U.S. patent application number 12/093245 was filed with the patent office on 2009-09-10 for defrost system.
This patent application is currently assigned to JOHNSON CONTROLS DENMARK ApS. Invention is credited to Alexander Cohr Pachai, Lennart Rolfsman.
Application Number | 20090223232 12/093245 |
Document ID | / |
Family ID | 35517028 |
Filed Date | 2009-09-10 |
United States Patent
Application |
20090223232 |
Kind Code |
A1 |
Rolfsman; Lennart ; et
al. |
September 10, 2009 |
DEFROST SYSTEM
Abstract
The present invention relates to a defrost system for defrosting
components on which frost is formed, where the defrost system
comprises at least one compressor, whish compressor has a hot gas
outlet, which is connected to condensing means, from where
primarily liquid refrigerant is connected to pressure reduction
means, from where the flushing refrigerant is led towards
evaporator means. The object of the invention is to perform
effective defrosting by a defrost system. This can be achieved if
the defrost system is formed as an independent cooling system,
where the condensing means are transmitting heat to the defrosting
components, where the evaporator is cooperating with external
cooling means or from the refrigeration system, enabling defrost
without deflecting the main system. It can hereby be achieved that
the defrost system can operate completely independent of another
refrigeration system. All negative effects with traditional defrost
operation of refrigeration systems are overcome by means of this
solution where the defrost system operates as a system without any
influence from the refrigeration system. Even the refrigeration
media can be different so that the refrigeration system can be a
CO2 system where the defrost system can operate with a traditional
refrigerant as 134A. In this way, it becomes possible to build the
defrost circuit with other pressure conditions than the
refrigeration system. In fact, this defrost system is operating as
a heat pump where the condensing heat from the heat pump is used
for defrosting. The defrost system can only operate if the
refrigerant after passing through the condensing means is sent
through at least an expansion valve and evaporator means before the
refrigerant is returned to a compressor. In this way, a waste of
cooling energy is performed. This cooling energy could be used in
combination with another refrigeration system. Depending on where
in the world a system is operating, the evaporator from the
defrosting system could be used as a part of an air condition
system. Also in combination with refrigeration systems, the
evaporator can be used in combination with condensing or sub
cooling of refrigerant.
Inventors: |
Rolfsman; Lennart;
(Norrkobing, SE) ; Pachai; Alexander Cohr;
(Skoedstrup, DK) |
Correspondence
Address: |
ROBERTS MLOTKOWSKI SAFRAN & COLE, P.C.;Intellectual Property Department
P.O. Box 10064
MCLEAN
VA
22102-8064
US
|
Assignee: |
JOHNSON CONTROLS DENMARK
ApS
Hoejbjerg
DK
|
Family ID: |
35517028 |
Appl. No.: |
12/093245 |
Filed: |
November 10, 2006 |
PCT Filed: |
November 10, 2006 |
PCT NO: |
PCT/DK06/00621 |
371 Date: |
October 6, 2008 |
Current U.S.
Class: |
62/80 ; 62/291;
62/498 |
Current CPC
Class: |
F25B 47/02 20130101;
F25B 2309/06 20130101; F25B 9/008 20130101; F25B 40/02 20130101;
F25B 7/00 20130101; F25B 2400/23 20130101 |
Class at
Publication: |
62/80 ; 62/498;
62/291 |
International
Class: |
F25D 21/06 20060101
F25D021/06; F25B 1/00 20060101 F25B001/00; F25D 21/14 20060101
F25D021/14 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 11, 2005 |
DK |
PA 2005 01574 |
Claims
1. Defrost system for defrosting components on which frost is
formed, where the defrost system comprises at least one compressor,
which compressor has a hot gas outlet, which is connected to
condensing means, from where primarily liquid refrigerant is
connected to pressure reduction means, from where the e refrigerant
is led towards evaporator means, wherein the defrost system is
formed as a independent cooling system, where the condensing means
are transmitting heat to the defrosting components.
2. Defrost system according to claim 1, wherein the evaporator is
cooperating with external cooling means enabling defrost without
deflecting the maim system.
3. Defrost system according to claim 2, wherein the defrost system
are operating in conjunction with a refrigeration system, which
refrigeration system is in operation, where the condensing means of
the defrost system is cooperating with defrosting components cooled
by the refrigeration system for defrosting the components.
