Energy and Ventilation Performance Analysis for CO2-based Demand-Controlled Ventilation in Multiple Zone VAV systems with Multiple Recirculation Paths

CO2-based Demand-Controlled Ventilation (DCV) has been proved to be energy-efficient by altering ventilation rates according to surrogated indications of CO2 levels. Numerous studies have implemented CO2-based DCV strategies for single zone Heating, Ventilation, and Air-conditioning (HVAC) systems and multiple zone single-path Variable Air Volume (VAV) systems. However, DCV for multiple zone VAV systems with multiple recirculation paths is still untapped, including VAV systems with Series Fan-Powered Terminal Units (SFPTUs), Parallel Fan-Powered Terminal Units (PFPTUs), and Dual-Fan Dual-Duct (DFDD) system. In this paper, energy and ventilation performance of the DCV strategies with system- and zone-level dynamic resets for these three systems are evaluated. The DCV control sequences for three systems are first briefly summarized. A co-simulation combining EnergyPlus with CONTAM is adopted. All the ventilation related control strategies satisfy ASHRAE standard 62.1 and other control sequences (e.g., local terminal unit controls) follow ASHRAE Guideline 36. DCV controls for three systems are implemented in Energyplus Energy Management System (EMS) module. New EnergyPlus actuators (e.g., zone minimum airflow) are added and a customized Energyplus is built to achieve the DCV control for each system. An office building is used as a case study to demonstrate the benefits from DCV strategies for multiple recirculation path systems in four different climates. For each system, two baselines for ventilation requirements (ASHRAE 62.1, California Title 24) are considered. The simulation results show that the DCV control logic could lead to 7-14%, 7-21%, 1-8% HVAC source energy savings for SFPTU, PFPTU,and DFDDTU systems respectively compared with thebaseline ASHRAE 62.1 approach. Three systems havesimilar ventilation performance and could achieve agood compliance with the ventilation requirements inStandard 62.1.