An investigation on CO₂ concentration, energy use and differential performance of mixed-mode ventilation control strategies in a lecture theatre during winter

Intelligent Efficiency Research Group (IERG), University College Cork, Cork, Ireland

^* Corresponding author: 120222839@umail.ucc.ie

Abstract

This research presents a methodology for evaluating different mixed-mode ventilation control strategies through the measurement of CO2 concentration and energy performance simulation. The method was applied to a lecture room in a university building in Ireland during the winter season. Indoor CO₂ concentration levels recorded over one week in the lecture theatre were used as experimental input data for developing the method and calibrating the indoor air quality (IAQ) performance of an EnergyPlus building model. The study investigates the effectiveness of diverse natural ventilation (NV) and mechanical ventilation (MV) control strategies. It compares the ventilation sensible heat loss energy in such a high-occupancy density indoor environment. To this end, CO2 concentration in a lecture room, ventilating by NV and a mechanical ventilation heat recovery (MVHR) system, has been measured, gaining information on differences between CO2 values when varying the window opening positions and the MVHR system speed. Each scenario’s corresponding ventilation sensible heat loss energy is then simulated and compared in EnergyPlus. The results confirm that an adequate supply of fresh outdoor air requires using mixed-mode ventilation, mainly with energy-efficient operation of an MVHR system. The CO2 readings are shown to depend on the zone air change rate (ACR), particularly the MVHR fan speed. This evaluation provides valuable and novel information for the correct NV and MV operations to provide standard limits of IAQ in educational environments in light of the COVID-19 pandemic or future health and environmental concerns.