this paper. The system is composed of a 20 m2 solar field of evacuated tube collectors, a natural gas fired micro combined heat and power system delivering 12.5 kW of thermal power, an absorption heat pump (AHP) with a nominal cooling power of 17.6 kW, two storage tanks (hot and cold) and an electric auxiliary heater (AH). The plant satisfies the energy demand of an office building located in Naples (Southern Italy). The electric energy of the cogenerator is used to meet the load and auxiliaries electric demand; the interactions with the grid are considered in cases of excess or over requests. This hybrid solution is interesting for buildings located in cities or historical centers with limited usable roof surface to install a conventional solar heating and cooling (SHC) system able to achieve high solar fraction (SF). The results of dynamic simulation show that a tilt angle of 30° maximizes the SF of the system on annual basis achieving about 53.5%. The influence on the performance of proposed system of the hot water storage tank (HST) characteristics (volume, insulation) is also studied. It is highlighted that the SF improves when better insulated and bigger HSTs are considered. A maximum SF of about 58.2% is obtained with a 2000 L storage, whereas the lower thermal losses take place with a better insulated 1000 L tank.

In this work, a system consisting of a small scale trigeneration system, in which a heat-led microcogenerator interacts with a desiccant-based cooling system, equipped with a silica-gel desiccant wheel, is analyzed. The system provides the air-conditioning service to a lecture room during summer and winter periods and, over the whole year, thermal energy for domestic hot water production to a nearby multifamily house. Electricity from the cogenerator is used to drive the electric chiller, the auxiliaries as well as further electric appliances of the lecture room. This trigeneration system is compared with a reference system, equipped with a conventional air handling unit, based on cooling dehumidification for summer air conditioning. Electricity to power the electric chiller, the auxiliaries, as well as electric appliances is drawn from the grid. Thermal energy for winter space heating, air post-heating during summer and domestic hot water purposes is provided by a natural gas boiler. Experimental tests, as well as data derived from manufacturers, are used to implement a model of both systems. Simulations were then performed by means of TRNSYS software to compare their thermo-economic performance. A sensitivity analysis has been performed, to analyse the effect of the share of cogenerated electricity consumed on-site. The analysis shows encouraging results, given the Italian energy context for the small scale trigeneration system, in terms of primary energy consumption and equivalent carbon dioxide emissions reductions, with maximum values of 7.70% and 15.3%, respectively; on the other hand, it is difficult to achieve a reasonably short pay-back period for the system, even if it accesses all the support mechanisms introduced by Italian legislation for small scale gas fuelled trigeneration systems and a very high amount of cogenerated electricity is used on-site.