HEAT PUMP SYSTEM AND METHOD FOR HEATING A FLUID

SYSTEME DE POMPE A CHALEUR ET PROCEDE DE CHAUFFAGE D'UN FLUIDE

English Abstract

This invention relates to a heat pump system and in particular to a heat pump
system and method for heating a fluid. According to one aspect of the
invention, there is provided a heat pump system for heating a fluid, said
system including: an evaporator for extracting heat from a heat source to
vaporise a refrigerant; a compressor fluidly connected to said evaporator for
compressing said refrigerant vapour; a condenser fluidly connected to said
compressor for transferring heat from said compressed refrigerant to said
fluid; a main expansion device fluidly connecting said condenser to said
evaporator for reducing the temperature of the refrigerant; means for
diverting and reducing the temperature of a portion of said refrigerant from
said condenser, and means for fluidly injecting said temperature reduced
refrigerant portion into said compressor such that said temperature reduced
refrigerant portion mixes with said refrigerant vapour at an intermediate
pressure and induces at least quasi-two- stage compression of said refrigerant
vapour and said refrigerant portion for discharge into said condenser.
According to another aspect of the invention, there is provided a method for
heating a fluid, said method including the steps of: extracting heat from a
heat source to vaporise a refrigerant; compressing said refrigerant vapour to
increase its temperature; transferring heat from said compressed refrigerant
vapour to said fluid; diverting and reducing the temperature of a portion of
said refrigerant after said transferring step; reducing the temperature of
said refrigerant; introducing said temperature reduced refrigerant portion
during said compressing step such that said temperature reduced refrigerant
portion mixes with said refrigerant vapour at an intermediate pressure and
induces at least quasi-two- stage compression of said refrigerant vapour and
said refrigerant portion, and discharging said compressed refrigerant to
transfer heat to said fluid in said transferring step.

French Abstract

Cette invention se rapporte à un système de pompe à chaleur et, en particulier, à un système de pompe à chaleur et à un procédé destiné à chauffer un fluide. Conformément à un aspect de l'invention, il est fourni un système de pompe à chaleur destiné à chauffer un fluide, ledit système incluant : un évaporateur destiné à extraire de la chaleur d'une source de chaleur afin de vaporiser un réfrigérant, un compresseur raccordé par fluide au dit évaporateur afin de comprimer ladite vapeur de réfrigérant, un condenseur raccordé par fluide au dit compresseur afin de transférer la chaleur depuis ledit réfrigérant comprimé vers ledit fluide, un dispositif principal de dilatation raccordant ledit condenseur au dit évaporateur afin de réduire la température du réfrigérant, un moyen destiné à dériver et à réduire la température d'une partie dudit réfrigérant à partir dudit condenseur et un moyen destiné à injecter par fluide ladite partie de réfrigérant à température réduite dans ledit compresseur de sorte que ladite partie de réfrigérant à température réduite se mélange à ladite vapeur de réfrigérant à une pression intermédiaire et induise au moins une compression a quasiment deux étages de ladite vapeur de réfrigérant et de ladite partie de réfrigérant en vue d'une éjection dans ledit condenseur. Conformément à un autre aspect de l'invention, il est fourni un procédé destiné à chauffer un fluide, ledit procédé incluant les étapes consistant à extraire de la chaleur d'une source de chaleur afin de vaporiser un réfrigérant, comprimer ladite vapeur de réfrigérant afin d'augmenter sa température, transférer la chaleur provenant de ladite vapeur de réfrigérant comprimée vers ledit fluide, dériver et réduire la température d'une partie dudit réfrigérant après ladite étape de transfert, réduire la température dudit réfrigérant, introduire à ladite partie de réfrigérant à température réduite pendant ladite étape de compression de telle sorte que ladite vapeur de réfrigérant à température réduite se mélange à ladite vapeur de réfrigérant à une pression intermédiaire et induise au moins une compression a quasiment deux étages de ladite vapeur de réfrigérant et de ladite partie de réfrigérant et éjecter ledit réfrigérant comprimé afin de transférer la chaleur au dit fluide dans ladite étape de transfert.

Claims

-9-
CLAIMS
1. A heat pump system for heating a fluid, said system including:
an evaporator for extracting heat from a heat source to vaporise a
refrigerant;
a compressor fluidly connected to said evaporator for compressing said
refrigerant vapour;
a condenser fluidly connected to said compressor for transferring heat from
said compressed refrigerant to said fluid;
a main expansion device fluidly connecting said condenser to said evaporator
for reducing the temperature of the refrigerant;
means for diverting and reducing the temperature of a portion of said
refrigerant from said condenser, and
means for fluidly injecting said temperature reduced refrigerant portion into
said compressor such that said temperature reduced refrigerant portion mixes
with
said refrigerant vapour at an intermediate pressure and induces at least quasi-
two-
stage compression of said refrigerant vapour and said refrigerant portion for
discharge
into said condenser.
2. A heat pump system for heating a fluid as claimed in claim 1 wherein the
diverting and temperature reducing means includes an expansion device fluidly
connected to the condenser and the compressor.
3. A heat pump system for heating a fluid as claimed in claim 2 wherein the
expansion device includes a capillary tube.
4. A heat pump system for heating a fluid as claimed in claim 2 wherein the
expansion device includes an expansion valve.
5. A heat pump system for heating a fluid as claimed in any one of claim 2 to
4
wherein the expansion device includes a heat exchanger, such as an
intercooler.
6. A heat pump system for heating a fluid as claimed in any one of claims 2 to
5
wherein the diverting and temperature reducing means includes a bypass passage
fluidly connecting the condenser and the expansion device.
7. A heat pump system for heating a fluid as claimed in any one of claims 2 to
6
wherein the fluid injecting means includes a fluid injection valve for
controlling the
flow of the refrigerant portion into the expansion device.

