U.S. patent application number 10/595294 was filed with the patent office on 2007-08-30 for heating and defrosting methods and apparatus.
Invention is credited to Rodney Mitchell Innes.
Application Number | 20070199335 10/595294 |
Document ID | / |
Family ID | 34420857 |
Filed Date | 2007-08-30 |
United States Patent
Application |
20070199335 |
Kind Code |
A1 |
Innes; Rodney Mitchell |
August 30, 2007 |
Heating And Defrosting Methods And Apparatus
Abstract
A heat pump includes a compressor 1, a condenser 2, an expansion
valve 3, an evaporator 4 and a heat exchanger 6a. The heat
exchanger 6a is located immediately downstream of the expansion
valve 3 and upstream of the evaporator 4. A controller 8 monitors
one or more variables which predict may be about to occur by means
of a sensor 11. When this is predicted the heat exchanger 6a will
receive hot refrigerant through line 17 from the high pressure side
of the compressor 1 so as to heat the refrigerant entering the
evaporator 4 until ice formation is no longer likely. In an
alternative embodiment, the heat exchanger may utilise an electric
element to heat the refrigerant before it enters the evaporator.
The heat exchanger 6a can preferably utilise a helically corrugated
tube in order to enhance its heat exchange characteristics.
Inventors: |
Innes; Rodney Mitchell;
(Coromandel, NZ) |
Correspondence
Address: |
SHELDON MAK ROSE & ANDERSON PC
100 East Corson Street
Third Floor
PASADENA
CA
91103-3842
US
|
Family ID: |
34420857 |
Appl. No.: |
10/595294 |
Filed: |
September 28, 2004 |
PCT Filed: |
September 28, 2004 |
PCT NO: |
PCT/NZ04/00234 |
371 Date: |
October 4, 2006 |
Current U.S.
Class: |
62/151 ; 62/278;
62/513 |
Current CPC
Class: |
F25B 2700/1933 20130101;
F25B 2700/2117 20130101; F25D 21/08 20130101; F25B 47/022 20130101;
F25B 2700/11 20130101; F25D 21/02 20130101; F25B 5/04 20130101;
F25B 2700/21175 20130101; F25B 30/02 20130101 |
Class at
Publication: |
062/151 ;
062/513; 062/278 |
International
Class: |
F25D 21/06 20060101
F25D021/06; F25B 47/00 20060101 F25B047/00; F25B 41/00 20060101
F25B041/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 6, 2003 |
NZ |
528678 |
Claims
1. A heat pump apparatus comprising an evaporator means, a control
means in communication with at least one sensor means adapted to
measure one or more variables representative of a temperature of an
outer surface of the evaporator means, and a heat exchanger means
operable to add heat from a working fluid from a high pressure side
of the heat pump apparatus to the working fluid entering the
evaporator means, wherein the control means is operatively
connected with the heat exchanger means to add the heat when the
control means determines that the temperature of the outer surface
of the evaporator means is below a pre-selected temperature,
thereby reducing or substantially eliminating the formation of ice
on the outer surface of the evaporator means.
2. A heat pump apparatus comprising an evaporator means, a control
means in communication with at least one sensor means adapted to
measure one or more variables representative of a temperature of an
outer surface of the evaporator means, and a heat exchanger means
comprising a heating element positioned upstream of the evaporator
means and downstream of an expansion means of the heat pump
apparatus, the heat exchanger means operable to add heat to a
working fluid entering the evaporator, wherein the control means is
operatively connected with the heat exchanger means so that when
the control means determines that the temperature of the outer
surface of the evaporator means is below a pre-selected
temperature, the heat exchanger means adds heat to the working
fluid thereby reducing or substantially eliminating formation of
ice on the outer surface of the evaporator means, and wherein the
heat exchanger comprises a helically corrugated tube positioned
within an outer housing, and the working fluid being heated is
caused to flow over the tube and between the tube and the outer
housing.
3. The heat pump apparatus as claimed in claim 1 wherein the at
least one sensor means comprises a temperature sensor adapted to
measure the temperature of the outer surface of the evaporator
means.
4. The heat pump apparatus as claimed in claim 1 wherein the at
least one sensor means comprises a temperature sensor adapted to
measure the temperature of the working fluid exiting the evaporator
means.
