Constant Speed Frost Prevention
When there is a threat of frost on the enthalpy wheel, the wheel
is jogged so that less enthalpy transfer occurs and frosting
of the wheel is avoided. Frosting can occur on the enthalpy
wheel when the exhaust air leaving the wheel is saturated. This
condition occurs when two lines intersect on a psychrometric
chart, and it does not occur when these two lines do not
intersect (see
Figure 63
).
Variable Speed Frost Prevention
When there is a threat of frost on the enthalpy wheel, the
wheel is slowed down so that less enthalpy transfer occurs
and frosting of the wheel is avoided. Frosting can occur on
the enthalpy wheel when the exhaust air leaving the wheel is
saturated. This condition occurs when two lines intersect on
a psychrometric chart, and it does not occur when these two
lines do not intersect (see
Figure 63
).
Energy Recovery Exhaust Hoods
Units with the optional energy recovery section have one
or two (depending on model) exhaust hoods. Each hood is
shipped in three pieces, consisting of one top and tow sides.
Install exhaust hood over the barometric relief dampers by
installing tow sides first and then install the top.
Variable Speed Frequency Control
A variable frequency drive is included with the frost protection
option and it controls the speed of the enthalpy wheel. The
unit has also been programmed for the recommended range
of wheel speed operation. Typical wheel speed is 45 RPM, but
the programming can allow for wheel speeds above or below
45 RPM. Check all factory settings to make sure they are
consistent with the application.
Enthalpy wheel speed will be controlled by exhaust
temperature measurement .
Slide-Out Wheel
The wheel can be pulled out to facilitate cleaning and servicing
(
Figure 64
). Unplug the control wires before sliding the wheel
out of position .
Figure 64: Slide-Out Energy Recovery Wheel
IM 1125-7 • REBEL ROOFTOPS
68
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