User Guide for Desiccant Dehumidification Technology

7/27/2019 User Guide for Desiccant Dehumidification Technology

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FACILITIES ENGINEERING

APPLICATIONS PROGRAM

User Guide for DesiccantDehumidification Technology

byThomas E. Durbin and Michael A. Caponegro

U.S. Army Construction Engineering Research LaboratoriesChampaign, IL 61826-9005

Approved for Public Release; Distribution Is Unlimited.


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The contents of this report are not to be used for advertising, publication,

or promotional purposes. Citation of trade names does not constitute an

official endorsement or approval of the use of such commercial products.

The findings of this report are not to be construed as an official

Department of the Army position, unless so designated by other authorized

documents.

DESTROY THI S REPORT WHEN IT I S NO LONGER NEEDED

DO NOT RETURN IT TO THE ORIG INATOR


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USACERL FEAP UG-97/107

Foreword

This study w a s done for t he U .S. Army Cent er for public Works (U SACP W) under

the Facilities Engineering Application Program (FEAP); Work Unit F56, FEAP

Desiccant Demonstrat ion at APG. The technical monitor was Dennis Vevang,

CECPW-EM.

The work was performed by the Troop Installation Operation Division (UL-T) of the

Util i t ies and Industrial Operations Laboratory (UL), U.S. Army Construction

Engineering Research Laboratories (USACERL). The USACERL princ ipa l

investigator was Thomas E. Durbin. Chang W. Sohn is Acting Chief, CECER-UL-U;

Mart in J . Sa voie is Act ing Operat ions Chief, CE CE R-U L; a nd G ary W. Schanche is

the associated Technical Director, CECER-UL. The USACERL technical editor was

William J . Wolfe, Technical R esources.

COL J am es T. Scott is Comman der an d Dr . Micha el J . OConnor is D irector of

USACERL.


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2 USACERL FEAP UG-97/107

Contents

Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1 Executive Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2 Pre-Acquisition: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Technology Description and Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5

Possible Solutions Offered by Desiccant Dehumidification . . . . . . . . . . . . . . . . . . . . . ...8

Costs and Benefits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12

Sample Cost Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Life Cycle Cost/Benefit Prediction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13

Utility and Space Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14

3 Acquisition/Procurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Acquisition/Procurement Strategy.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16

Potential Funding Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17

Procurement Documents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17

Procurement Scheduling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17

Design Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18

Construction Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19

4 Post Acquisition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20Acquisition Scheduling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20

Commissioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20

Operation and Maintenance issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20

Performance Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21

Appendix A: Vendors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Appendix B: Example Scope of Work for Two-Wheel Desiccant Dehumidification

Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Appendix C: Sample Specifications for Two-Wheel Desiccant

Dehumidification/Cooiing System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29


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USACERL FEAP UG-97/107 3

1 Executive Summary

Manufacturing industries have used desiccants in various applications for over 50

years, but have only recently begun to apply desiccant dehumidification systems

(DDSs) to Heating, Ventilation, and Air-Conditioning (HVAC) applications.

Depending on climat e an d fa cility loading, a high percent a ge of a buildings cooling

load can be la tent (moisture) load. C onventional cooling equipment operat es at low

temperat ures to cool the a ir to i ts dew point t empera ture, w here dehumidif ica t ion

via condensat ion on the coils begins. I t ma y t hen be necessary t o reheat the a ir to

a comfortable tempera ture before i t enters t he occupied space. DD Ss, by contr ast ,

remove water from the air by using a desiccant , or chemical drying agent. DDSs

offer several benefits when used in conjunction with air-conditioning systems.

Removing moisture from the air by desiccation decreases the amount of vapor-

compression energy needed to dehumidify the air being supplied to the user, and

increases the comfort level in the conditioned space. Desiccant systems also decrease

moisture accumulation in ducts and around coils, inhibiting the growth of mold and

mildew.

While research in desiccant dehumidification technology development has been

conducted for severa l yea rs, commercial a pplica tions of desiccant dehumidifica tiontechnology have been l imited in th e past by ma terial a nd ma nufacturing consider-

ations. Current desiccant dehumidification systems range in capacity to 30,000 cubic

feet per minute (cfm) and are near the commercialization stage. Since these systems

are heat driven (not electrically driven), conversion to a desiccant system can reduce

site peak electrical demand and levelize utility loads, allowing for more efficient

power plant operation. Energy cost savings result from reduced chiller loads,

reduced electrici ty peak demand, and el imination of air reheating requirements .

Desiccant dehumidification systems can also reduce or eliminate the use of harmful

CFC s in the HVAC system by using na tura l gas or l iquid propane gas (LPG ) as t he

prima ry fuel for dehumidifica tion.

AS yet , very few desiccant systems have been instal led at mil i tary instal la t ions, and

only then in specialized applications. Desiccant dehumidification systems may offer

advantages for military applications over other energy supply options by increasing

force readiness, providing greater system reliability, controlling humidity in areas

with sensit ive mat erial and equipment, a nd by reducing environmental impact a nd

energy costs.


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4 USACERL FEAP UG-97/107

Points of Contact :

Dennis Vevang

U .S. Army C enter for P ublic Works (U SACP W)

ATTN: CE CP W-E M

2701 Telegra ph R oadAlexandria, VA 22312-3862

Comm: (703) 806-6071

FAX: (703) 806-5220

Thomas E. Durbin

U .S. Army C onstruction En gineering Resear ch L aborat ories (U SACERL)

ATTN: CECER-ULU

P O B ox 9005

Champaign, IL 61826-9005tel : 217/352-6511, X5543

F AX: 217/373-7222

U RL : ht t p://w w w .cecer.a rm y.m il

Micha el A Ca ponegro

USACERL

ATTN: CECER-ULU

P O B ox 9005

Champaign, IL 61826-9005tel: 217/352-6511, X5552

F AX: 217/373-7222


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USACERL FEAP UG-97/107 5

2 Pre-Acquisition:

Technology Description and Application

Conventional Air-Conditioning/Ventilation Process

Conventional air-conditioning systems are typically controlled by a thermostat (or

simila r ty pe receiver/cont roller combina tion). They opera te in a ma nn er th a t keeps

the space dry bulb temperature from exceeding the thermostat setpoint. To

maintain that setpoint , condit ioned air is typical ly introduced into the space

approximately 20 F* lower than the setpoint, so that the conditioned air can absorb

the so-called sensible heat entering the space. Having absorbed this heat, air from

the space is drawn back to the air-handling unit , where i ts temperature is again

decreased before being returned to the space. The temperature decrease is

accomplished by the returned air being drawn (or blown) through a cooling coil

within the air handling unit. The coil is typically a specially designed finned-tube

heat exchanger, containing a relatively cold circulating fluid (usually chilled water

or a ref i igerant) into which heat from the air is transferred. Invariably, the

described situation is somewhat more complicated since some amount of outside air

is mixed with the returned air from the space, and then the mixture is cooled by thecoil. The most common reason for introducing outside (fresh) air is to provide

ventila tion for th e occupant s of the spa ce. As the cooling coil reduces t he dry bulb

temperature of the air so that the air, in turn, will provide sensible cooling for the

space, the dry bulb temperature of the air is reduced almost to i ts dew point

temperat ure. In fact , a considera ble portion of the a ir a ctua l ly reaches sat ura tion

due to its contact with, or proximity to, the cooling coil, which has a temperature

considerably lower than the air s dew point temperature. As a result , water

condenses from th e a ir ont o the coil, w here proper selection of a irflow velocities (