desiccant

Published on December 2016 | Categories: Documents | Downloads: 73 | Comments: 0 | Views: 418
of 10
Download PDF   Embed   Report

review of desiccant dehumidification technology

Comments

Content


NREL/TP-472-7010 y UC Category: 1300 yDE94011889
A Review of Desiccant
Dehumidification Technology









Ahmad A. Pesaran
National Renewable Energy Laboratory

Prepared for Proceedings of EPRI’s Electric
Dehumidification: Energy Efficient Humidity
Control for Commercial and Institutional
Buildings Conference, New Orleans, Louisiana
June 2-3, 1993


National Renewable Energy Laboratory
1617 Cole Boulevard
Golden, Colorado 80401-3393

A national laboratory of the U.S. Department of Energy
Managed by Midwest Research Institute
for the U.S. Department of Energy
under contract No. DE-AC36-83CH10093

October 1994

NOTICE

This report was prepared as an account of work sponsored by an agency of the United States
government. Neither the United States government nor any agency thereof, nor any of their employees,
makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy,
completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents
that its use would not infringe privately owned rights. Reference herein to any specific commercial
product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily
constitute or imply its endorsement, recommendation, or favoring by the United States government or any
agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect
those of the United States government or any agency thereof.


Available to DOE and DOE contractors from:
Office of Scientific and Technical Information (OSTI)
P.O. Box 62
Oak Ridge, TN 37831
Prices available by calling 423-576-8401

Available to the public from:
National Technical Information Service (NTIS)
U.S. Department of Commerce
5285 Port Royal Road
Springfield, VA 22161
703-605-6000 or 800-553-6847
or
DOE Information Bridge
http://www.doe.gov/bridge/home.html

Printed on paper containing at least 50% wastepaper, including 10% postconsumer waste
A REVIEW OF DESICCANT DEHUMIDIFICATION TECHNOLOGY
Ahmad A. Pesaran
National Renewable Energy Laboratory
Golden, Colorado
Prepared for Proceedings of
Electric Dehumidification: Energy Efficient Humidity Control
for Commercial and Institutional Buildings Conference,
sponsored by the Electric Power Research Institute,
New Orleans, Louisiana, June 2-3, 1993
Figure 1. Recent Growth Trend for the Desiccant
Dehumidification Equipment Market, from EPRI (1992),
except for 1991 and 1992, which are estimates based on
discussions with two manufacturers.
In recent years, the use of desiccants for dehumidification in
air-conditioning applications has been on the rise (see Figure I),
and their capital cost has been on the decline. The supermarket
industry was the first to realize the potential of desiccant
dehumidification, and there are currently more than 500
supermarkets that use desiccant dehumidification packages
integrated with electric-driven refrigeration systems (Harriman,
1994). In these integrated designs, the desiccant system works as
a pre-conditioner for outside (ventilation) air to remove the latent
load. Other applications of desiccant dehumidification are in ice
rinks, hotels and motels, office buildings, full-service and fast
food restaurants, medical facilities, and retirement homes. The
benefits of desiccant dehumidification are better humidity control,
more efficient latent load removal, and reduction of peak electric
demands. In regions of the country where the electric utilities are
having trouble servicing their peak air-conditioning loads, this
energy-efficient technology can assist in meeting that demand.
ABSTRACT
This paper overviews applications of desiccant technology for
dehumidifying commercial and institutional buildings. Because
of various market, policy, and regulatory factors, this technology
is especially attractive for dehumidification applications in the
I990s. After briefly reviewing the principle of operation, we
present three case studies-for supermarkets, a hotel, and an
office building. We also discuss recent advances and ongoing
research and development activities.
INTRODUCTION
The heating, ventilation, and air conditioning (HVAC)
industry is facing several challenges in the 1990s, including a
decrease of energy resources, an increase in energy demand due
to population growth, and new regulatory policies. To respond to
these challenges, more energy-efficient heating, cooling,
ventilation, and dehumidification technologies are needed.
However, there are a number of constraints for deployment of
energy-efficient HVAC technologies; among them are the
imminent phase-out of chlorofluorocarbons (CFCs), eventual
phase-out of hydrochlorofluorocarbons (HCFCs), and the increase
in ventilation rates for buildings because of concerns regarding
indoor air quality and occupant health. The higher ventilation
rates translate into greater cooling loads-in particular, greater
latent loads-<luring cooling seasons when the relative humidity
within a building must be kept sufficiently low to inhibit the
growth of micro-organisms that cause health problems and also
may damage building materials. As a result, air dehumidification
has become a very important part of the HVAC function.
Desiccant dehumidification and cooling technology can provide
energy-efficient solutions for the industry. Desiccant
dehumidification technology has a successful track record over
more than 60 years for industrial applications such as product
drying and corrosion prevention. It has also been used for many
years in clean rooms, hospitals, museums, and other special cases
requiring highly controlled humidity levels. Milton Meckler has
recently discussed various benefits of the desiccant technology, its
potential applications, and factors that drive its future growth
(AGCC, 1994).
1
300
-0
~ 250
.9-
s:
(/) 200
2
·c
~ 150
'0
... 100
OJ
.c
E
~ 50
Z
1987 1988 1989 1990
Year
1991
Figure 3. Schematic of a Solld-Deslccant
Air Conditioner (GRI, 1992)
DESICCANT DEHUMIDIFICATION TYPES
Air dehumidification can be achieved by two methods : (I)
cooling the air below its dew point and removing moisture by
condensation, or (2) sorption by a desiccant material. Desiccants
in either solid or liquid forms have a natural affinity for removing .
moisture. As the desiccant removes the moisture from the air,
desiccant releases heat and warms the air, i.e., latent heat becomes
sensible heat. The dried warm air can then be cooled to desired
comfortconditions by sensible coolers (e.g., evaporator coils, heat
exchangers, or evaporati ve coolers.) . To re-use the desiccant, it
must be regenerated or reactivated through a process in which
moisture is driven off by heat from an energy source such as
electricity, waste heat, natural gas, or solar energy.
. Regenerallon Side
DlreClor i/!direC!

