PoolPak R-410A SWHP Series, Engineering Manual

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9 EGW05-SWHPEG-20140724
TM TM
ROOM DEW POINT CONTROL
PoolPak™ units with the ECC controller operate using an advanced type of control utilizing dew point and dry bulb
temperature control. This method of control is more accurate than conventional relative humidity control. The main
purpose of a dehumidification system is to maintain the amount of moisture in the pool area below a level that would
cause damage to the building. Relative humidity is a measurement of the percentage of moisture which is in the air at a
given dry bulb temperature in proportion to the maximum amount of moisture that could be contained at this particular
dry bulb temperature. Warmer air can hold more moisture than colder air, therefore, changes in dry bulb temperature
will change the relative humidity reading without any change in the actual amount of moisture in the air. The amount
of moisture in the air is expressed as “grains of moisture per pound of dry air” and is directly related to the dew point
temperature.
The ECC uses dew point control to operate the PoolPak™ unit and maintain the moisture level below the setpoint (see
Figure 2-1). The space dry bulb temperature and relative humidity determine the dew point temperature. By varying the
space temperature and space relative humidity set points, the dew point set point is changed. When the space dew point
temperature rises more than 1/2 degree Fahrenheit above the space dew point temperature set point, the ECC controller
energizes the compressor for dehumidification. As the dew point temperature drops more than 1/2 degree Fahrenheit
below the dew point temperature set point, the controller de-energizes the compressor.
Figure 2-1. Dew Point Control Psychrometric
0.000
30˚F/-1˚C
Dry Bulb Temp.
40˚F/4˚C 50˚F/10˚C 60˚F/16˚C 70˚F/21˚C 80˚F/27˚C 90˚F/32˚C 100˚F/38˚C 110˚F/43˚C 120˚F/49˚C
0.030
0.028
0.024
0.020
0.016
0.012
0.008
0.004
Humidity Ratio
lb
w
/ lb
a
Dew Point
82˚F / 28˚C
80˚F / 27˚C
75˚F / 24˚C
70˚F / 21˚C
65˚F / 18˚C
60˚F / 16˚C
55˚F / 13˚C
50˚F / 10˚C
45˚F / 7˚C
40˚F / 4˚C
35˚F / 2˚C
30˚F / -1˚C
80%
60%
40%
20%
If RA here, space too
cold, too humid
If RA here, space too
hot, too humid
If RA here, space too
cold, humidity OK
If RA here, space too
hot, humidity OK
ALL_DewpointControlPsychro_20131220.eps