L. Mei

Thermal modelling of a building with an integrated ventilated PV façade

This paper presents a dynamic thermal model based on TRNSYS, for a building with an integrated ventilated PV facade/solar air collector system. The building model developed has been validated against experimental data from a 6.5 m high PV facade on the Mataro Library near Barcelona. Preheating of the ventilation air within the facade is through incident solar radiation heating of the PV elements and subsequent heat transmission to the air within the ventilation gap. The warmed air can be used for building heating in winter. Modelled and measured air temperatures are found to be in good agreement. The heating and cooling loads for the building with and without such a ventilated facade have been calculated and the impact of climatic variations on the performance such buildings has also been investigated. It was found that the cooling loads are marginally higher with the PV facade for all locations considered, whereas the impact of the facade on the heating load depends critically on location.

Nodal network and CFD simulation of airflow and heat transfer in double skin facades with blinds

The paper describes a modelling study of heat transfer and buoyancy-driven airflow in double skin facades consisting of a glass outer layer, a control device (venetian blind) and a double-glazed inner skin. The modelling study was based on two approaches — a component-based, lumped parameter simulation which used a public domain, open source differential/algebraic equation solver and a detailed, CFD calculation which included air flow, conduction, convection and radiation. The primary objective of the work was to compare the performance of the simplified model with the output of a rigorous CFD calculation.

Simulation and validation of a VAV system with an ANN fan model and a non-linear VAV box model

The results of modelling and simulating a laboratory variable air volume (VAV) test rig are presented. The modelling for each component, such as fan, duct and VAV terminal box, with their control systems, in the test rig has been achieved and the simulations via the logical connection of the component models have been performed by means of an HVACSIM+ platform. A polynomial curve fitting method and a ten neuron sigmoid artificial neural network (ANN) model are used to model the non-linear characteristic of the fan. The ANN is shown to be superior. A non-linear characteristic terminal box model based on the experimental modelling of a European box is developed. The ANN fan model and the terminal box model are inserted in the program of the HVACSIM+ platform as the new component subroutine. The accurate simulation results for the VAV test rig via HVACSIM+ are validated by the real system operation performance.

CFD modelling of naturally ventilated double-skin facades with venetian blinds.

This study describes computational fluid dynamics (CFD) modelling of naturally ventilated double-skin facades (DSFs) with Venetian blinds inside the facade cavity. The 2D modelling work investigates the coupled convective, conductive and radiative heat transfer through the DSF system. The angles of the Venetian blind can be adjusted and a series of angles (0°, 30°, 45°, 60° and 80°) have been modelled. The modelling results are compared with the measurements from a section of a prototype-facade testing facility and with predictions from a component-based nodal model. Agreement between the three methods is generally good. It is thought that discrepancies in the results are caused by the simplification of the CFD model resulting in less turbulence mixing within the facade cavity. The CFD simulation output suggests that the presence of the Venetian blinds is able to enhance the natural ventilation flow within the facade cavity and significantly reduce the heat gains to the internal environment. It was also found that the convective heat transfer coefficients on the glazing surfaces are insensitive to the blind angles. The work demonstrated the capability of CFD for modelling complicated heat transfer processes through the DSF system and offered some guidance for CFD practitioners who wish to model similar type of flow.