U.S. patent application number 12/371135 was filed with the patent office on 2009-08-20 for frosting dehumidifier with enhanced defrost.
This patent application is currently assigned to Applied Comfort Products Inc.. Invention is credited to Michael N. Brown.
Application Number | 20090205354 12/371135 |
Document ID | / |
Family ID | 40953835 |
Filed Date | 2009-08-20 |
United States Patent
Application |
20090205354 |
Kind Code |
A1 |
Brown; Michael N. |
August 20, 2009 |
FROSTING DEHUMIDIFIER WITH ENHANCED DEFROST
Abstract
A dehumidifier apparatus comprises a housing having an air inlet
for receiving incoming air, an air outlet spaced therefrom for
allowing the air to exit from the housing, the housing being
configured to provide an interior air passageway connecting the air
inlet to the air outlet; an air mover mounted within the air
passageway for moving the air through the air passageway from the
air inlet to the air outlet; a compressor mounted in the housing
for compressing a refrigerant; an evaporator located within the air
passageway for evaporating the refrigerant during a dehumidifying
cycle, and thereby cooling air flowing through the evaporator and
causing water in the air to condense on a surface of the
evaporator; a condenser for condensing the refrigerant during the
dehumidifier cycle, the condenser being located in the air
passageway downstream of the evaporator in series with the
evaporator; refrigerant flow lines configured to allow for a flow
of the refrigerant between the compressor, the condenser, and the
evaporator; and a defrosting cycle system for performing a
defrosting cycle during a frosting condition of the evaporator,
wherein during the defrosting cycle the flow of the refrigerant is
reversed, causing the evaporator to condense the refrigerant and
the condenser to evaporate the refrigerant. The compressor and the
air mover are configured to run continuously during the
dehumidifying cycle and the defrosting cycle.
Inventors: |
Brown; Michael N.;
(Waterloo, CA) |
Correspondence
Address: |
BERESKIN AND PARR LLP/S.E.N.C.R.L., s.r.l.
40 KING STREET WEST, BOX 401
TORONTO
ON
M5H 3Y2
CA
|
Assignee: |
Applied Comfort Products
Inc.
Cambridge
CA
|
Family ID: |
40953835 |
Appl. No.: |
12/371135 |
Filed: |
February 13, 2009 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
61030049 |
Feb 20, 2008 |
|
|
|
Current U.S.
Class: |
62/324.5 ;
62/426; 62/498 |
Current CPC
Class: |
F25B 47/025 20130101;
F24F 2003/1446 20130101; F24F 3/153 20130101; F24F 3/1405
20130101 |
Class at
Publication: |
62/324.5 ;
62/498; 62/426 |
International
Class: |
F25B 13/00 20060101
F25B013/00; F25B 1/00 20060101 F25B001/00; F25D 17/06 20060101
F25D017/06 |
Claims
1. A dehumidifier apparatus, comprising: a) a housing having an air
inlet for receiving incoming air, an air outlet spaced therefrom
for allowing the air to exit from the housing, the housing being
configured to provide an interior air passageway connecting the air
inlet to the air outlet; b) an air mover mounted within the air
passageway for moving the air through the air passageway from the
air inlet to the air outlet; c) a compressor mounted in the housing
for compressing a refrigerant, d) an evaporator located within the
air passageway for evaporating the refrigerant during a
dehumidifying cycle, and thereby cooling air flowing through the
evaporator and causing water in the air to condense on a surface of
the evaporator; e) a condenser for condensing the refrigerant
during the dehumidifying cycle, the condenser being located in the
air passageway downstream of the evaporator in series with the
evaporator; f) refrigerant flow lines configured to allow for a
flow of the refrigerant between the compressor, the condenser, and
the evaporator; and g) a defrosting cycle system for performing a
defrosting cycle during a frosting condition of the evaporator,
wherein during the defrosting cycle the flow of the refrigerant is
reversed, causing the evaporator to condense the refrigerant and
the condenser to evaporate the refrigerant; and h) wherein the
compressor and the air mover are configured to run continuously
during the dehumidifying cycle and the defrosting cycle.
2. The dehumidifier apparatus defined in claim 1, wherein the
defrosting cycle system comprises: a) a reversing valve located in
the refrigerant lines for reversing the flow of the refrigerant
during the defrosting cycle, thereby causing the At 53.degree. F.,
51% RH: Defrost time was 2 minutes out of every 30 minutes normal
run time, for a total cycle time of 32 minutes. Defrost time was
6.7% of run time. Water removal was 28% of its standard rating. It
can be seen from the above test results that a dehumidifier made in
accordance with the subject invention has both a lower defrost time
and a higher water removal rate than both of the prior art
dehumidifiers having conventional defrost systems. While the above
description includes a number of exemplary embodiments, it should
be apparent to one skilled in the art that various modifications
can be made to the embodiments disclosed herein, without departing
from the present invention, the scope of which is defined in the
claims. evaporator to condense the refrigerant and the condenser to
evaporate the refrigerant; b) a detector for directly or indirectly
detecting the presence of frost on the evaporator; and c) a
controller electrically coupled to the detector and the reversing
valve for operating the reversing valve so as to reverse the flow
of refrigerant when the temperature reaches pre-determined
values.
3. The dehumidifier apparatus defined in claim 2, wherein the
detector comprises a sensor for directly or indirectly sensing the
temperature of the refrigerant in the evaporator.
4. The dehumidifier apparatus defined in claim 1, wherein the air
inlet has bypass holes configured to allow a pre-selected portion
of the incoming air to enter a bypass passageway that bypasses the
evaporator and joins the air passageway upstream of the
condenser.
5. The dehumidifier apparatus defined in claim 4, wherein the
pre-selected portion of the incoming air falls in a range of about
5-25% of the incoming air.
6. The dehumidifier apparatus defined in claim 1, wherein the
refrigerant flow lines comprise a discharge line allowing
refrigerant to flow between the compressor and the reversing valve,
a condenser line allowing the refrigerant to flow between the
reversing valve and the condenser, a refrigerant metering device
allowing the refrigerant to flow between the condenser and the
evaporator, an evaporator line allowing the refrigerant to flow
between the evaporator and the reversing valve, and a suction line
allowing the refrigerant to flow between the reversing valve and
the compressor.
7. The dehumidifier apparatus of claim 1, wherein the compressor is
located in the air passageway downstream of the condenser.
8. The dehumidifier apparatus defined in claim 1, comprising a
drain pan located under the evaporator for collecting the water
that has condensed on the surface of the evaporator.
9. The dehumidifier apparatus defined in claim 1, comprising a
passive air pre-cooler for cooling the incoming air before the air
passes through the evaporator.
10. The dehumidifier apparatus defined in claim 9, wherein the
passive air cooler comprises an air-to-air heat exchanger located
within the air passageway, the air-to-air heat exchanger having a
first pre-cooling air pass upstream of the evaporator and a second
pre-heating air pass downstream of the evaporator.
11. The dehumidifier apparatus defined in claim 10, wherein the
housing is an upright enclosure having a top end and a bottom end,
the air inlet being positioned near the top end of the enclosure
and the air outlet being positioned near the bottom end of the
enclosure, and wherein the passive air cooler is located directly
below the air inlet, the evaporator is located horizontally
adjacent to the passive air cooler, and the air passageway is
configured to redirect the air exiting the first air pass of the
air pre-cooler by about 270 degrees into the evaporator.
12. The dehumidifier apparatus defined in claim 11, wherein the
condenser is located below the evaporator, and the air passageway
is configured to redirect the air exiting the second pass of the
air pre-cooler by about 90 degrees downwardly towards the
condenser.
