100% Outside Air Systems - The Importance of Ventilation

The EPA, CDC and ASHRAE advocate for increasing a building's outside air (OSA) rate to reduce the risk of infection and to improve indoor air quality. ASHRAE’s recently released new standard, Standard 241-2023 Control of Infectious Aerosols, states buildings are to provide additional requirements referenced as Infection Risk Management Mode (IRMM). Requirements for IRMM are given in terms of equivalent clean airflow (ECAi) in units of flow per occupant to each zone. ECAi can be achieved by increasing outdoor air rates or by incorporating into a HVAC system design prescribed technologies as reviewed by the standard. However, increasing OSA rates for conventional HVAC systems results in higher operating costs at a time when the construction industry is moving quickly toward carbon neutral building designs to meet the AIA’s 2030 Commitment and MEP 2030 initiatives.
This presentation demonstrates why properly designed 100% OSA systems can be more energy efficient even when designed with greater OSA airflow rates to meet the new ECAi flow rates assigned by Standard 241-2023’s with an added benefit of providing superior indoor air quality during normal times of operation.
This presentation will review:
IAQ contaminants in conventional buildings and the impact on human health
Reviewing language from the EPA, CDC and ASHRAE that advocate for increasing outside air rates including a general review of ASHRAE Standard 241-2023 and Equivalent Clean Air flow rates and what HVAC system designs or applied technologies will qualify for ECAi prescriptive flow rates
What is a 100% Outside Air (OSA) System and how does it’s layout differ from a conventional HVAC systems
Review various 100% OSA system design concepts, i.e. active and passive chilled beams, passive radiant cooling and heating systems, VRV and underfloor air systems, and why they are more energy efficient than conventional systems while achieving better indoor environmental quality (IEQ).
How building first costs can be reduced by reducing the mechanical and, consequently, architectural footprints.