How Does a Channel Blender Improve HVAC Performance?
That’s the question we asked Travis Starns, VP at Blender Products, at our most recent Coffee Break webinar. These 50-minute sessions earn attendees 1 PDH and give them an insider look into the most cutting-edge technologies and solutions in the world of HVAC. Ask your SVL Sales Engineer for an invite to our upcoming sessions.
The Problem of Air Stratification
Blender Products engineers solutions to combat the problem of air stratification in AHU mixing boxes. When two airstreams, the outdoor air (OA) and return air (RA), mix in an AHU, the resulting combined airstream is rarely uniform. It has hot and cold zones, and variable velocity and moisture content.
Temperature stratification in AHUs is a well-known problem. It leads to freeze-stat trips and frozen coils, and those repairs can be costly. Uneven moisture loading in the airstream can result in condensation and mold growth.
To extend economizer operations and ensure the highest performance of your AHU, improving the air uniformity coming out of the mixing box solves several potential problems. ASHRAE notes that good air mixing is essential for proper coil operation (Chapter 27, Section 2). Several mixing boxes, especially on older equipment, just don’t do an effective job.
What strategies exist to combat air stratification?
Some designs attempt to orient the dampers such that the airstreams mix on their own. The modeling data shows this strategy doesn’t usually work well. Air only remains in a mixing box for a fraction of a second—this isn’t much time for the airstreams to mix effectively. The RA will form a thermal barrier rising against the colder OA, and relatively little heat transfer will occur.
Another field fix is to install a baffle plate in the mixing box to direct the outdoor air directly in front of the return air dampers. This works a little better, but still has plenty of issues. It often creates greater velocity stratification in the mixing box, and it doesn’t address the root cause of poor stratification inside the unit.
What about a static blender?
Blender Products’ benchmark technology is the Series IV Air Blender. It does a fine job of combatting stratification, but it comes with trade-offs. The increase in pressure drop is significant, and it adds 43” of additional space to the mixing box. The feedback from engineers has always been that they love the mixing capabilities of the Series IV but say it’s hard to find 43” of extra space in the mechanical room.
How does the Channel Blender improve on the Series IV blender?
Introduced in 2018, the Channel Blender is a response to those space constraints, offering the same freeze protection without the added footprint. It eliminates the blender section of the AHU while providing the same level of mixing. It raises the minimum temperature before the coil above the freeze-stat threshold of 37–38 °F while needing only 8” of space for effective mixing.
Saving length means saving real money in AHU operations. Channel blenders replace traditional dampers and cabinetry, making them a great choice for retrofits that can’t accommodate more space for mixing.
How does it work?
The Channel Blender comprises a series of sheet metal channels that replace traditional dampers. The damper sections for the OA and RA streams are oriented into alternating channels that feature dual skin walls with insulating media in between. These channels create micro-collisions of airstreams that create a uniform mixing field just beyond the dampers.
What are some other benefits?
Protecting against freeze-stat conditions and extending economizer operations are only two of the benefits the Channel Blender offers:
- It features integrated, independently controlled OA and RA dampers for pinpoint accuracy on the mix of airstreams your application requires
- It is a custom-designed piece, and designs can fit almost any mixing box and orientation of incoming airstreams
- It prevents velocity stratification, improving the performance of downstream filters
- It improves coil performance through reduced variability of moisture in the airstream
Custom engineering reports are provided for each Channel Blender installation