| CONDENSATION AND FROSTING
In special situations condensation and frosting can occur. For this
reason, the VHR package includes a full drain pan and a frost-alert circuit complete with
sensor, indicating light, and fan operating controls.
Condensation occurs when the exhaust air stream is cooled below its
dew point. If this temperature also falls below freezing , ice will form. This
ice adds pressure loss which reduces the airflow through the heat wheel. In extreme
cases involving accumulated frost, the airflow could be blocked off entirely.
A psychromatic chart can be used to predict condensation and
frosting. For model VHRS, if a line connecting exhaust and supply air entering
condition crosses the saturating curve, the exhaust temperature must be kept above 34 deg
f to prevent frosting. If this line does not cross the saturation curve, the exhaust
temperature can drop to 20 deg F without the likelihood of icing
For model VHRE, if a line connecting the exhaust and supply air
condition crosses the saturation curve, the exhaust temperature at which icing will occur
is a t a point where the entering supply air specific humidity line intersects with a line
from the entering exhaust air drawn tangent to the saturation curve. Frosting will
not occur if the entering condition line does not cross the saturation curve. |
