DOAS
Dedicated Outdoor Air System
What is a DOAS System and How Does It Work?
What is a DOAS system and how does it work? Well, in short, a DOAS or dedicated outdoor air system is an HVAC system that is specifically designed to precondition the outside air that is being brought into a building. This specially designed system can be installed as an addition to your existing HVAC equipment or as part of an overall HVAC strategy for a new building or space.
Commercial DOAS systems will typically include filters on both the intake and return sides of the unit. Supply and exhaust fans, a cooling coil, a heat source (for cooler climates), a means of dehumidification, and a method of energy recovery. But, how does this benefit you and your building's occupants? Read on to learn more about DOAS systems to see if they could be the right fit for you and your building.
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What are the Pros and Cons of HVAC DOAS Systems?
While an HVAC DOAS (Dedicated Outdoor Air System) does cost more initially to install; it also offers several advantages over traditional HVAC systems that are worth taking into consideration. Some of those advantages include Improved indoor air quality, better energy efficiency, improved occupant comfort, reduced humidity issues, ventilation customization, as well as greater flexibility and adaptability.
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Energy Efficient - Uses energy recovery process without recirculating conditioned air to offset energy costs.
Better Indoor Humidity Control
Provides a dedicated supply of 100% fresh, outdoor air
Prevents moisture-related indoor air quality issues, such as mold and sick building syndrome
Separately addresses air conditioning and ventilation to save fan energy
Removes contaminants from outdoor air before it flows into the building
Increases energy savings
Allows for the independent control of space temperature and humidity
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Initial Cost: DOAS systems typically require additional equipment and infrastructure compared to traditional HVAC systems, which can increase the initial installation cost. The need for separate air handling units (AHUs) and ventilation equipment can add to the overall expenses.
Space requirements: DOAS systems may require additional space for the installation of outdoor air handling units, ductwork, and associated equipment.
Proper design and sizing of a DOAS system are crucial to its performance. The system must be carefully designed to meet the specific needs of the building, including factors such as occupancy levels, ventilation requirements, and climate conditions.
DOAS System Benefits Breakdown
Improved Indoor Air Quality: DOAS systems provide a dedicated source of fresh outdoor air, which is separately conditioned and distributed throughout the building. This helps to improve your building's indoor air quality by effectively diluting and removing indoor pollutants, including volatile organic compounds (VOCs), odors, and airborne contaminants, thus helping to provide a healthier environment for your building's occupants.
Energy Efficiency: DOAS systems can significantly improve energy efficiency compared to traditional HVAC systems. By separating the processes of outdoor air ventilation and space conditioning, DOAS systems allow for better control and optimization of each process. This enables the use of more efficient equipment, such as energy recovery ventilation systems, which can recover heat or coolness from the exhaust air and transfer it to the incoming fresh air, reducing the energy required for conditioning.
Enhanced Comfort: With a DOAS system, the space conditioning is typically handled by a separate system, such as a variable refrigerant flow (VRF) or a chilled water system. This allows for more precise control over temperature and humidity levels, leading to improved occupant comfort. The DOAS system can deliver neutral or slightly conditioned air, while the space conditioning system focuses on providing the desired comfort conditions.
Flexibility and Adaptability: DOAS systems offer greater flexibility in terms of system design and application. They can be integrated with various space conditioning systems, including hydronic systems, fan coil units, or VRF systems, allowing for compatibility with different building types and sizes. DOAS systems can also be easily retrofitted into existing buildings, enabling improved ventilation without significant modifications to the existing HVAC infrastructure.
Ventilation customization: DOAS systems allow for customized ventilation strategies based on the specific needs of the building and its occupants. The outdoor air intake rates can be adjusted to meet the ventilation requirements of different spaces, occupancy levels, and activities. This flexibility enables the optimization of ventilation while minimizing energy waste.
Reduced humidity issues: By decoupling the ventilation and space conditioning processes, DOAS systems can help mitigate humidity-related problems. By properly controlling and dehumidifying the fresh outdoor air before it enters the building, the risk of excessive humidity levels, condensation, and mold growth can be minimized.
