Development of Controllers for Temperature Control of a Room Deploying the Displacement Ventilation HVAC System

Abstract

By employing the fuzzy control theory and Dynamic Matrix Control (DMC) method, the controllers for temperature control of a room cooled by a displacement ventilation system are developed. The fluid flow and heat transfer inside the room is calculated by solving the Reynolds Averaged Navier-Stokes (RANS) equations including the effects of buoyancy in conjunction with a two-equation realizable k-epsilon turbulence model. Thus the physical environment is represented by a nonlinear system of partial differential equations. The system also has a large time delay because of the slowness of the heat exchange. Additionally, the temperature of the exterior wall of the room first increases and then decreases with time during a twenty four hour period, which acts as a strong disturbance in changing the temperature of the room. The goal of this paper is to develop controllers that will maintain the temperature in room within the specified upper and lower bounds by deploying the displacement ventilation system. In order to solve this temperature control problem, we develop a special fuzzy control method. At the same time, we analyze the peak value of the error and employ the DMC method to replace the fuzzy control method with success. Results show that the fuzzy controller is effective in saving energy and the DMC method can contain the error within specified bounds in the worst situation (when the temperature of the exterior wall is highest). This kind of fuzzy control and DMC method can also be employed for other HVAC systems such as Overhead VAV (Variable Air Volume) system and radiant cooling hydronic system.