A dedicated outdoor air system is an HVAC unit designed to deliver fresh, dry, and dehumidified cool air to the building in summers while providing dedicated ventilation. It also delivers heated outside air during the winters.
DOAS systems work to improve the quality of indoor air by eliminating pollutants and other contaminants from the air before delivering the air to the building.
Features of Dedicated Outdoor Air System
Dedicated outdoor air systems are increasing in popularity in the United States and various other parts of the world as a result of the following features that they boast-
Superior Energy Efficiency
DOAS systems have earned their reputation as the ideal alternative in terms of sustainable air-cooling designs. As DOAS utilized sensible cooling systems along with advanced ventilation systems, they help in energy conservation which makes them an energy-efficient alternative to conventional cooling and ventilation systems.
Precise Temperature & Humidity Control
One of the primary features and benefits of dedicated outdoor air systems is that they use two separate systems for controlling humidity and temperature. Since it can condition the ventilation air at a low dew point, it does not require an HVAC unit for controlling the indoor humidity levels.
What is Make-Up Air?
Make-up air replaces the air that’s removed from the interior space using exhaust fans. This is carried out by channeling outside air that is fresh and tempered to the building for maintaining proper ventilation when the air in the room cannot be recirculated, thus requiring it to be removed.
How Does a DOAS System Work?
DOAS systems often work in tandem with other HVAC units and are installed outside the building. They are specifically designed to work independently from heating and cooling units to deliver fresh air into the building. DOAS conditions the outdoor air and directs it into the building, a process that separates latent and sensible loads.
While the DOAS unit installed outside is designed to remove latent load which helps with humidity control, the HVAC unit removes sensible load and this helps regulate and control temperature.
What Problems Can Make-Up Air Solve?
A fresh air makeup system helps maintain the right pressure in buildings that are prone to unbalanced pressure when there is more exhaust than intake in production space. Furthermore, buildings with negative pressure try to neutralize the pressure by pulling the air through window and door cracks. This can cause a lot of stress on windows and doors (which, for instance, makes it difficult to open a door), and make-up air can help here.
Buildings with negative pressure try to draw the air from other areas with low resistance, such as flue pipes and put immense pressure on mechanical systems like exhaust fans and heaters. In these cases, make-up air can be a life-saving solution.
When Do I Need A Make Up Air Unit?
If the following conditions apply to you, you need HVAC make up air units to ensure your space is well ventilated and has fresh air.
You Live In A Small Kitchen
Small kitchens don’t have many cubic feet of air, and this can cause suffocation, especially when you have a range hood and an exhaust in the kitchen as well.
Your Kitchen Is Poorly Ventilated
When a kitchen is poorly ventilated, a make up air unit can help bring fresh air to the kitchen by replacing the air removed by the exhaust system.
Your Building Codes Require the Use of Make-Up Air System
Building codes generally require you to use a make-up air system when you use range hoods over 600 CFM. This is mostly the case for smaller apartments and condos.
You Run Your Range Hood for Several Hours At A Time
When your range hood is used for an extended period, the air keeps escaping your house and fails to have enough time to be replaced. This is when using a make up air unit helps constantly replace the air.
Benefits of A Make-Up Air Systems
Some of the notable benefits of a make-up air system have been mentioned below-
Improves Indoor Air Quality
Make-up air systems help clean the air by removing pollutants and contaminants from the air through ventilation. This in turn helps improve the overall air quality.
Protect the Health of Employees
When employees work in buildings with poor air quality, they experience the health consequences of this both shortly after exposure to the pollutant and in long term. While fatigue and headaches are common side effects of working in a building with poor air quality, more serious health issues related to this are heart and respiratory diseases.
Improves Appliance Efficiency
When a building has various appliances such as bathroom fans and exhaust ventilators, negative pressure is created. And this causes these appliances to take more time to work, causing wastage of energy. Buildings equipped with moisture barriers and sealants benefit from make up air units, thus improving the efficiency of different appliances.
Commercial and Industrial Make-Up Air Applications
Make up air units have a variety of commercial and industrial applications. They’re extremely useful for ventilation in high-bay buildings and distribution centers. Industries such as pharmaceutical manufacturing plants, sewage treatment facilities, and auto assembly plants require constant replacement of air. Therefore, a make up air system is an essential part of the ventilation systems in such facilities.
DOAS System
DOAS systems have become a preferred solution for controlling indoor temperatures and maintaining good air quality. They are designed to offer energy-efficient solutions by using heating and cooling efforts to channel fresh outdoor air to indoor spaces. There are plenty of benefits that they offer, which give them an edge over other ventilation and temperature regulation systems. Following are some of their benefits.
Benefits
Comfort by Design
DOAS is designed to offer comfort through effective humidity and temperature control while conserving energy. The system uses two separate systems for temperature control and humidity control to deliver air to all the space in a building.
Superior Efficiency
Floaire DOAS units utilize a rare earth magnet inverter scroll compressor. This prevents the system from experiencing inefficient hard starts, excessive power and energy consumption, premature aging of the unit, and reduction in cycling.