5. The heat pump apparatus as claimed in claim 1 wherein the at
least one sensor means comprises a temperature sensor adapted to
measure the temperature of the environment surrounding the
evaporator means.
6. The heat pump apparatus as claimed in claim 1 wherein the at
least one sensor means comprises a pressure sensor adapted to
measure the pressure of the working fluid exiting the evaporator
means.
7. The heat pump apparatus as claimed in claim 2 wherein the heat
exchanger means comprises an electric heating element.
8. The heat pump apparatus as claimed in claim 7 wherein the
electric heating element extends through the helically corrugated
tube.
9. The heat pump apparatus as claimed in claim 8 wherein the
helically corrugated tube forms part of an electrical circuit of
the electric heating element.
10. The heat pump apparatus as claimed in claim 1 further
comprising a compressor and a condenser and where the heat
exchanger means obtains heat from the working fluid between the
compressor and the condenser to transfer the heat to the working
fluid entering the evaporator means.
11. The heat pump apparatus as claimed in claim 2 wherein the
pre-selected temperature is between about 4.degree. C. and
0.degree. C.
12. The heat pump apparatus as claimed in claim 1 wherein the heat
exchanger means comprises a helically corrugated tube positioned in
an outer housing, the working fluid from the high pressure side
being caused to flow through the tube to add heat to the working
fluid caused to flow over the tube and between the tube and the
outer housing.
13. (canceled)
14. A method of operating a heat pump having an evaporator
downstream of an expansion means, the method comprising obtaining
heat as required from a working fluid on a high pressure side of
the heat pump to transfer to the working fluid on a low pressure
side of the heat pump, prior to the working fluid entering the
evaporator to reduce or substantially prevent ice from forming on
the outer surface of the evaporator.
15. The method as claimed in claim 14 wherein the method comprises
measuring one or more variables representative of a temperature of
an outer surface of the evaporator and adding the heat to the
working fluid entering the evaporator when the one or more
variables indicate that the temperature has dropped below a
pre-selected minimum.
16. The method as claimed in claim 15 wherein the method further
comprises providing a controller to determine when icing of the
evaporator is imminent based on the measurement of one or more
variables.
17. The method as claimed in claim 16 wherein the method comprises
heating the working fluid entering the evaporator with an electric
heating element.
18. The method as claimed in claim 17 wherein the high pressure
side is between a compressor and a condenser of heat pump.
19. The method as claimed in claim 18 in which the low pressure
side of the heat pump is provided with a heat exchanger; the method
comprising providing the heat exchanger with a helically corrugated
tube within an outer housing, the working fluid being caused to
flow over the tube and between the outer housing to be heated
before it enters the evaporator.
20. The method as claimed in claim 14 wherein the method comprises
adding heat to the working fluid while the heat pump is in
operation.
21. (canceled)
22. (canceled)
23. The heat pump apparatus as claimed in claim 2 wherein the at
least one sensor means comprises a temperature sensor adapted to
measure the temperature of the outer surface of the evaporator
means.
24. The heat pump apparatus as claimed in claim 2 wherein the at
least one sensor means comprises a temperature sensor adapted to
measure the temperature of the working fluid exiting the evaporator
means.
25. The heat pump apparatus as claimed in claim 2 wherein the at
least one sensor means comprises a temperature sensor adapted to
measure the temperature of the environment surrounding the
evaporator means.
26. The heat pump apparatus as claimed in claim 2 wherein the at
least one sensor means comprises a pressure sensor adapted to
measure the pressure of the working fluid exiting the evaporator
means.
27. The heat pump apparatus as claimed in claim 2 further
comprising a compressor and a condenser and where the heat
exchanger means obtains heat from the working fluid between the
compressor and the condenser to transfer the heat to the working
fluid entering the evaporator means.
28. A heat pump apparatus comprising an evaporator, a controller in
communication with at least one sensor adapted to measure one or
more variables representative of a temperature of an outer surface
of the evaporator, and a heat exchanger operable to add heat from a
working fluid from a high pressure side of the heat pump apparatus
to the working fluid entering the evaporator, wherein the
controller is operatively connected with the heat exchanger to add
the heat when the controller determines that the temperature of the
outer surface of the evaporator is below a pre-selected
temperature, thereby reducing or substantially eliminating the
formation of ice on the outer surface of the evaporator.
