DESSICANT
DEHUMIDIFCATION
Content
Review of Desiccant Wheel
Active Desiccant Dehumidification Vs
Passive Desiccant Dehumidification
Performance of Desiccant
Dehumidification
More about Desiccant Dehumidification
Review of Desiccant Wheel
Desiccant Wheel = Heat Wheel?
Seibu / BryAir / Heatex
Desiccant attract water our of the air as a
vapor rather than as condensed liquid
Type of Desiccant
◦ Activated Alumina
◦ Silica Gel
◦ 3Å Sieve
Wheel Design Parameters
Flute size – number of transfer units,
pressure drop
Media depth
Media density – matrix wall thickness,
desiccant type, desiccant loading, binder
level
Media strength / stability – manufacturing
stress, thermal cycling
Active Desiccant Dehumidification
Vs Passive Desiccant Dehumidification
Heating or not
Passive desiccant: RH ~70%: RPM: 15 ~ 20
Active desiccant: RH <10%: RPH: 12 ~ 24
OA
EA
RA’ RA
SA
Passive Desiccant
10 20 30 40 50
60
70
80
90
100
110
110
120
120
ENTHALPY - KJ PER KILOGRAM OF DRY AIR
10
20
30
40
50
60
70
80
90
100
ENTH
ALPY -
KJ PER
KIL
OG
RAM
OF D
RY A
IR
SATURATIO
N T
EMPER
ATURE -
°C
5 10
15
20
25
30
35
40
45
50
DR
Y B
UL
B T
EM
PE
RA
TU
RE
- °
C
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
10% RELATIVE HUMIDITY
20%
30%
40%
50%
60%
70%
80%
90%
5
5
10
10
15
15
20
20
25
25
30 WET BULB TEMPERATURE - °C
30
0.7
8
0.8
0
0.8
2
0.8
4
0.8
6 V
OLU
ME
- CU
BIC
ME
TE
R P
ER
KG
DR
Y A
IR
0.8
8
0.9
0
0.9
2
0.9
4
HU
MID
ITY
RA
TIO
- G
RA
MS
MO
IST
UR
E P
ER
KIL
OG
RA
M D
RY
AIR
OA
SA
RA
EA
R R
ASHRAE PSYCHROMETRIC CHART NO.1
NORMAL TEMPERATURE
BAROMETRIC PRESSURE: 101.325 kPa
Copyright 1992
AMERICAN SOCIETY OF HEATING, REFRIGERATING AND AIR-CONDITIONING ENGINEERS, INC.
SEA LEVEL
0
1.0 1.0
-
1.52.0
4.0
-4.0-2.0
-1.0
-0.5
-0.2
0.1
0.2
0.3
0.4
0.5
0.6
0.70.8
-5.0
-2.0
0.0
1.0
2.0
2.5
3.0
4.0
5.0
10.0
-
SENSIBLE HEAT Qs
TOTAL HEAT Qt
ENTHALPY
HUMIDITY RATIO
h
W
Active Desiccant
10 20 30 40 50 60 70 80 90 100110
120
130
140
150
160
170
180
190
200
210
220
230
240
250
260
270
280
290
290
300
300
310
310
320
320
330
330
340
340
350
350
360
360
ENTHALPY - KJ PER KILOGRAM OF DRY AIR
30
40
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
210
220
230
240
250
260
270
280
EN
TH
ALP
Y -
KJ P
ER
KIL
OG
RA
M O
F D
RY
AIR
SA
TU
RA
TIO
N T
EM
PE
RA
TU
RE
- °
C
20
30
40
50
60
70
80
90
10
0
11
0
12
0
DR
Y B
UL
B T
EM
PE
RA
TU
RE
- °
C
10
20
30
40
50
60
70
80
90
15%
25%
2%
4%
6%
8% R
ELA
TIVE H
UM
IDIT
Y10% RELATIVE HUMIDITY20%
30%
40%
50%
60%
70%
80%
90%
10
20
20
30
30
40
40
50 WET BULB TEMPERATURE - °C
50
0.8
2
0.8
6
0.9
0
0.9
4 V
OLU
ME
- CU
BIC
ME
TE
R P
ER
KG
DR
Y A
IR
0.9
8
1.0
2
1.0
6
1.1
0
1.1
4
1.1
8
1.2
2
1.2
6
HU
MID
ITY
RA
TIO
- G
RA
MS
MO
IST
UR
E P
ER
KIL
OG
RA
M D
RY
AIR
OA
SA
RA RA'
EA
R R
ASHRAE PSYCHROMETRIC CHART NO.3
HIGH TEMPERATURE
BAROMETRIC PRESSURE: 101.325 kPa
Copyright 1992
AMERICAN SOCIETY OF HEATING, REFRIGERATING AND AIR-CONDITIONING ENGINEERS, INC.
SEA LEVEL
0
1.0 1.0
-
1.52.0
4.0
-4.0-2.0
-1.0
-0.5
-0.2
0.10.
2
0.3
0.4
0.5
0.6
0.7
0.8-5.0
-2.0
0.0
1.0
2.0
2.5
3.0
4.0
5.0
10.0
-
SENSIBLE HEAT Qs
TOTAL HEAT Qt
ENTHALPY
HUMIDITY RATIO
h
W
Performance of Desiccant
Dehumidification Depth of wheel
Performance of desiccant
OA / RA’ condition
Performance of Desiccant
Dehumidification
Performance of Desiccant
Dehumidification (Wheel Size)
Performance of Desiccant
Dehumidification (OA Airflow)
Performance of Desiccant
Dehumidification (OA Temperature)
Performance of Desiccant
Dehumidification (OA Moisture)
Performance of Desiccant
Dehumidification (RA’ Airflow)
Performance of Desiccant
Dehumidification (RA’ Temperature)
Performance of Desiccant
Dehumidification (RA’ Moisture)
MORE ABOUT DESICCANT DEHUMIDIFICATION
Configuration of Desiccant
Dehumidification
OA:RA = 75:25
(Most Common)
OA:RA = 50:50
OA:RA :Purge = 60:20:20
Configuration of Desiccant
Dehumidification
Heat recovery opportunities
Most common: SA Vs RA
RA
SA
SA’
RA’ RA’’ EA
OA
Control of Desiccant
Dehumidification SA Fan Modulation
Closest tolerances, lowest operating cost
Variable Air Bypass
Close tolerances
Reactivation heat modulation
Moderate tolerances, low equipment cost
On-off heat modulation
Loose tolerances, lowest equipment cost
Internal Control of Desiccant
Dehumidification No RA’, No heater on
Running time delay for RA/RA’/EA fan
Stop heater if excessive temperature for
RA’ and EA
Alarm if wheel is not rotating
Suggestions for Desiccant
Dehumidification Use low-cost heat source
Clean or change filter frequently
Provide space to replace wheel
Desiccant Dehumidification in Hong
Kong Town Gas – Munters
Most are gas-fired system
Industrial means work on standalone mode
Most common installations are warehouse,
film archive, indoor pool
Installation Units
Commercial 23 61
Industrial 34 67
Total 57 128