Regenc'Ialion Healer
Moisture
E:<hausled
loAmbienl /'
Air tobeProcessed
(amblenlair0' return alri
Air
E;rJporaHve (amb,cnl airore<na"s! a;[)

• I ' . '
IV. vOO ....1110
Ccndillonea Space
DireCI EVapQ,alive
Ccuier
Sensible
Heal Exchaouer
Process Side
For industrial applications, solid desiccant cycles use
dual-column packed-bed dehumidifiers; however, the most
appropriate dehumidifier configuration for air-conditioning
applications is the rotary wheel (see Figure 2). The air to be
dehumidified enters the system, comes into contact with the
desiccant wheel, and exits the dehumidifier hot and dry. The
wheel is then rotated so that the desiccant portion that has picked
up moisture is exposed to hot reactivat ion air and its moisture
removed.
Allgenerallu
Exhau$t
ail
Figure 2. Solld-Deslecant-Wheel Dehumidifier
(Munters Cargocaire)
Since the air leaving the desiccant is heated because of the
release of heat adsorption, there is a need for cooling the dried air
in cooling applications. This can be accomplished with a sensible
heat exchanger such as a heat pipe or with a standard
vapor-compression cooling coil. Figure 3 shows schematics of a
desiccant air conditioner incorporating direct-evaporative coolers
and a rotary solid-desiccant wheel.
Figure 4 is a schematic of a liquid-desiccant dehumidification
system. In a liquid system, there are two separate chambers--one
to perform the dehumidification (or conditioning) and the other to
reactivate (or regenerate) the desiccant. The processed air from
the dehumidification chamber enters into the conditioned space.
The desiccant , leaving the dehumidification chamber containing
absorbed moisture, goes through a heat exchanger and down to
the regenerator, where heat is added to remove the moisture. The
liquid desiccant is pumped continually between the two chambers
when dehumidification is needed.
2
Pomp
Figure 4. Schematic of a Llquld-Desiccant
Dehumidification System
Pesaran et al. (1992) provide a complete report with
approximately 900 citations on various desiccant cooling cycles
and past research and development. An excellent tutorial on
psychometrics , methods of dehumidification, and many
applications are presented in a dehumidification handbook by
Harriman (1990). A special ASHRAE publication (ASHRAE,
1992) contains a collection of papers on desiccant system
applications, low-level humidity control, · and moisture load
calculations.
DESICCANT DEHUMIDIFICATION APPLICATIONS
Desiccant systems are especially useful when the latent load
is high (i.e., when the latent-to-sensible heat ratio is high),
because they remove moisture more economically than they
remove sensible heat. Another desirable situation is when the cost
of dehumidification with a desiccant is lower than the cost of
dehumidification with a refrigeration system. This is where
thermal energy comes into the picture: there are instances where
desiccant regeneration done by waste heat, natural gas, or off-peak
electricity is more economical compared to regular electric
refrigeration. Because there is no need for reheating with
desiccant dehumidification systems , another appropri ate use is
when conditioned air must be reheated after coming out of a coil
to reach a comfortable dry-bulb temperature. Finally, the use of
a desiccant is well-suited to the case where dehumidification is
required at levels below freezing dew-point temperatures. For
example, an ice arena has is a great deal of humidity, but the
cooling coil has to cool below the freezing point. In such an
environment, dehumidification with desiccants can play a major
role.
system has undergone several improvements including the use of
a heat-pipe heat exchanger instead of an air-to-air heat exchanger
and the replacement of a lithium chloride wheel with a silica gel
wheel. DESIIAIR desiccant systems manufactured by ICC
Technologies have also been installed in many supermarkets with
resultant energy cost savings.
Taking into consideration these "best" circumstances, several
sectors of the market have characteristics to be good marketing
opportunities for desiccant dehumidification. Supermarkets have
provided the best opportunity. Ice rinks, hotels and motels, and
retail stores have dehumidification needs that could be met very
efficiently with desiccants. Restaurants have provided another
opportunity for desiccants because of high ventilation-rate
requirements and high moisture levels generated by cooking.
Office buildings could use desiccants because of high
ventilation-rate requirements in response to the "sick building
syndrome" and the ASHRAE Standard 62-89 on indoor air
quality; office buildings in regions with high humidity (high latent
load) are especially good candidates. Hospitals and nursing
homes have been using liquid-desiccant systems for many years.
In the following sections, we will review three applications
