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.

The UK government has signed the Kyoto Protocol and it has committed to reducing C02 emissions to 20% below 1990 levels by 2010. As buildings are responsible for approximately half of the UK C02 emissions, of which the domestic sector accounts for 50%, meeting this target will require a significant contribution from the domestic sector.

The inherent unreliability of the forces which drive natural ventilation can make such systems unattractive for the designer. Developing interest in mixed-mode ventilation is prompting difficulties in sourcing components suitable for ultra-low velocity flow generation in large ducts. This work examines the possibility of using air induction. A theoretical analysis generates equations which assist the designer in sizing a suitable inducer for ventilation purposes. Preliminary tests which verify the theory are described.

Unsteady wind effects can be important in natural ventilation, but their treatment requires knowledge of instantaneous surface pressure distributions which are extremely difficult to obtain. The paper describes a theoretical investigation aimed at determining the effects of unsteadiness and, perhaps more important, the conditions for which it may be worth accounting for them in the design process. For generality the study uses nondimensional parameters. The effects of unsteadiness on both mean and instantaneous flow rates are covered.