1,720,992 research outputs found
Seasonal Performance Analysis of a Residential Heat Pump Using Different Fluids with Low Environmental Impact
No full textAbstractThe growing of the energy consumption, in particular from buildings, both residential and commercial has induced a major interest for the analysis of the seasonal performance of heat pumps. The same considerations are effective for the well-known environmental problems related to direct and indirect emissions of carbon dioxide into the atmosphere and the incentives to support energy efficiency. In this work an air to water heat pump working with R290 and HFO1234yf has been modeled and simulated using the software package IMST-ART in order to evaluate the seasonal performance. Two different types of applications were considered: fan coils and radiant heat floor panels. Different types of building are considered. The seasonal performance in heating mode, SCOP, is calculated by coupling the performance of the heat pump in different operative conditions to a heating demand curve, in two different climate zones (average and colder). The results of the simulations show better performance of the heat pump with propane in both climates and applications, which is probably due to the state of current technology of the different components. In particular, the global performance of the compressor working with R1234yf is not yet optimized. At the same time a new design of the evaporator is desirable to reduce the pressure drops with R1234yf
Experimental Validation of Critical Heat Flux (CHF) Predictive Methods for a New Synthetic fluid with Low Environmental Impact
No full textAbstractThis work presents experimental critical heat flux (CHF) values for a low environmental impact synthetic refrigerant and their comparison with well-known correlations from scientific literature. Tests were performed with HFO-1234yf in an aluminum heat sink made up of seven mini-channels, each of them 2mm wide and 1mm high. The heated length was 25mm. Experiments have been obtained in a variety of thermodynamic condition: the R1234yf saturation temperatures Tsat ranged from 25 up to 65°C (corresponding to medium-to-high reduced pressures), whilst the mass fluxes G had been fixed to 150 up to 300kg/m2 s. The tests have been carried out by increasing the heat dissipated by the boiling refrigerant until the thermal crisis occurred and the corresponding heat flux value was recorded as CHF. The experimental results were finally compared to the well-known correlations of Wojtan et al. [1], Kuan [2], Katto-Ohno [3], Zhang et al. [4] and Anwar et al. [5] to investigate their effectiveness with the present data. The latter correlation was found to better predict the experimental values
Experimental study of flow boiling of propane in a 6 MM internal diameter horizontal tube
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Process control and energy saving in the ladle stage of a metal casting process through physics-based and ANN-based modelling approaches
Get PDFThe process and temperature control of metal casting applications is of utmost importance both to guarantee the good quality of the final product and also to pursue an energy saving policy. For this purpose, in this paper two different modelling approaches have been proposed to predict the liquid steel temperature inside a ladle for metal casting, shortly before the casting process. The first is a physics-based grey-box model relying on equations for the characterization of the heat transfer mechanisms inside the ladle structure, whereas the second approach relies on artificial neural networks (ANNs). Both methods have been calibrated with experimental data of a case study plant, and subsequently assessed and compared in terms of prediction accuracy. Results show that the physics-based approach is able to predict the casting temperature with a higher mean absolute error (MAE) of 14 °C, whereas the ANNs predictions result to be better, with MAEs around 6 °C. On the other hand, it has been demonstrated that the ANNs approach may lack of reliability, especially if input data strongly differ from the calibration dataset, whereas the physics-based approach results to be more consistent and trustworthy. Finally, an energy analysis is conducted to demonstrate the feasibility of the model in evaluating the potential energy saving compared with situations in which decisions are taken by operators without the aid of a model predictive control
Sizing, safety, lifetime performance, environmental impact and costs of residential A-to-A heat pumps: Current and future scenarios according to new F-GAS regulation and EPBD
Get PDFThe 2024 F-GAS Regulation mandates the phase-out of fluorinated gases across multiple sectors, promoting the adoption of natural refrigerants like propane, which pose flammability risks. Simultaneously, the 2024 Energy Performance of Buildings Directive (EPBD) introduces stricter requirements for building thermophysical parameters, potentially reducing heating and cooling peak loads. Together, these changes will significantly influence the design and optimization of residential heat pump systems. This study aims to identify optimal heat pump design solutions for various building types—both existing and new EPBD-compliant structures—focusing on performance, environmental impact, and costs under the new F-GAS regulation. A numerical approach was used to simulate the performance of different air-to-air heat pump configurations, with cooling capacities ranging from 1.5 to 5 kW. Lifetime performance, total costs, and equivalent warming impact were evaluated across diverse climate conditions and room sizes, taking into account safety constraints from the EN378 standard on refrigerant charge limits. Preliminary comparisons of refrigerants show that R32 offers the best performance and cost-efficiency, while propane performs similarly but with the lowest environmental impact. R454C, however, performed the worst. In terms of lifetime performance, heat pumps in EPBD 2024-compliant buildings are projected to consume 30–40 % less energy compared to 2021 standards, and up to 70 % less than buildings from 1976. Furthermore, the reduced operational costs, especially in warmer climates, decrease the necessity for high-performance systems. Finally, we provide a methodology to extend these results to other European climates, in order to provide indications for both heat pump manufacturers, to face with correlation between required heating and cooling buildings loads, heat pumps energy classes and employed refrigerants, and policy makers, to remark the consequences on the heat pump market and to show various possible future scenarios
Critical heat flux in a multi-minichannel heat sink. Effect of the heated length-on-diameter ratio
No full textExperimental CHF for low-GWP fluids and R134a. Effect of the L h /D ratio at low and high mass velocities
No full textThermo-economic Design and Optimization of Cooling Systems Employed in Cruise Ship
Get PDFThe 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 optimization of vertical farms exploring multiple design options for the built environment and HVAC system
No full textNew challenges in the agricultural sector, arising from demographic growth, resource depletion, energy and environmental concerns, and food security, are driving the development of sustainable crop cultivation techniques such as vertical farming. This approach enables year-round, localized production while significantly reducing water and land use. However, its higher energy demand, particularly due to artificial lighting and climate control, necessitates a thorough analysis of energy consumption and economic factors, which may also be influenced by the external climate conditions where the system is implemented. This study aims to perform a multi-objective design optimization of vertical farms using a genetic algorithm, identifying the optimal combination of design parameters to achieve the best trade-off between specific primary energy consumption (SPEC), investment costs (SCI), and energy costs (SCE), and assuming the use of gas boiler, electric chiller and proper walls insulation materials. Key design variables include building dimensions, building envelope thickness and materials (such as phase change materials and different insulation types), as well as the design characteristics of chillers and boilers. The analysis considers three climate conditions, Athens (warm), Strasbourg (mild), and Helsinki (cold). Results indicate that SPEC, SCI, and SCE decrease when increasing building volume, air recirculation ratio, air temperature at the air conditioning outlet, and when minimizing solar radiation absorption, except in cold climates. The non-dominated solutions on the Pareto front range from 0.8 to 1.4 €∙kg−1 for SCI, with slightly lower SPEC observed in colder climates due to predominant cooling and dehumidification needs (until 42 kWh∙kg−1 for Athens, 40 kWh∙kg−1 for Strasbourg and 38 kWh∙kg−1 for Helsinki). The lowest values are achieved when ammonia is used as the chiller working fluid, due to its higher volumetric capacity compared to other refrigerants. Furthermore, using phase change materials as only layer may be beneficial in some optimal solutions in terms of energy savings, despite the increased costs
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