Did you know that DOAS systems are designed to meet or exceed building codes and standards related to ventilation rates and indoor air quality? In fact, Implementing a DOAS system can not only help to ensure compliance with local regulations and provide peace of mind regarding occupant health and safety. It will also bring additional comfort, reduce energy consumption, and save you money. All while directly benefiting the health of your building's occupants by ensuring only fresh clean filtered air enters your building. Helping you and your employees avoid the risks associated with sick building syndrome.
It's important to note however that the benefits of a DOAS system can vary depending on factors such as climate, building type, and system design. Which is why it's important to work with experienced HVAC professionals like the ones at Air Dynamics HVAC. At Air Dynamics, we make sure to consider all of your building's specific requirements to ensure that you are getting the most out of your DOAS system.
DOAS Systems vs Traditional HVAC Systems?
Though traditional HVAC systems such as Roof Top Units (RTU's) and Air Handling Units (AHU's) have been a mainstay in modern construction, they also come with potential problems. Including poor temperature and humidity control from zone to zone. This is partly due to the fact that a traditional HVAC system is designed to bring outdoor air directly into the HVAC equipment to be conditioned with the return air coming from the occupied spaces of a building. Whereas a DOAS system is designed to provide fresh, conditioned air to a building. It does this by separately conditioning the outdoor air and the recirculated air, which allows for more precise control of temperature and humidity.
But that's not all, DOAS systems don't just extend the overall lifespan of your HVAC system. They can also be an excellent choice when it comes to cross-contamination control with the enhanced filtration they provide.
DOAS Advantages over Traditional HVAC Systems
Improved indoor air quality - DOAS systems provide a dedicated source of fresh outdoor air, which is separately conditioned and distributed throughout the building. They help to improve your building's indoor air quality by effectively diluting and removing indoor pollutants, including volatile organic compounds (VOCs), odors, and airborne contaminants.
Increased energy efficiency - DOAS systems can help to reduce energy costs by recovering heat and humidity from the outgoing air.
Reduced operating costs - DOAS systems can help to reduce operating costs by requiring less maintenance and repairs than traditional HVAC systems.
Better Humidity Control - Allows for the independent control of space temperature and humidity.
Prevents Moisture-Related Indoor Air Quality Issues - Such as mold and sick building syndrome. Symptoms of which include cough, chest pain, shortness of breath, edema, palpitations, nosebleeds, cancers, as well as pregnancy problems & miscarriages. Legionnaire's disease, humidifier fever, pneumonia, extrinsic allergic alveolitis, and occupational asthma.
Longer equipment lifespan - DOAS systems can help to extend the lifespan of HVAC equipment by reducing the amount of wear and tear on the equipment.
DOAS systems offer flexibility in design and application. They can be integrated with various space conditioning systems, such as variable refrigerant flow (VRF), chilled water systems, or fan coil units. This adaptability allows DOAS systems to be implemented in a wide range of commercial buildings, including office spaces, retail establishments, hotels, and healthcare facilities.
Ventilation Approach - Traditional HVAC systems typically combine the functions of space conditioning (heating and cooling) and ventilation into a single system. They recirculate a portion of the indoor air, mixing it with outdoor air for ventilation purposes. In contrast, DOAS systems separate the functions of ventilation and space conditioning. They provide a dedicated outdoor air supply, which is treated and distributed separately from the space conditioning system.
Fresh Air Intake - DOAS systems supply a controlled amount of fresh outdoor air to the building. This outdoor air is typically treated to remove pollutants, cooled or heated as necessary, and then distributed to the occupied spaces. Traditional HVAC systems may also bring in outdoor air for ventilation, but it is often mixed with recirculated indoor air.
Air Treatment and Conditioning - In a DOAS system, the outdoor air is conditioned to provide appropriate temperature and humidity levels, and any necessary filtration or purification is applied. The DOAS system focuses on the treatment of outdoor air, while the space conditioning system (such as a VRF or chilled water system) separately handles the temperature control for the indoor spaces. In a traditional HVAC system, space conditioning and air treatment are typically combined in a single system.
