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Article

Nuno Serra and Viriato Semiao

This paper aims to clarify the necessity of taking into account the commonly neglected radiation in built environments. Ignoring radiation within acclimatized spaces with…

Abstract

Purpose

This paper aims to clarify the necessity of taking into account the commonly neglected radiation in built environments. Ignoring radiation within acclimatized spaces with moist air, which is a participating medium, can yield inaccurate values of the relevant variables, endangering the Heating, ventilation, and air conditioning design accuracy and leading to energy inefficiencies and discomfort.

Design/methodology/approach

The paper uses computational fluid dynamics to predict non-isothermal flows with radiation, for both mixing and displacement ventilation strategies. The tool is applied to a lab-scale model (scale 1:30), and the results are compared with experimental data and predictions without radiation. Furthermore, the radiation influence is also assessed at real-scale level, including a parametric study on the effect of the air relative humidity on radiation.

Findings

The paper demonstrates the unequivocal impact of radiation on the flows thermal-kinematics at real-scale: ignoring radiation yields average air temperature differences of 2ºC. This becomes more evident for larger air optical thicknesses (larger relative humidity): changing it from 20 per cent to 50 per cent and 70 per cent yields maximum relative differences of 100 per cent for the velocity components and 0.4ºC for the air temperature. Nevertheless, the results for the lab-scale case are not so conclusive about the effect of moist air radiation on the thermal flow characteristics, but they evidence its impact on the flow kinematics (maximum relative differences of velocity components of 35 per cent).

Originality/value

The paper fulfills an identified need to clarify the relevant effects of air moisture on radiation and on the flow turbulence and thermal-kinematic characteristics for forced convective flows inside built environments.

Details

Engineering Computations, vol. 37 no. 4
Type: Research Article
ISSN: 0264-4401

Keywords

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Article

Nuno Serra and Viriato Semiao

The purpose of this paper is to compare two different ventilation strategies, displacement and mixing, in heat, ventilating and air conditioning (HVAC) systems with…

Abstract

Purpose

The purpose of this paper is to compare two different ventilation strategies, displacement and mixing, in heat, ventilating and air conditioning (HVAC) systems with recourse to computational fluid dynamics (CFD).

Design/methodology/approach

The flow and the heat and mass transfer are numerically predicted inside an air‐conditioned room with a desk and an occupant for the cooling and heating periods in moderate climate regions, like Mediterranean countries. Focus is placed on energy efficiency, thermal comfort and internal air quality (IAQ), evaluated from the simulations of the three‐dimensional, turbulent, non‐isothermal and buoyant flow of moist air.

Findings

For the cooling period, displacement exhibits higher energy and ventilation efficiencies promoting simultaneously better comfort for the occupant. For the heating period, mixing performs better due to the short‐circuit phenomenon occurring with the displacement flow. Overall, mixing behaves better for air‐conditioning of typical office rooms in Mediterranean‐climate countries, where heating and cooling climatization modes have to be alternated according to the season.

Research limitations/implications

Room, desk and occupant are designed as parallelepipeds. No experimental work is performed but models used are previously validated by other authors against experimental data.

Practical implications

The results indicate a short‐circuit flow phenomenon that must be avoided when designing HVAC systems.

Originality/value

Use of grilles layout typical for the cooling period to study the air‐conditioning of a typical office room during the heating period, incorporating in the model a transport equation for the moisture. IAQ is simulated together with the flow, the heat and the comfort conditions: velocities, temperature, predicted mean vote (PMV), predicted percentage of dissatisfied (PPD), draught rating (DR), PPD due to air quality (PDQ) and air moisture content are calculated simultaneously.

Details

Engineering Computations, vol. 26 no. 8
Type: Research Article
ISSN: 0264-4401

Keywords

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Article

Gilberto Tavares, Zdena Zsigraiova, Viriato Semiao and Maria da Graça Carvalho

The high costs of collection and transportation of municipal solid waste (MSW) on the overall waste management budget (sometimes more than 75 per cent) makes it an issue…

Abstract

Purpose

The high costs of collection and transportation of municipal solid waste (MSW) on the overall waste management budget (sometimes more than 75 per cent) makes it an issue to be urgently addressed for improvement. The paper aims to focus on the optimisation of routing networks for waste collection/transportation.

Design/methodology/approach

The paper proposes herein the application of geographic information system (GIS) 3D route modelling for waste collection/transportation to optimise the route according to the minimum fuel consumption criterion to different municipalities of the island of Santo Antao of Cape Verde.

Findings

The optimisation for the lowest fuel consumption yields 52 per cent savings in fuel, when compared to that for the shortest distance, even travelling a 34 percent longer distance, which shows the importance of considering simultaneously the relief of the territory and the lowest fuel consumption criterion when optimising vehicle routes.

Practical implications

With such a supporting decision tool savings in fuel are huge, the efficiency of management systems is improved and the environmental impact during daily operation is reduced. The GIS 3D route modelling takes into account the effects of both the road inclination and the vehicle load.

Originality/value

The originality of the work lies in the chosen approach. To optimise vehicle routes the criterion of minimum fuel consumption rather than the commonly used shortest distance is used, since fuel consumption is the factor reflecting actual costs relative to MSW management.

Details

Management of Environmental Quality: An International Journal, vol. 19 no. 4
Type: Research Article
ISSN: 1477-7835

Keywords

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Article

Vítor Geraldes, Viriato Semião and Maria Norberta Pinho

A mathematical model to predict the concentration polarisation in nanofiltration/reverse osmosis is described. It incorporates physical modelling for mass transfer…

Abstract

A mathematical model to predict the concentration polarisation in nanofiltration/reverse osmosis is described. It incorporates physical modelling for mass transfer, laminar hydrodynamics and the membrane rejection coefficient. The SIMPLE algorithm solves the discretised equations derived from the governing differential equations. The convection and diffusive terms of those equations are discretised by the upwind, the hybrid and the exponential schemes for comparison purposes. The hybrid scheme appears as the most suitable one for the type of flows studied herein. The model is first applied to predict the concentration polarisation in a slit, for which mathematical solutions for velocities and concentrations exist. Different grids are used within the hybrid scheme to evaluate the model sensitivity to the grid refinement. The 55×25 grid results agree excellently for engineering purposes with the known solutions. The model, incorporating a variation law for the membrane intrinsic rejection coefficient, was also applied to the predictions of a laboratory slit where experiments are performed and reported, yielding excellent results when compared with the experiments.

Details

Engineering Computations, vol. 17 no. 3
Type: Research Article
ISSN: 0264-4401

Keywords

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