Note: Descriptions are shown in the official language in which they were submitted.
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TITLE
HUMIDITY CONTROL SYSTEM USING A DESICCANT DEVICE
[0001] This application Claims the benefit of U.S. Provisional Application No.
60/924,764 filed May 30, 2007.
Field of the Invention
[0002] The present invention relates to a humidity control system and in
particular to a humidity control unit which utilizes low grade waste heat to
aid in
regeneration of a desiccant device.
BACKGROUND OF THE INVENTION
[0003] Various systems have been proposed for providing air handling systems
which maintain humidity levels in indoor facilities in a comfortable range.
Certain of these systems have been particularly designed for use in ice arenas
in
which an ice surface is maintained at freezing temperatures or other
applications
such as cold storage facilities in which waste heat is available from a large
ice
plant. Such systems typically use a liquid refrigerant loop which is cooled by
a
primary refrigerant system of the direct vaporization type. Such systems are
shown for example in U.S. Patent No. 6,321,551 in which a dehumidifier unit
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connected to the ice rink coils is used to dry process air. Another such
system is
disclosed in U.S. Patent No. 6,935,131 which supplements the dehumidification
unit in the process air stream with a reheat coil coupled to a waste heat line
from
the compressor of the primary refrigeration unit. This reheat coil heats
regeneration air being supplied to the regeneration section of a desiccant
wheel to
increase the desiccant media's capacity to remove further moisture from the
process air stream. This reheat coil system is used with a dehumidification
coil in
the process air section of the dehumidification system which is connected to
the
liquid refrigeration system.
SUMMARY OF THE INVENTION
[0004] In accordance with an aspect of the present invention a reactivation
circuit is provided for preheating regeneration air supplied to a desiccant
unit of a
dehumidification system. The reactivation circuit consists of a reactivation
air
cooled condenser coil/dehumidifier coil connected to a direct vaporization
refrigeration circuit including a compressor and refrigerant heat exchanger
(using
water, brine, or other refrigerant) functioning as the evaporator for the
circuit.
This reactivation circuit functions as a water source heat pump to extract
heat
from the liquid refrigerant in a secondary refrigeration circuit that freezes
the ice
sheet. Low grade (low temperature 85-95 degrees F) heat is rejected from the
secondary refrigeration plant and extracted by the reactivation circuit to
generate
a higher grade heat (high temperature 115-130 degrees F) through the air
cooled
condenser coil to regenerate the desiccant material. The heated air drives
moisture from the desiccant and is discharged to the atmosphere.
[0005] In accordance with another aspect of the invention return air, or
return
air and fresh air, circulated to the interior space or enclosure containing
the ice
rink or the like is dehumidified in a continuous process by the desiccant
material.
Preferably the desiccant is a desiccant wheel which rotates through both the
supply process air stream and the reactivation air stream. A dehumidification
coil
is positioned in the reactivation air stream upstream of the regeneration
section of
the dehumidifier wheel and is connected to a direct vaporization refrigeration
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circuit having a series of compressors and then to a separate air cooled
condenser
coil. By this system, if the enclosure humidity level increases, and the
return air
and/or combination of return air and fresh air humidity is above a
predetermined
level, the second stage compressor will be energized to cool and dehumidify
the
air before it reaches the desiccant wheel. Third and fourth stage compressors
also
are successively energized if the humidity of the air entering the desiccant
continues to rise. When the return air humidity is returned to its controlled
set
point, the compressors stage off in the reverse order and the dehumidifier is
eventually de-energized.
[0006] In a more generalized embodiment of the invention the refrigeration
circuit which generates the heat for the condensing coil which heats the
desiccant
regeneration or reactivation air stream is coupled with any low grade liquid
heat
loop that is decoupled from atmospheric temperature. This means a system
which is not bound to atmospheric conditions and allows for control of
suitable
reactivation temperatures independent of ambient atmospheric temperatures.
Accordingly the water, glycol or brine loop need not be limited to the heat
rejected from secondary refrigerant loop such as the ice sheet cooling system
above, but will include known solar heat loops, cooling tower, ground water
loops, other heat of rejection cooling loops, or any loop that is designed to
be
maintained at a temperature between 45 F and 95 F year round. For example a
low grade solar heat loop using water heated by the sun at low temperatures
could be used.
[0007] The above and other objects, features and advantages of the present
invention will become apparent from the following detailed description of an
illustrative embodiment which is to be read in conjunction with the
accompanying drawings wherein:
DESCRIPTION OF THE DRAWINGS
[0008] Figure 1 is a schematic diagram of a dehumidifier system in accordance
with the present invention; and
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[0009] Figure 2 is a more detailed schematic view of one of the refrigeration
systems used in the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0010] As seen in Figure 1, the system 10 of the present invention includes a
refrigeration system 12 for freezing an ice sheet 141ocated within an enclosed
space or building (not shown). System 10 further includes a humidity control
unit 16 operable to control the humidity of a return air stream 18 coming from
the
enclosure and being returned thereto by the operation of a fan 20. If
required,
some proportion of fresh air can be introduced through a duct 22 in known
manner into the return air stream.
[0011] The refrigeration system 12 includes a liquid refrigerant secondary
refrigeration system 24 which includes a set of coils (not shown) located in
the
floor of the ice rink or ice plant 14 or the like and connected by supply and
return
lines 26, 28 and pump 29 to an evaporator 30.