using desiccant dehumidification and will then provide an
overview of recent development activities.
Supermarket Applications
Reactivation Section
CooUHeat
Section
Filler
RelurnAir
Gas
Heal
Aeaclivalion
Fan
The rise in supermarket applications has resulted in the
continuous increase in the number of desiccant dehumidification
units shipped during the last several years (see Figure I).
Problem Definition-In supermarkets, conventional refrigeration
systems tend to cycle on and off, which allows build-up of
humidity and frost. A conventional air-conditioning system that
handles both loads is not very efficient because there may be a
need for reheat. And because the cooling coils must be at a
temperature below dew point to allow for condensation, the
coefficient of performance (COP) or energy efficiency ratio (EER)
of the refrigeration system is not very high. If the humidity could
be controlled independently of temperature, supermarkets would
be more comfortable and the maintenance due to frost on freezer
cases (a cost problem to supermarkets) would be eliminated.
Solution-A more efficient means is to use a gas-fired desiccant
module to handle the latent load and a downsized electric
vapor-compression refrigeration system to take care of the
sensible load. This allows
the evaporator to have a higher temperature, so the EER (the
refrigeration COP) will rise;
separate control of humidity and temperature;
potential for energy cost savings through
- reducing refrigeration COP and the energy cost of defrost
and anti-sweat heaters, and
- circulating less air because drier air has more
dehumidification capacity.
The principle of splitting the sensible and latent loads is used
in desiccant equipment for supermarket applications. Figure 5 is
a schematic of one of the latest supermarket desiccant
dehumidification systems-the SuperAire system from Munters
DryCool. In the last several years since its development, the
3
Figure 5. Schematic of the Munters SuperAire System for
Supermarket Dehumidification (Munters DryCool)
Example Result-In one example, a SuperAire dehumidification
and cooling system helped a Shaw's supermarket in New
England to realize energy cost savings of $8,500/year with a
simple payback of less than 3 years. A rebate from the local gas
utility lowered the payback to under 2 years (GRI, 1994). Using
desiccant systems, stores provide a drier, more comfortable store
environment for shoppers and employees, while extending product
shelf life and reducing frost buildup on frozen products and
refrigerated cases.
Hotel Case Study
Problem Definition - Mold, mildew, and musty odors are
problems in many hotels, and especially in humid climates,
costing members of the American Hotel and Motel Association
over $68 million each year (AHMA, 1991). Carpet and wallpaper
must often be removed because trapped humidity causes mold and
mildew to grow on the back surfaces. Mold and mildew are
forms of fungus whose growth and reproduction create the
familiar musty odor we smell in damp rooms and humid climates.
Fungus growth may be eliminated in three ways: kill the fungus,
remove its food, or remove its water (humidity). Removing
excessive moisture from materials is usually the most practical
and effective means of stopping mold and mildew. Air humidity
must be controlled below 60% relative humidity (RH) to avoid the
growth of mold and mildew.
One hotel in West Palm Beach, Florida-a small three-story
building with 150 rooms in two wings-had problems with indoor
moisture. Only I year after opening, two-thirds of the rooms were
experiencing mold and mildew and were either undergoing repairs
or had already undergone major repair such as removal of the
carpet and wallpaper; the ceiling gridwork in corridors was also
rusting (Banks, 1992). The existing HVAC system consists of a
25-ton split system for each wing, supplying about 5000 scfm air
through a ceiling plenum. The guest rooms had individual l-ton
packaged terminal air-conditioner units.
Remedial Measures-In an attempt to improve dehumidification,
the HVAC system on the north wing was retrofitted with a
desiccant module (Banks, 1992). In the north wing, a desiccant
system was installed as an add-on to the existing
vapor-compression system, with the addition of more capacity to
dehumidify the wing. The south wing maintained its conventional
cool/reheat system using vapor-compression equipment, but the air
distribution system was changed, using more air volume in each
wing (6000 scfm) and a positive air pressure in the building to
reduce air infiltration. The two wings were instrumented and
monitored for 9 months.
obtained test data at this location, a properly sized cool/reheat
system can cost more to operate than a gas-fired desiccant module
plus a downsized cooling system. In this building, the total
installed direct-expansion tonnage for conditioning outside air
