Design and Simulation of a Temperature-Controlled Ventilation System for a Greenhouse

Abstract

This thesis presents the engineering design of a temperature-controlled forced ventilation greenhouse system adapted to the continental semi-arid climate of Ulaanbaatar, Mongolia. The study follows a dual methodology: a parametric three-dimensional structural model developed in Autodesk Inventor 2026, and a discrete-time PID temperature controller implemented and verified within the Wokwi embedded systems simulator. A thermal load analysis, using a peak solar irradiance of 800 W/m² and an ambient design temperature of 35°C, established a peak solar heat gain of 58.3 kW for a single-span greenhouse of 189 m³ internal volume clad in 16 mm twin-wall polycarbonate. The resulting design ventilation rate of 30 air changes per hour corresponds to a volumetric flow of 1.57 m³/s, delivered by a North-wall intake fan through a three-branch perforated PVC duct network. Perforation spacing is tapered from 300 mm at the inlet to 200 mm at the capped end, following the Teitel hydraulic pressure-compensation model, to promote uniform jet discharge across the full branch length. The PID controller was tuned using the Ziegler-Nichols closed-loop method, yielding gains of Kp = 4.8, Ki = 0.16, and Kd = 36.0. Four simulation scenarios step response, setpoint tracking, disturbance rejection, and anti-windup verification confirmed all twelve specified control behaviors, including proportional fan modulation, integral setpoint convergence, derivative disturbance response, anti-windup clamping, and independent safety cutoff at 45°C. The thesis explicitly acknowledges that CFD spatial validation and physical hardware testing constitute the primary recommended continuation of this work.