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