Ventilation is pivotal both in terms of indoor air quality and environmental issues such as greenhouse gas emissions. It also has a major impact on energy use in buildings. It is important, therefore that the role md impact of ventilation is filly understood. The purpose of this paper is to review these aspects with particular reference to recent research and developments. Key aspects are concerned with the role of ventilation in maintaining good indoor air quality, ensuring the quality of the outdoor air and incorporating strategies to ensure good ventilation performance.

Architecture and engineering journals have been increasingly attentive to innovative non-residential buildings designed with operable windows. Such buildings may rely exclusively on natural ventilation for cooling, or may operate as mixed-mode, or "hybrid" buildings that integrate both natural and mechanical cooling. Architects who want to incorporate natural ventilation as an energy-efficient feature need to collaborate closely with mechanical engineers.

Calculation of design cooling loads is of critical concern to designers of HVAC systems. The work reported here has been carried out under a joint ASHRAE-CIBSE research project to compare design cooling calculation methods. Peak cooling loads predicted by the ASHRAE heat balance method are compared with these predicted by a number of implementations of the admittance method using different window models. The results presented show the general trends in overprediction or underpredictiori of peak load. Particular attention is given to different window modelling practices.