4. Defrost system according to claim 3, wherein the defrost system
is operating in conjunction with a refrigeration system, which
refrigeration system is in standstill, where the condensing means
of the defrost system is cooperating with defrosting components
cooled by the second refrigeration system for defrosting the
components.
5. Defrost system according to claim 4, wherein the defrost system
comprises a liquid receiver, which receiver is connected to an
expansion valve, where a gas connection from the upper part of the
receiver is connected to the receiver.
6. Defrost system according to claim 5, wherein the evaporator of
the defrost system cooperates with the second refrigeration system
by forming the evaporator in a second heat exchanger which is
heated by partly or full liquefied refrigerant of the second
refrigeration system.
7. Defrost system according to claim 5, wherein the top of the
receiver in the defrost system is used as a liquid separator, where
the top of the receiver is connected through a first heat exchanger
for liquefying the gas, which liquid gas is led back towards the
receiver, where the first heat exchanger is part of a cascade heat
exchanger, which is part of the second refrigeration system.
8. Defrost system according to claim 7, wherein the receiver
comprises a heat-exchanging coil in the upper part, which coil is
connected to the liquid outlet from the receiver, where the coil is
reducing the temperature of the gas in the top of the receiver.
9. Method for defrosting a refrigeration system comprising at least
one refrigeration system component on which frost is formed, where
defrosting is performed by heating the refrigeration system
component in periods of no operation of that refrigeration system
component, wherein defrosting is performed by an independent
defrost system, which defrost system comprises at least compressing
means for compressing and heating a defrost gas, which defrost gas
is heating the refrigeration system components by condensing the
defrost gas, which defrosting is performed in periods of no supply
of refrigerant to the refrigeration system component from the
refrigeration system, where the defrost system comprises a closed
circuit for defrost fluid without connection to the refrigeration
system.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a defrost system for
defrosting components on which frost is formed, where the defrost
system comprises at least one compressor, which compressor has a
hot gas outlet, which is connected to condensing means, from where
primarily liquid refrigerant is connected to pressure reduction
means, from where the flashing refrigerant is led through
evaporator means.
[0002] The present invention further relates to a method for
defrosting a refrigeration system comprising at least one
refrigeration system component on which frost is formed, where
defrosting is performed by heating the refrigeration system
component in periods of no operation of that refrigeration system
component.
BACKGROUND OF THE INVENTION
[0003] Prior art shows that it is possible to use glycols or brines
to defrost a refrigeration coil. The disadvantage of this solution
is the associated problems with erosion if the liquid moves too
fast through the pipes especially in the bends. A way to solve this
problem would be to use traditional hot gas-defrost with a
compressor also as seen in prior art. The disadvantage of this
system is the oil management problems when working with many
compressors at different suction pressures as in the European
patent EP 1 409 936. A way to solve this problem could be to pump
the CO2 into a vessel and then heat/evaporate this and use the
generated hot gas to defrost the coil as in the patents U.S. Pat.
No. 5,400,615 or GB 2,258,298. The simple solution to solve this
problem is to use the brine circuit at a pressure designed for a
high working pressure and with CO2 as the working fluid condensing
at an appropriate temperature. This solution solves the problems
found in the brine solution and eliminates the problems seen with
oil management in the traditional hot gas solutions. It also
eliminates the use of high-pressure pumps as seen in the boiling
out system.
[0004] U.S. Pat. No. 6,588,221 describes a method of defrosting a
refrigeration system having a main compressor connected by a main
hot gas discharge line to a condenser, the condenser being
connected by a main liquid line to thermal expansion valves and
subsequent cooling coils, each thermal expansion valve and cooling
coil being in parallel connection with the other thermal expansion
valves and cooling coils, and each cooling coil being connected by
a suction line to the main compressor. The defrosting method
includes passing hot gas from the main hot gas discharge line
through a selected cooling coil to defrost same, compressing cooled
gas which has passed through the cooling coil by means of a
separate dedicated defrost compressor, and returning the compressed
hot gas to the main hot gas discharge line.
OBJECT OF THE INVENTION
[0005] The object of the invention is to perform effective
defrosting by means of a separate defrost system thus avoiding oil
management problems. A further object is to achieve a lower system
cost.
DESCRIPTION OF THE INVENTION
[0006] This can be achieved if the defrost system is formed as an
independent cooling system, where the condensing means are
transmitting heat to the defrosting components.
