Exergy analysis of a cooling system: experimental investigation on the consequences of the retrofit of R22 with R422D

In this article, the performances of a walk-in air cooler working with R22 and its substitute R422D are experimentally studied. To define a full comparison on the performance characteristics of R22 and R422D, both an energetic and an exergetic analyses are proposed. The experimental investigation was carried out considering four levels of refrigeration capacity: 920, 1340, 1925 and 2250 W. All tests were run at steady-state conditions and by keeping the value of the external air temperature equal to 22°C. The experimental analysis allowed the determination of the COP, the exergetic efficiency, the exergy flow destroyed in each component and other variables characterizing the working of the plant. The results demonstrated that COP of R422D is, on average, 20% lower than that of R22. Furthermore, for plant whose condenser is air cooled, R422D could lead to increase the fan speed or to adopt bigger blowers

EXPERIMENTS DURING FLOW BOILING OF A R22 DROP-IN: R422D ADIABATIC PRESSURE GRADIENTS

R22, the HCFC most widely used in refrigeration and air-conditioning systems in the last years, is phasing-out. R422D, a zero ozone-depleting mixture of R125, R134a and R600a (65.1%/31.5%/3.4% by weight, respectively), has been recently proposed as a drop-in substitute. For energy consumption calculations and temperature control, it is of primary importance to estimate operating conditions after substitution. To determine pressure drop in the evaporator and piping line to the compressor, in this paper the experimental adiabatic pressure gradients during flow boiling of R422D are reported for a circular smooth horizontal tube (3.00 mm inner radius) in a range of operating conditions of interest for dry-expansion evaporators. The data are used to establish the best predictive method for calculations and its accuracy: the Moreno-Quibèn and Thome method provided the best predictions for the whole database and also for the segregated data in the annular flow regime. Finally, the experimental data have been compared with the adiabatic pressure gradients of both R22 and its much used alternative R407C available in the literature

A thermoeconomic model of a photovoltaic heat pump

In this paper the model of a heat pump whose evaporator operates as a photovoltaic collector, is studied. The energy balance equations have been used for some heat pump components, and for each layer of the photovoltaic evaporator: covering glaze, photovoltaic modules, thermal absorber plate, refrigerant tube and insulator. The model has been solved by means of a program using proper simplifications. The system input is represented by the solar radiation intensity and the environment temperature, that influence the output electric power of the photovoltaic modules and the evaporation power. The model results have been obtained referring to the photovoltaic evaporator and the plant operating as heat pump, in terms of the photovoltaic evaporator layers temperatures, the refrigerant fluid properties values in the cycle fundamental points, the thermal and mechanical powers, the efficiencies that characterize the plant performances from the energy, exergy and economic point of view. This study allows to realize a thermoeconomic comparison between a photovoltaic heat pump and a traditional heat pump under the same working conditions

Carbon Dioxide Heat Transfer Coefficients And Pressure Drops During Flow Boiling: Assessment Of Predictive Methods

Among the alternatives to the HCFCs and HFCs, carbon dioxide emerged as one of the most promising environmentally friendly refrigerants. In past years many works were carried out about CO2 flow boiling and very different two-phase flow characteristics from conventional fluids were found. In order to assess the best predictive methods for the evaluation of CO2 heat transfer coefficients and pressure gradients in macro-channels, in the current article a literature survey of works and a collection of the results of statistical comparisons available in literature are furnished. In addition the experimental data from University of Naples are used to run a deeper analysis. Both a statistical and a direct comparison against some of the most quoted predictive methods are carried out. Methods implemented both for low–medium pressure refrigerants and specifically developed for R744 are used in the comparison. Some general indications about the choice of the predictive methods dependently on the operating conditions are given

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)