Energy Efficiency - DOAS systems can improve energy efficiency compared to traditional HVAC systems. By separating the ventilation and space conditioning processes, DOAS systems allow for independent control and optimization of each function. Energy recovery ventilation (ERV) or heat recovery ventilation (HRV) systems in DOAS can recover heat or coolness from the exhaust air and transfer it to the incoming fresh air, reducing the energy required for conditioning. This can result in energy savings and lower operating costs for commercial building owners.
Control and Flexibility - DOAS systems offer more precise control over ventilation rates, temperature, and humidity levels. The space conditioning system can be tailored to the specific comfort requirements of each zone, while the DOAS system can be adjusted to meet the desired ventilation rates. This flexibility allows for customization and optimization based on building occupancy, activity levels, and climate conditions.
Indoor Air Quality Focus - DOAS systems prioritize indoor air quality by providing a constant supply of fresh outdoor air and removing pollutants effectively. Traditional HVAC systems often rely on recirculated indoor air, which may lead to a buildup of contaminants if not properly managed.
Retrofit Possibilities - DOAS systems can be relatively easier to retrofit into existing buildings compared to traditional HVAC systems. The separate ventilation system can be added or modified without significant disruptions to the existing space conditioning infrastructure, making DOAS systems a viable option for improving ventilation in older buildings.
It's important to note that both DOAS systems and traditional HVAC systems have their applications and advantages. The choice between the two depends on factors such as building type, climate conditions, energy goals, and occupant requirements. Consulting with HVAC professionals like the ones at Air Dynamics can help determine the most suitable system for your building and its needs.
A FEW OTHER WAYS DOAS SYSTEMS DIFFER FROM TRADITIONAL HVAC SYSTEMS INCLUDE
DOAS Systems and Commercial Buildings
DOAS systems are an ideal choice for new construction; retrofit installations or simply adding onto to your existing HVAC system in order to improve performance. Why? Well, simply put DOAS units allow for the system to be customized to meet the specific needs of your building. This often includes enhanced filtration, desiccant dehumidification, and cross-contamination control features that can be tailored specifically around your project’s unique specifications.
But that's not all! HVAC DOAS (Dedicated Outdoor Air System) systems can provide several benefits to commercial buildings and their owners. Here are some additional ways in which HVAC DOAS systems can benefit your commercial building(s):
Enhanced occupant comfort - DOAS systems, when combined with appropriate space conditioning systems, offer precise control over temperature, humidity, and ventilation rates. This allows for better customization and optimization of comfort conditions in different areas of the building. Occupants can enjoy comfortable environments tailored to their specific needs, leading to increased satisfaction and productivity.
Compliance with building codes and standards - DOAS systems are designed to meet or exceed building codes and standards related to ventilation rates and indoor air quality. By implementing a DOAS system, commercial building owners can ensure compliance with local regulations, creating a healthier and safer environment for occupants while avoiding potential penalties or fines.
Sustainability and green building certification - The energy efficiency and improved IAQ provided by DOAS systems align with sustainable building practices and can contribute to achieving green building certifications such as LEED (Leadership in Energy and Environmental Design). Commercial building owners can enhance their reputation, attract tenants who prioritize sustainability, and potentially qualify for incentives or rebates related to energy efficiency initiatives.
Implementing a DOAS system can future-proof commercial buildings by accommodating changing ventilation requirements and regulations. As indoor air quality standards evolve and become more stringent, having a DOAS system in place ensures that the building is well-prepared to meet future requirements without significant modifications or disruptions.
Cross Contamination Control - A dedicated outdoor air system (DOAS) is designed to provide clean, fresh air to the indoor space, however, their construction is not always perfect. Some leakage can occur between the outgoing air stream and the incoming airstream due to the fact that both airstreams are in the same physical cabinet and pass through the same energy recovery system. A cross-contamination control strategy can be employed so that if any contaminants exist in the outgoing air, they cannot leak into the incoming air stream and enter the space. This can make DOAS systems an excellent choice for nursing facilities, hospitals, and laboratories.
Enhanced Filtration - Some facilities may require an even higher level of filtration than what a typical HVAC system can effectively provide. This could be due to poor outdoor air conditions in the area or due to special requirements within the building. A DOAS can be customized to provide whatever level of filtration is required, up to and including HEPA filtration. While desiccant dehumidification systems can provide even lower levels of humidity.
