Energy savings and ventilation performance from CO2-based demand controlled ventilation: Simulation results from ASHRAE RP-1747 (ASHRAE RP-1747)
This is the first journal paper from the ASHRAE research project RP-1747 "Implementation of RP-1547 CO2-based Demand Controlled Ventilation for Multiple Zone HVAC Systems in Direct Digital Control Systems." HVAC designers face challenges in complying with the ventilation requirements in ASHRAE Standard 62.1 due to the complexity of the ventilation rate procedure (VRP) and the lack of direction on how to appropriately apply demand controlled ventilation (DCV) within the context of the VRP. The RP-1747 project aimed to address those issues by developing and testing DCV control sequences that are practical and implementable in typical single-duct variable air volume (VAV) systems with direct digital control (DDC) Systems. These control sequences were also tested for energy and ventilation performance by using a co-simulation of EnergyPlus and CONTAM coupled by a functional mockup unit (FMU). This paper presents the simulation-based study of one office building in four climate zones including Miami (1A), Atlanta (3A), Oakland (3C), and Chicago (5A) for both DCV and non-DCV baselines. The ventilation requirements in non-DCV baselines were set following a simplified ASHRAE 62.1 approach and California Title 24. Simulation results show that RP-1747 DCV control logic could lead to 9% to 33% HVAC energy savings on a source energy basis compared with the non-DCV baseline with the simplified ASHRAE 62.1 approach. The simulated hourly outdoor airflow provided met or exceeded the ASHRAE Standard 62.1 ventilation requirement in the four climate zones for 83% to 97% of the time for the simulated building. Transients and simulation artifacts associated with the discretization of time steps appear to account for a large portion of the time steps when the ventilation provided is less than required by the Standard. After applying a tolerance to account for sensor and control error in real life and time averaging as allowed by Standard 62.1, the DCV strategy met ventilation requirements for 96% to 98% of the time. This indicates the RP-1747 DCV control logic achieves good compliance with the ventilation requirements in Standard 62.1.