Effect of room modelling and sensor position on performance assessment of variable air volume control systems

摘要

Variable air volume (VAV) systems are commonly used for air conditioning in buildings. The testing of different control strategies and controllers for this application has been a main concern in several simulation studies. In these simulations much attention has been paid to the accuracy of the models of the VAV system while very simple models are often used at the room level. These room models assume that the air in the room is perfectly mixed, even when the prevailing conditions are not at all homogeneous. Another important issue when testing controllers is the method used to assess the control performance. Since it makes no sense to use very detailed room models, if the method of performance assessment is insensitive to the way in which the room is modelled, both issues must be treated simultaneously. The paper considers the problem of assessing the performance of VAV systems that use ceiling diffusers. The study includes the development of a convection model for a room. Its complexity is reduced to a minimum to allow detailed dynamic simulation of a whole building, complete with its VAV system and other building services (e.g., sun-blinds, lighting, etc.). Since airflow in a room depends strongly on the type of diffuser that is used, the study is carried out for both round and slot diffusers. Results are presented that show that the room model and the position of the sensor affect the performance in different ways depending on the diffuser type and the operating mode. It is concluded that there are only small differences in terms of thermal comfort but significant differences in terms of overall energy consumption. The effect of sensor position on energy consumption is found to be a function of steady state temperature differences.