Dedicated Outdoor Air Systems Explained

A dedicated outdoor air system, or DOAS, is a type of HVAC system that brings in fresh air from outside while exhausting stale air.

A DOAS can be a standalone system or integrated with a traditional HVAC system. It's often used in commercial buildings, schools, and hospitals where indoor air quality is a top priority.

DOAS systems are designed to handle a high volume of outside air, typically 100% of the building's ventilation needs. This is in contrast to traditional HVAC systems, which often recirculate a portion of the building's air.

The benefits of a DOAS system include improved indoor air quality, reduced humidity, and lower energy bills.

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A Dedicated Outdoor Air System, or DOAS for short, is a system used extensively in Europe and in various forms in the US.

Traditional HVAC systems, such as variable air volume (VAV) systems serving multiple zones, have potential problems in terms of poor thermal comfort and possible microbial contamination.

DOAS is designed to provide dedicated ventilation, rather than ventilation as an incidental part of the process of conditioning interior air.

The main point of a DOAS system is to handle some of the sensible load in addition to the latent load, with the parallel system handling the remaining sensible load.

This approach allows for more efficient and effective ventilation, reducing the risk of microbial contamination and improving overall thermal comfort.

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A Dedicated Outdoor Air System (DOAS) is designed to precondition outdoor air, improving indoor air quality by diluting pollutants and controlling humidity.

The DOAS design requirements include separating the OA system from the thermal control system to ensure proper ventilation in all occupied spaces. This ensures that the outdoor air is properly handled and conditioned.

Conditioning the outdoor air to handle all the space latent load and as much of the space sensible load as possible is crucial. This helps to maintain a comfortable indoor environment and reduces the load on the main HVAC system.

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To design a DOAS, the following steps can be taken: calculating the space sensible and latent cooling loads on the summer design day based on the design conditions for the space, determining the minimum air flow rate that each space requires, and determining the supply air humidity ratio for each space.

The supply air dry bulb temperature will typically equal the required supply air dew point temperature. This ensures that the outdoor air is properly conditioned and prepared for use in the building.

The following equipment is used in DOAS systems: total energy wheels, passive dehumidifier wheels, and other relevant equipment. The effectiveness of the total energy wheel is an important factor for improving the efficiency of DOAS.

Here are the key components of a DOAS system:

The DOAS unit's advanced filtration further removes pollutants from outdoor air, improving indoor air quality and helping to meet strict ventilation standards.

A dedicated outdoor air system (DOAS) can make a big difference in maintaining a comfortable and healthy indoor environment.

The first step is to understand the local building codes and ventilation standards, which can vary depending on factors like occupancy, building type, and indoor air quality requirements.

To ensure optimal indoor comfort and energy efficiency, effective integration of your DOAS with your building's heating and cooling systems is crucial. This can be achieved through direct, indirect, or passive systems.

Here are some key considerations for each system:

By understanding these options, you can tailor your DOAS to meet the specific needs of your building and occupants.

Energy and cost savings are significant benefits of DOAS systems. Studies have shown that DOAS systems can reduce annual energy usage by 14% to 27% and require 15% to 23% smaller equipment capacity.

In one study, a DOAS system with parallel ceiling radiant panels reduced annual energy usage by 42% in a 3,000 square foot office space. This substantial energy savings is attributed to reduced fan and chiller energy use.

The potential energy savings of DOAS systems in U.S. commercial buildings is substantial, with full DOAS systems resulting in annual HVAC energy cost savings ranging from 21% to 38%.

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When designing a DOAS system, it's essential to consider the ventilation standards and requirements set by local building codes. AAON units are designed to comply with these regulations, but understanding the specific standards will ensure your system meets the unique needs of your environment.

Factors like occupancy, building type, and indoor air quality requirements help determine the appropriate outdoor air intake rates. For instance, a building with high occupancy may require more outdoor air intake to maintain good indoor air quality.

Effective integration with space conditioning systems is crucial for maintaining optimal indoor comfort and energy efficiency. This can be achieved through direct, indirect, or passive systems, each with its own benefits and considerations.

Precise temperature and humidity control is vital for consistent comfort in your building. AAON's equipment features modulating compressors and hot gas reheat control to prevent over-cooling, while high turn-down modulating heat provides space-tempering in various outdoor temperatures.

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To enhance air quality, consider using advanced filtration systems that prevent contaminants from entering the space. High-efficiency filters with a MERV rating up to 14 or HEPA-rated filters can capture smaller airborne particles, creating a healthier indoor environment.

Some industries have specific air quality requirements, such as:

Traditional systems typically focus on controlling temperature and humidity within a building, but they often sacrifice indoor air quality.

A Dedicated Outdoor Air System (DOAS) is a game-changer in this regard, as it provides 100% outdoor air and manages humidity independently.

