Originally published November 5, 2021 | Last updated: August 13, 2026
The Need for Dedicated Outdoor Air Systems (DOAS)
Commercial buildings requiring 100% outdoor air to meet ventilation standards—such as ASHRAE Standard 62.1—and maintain indoor air quality (IAQ) is nothing new in the engineering world. However, post-pandemic guidelines have driven calls for increased ventilation rates to further enhance occupant health, creating severe operational challenges for traditional HVAC equipment.
The main responsibility of a 100% outdoor air unit is to precondition incoming ventilation air. In this process, the system inherently handles massive peak heating and cooling loads, along with high moisture levels. Traditional HVAC systems struggle to introduce raw outdoor air while simultaneously controlling space temperatures and managing latent dehumidification loads. This is why mechanical engineers and facility managers are turning to dedicated outdoor air systems (DOAS) with total energy recovery.
So, how does DOAS solve the performance gaps of conventional HVAC to drive efficiency, utility savings, and healthier indoor air?
How DOAS Works
A DOAS unit functions fundamentally differently than standard recirculating HVAC equipment. Here’s how:
Decoupling
A DOAS unit uses dedicated equipment to handle 100% of the outdoor air brought indoors for ventilation, delivering it directly to occupied spaces or in conjunction with local terminal equipment (such as VRF, chilled water coils, or heat pumps) serving those same areas to maintain room thermal setpoints. By separating ventilation from space temperature control, outdoor air undergoes filtration and thermal conditioning with high-efficiency energy recovery before being distributed through independent ductwork. This decoupled architecture allows each system to operate in its optimal design envelope with each function working in dedicated silos.
Energy Recovery
Integrating total energy recovery significantly neutralizes outdoor air loads, enabling mechanical designers to downsize primary heating and cooling equipment. A DOAS with energy recovery uses a static-plate, cross-flow enthalpy core to isolate the outgoing, stale indoor airstream from the incoming fresh outdoor air. It’s during this process that total energy (sensible heat and latent water vapor) is transferred between the two airstreams.
Because the airstreams are physically separated by specialized partition plates, cross-contamination, short-circuiting, and pollutant transfer are prevented:
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Winter Operation: Cold, dry outdoor air is preheated and humidified by the outgoing warm indoor air.
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Summer Operation: Hot, humid outdoor air is pre-cooled and dehumidified by the outgoing air-conditioned indoor air.
Commercial Solutions in Action: The RenewAire DN Series
Units like the RenewAire DN Series exemplify this approach by pairing static-plate total energy recovery with flexible commercial performance:
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Integrated Total Energy Recovery: Unlike standard DOAS solutions, every DN model includes integrated static-plate enthalpy cores, maximizing efficiency by pre-conditioning incoming outdoor air to slash utility costs.
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Versatile Airflow Range: Delivering 375 to 4,950 CFM, the DN Series provides a scalable platform tailored to diverse commercial facility sizes.
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Flexible Configuration: Available in both indoor and rooftop (outdoor) configurations to easily accommodate unique architectural and mechanical footprint constraints.
Size Optimization: Eliminating the “Oversizing Penalty”
When engineers rely on conventional HVAC to handle 100% outdoor air, they are forced to massively oversize primary equipment to meet peak heating, cooling, and humidity loads. But bigger isn’t better—oversized systems struggle during typical part-load conditions, leading to wasted utility dollars and uncomfortable, clammy indoor air.
Decoupling ventilation eliminates this “oversizing penalty” through precise system sizing and streamlined physical footprints:
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Right-Sized Infrastructure: Because the DOAS handles the heavy lifting of outdoor air preconditioning, primary heating and cooling equipment can be downsized—slashing upfront capital costs and saving mechanical space.
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Peak Efficiency at Part-Load: Right-sized zone units run smoother and longer, eliminating short cycling, extending equipment lifespan, and drastically trimming monthly energy bills.
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Integrated DX Coil Flexibility: For tight mechanical spaces, options like RenewAire’s award-winning HE+DX Coil Integrated System combine total energy recovery with direct expansion (DX) cooling/heating coils in a single unit. This eliminates separate, bulky coil cabinets while giving designers precise temperature and humidity control.
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Conquering Humid Climates: In warm, muggy regions, standard HVAC systems lack the dedicated latent capacity to dehumidify high volumes of outdoor air, leaving spaces prone to mold growth and occupant discomfort.
