air movement

This paper presents the results of a monitoring programme on a medium sized educational building which has had the external walls re-clad. The objective behind the re-cladding was to improve the durability of the building and to improve the thermal performance. The objectives of this work were to establish the viability of the calculation techniques used to simulate the ventilation, thermal and moisture performance of the re-cladding system. The results have shown that there is a good agreement between the methods currently being used and the actual performance.

In the UK the increased use of natural ventilation in buildings is being encouraged, particularly during hot weather as an alternative to air conditioning or mechanical ventilation. In order to take advantage of this option building designers need to be able to estimate potential air flows. Conventional calculation methods assume windows to be simple openings, however in practice the situation is more complex since during hot weather the opening is likely to be shielded by some form of solar shading device.

A fundamental objective of this report is to investigate the techniques used in the design and research fields for the evaluation of thermal and air flow simulations. The scope is restricted to the whole building rather than flow and heat transfer within individual structural elements (e.g. cavity walls). Considerable developments are taking place in the field of air flow and thermal simulation. Rather than present an in-depth study of these developments, this report concentrates on the rather more general aspects of the combined simulation.

Starting from the basic governing equations for fluid flows, a three-dimensional computational fluid dynamics (CFD) code is described. The pre-processing and post-processing software was integrated with the CFD code to form a more user-friendly computer package. This new computer package has been used to carry out several simulations on air and smoke movement in atrium with balconies. It has been found that the pre?processing and post-processing software can greatly reduce the data preparation and analysis time. It can also reduce the likelihood of making errors in data entry.

Experimental U-values based on measured heat flows through the walls of some houses have been found to be significantly higher than predicted by conventional calculation procedures. The work was carried out in ordinary occupied houses, and included measurements on party, internal and external walls. There are a number of possible reasons for the differences including thermal bridging, high thermal conductivities and excessive air movement in the wall cavities and behind plasterboard dry lining.