could be reduced by 40-50 tons by using a desiccant module-a
reduction of more than 50%. A desiccant system could reduce
peak demand, which is an important factor in areas where the
peak-demand electric charges are high. In this particular
application, the hotel could achieve a $3,000 energy savings
annually over the cool/reheat system (Banks, 1992). Currently, a
desiccant system does have a higher initial cost, but the life-cycle
cost must be considered, including avoided repair costs, as well
as the benefits of lower humidity in the walls and improved
customer comfort.
Office Building Case Study
Figure 6. Average Moisture in the Wall Cavity, North
Wing versus South Wing, November 1990-July 1991,
for a Three-Story Hotel (Banks, 1992)
Figure 7 shows a schematic of an existing all-air VAV
system located in a six-story, 346,600 sq-ft Houston office
building (Meckler, 1993). The current HVAC system with 1000
tons of capacity provides 0.1 cfm per square foot of outdoor air
based on 143 sq ft per person and 15 cfm per person. If the
ventilation rate is increased to 20 cfmlperson, in accordance with
ASHRAE 62-89 with 100 sq ft per person, then the cooling load
will increase to about 1347 tons. If the chiller is converted to
HCFC use, its capacity may drop to 850 tons.
Problem Definition-The new requirements of revised ASHRAE
Standard 62-89, "Ventilation for Acceptable Indoor Air Quality,"
call for outside-air ventilation rates of 3-4 times the current
practice, thus increasing the latent load. Most variable air volume
(VAV) all-air systems do not meet the ASHRAE standard under
certain load conditions during much of the year (Meckler, 1993).
In addition, CFC refrigerant production will be banned by 2000,
and commonly used CFC refrigerants are expected to soar in
price. Chiller conversion to replace these refrigerants sooner will
become an important issue to building managers, but the switch
to non-CFC refrigerants may reduce the capacity of the chillers.
These issues (increased ventilation rates and CFC replacement)
must be addressed and the HVAC systems in many office
buildings will have to be retrofitted and new systems added. This
situation provides an opportunity for desiccants to precondition
the ventilation air, rather than dealing with the addition of a new
conventional system. In some areas of the country, this change
will actually save energy costs.
Retrofit Options-To meet the higher cooling load of 1347 tons,
Meckler (1993) studied two retrofit options. The first option was
to add another chiller with 498-ton capacity to handle the
increased ventilation rates and HCFC replacement. The second
retrofit option was to add a desiccant system to the existing
HCFC-converted 850-ton chiller to take care of the increased
ventilation rate (see Figure 8).
Temp %RH
Ambient
Temp %AH %Molsture
Exterior
mil NorthWing- DesiccantSystem
• SouthWing- CooVReheat System
Temp %AH %Molstufe
Dividing
Results-The cool/reheat equipped south-wing moisture problems
were improved by operating under humidistat control, but the odor
still existed and the rust on ceiling tile reappeared (Banks, 1992).
The north-wing condition showed much more improvement than
the south wing, having lower humidity and no recurrence of
musty odors after several weeks. Figure 6 compares moisture
level in cavities behind the walls of the south wing and the north
wing. In the north wing's first floor, the moisture in the
wallboard measured 13 on the Delmhorst reference scale
compared to 20 in the south wing-a trend which held throughout
the other floors. The average humidity level in the wall cavity
was 60% RH on the wing with the desiccant system, whereas the
wall cavities on the cool/reheat wing experienced average
humidity of 69% RH. According to microbiologists, significant
mold/mildew problems can occur when humidity levels exceed
65% RH. The first floor of the two wings is connected by a
restaurant and a lobby, and some of the moisture from the south
side may have entered the north side. On the desiccant side, the
humidity problem on the second and third floors disappeared after
a few months of testing, and the rust on the ceiling-tile grid was
also eliminated.
Another item examined was the amount of fungal samples
found in the two wings. The count of fungi in the desiccant wing
was about one-fourth of that in the cool/reheat wing-a very
encouraging result. According to a computer model based on the
Atwo-stage desiccant preconditioner systemwith an enthalpy
wheel (a total heat exchanger) and a desiccant wheel was
proposed. The enthalpy wheel preconditions the outside air before
it goes to the desiccant dehumidifier, removing some moisture and
4
Figure 7. Schematic of an Existing All-Air VAV System of
an Office Building in Houston, Texas (Meckler, 1993)
RELIEF
AlR
RELIEF AIR
ANDOUTDOOR
AIRBYPASS
I

