DOAS and VRF
The choice of installing an Indoor DOAS unit, especially if the existing HVAC system already includes provisions for OA, is for operating efficiencies. Therefore they need to meet ventilation code requirements or occupant comfort. But we are now seeing new cooling technology being specified having no provisions for OA and requires a dedicated outside air system. One of these systems is the variable refrigerant flow (VRF) system.
Japan was the first to introduce the variable refrigerant flow technology in the 1980s. This was for a flexible way to condition spaces without the complexity of large HVAC systems. Furthermore, they did not require bulky mechanical rooms and expensive ducting. As technology improved, the American market embraced VFR systems but to a lesser degree.
Today’s VRF units offer the building owner/manager many benefits including low first cost, simple installation. Other benefits are minimal maintenance, and the ability to run multiple evaporator units from a single condensing unit. With all its benefits, VRF systems have limited to no ability to satisfy ASHRAE ventilation requirements. Also, these systems cannot remove excess latent loads typical of certain geographical regions.
With rising energy costs and expanding energy consumption awareness, it’s no wonder VRF technology continues to popularize in the U.S. marketplace. VRF has the potential to achieve significant energy savings compared to older HVAC systems, according to a study by the U.S. General Services Administration.
Reports going as far back as 2012, estimates indicated the U.S. Market to be worth over $7 billion for VRF systems. More recent estimates of the U.S market indicate a compound annual growth rate of 5.2 percent expected through 2019. You can expect the sales of DOAS systems will grow as much if not better to match the upcoming surge in OA units.
DOAS Are Not all Built Alike
Dedicated Outside Air Systems is an ideal choice for new construction
Retrofit installations add to your existing HVAC system to improve performance. Traditional HVAC roof-top systems require adequate space for the air handler location and ducting large enough to handle both the ventilation/supply and return air. DOAS is ideal to handle the latent load requirements for OA requirements and dehumidification while the existing HVAC system manages the sensible load.
A DOAS system is ideally suited for retrofit applications where the new HVAC system (air handler and DOAS) must work within the confines of the existing space. The installation of original HVAC systems in one of many configurations, require the design engineer and contractor to manage challenges as needed. Some manufacturers of DOAS units like United CoolAir Corporation have taken this serious problem into account. Because they designed their units with special features to overcome even the most perplexing installation challenges.
United CoolAir’s DOAS design, like their entire line of air conditioning equipment, is specifically for indoor installation. This feature is extremely important for multi-story buildings that have limited or no access to the roof or ground pad. Unit sizing to accommodate floor-by-floor installations and multiple units are easily installed if more cooling capacity is needed. Easy mounting of air-cooled condensers indoors near an outside wall for waste heat removal. Additionally, a water-cooled condenser option is available if using a water tower.
One Size does not Fit All
Unlike the “one size fits all” approach by some manufacturers, the United CoolAir outside air system is made specifically for each project. Vertical configurations are ideal for small mechanical rooms, including closets while horizontal styles offer in-ceiling mounting, saving valuable floor space.
Having the ability to customize your DOAS unit to fit your installation requirements can save thousands of dollars in contractor charges and shorten installation time. United CoolAir’s OmegaAir II allows modification in air paths, component configuration, and utility placement before leaving the factory. They also offer a comprehensive list of factory-installed options to meet even the most complex cooling requirements.
Retrofit applications generally have limited access to the job site. United CoolAir’s indoor, customizable DOAS units can break down into sections that fit through standard doorways, halls, and elevators. Lifting units by crane and modifying the building structure to accommodate equipment becomes a thing of the past. Additionally, this saves time and thousands of dollars in building modifications. United CoolAir charges and tests each of their units before leaving the factory. DOAS units include resealable refrigerant couplings between separable sections to preserve the factory refrigerant charge. The refrigerant couplings reattach during job site assembly and are ready for immediate operation. The elimination of Brazing, recharging, and testing saves additional time and money.
Dedicated outside air systems are as necessary to the safe and efficient cooling and dehumidification operation in commercial buildings. It is important to investigate the many systems available to find a DOAS that best fits your unique installation requirements.