13. The dehumidifier apparatus defined in claim 12, wherein the air
mover comprises a blower located below the condenser, the blower
being configured to direct the air towards the air outlet.
14. The dehumidifier apparatus defined in claim 10, comprising a
drain pan located under the evaporator and the air pre-cooler for
collecting the water that has condensed on the evaporator and the
air pre-cooler.
15. The dehumidifier apparatus of claim 1, comprising a handle
extending backwardly from a back side of the top end of the
housing, and a pair of spaced wheels mounted on an axle extending
from the back side of the bottom end of the housing, and wherein
the evaporator and the condenser are configured within the housing
so that the housing may be transported by holding the handle and
pivoting the housing backwardly on the wheels without causing
gravity drainage of refrigerant from the evaporator to the
condenser.
16. The dehumidifier apparatus of claim 15, wherein the evaporator
is mounted above the condenser, and the refrigerant lines include a
capillary tube having a portion that extends above the top of the
evaporator, and wherein the condenser is mounted below the
evaporator, with a tilt upward from front to back to prevent
drainage of the refrigerant from the condenser to the compressor
when the housing is pivoted backwardly on the wheels.
17. A dehumidifier apparatus, comprising: a) a housing having an
air inlet for receiving incoming air, an air outlet spaced
therefrom for allowing the air to exit from the housing, the
housing being configured to provide an interior air passageway
connecting the air inlet to the air outlet; b) a blower mounted
within the air passageway for moving the air through the air
passageway from the air inlet to the air outlet; c) a compressor
mounted in the housing for compressing a refrigerant, d) an
evaporator located within the air passageway for evaporating the
refrigerant during a dehumidifying cycle, and thereby cooling air
flowing through the evaporator and causing water in the air to
condense on a surface of the evaporator; e) a condenser for
condensing the refrigerant during the dehumidifier cycle, the
condenser being located in the air passageway downstream of the
evaporator in series with the evaporator; f) refrigerant flow lines
configured to allow for a flow of the refrigerant between the
compressor, the condenser, and the evaporator; g) a reversing valve
located in the refrigerant lines for reversing the flow of the
refrigerant during a defrosting cycle, thereby causing the
evaporator to condense the refrigerant and the condenser to
evaporate the refrigerant; h) a temperature sensor for sensing the
temperature of the refrigerant in the evaporator; and i) a
controller operatively coupled to the temperature sensor and the
reversing valve for operating the reversing valve so as to reverse
the flow of refrigerant when the temperature reaches pre-determined
values.
18. The dehumidifier apparatus defined in claim 17, wherein the
controller is operatively coupled to the blower and the compressor
and is configured to enable the compressor and the blower to run
continuously during both the dehumidifying cycle and the defrosting
cycle.
19. The dehumidifier apparatus defined in claim 17, wherein the air
inlet has bypass holes configured to allow a pre-selected portion
of the incoming air to enter a bypass passageway that bypasses the
evaporator and joins the air passageway upstream of the
condenser.
20. The dehumidifier apparatus defined in claim 17, comprising a
passive air pre-cooler for cooling the incoming air before the air
passes through the evaporator, wherein the passive air cooler
comprises an air-to-air heat exchanger located within the air
passageway, the air-to-air heat exchanger having a first
pre-cooling air pass upstream of the evaporator and a second
pre-heating air pass downstream of the evaporator.
Description
RELATED APPLICATION
[0001] This application claims the benefit of U.S. provisional
application Ser. No. 61/030,049, entitled "Frosting Dehumidifier
with Enhanced Defrost", filed on Feb. 20, 2008.
FIELD
[0002] The present invention relates to dehumidifier apparatus, and
in particular, to refrigerant-based vapor compression dehumidifiers
for removing moisture from air.
BACKGROUND
[0003] Any refrigerant-based vapor compression dehumidifier
applications that require drying air at low refrigerant
temperatures, where the evaporator surface temperatures operate
below the freezing point of water, and the dew point temperature of
the air is above the evaporator surface temperature, will cause
frost to build up on the evaporator surface. Frost build-up on the
evaporator surface will cause reduced evaporator capacity due to
the frost creating a physical restriction to air flow and/or the
frost reducing heat transfer ability due to the insulating effect.
Hence the evaporator must be periodically defrosted. Frosting
evaporator applications include those where the evaporator load is
low, due to a lack of availability of heat in the air, such as when
dehumidifying cool damp air, or cool dry air. Low refrigerant
temperatures are also required to dehumidify warm dry air, where
the air dew point is very low. Such applications require the
evaporator surface temperature to operate below the dew point of
the dry air, in order to extract any moisture, which can end up
being below the freezing point of water. For example, commercial
Low Grain Refrigerant (LGR) dehumidifiers serve the function of
drying air that is already very dry. "Low Grain" refers to the
unit's ability to remove moisture from air that is already very
dry. "Refrigerant" refers to the principle of dehumidification,
being based on the vapor compression principle using a refrigerant,
as opposed other approaches to dehumidification such as desiccant
drying.
[0004] Effective and efficient defrosting is essential to good
dehumidifier performance. This is not an easy characteristic to
rationalize, as there are usually trade-offs with all the
established approaches. Various methods and variations of defrost
approaches exist that use the heat contained in compressed
refrigerant vapor to defrost the evaporator. Fundamentally, the
energy-efficient methods for defrosting evaporators, where the air
temperature is above the freezing point of water can be categorized
as follows: Air Defrost, Conventional Hot Gas Bypass Defrost, and
Reverse Cycle Defrost. Each of these methods can be further
differentiated by the type of control means, and air flow
configuration.
[0005] The Air Defrost method involves shutting down the compressor
and leaving the air moving device operating. Air flows continuously
through the evaporator and melts the frost. Since the air
temperature is above freezing, some temperature differential
between the air and frost always exists to some degree. However,
the effectiveness of Air Defrost declines with reduced incoming air
temperatures. The advantage to this system is low cost. The
disadvantages are severely elongated defrost times, particularly as
air temperature drops, and long recovery times after the unit
terminates the defrost cycle. During defrost, the component and
refrigerant temperatures within the unit soak out to that of the
surrounding air temperature and when the compressor starts up, it
takes a long time for the refrigeration system to stabilize and
begin to remove water again. Another disadvantage is that residual
water in the coil fins is re-evaporated into the air stream due to
the long defrost time and thus partially re-humidifies the
conditioned space. The only heat available for defrost is the heat
contained in the surrounding air.
[0006] The Conventional Hot Gas Bypass Defrost method is very
common. When defrosting is necessary, a valve in the discharge line
opens and diverts hot refrigerant gas into the evaporator coil,
which is already very full of liquid refrigerant. The blower is
shut down during defrost so there is no airflow over the condenser
or evaporator. Once the defrost cycle has initiated, the only
continual source of heat available to heat the gas is the
electrical/mechanical energy input to the compressor, which is
quite small relative to the amount of heat required to defrost the
evaporator. The compressor does not draw much power because the
compression ratio is low during defrost. The advantage to this
defrost method is that it is relatively inexpensive and simple. The
disadvantages are long defrost times, and long recovery times after
termination of the defrost cycle, before steady state effective
dehumidification resumes. Another disadvantage is that excessive
amounts of liquid refrigerant accumulate in the evaporator which
can potentially flood back to the compressor and cause mechanical
damage. To protect against refrigerant floodback to the compressor,
some refrigerant control means, such as a large refrigerant
accumulator, must be used, at increased cost. Defrosting
performance deteriorates with decreasing ambient temperature.