NEWAIR FlOW
MEASURING
STATION(1YPlCAL)
RETURNFAN
EXISTING
COOLING
TOWER
EXISTINGVAV
BOX(TYPICAL)
dehumidification technology intended to improve
cost-effectiveness and performance.
For many years, the Gas Research Institute (GRI) has been
supporting the development of desiccant technology for
air-conditioning applications. The GRI program has already
produced the well-received product, SuperAire, for supermarkets .
In 1992-1993, the main thrust of the GRI program was to develop
lower-cost, higher-performance desiccant wheels, to develop
design and analysis tools, and to generate data and information.
GRI has focused on cost-effective niche-market initiatives such as
supermarkets, and recently, hotels and motels. Laroche Chemical
and Semco Manufacturing have been working with GRI to
develop dehumidifiers based on a new class of desiccant called
Type 1M. Laroche Chemical 's Type 1M wheel is very efficient
for moisture removal and regeneration at 350°-400°F and requires
a gas-fired system to provide the desired regeneration
temperatures. GRI has also been exploring residential applications
with Hermidifier Co., which has developed a water-heater-
powered desiccant dehumidifier. Munters DryCool and GRI have
been working to develop and test desiccant make-up air systems
for hotels and motels.
EXISTING VAV AIR-
HANDLING UNIT
(TYPICALOF 8) RETURN FAN
r
- -;:===:' I RELIEF AIR
.....,..;-
--
r-J'--r;..-........, OUTDOOR
AIR (0.' CFMI
SO. FT.)
EXIST ING VAV
BOX(TYPICAL)
EXISTING
COOLING
TOWER
sensible load to reduce the amount of regeneration energy needed;
regeneration of the enthalpy wheel was done by outside air. In
the desiccant portion, the air is dried deeply. The energy for
regeneration can be provided by an air-to-air heat exchanger,
waste heat from the system, .and natural gas. According to
Meckler (1993), the average annual thermal COP for this system
in Houston weather conditions was 2.19, ranging between 1.2 and
3.3. In this second option, the desiccant preconditioner removed
566 tons of cooling, with 781 tons handled by the HCFC-
converted chiller.
Energy Costs Savings-Retrofit 1 uses electricity and retrofit 2
uses both gas and electricity. The economics of retrofit 1 versus
retrofit 2 depend on location, so the local utility's rate structure
must be considered. In Houston, utility rates are about $.087/kWh
and $4.25/MBtu gas. In this particular example, Meckler (1993)
included the following energy costs:
TWO-STAGE DESICCANT PRECONDITIONER
Figure 8. Houston All-Air VAV System Retrofitted with a
Desiccant Preconditioning System (Meckler, 1993)
ICC Technologies, Inc., manufactures single factory-package
systems that provide desiccant dehumidification. Some of their
systems (e.g., the DESI/AIR models) that use evaporative coolers
provide cooling and have been installed in supermarkets and other
0 OUTDOOR

