Dectron, Inc. March 2012
DECTRON
DSH/DSV/RSH/DBH/RBH Series Dehumidifier Owner’s Manual
Building Construction Moisture Migration
Data subject to change without notice.
20
The pool enclosure should be built to the latest
building codes and must be suitable for year-
round operation at 50% to 60% relative humidity.
Vapor Retarder
Before the design of the roof and walls is
finalized, the enclosure temperature and relative
humidity must be known; thus determining the
dew point (the temperature at which condensa-
tion will occur). For common dew points, see the
graph below.
If the room air goes below this dew point
temperature, water will condense from the air.
IMPORTANT!
Check the pool enclosure design (exterior
walls AND ceilings) for proper vapor retarder
location.
When the outdoor air temperature is sufficiently
low, parts of the exterior wall and ceiling will be
at or below the dew point temperature. These
parts MUST be on the outdoor (or cold side) of
the vapor retarder.
The vapor retarder should be adequate for the
purpose and should be continuous. All seams
should be completely sealed. Penetrations, as
for conduit, etc., should be sealed.
NOTE: Where the inside building finish includes
a perforated material, a continuous vapor
retarder must be installed behind it.
Failure to install the vapor retarder properly will
result in condensation forming in
the structure,
with all the consequent damages.
See Water Vapor Retarders in ASHRAE
Handbook of Fundament
als.
CONDENSATION
RESULTS IN
SOGGY
INSULATION
OUTDOOR 32°F
DRY
INSULATION
OUTDOOR 32°F
NO VAPOR
RETARDER
MOISTURE-LADEN
WARM AIR
INDOOR 84°F (29°C),
50% RH
VAPOR
RETARDER
MOISTURE-LADEN
WARM AIR
INDOOR 84°F (29°C),
50% RH
For this example, the dew point of
the room air is 63.4°F (17.4°C).
This temperature will occur some-
where in the wall.
BUILDING
CONSTRUCTION
75°F
24°C
80°F
27°C
85°F
29°C
90°F
32°C
80°F
27°C
70°F
21°C
60°F
16°C
50°F
10°C
DEW POINT
Dry-Bulb Temperature
40% RH
50% RH
60% RH
DEWPOINTS vs. DRY-BULB TEMPERATURES
Example:
An indoor pool enclosure has air
at 85°F and 60% relative humidity.
What is the dew point?
On the chart at left, start at 85°F
dry-bulb temperature. Go up to
the blue 60% RH line, then left to
70°F dew point.
The dew point of this air is 70°F.
Surfaces allowed to go below this
temperature will sweat.
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