[0007] The Reverse Cycle Defrost also uses the heat contained in
the refrigerant gas to melt frost. When defrosting is necessary, a
reversing valve shifts and re-distributes the refrigerant flow so
that the cold evaporator becomes the condenser, and the hot
condenser becomes the cold evaporator. The air flow over the
evaporator (now condenser) is stopped, either by shutting down a
fan, or closing a damper, in order to prevent water re-evaporating
into the air steam and re-humidifying the conditioned space. The
air over the condenser (now cold evaporator) continues to flow,
thereby adding more heat to the refrigerant. The heat picked up is
finally rejected in the evaporator (now condenser) in order to melt
the frost. Once the frost has melted, some control means is used to
terminate the defrost and restores the reversing valve to its
original state. The normal refrigeration cycle then resumes with
the evaporator acting as an evaporator, once again. The advantage
to this defrost method is that Reverse Cycle Defrost uses heat from
two sources to accomplish the melting of frost. Heat is extracted
from the surrounding air using the wide temperature difference
available using the active refrigeration cycle.
Electrical/mechanical input is also added to the compressor; both
these energies are imparted to the refrigerant gas, and is used to
defrost the evaporator. The reversed refrigeration cycle during
defrost also helps to add load to the compressor, which causes the
electrical/mechanical input to increase, relative to that
experienced with Conventional Hot Gas Bypass Defrost. Refrigerant
floodback to the compressor is still a concern after valve
reversal, but it is not as much of a problem as with Conventional
Hot Gas Bypass Defrosting, where significantly larger accumulator
volumes are typically necessary to control refrigerant, for a given
size of system. Defrosting performance deteriorates with decreasing
ambient temperature, but not to the same degree as seen in
Conventional Hot Gas Bypass Defrost systems.
[0008] A dehumidifier's effectiveness and efficiency depends on
many things. When no frost develops, a dehumidifier can run
steady-state at peak efficiency and output for a given condition.
When frosting occurs, operating too long with a frosted evaporator
impacts water removal capacity and efficiency. Conversely, running
short dehumidification cycles and frequent defrosts means there is
little time spent actively dehumidifying the space, which also
impacts efficiency and capacity. Defrosting also upsets the
refrigeration system balance, and there is always some measurable
recovery time required until the system can resume dehumidifying at
full capacity and efficiency after defrost termination. One can
see, control of defrosts is very important, as short or unnecessary
defrost cycles, coupled with long recovery times, can severely
limit the time the equipment is actually dehumidifying.
[0009] There is accordingly a need for a dehumidifier apparatus,
having an improved defrost system, which overcomes at least some of
the disadvantages associated with the prior art dehumifiers.
SUMMARY
[0010] According to one aspect of the invention, there is provided
a dehumidifier apparatus comprising a housing having an air inlet
for receiving incoming air, an air outlet spaced therefrom for
allowing the air to exit from the housing, the housing being
configured to provide an interior air passageway connecting the air
inlet to the air outlet; an air mover mounted within the air
passageway for moving the air through the air passageway from the
air inlet to the air outlet; a compressor mounted in the housing
for compressing a refrigerant; an evaporator located within the air
passageway for evaporating the refrigerant during a dehumidifying
cycle, and thereby cooling air flowing through the evaporator and
causing water in the air to condense on a surface of the
evaporator; a condenser for condensing the refrigerant during the
dehumidifier cycle, the condenser being located in the air
passageway downstream of the evaporator in series with the
evaporator; refrigerant flow lines configured to allow for a flow
of the refrigerant between the compressor, the condenser, and the
evaporator; and a defrosting cycle system for performing a
defrosting cycle during a frosting condition of the evaporator,
wherein during the defrosting cycle the flow of the refrigerant is
reversed, causing the evaporator to condense the refrigerant and
the condenser to evaporate the refrigerant. The compressor and the
air mover are configured to run continuously during the
dehumidifying cycle and the defrosting cycle.
[0011] The defrosting cycle system may comprise a reversing valve
located in the refrigerant lines for reversing the flow of the
refrigerant during the defrosting cycle, thereby causing the
evaporator to condense the refrigerant and the condenser to
evaporate the refrigerant, a detector for directly or indirectly
detecting the presence of frost on the evaporator, and a controller
operatively coupled to the detector and the reversing valve for
operating the reversing valve so as to reverse the flow of
refrigerant when the temperature reaches pre-determined values. The
detector may comprise a sensor for directly or indirectly sensing
the temperature of the refrigerant in the evaporator.
[0012] In some embodiments, the housing has a bypass passageway
that bypasses the evaporator and joins the air passageway upstream
of the condenser, and the air inlet has bypass holes configured to
allow a pre-selected portion of the incoming air to enter the
bypass passageway.
[0013] In some embodiments, the dehumidifier apparatus includes a
passive air pre-cooler for cooling the incoming air before the air
passes through the evaporator, the passive air cooler comprising an
air-to-air heat exchanger located within the air passageway, the
air-to-air heat exchanger having a first pre-cooling air pass
upstream of the evaporator and a second pre-heating air pass
downstream of the evaporator.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] Examples will now be disclosed in particular reference to
the following drawings, in which:
[0015] FIG. 1 is a schematic diagram of the air handling section of
a prior art parallel flow dehumidifier;
[0016] FIG. 2 is a schematic diagram of the air handling section of
a series flow dehumidifier made in accordance with the subject
invention;
[0017] FIG. 3 is a schematic diagram of the air handling section of
a modified series flow dehumidifier made in accordance with the
subject invention;
[0018] FIG. 4 is a schematic diagram of a dehumidifier apparatus
made in accordance with an embodiment of the subject invention,
operating in dehumidifying mode;
[0019] FIG. 5 is a schematic diagram of the subject dehumidifier
apparatus, after a period of time in operation, where the
evaporator is frosted;
[0020] FIG. 6 is a schematic diagram of the subject dehumidifier
apparatus, operating in defrosting mode;
[0021] FIG. 7 is a schematic diagram of the subject dehumidifier
apparatus, shown as it first resumes normal humidifier
operation;
[0022] FIG. 8 is a right side cut-away elevational view of a
dehumidifier apparatus made in accordance with an embodiment of the
subject invention;
[0023] FIG. 9 is a front cut-away elevational view of the
dehumidifier apparatus shown in FIG. 8; and
[0024] FIG. 10 is a perspective view of a dehumidifier apparatus
shown FIG. 8, with the top cover open and the air filter
removed.
DETAILED DESCRIPTION
[0025] Dehumidifiers using the vapor compression refrigeration
principle aspirate air from the conditioned space, remove some
water from that air, and then discharge it back into the
conditioned space, with the discharged air being warmer and dryer
than the incoming air. The air is warmer because some energy is
required to be inputted to drive the compressor and the air
mover.
[0026] As noted above, the concepts of Air Defrost, Hot Gas Bypass
Defrost, and Reverse Cycle Defrost, are known in the art. One known
application of Reverse Cycle Defrost in frosting dehumidifiers
involves the use of a parallel airflow dehumidifier. FIG. 1 refers
to the air handling section of a prior art parallel flow
dehumidifier 30, omitting the compressor and refrigeration circuits
for simplicity. Air from the conditioned space enters the
evaporator 12 where it loses heat to the refrigerant, is
subsequently cooled, and the condensed water flows into the drain.