[0012] Evaporator 30 forms a part of a primary refrigeration system 32 which
includes a condenser 34 and a compressor 36 connected by lines 38 to a coil
within the evaporator 30. The primary refrigeration system is a conventional
direct vaporization system which absorbs heat from the liquid refrigeration
system in the evaporator and discharges that heat in the condenser 34 to the
atmosphere. The primary refrigeration system 32 includes an additional heat
exchanger 40 connected by lines 42, 44 to the refrigerant line 38. This heat
exchanger functions as an evaporator for a third refrigeration system 50 which
is
also a direct vaporization refrigeration system. The system 50 includes a
compressor 521ocated in the housing 54 of the humidity control device 16. That
device includes a regeneration air duct 56 and process air duct 58 separated
from
each other by conventional walls and baffling.
[0013] Dehumidification system 16 also includes a desiccant wheel device 60 of
known construction rotatably mounted in the housing such that it is
regenerated
in the regeneration duct 56 and dehumidifies air in the process air duct 58.
The
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desiccant wheel is of known construction and rotatably mounted in any known
manner.
[0014] Regeneration air is drawn into the regeneration duct 56 from the
atmosphere through an opening 62 in the housing 54 by a fan 64 which
discharges the regeneration air, after it passes through the desiccant wheel,
to the
atmosphere.
[0015] The refrigeration system 50 includes a condenser coi166 mounted
upstream of the desiccant wheel in the regeneration conduit 56. The coil is
connected by refrigerant lines 68 to the compressor 52 which is in turn
connected
by lines 70 to the heat exchanger 40.
[0016] When it is necessary to dehumidify return air and/or return and fresh
air
being supplied to the interior of the enclosure, the compressor 52 is operated
and
supplies cooled refrigerant from the condenser to the heat exchanger 40. The
temperature of the coolant in line 70 is raised in the heat exchanger 40 (by
the
coolant in lines 38 flowing from the line 42 through heat exchanger 40 to line
44)
and returned to the compressor 52 where the refrigerant is compressed, heated
and supplied to the condenser coi166. In the condenser coil the refrigerant is
cooled by the supply air entering the duct 62 and transfers heat to the
regeneration air which then enters the regeneration portion of the rotating
desiccant whee160 before being charged to the atmosphere. As a result, some of
the low grade heat (from the liquid in loop 24, 28 at between 45 F and 95 F)
rejected from the ice refrigeration plant or the like is extracted by this
heat pump
arrangement to generate a higher grade heat (e.g., liquid in line 68 at 105 F
to
135 F) through the air cooled condenser coil to regenerate the desiccant
wheel.
This heated air drives the moisture from the desiccant and regenerates it. It
also
contributes to cooling of the refrigerant in system 32.
[0017] The above dehumidification process is continuous as the desiccant wheel
rotates through the supply and reactivation air streams. However, if the rink
humidity level rises above a predetermined point, requiring additional
dehumidification, the humidity control device 16 is arranged to provide
additional dehumidification, before the return air and/or fresh air/return air
pass
through the desiccant wheel. As seen most clearly in Figure 2, to accomplish
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this, the dehumidifier includes an additional refrigeration circuit 80
connected to
multiple compressors 82, 83 and 84 which are connected by lines 86 to a
dehumidification coil 88 and to an air cooled condenser coil 90 mounted at one
end of the housing 54. Thus, when additional dehumidification is required,
beyond what the desiccant wheel can provide by itself, the compressor 82 is
operated to supply compressed refrigerant to the dehumidification coil which
removes moisture from the air before it enters the desiccant wheel device. At
the
same time it cools the air before it reaches the desiccant wheel. The heat
absorbed from the air in the dehumidification coil by the refrigerant is
discharged
to the atmosphere in the condensation coi190 which is cooled by the fans 92,
and
returned to the compressor 82. If still further dehumidification is required,
the
second and third stage compressors 83 and 84 can be energized.
[0018] As seen more clearly in Figure 2, the refrigeration circuit 80 is
actually
three independent refrigeration circuits which use different sections of the
coils
88, 90 in their individual refrigeration circuits. Thus compressor 82 is
connected
by lines 82' to coil sections 88' and 90'; compressor 83 is connected by lines
83'
to coil sections 88" and 90" and compressor 84 is connected by lines 84' to
coil
sections 88"' 90"'. Each circuit is separately energized as required. and By
cooling and dehumidifying the return air before it enters the desiccant wheel
in
this way the capacity of the desiccant wheel to remove further moisture from
the
process air stream in increased and the return air is reheated by the wheel to
the
desired process return temperature.
[0019] If desired or necessary some or all of the process air can be made to
bypass the desiccant wheel using appropriate duct work 100 as is known in the
art. Also, appropriate temperature and humidity sensors and related controls
are
provided to selectively activate the various compressors as would occur to
those
skilled in the art.
[0020] Accordingly, the system provides sufficient capacity to handle varying
conditions and variable amounts of make up air without modifying the basic
refrigeration systems 12 or 32.
[0021] Although illustrative embodiments of the present invention have been
described herein in detail in connection with the accompanying drawings, it is
to
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be understood that the invention is not limited to those precise embodiments
but
that various changes and modifications may be effected therein by those
skilled
in the art without departing from the scope or spirit of this invention.
