A Dedicated Outdoor Air System (DOAS) is an HVAC system designed to handle a building’s ventilation needs separately from its heating and cooling functions. Traditional HVAC setups mix recirculated and outdoor air to condition the space while supplying fresh outside air to meet air quality needs. A DOAS on the other hand exclusively conditions and supplies fresh outside air to maintain indoor air quality (IAQ) and regulate humidity. This independent approach ensures a consistent intake of filtered, conditioned outdoor air while reducing the strain on heating and cooling equipment.
How DOAS Works
Unlike traditional HVAC systems, which mix outdoor and recirculated air for ventilation, DOAS units condition and deliver only outdoor air.
The process begins with air intake, which draws in outdoor air through a filtration system to remove particulates and contaminants. The air then passes through heating and cooling coils. This adjusts the temperature to the desired level before reaching a dehumidification unit that removes excess moisture. Finally, supply fans distribute the conditioned air throughout the building, helping to achieve better air quality and comfort.
Benefits of DOAS in Commercial and Industrial Buildings
One of the primary advantages is the improvement of indoor air quality. Traditional HVAC systems often struggle to meet ventilation requirements efficiently, leading to inconsistent fresh air supply. DOAS ensures that the right amount of outdoor air is introduced into a space, diluting pollutants and maintaining healthy oxygen levels.
Another advantage is design flexibility. Dedicated Outdoor Air Systems can be integrated into both new and existing buildings, making it a versatile option for various applications. In large industrial plants, for example, traditional HVAC systems may struggle to balance airflow across extensive spaces. A DOAS can supplement existing systems, ensuring consistent ventilation without overburdening the primary heating and cooling infrastructure.
Applications in Commercial and Industrial Settings
DOAS Being Installed at a Pork Manufacturer in Iowa!
DOAS units are particularly beneficial in some spaces. In industrial plants, its not uncommon to have airborne pollutants from manufacturing processes. These can pose health risks and DOAS units can be used to provide a reliable ventilation solution to maintain compliance with occupational health regulations.
Office buildings can also benefit significantly from these units. Stale air and poor air quality can lead to decreased productivity and employee discomfort. By ensuring a consistent exchange of outdoor air, DOAS units helps create a healthier work environment.
Hotels and other hospitality venues also implement DOAS to enhance guest comfort. Controlling humidity and air quality in large buildings with varying occupancy levels can be challenging. Dedicated Outdoor Air Systems allow precise management of these factors, improving overall indoor comfort.
Decoupling HVAC Systems and Energy Efficiency
Decoupling ventilation from heating and cooling means separating the process of bringing in fresh outdoor air from the task of conditioning indoor air. In conventional HVAC systems, a single unit is responsible for both functions. This often leads to inefficiencies as it conditions more air than necessary to meet ventilation and comfort demands.
By contrast, a Dedicated Outdoor Air System manages ventilation independently, delivering only the required amount of fresh air. This allows the primary HVAC system to focus solely on recirculating and conditioning indoor air. This approach significantly reduces unnecessary heating and cooling loads.
Research Study
The study also found in addition to energy savings, occupants felt more comfortable.
A study by the Pacific Northwest National Laboratory evaluated the performance of HVAC systems integrated with Dedicated Outside Air Systems across eight diverse sites. They found that buildings retrofitted with Very High Efficiency Dedicated Outdoor Air Systems achieved an average 48% reduction in total energy consumption compared to traditional HVAC setups. (PNNL, 2022) By preventing the over conditioning of air, DOAS enhances overall system efficiency, leading to substantial energy savings in commercial and industrial buildings.
DOAS Unit Integrations
Some Dedicated Outdoor Air Systems are equipped with VAV systems that adjust airflow based on demand. These units use smart sensors to track occupancy, CO₂ levels, humidity, and temperature. The sensors adjust airflow dynamically, ensuring the right amount of ventilation is provided without wasting energy.
A heat recovery DOAS system integrates an energy recovery ventilator (ERV) or heat recovery ventilator (HRV) to maximize efficiency. These systems capture waste heat from exhaust air and use it to precondition incoming outdoor air, reducing the overall heating and cooling load.
Key Considerations for Implementation
Before installing a DOAS, it is essential to evaluate several factors. Climate conditions play a significant role in system design, as temperature and humidity levels vary across regions. In colder climates, additional heating capacity may be required to condition outdoor air before distribution. In warmer, humid climates, dehumidification must be factored in.
Building design and usage should also be taken into account. The number of occupants and the activities conducted within the space influence ventilation needs. Manufacturing facilities, for instance, may require higher ventilation rates than office buildings due to airborne contaminants generated during production processes. The integration of DOAS with existing HVAC systems is another key consideration. Compatibility with existing infrastructure, along with the implementation of advanced control systems, ensures seamless operation and optimal performance.