Simultaneously, air directly aspirated from the conditioned space
enters the condenser 13 where it picks up heat from the
refrigerant, and is subsequently heated. The cold air coming off
the evaporator 12 combines with the warm air coming of the
condenser 13 to blend into a warm mixture that is discharged
through the action of fan 16. In the latest art, as the evaporator
frosts to a certain degree, a defrost cycle is initiated where the
evaporator 12 and condenser 13 reverse roles by action of a
refrigerant reversing valve. Air ceases to flow over evaporator 12
either by activation of dampers 31, or by shutting down one fan in
a dual fan system. The rationale for doing so is to not allow air
to re-evaporate water droplets on the evaporator surface 2 into the
air stream and subsequently into the conditioned space that is
supposed to be reducing its water content. However, if the defrost
cycle can be made to be quick, there is minimal re-evaporation. The
evaporator 12 then becomes the condenser and rejects heat from the
refrigerant to melt the frost. The condenser 13 becomes the
evaporator and removes heat from the entering air and directs it to
the defrosting coil via the refrigeration circuit. Once defrosting
is complete, air flow resumes over the condenser 13 and the system
either reverts back to its original state, or continues to operate
until the condenser 13, acting as evaporator, frosts to the point
of requiring defrosting. In any case, the reversing valve then acts
to resume operation in the original state, and the cycle continues
until defrosting is once again required. If in the previous cycle
the condenser was allowed to frost, then air flow through the
condenser 13 would be suspended to prevent re-evaporation to the
air stream during defrosting as in the previous case. The total
required air flow is the sum of the individual air flows required
by the each of the condenser and evaporator. Control of the
stopping and starting of air flow must be accomplished at increased
complexity and cost, either by using two fans, each in separate
parallel air channels, or by using close-off dampers with one
common fan in a combined air channel, as is depicted in FIG. 1.
[0027] One of the disadvantages with these prior art parallel
systems is that in an effort to reduce re-evaporation of water into
the conditioned space, the energy efficiency is compromised during
the active dehumidification cycle. The air entering the condenser
13 is at the conditioned space temperature. The temperature
difference between the condensing refrigerant and the air
temperature is narrower than need be. This leads to higher
refrigerant condensing temperatures, resulting in the compressor
operating at higher compression ratios, hence consuming more power.
There is cold air leaving the evaporator 12 that could be put to
use to lower the condensing temperature difference, but the
potentially high temperature difference inherent in the cold air is
squandered as it blends with the hot air coming off the condenser;
the combined streams are just directly discharged out of the
dehumidifier. This is a major drawback of operating a parallel flow
dehumidifier. Another drawback to parallel flow, where the air flow
through the defrosting coil ceases, is that in applications where
the air temperature is above the freezing point of water, the air
itself can be used as a defrosting medium to defrost the evaporator
12 from its outer surfaces inward, as is the case with Conventional
Air Defrost systems. Parallel flow is typically used for heat pump
systems where the evaporator and condenser air flow paths are
already separated from each other, because the evaporator is
located indoors and the condenser is located outdoors, with each
component handling air at different temperatures, humidity and air
volumes, by design.
[0028] For dehumidifiers, series air flow offers the advantages of
energy efficiency, simplicity, low cost and compactness. FIG. 2
refers to the air handling section of a series flow dehumidifier 32
made in accordance with the present invention, omitting the
compressor and refrigeration circuits for simplicity. Air from the
conditioned space enters the evaporator 12 where it loses heat to
the refrigerant and is subsequently cooled and the condensed water
flows into the drain. The cold wet air leaving the evaporator 12
enters the condenser 13, where it picks up heat from the
refrigerant, is subsequently heated, and is discharged through the
action of fan 16. In this case, the air entering the condenser 13
is well below the conditioned space temperature. The temperature
difference between the condensing refrigerant and the air entering
the condenser is very wide leading to lower refrigerant condensing
temperatures. This results in the compressor operating at lower
compression ratios, hence consuming much less power. To apply
reverse cycle defrost to a series air flow system, one must keep
the fan 16 operating continuously during defrost, in order to
provide a continuous supply of heat to condenser 13, as it
temporarily acts as the evaporator during defrosting.
[0029] The reverse cycle defrost has not to the inventor's
knowledge been applied to a series air flow dehumidifier. Reverse
cycle defrost is very fast, and hence minimizes any re-evaporation
time as a result of leaving the fan operating during defrost. As
the evaporator 12 frosts to a certain degree, a defrost cycle is
again initiated where the evaporator and condenser reverse roles by
action of a refrigerant reversing valve. Air continues to flow over
evaporator 12. The evaporator 12 then becomes the condenser and
rejects heat from the refrigerant to melt the frost. The condenser
13 becomes the evaporator and removes heat from the cold wet
entering air, and ultimately directs this heat to the defrosting
coil using the refrigeration cycle. Cold wet air still contains
much heat, which can be extracted using the refrigeration effect of
the system to create a wide temperature difference between the
refrigerant and the air. Once defrosting is complete, the reversing
valve acts to restore the system to its original state and the
evaporator 12 resumes removing water from the air again. The
refrigerant is evenly distributed through the system, and the
compressor is not stopped, so there is quick recovery to normal
operation and hence optimal water removal. Energy efficiency is
increased through lower compressor power consumption resulting from
the significantly lower condensing temperature by using the chilled
evaporator air to enhance refrigerant condensing effect. The
required air flow over each of the evaporator 12 and condenser 13
is not additive, requiring the fan to handle less total air flow,
albeit at a higher fan pressure. The need for a second fan or
dampers is not required as the air flow is constant during the
entire operation.
[0030] A perceived potential drawback to series air flow is that as
the evaporator 12 frosts, the physical restriction of the frost may
cause the total air flow to drop, depending on the design of the
evaporator. Hence, as the air flow through the evaporator reduces,
so will the air flow through the condenser 13 reduce as well.
Condenser capacity is partly dependent upon air flow, so at first
glance it appears as though condenser capacity may drop. However,
due to the series flow configuration, as the air flow is reduced,
the evaporator 12 refrigerant temperature will drop because of the
lower load. This coupled with less air moving through the
evaporator, will cause the evaporator air exit temperature to drop.
This colder air will flow over the condenser at a reduced rate,
substantially offsetting any impact on net condenser capacity due
to reduced air flow. This will hold true for moderate reductions in
air flow and moderate frosting. Total air flow reduction can be
minimized due to frosting by careful design, such as using
increased evaporator fin spacing, and not allowing the evaporator
to become heavily frosted before initiating a defrost, which should
be done anyway in order to preserve evaporator capacity.
[0031] Another drawback to series air flow is that one cannot
control the amount of air flowing through the evaporator 12,
separate from the condenser 13, as can be done with a parallel
system because series air flow passes the same air first through
the evaporator 12, and then through the condenser 13. To obtain the
benefit of using cold evaporator discharge air to feed the
condenser and obtain greater energy efficiency, some embodiments of
the invention, such as dehumidifier 34 shown in FIG. 3, utilize a
Modified Series Air Flow. By using bypass holes 29 and introducing
some conditioned space air downstream of the evaporator 12, the
blended air temperature entering the condenser 13 is still well
below the conditioned space air temperature. This is beneficial
when one wants to fine tune the amount of air aspirated by the
evaporator 12 to achieve an optimum design evaporator performance
at a specific set of conditions. Increasing the bypass openings 29
will reduce the amount of air flowing through the evaporator 12,
and cause a small net increase in total blended air flowing through
the condenser 13, because the total system pressure that fan 16
must work against will be reduced. The additional air over the
condenser 13 does not tend to increase condenser capacity much
because the blended air temperature of the bypass air and the
evaporator leaving air, as it enters the condenser 13, is higher
than if the bypass openings 29 were closed. This approach allows
some degree of control to set the evaporator air volume, and to
tweak a bit more condenser capacity, by taking advantage of the fan
16 being able to operate against a lower overall system resistance.
Opening up the bypass holes 29 too much causes other problems, such
as a quickly deteriorating airflow as the evaporator frosts, due to
the air taking the path of least resistance, preferring to enter
the bypass openings 29, instead of through the fouling evaporator
12.
[0032] To summarize, the benefits of the Series or Modified Series
Air Flow Reverse Cycle dehumidifier are as follows: compactness,
which is especially important for portability, simplicity in
control and component complexity, fast defrosting, energy
efficiency, low cost, and reliability/minimal number of parts to
fail.