29. A heat pump apparatus comprising an evaporator, a controller in
communication with at least one sensor adapted to measure one or
more variables representative of a temperature of an outer surface
of the evaporator, and a heat exchanger comprising a heating
element positioned upstream of the evaporator and downstream of an
expansion valve of the heat pump apparatus, the heat exchanger
operable to add heat to a working fluid entering the evaporator,
wherein the controller is operatively connected with the heat
exchanger so that when the controller determines that the
temperature of the outer surface of the evaporator is below a
pre-selected temperature, the heat exchanger adds heat to the
working fluid thereby reducing or substantially eliminating
formation of ice on the outer surface of the evaporator, and
wherein the heat exchanger comprises a helically corrugated tube
positioned within an outer housing, and the working fluid being
heated is caused to flow over the tube and between the tube and the
outer housing.
30. The heat pump apparatus as claimed in claim 28 wherein the at
least one sensor comprises a temperature sensor adapted to measure
the temperature of the outer surface of the evaporator.
31. The heat pump apparatus as claimed in claim 28 wherein the at
least one sensor comprises a temperature sensor adapted to measure
the temperature of the working fluid exiting the evaporator.
32. The heat pump apparatus as claimed in claim 28 wherein the at
least one sensor comprises a temperature sensor adapted to measure
the temperature of the environment surrounding the evaporator.
33. The heat pump apparatus as claimed in claim 28 wherein the at
least one sensor comprises a pressure sensor adapted to measure the
pressure of the working fluid exiting the evaporator.
34. The heat pump apparatus as claimed in claim 29 wherein the heat
exchanger comprises an electric heating element.
35. The heat pump apparatus as claimed in claim 34 wherein the
electric heating element extends through the helically corrugated
tube.
36. The heat pump apparatus as claimed in claim 35 wherein the
helically corrugated tube forms part of an electrical circuit of
the electric heating element.
37. The heat pump apparatus as claimed in claim 28 further
comprising a compressor and a condenser and where the heat
exchanger obtains heat from the working fluid between the
compressor and the condenser to transfer the heat to the working
fluid entering the evaporator.
38. The heat pump apparatus as claimed in claim 29 wherein the
pre-selected temperature is between about 4.degree. C. and
0.degree. C.
39. The heat pump apparatus as claimed in claim 28 wherein the heat
exchanger comprises a helically corrugated tube positioned in an
outer housing, the working fluid from the high pressure side being
caused to flow through the tube to add heat to the working fluid
caused to flow over the tube and between the tube and the outer
housing.
40. A method of operating a heat pump having an evaporator
downstream of an expansion valve, the method comprising obtaining
heat as required from a working fluid on a high pressure side of
the heat pump to transfer to the working fluid on a low pressure
side of the heat pump, prior to the working fluid entering the
evaporator to reduce or substantially prevent ice from forming on
the outer surface of the evaporator.
41. The method as claimed in claim 40 wherein the method comprises
measuring one or more variables representative of a temperature of
an outer surface of the evaporator and adding the heat to the
working fluid entering the evaporator when the one or more
variables indicate that the temperature has dropped below a
pre-selected minimum.
42. The method as claimed in claim 41 wherein the method further
comprises providing a controller to determine when icing of the
evaporator is imminent based on the measurement of one or more
variables.
43. The method as claimed in claim 42 wherein the method comprises
heating the working fluid entering the evaporator with an electric
heating element.
44. The method as claimed in claim 43 wherein the high pressure
side is between a compressor and a condenser of heat pump.
45. The method as claimed in claim 44 in which the low pressure
side of the heat pump is provided with a heat exchanger; the method
comprising providing the heat exchanger with a helically corrugated
tube within an outer housing, the working fluid being caused to
flow over the tube and between the outer housing to be heated
before it enters the evaporator.
46. The method as claimed in claim 40 wherein the method comprises
adding heat to the working fluid while the heat pump is in
operation.
47. The heat pump apparatus as claimed in claim 29 wherein the at
least one sensor comprises a temperature sensor adapted to measure
the temperature of the outer surface of the evaporator.
48. The heat pump apparatus as claimed in claim 29 wherein the at
least one sensor comprises a temperature sensor adapted to measure
the temperature of the working fluid exiting the evaporator.
