Many existing offices either overheat in the summer or use excessive amounts of energy to maintain acceptable temperatures. The reasons are increasing internal heat gains from office IT equipment, poor efficiency lighting systems, density of staff and original poor building design causing excessive solar gains. The trend is for problem offices to have AC systems replaced - at the end of the life of the existing services - or installed in previously naturally ventilated offices when refurbishment occurs.

This paper aims to identify major characteristics of hybrid ventilation systems, whereby a clear distinction is made between ventilation for Indoor air quality control and ventilation as part of a strategy for thermal comfort in summer. Various building projects are used as illustration for the classification.

Mechanical and natural ventilation systems have developed separately during many years. The natural next step in this development is development of ventilation concepts that utilizes and combines the best features from each system into a new type of ventilation system - Hybrid Ventilation. Buildings with hybrid ventilation often include other sustainable technologies and an energy optimisation requires an integrated approach in the design of the building and its mechanical systems. Therefore, the hybrid ventilation design procedure differs from the design procedure for conventional HVAC.

An historical background of fluid mechanics used in computation of natural ventilation is provided. Unresolved issues in computation of natural ventilation for thermal comfort are discussed. These issues include the influence of building porosity on wind pressure difference coefficients; wind shelter effects; indoor air flow resistance; air flow for thermal comfort and heat stress relief; air flow computation techniques; and natural ventilation in home energy rating schemes.

The Air Infiltration and Ventilation Centre was established as a jointly funded International Energy Agency activity in 1979. This paper seeks to describe some of the work of the AIVC and outline its evolving structure which is aimed at strengthening the link between research and application.

The conversion efficiency of solar cells is dependent on the cell temperature and they perform better the colder the cells are. The paper discusses cooling of solar cells by providing solar cell modules with an air gap behind the modules. The stack effect in the air gap drives the ventilation flow in a hybrid ventilation system. Expressions for the bulk flow properties (volumetric flow rate, mass flow rate and temperature) are presented as a function of the geometry of the air gap and the location of the heat input (configuration factor).

Current thermal comfort standards and the models underpinning them purport to be equally applicable across all types of buildings, ventilation systems, occupancy patterns, and climate zones. A recent ASHRAE-sponsored research project (RP-884) critically evaluated this by statistically analysing a large thermal comfort field research database from 160 buildings scattered all over the would (n=22,000).

Demand Based Ventilation systems are potentially valuable in terms of energy saving in building with fluctuating occupation patterns. Most demand based ventilation systems are controlled by C02 measurement. However this approach cannot take account of other polluting elements found in indoor air. This paper will describe the results of a study of the indoor air quality in a recently built university library with continuous ventilation. The literature relating to typical levels of naturally occurring gases, volatile organic compounds and microbes, in indoor air is considered.