Mechanical contractors are navigating a new set of expectations for commercial building performance. Topping the list is the need for higher energy efficiency, improved indoor air quality (IAQ) and tighter humidity control. These priorities are bringing renewed attention to dedicated outdoor air systems (DOAS), a targeted solution that is gaining traction.
A DOAS is designed solely to condition outdoor ventilation air and deliver it to occupied spaces or downstream HVAC equipment. Simply put, a DOAS decouples a building’s ventilation loads (including humidity) from its space cooling and heating loads. Instead of relying on a single rooftop unit to manage everything—temperature, ventilation, and humidity—a DOAS handles ventilation and the corresponding latent load independently, delivering clean, dry, and conditioned outdoor air where it is needed.
This decoupling offers three key advantages: enhanced efficiency, improved IAQ, and more reliable dehumidification. While DOAS provides a significant step forward in these areas, mechanical cooling alone may not meet modern building performance requirements. However, when paired with a dedicated dehumidification technology—such as Copeland’s HMX liquid desiccant module—a DOAS can achieve even higher efficiency levels, active moisture management, and built-in air-cleaning benefits.
As higher ventilation requirements, electrification strategies, and efficiency mandates drive DOAS adoption, contractors have an opportunity to deliver more reliable performance across a wider range of building types.
Reason 1: Energy Efficiency—Reducing Operating Costs and Meeting New Metrics
Increasing energy efficiency has become a driving factor behind HVAC, DOAS, and dehumidification system design. In the Air Conditioning, Heating, and Refrigeration Institute’s 920-2020 standard, the integrated seasonal moisture removal efficiency (ISMRE2) metric signals a shift toward real-world performance that rewards systems that can remove moisture more effectively and efficiently.
Copeland’s HMX liquid desiccant module technology enhances DOAS efficiency by cooling and dehumidifying in one step. Compared to conventional HVAC systems, HMX can enable DOAS units to reduce energy use up to 40 percent while delivering superior ISMRE2 ratings.
A DOAS equipped with Copeland’s HMX technology also offers the ability to reduce peak load energy consumption. By running its liquid desiccant regeneration cycle during non-peak hours, HMX can shed peak energy loads, which often occur when daytime heat and humidity levels are at their highest. Effectively, the desiccant acts as an energy storage medium that can be used during the day for dehumidification.
For contractors serving schools, high-ventilation office spaces, supermarkets, pharmacies, nursing and other healthcare facilities, or humid-climate installations, DOAS with HMX liquid desiccant modules help meet stringent energy requirements while lowering lifecycle costs.
Reason 2: IAQ—Delivering Cleaner, Conditioned Ventilation Air
Improving IAQ remains one of the strongest drivers of DOAS adoption. The ASHRAE 62.1 standard specifies minimum ventilation rates to maintain acceptable IAQ, emphasizing the role of humidity control in delivering fresh air and mitigating the risk of microbial growth.
Building owners are increasingly aware that high ventilation rates alone don’t necessarily guarantee better IAQ, especially when outdoor air is hot, humid, or high in contaminants. A DOAS directly addresses this challenge by preconditioning ventilation air before it enters an occupied space. The result is a stable supply of cleaner, dehumidified air, which prevents moisture spikes that lead to mold or poor comfort.
Copeland’s HMX liquid desiccant module solution adds a vital layer of IAQ protection. Liquid desiccant technology effectively dehumidifies and suppresses microbial growth. HMX modules can scale to meet specific humidity and cooling requirements, providing flexibility for a wide range of environmental conditions and applications. The HMX design also eliminates the possibility of cross-contamination between regeneration and conditioned airstreams.
For contractors working in healthcare, rental housing, or educational facilities, these IAQ benefits translate directly into fewer callbacks, improved occupant satisfaction, and stronger performance guarantees.
Reason 3: Dehumidification—Reliable, Year-Round Moisture Control
Humidity is one of the most persistent challenges in commercial HVAC, particularly in mixed-humid and hot-humid climates where moisture loads vary throughout the year. Traditional HVAC systems often struggle to provide adequate dehumidification during part-load or shoulder-season conditions. Even though a DOAS manages ventilation independently, it too can struggle with dehumidification.
With Copeland’s HMX liquid desiccant module solution, a DOAS can provide stable humidity control and more effective decoupling of ventilation dehumidification from space temperature loads. Hence, a DOAS equipped with an HMX helps maintain low dewpoints even when the building’s cooling requirements are minimal. Its modular flexibility enables contractors to configure each DOAS-HMX pairing to offer precise dehumidification control, potentially downsizing systems to address sensible loads.
HMX liquid desiccant modules are easy to install and require no additional maintenance for contractors beyond an occasional filter change. From a building resource perspective, no added water is needed to support system operation.
At the end of the day, this pairing gives contractors the assurance of consistent, reliable performance, reduced service calls, and better adherence to ASHRAE humidity guidelines.
A Smarter, Cleaner Path Forward
As expectations for IAQ, humidity control, and energy efficiency continue to rise, DOAS offers a clear, future-forward strategy for managing outdoor ventilation air in commercial buildings. For mechanical contractors, learning how to apply these systems is an opportunity to expand capabilities, differentiate themselves in the industry, and deliver better outcomes for clients.
DOAS is no longer a niche solution. With the added performance of technologies like Copeland’s HMX system, it is becoming one of the most practical and efficient paths to healthier, more resilient buildings.
For more information, visit www.copeland.com.
