HomeVision® Pro/Lite
© Corroventa Avfuktning AB
Rev A
6 (30)
Relative humidity and its effect on substances
All air contains more or less moisture but the naked eye cannot see it until it condensates in small
droplets on for instance a metal or glass surface. Already before it is visible however, the moisture
affects substances and production processes, causes corrosion and micro organism growth. In the
Nordic climate in particular, one must always count on ambient humidity due to the large water
surfaces of the many thousands of lakes and of the surrounding sea.
Air humidity is measured and referred to in terms of relative humidity (%RH) which is a measure how
much water it contains relative how much it can contain at given temperature. The higher the
temperature, the more water the air can contain but it is still the Relative Humidity that counts and
that needs to be controlled.
At RH 100% the air is saturated – there is fog and the moisture condensates in small droplets.
Already at RH 60% steel corrodes and at 70% there is a risk for mould growth. As a rule of thumb, RH
50% is a good climate for most substances but in the Nordic countries the humidity is rarely that low.
The yearly average for most places is closer to 80% and it can be as high both summer and winter.
Control of crawl space humidity
When a dehumidifier is installed in the crawl space in accordance with instructions in manual, vents,
cracks and other openings are sealed and the ground is covered with non-aging plastic foil, all
prerequisites are there for achieving and sustaining a good climate where rot, mould and bad smell
are prevented. As an extra prevention, downpipes that end by the foundation wall should be
modified so that the water is lead away from the building and do not leak into the crawl space.
HomeVision® with its wireless Control Panel offers easy and convenient monitoring of the crawls
space environment and allows the user to set desired operating parameters for Fixed RH control and,
for Pro also Mould Growth Index RH control.
Fixed RH control
With RH control a setpoint is selected, a relative humidity one wants the system to use as basis for its
dehumidification. Furthermore, one defines an upper and a lower hysteresis as well as an alarm limit,
the latter defining an alarm level at which, should it ever be reached, an automatic alert is triggered
on the Control Panel. The diagram is not to scale but only intended as an illustration of the principle
presented and its different parameters.
%
-
RH
Temperature
Hysteresis Upper
Hysteresis Lower
Dehumidification On
Dehumidification Off
Alarm +%RH
Alarm level
Setpoint
