IAQ And Dedicated Outdoor Air Systems

By Matt Dodds

T he usage of dedicated outdoor surroundings techniques (DOAS) has increased recently to meet up higher ventilation requirements also to improve indoor quality of air (IAQ). While IAQ is a growing topic during the last decade, the prevalence of requests for clean interior environments is unprecedented because of concerns linked to COVID-19 now, along with other airborne diseases and contaminants. To help meet up with the exponentially increased requirement, HVAC contractors and engineers, and facility supervisors and building proprietors are embracing DOAS to meet probably the most stringent ventilation and power efficiency circumstances while providing convenient environments and better quality of air.

IAQ Begins With Ventilation

Nearly all ventilation specifications originate with skin tightening and (CO2) administration for occupied areas. When humans breathe oxygen, they exhale CO2. So when 20, 30, or 50 individuals occupy a workspace or classroom for many hours, the CO2 ranges rise invariably, dramatically sometimes. Concentrations of CO2 in the exterior air average around 400 components per million (ppm), and in occupied heavily, ventilated areas these can elevate to as high as 2 poorly,000 to 5,000 ppm. Proper ventilation inside these areas keeps CO2 levels IAQ and low high.

DOAS technologies helps to ensure that a continuous supply of fresh, dehumidified air will be distributed through the entire facility evenly. Right here, a Daikin Rebel Applied DOAS rooftop program is set up at West Midtown Flats in Atlanta, GA. (Photograph: Daikin Applied)

Ventilation specifications like ASHRAE 62.1 have helped designers incorporate outside air loads to complement developing use and occupant types-to promote great CO2 management and offer sufficient air changes each hour, which is essential for reducing the spread of pathogens and removing impurities in the new air. Volatile organic substances (VOCs), for example, enter occupied areas through off-gassing procedures from building and furnishings materials, or routines in a service such as for example cooking. ASHRAE 62.1-2019 Addendum aa offers a set of appropriate targets to take into account to control VOC contamination.

The very first line of protection for managing CO2, pathogens, and pollutants is correct ventilation, and DOAS technologies is really a powerful tool compared to that final end.

Decoupling With DOAS

There are many benefits that push creative designers to utilize DOAS over main station ventilation; this consists of ventilation quality, decoupled power efficiency, and temp and humidity control. Main station air flow handlers and rooftop devices process outside and recirculated return atmosphere by mixing typically, conditioning, and providing air to the area all without trouble of equipment, with outside surroundings as a fractional percent of provide air. For several years, this has already been the standard way for outdoor air flow distribution in variable atmosphere volume systems.

The essential problem with one of these systems may be the inability to gauge or control where in fact the outdoor air eventually ends up. Did it obtain distributed to all or any occupied spaces evenly? Are the climate changes in each area equivalent? Decoupling the ventilation surroundings from the main recirculated air flow with a DOAS device guarantees that filtered, oxygen can be acquired and equally distributed within a building always.

In addition, by decoupling the new atmosphere to a DOAS device, the ventilation air could be delivered just to regions of a facility which are used, which saves power when serving reduced- or mixed-occupancy spaces. This degree of control can’t be achieved with distributed ventilation systems centrally.

Moreover, ventilation air may be the priciest air that HVAC techniques condition. From humid and warm to frigid climates, it takes a whole large amount of energy to condition and offer ventilation air to areas, and to take action without disrupting occupant ease and comfort. Extreme temperature ranges and latent loads is able to overwhelm traditional main station or little terminal conditioning equipment, leading to spaces with temperature handle issues, and too much moisture and humidity.

A DOAS is made to deal with the extremes of processing ventilation surroundings and to take action effectively. By decoupling the ventilation air flow from the recirculated program, service operators can manage room humidity and temperature individually utilizing the DOAS because the primary dehumidification device for the area and the recirculating products for temperature handle. This promotes thermal comfort and ease and means that fresh atmosphere is sent to occupied spaces.

Packaged For Efficiency

DOAS delivers the aforementioned benefits by leveraging the most recent refrigeration, control, and energy-recovery technology. Most DOAS units are packaged direct expansion (DX) systems that incorporate efficient variable-speed or multi-stage compressors for the precision temperature and humidity control necessary for operation. An array of compressor capacity modulation is essential to provide the perfect comfort while expending the very least quantity of energy. Plus, by coupling variable-speed DX technology with energy recovery solutions, such as for example enthalpy wheels, plate temperature exchangers, and hot liquid and gas sub-cool reheat systems, high efficiency can be done in demanding circumstances even.

As ventilation and quality of air continue being a primary focus for facility managers and building owners, a need that’s only expected to upsurge in the coming years, DOAS systems is now a far more prevalent choice to market healthy buildings within an energy conserving package.

Dodds may be the product manager for rooftop and self-contained systems at Daikin Applied . In charge of product management and development, he’s got specialized expertise in variable speed rooftop equipment. Dodds holds a Bachelor’s degree in mechanical engineering from the University of Minnesota and an MBA from the University of St. Thomas in St. Paul, MN.

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