Guest Bio
Brian Dail is an Application Engineering Manager at Danfoss Climate Solutions. Mustafa Yanik is the director of global solutions at Danfoss Climate Solutions. He has a bachelor’s degree in mechanical engineering with nearly 20 years of experience in HVAC.
Episode Summary
Host Vic Marinich is joined by Brian Dail, application engineering manager at Danfoss Climate Solutions, to discuss dedicated outdoor air systems, or DOAS, and their growing popularity in the industry.
Main Points
- A DOAS is a specialized type of rooftop unit (RTU). While both rooftop units and DOAS units heat and cool air, a Dedicated Outdoor Air System (DOAS) is specifically designed to bring in and condition 100% outdoor air.
- RTUs and DOAS units serve different primary functions. Traditional rooftop units mainly recirculate indoor air and maintain building temperature, while DOAS units focus on ventilation and improving indoor air quality by supplying fresh outdoor air.
- Filtration is more critical in DOAS applications. Because DOAS units continuously bring in outdoor air, they often require more advanced filtration to remove pollen, allergens, pollutants and other contaminants before air enters the building.
- DOAS performance is measured differently than RTU performance. RTU efficiency is typically evaluated based on cooling capacity versus energy consumption, while DOAS efficiency is largely evaluated on how effectively the system removes moisture (latent load) from incoming air.
- DOAS units primarily handle humidity control (latent cooling). Unlike RTUs, which focus mainly on temperature reduction (sensible cooling), DOAS systems are designed to remove significant amounts of moisture from outdoor air before it enters the building.
- Variable-speed compressors and advanced controls are important in DOAS systems. Outdoor air conditions change dramatically throughout the year, so DOAS units often use variable-speed compressors, electronic expansion valves (EXVs) and sophisticated controls to manage varying loads efficiently.
- Reheat coils are a standard feature in many DOAS units. To remove humidity, air is often overcooled first. A reheat coil, typically using compressor discharge gas, then warms the air back to a neutral supply temperature of about 70°F to 75°F before it enters the building.
- Many DOAS units are now being designed as heat pumps. Heat pump DOAS systems are becoming more popular because they can provide energy-efficient heating while reducing reliance on fossil fuels, although very cold outdoor temperatures can create significant heating challenges.
- DOAS units help buildings meet ventilation and indoor air quality requirements. Building codes and ASHRAE standards often require minimum fresh air ventilation rates. DOAS systems are a common and effective way to satisfy these requirements, especially in schools, offices, and VRF/VRV-based buildings.
- DOAS adoption is increasing due to tighter building envelopes and post-COVID air quality concerns. Better-sealed, more energy-efficient buildings require mechanical ventilation systems to maintain fresh air levels, and heightened awareness of indoor air quality has further accelerated interest in DOAS technology.
Links
Read how a customer used Danfoss variable-speed scroll compressors with built-in VLT® drives to build its high efficiency DOAS unit: https://www.danfoss.com/en-us/service-and-support/case-stories/dcs/captiveaire-and-danfoss-improve-indoor-air-quality-with-variable-speed-dedicated-outdoor-air-systems-doas/
Learn more about DOAS in this study shared by ACEEE: https://www.aceee.org/sites/default/files/proceedings/ssb24/pdfs/20240722163115517_815332ea-2c50-487d-9d4b-0e91acb12190.pdf
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