Kanomax 2212, User Manual, Page: 45 / 52

10. Calculation Result: DT, WB, AH and HR 42
10. Calculation Result: DT, WB, AH and HR
10.1 What is DT?
DT -- Dew Point Temperature
Warmer air contains much water vapor. As the air gets cooled, it reaches saturation at a certain temperature (Relative
Humidity: 100%). As the temperature continues to get lowered, water vapor starts condensing into water. The
condensed water is called dew. This temperature is called Dew Point Temperature.
There are many formulas to calculate the Dew Point Temperature. In this manual calculation in conformity with JIS
standard Z8806 is used.
ln (e
w
) = -6096.9385×T
-1
+21.2409642-2.711193×(10
-2
) ×T
+1.673952×(10
-5
) ×T
2
+2.433502×ln(T)
e = U/100×e
w
y = ln (e/611.213)
In case of y
≧
0;
td = 13.715×y+8.4262×(10
-1
) ×y
2
+1.9048×(10
-2
) ×y
3
+7.8158×(10
-3
) ×y
4
In case of y < 0;
td = 13.7204×y+7.36631× (10
-1
) ×y
2
+3.32136×(10
-2
)×y
3
+7.78591×(10
-3
)×y
4
e
w
: Saturated Vapor Pressure (Pa)
T: Absolute Temperature (K) = t(
o
C) + 273.15
T: Dry-bulb Temperature (
o
C)
E: Water Vapor Pressure (Pa)
U: Relative Humidity
Td: Dew-point Temperature (
o
C)
10.2 What is WB?
WB: Wet-bulb Temperature
Wet-bulb temperature is measured using a wet-bulb thermometer that has its bulb wrapped in cloth that is kept wet with
water.
To calculate wet-bulb temperature without using a wet-bulb thermometer, existing dry-bulb temperature and relative
temperature are normally used on the aspirated psychrometer humidity table that is JIS standard Z8806 compliant. In
this manual, however, we use Newtonian approximation based on the assumption of a temperature measured on a
wet-bulb thermometer being lower than a dry-bulb thermometer.