[0033] In some embodiments, the dehumidifier apparatus of the
present invention also includes a passive pre-cooler, which
leverages the benefits of the Modified Series Air Flow Reverse
Cycle dehumidifier. The pre-cooler boosts energy efficiency
significantly, reduces the necessary refrigeration system capacity,
and reduces refrigeration component sizing and cost necessary to
derive a dehumidifier of a particular target capacity. Series Flow
and Modified Series Flow has an additional side-benefit when trying
to integrate the passive pre-cooler into applications where
frosting of the evaporator and frosting at the pre-cooler re-heat
entrance occurs. Near the end of a defrosting cycle, once the frost
is almost completely melted, the air exiting the evaporator is warm
enough to melt any frost that may have accumulated at the entrance
to the re-heater channels of the pre-cooler, using the continuous
air movement provided by the fan during defrosting. Additional
explanation of the integration of the pre-cooler in the
dehumidifier of the present invention is set out hereinafter.
[0034] FIG. 4 illustrates a simplified dehumidifier apparatus 10,
made in accordance with the subject invention, operating in the
dehumidifying mode. The dehumidifier apparatus 10 comprises a
refrigerant compressor 15, reversing valve 14, refrigerant
evaporator 12, refrigerant condenser 13, motorized fan 16,
refrigerant metering device 17, and temperature sensor 27. The heat
transfer components are contained in an insulated housing 11, with
an air inlet 23 and an air outlet 26. The dehumidifier entering air
23 passes through a refrigerant evaporator 12, where it is cooled
below the dew point, thereby causing water to condense onto the
surface of the evaporator 12. The refrigerant flowing through the
evaporator 12 picks up the sensible and latent heat lost by the
air. The water drains off the evaporator 12 into a drain pan/drain
hose 18, where it is directed to a suitable remote location. Cool
saturated or near-saturated evaporator 12 leaving air 24 passes
through the refrigerant condenser 13, where the air picks up heat
rejected by the condensing refrigerant. The condenser leaving air
25 is warm and dehumidified as it enters the air moving device, in
this case, a motorized fan 16. The fan leaving air 26 is further
heated by the heat rejected from the motor 28 and the air friction
of the fan 16. The fan leaving air 26 is always warmer than the
dehumidifier entering air 23 due to the external energy input to
the compressor 22 and the motorized fan 16.
[0035] The refrigerant flow explanation will begin at the
compressor 15. Cool refrigerant gas from the reversing valve 14
flows to the compressor 15 through the suction line 22. Mechanical
or electrical energy is supplied to the compressor 15 to compress
the gas to high pressure and high temperature. Hot discharge gas
flows toward the reversing valve 14 via the discharge line 21. The
reversing valve 14 directs the refrigerant flow to the condenser
inlet via the condenser line 20. Hot refrigerant gas moves through
the condenser 13 giving its heat up to the air flowing through it.
The condensed refrigerant leaves the condenser 13 and travels to
the evaporator inlet via the refrigerant metering device, in this
case a capillary tube 17. As the refrigerant moves toward the
evaporator 12, it loses pressure and temperature until it enters
the evaporator 12 at the evaporating temperature corresponding to
the evaporator pressure. As the refrigerant flows through the
evaporator 12, it picks up heat from the air and boils the
refrigerant into a gas. The cold gas is drawn out of the evaporator
12 by the suction of the compressor 15 and travels to the reversing
valve 14 via evaporator line 19. The reversing valve 14 position
directs the refrigerant to the compressor suction connection via
suction line 22. The cycle then repeats itself.
[0036] FIG. 5 shows the dehumidifier apparatus 10 of the subject
invention after a period of time in operation at low load either
caused by a low humidity condition, a cold entering air condition,
or both. Frost forms on the fins of evaporator 12, reducing to some
degree the total air flow through the dehumidifier. The decreased
evaporating capacity of the fouling evaporator 12 causes the
refrigerant temperature in the evaporator 12 to drop, as sensed by
the temperature sensor 27. Reduced airflow and colder refrigerant
in the evaporator 12 causes cooler air to flow through the
condenser 13, thereby effectively maintaining condenser heat
rejecting capacity. No water drains off the evaporator 12 as the
water is frozen. Temperature sensor 27 detects whether the
evaporator temperature is in a range where the evaporator is
frosting. If so, a control algorithm, implemented by a controller
(not shown) electrically connected to the temperature sensor 27,
determines how long operation should continue before a defrost
cycle is initiated. The frosting temperature is experimentally
determined, and tends to fall in a range of about 29-34.degree. F.,
depending on the parameters of the apparatus.
[0037] FIG. 6 shows the dehumidifier apparatus of the present
invention in the defrosting mode. The reversing valve 14 changes
position and connects the evaporator line 19 to the discharge line
21, and also connects the condenser line 20 to the suction line 22.
This has the effect of reversing the roles of the evaporator 12 and
the condenser 13. The dehumidifier entering air 23 passes through
the refrigerant evaporator 12, where it loses heat to the
evaporator 12 as it melts the frost from the outside-in. The
evaporator 12 is now acting as a condenser and the hot refrigerant
flowing through it loses its heat to the frost, as it melts frost
from the inside-out. The water drains off the evaporator 12 into a
drain pan/drain hose 18, where it is directed to a suitable remote
location. Cool saturated or near-saturated evaporator leaving air
24 passes through the refrigerant condenser 13, which is now acting
as an evaporator. The cold refrigerant picks up heat rejected by
the cool evaporator leaving air 24. The condenser leaving air 25 is
cold as it enters the air moving device, in this case, a motorized
fan 16. The fan leaving air 26 is heated slightly by the heat
rejected from the motor 28 and the air friction of the fan 16. The
fan leaving air 26 is often cooler than the dehumidifier entering
air 23, as heat is extracted from the air by refrigeration effect
occurring in the condenser coil, which is then ultimately used to
assist in melting frost on the evaporator 12. Depending upon the
length of time the dehumidifier is defrosting, some frost may
accumulate on the condenser 13. Temperature sensor 27 monitors when
the liquid refrigerant exiting the evaporator has warmed up to a
pre-determined termination temperature which has been
experimentally determined, to indicate that all the frost has been
melted off the evaporator 12 surface. The defrost termination
temperature is affected by the thermal lag of the temperature
sensor 27, and tends to fall within a range of about 45-50.degree.
F. Once the defrost termination temperature has been reached, the
controller causes the reversing valve 14 to shift and the
dehumidifier resumes normal operation. If there is very little
frost on the fins, due to operation in very low humidity locations,
the temperature sensed by temperature sensor 27 will rise very
quickly upon defrost initiation, due to the absence of frost load.
Subsequently, the defrost will be quickly terminated, and normal
dehumidification operation will resume.
[0038] FIG. 7 shows the dehumidifier apparatus 10 of the present
invention as it resumes normal dehumidifying operation. The
reversing valve 14 is shifted back into its normal position. The
evaporator 12 begins to chill and the condenser 13 begins to be
heated by the action of the refrigerant flowing. Any frost that has
accumulated on the condenser 13 is subsequently warmed and drips
into drain pan/drain hose 18. The possibility of water dripping
from the condenser 13, and the need for a drain pan under the
condenser 13, can be eliminated by proper control of the defrost
cycles. Reverse cycle defrosting is very fast. A severely frosted
evaporator 12 will require longer defrost cycles to melt the frost,
which increases the probability that a drain pan will be required
under the condenser 13. Long defrost cycles will give the condenser
13 long enough to establish active water removal on the chilled
surfaces of the condenser 13. However, with proper sensing and
control, a severely frosted coil can be avoided by triggering the
defrost sooner, hence the defrost will be quicker, and no drain pan
under the condenser 13 will be required.