[0007] It can hereby be achieved that the defrost system can
operate completely independent of the refrigeration system. All
negative effects with traditional defrost operation of
refrigeration systems are overcome by this solution where the
defrost system operates as a system without any influence from the
refrigeration system. Even the working fluid can be different so
that the refrigeration system can use CO2, the defrost system can
operate with a traditional refrigerant like 134A. In this way, it
becomes possible to build the defrost circuit with other pressure
conditions than those of the refrigeration system. In fact, this
defrost system is operating as a heat pump where the condensing
heat is used for defrosting. The defrost system can only operate if
the refrigerant after passing through the condensing means is sent
through at least an expansion valve and evaporator means before the
refrigerant is returned to a compressor. In this way, a waste of
cooling energy is performed. This cooling energy could be used in
combination with the refrigeration system. Depending on the
environmental operating conditions, the evaporator from the
defrosting system could be used as a part of an air condition
system. Also in combination with refrigeration systems, the
evaporator can be used in combination with condensing or subcooling
of refrigerant.
[0008] Preferably, the evaporator of the defrost system can be
cooperating with external cooling means or with the refrigeration
system. This can lead to a reduction of the power consumption of
the refrigeration system.
[0009] The defrost system can be operating in conjunction with a
refrigeration system, where the condensing means of the defrost
system is cooperating with cooling components cooled by the
refrigeration system. It can hereby be achieved that for example an
evaporator can comprise another circuit for circulating and
condensing the defrost refrigerant. In this way, it is possible to
perform defrost in non-operating periods of the refrigeration
system. In a refrigeration system, evaporators can be cut out of
operation, and defrost can be performed in different evaporators.
In single evaporator systems, the refrigeration system can be
stopped, and the defrost system can be started. Hereby, the
refrigeration system can be defrosted without having to reverse the
refrigeration system.
[0010] The defrost system can operate in conjunction with a
refrigeration system, which refrigeration system is in standstill,
where the condensing means of the defrost system is cooperating
with cooling components cooled by the refrigeration system. This
can lead to a fast defrosting of evaporators or other cooling
means.
[0011] Preferably the defrost system comprises a liquid receiver,
which receiver is connected to an expansion valve, where a gas
connection from the upper part of the receiver can be connected to
the evaporator through a modulating valve. The receiver can be
installed either in the liquid line or in the compressor suction
line.
[0012] It can hereby be achieved that if the amount of defrost
fluid in gas form and under high pressure reduces the liquefying of
defrost fluid, and pressure is still increasing in the liquid
receiver, then it is possible to open the modulating valve and let
some of the high pressure defrost gas flow towards the expansion
valve. This high pressure defrost gas is mixed with the defrost
fluid, which after passing the expansion valve will flash, and the
cooling energy that will be delivered to the evaporator will in
this way be reduced, but the defrost system can continue in normal
operation.
[0013] The evaporator of the defrost system can cooperate with the
refrigeration system by forming the evaporator in a second heat
exchanger which is heated by partly or fully liquefied refrigerant
of the refrigeration system. It is hereby achieved that all the
cooling effect that is achieved by the defrost operation is
transmitted to the refrigeration system as cooling energy. This can
lead to a very effective combination of a refrigeration system and
a defrost system. The cooling energy can be transmitted
independently of the fact that the two systems can operate quite
differently in pressure and also in the type of refrigerant.
[0014] The upper part of the receiver in the defrost system can be
used as a liquid separator, where the top of the receiver is
connected through a first heat exchanger for liquefying the gas,
which liquid is led back towards the receiver, where the first heat
exchanger is part of a cascade heat exchanger, which is part of the
refrigeration system. It can hereby be achieved that if the defrost
operation is not led to a complete condensation of the refrigerant;
a relatively high amount of gas will enter the receiver. This can
lead to a pressure increase in the receiver, and it is therefore
necessary to condensate a part of that gas. This condensation
process can take place in a heat exchanger so that the extra heat
is transported by a cascade refrigeration system to the
refrigeration system where the extra heat simply is sent directly
to existing condensing means. By reducing the amount of gas in the
receiver, the pressure is reduced, and as such the defrost system
is operating more efficiently.
[0015] The receiver can comprise a heat-exchanging coil in the
upper part, which coil is connected to the liquid outlet from the
receiver, where the coil is reducing the temperature of the gas in
the top of the receiver. This is an alternative method to
condensate the amount of gas that might end in the receiver in
certain operation situations. This coil will automatically lead to
condensation of the gas, which also reduces the pressure.