49. The heat pump apparatus as claimed in claim 29 wherein the at
least one sensor comprises a temperature sensor adapted to measure
the temperature of the environment surrounding the evaporator.
50. The heat pump apparatus as claimed in claim 29 wherein the at
least one sensor comprises a pressure sensor adapted to measure the
pressure of the working fluid exiting the evaporator.
51. The heat pump apparatus as claimed in claim 29 further
comprising a compressor and a condenser and where the heat
exchanger obtains heat from the working fluid between the
compressor and the condenser to transfer the heat to the working
fluid entering the evaporator.
Description
TECHNICAL FIELD
[0001] The present invention in one embodiment relates to heat pump
apparatus and to methods of operating a heat pump, and in
particular, but not exclusively, to heat pumps which reduce or
eliminate icing of the evaporator. It does, however, have
application wherever fluid heating may be required.
BACKGROUND OF THE INVENTION
[0002] The term "heat pump" is used herein to define a system which
absorbs heat (heat energy), at one or more temperatures and emits
heat at a higher temperature, and which includes, in order, a
compressor to pump refrigerant vapor around a closed circuit, a
condenser to extract heat from the vapor, thereby condensing the
refrigerant, an expansion valve to expand the refrigerant to a
gaseous phase, thereby causing the temperature of the refrigerant
to fall, and an evaporator to allow the cool refrigerant vapor to
absorb heat.
[0003] The refrigerant then returns to the compressor and repeats
the cycle. Elements such as accumulators and receivers may also be
used to ensure that the fluid is in the correct phase before it
proceeds around the cycle.
[0004] It is to be understood that the term heat pump may be
applied equally to such systems when used to remove heat from a
space or medium, such as for the purposes of air conditioning and
refrigeration, or to systems used for heating a space or medium,
such as water or space heating. Typically a four-way valve will be
included in the heat pump system before the compressor to
change-over the condenser to an evaporator and vice versa. The
terms "evaporator" and "condenser" are therefore used
interchangeably herein depending on whether the heat pump is being
used in its heating or cooling mode. Other uses such as the heating
of a gas or other fluids will also be included. Such uses could
include the heating of a fluid such as in a hydraulic system or in
an engine where lowering of the viscosity of the fluid could be of
benefit. Further uses could include the heating of a gas, such as a
compressed gas before its release when its cooling could create
problems.
[0005] Heat pump technology is now very common and the savings
gained through using this method for heating in addition to its
more traditional role in air conditioning are now more widely
appreciated. Many Governments and Authorities as well as Industry
and Commerce are realizing the benefits. The need to save energy
has become a priority around the world.
[0006] A disadvantage of using current heat pumps for heating is
that ice may form on the evaporator when the ambient temperature
around the evaporator drops below a minimum temperature, typically
around +10.degree. C. When this happens the efficiency of the heat
pump reduces dramatically due to the low thermal conductivity of
the ice reducing the rate at which heat can be absorbed by the
evaporator.
[0007] One of the options currently used to combat icing of the
evaporator is the provision of electric heating elements attached
to the evaporator or embedded within it. In such systems the heat
pump may be stopped and the refrigerant pumped down to the receiver
before the evaporator is heated. Failure to stop the device may
lead to liquid refrigerant entering the compressor, which may
damage or even destroy it. Once the heat pump has been stopped the
heating elements defrost the coil until the ice is melted and the
unit can be run again. The heating element may cycle on and off
many times until the ambient temperature increases.
[0008] A second method in use at present is a hot gas by-pass
system. When the evaporator coil ices, a solenoid valve opens, and
hot gas is directly injected into the evaporator just after the
expansion device. This method of evaporator de-icing may affect the
system's operation dramatically and performance may drop
accordingly.
[0009] A further method currently in use is to reverse the heat
pump so that the functions of the evaporator and condenser are
reversed. A disadvantage of this method is that the heat transfer
path is reversed, and the element which the heat pump is intended
to heat is instead cooled for the duration of the de-icing
cycle.
OBJECT OF THE INVENTION
[0010] It is an object of a preferred embodiment of the present
invention to provide a heat pump apparatus and/or a method of
operating a heat pump which will overcome or ameliorate problems
with such apparatus or methods at present.
