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

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

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

Determinazione sperimentale e studio analitico delle perdite di carico durante l'evaporazione in convezione forzata di fluidi refrigeranti

Sono riportati i risultati di un' indagine per la determinazione delle perdite di carico durante l'evaporazione dei seguenti fluidi refrigeranti: R22, R134a, R404A, R407C, R417A, R507A. L'apparato sperimentale è costituito da un tubo orizzontale, liscio, di diametro interno di 6.00 mm riscaldato per effetto Joule. Le condizioni operative variate sono: la temperatura di saturazione tra -10°C e +40°C, il flusso di massa tra 200 e 1200 kg/m2s e il flusso termico in parete tra 5 e 40 kW/m2. Il database sperimentale raccolto (circa 800 punti) è stato utilizzato per implementare un'analisi statitistica per determinare il migliore tra i metodi predittivi in letteratura per opportune condizioni operative