Clito Afonso

Solar chimneys: simulation and experiment

The use of solar chimneys in buildings is one way to increment natural ventilation and, as a consequence, to improve indoor air quality. They are similar to conventional chimneys except that the south wall is replaced by a glazing. In order to compare the behaviour of a solar chimney with a conventional one, one of each was built in Porto. Results of measurements carried out in both chimneys are shown in this paper, as well as results of a thermal model specially developed for simulating solar chimneys, taking into account the wind effect. It was concluded that there is a significant increase in ventilation rate with solar chimneys, and that the thermal model predicts with good accuracy the measurements carried out.

Natural refrigerants for refrigeration and air-conditioning systems

In the past, several natural working fluids were used in refrigeration and air-conditioning systems. However, the appearance of CFCs caused a drastic reduction in the utilisation of those fluids. Understanding of the environmental damage of CFCs focused attention on alternative refrigerants. From these, the ones that have minimum (or nil) environmental impact are natural ones. This paper presents a review of the application of the main natural refrigerants, for refrigeration and air-conditioning systems, as an alternative to synthetic new refrigerants (HFCs). Recent research and development in this area is analysed and various cycles are considered.

A combined heat and power system for buildings driven by solar energy and gas

A novel hybrid solar/gas system intended to provide cooling/heating and electricity generation for buildings was developed. The system is based on the combination of an ejector heat pump cycle with a Rankine cycle. It is driven by solar energy and supplemented by a gas burner. The system also uses an environmentally friendly refrigerant to have minimal impact on the environment. Results of system computer modelling, prototype tests and economic analysis are reported. The system was judged to be viable and reliable. Technical improvements still have to be achieved to improve system economics.

Thermal performance of a novel air conditioning system using a liquid desiccant

A new air conditioning system using a liquid desiccant and needle impeller rotors has been modelled. Experimental data obtained for different components, i.e., evaporators and absorber, were used in the model. System performance was quantified through the definition of thermal coefficient of performance. Simulation results show the effect of different system parameters: ambient temperature, ambient humidity and heat exchanger efficiency.

Characterisation of Thermal Diode Panels For Use in the Cooling Season in Buildings

Thermal diode panels, incorporating heat pipes, were tested under cooling season conditions. Their thermophysical properties were evaluated by measuring temperature distributions in an experimental test facility and by using numerical simulation together with an optimisation procedure. The method allowed the quantification of thermal characteristics for both operating modes: forward and backward heat transfer. Forward heat transfer led to an apparent thermal conductivity up to five times, the one for backward mode.

A single tracer-gas method to characterize multi-room air exchanges

Abstract Quantification of whole-building infiltration rates is not enough to properly characterize indoor air quality and energy consumption in a building. It is also necessary to know the air exchanges between each room and outdoors, and among the different rooms themselves. A method to accomplish this objective using a single tracer gas was developed and experimentally verified under laboratory conditions. The method proved to be feasible and able of predicting airflows to within 10%. The advantages and disadvantages of this method, compared with multiple tracer-gas procedures to solve the same problems, are examined. Potential applications and perspectives for further developments are finally discussed.

Experimental and Numerical Analysis of Natural Ventilation With Combined Light/Vent Pipes

Abstract Both experimental and numerical procedures were developed for studying natural ventilation in combined light/vent pipes. An experimental tracer gas technique was used to measure ventilation rates in a test cell. Two different pipe terminals were simultaneously used, dividing the cell in two identical volumes, in order to allow a direct comparison of their performance. A 3D numerical model was developed using ansys5.5/flotran . Experimental and numerical results are shown and compared. It is concluded that pipe terminals significantly enhance ventilation, that one type of terminal has a better performance and that the numerical model underestimates measured flows.

Heat and Water Vapour Transfer Trough the Envelope of a Cold Chamber

The diffusion of water vapour in the atmospheric air through the elements of the envelope of a cold storage room, caused by the pressure gradient between the external and internal environment is inevitable in most situations. In fact, if the conditions in the interior of an envelope element are such as to enable the vapour freezing of the migrant water, the increase in volume from the formation of ice will causes the deformation of this element with very serious consequences, which can go up to its partial or total destruction. In this scenario, readily note the importance of vapour barriers associated with a properly designed insulation, tend to not only reduce the amount of water diffused, but also prevent the achievement of the conditions for freeze inside the engaging elements. The purpose of this work is to formulate the procedure for design of vapour barriers connected with the design of optimized thermal insulation, and then apply it to a cold chamber located in Portugal. Vapour barriers and the procedure for its design are both mandatory. The required thickness of the vapour barrier is relatively small, and the most appropriate insolation (maintaining the optimal thickness) is the black cork agglomerate.

Utilities and Effluent Treatment | Refrigeration

This article presents the general principles of refrigeration as well as the most common refrigeration systems, including a reference to recent developments. Refrigerants used are also described, including their environmental impact.