کنترل کیفیت هوای داخل سالن در صورت برنامه ریزی شده و یا متناوب بر اساس ساختمان اشغال: توسعه یک مدل در مقیاس

When a building is used only for intermittent occupancy, continuous operation of ventilation system is not necessary for achieving good indoor air quality during the occupation periods. Such buildings have a great energy saving potential which is not harnessed enough yet. Indeed, energy loss can be avoided by promoting natural means and managing mechanical ones. Therefore, control strategies based on time and/or occupancy scheduled ventilation associated to pre-purge ventilation constitute a key for an energy efficient ventilation system. The purpose of this paper is to demonstrate the robustness of an experimental scale model that can be used to provide recommendations on the management and the control of ventilation systems in case of intermittent occupancy. Thus, several surveys and experimentations were carried out using both ENTPE classrooms and an experimental apparatus in order to characterise existing ventilation systems and to test a number of control strategies, which have been developed and tuned using a simulation tool (HYBCELL) based on finite differences and pressure air flow models.

At present, there is a great interest in ventilation systems as an energy efficient way to achieve thermal comfort and indoor air quality. To reach those targets and manage complex ventilation systems such as hybrid ventilation, intelligent control of ventilation is needed. In addition, several studies have shown the potential of ventilation control for occupants' productivity improvement [1] and [2]. Recent French surveys on energy consumption in buildings subject to variable occupancy (intermittent occupancy) published by the French Energy Agency (Agence de l'Environnement et de la Maîtrise de l'Energie) in 2005 [10] have highlighted a great potential of energy saving in such buildings. Those surveys have also shown that educational buildings (21% of French buildings) represent 166.4 million m2 of heated area and an annual heating energy consumption of more than 26 TWh. Given that ventilation has a major impact on the global performance of buildings, in terms of energy consumption as well as regarding indoor climate, the energy benefits of a well-managed ventilation system for intermittently occupied buildings are clear [3]. The aim of the work described in this paper was to test the performance of basic ventilation control strategies for indoor air quality. For this purpose, an experimental device representing a prototype of a classroom equipped with controlled ventilation system has been developed. This work aimed also to assess the robustness of this device. Indeed, this prototype will serve to provide recommendations on the management and on the control of ventilation systems in case of intermittent occupancy instead of using a real classroom. The methodology adopted to reach this target consisted on a retroactive approach based on experimental and numerical studies. To begin with, several indoor air quality in terms of CO2 concentration surveys have been carried out at the ENTPE school (Lyon, France) in order to assess the performance of the existing mechanical ventilation system. Then, as previous studies held at the ENTPE/DGCB/LASH showed that the simulation tool “HYBCELL” could be used to predict the performances of ventilation systems [4], this numerical model has been used to model the ENTPE classroom. It was also used in a further phase of the study to develop and to assess several control strategies for ENTPE mechanical ventilation systems. Finally, an experimental device representing a scale model of the ENTPE classroom has been designed and used both to calibrate the HYBCELL pollutants' model and to experimentally test and validate developed control strategies.

Through numerical and experimental studies, this paper has reported the interest of using the HYBCELL numerical model and the necessity of the experimental scale model in order to take CO2 sensors' characteristics, the real air mixture and occupancy into account. In addition, this study has also revealed the robustness of developed scale model toward tested control strategies. Thus, this experimental tool can be used to develop further control strategies instead of ENTPE classroom. The obtained results have shown that time or CO2 based control strategies give better results in terms of indoor air quality or heat energy consumption compared to the control strategies that are actually used to ventilate ENTPE classroom but don't allow energy saving while maintaining good indoor air quality. Thus, advanced control strategies based on multicriteria approach [8] have to be tested in the future. The complexity of those control strategies will depend on the major purpose of the ventilation system. Thus, if the major purpose is to guarantee appropriate indoor air quality, there is clearly a need for optimisation: air flow rates that are too low will lead to unacceptable indoor air quality, whereas air flow rates that are too high will result in unnecessary energy use. On the other hand, if the major purpose is to contribute to acceptable thermal comfort conditions in summer, the optimisation challenge is not so crucial (unless very strict thermal comfort conditions are specified). In this case, a less advanced control strategy is possible. It might be added, finally, that a degree of control can also be left to occupants, given that people's self-assessment of their comfort conditions depends to a non-negligible extent on the amount of control they are allowed to exercise over their environment [9].