[0011] Other objects of the present invention may become apparent
from the following description, which is given by way of example
only.
SUMMARY OF THE INVENTION
[0012] According to a first aspect of the present invention there
is provided a heat pump apparatus including an evaporator means, a
control means in communication with at least one sensor means
adapted to measure one or more variables representative of a
temperature of an outer surface of said evaporator means, and a
heat exchanger means operable to add heat from a working fluid from
a high pressure side of said heat pump apparatus to said working
fluid entering said evaporator, wherein said control means is
operatively connected with said heat exchanger means to add said
heat when said control means determines that said temperature of
said outer surface of said evaporator means is below a pre-selected
temperature, thereby reducing or substantially eliminating
formation of ice on said outer surface of said evaporator.
[0013] Preferably, said heat exchanger means includes a helically
corrugated tube positioned within an outer housing, said working
fluid from said high pressure side being caused to flow through
said tube to add heat to said working fluid caused to flow over
said tube and between said tube and said outer housing.
[0014] Optionally, said at least one sensor means includes a
temperature sensor adapted to measure the temperature of said outer
surface of said evaporator.
[0015] Optionally, said at least one sensor means includes a
temperature sensor adapted to measure the temperature of the
working fluid exiting the evaporator.
[0016] Optionally, said at least one sensor means includes a
temperature sensor adapted to measure the temperature of the
environment surrounding the evaporator.
[0017] Optionally, said at least one sensor means includes a
pressure sensor adapted to measure the pressure of the working
fluid exiting the evaporator.
[0018] Optionally, said heat exchanger means includes an electric
heating element.
[0019] Optionally, said heat exchanger means obtains heat from said
working fluid between a compressor and a condenser of said heat
pump apparatus to transfer said heat to said working fluid entering
said evaporator means.
[0020] Optionally, said pre-selected temperature is between about
4.degree. C. and 0.degree. C.
[0021] According to a second aspect of the present invention there
is provided a heat pump apparatus including an evaporator means, a
control means in communication with at least one sensor means
adapted to measure one or more variables representative of a
temperature of an outer surface of said evaporator means, and a
heat exchanger means including a heating element positioned
upstream of said evaporator means and downstream of an expansion
means of said heat pump, the heat exchanger means operable to add
heat to a working fluid entering said evaporator, wherein said
control means is operatively connected with said heat exchanger
means so that when said control means determines that said
temperature of said outer surface of said evaporator means is below
a pre-selected temperature the heat exchanger means adds heat to
said working fluid thereby reducing or substantially eliminating
formation of ice on said outer surface of said evaporator and
wherein said heat exchanger means includes a helically corrugated
tube positioned within an outer housing and said working fluid
being heated is caused to flow over said tube and between said tube
and said outer housing.
[0022] Optionally the helical tube includes said heating elements
extending there through.
[0023] Optionally the helical tube forms part of the heating
element.
[0024] Optionally, said at least one sensor means may include a
temperature sensor adapted to measure the temperature of said outer
surface of said evaporator.
[0025] Optionally, said at least one sensor means may include a
temperature sensor adapted to measure the temperature of the
working fluid exiting the evaporator.
[0026] Optionally, said at least one sensor means may include a
temperature sensor adapted to measure the temperature of the
environment surrounding the evaporator.
[0027] Optionally, said at least one sensor means may include a
pressure sensor adapted to measure the pressure of the working
fluid exiting the evaporator.
[0028] Optionally, said heat exchanger means may transfer heat from
the working fluid on the high pressure side of said heat pump
apparatus to the working fluid entering said evaporator.
[0029] Optionally, said heat exchanger means may transfer heat from
the working fluid between said compressor and said condenser to the
working fluid entering said evaporator.
[0030] Optionally, said working fluid may be returned to between
said condenser and said expansion device after it has passed
through said heat exchanger.
[0031] Optionally, said pre-selected temperature may be between
4.degree. C. and 0.degree. C.
[0032] According to a third aspect of the present invention there
is provided a method of operating a heat pump having an evaporator
means downstream of an expansion means, the method including adding
heat as required from a working fluid from a high pressure side of
said heat pump to said working fluid, from a low pressure side of
said heat pump, prior to said working fluid entering said
evaporator means, to reduce or substantially prevent ice from
forming on an outer surface of said evaporator means.