[0016] The invention comprises one or more compressors, one or more
coils to be defrosted with a separate defrost circuit designed for
the refrigerant used, a liquid receiver, an expansion valve and an
evaporator in thermal connection to a heat source that can be air
or any type of liquid e.g. from other processes or heat loads
coming from cooling other products. The refrigerant can be any
refrigerant pure or mixtures of HFC e.g. R134a or CO2.
[0017] The advantage of the system is the fact that the defrost
system is operating independently of the primary and secondary
refrigeration system operating as a cascade refrigeration system.
The defrost system can be thermally connected whenever the design
gives an opportunity to optimise the process. The interaction is
not limited to the refrigeration system itself, but it can be
connected to other processes as well.
[0018] An advantage is also that defrost can take place regardless
of whether the refrigeration system is running or not. The defrost
system can also be used with a one-evaporator system without
requiring the refrigeration system to work. Another advantage of
the system is the freedom of choice of refrigerant. All
refrigerants can be used, but the preferred refrigerant is CO2.
[0019] The defrost method can be performed by an independent
defrost system, which defrost system comprises at least compressing
means for compressing and heating a defrost gas, which defrost gas
is heating the refrigeration system components by condensing the
defrost gas, which defrosting is performed in periods of no supply
of refrigerant to the refrigeration system component from the
refrigeration system, where the defrost system comprises a closed
circuit for defrost fluid without connection to the refrigeration
system.
[0020] This method can lead to a very energy effective defrost
because the heat is generated from the defrost system operating as
a heat pump, and the defrost fluid can be expanded in evaporation
means connected to the refrigeration system. Because the defrost
system is independent of the refrigeration system can different
refrigeration media be used.
DESCRIPTION OF THE DRAWING
[0021] FIG. 1 shows an example of how a CO2 system can be connected
to the defrost coil,
[0022] FIG. 2 shows an example of how the defrost system and the
cooling system can be combined in operation,
[0023] FIG. 3 shows an alternative embodiment for the
invention,
[0024] FIG. 4 shows an external load as the evaporator,
[0025] FIG. 5 shows a receiver comprises a coil, and
[0026] FIG. 6 shows an alternative embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0027] FIG. 1 shows an example of how a CO2 system can be connected
to the defrost coil in an air-cooled evaporator. FIG. 1 shows a
defrost system 2 and a refrigeration system 4. The defrost system 2
comprises a compressor 10 which has a gas outlet line 12,14, where
the line 12 is connected to a solenoid valve 20 from where a line
22 leads to condenser 30 placed in conjunction with a cooling
system. From here, a line 32, which is combined with another line
34, ends up in a line 36, which leads to a liquid receiver 40. This
liquid receiver has a liquid outlet 42, which leads to an expansion
valve 50, from where a line 52 leads to an evaporator 70. From the
upper part of the receiver 40, a line 44 leads to a magnetic
modulating valve 60 from where a line 62 leads to the line 52 near
the inlet to the evaporator 70. From the evaporator 70, a line 72
is arranged, which leads to the inlet of the compressor 10.
[0028] The refrigeration system 4 comprises a compressor 80 which
has a hot gas outlet line 82 connected to a cascade condenser 90.
The cascade condenser 90 is by a line 92 connected to a receiver
100 from where a line 102 over a control valve 110 is connected to
a main receiver 120. The main receiver 120 has an outlet line 122
connected to pumping means 130, from where a line 132 continues in
not shown lines 134. The line 132 is connected to an expansion
valve 140 from where a line 142 leads to the evaporator 150. From
the evaporator 150, a line 152 is combined by a line 154 to a line
156, which leads into the main receiver 120. From the top of the
receiver 120, a line 124 connected to the suction side of the
compressor 80 is arranged.
