A CO2 Buildup and Leakage Rate Model to Assess a Demand-Based Ventilation Control Strategy for Energy Savings

Small offices and residences in tropical climates like India have a risk of poor Indoor Air Quality (IAQ) due to the absence of any provision for ventilation in the type of air conditioners commonly used. A general improvement in the quality of doors and window seals in buildings and a natural tendency to keep doors shut as long as possible to preserve cooling has created conditions conducive to compromised IAQ. A study has been carried out in one such small office to measure CO2 concentration levels and it validates the IAQ risk. An empirical equation for CO2 concentration buildup based on occupancy has been validated for the experimentally observed values. To get the desired IAQ, a prototype ventilation system was designed, built, and tested with 3-tier air filtration and maximum airflow to meet ASHRAE 62.1. The claims made for improvements to indoor air quality were validated through a post-occupancy feedback survey. The estimated costs of energy for cooling and dehumidifying fresh air to comply with the requirements of ASHRAE standard 62.1 have been calculated. A relatively inexpensive occupancy sensor-driven demand-based ventilation strategy has been proposed and savings in energy is compared to a high initial cost enthalpy wheel-equipped fresh air system of the type used for large well-designed offices. An accelerated decay term has been introduced and validated in the equation developed in this study for CO2 prediction. This has been done using CO2 measurements in a room ventilated by the prototype developed.