Bringing more fresh air into a commercial building improves Indoor Air Quality (IAQ) and occupant health, but it often comes at an increased energy cost. Standard RTUs and AHUs pull untreated outdoor air directly into the main HVAC loop, conditioning it alongside return air. In humid climates, that often means overcooling to strip moisture, then reheating to a comfortable supply temperature. Energy can be wasted twice.

A Dedicated Outdoor Air System (DOAS) can offer a viable design approach to such conditions and energy penalties.  A DOAS system is a specialized HVAC system that conditions 100% outdoor air brought into a building for ventilation and is separate from the building’s primary heating and cooling systems.

Unlike traditional HVAC systems that mix outdoor and return air, a DOAS system draws in fresh air, filters it, cleans it, and then conditions it for the desired temperature and humidity before being distributed into the building. In short, a DOAS system preconditions incoming outdoor air before it ever reaches occupied spaces.

At AirGreen, our patented liquid desiccant technology is uniquely capable of removing moisture at the source, eliminating the need for traditional subcooling and reheat cycles. This novel approach provides distinct operational advantages:

  • Maintained occupant comfort. Precisely stabilizes indoor relative humidity across varying sensible loads.
  • Direct humidity absorption. Absorbs moisture directly rather than relying on condensation loops that often subcool and require reheat.
  • Enhanced Indoor Air Quality (IAQ). Supplies conditioned, clean outside air directly to spaces.
  • Flexible equipment integration. Utilizes modular design elements compatible with standard existing infrastructure.
  • Substantial summer energy savings. Achieves up to 50% energy savings during peak cooling months compared to conventional dehumidification.

What Is a Dedicated Outdoor Air System (DOAS)?

ASHRAE defines a Dedicated Outdoor Air System as a standalone HVAC unit that conditions 100% of a building’s ventilation air before delivery to occupied zones. It decouples the latent (humidity) load from the sensible (temperature) load and typically works alongside a parallel space-conditioning system.

In practice, these systems divide mechanical responsibilities to optimize efficiency:

  • The DOAS unit. Isolates outdoor air intake, filtering, cooling, and removing moisture before distribution.
  • The primary HVAC equipment. Generally manages internal room temperature and sensible loads exclusively.

A DOAS unit can be added to existing equipment and installation as a preconditioning layer or integrated into a full HVAC strategy for new construction. Either way, it enables higher ventilation rates without the energy penalties traditional systems either can’t avoid or are not designed to handle effectively.

Decoupling Ventilation from Sensible Cooling

When humidity is not controlled upstream, it becomes a severe space-conditioning burden on existing internal systems. Traditional HVAC configurations respond to these high latent loads with subcool/reheat cycles, a process that is both energy-intensive and operationally inefficient.

A properly configured DOAS resolves this problem by delivering supply air at a tightly controlled dew point, allowing the downstream or parallel equipment to handle sensible cooling exclusively and more efficiently. By eliminating the reheat penalty, facilities can scale up ventilation rates to meet modern health standards without incurring proportional energy spikes or creating unsafe indoor air quality conditions

This applies to both retrofit projects supplementing existing equipment and new construction designed around decoupled load management from the start.

AirGreen’s Humidity-First DOAS Design

Most commercial dedicated outdoor air systems use refrigerant-based cooling to manage moisture. AirGreen’s liquid desiccant process works differently — by absorbing humidity directly into its brine solution, not by subcooling past the dew point.

Demonstrated System-level results:

  • Can operate at sensible heat ratios (SHR) as low as 25% vs. the 70-90% most traditional HVAC systems can provide.  Thus, you get dehumidification capacities among the largest in our industry.
  • Provides precise humidity control at a variety of demand levels, as this system can ramp up and down easily.
  • Scrubs the air of a variety of airborne pathogens, including molds, viruses, and bacteria – thus providing the cleanest possible indoor air quality (IAQ).
  • Saves up to 50% energy savings vs. conventional mechanical dehumidification

Performance advantages are particularly strong in hot, humid climates where conventional systems are under the most stress.  Our systems shine when the load is the heaviest.

Engineering Details and System Integration

AirGreen engineered its equipment to integrate seamlessly with existing or centralized mechanical HVAC systems. Unlike others, we seek to work with and integrate with a variety of HVAC OEM equipment in both retrofits and new construction, and most of our prior applications have included other equipment and the total package. Our AG1000, AG200, AG3000, and AG4000 modular platforms offer flexible integration paths with a variety of existing systems:

  • Existing air handlers (AHUs). Adapts to current central air distribution systems.
  • Hydronic loops. Interfaces directly with existing chilled and hot water loops.
  • High-efficiency heat pumps. Couples with water-to-water heat pumps operating at COPs of 5.0+.
  • Energy recovery infrastructure. Pairs with systems achieving enthalpy recovery rates up to 85%.

Design considerations vary by project. Supply dew point, ventilation CFM, exhaust routing, filtration goals, and control sequences all factor in. Modular construction keeps these systems practical for tight mechanical rooms and phased retrofits.

Where DOAS Delivers the Most Value

DOAS applications are really unlimited, and range from schools and cold storage to biopharma, hospital, and food production applications. DOAS system benefits are greatest where humidity control, IAQ, or occupant sensitivity is a priority:

  • Indoor agriculture. Humidity directly affects product yields and accelerates mold risk
  • Schools. Fresh air rates tied to health and cognitive performance
  • Grocery stores and cold rooms. Condensation control near refrigerated cases, safety, energy savings from proper humidity control
  • Museums. Stable humidity for artifact preservation as well as comfort
  • Biopharma manufacturing. Precise humidity control for material handling, product quality, and regulatory compliance
  • Indoor recreation facilities. Comfort under high occupancy, safety
  • Conference centers. Variable load management, comfort, and IAQ
  • Commercial and industrial facilities. Process and product protection, materials handling, safety, and comfort

Performance, Recognition, and Compliance

AirGreen’s expertise as a category-leading designer and manufacturer of such unique systems was recognized as both a 2023 AHR Innovation Award Finalist (IAQ) and a 2024 AHR Innovation Award Winner.

Our DOAS design supports ASHRAE ventilation targets and consistent humidity control. It also helps reduce mold risk and remove pathogens from the supply airstream, supporting both operational performance and green building compliance documentation.

Project Support and Lifecycle Services

Our engineers work with project teams through every project phase:

  • Sizing and load calculations and system selection
  • Controls integration and commissioning
  • Long-term service and maintenance requirements

A correctly commissioned DOAS system delivers its efficiency and IAQ benefits from day one. AirGreen is committed to working closely with its customers to ensure performance right from the start.

Most DOAS systems are essentially designed to independently manage and condition moist outside air in a way that improves overall system performance and efficiencies. Why not use a system that was specifically designed to manage humidity and lower energy costs, while also scrubbing out pathogens?

Optimize Your Facility Dehumidification with AirGreen

The right dedicated Outdoor Air System depends on your climate, ventilation loads, and IAQ goals. AirGreen boosts the reliability and efficiency of your facility dehumidification system with improved ventilation and reduced energy costs. Contact AirGreen to discuss your DOAS project and get a system designed to perform from day one.