Fields Mechanical Systems
Missouri Plant Managers Association – “HVAC Technology Advancements: Why (DOAS) Dedicated Outdoor Air Units?”
Commercial buildings require outside air ventilation to meet indoor air quality requirements. Ventilation air can be provided with conventional HVAC units with both a return and outside air intake, or with a separate Dedicated Outdoor Air System (DOAS) ventilation HVAC unit. A DOAS unit must be able to handle the extreme temperatures and relative humidity ratios of ventilation air to provide neutral air to the space, or to the units that are conditioning the space of the building.
A Dedicated Outdoor Air System (DOAS) consists of two systems. One system conditions the air in the space to control the indoor air conditions and maintain comfortable occupants. The other system conditions 100% outdoor air, which is then supplied to the space. This DOAS unit must be able to control the temperature and humidity of ventilation air at nearly any condition throughout the year. A dedicated DOAS system allows easy measurement of the outdoor ventilation air supplied to the space.
AAON DOAS units are available with a variety of options to address temperature and humidity control concerns. Options include variable capacity compressors, energy recovery wheels, modulating gas heating, high capacity coils, and modulating hot gas reheat. Variable capacity scroll compressors modulate cooling capacity from 10-100% to tightly control the supply air temperature. With longer run times than on/off compressors, they also dehumidify the air significantly better. Energy recovery wheels reclaim exhaust air energy to pre-cool, pre-heat, dehumidify, and humidify the ventilation outside air. This reduces the load on the refrigeration system and heating system of the unit. Modulating gas heating allows tight control of the supply air during the heating season. High capacity coils handle low airflows of DOAS units and provide more dehumidification (latent capacity) than a standard coil. Modulating hot gas reheat is available to provide precise humidity control for consistent occupant comfort without temperature swings common to on/off reheat systems.
AAON DOAS equipment is built with premium performance in mind and configurable for nearly any application. AAON rooftop units are constructed with double wall rigid polyurethane foam cabinets, and available with corrosion resistant exterior and interior paint for unit durability. Foam panel construction saves energy by reducing heat transfer through the cabinet and reducing air leakage through the cabinet. A stainless steel drain pan and optional polymer e-coating coils offer increased corrosion resistance, while also improving air quality.
AAON DOAS units are manufactured with maintenance in the forefront of the design, every AAON unit features elements that make it one of the easiest to service in the industry. Run test report, wiring diagrams, Operation and Maintenance Manual with startup form are provided in control access compartment of every unit. Color-coded wiring diagrams allow fast connection identification and analysis and thus a reduction in down time and cost. Individual components and wires are also labeled for quick circuit evaluation. AAON DOAS Rooftop units come with access doors with full length stainless steel piano hinges and quarter turn, lockable handles provide improved reliability over single point hinges and make the unit easily serviceable. AAON DOAS Rooftop unit compressors and unit controls are contained within a compartment isolated from the air stream for ease of service and increased sound dampening. Readily accessible compressors and control components allow timely evaluation of service issues without delay. The result of this AAON standard procedure is low service cost and greater unit run time.
DOAS systems must be designed to handle extreme conditions. AAON DOAS equipment is designed from concept to completion for durability, easy maintenance, high efficiency, and premium performance. www.aaon.com
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