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The recovery of the available waste heat from the operating engines of a modern cruise ship plays an important role in the reduction of the environmental impact of these huge means of transport. The cooling load required by the ship passengers can be handled with innovative air-conditioning systems that employ a vapor single-phase ejector and are fed by waste heat. On the contrary, these systems are usually more expensive than vapor compression cycles, representing the conventional technology. In this paper, a thermo-economic-environmental analysis of a combined cooling system for a cruise ship operating in the Baltic Sea is proposed. Two different cooling plants are compared, namely a typical vapor compression cycle and a multiejector hybrid ejector cycle integrated with a cold storage tank aiming to buffer the load variations. The approach is numerical, and the simulations are carried-out with dedicated sub-models for each component. Volumetric machines (pumps, compressor) are modeled through phenomenological equations, calibrated and validated on real data, whereas the heat exchangers are simulated by using specific heat transfer prediction methods and typical geometries. The objective is to size the whole system and optimize the tank size and the control strategy, to minimize the investment cost and maximize the seasonal performance. Also, an economic comparison, concerning the total costs (investments costs plus operating costs) between the solution chosen and the reference one has been carried out considering the fuel cost as a parametric input. Finally, an environmental analysis is performed to assess the reduction in pollutant emissions with the proposed system.

Nowadays more than 5 billion of refrigeration and air-conditioning units are employed worldwide. Internet of Things technology is becoming widely used also in these applications. Operational data can be collected from units installed worldwide and used to train artificial intelligence (AI) tools and black box digital twins. These models can predict energy consumption or detect fault and inefficiencies, allowing a timely intervention on the unit before a total lack of cold occur. In this paper a state-of-the-art review regarding the implementation of AI in refrigeration sector is presented. Works are classified according to the following topics: machine learning tools for fault detection and diagnosis (FDD), black box digital twin to predict energy consumption and performances, AI application for demand defrost, optimization algorithms for complex system.

According to the COP26 conference, the main goal of the European Union is to limit both the pollutant emissions to become climate neutral in 2050 and the global warming, by setting to +1.5 °C the upper threshold for the ambient temperature increase. In this regard, sectors of heating and cooling in buildings must be decarbonized. This aspect can be faced by limiting the direct and indirect global warming contributions, through the use of environmentally friendly refrigerants, high-performance components and the employment of renewable sources. In this context, solar-assisted heat pumps (SAHPs) can be considered as interesting alternatives to conventional systems, in order to reach all the European targets in terms of reduction of the yearly energy consumption. This work proposes a numerical model of an indirect expansion solar assisted ground multi-sources (air, sun, ground) heat pump for residential heating. To cope with the mismatch between the solar availability and the thermal energy demand and to take full advantage of the solar radiation, a storage tank on the source side has been considered. A control strategy between different operating modes has been established in order to maximize the system coefficient of performance (COP), and dynamic simulations in Naples climate conditions have been performed. An optimization of several design parameters of the machine such as solar collector surface, storage tank volume and heat transfer surfaces of heat exchangers has been carried out, to maximize the seasonal performance (SCOP) of the system and minimise the investment costs. Although the adoption of a solar side and a geothermal heat exchanger (GHE) led to higher SCOP values, results show that more convenient solutions in term of total costs are the ones of a traditional heat pump for short lifetime periods, and the ones with solar loop and heat pump working in parallel for higher lifetime periods.

The building sector, especially for heating and cooling systems, represents approximately the 28% of the global CO2 emissions, and has to be de-carbonized according to the European greenhouse gas emissions target of 2050. Indirect and direct environmental impacts can be reduced by both increasing the use of renewable energy sources and employing natural fluids such as propane or CO2 instead of high-GWP fluids, especially for small capacity machines. In this context, solar-assisted heat pumps have been developed to take advantage of solar energy to increase the evaporation level and therefore the system performance. This paper deals with the modelling of a propane (R290) dual source (air/solar) heat pump in commercial applications, operating in heating mode, in which evaporation can take place alternatively through a fin-and-tube heat exchanger and directly inside solar collectors. Through the model, a control strategy to maximise system performances has been developed, defining a threshold for solar irradiance for switching evaporation through air or solar collectors. Furthermore, a dynamic performance analysis has been carried out in different climates conditions of Naples, Berlin, Bergen, for which higher SCOP up to respectively 14.2%, 8.9% and 7.8% are obtained. Finally, an economic analysis shows that, despite the high conveniences in term of seasonal performances, total costs of solar assisted heat pumps are still higher than only-air evaporation technology, without the employment of any incentives.

Refrigerant leakages in stationary air-conditioning and heat pumps represent almost the 50% of the amount of F-gas emissions declared by European Commission. Reducing leakages becomes crucially important because they cause both a high environmental impact and a decline of system performances. Typically, small leakages remain unidentified for a long period of time, causing a considerable long-term performance degradation of the machine. This paper deals with a mechanistic approach to simulate an air-to-air heat pump for domestic air conditioning, in different refrigerant loss rate scenarios, to evaluate the corresponding degradation of its seasonal performances. Results shows an average of 10% improvement of seasonal performances of the machine, with the employment of tools for fault detection and diagnosis (FDD) able to detect a refrigerant leakage through data collected by sensor mounted on the machine. Furthermore a 11% reduction of indirect contribute to global warming impact is achieved for small refrigerant leakages, whereas for larger leakages the direct emissions of CO2 become 65% lower.

Refrigerant R404A is going to be banned in Europe for different applications due to its very high GWP of 3943. R448A is a suitable alternative (GWP of 1390) among other new mixtures, and is thus receiving considerable attention in literature. However, despite several overall system studies, there is a lack of flow boiling data for this new blend. This paper therefore presents an experimental investigation on two-phase heat transfer and pressure drop of R448A in a single horizontal stainless steel (AISI 316) tube with an internal diameter of 6.0 mm. The effect of the operating parameters is firstly analyzed for the whole range of vapor qualities, by changing the mass flux from 146 to 601 kg/m2 s and the bubble saturation temperature from 23.3 to 56 °C (reduced pressures from 0.266 to 0.554). For the heat transfer coefficient measurements, the imposed heat flux is also varied from 2.5 to 40 kW/m2, leading to a total amount of 460 data points. Several pressure drop and heat transfer coefficient data are then compared to those of conventional refrigerant mixture R404A at the same operating conditions, showing different relative importance of nucleate and convective boiling contributions. Finally, the agreement between the R448A experimental database and some two-phase boiling heat transfer coefficient and frictional pressure drop prediction methods is evaluated with a statistical analysis. The best results are respectively obtained with the correlations of Gungor and Winterton and of Friedel.