A DOAS with total energy recovery—backed by integrated DX coil options—is explicitly engineered to conquer these high-latent environments, stripping out moisture before it ever reaches the space so facilities can comfortably exceed indoor air quality standards without blowing their energy budgets.
Key Applications for DOAS
Decoupling ventilation handling from space conditioning makes DOAS ideal for high-performance buildings, strict green standards like ASHRAE 189.1, and specialized, high-demand environments:
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Educational Spaces: Facilities like chemistry labs, gymnasiums, and cafeterias require significantly higher volumes of continuous outdoor air to exhaust fumes, control moisture, and clear high occupant metabolic loads. A DOAS pre-conditions this high-volume outdoor air, meeting code demands without overburdening primary heating and cooling systems.
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Healthcare & Laboratories: Sterile environments and patient facilities demand continuous, high-volume outdoor air exchange. Static-plate energy recovery preconditions fresh air while keeping airstreams completely separate to eliminate cross-contamination.
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Multi-Family & Senior Living: High-density living spaces require constant humidity management to protect building envelopes, prevent mold growth, and maintain occupant comfort.
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LEED, WELL & Net-Zero Projects: Any commercial facility targeting top-tier green certifications or net-zero goals relies on DOAS to eliminate the energy penalty of required ventilation air.
DOAS Wins with the Numbers
Building owners are under increasing pressure to reduce baseline energy consumption and lower operating costs. A DOAS with total energy recovery allows facilities to significantly increase outdoor air ventilation above code minimums without inflating utility bills. When evaluating financial performance metrics—including lifecycle cost analyses, net present value (NPV), and internal rate of return (IRR)—experts agree that energy recovery DOAS is an exceptional investment with a rapid payback period and long-term operational savings.
Further Discussion on DOAS
We previously hosted a panel discussion on how DOAS strategies lower energy costs while dramatically improving IAQ. Industry experts Nick Agopian and Alex Smith of RenewAire were joined by Rich Gerbe, CEO and Co-Founder of HIGHMARK NY LLC, to break down system design, code compliance, and practical field application.
[Watch the full panel discussion to learn more about DOAS technology, ventilation strategies, and indoor air quality.]
Frequently Asked Questions (FAQs)
What is a Dedicated Outdoor Air System (DOAS)?
A Dedicated Outdoor Air System (DOAS) is a specialized HVAC unit designed to handle 100% of the outdoor ventilation air brought into a building, conditioning it separately from the main heating and cooling equipment. By decoupling ventilation handling from space temperature control, a DOAS manages moisture, filtration, and fresh air delivery independently, allowing primary heating and cooling systems to operate at maximum efficiency.
What is the difference between DOAS and traditional HVAC systems?
The primary difference is that traditional HVAC systems mix recirculated indoor air with outdoor ventilation air in a single unit, whereas a DOAS separates ventilation entirely into a dedicated system. Traditional units struggle to handle heavy dehumidification and ventilation loads simultaneously, while a DOAS preconditions 100% outdoor air before delivering it to occupied zones or local terminal units.
Can a DOAS improve energy efficiency?
Yes, if the unit includes energy recovery. A DOAS is inherently designed to deliver 100% outdoor air to a space—it is not automatically designed to optimize energy efficiency on its own. That is where total energy recovery becomes a critical partner. With RenewAire DOAS units, static-plate enthalpy cores are used to transfer sensible heat and latent moisture between outgoing and incoming airstreams. By preconditioning the incoming outdoor air, a RenewAire DOAS unit can slash ventilation energy loads.
Do all DOAS units come with energy recovery?
No, not all Dedicated Outdoor Air Systems (DOAS) come with energy recovery. A DOAS is defined by its core function—delivering 100% conditioned outdoor air separately from local heating and cooling equipment—rather than the presence of an energy recovery component. However, while basic DOAS units without energy recovery exist, incorporating static-plate total energy recovery is often necessary to meet modern energy codes (like ASHRAE 90.1 and 189.1), optimize building performance, and prevent severe energy penalties.
To learn more, read our white paper on ASHRAE 189.1 and DOAS units.
What types of commercial applications benefit most from DOAS?
DOAS is ideal for facilities requiring high ventilation rates, precise humidity control, or separate airstream isolation. Key applications include K-12 and higher education spaces (such as chemistry labs, gymnasiums, and cafeterias), healthcare and lab facilities, multi-family residential developments, senior living communities, and high-density commercial spaces