Hybrid ventilation - development of design methods and control strategies. Phase 2
Design of energy-efficient ventilation systems in office buildings is often turned into a question of using either natural ventilation and passive cooling or mechanical ventilation and cooling. This prevents a widespread use of sustainable technologies because a certain performance cannot be guaranteed under all conditions. In fact in the large majority of the cases a combination of systems would be beneficial depending on outdoor climate, building design, building use, and the main purpose of the ventilation system. Suitable design tools are not available for sustainable ventilation systems as it is the case with mechanical systems. Valid design tools would give architects and engineers the necessary confidence in system performance which in many cases is the decisive factor for choice of system design. The present project is the second phase of the Danish contribution to IEA ECB and CS Annex 35 HybVent - Control Strategies for Hybrid Ventilation in New and Retrofitted Office Buildings, which will be carried out from 1/8-1998 to 31/7-2002. Annex 35 will have the Department of Building Technology and Structural Engineering, Aalborg University, as Operating Agent. The research project aims at a better knowledge of the use of sustainable ventilation technologies and is focusing on development of control strategies and design tools for hybrid ventilation in new and retrofitted office buildings and promotion of energy and cost-effective hybrid ventilation systems in office and educational buildings. Hybrid ventilation is ventilation sytems where mechanical and natural forces are combined in the ventilation of buildings. Control strategies are ways to control hybrid ventilation dependent on building design, internal loads, natural driving forces, outdoor conditions and season to fulfil the immediate demands to the indoor environment in the most energy-efficient manner. The project approach includes in the second phase an analysis of the capacity and function of hybrid ventilation with focus on characterization of window openings, optimization of location of openings and analysis of air flow conditions in individual rooms and in whole buildings. The work will result in improved design methods. The results of the second phase will be presented in articles in relevant magazines and at conferences. Information about Annex 35 can be found in the web-site http://hybvent.civil.auc.dk
Annex 35 started with a one year preparation phase August 1, 1997, followed by a four year working phase from August 1, 1998 to July 31, 2002. The project objective is to promote the application of hybrid ventilation in office buildings in Denmark, to improve existing design methods, to develop a new probabilistic analysis method for prediction of potential and capacity of hybrid ventilation on a yearly basis, and to develop control principles and strategies for hybrid ventilation in office buildings, which ensure optimal use of natural driving forces and which at the same time ensure fulfillment of indoor air quality demands, thermal comfort demands and energy and environmental demands. The project is divided in a number of parts, each with a specific objective. Phase 2 contains the following part: Experimental and theoretical study of hybrid ventilation air flow process. The objective of this project part is to investigate the hybrid ventilation air flow process, especially with regard to characterisation of air flow through different opening types and sizes under different environmental conditions as well as air flow and thermal comfort conditions in the occupied spaces. The gained knowledge is used to improve existing design methods. In natural and hybrid ventilation systems fresh air often is supplied through window openings. Knowledge of window performance as 'air supply devices' is very limited and the focus of the project has therefore been on investigations on the air flow through different opening types, i.e. air flow capacity at different opening, pressure and temperature conditions and air flow condition and thermal comfort. The results' show that window performance is not at the level of air supply devies for mechanical ventilation. However, the results also show that the potential for further develoment and improvement of opening for hybrid ventilation is large. The wind has a large impact on the air flow through window openings. Therefore, it is investigated how the air flow depends on opening area, opening location in the facade as well as wind direction and methods to predict pressure distribution on building facades. Finally, air flow conditions in buildings with both wind and thermal driving forces are investigated. It has been shown theoretically, by scale experiments and by CFD calculations that multiple steady state solutions exist when wind forces and thermal bouyancy are working against each other, and that the solution not only depends on the existing situation but also on the previous conditions
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Participants
| Partner | Subsidy | Auto financing |
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| By og Byg |
Contact
Sohngårdsholmsvej 57
DK-9000 Aalborg, Denmark
Heiselberg, Per (lektor), 96358080, ph@civil.auc.dk
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