INDIRECT EVAPOR-
AllVE COOLER
RELIEF AIR ------------
OUTOOOR
AIR-TO-AIR
HANOLING UNIT
DESICCANT
AIR-TO-AIR HEAT DEHUMIDIFIER

EXHAUST . . DESICCANT
AIR NATURAL GAS REGENERATION
FURNACE
OUTDOOR ..
AIR
• U.S. PATENTNO. 4.723.417
AND PATENTS PENDING
For retrofit 2 (the gas-fired desiccant system plus the existing
chiller) the annual energy cost was $205,400.
For the existing system (which cannot meet the requirement
because it supplies only 0.1 cfm/sq-ft), the annual energy
cost was $196,400.
For retrofit 1 (all vapor-compression chilling), the annual
energy cost was $232,500.
RECENT DESICCANT DEHUMIDIFICATION
TECHNOLOGIES
Although desiccant dehumidification is cost-effective for
some niche-market application, the first-cost of desiccant systems
is still high for broad air-conditioning applications . In this
section, we will review recent developments in desiccant
In this Houston applicat ion, the desiccant option resulted in
a $27,100 annual saving in energy costs over vapor-compression
chilling.
5
retail stores. ICC will also be producing a smaller version, Desert
Cool, for small commercial and residential applications. ICC is
working with Engelhard Corporation to produce a dehumidifier
based on a family of desiccant materials called ETS, which is
suitable for low-temperature applications. One form of ETS
(Engelhard Titanium Silicate) desiccant could be regenerated at
less that 140°F, so waste heat from condensing units of electric
chillers could be used. Figure 9 shows ICC's DESIIAIRSystem
which has a desiccant wheel, heat-exchanger wheel, and
evaporative cooling pads, and can be used as a preconditioner for
ventilation air. One of these units will be installed in a lC.
Penney store in White Plains, New York, which currently has a
two-chiller HVAC system. The first chiller is usually sufficient
for meeting the sensible load, so the second chiller seldom is
required during the day. However, the store experiences a peak
cooling demand at 9:00 a.m. because of residual moisture from
overnight, prompting the second chiller to run with a high kW
demand. Instead of operating the second chiller, the addition of
the DESIIAIR System to the first chiller is expected to eliminate
the need for the other, and thus, will eliminate about 140 kW of
demand.
A number of other organizations are also working on
desiccant research and development:
Albers Air Conditioning Corporation is looking. at
liquid-desiccant air conditioners as a single-package system.
• An analytical comparison showed that the DEAC's
energy-efficiency-ratio values at low sensible-heat ratios are
higher than the values for alternative systems (Nimmo et al.,
1993).
• The University of Texas at Austin has been developing an
all-electric hybrid vapor-compression/desiccant air condi-
tioner.
• AIL Research, Inc., is working on falling-film desiccant
absorbers and advanced regenerators for next-generation
liquid desiccant air conditioners.
The Meckler Energy Group has been using the approach of
integrating desiccant systems with conventional HVAC
systems and cogeneration systems. Meckler has developed
an integrated desiccant cold-air distribution system which
allows for significant reductions in building's return
ductwork and in energy costs (Meckler, 1989). In another
study, Meckler has shown that desiccant-assisted ductless
split HVAC systems are viable alternatives for small office