[0039] The present invention is directed at providing a
dehumidifier apparatus having a number of attributes, including
simplicity, reliability, minimization of moving parts, low cost,
robust construction, portability, serviceability, cleanability,
energy efficiency, dehumidification effectiveness, and effective
defrost control. Energy efficiency as described herein refers to
the amount of water that can be removed per unit energy input, when
operated at a particular set of conditions.
[0040] Referring now to FIGS. 8, 9 and 10, illustrated therein is a
dehumidifier 40 made in accordance with an embodiment of the
subject invention. Dehumidifier 40 comprises an insulated housing
41 having an air inlet 71 for receiving incoming air covered by an
air filter 58, and an air discharge opening 46 that allows the air
to exit from the housing 41. The housing 41 is configured to
provide an interior airflow passageway A shown by the dashed line.
Mounted within the airflow passageway A of the housing 41 is a
blower 53 for moving the air through the airflow passageway A,
although other types of air movers, such as a high rpm, high static
pressure fan, could be used instead of blower 53.
[0041] The dehumidifier 40 comprises a compressor 47 located in a
compressor compartment 48 for compressing a refrigerant, an
evaporator 42 located with the airflow passageway for evaporating
the refrigerant during a dehumidifying cycle, thereby cooling the
incoming air below the dew point and thereby causing water to
condense on the surface thereof, an insulated drain pan 43 located
under the evaporator 42 for collecting the water that condenses on
the evaporator 42, a condenser 54 for condensing the refrigerant
located in the airflow passageway A downstream of the evaporator 42
in series with the evaporator 42.
[0042] The dehumidifier 40 also comprises a defrosting cycle system
for performing a defrosting cycle during a frosting condition of
the evaporator 42, wherein during the defrosting cycle the flow of
the refrigerant is reversed, causing the evaporator 42 to condense
the refrigerant and the condenser 54 to evaporate the refrigerant.
The defrosting cycle system comprises a reversing valve 45 that
reverses the flow of the refrigerant during the defrosting cycle,
which essentially reverses the functions of the evaporator 42 and
condenser 54 during defrosting, causing the evaporator 42 to
condense the refrigerant and the condenser 54 to evaporate the
refrigerant. The defrosting cycle system also comprises a frosting
condition detector for directly or indirectly sensing the presence
of frost on the evaporator 42, and a controller 35 electrically
coupled to the detector for operating the reversing valve 45. As
shown the detector comprises a temperature sensor 52 such as an
insulated thermistor for directly sensing the temperature of the
refrigerant in the evaporator 42. Alternatively, the detector could
comprise a sensor for indirectly detecting the temperature of the
refrigerant in the evaporator, such as a pressure sensor for
detecting the refrigerant evaporating pressure and determining the
refrigerant temperature using the saturated temperature - pressure
relationship for the specific refrigerant being used.
Alternatively, other types of frosting condition detectors, such as
an airflow detector for detecting the air flow through the
evaporator 42, could be used in place of the sensor 52.
[0043] The dehumidifier 40 also includes various refrigerant flow
lines configured to enable the refrigerant to flow between the
compressor 47, the condenser 54 and the evaporator 42. These
refrigerant flow lines include an insulated evaporator line 59
allowing the refrigerant to flow between the reversing valve 45 and
the evaporator 42, a condenser line 62 allowing the refrigerant to
flow between the condenser 54 and the reversing valve 45, a
refrigerant metering device such as capillary tube 55 allowing the
refrigerant to flow between the evaporator 42 and the condenser 54,
an insulated suction line 60 allowing the refrigerant to flow
between the compressor 47 and reversing valve 45, and a discharge
line 61 allowing the refrigerant to flow between the compressor 47
and reversing valve 45.
[0044] The dehumidifier 40 also comprises a pump 49 with an
integral sump for pumping out the condensation collected in the
drain pan 43, using drain hose 44 connecting the drain pan 43 to
the pump 49, and a pump outlet hose having a quick release coupling
51, for the purpose of attaching a releasable remote drain hose of
unspecified length and diameter.
[0045] In some embodiments, the dehumidifier 40 includes a passive
air pre-cooler in the form of an air-to-air heat exchanger 56 that
pre-cools the incoming air. The air-to-air heat exchanger 56 is
configured to provide a first pre-cooling air pass 76 upstream of
the evaporator and a second pre-heating air pass 77 downstream of
the evaporator.
[0046] In some embodiments, the dehumidifier 40 also includes
bypass holes 57 that are configured to allow a pre-selected,
relatively small portion of the incoming air to enter a bypass
passageway 64 that bypasses the evaporator 42, and also the
air-to-air heat exchanger 56, if present, and joins the airflow
passageway A upstream of the condenser 54. The pre-selected portion
of the air may fall within a range of about 5 to 25 percent of the
incoming air during normal operation. In the embodiments that have
bypass holes 57, the subject dehumidifier uses a modified series
airflow where the mass flow of air through the condenser 54 and
blower 53 are slightly higher than the mass flow of air through the
evaporator 42 and air-to-air heat exchanger 56.
[0047] In other embodiments without bypass holes 57, the subject
dehumidifier uses a series airflow, where the blower 53, the
evaporator 42, air-to-air heat exchanger 56 and the condenser 54
are all in the same flow path. In other words, the mass flow of air
through the evaporator, condenser, and blower are equal.
[0048] In the embodiment shown in the FIGS. 8-10, housing 41 of the
dehumidifier 40 comprises an upright enclosure having a top end and
a bottom end, with the air inlet 71 being positioned near the top
end of the enclosure and the air outlet 46 being positioned near
the bottom end of the enclosure. The enclosure comprises a front
panel 81, a back panel 82, side panels 83, a top lid 84 hingedly
connected to a top end of the rear panel 82, and an inclined
control panel 85 having a user interface 86 connected to the
controller 35. As best shown in FIG. 10, the air inlet 71 includes
a bypass flange 88 having bypass holes 57.
[0049] The housing 41 is preferably a portable housing having a
handle 72 extending transversely from a back side of the housing 41
and a pair of spaced wheels 50 extending from the back side of the
bottom end of the housing 41, and pair of front legs 89 at the
front corners of the bottom of the housing 41.
[0050] This dehumidifier 40, as shown, is intended to be operated
in the upright position, but can be transported on its side, on its
back (with the handle 72 to the floor), or in a position anywhere
in-between. With the spatial relationship of the evaporator 42
relative to the condenser 54, care must be taken to prevent gravity
drainage of the refrigerant in the evaporator 42 down into the
condenser 54 or into the compressor 47, or drainage from the
condenser 54 into the compressor 47, when the unit is "off".
Referring to FIG. 9, this is accomplished by routing the capillary
tube 55 at the inlet of the evaporator 42 horizontally to the left
past the plane of the evaporator air inlet, then vertically to
above the highest point in the refrigerant circuit, before dropping
down to the condenser 54 outlet connection. In the embodiment
shown, the condenser 54 is circuited as a cross/counter-flow heat
exchanger, with a tilt upward from front to back, causing
refrigerant to be trapped within it and prevented from flowing back
to the compressor. Refrigerant will not flow back to the compressor
47 if the housing 41 is upright, on its back, or anywhere
in-between. Liquid refrigerant in the compressor 47 can cause
mechanical damage to the compressor 47, either by diluting the
lubricating oil with the solvent effect of the liquid refrigerant,
or by the catastrophically high mechanical stresses associated with
trying to compress a liquid.
