UV-PRC001-EN 7
away from the cold outside air
stream, and also mixes this cold
air with return air to provide a uni-
form coil inlet temperature. An ad-
ditional benefit in freeze
avoidance is the heat of the fan,
motor, and return air are mixed
into the air stream before entering
the coil, instead of after the coil.
This blow-thru design also acts as
a noise attenuator. The coil place-
ment near the discharge air allows
fan noise absorption which re-
stricts sound from the unit’s fan to
pass freely into the conditioned
space.
Draw-thru Design
A typical draw-thru design allows
little mixing of the return and out-
side-air stream while locating the
coil very close to the outside air in-
let. This process creates cold spots
on the coil that could lead to coil
freeze-up. See Table 3 for
mixed-air temperature at vari-
ous outside-air conditions.
Features and
Benefits
Blow-thru Design
A blow-thru unit ventilator design
places the blowers below the coil
to aid in the elimination of debris
(coins, paper clips, etc.) from fall-
ing into the spinning fan. This
safety consideration helps prevent
personal injury, noise or equip-
ment damage.
Another key advantage in the
blow-thru design is the protection
against coil freezing. The blow-
thru design keeps the coil farther
Trane - Blow-thru Design Competition - Draw-thru Design
Table 3: Mixed-air temperature at various outside air (OA) conditions
Outside Air
Temperature
Percent Outside Air
16-2/3 20 25 33-1/2 50
-10 Degree 56.80 54.00 50.00 43.40 30.00
0 Degree 58.50 56.00 52.50 46.80 35.00
10 Degree 60.10 58.00 55.00 50.00 40.00
20 Degree 61.90 60.00 57.60 53.40 45.00
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