Commercial DOAS Installation — Dallas Dedicated Outdoor Air Systems

Dedicated Outdoor Air Systems (DOAS) for Dallas commercial buildings — properly engineered for hot-humid Climate Zone 2A and integrated with VRF, RTU, or chilled-water primary equipment. The commercial side of HVAC+D. Call 214-238-4349 for project consultation.

What a DOAS Actually Does

A Dedicated Outdoor Air System (DOAS) is a separate piece of commercial HVAC equipment whose only job is conditioning outdoor ventilation air before it enters the building. It decouples ventilation from cooling and heating, allowing the primary HVAC equipment (VRF, RTU, or chilled water) to handle only sensible space loads.

The mechanism:

Outdoor air enters the DOAS through a dedicated intake
Energy recovery (typically wheel or plate exchanger) pre-conditions the outdoor air using exhaust energy
Cooling coil + dehumidification brings the outdoor air down to a low dew point (typically 50-55°F)
Reheat (optional, depending on application) brings the air back up to neutral or slightly cool delivery temperature
Conditioned outdoor air distributes directly to occupied zones or mixes with return air at the primary HVAC unit

Why this matters for Dallas commercial:

Standard rooftop units (RTUs) attempt to handle both space load AND outdoor air conditioning on the same coil. In Dallas hot-humid climate, this creates a fundamental conflict — the RTU short-cycles trying to satisfy thermostat-driven sensible demand while never running long enough to dehumidify the outdoor air properly. Result: oversized RTUs, high indoor humidity, mold complaints, comfort issues, energy waste.

A DOAS solves this by doing one job correctly: conditioning outdoor air to a controlled, low dew point regardless of what the primary HVAC is doing.

Why Dallas Commercial Buildings Need DOAS

A DOAS becomes necessary (not optional) when ANY of these conditions apply:

1. High outdoor air requirement. ASHRAE 62.1-2022 requirements for restaurants, schools, medical buildings, and densely occupied office space frequently push outdoor air rates to 20-30% of total supply — too much for standard RTU coils to dehumidify reliably in Dallas summer.

2. Variable occupancy. Restaurants, conference centers, classrooms, and event spaces have dramatically variable occupancy. CO2-based demand-controlled ventilation paired with DOAS lets ventilation rate flex with actual occupancy.

3. VRF primary equipment. VRF systems (Mitsubishi CITY MULTI, Daikin VRV IV, LG Multi V) don't have an outside-air intake by design. Adding outside air requires a DOAS or equivalent. See Commercial RTU vs VRF Dallas TX for the equipment-selection context.

4. Humidity-sensitive applications. Medical buildings, dental offices, museums, computer rooms, restaurants with proofing/baking zones, breweries — anywhere indoor humidity matters for product, equipment, or comfort beyond standard office requirements.

5. Tight envelope new construction. Post-2021 IECC commercial construction is tight enough that natural infiltration no longer satisfies ventilation requirements. Mechanical ventilation is required and DOAS is the correct way to deliver it.

DOAS vs ERV — The Commercial Distinction

A common point of confusion: residential applications use Energy Recovery Ventilators (ERVs), commercial applications use DOAS. The distinction:

ERV (residential): Balanced ventilator with energy recovery, low CFM (50-200), no integrated cooling coil. Sized for single-family or small commercial. See ERV / HRV Installation Dallas TX.

DOAS (commercial): Includes the energy recovery PLUS dedicated cooling coil with dehumidification capability and (often) reheat. Sized for higher CFM (300-10,000+). Handles latent load that an ERV alone cannot.

For Dallas commercial: Almost always DOAS, not ERV. The latent load in Dallas commercial applications is too high for an ERV alone to satisfy — the DOAS's dedicated cooling coil is what makes the architecture viable in hot-humid climate.

Equipment Configurations for Dallas Commercial

Packaged DOAS Units

Self-contained equipment with energy recovery, cooling coil, dehumidification, and reheat in a single packaged unit. Examples:

Aaon RN/RQ Series — workhorse commercial DOAS, broad capacity range
Greenheck Energy Recovery DOAS — high-efficiency commercial line
Daikin Rebel Applied DOAS — pairs with Daikin VRV ecosystem
Mitsubishi LGH-RVX commercial / kumo cloud commercial — pairs with Mitsubishi CITY MULTI
Trane Performance Climate Changer DOAS — premium commercial spec

Custom Air Handler DOAS

For larger commercial applications (>10,000 CFM), DOAS is typically a custom air handler with separate energy recovery wheel, cooling coil, dehumidification, and supply fan sections. Engineering firms specify these per project; Truficient executes installation and commissioning.

Split DOAS

Two-piece configuration — outdoor unit and indoor air handler — used where mechanical room space is constrained or where the DOAS needs to serve multiple zones with separate ductwork.

DOAS Sizing for Dallas Hot-Humid Climate

Dallas commercial DOAS sizing follows specific engineering rules different from cooler climates:

1. Latent capacity at design. DOAS must remove all latent load from the outdoor air at the design dew point — for Dallas, that's typically 78°F dew point at the 1% summer design condition. Many out-of-region engineers spec coils sized for 72°F dew point and the equipment fails to dehumidify on the worst Dallas days.

