Work carried out in the UK, on behalf of, and fully funded by the Department Transport and Regions, has produced guidelines for the cost effective refurbishment of offices for natural and low energy ventilation. The aim of the work is to counteract the current trend towards the installation of air conditioning when other low energy strategies will provide suitable comfort conditions. This paper shows ways in which comfort conditions can be achieved with zero or minimal energy use in a range of office types, using natural ventilation or simple mechanical low energy systems.

This paper describes the first results of a series of laboratory investigations that is performed to characterise three different window types. The results show the air flow conditions for different ventilation strategies and temperature differences. For one of the windows values of the discharge coefficient are shown for both isothermal and non-isothermal flow conditions and the thermal comfort conditions are evaluated by measurements of velocity and temperature levels in the air flow in the occupied zone.

The international project Annex 35 "Hybrid ventilation in New and Retrofitted Office Buildings was accepted by the IEA at the Energy Conservation in Buildings & Community Systems Executive Committee Meeting in Washington June 1 997. The first year, starting August 1 1997, was a preparatory year and the four year working phase started August 1 998. The Annex have participants from 1 5 countries: Australia, Belgium, Canada, Denmark, Finland, France, Germany, Greece, Italy, Japan, Norway, Sweden, The Netherlands, United Kingdom and USA.

The simulation of room airing (ventilation by means of door/window opening) by means of CFD techniques requires a specially skilled user, because a number of difficulties arise since the first stage of simulations development, when the user is asked to choose the calculation domain and the time step, and choices which in principle appear correct may frequently lead to meaningless results. This work is centered on the 20, transient analysis of a single side enclosure where the ventilation is only due to temperature differences. Wind effect has not been taken into consideration.

When buoyancy forces, wind forces and envelope heat losses interact in a naturally ventilated building, the behaviour of the flow rate as a function of these parameters can be quite complex. This paper derives the equations for the flow rate in a two-zone building where one zone is above the other, and where each zone has a high and a low opening.

This paper attempts to answer questions like when thermal stratification is important and how to consider it in simple multi-zone models of natural ventilation. Both simple analytical solutions and comparison of CFO and multi-zone analysis suggest that the multi-zone modelling approaches with the assumption of uniform zonal air temperatures can significantly underestimate the neutral levels in buildings with large ventilation openings, indicating that the flow directions through some openings may not be correctly predicted.