Design and Simulation of a PID-Controlled Temperature Regulation System for Pharmaceutical Cold Chain Storage in Oyo State

The integrity of temperature-sensitive pharmaceutical products stored and distributed in Oyo State, South West Nigeria, is frequently compromised due to unreliable cold chain management in public health warehouses and retail pharmacies. This project presents the design and simulation of a proportional-integral-derivative controlled temperature regulation system for pharmaceutical cold storage units. A DS18B20 temperature sensor provides feedback to an Arduino Uno microcontroller running a discrete PID control algorithm. The controller modulates a pulse-width-modulated output driving a solid-state relay that controls a compressor unit in a modified household refrigerator serving as the cold storage prototype. The PID gains were tuned using the Ziegler-Nichols method and further refined through iterative simulation in MATLAB Simulink before hardware deployment. Setpoint temperature was established at 4 degrees Celsius, consistent with World Health Organization guidelines for vaccine storage. Testing under varying ambient temperatures representative of the Ibadan climate showed that the PID controller maintained storage temperature within a tolerance of plus or minus 0.6 degrees Celsius, outperforming the original thermostat which exhibited a tolerance of plus or minus 2.8 degrees Celsius. An LCD display and a SIM800L GSM module provide local readout and remote temperature alerts respectively. The study discusses calibration procedures and recommends a six-monthly sensor recalibration schedule. Findings are directly relevant to improving vaccine storage compliance in primary health care facilities across Oyo State. Keywords: PID control, cold chain, pharmaceutical storage, temperature regulation, Oyo State