This is why it is imperative to work with an HVAC professional who will consider the specific needs and requirements of your building when evaluating the potential benefits of adding a DOAS system to your commercial building. Working with experienced HVAC professionals at Air Dynamics HVAC and conducting a thorough cost-benefit analysis can help you make informed decisions regarding the implementation of HVAC DOAS systems in your building.
Are There Any Other Benefits to Adding an HVAC DOAS System to My Building?
Yes, it can help you to avoid what's commonly known as Sick Building Syndrome
Sick Building Syndrome Explained
Sick Building Syndrome is a term used to describe symptoms including nose or throat irritation, headache, dry cough, itchy skin, sensitivity to odors, nausea, and eye discomfort directly associated with the amount of time spent inside of a building.
The First Reported Case of Sick Building Syndrome
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The first reported case of Sick Building Syndrome dates back to the 1970s and revolved around a modern office building in Philadelphia. This case marked a significant turning point in our understanding of the relationship between building design, indoor air quality, and occupant health. The issue was initially brought to light when a significant number of employees within the building began complaining of a range of health problems, including headaches, eye and throat irritation, fatigue, and general discomfoThe building in question was characterized by sealed windows and a ventilation system that prioritized energy efficiency over adequate air exchange. Upon further investigation, experts concluded that the sealed windows and the building's mechanical ventilation system were not providing sufficient fresh air exchange. This limited the dilution and removal of indoor air pollutants, leading to an accumulation of volatile organic compounds (VOCs), airborne particles, and other contaminants emitted from materials used in construction and furnishings.
Think sick building syndrome is a thing of the past? It's not. While advancements in building design, construction practices, and HVAC systems have led to improvements in indoor air quality and occupant comfort, Sick Building Syndrome (SBS) continues to be a concern in modern times. Factors contributing to SBS today include inadequate ventilation, poor air circulation, the presence of indoor pollutants (such as volatile organic compounds, allergens, and mold spores), improper use of building materials, and insufficient maintenance of HVAC systems. It's also worth noting that some modern energy-efficient buildings that are well-sealed to conserve energy can sometimes lead to reduced ventilation rates and an accumulation of indoor pollutants.
While awareness of indoor air quality and its impact on health has increased; leading to improved building standards and guidelines designed to minimize the risk of SBS challenges can still arise. This is especially true for older buildings, poorly maintained spaces, and situations where indoor air quality is not given proper consideration during construction and operation.
Outside air is an important component of a building’s overall health and well-being. A dedicated outdoor air system ensures that it can be provided without compromising on indoor air quality or occupant comfort. Helping to provide a healthy environment in your facility while keeping energy costs down and lowering your carbon footprint. Some other measures that can be taken to help mitigate the risks of SBS include regular maintenance of HVAC systems, proper ventilation, use of low-emission building materials, and maintaining appropriate humidity levels.
What HVAC Systems Work With DOAS Units?
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How do Dedicated Outdoor Air Systems (DOAS) and VRF units work together? In this configuration, the DOAS would supply treated conditioned air to the VRF units. The VRF units are then tasked with distributing that conditioned air throughout your building to provide the desired amount of heating or cooling to each zone.
Integrating DOAS and VRF systems offers several benefits including enhanced ventilation and air quality, precise temperature control, energy efficiency, and zoning capabilities. Overall, the combination of DOAS and VRF systems offers a comprehensive and energy-efficient solution that addresses both ventilation and space conditioning needs in commercial buildings.
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Chilled beams are a type of air distribution system that uses convection and radiant cooling to provide proper conditioning to your space. When integrated with a DOAS (Dedicated Outdoor Air System), the chilled beams operate in harmony with the DOAS, delivering both ventilation and a fresh air source while effectively conditioning the indoor space of your building.
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DOAS units effectively remove large amounts of moisture from the air. As a result, the water source heat pump (WSHP) only needs to be sized for the sensible load. Occasionally, the DOAS can provide cooler air, thereby reducing the sensible load on the WSHP. This is effective as long as no reheating is necessary.
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