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THE EQUIPMENT GUIDE / Commercial & building systems

Dedicated outdoor air systems

Treat ventilation air as its own design job.

A dedicated outdoor air system, or DOAS, conditions ventilation air separately from local space-conditioning equipment. It needs a coordinated relationship with the systems serving each zone.

Plan the project ↓
HVACR / SYSTEM NOTES01Outdoor intake02Air treatment03Ventilation ducts
Dedicated outdoor air systems: Outdoor intake / Air treatment / Ventilation ducts. Original HVACR.tv conceptual illustration; labels identify project elements, not an installation sequence or construction drawing.

PLANNING / SELECTION / HANDOVER

Before choosing the equipment

Discuss occupancy, operating schedules and moisture loads with the designer. Ask how ventilation air is distributed and how local equipment and the DOAS divide the work.

What belongs in the quote

Request the outdoor-air design criteria, controls sequence and commissioning scope. Include drainage, filters and access requirements in the procurement documents.

Think about the surrounding system

Bring operating hours, occupancy patterns, tenant constraints and existing equipment schedules to the first discussion. Agree who owns design, electrical work, structural review, roof penetrations, controls and commissioning. Plan shutdowns around the building rather than discovering access restrictions when replacement equipment arrives.

Three questions for your contractor

  1. How are ventilation quantities determined?
  2. Which system handles humidity loads?
  3. How do local units and DOAS coordinate?

Prepare a useful first conversation

Bring the site location, building use, equipment model details and photographs of accessible equipment. Describe the problem or planned change and any access or shutdown constraints. Ask the contractor to identify design assumptions, excluded work, required approvals and who will commission the finished system.

This is a project-planning guide. Final equipment selection and installation details need a qualified contractor or designer familiar with the site.

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