To obtain stable control of VAV systems, many considerations must be accommodated properly. Local and central control loops affect each other in ways that in many cases can lead to problems of poor control and even instability. In a VAV system (utilizing demand controlled ventilation), the stability of the supply air temperature must be very carefully commissioned. While stable control can be obtained more easily at full flow rates, instability can often become a problem during reduced flow rates.
For energy savings, DCV systems are more and more used on ventilation systems. In France, in non residential buildings, these systems are generally controlled by either a CO2 sensor, or an optical movement detection (infrared). To achieve correct performances, pressure conditions in duct and fan regulation must be considered.
A supervisory control scheme for a sensor based demand-controlled ventilation system is described in this paper. The strategy based on neural network models is used to diagnose the measurement faults of outdoor and supply air flow sensors, and makes the fault-tolerant control of outdoor air flow when faults occur. Tests using that dynamic system simulation have been conducted to validate the strategy.
This guide describes the principles of demand controlled ventilation, gives information about the type of buildings where it can be used, and underlines the benefits of such systems with regard to energy consumption. It also shows how to design a demand controlled ventilation system according to the type of control. It explains the importance of choosing the right type of sensor and the correct way to posiiton it in the room.
This paper presents the European Research project RESHYVENT with its structure (partners and different work packages) , and its objectives : to develop demand controlled hybrid ventilation systems, including the development of four prototypes of hybrid ventilation systems for specific climates.
Three algorithms (steady-state, dynamic, proportional) for CO2-demand controlled ventilation, coupled with three methods for determining minimum air flow rates (Ashrae 62, CEN CR 1752, Polish standard) and three occupancy scenarios, have been analysed in a research project to promote such systems in Poland. Results show that not only algorithms, but also minimum flow rate requirements, influence the operation of the system.
Design process of buildings currently addresses indoor air quality through ventilation flow rates requirements. In some circumstances, this approach may be not sufficient and an alternative is to determine ventilation rates through contaminant-based design methods. The authors present several examples of such approach, especially using multizone modeling (CONTAMW model) in a two-story classroom/office building equipped with a CO2 demand-controlled ventilation.
Laboratory experiments were performed to evaluate the effect of different CO2-based demand-controlled ventilation strategies (on/off, proportional, linear, PID) on energy consumption and indoor air quality, with various ventilation rates and occupancy profiles, and with one- or two-zones controls. Results show the capability of different strategies to maintain acceptable indoor CO2 level with the minimum outdoor air requirement.
DCV systems have proved to be energy saving with correct IAQ in previous studies. In order to achieve correct performance, these systems must be properly designed and tested. The purpose of this study is to identify the possibility of using presence sensors based on movement detection to evaluate the number of people present in a room, and also gather some more information about the real occupation rate of meeting rooms. For that, an experiment in several kinds of meeting rooms, located in different buildings and having different uses has been run.
In order to assess the real performances of different demand controlled ventilation (DCV)systems, two of them were installed in meeting rooms of an office building.The first system is controlled by movement detection on terminal units and has been installedin a small meeting room which is regularly used.The second system is controlled by CO2 detection and frequency variation on fan. It has beeninstalled in a large meeting room (30 persons seated, up to 50 persons standing).The systems have proved to be energy saving with correct CO2 levels.
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