PROBLEMS OF AIR STRATIFICATION – In the HVAC Air Handling system, air stratification resulted from the improper design inherent in moving air streams by keeping air streams of different air temperatures from mixing effectively for a long distance. As a result, it was very difficult to effectively operate an Air handler as well as maintaining the Indoor air quality.
In the winter as a result of no air mixing, coils often got frozen, which damaged the coil as well causing freeze stat trips and sensing errors. In summer, both streams of air were not mixed properly causing additional load on the heat transfer coils leading to large energy bills. Over time the air mixing problem became a serious matter as Outdoor air percentage started increasing as a result of the mandate IAQ requirement. Read More
CURRENT PROBLEMS VS. EFFECTIVE ECONOMICAL SOLUTION
We have seen many solutions adopted in the market to resolve the problem of air stratification and non-mixing of two temperature air that was brought into a given space.
Earlier glycol additives were used to prevent frozen coils, dampers, high-velocity jets, baffles and specially designed apparatus were conceived to help in mixing. In each case use of a technique slacked the capacity of the air handler like lower capacity, higher pressure drop and increase of motor horsepower.
Some custom-designed air mixers were offered in the past to improve air mixing criteria however it was found that air was forced to pass under high velocity through a narrow chamber. These air mixers required more downstream space, non-uniform velocity profile and high-pressure drop. Also, it was seen that non-uniform velocity caused additional pressure drop at the downstream components like coils, filters etc.
EB Air Mixer provides a full solution to reducing air stratification in the plenum. The design was conceptualized by looking at existing problems and devising solutions that best fit the market requirement at an affordable cost. Various programs were used and were studied to see what design and size worked the best.
The following principles were taken into consideration;
a. Layer by layer meshing of two gradients of air across the full plenum. b. Effectively churning the air within the Plenum/ box itself without requiring additional space c. Optimizing the flow field of the air and creating the right blend. d. Energy savings
In the present case, the new compact design allowed to bring air from the side of the plenum effectively at the same time able to mix warm and cold air effectively inside the whole cross-section of the mixer with minimum fallout of temperature and mixing.
The air mixing takes help with thermal dispersion across the thin sheet metal wall inside the mixer along with aerodynamic braiding bars to accentuate mixing within a short distance. This combined with effective air mixing and low-pressure drop makes the unit a suitable choice for most Air Handling Unit AHU manufacturers.
The air-mixing device is one of the most effective means of stirring air as well uniformly mixing two gradients of air temperature homogeneously without causing abrupt temperature blocks in certain areas at the entry to the coil. The downstream area is of the air mixing device is shorter than standard mixing devices in the industry given only 2-3ft of distance is required to optimize mixing without causing stratification.
The Mixing device uses alternating layers of Cold (O/A) and Warm (R/A) passageways. The R/A is then directed towards the O/A using diverters located on alternate R/A passageways. If the O/A and R/A dampers are located on the sidewalls of the mixing plenum, the design must ensure that the bottommost passageway is dedicated to the R/A so that cold O/A does not stratify the bottom and thereafter free the coils.
Alternately, if the O/A is on the sidewall and R/A is on the top (or vice versa) then it must be checked that there are no outer passageways on the edges of the mixer where the O/A is not mixing air with R/A (Return Air is not deflected toward that particular passageway if so the opening passage to be blocked).
(Alternately EB Air’s innovative VAV Mixer allows air to be churned at a certain speed by braiders allowing complete mixing without any block of unmixed air. Variable Air Volume VAV Mixer is designed and suited for heavy mixing with a control mechanism that adjusts to changing conditions)
The noise of the mixing device should be checked for low attenuation requirements. Special acoustical media can be embedded in the construction to prevent any unwanted noise from breaking out of the device. For details on design and others, please contact the factory.
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