[0051] Airflows During Normal (Non-Frosting) Operation:
[0052] Air from the surroundings enters the air filter 58 at top of
the dehumidifier 40, traveling in a downward direction due to the
suction created by the blower 53. A small portion of the air is
bypassed directly into the bypass passageway 64 that is downstream
of the air-to-air heat exchanger 56 re-heater pass via the bypass
holes 57. The air bypass allows air flow reduction fine tuning
through the evaporator 42, and to slightly enhance air flow through
the condenser 54.
[0053] Air enters first pass of air-to-air heat exchanger 56 where
it is pre-cooled to a temperature at or below the dew point. Any
condensation on the walls of the heat exchanger plates 56 will drip
into the drain pan 43 below, then drain into the pump 49 via a
looped trapped hose 44, and pumped to a quick-connect hose coupling
51 by the action of the pump 49.
[0054] The air is turned 270 degrees and enters the evaporator 42
where it is further cooled by the action of the evaporating
refrigerant and water condenses out onto the fins of the evaporator
42, and on any other evaporator exposed surfaces such as on return
bends 63. Any condensation drains into the drain pan 43 below.
[0055] Cold saturated air then enters the pre-heating pass 77 of
the air-to-air heat exchanger 56 where it picks up the heat that
was lost by the air in the pre-cooling pass. The air-to-air heat
exchanger 56 is not 100% efficient, so the temperature of the air
entering condenser 54 is still below the incoming air temperature
through air filter 58, and hence derives all the benefits of a
series or modified series air flow configuration.
[0056] Air is turned 90 degrees where it enters bypass passageway
64 and blends with bypass air flowing in through bypass holes 57,
causing an increase in blended air temperature, and then enters
condenser 54 where it picks up the heat rejected by the condensing
refrigerant, thereby further increasing the air temperature.
[0057] The air then enters the blower 53, where it is turned 90
degrees and is then blown over the compressor 47. The action of the
turbulent air blowing over the compressor 47 removes heat from the
hot compressor shell thereby further reducing the condenser load
and improving system efficiency.
[0058] The compressor compartment 48 is pressurized by the blower
53 and air flows out to the surroundings via the air discharge
opening 46. The air leaves the unit at a higher temperature than
when it entered, due to the electrical power that was input to the
compressor 47 and the blower 53. The air exits the unit as warm dry
dehumidified air, with the potential to draw out moisture from the
surroundings.
[0059] Airflows During Normal (Frosting) Operation:
[0060] Air from the surroundings enters air filter 58 at top of the
housing 41 traveling in a downward direction due to the suction
created by the blower 53. A small portion of the air is bypassed
directly into bypass passageway 64 that is downstream of the
air-to-air heat exchanger 56 re-heater pass via the bypass holes
57.
[0061] Air enters first pass of air-to-air heat exchanger 56 where
it is pre-cooled to a temperature at or below the dew point. Any
condensation on the walls of the heat exchanger 56 plates will drip
into the drain pan 43 below, then drain into the pump 49 via a
looped trapped hose 44, and pumped to a quick-connect hose coupling
51 by the action of the pump 49. If the walls of the heat exchanger
56 plates are cold enough (depending on the air temperature leaving
the evaporator) frost may form on the plates.
[0062] The air is turned 270 degrees and enters the evaporator 42
where it is further cooled by the action of the evaporating
refrigerant. A combination of water and frost, or pure frost forms
on the evaporator 42 fins and on any other evaporator exposed
surfaces such as on return bends 43. Any condensation drains into
the drain pan 43. Any frost stays on the evaporator 42 surfaces
until a defrost cycle is initiated.
[0063] Cold saturated air then enters the pre-heating pass 77 of
the air-to-air heat exchanger 56 where it picks up the heat that
was lost by the air in the pre-cooling pass 76.
[0064] Air is turned 90 degrees where it blends with bypass air
flowing in through bypass holes 57, causing an increase in blended
air temperature, and then enters condenser 54 where it picks up the
heat rejected by the condensing refrigerant, thereby further
increasing the air temperature.
[0065] The air then enters the blower 53, where it is turned 90
degrees and then is blown over the compressor 47.
[0066] The compressor compartment 48 is pressurized by the blower
53 and air flows out to the surroundings via the air discharge
opening 46. The air leaves the unit at a higher temperature than
when it entered. The air exits the unit as warm dry dehumidified
air, with the potential to draw out moisture from the
surroundings.
[0067] Airflows during Defrosting:
[0068] Air from the surroundings enters the air filter 58 at top of
unit traveling in a downward direction due to the suction created
by the blower 53. A small portion of the air is bypassed directly
into the bypass passageway 64 that is downstream of the re-heater
pass 77 of the air-to-air heat exchanger 56 via the bypass holes
57. The air bypass holes 57 allow for fine tuning of the air flow
fed to the evaporator 42.
[0069] Air enters first pass of air-to-air heat exchanger 56 where
it is pre-cooled, perhaps below the dew point, depending on the
humidity of the entering air, and how much time has elapsed since
defrost initiation. Any condensation on the walls of the plates of
the heat exchanger 56 will drip into the drain pan 53 below, then
drain into the pump 49 via a looped trapped hose 44, and pumped to
a quick-connect hose coupling 51 by the action of the pump 49.
[0070] There are important benefits to allowing the air to continue
to flow through evaporator 42 during defrost. Any frost formed on
the plates of the heat exchanger 56 in the pre-cool pass will begin
to melt as the evaporator 42 warms and increases the air
temperature of the air entering the re-heat pass of the heat
exchanger 56. In the early stage of defrosting, depending on the
incoming air condition, the incoming air may continue to be
dehumidified as it makes its first pass through the air-to-air heat
exchanger 56, because the air exiting the evaporator 42 and
entering the re-heater pass 77 is still cold due to the action of
melting frost on the fins 74 of the evaporator 42. Therefore, some
dehumidification can still occur during defrost within the
pre-cooling pass of the heat exchanger 56. The other effect is that
any hoar-frost formed at the entrance of the re-heating pass of the
heat exchanger 56, will also be melted by the air coming off the
evaporator 42, particularly near the end of the defrost cycle when
most of the frost has melted and the evaporator 42 is becoming
quite warm.
[0071] The air is turned 270 degrees and enters the evaporator 42
where it gives up its heat in an effort to melt frost that has
accumulated on the fins 74 of the evaporator 42 and on any other
exposed surfaces of the evaporator coil 63 such as return bends.
The action of the air wiping through the fins 74 acts to defrost
the coil from the outside-in. The action of the hot refrigerant gas
being pumped into the refrigerant tubes by the compressor 47 acts
to defrost the evaporator from the inside-out, as the evaporator 42
is now acting as a de-superheater/condenser. The melting frost on
the walls of the heat exchanger 56 plates and on the evaporator
surfaces will drip into the drain pan 43 below, then drain into the
pump 49 via a looped trapped hose 44, and pumped to a quick-connect
hose coupling 51 by the action of the pump 49.
[0072] Cold saturated, or near-saturated air then enters the
pre-heating pass of the air-to-air heat exchanger 56 where it picks
up the heat that was lost by the air in the pre-cooling pass.
[0073] Air is turned 90 degrees where it blends with bypass air
flowing in through bypass holes 57, causing an increase in blended
air temperature, and then enters condenser 54 where it loses heat
to the coil 75 of the condenser 54, which is now acting as an
evaporator. The heat removed from the air is picked up by the
evaporating refrigerant, which is also ultimately used to defrost
the coil 63 of the evaporator 42 as a result of the refrigeration
cycle. The saturated air will also begin to condense water onto the
cold fins of the coil 75 of the condenser 54. A drain pan 43 under
the condenser 54 may be necessary to catch any water, but for this
particular design, the defrost time is extremely short and by
properly controlling the defrost intervals, virtually no water or
frost accumulates on the condenser 54.