buildings and could save energy costs (Meckler, 1994).
New Thermal Technology, Incorporated, with support from
the Florida Power Corporation, has been using desiccant
systems integrated with standard vapor-compression units for
restaurant application, taking heat for regeneration from
condenser coils and solar collectors. The goal of the system
is to reduce peak demand.
6
• The National Renewable Energy Laboratory (NREL), with
U.S. Department of Energy support, is examining low-
temperature desiccants for solar cooling applications;
however, the work can also be extended to electric
applications with waste heat-recovery. NREL and the
Meckler Energy Group, with funding from GRI, have studied
a liquid-desiccant-enhancedheat-pipe unit for preconditioning
ventilation air. Initial test results indicated that this approach
could result in a efficient preconditioner.
CONCLUDING REMARKS
Desiccant dehumidification is an established technology that
has been used successfully for many years in institutional and
industrial applications. Commercial applications are now gaining
acceptance. Desiccant systems have been applied successfully in
supermarkets and ice rinks. Hotels and motels, office buildings,
and restaurants provide the next opportunity.
Lowering the cost of desiccant dehumidification systems and
improving their performance will clearly provide more
opportunities for desiccant dehumidification technology.
Currently, a number of cost-effective applications in the market
will result in increased sales during the next several years; but as
in other technologies, further R&D and demonstration programs
will enhance broader applications of the technology. Low-
temperature desiccants can effectively use waste heat from electric
air conditioners and improve their efficiency and
effectiveness-an area that utilities and EPRI need to participate
for further development. Desiccant dehumidification systems as
add-on modules to electrical refrigeration systems could help
solve the challenges facing the HVAC industry in the 1990s:
increased ventilation rates, need for improved indoor air quality
and better humidity controls, phase-out of CFCs, national
standards requiring higher efficiency for cooling systems, and
desire for lowered peak electric demands. These factors, and the
ability for desiccant systems to solve specific problems, are
driving these desiccant technologies to the mainstream of the
air-conditioning market.
Disclaimer: The products, concepts, and organizations mentioned
in this paper are given as examples. The author does not endorse
any of them. There are a number of other products, concepts, and
organizations that could have been presented.
HEATING COIL: HOT WATER
ORSTEAM Heats air before air
enters building in winter.
NATURAL GAS BOILER OR
STEAM CONVERTER
BACKWARD CURVED AIR
FOIL FANS Maximize
efficiency. provide high static
pressure ability and low
operating sound levels.
MAKE-UP
OR
RECIRCULATED
AIR
HUMIDITY WHEEL
Desiccant-impregnated. il wrings
moisture from either make-up or re- . .
circulated air efficiently achieves
ideal relative humidity levels even in
humid climates. Dehumidification
rates of up 10 500 los.hr are easy
10 attain. permitt ing increased
venti lation air wilhout the burden of
higher energy costs.
Specs: Slow speed (10 RPH) Low
power (200 Watts)
THERMAL WHEEL does double duty.