[0033] Optionally the method includes passing said working fluid
through a heat exchanger and providing for the heat exchanger a
helically corrugated tube over which the working fluid can flow as
it is heated.
[0034] Optionally, the method includes measuring one or more
variables representative of a temperature of an outer surface of
said evaporator means and adding said heat to the working fluid
entering said evaporator when said one or more variables indicate
that said temperature has dropped below a pre-selected minimum.
[0035] Optionally, the method includes providing a controller to
determine when icing of said evaporator means is imminent based on
said measurements of said one or more variables.
[0036] Optionally, the method includes heating the working fluid
entering said evaporator means with an electric heating
element.
[0037] Optionally, the method includes heating the working fluid
entering the evaporator means with heat from said working fluid
between a compressor and a condenser of said heat pump.
[0038] Optionally, the method includes adding said heat to said
working fluid while said heat pump is in operation.
[0039] According to a fourth aspect of the present invention, a
heating apparatus for a fluid circuit includes a heat exchanger
means operable to add heat to a fluid flowing in said circuit, at
least one sensor means adapted to measure one or more variables
representative of a temperature of said fluid, a control means in
communication with said at least one sensor means and operatively
connected with said heat exchanger means to add heat to said fluid
when said control means determines that said temperature is below a
pre-selected temperature.
[0040] According to a fifth aspect of the present invention, a heat
pump and/or a method of operating a heat pump and/or a heating
apparatus is substantially as herein described with reference to
the accompanying drawings.
[0041] Further aspects of the present invention, which should be
considered in all its novel aspects, will become apparent from the
following description, given by way of example only and with
reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0042] FIG. 1: Is a schematic diagram of a heat pump apparatus
according to one possible embodiment of the present invention;
[0043] FIG. 2A: Is a very diagrammatic cross-sectional view through
a heat exchanger and heating element according to one possible
embodiment of the present invention, with the spacing between the
corrugated conduit and the outer layer of the heating element
exaggerated for clarity;
[0044] FIG. 2B: Is a very diagrammatic cross-sectional view through
a heat exchanger and heating element according to another possible
embodiment of the present invention;
[0045] FIG. 3: Is a schematic diagram of a heat pump apparatus
according to a further possible embodiment of the present
invention, with two alternative flow paths for the refrigerant
shown;
[0046] FIG. 4: Shows very diagrammatically, and in part a cross
section, a heat exchanger for possible use with the present
invention;
[0047] FIG. 5: Shows very diagrammatically, and in part a cross
section, an alternative embodiment of a heat exchanger for use in
the present invention;
[0048] FIG. 6: Shows very diagrammatically, and in part a cross
section, a further possible embodiment of a heat exchanger for use
in the present invention;
[0049] FIG. 7A: Shows very diagrammatically, and in part cross
section, a prior art heat exchanger for possible use with the
present invention;
[0050] FIG. 7B: Shows very diagrammatically a cross sectional view
of the heat exchanger of FIG. 7A.
BRIEF DESCRIPTION OF POSSIBLE EMBODIMENTS OF THE INVENTION
[0051] Referring first to FIG. 1, a heat pump apparatus in
accordance with one possible embodiment of the present invention is
generally referenced 100. The heat pump 100 is illustrated with
reference to its use as a heating circuit for heating water, but it
is to be appreciated that the invention may also be used in
applications where refrigeration or air conditioning are
required.
[0052] The heat pump includes a compressor 1, condenser 2, an
expansion means, for example an expansion valve 3, and an
evaporator 4, in the same order and performing the same functions
as those of the heat pumps of the prior art. A receiver and/or
accumulator (not shown) may also be present as required. The
condenser 2 provides heat to a suitable medium, for example a
domestic hot water supply 5, the water flow being indicated by the
upper arrows shown entering and leaving the condenser 2.
[0053] References herein to the "high pressure" side of the heat
pump refer to that part of the circuit which the working fluid or
"refrigerant" passes through between the compressor 1 and the
expansion valve 3. References to the "low pressure" side of the
heat pump refer to the remainder of the heat pump circuit.
[0054] According to one embodiment of the present invention the
heat pump 100 further includes a heat exchanger 6 shown located
immediately downstream of the expansion valve 3 and upstream of the
evaporator 4.
