After years of research and field testing, nonprofit Northwest Energy Efficiency Alliance (NEEA) identified an HVAC design approach, referred to as very high efficiency DOAS, that they have determined to be the most effective and efficient way to provide comfort and clean, healthy air to a commercial building. Among the equipment and design considerations for very high efficiency DOAS—which include using a high efficiency heat/energy recovery ventilator, a high-performance electric heat pump, and a right-sized heating and cooling unit—it is the approach’s decoupling (i.e., separating) of ventilation from heating and cooling air that allows the system to provide filtered, fresh outdoor air to significantly enhance air quality and reduce viral risk. All of this is done while using less energy than relatively efficient HVAC options with the same ventilation rates.
This article defines that various approaches to fully and partially decoupling and showcases the proven benefits of applying this approach in new construction and major retrofits.
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Separating the ventilation from the heating and cooling system is a key component to making very high efficiency DOAS the most efficient and effective HVAC approach available. And while all DOAS configurations are at least partially decoupled to provide some level of reduced fan power and improved air quality, the very high efficiency DOAS approach enhances these benefits to an exemplary degree. The most profound benefits come from complete decoupling, in which the heating and cooling airflow is never in contact with ventilation airflow. However, partial decoupling configurations in which ventilation air is ducted into the supply side (as opposed to the return side) of the terminal units, also provides efficiency and air quality benefits over a coupled system.
