CO2-Based Demand Controlled Ventilation for Variable Air Volume Systems Serving Multiple Zones

Abstract

My research team and I have been working on a research project, which finishes in August 2013. This project was the first awarded research project for which I served as the Principle Investigator during the beginning of my career. It holds a unique position in my heart and I would like to take this opportunity to share the significances and the main findings of this project with you. Demand-controlled ventilation (DCV) is a ventilation control strategy that provides automatic reduction of outdoor air (OA) intake below designed rates when the actual occupancy of spaces served by the system is less than the designed occupancy. American Society for Heating, Refrigeration, Air-conditioning Engineers (ASHRAE) Standard 90.1 [1] requires installation of DCV for densely occupied spaces and that the DCV system should comply with ASHRAE Standard 62.1 [2]. Many engineers have applied DCV in large office buildings, lecture rooms or conference rooms. However, there are many complexities and issues in applying DCV in multiple zones (MZs) with a recirculating heating, ventilation and air-conditioning (HVAC) system. Until the completion of this project, there was no recommended DCV control method for MZs in ASHRAE Standard 62.1 for design engineers to adopt or apply. Therefore, this research project was conducted to: (1) develop the fundamental equations for CO2-based DCV; (2) propose a CO2-based DCV for MZ HVAC systems and (3) evaluate the proposed DCV control strategies with energy simulation and airflow simulation. First of all, the validity of assumptions underlying CO2based DCV was validated. The literature review concluded that: (1) since the CO2 generation rate and odour generation rate are proportional,CO2 concentration can be adopted as a signifier of human odours in a space; (2) the bioeffluent generation rate is proportional to the number of occupants and their activity levels and (3) even though this research projectdoesnot include researching the types andaccuracyof CO2 sensors, we are aware of the facts thatmany commercial CO2 sensors that have been installed in the field have errors greater than 75ppm [3]. Therefore, more research work and development to optimize the CO2 sensors and to improve accuracy and reliability would be highly recommended. There are three control logics proposed and developed in this research project. They are: