| In the United States, particularly the commercial sector, maintaining our buildings by Heating Ventilation and Air Conditioning (HVAC) consumes up to 40% of our total energy use. The temperature of an individual room in a building is controlled by a thermostat, which relies on feedback control, hysteresis and a well-placed location to sample the room temperature. The thermostat controls the Variable Air Volume (VAV) box that supplies conditioned air into the room. This model does not guarantee the thermal comfort of the occupant inside the room since the air around the occupant is different than the air near the thermostat. Historically, there are three main types of models that have been used to study rooms inside buildings: Multizone, Zonal and Computer Fluid Dynamics (CFD). Multizone models assume homogenous properties of zones while uses Partial Differential Equations (PDE's) to describe the room. Both models present problems from a control standpoint: Multizone cannot make meaningful decisions about the room's energy and mass characteristics, while CFD is not easily integrated into existing control design. Zonal models are an intermediary technique, which uses linearized mass and energy balance equations. These Ordinary Differential Equations (ODE) can be assembled into a State-Space (SS) model which can be solved by programs such as MATLAB with relative ease. Using a validated zonal model of the room, the set point of the thermostat will be adjusted to meet the requirements for the occupants' thermal comfort needs. This design process can be seen in three parts: Implement the zonal model to simulate the room, integrate a controller to adjust the set point of the thermostat and compare the performance of this controller to the system as it is now. |