1. Cooling the warm air leaving the desiccant wheel and
capturing 80% of the heat removed to preheat the regeneration
: air stream ... cuts gas boiler energy costs by up to 40%.
2. Utilizes "FREE COOLING" from either outdoor or wasted
bui lding exhaust air to cool the warm air before it enters the
structure. Displaces energy-consuming conventional air
conditioning equipment in summer and captures wasted heal
from building exhaust air system in winter .
Specs: Slow speed (10 RPM) Low Power (400 Watts)
REGENCOIL: HOT WATEROR
STEAM Reheats air to dissipate
. moisture from the desiccant
wheel to the atmosphere in
summer.
EVAPORATIVECOOLER
On hot days, it cools the
outdoor or building exhaust
air stream. In effect, it
provides a second stage of
cooling . taking advantage
of the much lower wet-bulb
air temperatures. Replaces
energy-consuming
conventional air
conditioning equipment.
Specs: Low power 1/ 15
H.P. pump)
OUTDOOR
OR
BUILDING
EXHAUST
AIR
Figure 9. ICC Technologies DESIIAIR System
7
REFERENCES
AGCC, March/April 1994, "Hot on Desiccants," Cool Times,
Vol. 5, No.2, pp. 18-20, American Gas Cooling Center,
Arlington, VA.
American Hotel and Motel Association, 1991, Survey of
Mold and Mildew in Hotels and Motels, New York, NY.
ASHRAE, 1992, Desiccant Cooling and Dehumidification,
Special Publication, American Society of Heating, Refrigerating,
and Air Conditioning Engineers, Atlanta, GA.
Banks, N.J., 1992, "Field Test os a Desiccant-Based HVAC
System for Hotels," ASHRAE Transactions, Vol. 98, Pt. 1, pp.
1303-1310.
EPRI, August 1992, Assessment of Gas and Electric Cooling
Equipment, EPRI TR-101142, Electric Power Research Institute,
Palo Alto, CA.
GRI, 1994, "SuperAire Systems Applications," PaceSetters,
3194 GND 10,000, Gas Research Institute, Chicago, IL.
GRI, December 1992, "Dehumidification-A Major
Opportunity for Natural Gas," GRI Technology Focus, Gas
Research Institute, Chicago, IL.
Harriman, L.G., III, 1990, The Dehumidification Handbook,
2nd Edition, Munters Cargocaire, Amesbury, MA.
Harriman, L.G., III, January 1994, "Field Experience with
Desiccant Systems," Engineered Systems, pp. 63-68.
ICC Technologies, Inc., DESI/AIR Product Literature,
Philadelphia, PA.
Meckler G., March 1993, "Integrated IAQ-CFC Retrofit
Saves Energy," Consulting-Specifying Engineer, pp. 42--48.
Meckler, M., 1994, "Comparing Conventional and Desiccant-
Assisted Ductless Split HVAC Systems for Offices in Several
U.S. Cities," ASME Solar Energy Conference Proceedings, San
Francisco, CA, March 27-30, 1994.
Meckler, M., May 1989, "Integrated Desiccant Cold Air
Distribution," Heating/Piping/Air Conditioning, pp. 67-127.
Munters Cargocaire, Dehumidifiers Product Literature,
Amesbury, MA.
Munters DryCool, The SuperAire System Product Literature,
Selma, TX.
Nimmo, B.G., R.K., Collier, and K. Rengarajan, 1993,
"DEAC: Desiccant Enhancement of Cooling-Based
Dehumidification," ASHRAE Transactions, Vol. 99, Pt. 1, pp.
842-848.
Pesaran, A.A., T,R. Penny, and A.W. Czanderna, October
1992, Desiccant Cooling: State-of-the-Art Assessment, NRELffP-
254-4147, National Renewable Energy Laboratory, Golden, CO.
8

Sponsor Documents

Or use your account on DocShare.tips

Hide

Forgot your password?

Or register your new account on DocShare.tips

Hide

Lost your password? Please enter your email address. You will receive a link to create a new password.

Back to log-in

Close