Reliable Service & Technical Support
HVAC experts are well-informed about the working and components of dedicated outdoor air systems, and the increase in demand for DOAS has improved the quality of technical support and reliability of services pertaining to this system.
24/7 Real-Time Unit Monitoring Included with Every DOAS unit
Dedicated outdoor air units feature round-the-clock real-time unit monitoring which helps keep track of the performance of the equipment so that potential problems can be identified and addressed in a timely manner.
Know the DOAS System
Mixed Air Temperature/ Humidity Sensor
This component helps in monitoring the mixed air temperature and humidity and is available in various measurements, which include mixed, outdoor, discharge, space, and return humidity and air temperature measures.
Upto 3 layers of outdoor air filtration
Additional layers of outdoor air filtrations help deliver fresh and cleaner air indoors. Additional filtration of 4 inches and a standard outdoor filter made from mesh metal of 2 inches helps with efficient filtration.
Low Leakage Outdoor Air Damper
Low leakage outdoor air dampers exceed the leakage standards and help meet outdoor air requirements that may be variable.
Wide Indoor Coil Design
When the indoor coil design is wider, it helps in improving the efficiency of compressors and helps with the complete conditioning of the outside air. It also offers superior moisture control. When the coil is staggered and features up to 7 rows, it helps in the reduction of supply air bypass.
Electronic Expansion Valve
This feature modulates from 0 to 100% for providing automated monitoring and superheat control. It also helps in preventing off-duty cycle liquid migration with the help of precise control of the position.
Fully Modulating Hot Gas Reheat Coil
While an optional feature, a DOAS unit equipped with a fully modulating hot gas reheat coil helps in increasing the accuracy of humidity control. It further facilitates capacity control with precision with the help of electronic reheat valves.
Stainless Steel Sloped Condensate Drain Pan
Sloped condensate drain pans made from stainless steel when made to be removable and insulated, help in easy serviceability and maintenance. Condensate overflow can be prevented when the drain pan features a float switch, which can monitor the levels of water.
Modular Heating
Modular heating is available in various options such as propane, electronic heat, and heat pump. This component offers a constant efficiency of 80% throughout modulation.
Variable Speed Direct Drive Supply Fan
Variable-speed direct drive supple fans are both highly efficient and low maintenance as they don’t come with belts that require adjustments.
Variable Speed Outdoor Fans with EC Motors
These fans equipped with EC motors offer 10:1 turndown, and this keeps a constant peak efficiency for outside air conditions. They feature bionic blades that are designed aerodynamically, and this helps in reducing the noise levels during operation.
Double Wall, Galvanized Steel Construction
Galvanized steel construction of the system along with double walls proves to be corrosion resistant. Insulation of foil-faced 2 inches provides high efficiency.
Removable Hinged Access Doors
Removable hinged access doors, like many other features, add to the ease of serviceability and maintenance of the dedicated outside air system.
Human Machine Interface
With a human-machine interface, it becomes easier and simpler to program different settings such as humidity and temperature. With this user-friendly interface, you have access to real-time data and measurements that helps keep track of the operations.
Integrated Controls
DOAS systems have completely insulated control cabinets that prevent excessive condensation. This in turn prevents the controls from being damaged.
Danfoss Variable Speed Inverter Scroll Compressor
This feature offers precise load matching by modulating capacity. It also helps in conserving energy.
Make-Up Air Accessories
There are multiple accessories for various operations of a make up air unit that are involved in the proper circulation of air for adequate ventilation. Here’s a list of the different modules of a make-up air system and the accessories that form a part of these modules.
Cooling Modules
Cooling modules are useful in warmer air conditions for providing comfortable air tempering and restoring exhaust load. While one of the accessories helps in delivering humidified and cool air in hot and dry weather conditions, modular packaged units find their use in a variety of air tempering applications.
Heating Modules
Some of the essential heating modules in a make-up air system are direct-fired heaters, indirect-fired heaters, and electric heaters. Direct-fired heaters are useful for commercial and industrial requirements where gas heat is required. They deliver tempered make-up air that is extremely efficient while their indirect counterparts deliver clean tempered make-up air when a heat exchanger is used. Commercial and industrial requirements using electric heat make use of electronic heaters. All these accessories can be installed both outdoors and indoors.
Intake/ Discharge Accessories
A make up air unit primarily helps in the even distribution of fresh air all throughout the space using a specific accessory called a discharge diffuser. A downturn plenum helps with the downward discharge of air. When the plenum is insulated, it helps prevent excessive buildup of condensation while reducing noise levels. Among other crucial intake and discharge accessories for a make-up air system include intake hoods, mixing box, v-bank, screen intake, and trunkline among others.
Conclusion
DOAS systems are an innovation in the area of HVAC systems that have proven to be highly efficient as an energy-conserving system. They help maintain the right temperature and offer humidity control in a building, which is an essential requirement in many workplaces and industries.
Make up air units, which are also a crucial element of HVAC systems, help in optimizing the conditions of buildings where proper ventilation is required, but the plan and structure of the building do not allow for ventilation, or the building uses certain appliances that inhibit proper ventilation.