[0055] A controller 8, for example a computer or microprocessor,
but more preferably a Programmable Logic Controller (PLC), monitors
one or more variables which allow it to predict that icing of the
evaporator 4 is about to occur. Preferably, icing may be predicted
by determining that the temperature of an exterior surface of the
evaporator 4 is below a predetermined temperature, for example
between 4.degree. C. and 0.degree. C.
[0056] The temperature of the exterior surface of the evaporator 4
may be determined by direct measurement or may be calculated
through measurements of other variables, for example through use of
a lookup table.
[0057] The variables measured may include one or more of the
temperature of the ambient air around the evaporator 4, the
temperature of the refrigerant leaving the evaporator 4, the
surface temperature of the evaporator 4 or the pressure of the
refrigerant leaving the evaporator 4, this pressure known as the
"suction pressure" being well known as having a direct relationship
to the icing of the evaporator of a heat pump. Other variables may
also be monitored as will be apparent to those skilled in the art.
FIG. 1 shows a sensor 10 monitoring the temperature of the
refrigerant leaving the evaporator 4 and communicating information
related to the temperature to the controller 8.
[0058] When the variable(s) sensed by the controller 8 is/are
indicative of a state in which ice may form on the evaporator 4,
that is, on an exterior surface of the evaporator coils (not
shown), the controller 8 may activate the electric heating element
7, thereby heating the refrigerant entering the evaporator 4. This
may be continued until the variables sensed by the controller 8
reach a threshold at which ice formation is no longer likely. At
this point the controller 8 may switch the heating element 7 off.
The controller 8 may continue to monitor the variables and may
continue to switch the heating element 7 on and off as
required.
[0059] Heating the refrigerant in this way may avoid icing of the
evaporator 4 without the need stop the heat pump 100. Those skilled
in the art will appreciate that at least a portion of the energy
added to the system by the heating element 7 may be recovered as
heat from the condenser 2.
[0060] Referring next to FIG. 2, as will be known to those skilled
in the art, a typical electric element 7 includes a resistive
element 12, a heat conducting but electrically resistive material
13 surrounding the resistive element 12, and an outer layer 14. In
the heat exchanger 6 of the present invention a helically
corrugated tube or conduit 15 may be provided over the outer layer
14 in sufficiently close contact to allow conduction of heat from
the outer layer 14 to the conduit 15. The helically corrugated tube
or conduit 15 may preferably be formed using the method described
in the Applicant's PCT specification WO 94/07071, in order to
improve the exchange of heat between the element 7 and the
refrigerant 16.
[0061] In an alternative embodiment of the present invention, as
illustrated in FIG. 2B, a helically corrugated layer 15 may replace
the outer layer 14.
[0062] Referring next to FIG. 3, a second possible embodiment of
the heat pump is shown generally referenced by arrow 200, with
similar reference numerals used for similar features.
[0063] The heat pump 200 also includes a heat exchanger 6a and a
controller 8. The controller 8 may sense the "suction pressure" in
the compressor suction line 9 with a pressure sensor 11, although
other variables may additionally or alternatively be sensed as
described above.
[0064] When the pressure in the suction line 9 falls below a
pre-selected minimum, the controller 8 may allow hot refrigerant
from the high pressure side of the heat pump to flow through an
intake pipe 17 to the heat exchanger 6a, thereby heating the
refrigerant immediately upstream of the evaporator 4 and preventing
ice from forming on the evaporator 4.
[0065] The hot refrigerant may be taken from anywhere on the high
pressure side of the cycle, but preferably from between the
compressor 1 and condenser 2, where the refrigerant is at its
highest temperature. The hot fluid is preferably returned via an
outlet pipe 18 to the downstream side of the condenser 2 after
passing through the heat exchanger 6a, although in some embodiments
the fluid may be returned to substantially the same point in the
cycle after passing through the heat exchanger 6a, as illustrated
in outline by outlet pipe 18a.
[0066] When the controller 8 determines that icing is no longer
imminent the flow of hot refrigerant to the heat exchanger 6a may
be ceased to allow the apparatus 200 to perform at maximum
efficiency. In a preferred embodiment the controller 8 may be a
simple mechanical valve which is activated by changes in the
pressure of the compressor suction line 9.
