Adolfo Palombo

R407C as an alternative to R22 in vapour compression plant: an experimental study

The problem of HCFC22 phase-out in refrigeration plants is analysed. A comparison is performed between R22 and R407C. The latter seems a promising drop-in substitute. Indeed, its use in existing plants would only require discharge of mineral oil and refilling with a compatible polyolester oil. The experimental tests are performed in a plant consisting in a water-cooled vapor-compression circuit employed for cooling a water–glycol mixture in a closed-loop system. Both the thermodynamic properties and general performance of R407C are comparable with those of R22. The COP, however, is 5–17% lower. As a consequence, in order to provide the same refrigerating load, a plant working with R407C requires higher electric-power consumption. The operational behaviour of R407C is increasingly better with increasing condensation and evaporation temperature. Therefore, R407C is a good R22 substitute in all applications requiring high evaporation temperatures, such as air-conditioning plants.

Economic evaluation of hybrid evaporative technology implementation in Italy

Abstract Evaporative cooling can be adopted in wet areas by integration into HVAC systems. Processing TRY data for Italy, the economics of three-stage evaporative cooling systems were examined. Summertime conventional system operating costs and hybrid system savings were evaluated. The method was based on a simplified approach that is not intended as a substitute for accurate dynamic modelling, but as a simple analysis tool. The results were found to be strongly dependent on: climatic area, internal set point, initial cost of extra equipment. The highest savings appeared to be achieved in the middle-south of Italy.

Weather data for building energy cost-benefit analysis

This paper deals with European TRY weather data processing for climatic indexes generation, useful for HVAC energy and cost simplified evaluation. For nine Italian locations are presented: 99 and 2.5% dry bulb temperatures, 2.5% wet bulb temperatures, heating and cooling degree days, latent enthalpy days, unitary sensible and latent loads. TRY psychrometric data were processed according to a bin method that preserves the correlation between dry bulb temperature and moisture content, and then reduced by an averaging technique. An example is worked out in order to present an engineering shorthand for energy and cost evaluation of HVAC system.

One-Dimensional Model of a Tubular Solid Oxide Fuel Cell

In this paper, a detailed model of a solid oxide fuel cell (SOFC) tube is presented. The SOFC tube is discretized along its longitudinal axis. Detailed models of the kinetics of the shift and reforming reactions are introduced in order to evaluate their rates along the SOFC axis. Energy, moles, and mass balances are performed for each slice of the components under investigation, allowing the calculation of temperature profiles. Friction factors and heat-exchange coefficients are calculated by means of experimental correlations. As for the SOFC overvoltages, the activation overvoltage is calculated using the Butler‐Volmer equation and semiempirical correlations for the exchange current density, Ohmic losses are evaluated introducing an appropriate electrical scheme and material resistivities, and concentration overvoltage is calculated by means of both binary and Knudsen diffusion coefficients. On the basis of this model, a case study is presented and discussed, in which temperatures, pressures, chemical compositions, and electrical parameters are evaluated for each slice of the SOFC tube under investigation. Finally, a sensitivity analysis is performed, in order to investigate the influence of the design parameters on the performance of the system. DOI: 10.1115/1.2784296

Solar heating and cooling systems by absorption and adsorption chillers driven by stationary and concentrating photovoltaic/thermal solar collectors: Modelling and simulation

Solar heating and cooling systems are a promising technology which may significantly contribute to the reduction of greenhouse gas emissions, the enhancement of energy efficiency, and the increase of renewables share in the building sector. The available literature show a high number of papers aiming at investigating solar heating and cooling systems based on heat driven and solar technologies, configurations, operating strategies, and financing issues. Nevertheless, none of the papers available in literature investigates the possibility to replace conventional solar thermal collectors by flat plat and concentrating photovoltaic/thermal systems, also producing renewable electricity. To cover this lack of knowledge, in this paper a dynamic simulation model of novel solar polygeneration heating and cooling systems is presented. Such dynamic simulation model is developed and implemented in a computer code, written in MatLab, and allows investigating the energy, economic and environmental performance of such novel solar polygeneration systems, based on both adsorption and absorption chiller technologies fed by dish-shaped concentrating and flat photovoltaic/thermal collectors. In order to show the potentiality of the presented tool, a comprehensive parametric case study is carried out to find out the optimal system configurations, as a function of crucial design and operating parameters and of weather conditions. The presented case study analysis refers to a small cluster of four buildings, including office and residential spaces, located in different European weather zones. The modelled solar polygeneration systems simultaneously produce electricity, space heating and cooling, and domestic hot water; electricity is self-consumed or delivered to the electrical grid. For comparative purposes, two different back-up system configurations, based on an electric chiller and a condensing gas-fired heater are also taken into account as conventional reference building-plant systems. By means of this systematic parametric analysis, comprehensive guidelines for system designers, practitioners and/or researchers focused on the development and use of solar heating and cooling systems are provided.

