Energy efficiency and indoor climate benefits of demand-based ventilation in simulated office rooms

Abstract

The demand for high energy efficiency of office buildings with an increasing focus on safety and good indoor air climate has increased the use of demand-based HVAC systems. The varying occupancy of office spaces can lead to unnecessarily high ventilation airflow rates and cooling of the room when there are no occupants. To achieve the same level of indoor climate with a more traditional ventilation system causes high energy consumption and inefficient operation of the HVAC system. A comparison of three active chilled beam systems was made with energy simulation software for finding the best performing room configuration in realistic operating conditions. Office room and meeting room cases) were simulated with 1) traditional CAV (Constant Air Volume) ventilation system, 2) BCV (Boost Controlled Ventilation) system with 2 automatic operating modes and 3) DCV (Demand-Controlled Ventilation) system with 3 automatic operating modes. For BCV and DCV systems same active chilled beam unit was used for office and meeting room cases to highlight the possibility of office layout changes without additional modifications to the ventilation system. CAV ventilation system required change between two different chilled beam units for office and meeting room cases to maintain the same level of indoor climate. Energy consumption, indoor climate conditions, and cooling system operation were simulated. The office building was located in a middle European temperate climate and had generic building materials and energy-efficient window characteristics Operation of demand-based ventilation system control logic for controlling airflow rates was studied between CO2 control and CO2 control with added presence control. The most energy-efficient solution was DCV system having 3 operating modes as the energy savings based on the ventilation airflow rates required at minimum operating mode is large compared to normal or maximum operating mode. With BCV active chilled beam ventilation system having 2 operating modes, energy efficiency can be increased notably compared to CAV active chilled beam ventilation system. BCV ventilation system could have performed with lower energy consumption for office room case if the active chilled beam was designed to be used for only office room operation, and not for meeting room operation as well.