[0067] Referring now to FIG. 4 of the accompanying drawings, this
shows very diagrammatically a heat exchanger for suitable use in
the present invention and with corresponding reference numerals as
those used in the previous drawings being also used. The heat
exchanger 6 is shown having an outer housing or sleeve 20 provided
with an inlet 21 and an outlet 22 for the flow in a direction
indicated by arrows X of the refrigerant to be heated. Within the
outer housing or sleeve 20 is shown a helically corrugated tube or
conduit 15 defining a refrigerant flow passage 16 between the tube
15 and the outer housing or sleeve 6. An electric element 12 is
shown extending through the helical tube 15 with electrical
connections 17 and 18. Typically, surrounding the electric element
12 will be a core of magnesium oxide or the like. The helical tube
15 of FIG. 4 and the subsequent FIGS. 5 and 6 may suitably be
manufactured in accordance with the applicant's PCT specification
WO 94/07071.
[0068] Turning then to FIG. 5, in an alternative embodiment of heat
exchanger 6, a helically corrugated tube or conduit 15 is again
provided within an outer housing or sleeve 20 to provide the
helical flow path 16 for the refrigerant flowing in the direction
of arrows X. However, the helical tube 15 may, in this embodiment,
form part of the electrical heating element and be part of the
electrical circuit between terminals 18 and 17, so as to provide a
direct heating of the refrigerant flowing over the helical
corrugated surface.
[0069] Referring then to FIG. 6, in a further embodiment a working
fluid will be caused to flow in a direction indicated by arrows B
through the helical tube 15, the fluid being at an elevated
temperature so as to provide a heat energy transfer through the
helically corrugated tube 15 to the refrigerant flowing in the
direction of arrows X-X.
[0070] This embodiment of heat exchanger 6 will be of particular
use in the embodiment of FIG. 3.
[0071] Referring then to an alternative form of heat exchanger as
shown in FIG. 7, this type of heat exchanger is disclosed in WO
98/27395 and is again shown with an outer housing or sleeve 20
providing an inlet 21 and an outlet 22 for refrigerant flow in a
direction of arrows X. Within the outer sleeve 20 is shown a tube
or conduit 23 with corrugations 24 which in this example are
indicated as extending longitudinally along the axis of the heat
exchanger 6. An electric heating element 12 is shown extending
through the tube or conduit 23 as shown in FIG. 7B. A barrier 25
extends the length of the heat exchanger 6 so that the refrigerant
must traverse both circumferentially and longitudinally about the
tube or conduit 23 between the inlet and outlet 21 and 22 to
maximize heat transfer.
[0072] Those skilled in the art will appreciate that the
embodiments shown in FIGS. 1 and 3 may be combined as necessary,
and the controller 8 may determine whether to use either heating
method alone or both in combination.
[0073] Those skilled in the art will also appreciate that by
preventing ice from forming on the evaporator 4 without stopping
the refrigerant flow, the present invention may be more efficient
than the heat pumps of the prior art when used in environments
where icing of the evaporator may occur, for example those in which
the ambient temperature drops below around 10.degree. C.
[0074] Also it will be appreciated that the present invention could
be used in numerous other situations for the heating of a fluid. It
is envisaged, for example, that liquid petroleum gas (LPG) being
removed from an LPG cylinder could be heated using a heat
exchanger, such as shown in FIG. 4, 5 or 6 for example. In this way
the LPG can be converted to a gas external of the LPG cylinder
which could otherwise be in danger of freezing if LPG is drawn off
at too fast a rate. Alternatively, a compressed gas could be heated
before it is released so as to avoid the unwanted cooling of the
gas at its lowering of pressure. Further, a fluid in a hydraulic
circuit or engine could be heated when required to thin it and
lower its viscosity which can be of benefit such as in the starting
of diesel engines for example. Also, the present invention could be
used in refrigeration circuits such as of a domestic or commercial
refrigerator.
[0075] Where in the foregoing description, reference has been made
to specific components or integers of the invention having known
equivalents then such equivalents are herein incorporated as if
individually set forth.
[0076] Although this invention has been described by way of example
and with reference to possible embodiments thereof, it is to be
understood that modifications or improvements may be made thereto
without departing from the scope of the invention as defined in the
appended claims.
* * * * *