F. de Rossi

Experimental evaluation of R22 and R407C evaporative heat transfer coefficients in a vapour compression plant

The mean heat transfer coeAcients of R22 and R407C in the coaxial counterflow evaporator (20 mm ID) of a refrigerating vapour compression plant have been experimentally measured. The experimental conditions under which heat transfer coeAcients were determined reflect a typical working situation for small-scale refrigeration systems. The heat flux ranged from 1.9 to 9.1 kW/m 2 and the mass flux was varied from 30 to 140 kg/m 2 s. The results illustrate that the R22 heat transfer coeAcient is always greater than that of R407C. Furthermore, a comparison carried out between the experimental data and those predicted by means of the most credited literature relationships showed a strongly overprediction for R407C coeAcients. # 2000 Elsevier Science Ltd and IIR. All rights reserved.

Behaviour and performances of R502 alternative working fluids in refrigerating plants

Abstract This is an experimental study that aims to evaluate both general characteristics and system performances of the most credited fluids that are likely to substitute for R502 in a refrigeration plant. R402A, R402B, R403B and R408A (still containing HCFC) and R404A, R407A and FX40 (chlorine free) have been tested. Generally, both of them have showed performances very close to those of R502 except R403B, whose COP has been found to be about 8% lower than that of R502.

Mitigating the cooling need and improvement of indoor conditions in Mediterranean educational buildings, by means of green roofs. Results of a case study

Indoor overheating risk and increased energy demand for cooling are becoming more and more frequent in the building sector of the Mediterranean area. In detail, for the reduction of the energy consumption of educational buildings, characterized by high endogenous gains, the particular boundary conditions affecting their use should be taken in consideration, and thus schedules of occupancy, wide necessity of air-changes for air quality. This paper, with reference to a case study, proposes deep investigations aimed at optimizing the annual energy performance of an educational building of the University of Sannio, located in the Southern Italy. A numerical model of the building has been designed and validated according to monitored data. Starting from the present scenario, after a complete refurbishment of the building envelope, the potentialities of several typologies of green roofs - by considering also the implementation of the adaptive approach in the comfort standard - have been tested. The scope is the optimization of the energy demand for the annual microclimatic control, by avoiding an energy-intensive operation of the air-conditioning devices during the warm season.

Technical and economic analysis of green roofs to reduce building cooling needs

Several public/private institutions, at international and national levels, consider green roofs effective energy efficiency measures. A large feasibility study of their technical and economical profitability is proposed here. The main heat transfer phenomena and a brief literature state of the art are presented. Congruent with the cost-optimal approach, the economic indicators are described, as well as the physical set of equations for evaluating the energy performances of green roofs. Moreover, the case studies are shown by describing the various climates considered, energy and water costs, efficiency of power systems, emissions factors, and all parameters necessary for suitable feasibility studies. Various climates and building technologies are taken into account, as well as common typologies of extensive green roofs. The results show a relative feasibility of green roofs, when the watering costs are limited, and if the buildings are not properly insulated, so that the installation of greenery, combined with the added thermal insulation, provides energy savings for both heating and cooling. A final section proposes some considerations for improving the profitability of green roofs by adopting rainwater harvesting systems.