[0074] The cold air then enters the blower 53, where it is turned
90 degrees and then blown over the compressor 47.
[0075] The compressor compartment 48 is pressurized by the blower
53 and air flows out to the surroundings via the air discharge
opening 46. The air leaves the unit cold and near saturated,
depending on the stage of the defrost cycle. The humidity of the
air stream leaving the unit is higher than the entering air stream,
which serves to undo some of the dehumidification effort gained
during normal operating cycle. However, with this method of
defrosting, the defrost time is so short that quick resumption of
normal dehumidifying operation outweighs any short-lived
re-humidification of the air.
[0076] Refrigerant Flows during Normal Operation:
[0077] Cold refrigerant liquid exits the capillary tube 55 and
enters the evaporator 42 at low pressure. Refrigerant boils in the
evaporator 42, removing heat from the air and converting
refrigerant liquid into refrigerant gas. The boiling temperature of
the refrigerant is monitored by the insulated temperature sensor
52. If the temperature sensor 52 determines that the evapoator 42
is operating in the frosting range, the controller 35 will apply a
control algorithm to determine how long the dehumidifier 40 should
run in dehumidifying mode before initiating a defrost cycle.
[0078] Refrigerant gas exits the evaporator 42 and enters the
reversing valve 45 via the evaporator line 59. In the normal
operating state, the reversing valve 45 directs the cool
refrigerant gas to the suction gas connection of the compressor 47
via suction line 60. The refrigerant gas is compressed to high
temperature and pressure and is delivered to the reversing valve 45
via the discharge line 61.
[0079] In the normal operating state, the reversing valve 45
directs the hot refrigerant gas to the condenser 54 via the
condenser line 62. The hot gas condenses into a liquid, at high
pressure, giving up its heat to the air flowing through the
condenser 54.
[0080] The liquid refrigerant is fed through the capillary tube 55
where its pressure and temperature are reduced as it moves from
entrance to exit. The cycle then begins again.
[0081] Refrigerant Flows During Defrost:
[0082] The state of the reversing valve 45 is reversed. The flow
direction of the refrigerant changes between the condenser 54 and
evaporator 42. Cold refrigerant liquid exits the capillary tube 55
and enters the condenser 54 at low pressure. Refrigerant boils in
the condenser 54, removing heat from the air and converting
refrigerant liquid into refrigerant gas.
[0083] Cold refrigerant gas exits the condenser 54 and enters the
reversing valve 45 via the condenser line 62. In defrost, the
reversing valve 45 directs the cold refrigerant gas to the suction
gas connection of the compressor 47 via the suction line 60. The
refrigerant gas is compressed to high temperature and pressure and
is delivered to the reversing valve 45 via discharge line 61.
[0084] In defrost, the reversing valve 45 directs the hot
refrigerant gas to the top of the evaporator 42 via the evaporator
line 59. The hot gas condenses into a liquid, at high pressure,
giving up its heat to melt the frost on the surface of the
evaporator 42. Near the latter part of the cycle, once most of the
frost has melted, the refrigerant will begin to give up heat to the
air flowing through the evaporator 42 fins. This will also assist
in melting any frost at the entrance of the re-heating pass 77 of
the air-to-air heat exchanger 56.
[0085] The liquid refrigerant exits the bottom of the evaporator 42
and is fed through the capillary tube 55 where its pressure and
temperature are reduced as it moves from entrance to exit.
[0086] Prior to exiting the evaporator 42, the refrigerant must
pass by the insulated temperature sensor 52. The controller 35
monitors the temperature of the refrigerant sensed by temperature
sensor 52 and determines if the liquid is warm enough to indicate
that all the frost has been melted off the surfaces of the
evaporator 42. The qualifying temperature is determined by
experimentation. If the termination temperature is reached, the
temperature sensor controller 35 will terminate the defrost and
cause the reversing valve 45 to shift back into its normal
operating state and resume active dehumidification. If there is
very little frost on the fins, due to operation in very low
humidity locations, the temperature sensed by the temperature
sensor 52 will rise very quickly upon defrost initiation, due to
the absence of frost load. Subsequently, the defrost will be
quickly terminated, and normal dehumidification operation will
resume. To take this effect to an ultimate benefit, one can
simplify the defrost initiation trigger to merely an operating time
interval, and initiate a defrost whether the evaporator 42 is
frosting or not. If the evaporator 42 is simply condensing water
with no frost present, initiating a "false defrost" will cause the
temperature sensed by the temperature sensor 52 to rise extremely
fast at the designated sensing location, such that the defrost
termination temperature is reached in 10 to 20 seconds typically.
After defrost termination, the quick recovery of the subject
dehumidifier 40 renders only a very slight performance loss after
having experienced the "false defrost".
[0087] If the defrost termination temperature is not yet reached,
then the refrigerant cycle continues until the defrost termination
is finally reached. If the defrost termination temperature is not
reached within four minutes of defrost initiation, a control
overrides the defrost and resumes normal operation. However, the
control remembers events of premature defrost termination. If there
are three incomplete defrosts in a row, the dehumidifier will shut
off and indicate an error on the display. Incomplete defrost could
be caused by low refrigerant charge (leak) or too cold ambient air
temperature.
[0088] The dehumidifiers made in accordance with the subject
invention are configured so as to direct three sources of heat
toward defrosting the evaporator during the defrost cycle:
[0089] (1) Air flows through the coil fins of the evaporator,
allowing the heat contained in the air to melt the frost, as if the
system was an air defrost system only. This melts the frost from
the outside-in.
[0090] (2) Electrical input to the compressor raises the
temperature of the refrigerant gas as if it was a conventional hot
gas bypass defrost system.
[0091] (3) Heat is picked up by the refrigerant from the air stream
moving through the condenser. This additional heat finds its way to
the defrosting evaporator by the action of the compressor using the
vapour compression cycle.
[0092] The three sources of heat are the key to the quick defrost.
The hot gas serves to defrost the coil of the evaporator from the
inside-out. The air moving through the evaporator defrosts from the
outside-in. The advantages are quick defrost, quick recovery, and
good control of liquid refrigerant (floodback).
[0093] Another functional reason to keep the air flowing during
defrost relates to the potential for frost accumulating on the
pre-cooler plates of the air-to-air heat exchanger. There is no
refrigerant heat to melt any frost in that zone, so we count on the
heat from the air flowing through the plates to effect the
defrosting of those plates.
EXAMPLES
[0094] In order to assess the performance of the subject
dehumidifier apparatus, tests were conducted, which measured the
defrost time and the water removal for three Low Grain Refrigerant
(LGR) dehumidifiers, a first commercial dehumidifier having a
conventional hot gas bypass defrost, a second commercial
dehumidifier having an air defrost, and a third dehumidifier made
in accordance with the present invention having a modified series
airflow reverse cycle defrost.
[0095] Typical test results for a commercial LGR dehumidifier
having a conventional hot gas bypass defrost:
[0096] At 53.degree. F., 51% Relative Humidity: Defrost time was 8
minutes out of every 16 minutes normal run time, for a total cycle
time of 24 minutes. Defrost time was 50% of run time. Water removal
was 16.6% of its standard rating. Standard Rating conditions are
dictated by the ANSI/AHAM Standard DH-1 for dehumidifiers.
[0097] Test results for a commercial LGR dehumidifier having an air
defrost:
[0098] At 53.degree. F., 51% RH: Defrost time was 16 minutes out of
every 29 minutes normal run time, for a total cycle time of 45
minutes. Defrost time was 55% of run time. Water removal was 20.3%
of its standard rating. [0099] Test results for the LGR dehumidifer
made in accordance with the subject invention, having a modified
series reverse cycle defrost:
* * * * *