Simulation Model and Analysis of a Small Solar-Assisted Refrigeration System: Dynamic Simulation and Optimization

In this paper, a complete zero-dimensional transient simulation model of a solar-assisted refrigeration plant is presented. In addition, a case study is discussed, aiming at determining the optimal configuration of the system, from the energetic point of view, in a specific application. The system under analysis consisted of several components: evacuated solar collectors, circulation pumps, variable speed pump, water storage tanks, auxiliary heater, single-stage H2 O-LiBr absorption chiller, cooling tower, feedback controller, on/off hysteresis controller, single lumped capacitance building and controllers. The simulation was performed using the TRNSYS environment which is provided by a large component library. This software also includes a detailed database with weather parameters for several European cities. The system and the building were simulated using TRNSYS built in models. The system was simulated using specially designed control strategies and varying the main design variables. In particular, a variable speed pump on the solar collector was implemented in order to maximize the tank temperature and minimizing the heat losses. Finally a sensitivity analysis was also performed in order to calculate the set of synthesis/design parameters that maximize the total system efficiency.Copyright

Cold potable water measurement by means of a combination meter

In this paper an accurate description of a combination water meter is provided. Therefore, the main results of calibration tests are presented. Final considerations about the reliability of a combination meter in very wide flow range applications are also reported.

Push-pull ventilation system: a CFD approach for the performance analysis

SYNOPSIS In this paper the results of a CFD investigation for a push-pull local ventilation system are presented. The velocity field and the capture efficiency prediction are investigated for different system arrangements. The analysis is carried out for systems respectively with and without fluid-dynamic obstacle in the working plane and for dust pollutants with particle diameters ranging from 1.0 to 100 μm and emission velocities between 1.0 and 7.0 m/s. The analysis, carried out using the commercial code FLUENT, shows that the system performances are dependent on operating conditions and are influenced by the presence of the above-mentioned obstacle on the working plane. In the case of working plane emission without obstacle the system capture efficiency is in general very low never exceeding 25%. Higher efficiencies are instead achieved for particle emission from a vessel placed in the systems working plane centre. In this case even unitary peak efficiencies are reached for particular operating conditions.

Outdoor-air design conditions relating to the capacity of air-conditioning systems

In this paper we present work involving the processing of climatic data relating to some Italian cities, taken from a set of data known as European ‘test reference year’ (TRY). We aim to make a critical comparison of the thermohygrometric conditions of outdoor air in the summer season thus obtained with those design conditions as laid down by Italian regulations (UNI 10339) and with those recently suggested by ASHRAE. Subsequently, and with reference to some traditional and recent applications in the field of air-conditioning, we report on how performance differs according to outdoor summer thermohygrometric design conditions, such as those indicated by UNI 10339, by ASHRAE and by the processing of TRY data. Finally, we discuss the optimal choice of design conditions according to the type of application. Copyright

Water flow measurement in large bore pipes: an experimental comparison between two different types of insertion flowmeters.

In this paper the metrological behavior of two different insertion flowmeters (magnetic and turbine types) in large water pipes is described. A master-slave calibration was carried out in order to estimate the overall uncertainty of the tested meters. The experimental results show that (i) the magnetic insertion tested flowmeter performs the claimed accuracy (+/- 2%) within all the flow range (20:1); (ii) the insertion turbine tested meter, instead, reaches the claimed accuracy just in the upper zone of the flow range.