October 2017 chapter mtg

October 17, 2017
11:30 AM to 1:00 PM
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DoubleTree by Hilton San Antonio Airport
37 NE Interstate 410 Loop, San Antonio, TX 78216
San Antonio, TX 78216
http://doubletree3.hilton.com/en/hotels/texas/doubletree-by-hilton-hotel-san-antonio-airport-SATNSDT/index.html
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October Monthly Chapter Meeting

Tuesday October 17, 2017

11:30-1PM

Location: DoubleTree Hotel, 37 NE Interstate 410 Loop, San Antonio, TX 78216

Meeting Room Salon II

 

Speaker Bio

 Fred Gleeson is the Western Sales Manager for Specified Air Solution’s DOAS brands, Addison & Ecotron by Dectron. Fred has over 30 years of sales and management experience with commercial HVAC equipment manufacturers, primarily focused on DOAS and dehumidification. Throughout his career, he has been active in ASHRAE and served in various leadership positions including Alamo Chapter President and Region VIII RVC, Region VIII Treasurer. Currently, Fred is the 2018 CRC Chair for Region VIII.

 

 

The Changing Paradigm of DOAS

 

Since the mid-1960s, Dedicated Outdoor Air System (DOAS) units have evolved into a specialized category of HVAC products that handle both the latent and sensible loads of conditioning ventilation air. Modern DOAS technology strives to meet the minimum ventilation levels mandated by ASHRAE Standard 62.1, while maximizing energy performance beyond the requirements of ASHRAE Standard 90.1. Demand Control Ventilation (DCV) is a DOAS control strategy for delivering only the required ventilation rate based on occupancy, allowing for substantial energy savings anytime occupancy is below maximum. Unfortunately, the limitations of DX-based packaged DOAS units have prevented the full realization of the promise of DCV.

The high latent load representative of OA design conditions requires low face velocities across a deep row evaporator coil. Packaged DOAS manufacturers use digital scrolls or inverter compressors to effectively modulate cooling capacity during part load, but that does not enable much VAV turndown. Risks associated with low airflow across the evaporator coil include loss of supply air dew point control, problems with refrigerant P/T management, and freezing in portions of the coil where heat transfer is restricted. Most manufacturers designate 70%-60% of full airflow as the lowest limit a packaged DOAS can predictably operate.

Since conventional packaged DOAS units cannot vary CFM low enough to track the minimum required ventilation rate based on occupancy, it’s generally accepted that these systems will over-ventilate during most of their operating schedule. Modulating hot gas reheat is used to maintain a constant “space neutral” supply air temperature to avoid over-cooling the space. But this practice is coming under scrutiny, since a DOAS expends so much cooling energy to dehumidify but then wastes all its sensible cooling capacity by reheating the air. If the DOAS ventilation rate could be modulated to track occupancy and prevent over-ventilation, the need for reheat would be eliminated.

Recent advancements in VRF technology have enabled a mechanical means of adjusting evaporator coil geometry in DOAS units. This prevents associated problems with laminar flow at the coil boundaries, and allows a packaged DX DOAS unit to maintain dew point control down to 20% of maximum air flow. Aside from the obvious benefits of reducing the amount of OA that needs to be conditioned, this approach also allows ventilation air to provide required sensible cooling. That offsets the load on zone air conditioning equipment, and allows for downsizing of terminal cooling units throughout the building. When conditions dictate some reheat is desirable, series heat recovery technologies can be employed in lieu of hot gas reheat to further enhance DOAS energy efficiency.

Tickets

$25.00 Regular Meeting Ticket
$30.00 after 12:00 pm October 15

$30.00 Guest Ticket
$35.00 after 12:00 pm October 15