2. Low leaving air dew point. Coil should be sized to deliver outdoor air at 50-55°F dew point — dry enough that mixing with return air doesn't push indoor humidity up.

3. Reheat strategy. Decision point — to reheat or not. Options:

No reheat — supply at 55°F dew point. Cools the space AND dehumidifies, but may overcool if outdoor airflow is large relative to space load.
Reheat to neutral (75°F dry bulb, 55°F dew point) — air enters space dehumidified but doesn't actively cool. Typical for restaurants, schools, medical.
Reheat to space setpoint — DOAS strictly handles ventilation/dehumidification; primary HVAC handles all sensible space load.

4. Energy recovery effectiveness. Wheel or plate exchanger should target 70%+ total energy recovery (sensible + latent). In Dallas hot-humid climate, latent recovery is especially valuable — high-effectiveness wheels deliver meaningful operational cost reduction.

DOAS Integration with Primary HVAC

The DOAS doesn't replace primary HVAC — it complements it. Integration patterns:

With VRF. DOAS delivers ventilation air to occupied zones via dedicated ductwork. VRF indoor units handle sensible space load. See Commercial RTU vs VRF Dallas TX.

With RTU. DOAS pre-conditions outdoor air before it enters the RTU mixed-air plenum. RTU then handles sensible cooling at much smaller required tonnage. Often allows downsizing of RTUs by 30-40%.

With chilled water. DOAS delivers conditioned outdoor air to terminal units (VAV boxes, fan coils, chilled beams). Terminals handle final temperature trim.

With water-source heat pumps / geothermal. DOAS provides ventilation; heat pumps handle space load. Common architecture for net-zero commercial buildings.

Application-Specific Considerations

Restaurants

Kitchen ventilation creates dramatic negative pressure. DOAS provides positive makeup air without the kitchen-grease and kitchen-heat problems that come with simple makeup air units. See Restaurant Kitchen HVAC Dallas TX.

Multi-Tenant Office

Each tenant has different schedule and occupancy. CO2-based demand-controlled ventilation through DOAS lets each zone get appropriate fresh air without over-ventilating empty space.

Schools

ASHRAE 62.1 ventilation rates per classroom occupant are aggressive. DOAS is essentially required for new construction or major renovation. CO2 sensors per classroom give real-time ventilation control.

Medical / Dental

Infection control requires high outdoor air rates and tight humidity control (typically 30-60% RH year-round). DOAS handles both.

Multi-Family Mid-Rise

In-unit HVAC + corridor pressurization DOAS provides fresh air without simply blowing humid Dallas air into the units. See Multi-Family HVAC Dallas TX.

Cost Framework

Commercial DOAS pricing varies dramatically by capacity, configuration, and integration complexity:

| Capacity | Application Type | Equipment + Install (Range) | |---|---|---| | 1,000-2,000 CFM | Small office, single restaurant | $25,000-$55,000 | | 2,000-5,000 CFM | Mid-size office, school wing, multi-tenant | $50,000-$110,000 | | 5,000-10,000 CFM | Large office, full school, medical building | $100,000-$220,000 | | 10,000+ CFM | Custom air handler applications | Engineering-specified |

The cost is meaningful but typically allows downsizing of primary HVAC equipment by 25-40%, which partially offsets the DOAS investment. Operating-cost savings from energy recovery and right-sized primary equipment make total cost-of-ownership favorable on a 10-15 year horizon for most applications.

Why Most Dallas DOAS Installations Underperform

We see chronic underperformance in Dallas commercial DOAS installations driven by these specific failures:

1. Wrong design dew point. Coil sized for 72°F dew point fails on 78°F Dallas summer days.

2. No latent capacity verification at commissioning. Equipment specified correctly but never measured against actual delivered dew point.

3. Energy recovery wheel bypass left active. Many DOAS installations have economizer/bypass dampers that get left in wrong position, defeating energy recovery.

4. No humidistat control on primary HVAC. If primary HVAC doesn't see indoor humidity, it can't compensate when DOAS is undersized.

5. Improper integration with kitchen exhaust or process exhaust. Negative pressure overwhelming DOAS supply capacity.

Truficient commissions DOAS installations for actual measured performance — supply dew point, delivered CFM, energy recovery effectiveness — not just equipment specification compliance.

Adjacent Pages

DFW Humidity Hub — comprehensive humidity context
HVAC+D Framework Explained — Truficient signature framework (residential)
ERV / HRV Installation Dallas TX — residential side
Commercial RTU vs VRF Dallas TX — primary equipment selection
Restaurant Kitchen HVAC Dallas TX — restaurant-specific
Multi-Family HVAC Dallas TX — multi-family applications
Part 3 of DFW Humidity Series — technical guide

Get a Commercial DOAS Project Consultation

Call 214-238-4349 or request a consultation.

Truficient is one of the few Dallas commercial HVAC contractors who properly engineers DOAS for hot-humid climate, integrates with VRF/RTU/chilled-water primary equipment, and commissions against actual measured performance.