Dry Faster
With Energy (Heat)
The acronym of HAT is used for
teaching drying Humidity, Airflow and Temperature. These three
elements make up what is called the drying pie. Increasing any
of the slices would decrease the need for the others. The
inverse would be true, as well.
Humidity and Airflow seem to get the most attention. Temperature
control is usually limited to keeping the temperature in optimum
range for dehumidifiers and the comfort of the occupants, but
when properly applied, temperature, in the form of heat energy,
can be a great help to drying.
Great advances have been made in recent years in drying
equipment and methods, but there remains a bottleneck to our
current drying systems. This bottleneck is evaporation. We have
excellent equipment for removing water vapor from the air, but
we have been limited in the ability to get the vapor into the
air evaporation. The surface water evaporates very quickly,
but the water contained in the materials
(hardwoods, carpet cushion, sub-floors, sill plates and wall
boards) can take days to remove. If we could speed that
process, we could speed the overall drying process.
How does evaporation work?
Water exists in three different phases solid, liquid and
vapor. What causes it to change from one phase to another? It is
the addition of energy or heat. The phase change from liquid to
vapor is our main concern and what we call evaporation.
Energy (heat) and airflow applied to directly to water (liquid)
will speed the phase change to vapor causing evaporation. You
have experienced this all your life. Here are two examples: One
is a hair dryer how can you step out of a long shower into a
small room with water condensed on the all the surfaces,
including the fogged mirror and even have visible vapor (steam),
yet dry your hair with a hair dryer? Or why does it take water
from an aquarium so long to evaporate, but a pot of water on a
stove burner will evaporate very quickly? The answer is, of
course, energy (heat).
Is there a way to gauge the evaporation potential of liquid in a
material to see if the evaporation rate can be increased? Yes
and here it is:
VS VA = E
VS is the vapor
pressure of the surface containing the liquid water. This is
calculated using the temperature of the surface at equilibrium
vapor pressure (100% RH).
VA is the vapor pressure of the air directly
above the surface of which we are trying to remove the moisture.
This is calculated by measuring the temperature and relative
humidity.
E is the evaporation potential. The higher the
evaporation potential (difference in the vapor pressure of the
surface and the surrounding air), the faster the evaporation may
happen as long as there are no barriers preventing vapor
transfer.
Raising the temperature (applying energy or heat) to the surface
will have a much greater effect on the evaporation potential
then lowering the grains (vapor pressure) in the air.
If you want to dry structures faster;
consider using energy (heat) to your drying process.
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