[0029] When the defrost cycle is required, one or more defrost
compressors 10 and the solenoid valve 20 in front of defrost coil
30 that is to be defrosted start/open. In the beginning of the
process, there will be a lot of defrost liquid returning to the
liquid receiver 40. Later in the defrost cycle, there is a larger
amount of defrost gas returning to the receiver 40, and the
pressure will increase. The surplus defrost gas can be removed by a
modulating valve 60 and led to the evaporator. The efficiency of
the evaporator will deteriorate but the main object of the
evaporation is to generate warm defrost gas for the defrosting of
the coil 150. The defrost system can be designed with CO2, R744 as
two phase defrost agent. It must be ensured that the pressure in
the receiver 40 is controlled by means of cooling by air or by the
circuit itself. The defrost system can be equipped with an
additional condenser allowing it to act as an independent
refrigeration system when not used for defrosting. Then it can be
used for other purposes like air conditioning or as a cooling
process. The heat can when not needed be used for heating with an
air coil or heating of water for other purposes when there is no
need for the defrost capacity, or if parts of the full capacity are
not needed. The compressors 10 are built into a centrally based
system. The capacity on each rack can be adjusted to fit all sorts
of capacities. In a total plant, there can be a need for many sizes
of evaporators and some can have a high need when the defrost
starts while some evaporators has a lower need. This can require
special control strategy that can be handled from a central
processing unit.
[0030] The system comprises: [0031] 1. A closed refrigerant loop
designed only to defrost with a compressor, defrost coil/condenser,
expansion valve and evaporator and may be a modulating bypass
valve. [0032] 2. The evaporator can be heated by the main system or
other heat load. [0033] 3. 1 and 2 the refrigerant can be the same
as in the refrigerant used in the main system [0034] 4. 1 and 2 the
refrigerant can be different from the refrigerant used in the main
system [0035] 5. 3 with the same medium as in the main system,
there can be an equalising connection for charge
exchange/equalisation. [0036] 6. The defrost cycle can be part of
another process and defrost on demand enhancing the running
conditions of the process because the condensing pressure might be
lowered.
[0037] FIG. 1 shows an example of how the defrost system and the
cooling system can be combined in operation. Most of the components
are equal to the description of FIG. 1, and the following
description will only concern features not mentioned before. The
first difference is that the liquefied refrigerant from the
refrigeration system 4 in the line 102 passes through a heat
exchanger 210 where this liquid refrigerant is heat exchanged with
the defrost refrigerant from the line 52 which is expanded in the
expansion valve 50 where this refrigerant is evaporated in the heat
exchanger 210 before the defrost refrigerant is led through the
line 72 towards the compressor 10. The sub-cooled refrigerant is
from the heat exchanger 210 by line 212 led to a control valve 110
from where it is sent to the main receiver 120.
[0038] A second difference to FIG. 1 is a heat exchanger 200, which
is placed as part of the cascade heat exchanger 90 for heat
exchanging to a primary refrigerant, where the heat exchanger 200
is connected to the top of the receiver 40 by a line 202 and where
a line 204 leads primary liquid defrost refrigerant into the line
36 towards the receiver 40. Gas with high temperature and high
pressure can hereby be sent to condensing in the cascade heat
exchanger 200.
[0039] The main idea about this cycle is to use the cooling
capacity for sub-cooling the liquid used in the main system. The
disadvantage of this solution is that defrost can only take place
when the main system is working, and the capacity is dependent on
the liquid available.
[0040] FIG. 3 shows an alternative embodiment for the invention,
where it is assumed that all or nearly all refrigerant is condensed
when returned to the receiver. Adding an air-coil to the defrost
circuit will help giving the capacity even if the main system is
not running
[0041] FIG. 4 shows nearly the same system as shown in FIG. 1 and
the only difference is that an external load 220 is shown as the
evaporator.
[0042] In this case, the cooling capacity is used for cooling an
external load. This solution requires a constant load on the
cooling side of the defrost cycle.
[0043] In FIG. 5, another receiver 240 is shown where this receiver
comprises a coil 242 for internal heat exchange in the top of the
receiver 240. The outlet 42 from the receiver 240 leads to a
regulation valve 244 from where a line 245 leads to the coil 242.
The outlet from this coil 242 leads to the expansion valve 50.
[0044] The expansion valve 50 keeps up the pressure in the defrost
coil, and the valve 60 controls the superheat on the air-coil. The
valve 60 opens only in case of an increase in pressure of the
receiver 40.
[0045] FIG. 6 describes an alternative embodiment of the invention.
The same numbers are used as in previous figures so only the
differences will hereafter be described. The cooling energy
generated by the defrost system is now transmitted by a heat
exchanger 370 into the cascade condenser 390 of the refrigeration
system 4. A receiver 340 is operating as previously described, and
from here, liquid defrost fluid is sent through the expansion valve
50 towards the heat exchanger 370.
[0046] This leads to a very effective evaporation of the defrost
liquid, and waste heat from the cascade condensing unit is used for
this evaporation.
* * * * *