Daikin MICROTECH 4 Operation Manual page 93

ENERgY RECOvERY
Energy Wheel Frost Prevention Initiation
Condensation and frosting on the energy recovery wheel is possible when the exhaust air leaving the wheel is saturated . This condition
is only possible when the energy recovery psychrometric saturation process line between the indoor and outdoor design points
intersect the psychrometric saturation curve . The two ends of the energy recovery process line will be the outdoor air temperature at
95% relative humidity and the return air temperature at the return air relative humidity . The process line example shown below depicts
one process line that intersects the saturation curve, and one that does not . The one that does intersect does so at two points, which
indicates a potential for energy recovery wheel frosting . The higher of the two points is the intersection point that will be used by the
frost prevention functions . The curve that does not intersect indicates no potential for frosting .
Figure 29: Frost Prevention Curve
Modulating Wheel Frost Prevention
Modulating Wheel Frost Prevention is initiated when the exhaust air temperature leaving the wheel is below the intersection point,
plus an adjustable minimum temperature difference. In the example below, the Exhaust air (EA) is significantly below the intersection
point .
During modulating wheel frost prevention, the wheel is controlled to its minimum wheel speed (default 15%) When the wheel is at its
minimum speed, the wheel effectiveness is reduced. The resulting exhaust air temperature during frost prevention (EAF) is warmer than
the intersection point and frost is prevented . The leaving wheel temperature (LWF) during frost prevention is also reduced .
Figure 30: Modulating Wheel Frost Prevention Curve
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