Unlike traditional systems, a DOAS unit preconditions outdoor air, improving indoor air quality by diluting pollutants and controlling humidity.

This is achieved through a heat exchanger that recovers energy from exhaust air, which is then used to precondition incoming air.

DOAS units also feature advanced filtration that removes pollutants from outdoor air, further improving indoor air quality.

Here's a comparison of traditional and modern systems:

By choosing a DOAS system, you can enjoy a healthier indoor climate while reducing energy consumption.

Traditional systems have been a mainstay in modern construction for decades, but they come with potential problems, such as poor thermal comfort due to temperature and humidity fluctuations from zone-to-zone.

Traditional HVAC systems bring un-tempered outdoor air directly into the HVAC equipment to be conditioned along with the return air coming from the occupied spaces.

This approach can meet the needs of most occupancies, but there are special situations that require either more fresh air or higher quality (cleaner/less humid) fresh air.

Some traditional systems, like Roof Top Units and Air Handling Units, are not well equipped to handle the high latent loads introduced by un-tempered fresh air, which can be a challenge for newer energy efficient comfort conditioning systems.

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Most Americans spend nearly 90% of their time indoors, where buildings serve as refuges from extreme weather, excessive humidity, and unhealthy air quality.

Trane's Horizon DOAS addresses the need for maintaining proper indoor air quality (IAQ) by effectively managing ventilation and humidity.

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ASHRAE 62.1 and AHRI 920-2020 are the baseline for Trane's Horizon DOAS, ensuring it meets industry standards for ventilation management and DOAS equipment performance.

Trane DOAS sets new standards for humidity and air conditioning ventilation management, preconditioning up to 100% outdoor air to reduce the load on central HVAC systems.

The Horizon DOAS is engineered to manage humidity levels effectively during peak and off-peak, preventing the growth of mold, mildew, viruses, and other hazardous organisms.

All Trane equipment, including the Horizon DOAS, uses refrigerants with low Global Warming Potential (GWP), supporting sustainability and reducing carbon emissions.

The Horizon Flex is also AHRI 340/360 certified and ASHRAE 90.1 compliant, ensuring it meets industry standards for performance and efficiency.

Here's a summary of the benefits of Trane's Horizon DOAS:

Trane's Horizon DOAS is designed to maintain proper indoor air quality by effectively managing ventilation and humidity. This is crucial because most Americans spend nearly 90% of their time indoors.

ASHRAE 62.1 and AHRI 920-2020 are the baseline standards for ventilation management and DOAS equipment, respectively. Trane's Horizon DOAS sets new standards for humidity and air conditioning ventilation management.

Here are some key benefits of Trane's Horizon DOAS:

Trane's Horizon DOAS preconditions up to 100% outdoor air, reducing the load on central HVAC systems. This leads to improved system energy efficiency.

The Horizon Flex unit is a great choice for buildings that don't require 100% outdoor air or a very low dewpoint, as it can deliver 100% outdoor air while keeping upfront costs lower.

Many customers use the Horizon Flex in education, commercial office space, and retail applications, making it a versatile option.

This unit is ideal for those who need more than a standard unit provides, but less than 100% outdoor air, which can be a common scenario in many buildings.

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The Horizon Flex is a great choice for buildings that don't require 100% outdoor air. It's designed to deliver more than a standard unit provides, but not as much as a full 100% outdoor air system.

This flexibility makes it an ideal choice for applications like education, commercial office space, and retail.

The Horizon Flex is also a cost-effective option, with lower upfront costs compared to a full DOAS system.

Here are some of the key benefits of the Horizon Flex:

Horizon Water Source Heat Pumps offer a sustainable and eco-friendly method for heating and cooling buildings. They use a water source to provide heating and cooling, which can be more efficient than traditional methods.

The Trane Horizon Dedicated Outdoor Air Units offer Water-Source Heat Pumps, making them a reliable choice for building owners. These units can provide both heating and cooling, depending on the season.

One of the key benefits of Horizon Water Source Heat Pumps is their ability to provide consistent temperatures throughout the building. This is especially useful in commercial and industrial settings where consistent temperatures are crucial.

Horizon Water Source Heat Pumps can also help reduce energy costs by using free heat from the earth or a nearby water source. This can lead to significant savings over time, especially in areas with mild winters and cool summers.

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DOAS units deliver optimal performance across diverse industries, with reliable operation in every sector. This flexibility is a major advantage for businesses and organizations.

DOAS units can be found in various industries, including healthcare, where they provide clean air for patients and staff. They also perform well in office buildings, where they help maintain a healthy indoor environment.

DOAS units can handle high-temperature applications, such as in manufacturing facilities. This makes them a reliable choice for a wide range of industries.