Thermo-economic Design and Optimization of Cooling Systems Employed in Cruise Ship

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

Thermo-economic Design and Optimization of Cooling Systems Employed in Cruise Ship

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

EPBD 2023, F-GAS 2024, Eco-design and safety standards: Which design margins to be compliant with? An assessment of heat pumps for cooling

To decarbonize Europe achieving almost zero emissions in 2050, more stringent regulations are going to be applied. Particularly, Europe is investing in the emissions’ re-duction of buildings (existing and new ones), and strong improvements in energy performance of building are expected according to novel energy performance of building directive (at last phase of negotiation). At the same time, the production and use of fluorinated gases will be further reduced with the novel F-Gas regulation (under Parliament approval). New F-Gas will affect remarkably the small size, air-to-air split systems for air-conditioning, since no fluorinated gases will be used after 2035, forcing manufacturers to the use of natural refrigerants. Being propane the most efficient among the non-toxic natural refrigerants, less refrigerant would be charged into systems according to current safety standards: this would potentially reduce the heat transfer surfaces and, consequently, for the same capacity, the energy efficiency or, for the same efficiency, the capacity would decrease. In this paper, some scenario analyses, complying with actual and future plausible dispositions, are presented, in order to showing the margins for de-sign and commenting criticalities. In particular, the optimal design options are proposed for different fluids, in terms of costs vs energy performance, under representative cases, in terms of weather conditions and building types in Italy (existing ones and new ones respecting high-efficiency standards, trying to meet the requirements of hypothesized national law following the draft of the novel EPBD)

Notulae to the Italian alien vascular flora: 17

In this contribution, new data concerning the distribution of vascular flora alien to Italy are presented. It includes new records and status changes from casual to naturalized for Italy or for Italian administrative regions for taxa in the genera Callianthe, Chamaecyparis, Chamaeiris, Cotoneaster, Erigeron, Freesia, Hemerocallis, Juglans, Kalanchoë, Ludwigia, Nassella, Paulownia, Physocarpus, Pistia, Saccharum, Setaria, and Vachellia. Nomenclatural and distribution updates, published elsewhere, and corrections are provided as supplementary material

Effect of refrigerant leakages on energy consumption of an electric heat pump for domestic air-conditioning

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

Use of artificial intelligence in the refrigeration field

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

Performance degradation of air source heat pumps under faulty conditions

The ongoing European regulations towards the decarbonization of energy intensive sectors such as heating and cooling will lead to an increase of heat pump appliances. Apart from anomalies that can be detected in a preliminary phase after the start-up, soft faults such as refrigerant leakage and heat exchanger fouling may cause a performance degradation in such systems that evolves in time and that must be detected before it becomes too big. From this perspective, in a previous paper (Pelella et al. [1]) it has been demonstrated that, in cooling mode, a seasonal performance penalization up to 50% can be reached in case of a not-planned maintenance scenario, whereas wherever a timed or intelligent maintenance strategy is implemented based on data-monitoring, this impact can be significantly reduced. Therefore, in order to extend the analysis previously carried out to the heating cases, and to evaluate the consequent energetic degradation of the system in case of soft faults occurring, depending on different climate conditions and maintenance scenarios, this paper develops a physic-based model to simulate system components and to describe the fault phenomenology on a residential 2.6 kW air-to-air heat pump, operating in winter mode. The results show that in heating mode a 40% condenser fouling and a 30% refrigerant leakage cause a performance degradation of respectively 16% and 12%, whereas in case of evaporator fouling the performance penalization is only of 3.2%. Moreover, the performance degradation is enhanced by the overlapping effect of simultaneous faults. Finally, from seasonal simulations of the heat pump along an entire machine lifetime of 12 years, it is found that none of the maintenance strategies analysed is able to significantly reduce the number of scenarios penalized by faults, opening to the potential development of systems for the automatic fault detection, diagnosis, and evaluation (FDDE)

A comparison of heat transfer correlations applied to an Organic Rankine Cycle

Organic Rankine Cycles (ORC) are often based on the utilization of special dry or isentropic fluids, namely substances with a vertical or positive slope of the saturated steam curve.Several heat transfer correlations for boiling process are available in literature.However, only a few of them are specifically developed and validated for the case of the organic fluids. Such correlations are tested and extrapolated by means of suitable experimental devices and with a specific organic fluid, presenting non-negligible percentage error variations when compared with experimental results concerning different organic fluids.This paper investigates the impact of the overall heat transfer coefficient evaluated by means of different correlations available in literature on the main output parameters of an Organic Rankine Cycles, using a zero-dimensional numerical model.Two case studies are investigated, both of them powered by medium-enthalpy geothermal source which provides a constant thermal load. The first case study concerns a 1.20 MWel ORC, powered by geofluid at 160 °C and 7.00 bar and using n-pentane. The second ORC case study is supposed to provide 8.00 kWel and to be powered by geofluid available at 95.0 °C and 3.00 bar and using R245fa, in agreement with the results available in literature. Both of the models are developed and simulated in Engineering Equation Solver (EES) environment. Keywords: Heat transfer correlations, Organic Rankine Cycle, Geothermal, Numerical model, Organic fluids, Shell&Tube heat exchange

Dual source (air-solar) heat pump: thermo-economic analysis of sizing factors depending on climate conditions

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

NUMERICAL ANALYSIS OF A SOLAR-ASSISTED DUAL-SOURCE HEAT PUMP COUPLED WITH A THERMAL STORAGE FOR RESIDENTIAL HEATING

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