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.
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).
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.
The governing parameters for flows generated by heat transfer from solar cell modules to air gaps are discussed. Experimental results are presented from measurements in mock-ups of ventilated facades and roofs. The heat transmitted from the solar cells to the air have been mimicked by the use of heating foils. The inclination angle of the roof, position of solar cell module and the height to width ratio (aspect ratio) have been varied. The bulk properties as the air flow rate in the air gap, local temperatures and velocities have been measured.
Several energy efficiency and renewable energy principles have been implemented in a recently refurbished and extended primary school building in Grong, Norway,. The building is located in the centre of Grong, a small town slightly north of Trondheim. The local authority's aim was to build an economical and modern school building with an attractive and healthy indoor environment and a minimal energy demand.
The use of air solar collector realised on the north facade of a new hospital building in Rome is hereby described. The integration of solar and structural element has been studied during the design phase; the development of air gaps integrated within enclosures is related to the possibility to activate both natural (ejecting indoor air outside) and forced (preheating outside air incoming to the air handling units) ventilation. The energy gained by the solar elements has been evaluated.
Climatisation and natural ventilation concepts are today, in most countries, considered to be an essential aspect of the building project. In fact they are utilised to guarantee summer thermal comfort and indoor air quality control. Also there are many other advantages including low energy use, reduction of noise levels and easy plant maintenance. In recent years the use of hybrid ventilation systems in office buildings has been developed. The achievement of thermal comfort conditions in buildings is an important aim in order to satisfy occupants.
A hybrid ventilation system combines both mechanical and natural ventilation modes. The natural ventilation mode, especially, causes some challenges for analysis tools since the varying nature of naturally driven flow means that transient calculations should be used to predict the flow fields. Analysis tools based on CFD have some advantages for detailed investigations since, in addition to evaluating the flow and temperature fields, it is possible to use CFD methods to calculate air exchange efficiency and other flow indices.
This paper focuses on hybrid ventilation performance in an office building. It presents measurement results from the new headquarters of the company Bang & Olufsen, which served as one of the case study buildings in IEA ECBCS Annex 35. Ventilation and control strategy, as well as operational experience of the hybrid ventilation system is presented. Measurement results include long-term values of temperatures, CO2 and energy use for assisting fans and heating of ventilation air as well as electricity use for appliances.