-10-
8. A heat pump system for heating a fluid as claimed in any one of claims 1 to
7
wherein the compressor includes a fluid injection port connected to the fluid
injection
means.
9. A heat pump system for heating a fluid as claimed in claim 8 wherein the
fluid
injection means includes a check valve connected to the fluid injection port.
10. A heat pump system for heating a fluid as claimed in any one of claims 1
to 9
wherein the main expansion device is fluidly connected to the condenser by a
first
pipe.
11. A heat pump system for heating a fluid as claimed in claim 10 wherein the
capillary tube is in close proximity with the first pipe to cool the
refrigerant passing
through the first pipe to the main expansion device.
12. A heat pump system for heating a fluid as claimed in claim 11 wherein the
capillary tube is helically wound around the first pipe.
13. A heat pump system for heating a fluid as claimed in claim 1 wherein the
temperature reducing means includes an expansion device and an intercooler,
said
intercooler fluidly connected to the condenser and the main expansion device
such
that refrigerant passes through the intercooler to the main expansion device
and
exchanges heat with the refrigerant portion passing through the intercooler.
14. A method for heating a fluid, said method including the steps of:
extracting heat from a heat source to vaporise a refrigerant;
compressing said refrigerant vapour to increase its temperature;
transferring heat from said compressed refrigerant vapour to said fluid;
diverting and reducing the temperature of a portion of said refrigerant after
said transferring step;
reducing the temperature of said refrigerant;
introducing said temperature reduced refrigerant portion during said
compressing step such that said temperature reduced refrigerant portion mixes
with
said refrigerant vapour at an intermediate pressure and induces at least quasi-
two-
stage compression of said refrigerant vapour and said refrigerant portion, and
discharging said compressed refrigerant to transfer heat to said fluid in said
transferring step.

-11-
15. A method for heating a fluid as claimed in claim 14 wherein said method
includes the step of returning said refrigerant from said temperature reducing
step to
said vaporising step.
16. A method for heating a fluid as claimed in claim 14 or 15 wherein fluid to
be
heated is water.
17. A method for heating a fluid as claimed in any one of claims 14 to 16
wherein
the heat source is ambient air.

Description

CA 02608688 2007-11-16
WO 2006/122367 PCT/AU2006/000663
-1-
TITLE: HEAT PUMP SYSTEM AND METHOD FOR HEATING A FLUID
FIELD OF THE INVENTION
This present invention relates to a heat pump system and in particular to a
heat
pump system and method for heating a fluid.
The invention has been developed primarily for use as a heat pump system and
a method for water heating in a cold environment or an environment with large
variations in ambient temperature and will be described hereinafter witli
reference to
this application. However, it will be appreciated that the invention is not
limited to
this particular field of use.
BACKGROUND OF THE INVENTION
Any discussion of the prior art throughout the specification should in no way
be considered as an admission that such prior art is wid,ely known or forms
part of the
common general knowledge iri the field.
Sanitary water needs to be heated to a temperature at or above 60 C. Quite
often the water for building heating also needs to be heated to this
temperature. An air
sourced heat pump system has been used for this type of water heating and
conventionally uses an air conditioning compressor. However, owing to the
narrow
operational temperature range of the air conditioning compressor, the
conventional
heat pump system cannot work in envirozltnents with a wide ambient temperature
range, such as an environment where it is very hot in summer but very cold in
winter.
Similarly, the conventional system cannot work where there is a relatively
large
temperature difference between the water and the heat source. For example,
where
the ambient teinperature is constantly low, such as a cold environment.
An approach to overcome this problem is to use a two-stage compression
system, a multi-stage compression system, or a cascade system. However, such
systems require two or more compressors, making the heat pump system
complicated,
expensive, and difficult to make suitable for large variations iri ambient
temperatures.
The compression system also becomes unnecessary when the ambient temperature
is
warm.
In cold environments, fossil fuel burning boilers are frequently used to heat
water with high running costs and adverse effects on the environment.

CA 02608688 2007-11-16
WO 2006/122367 PCT/AU2006/000663
-2-
OBJECTS OF THE INVENTION
It is an object of the present invention to overcome or ameliorate at least
one of
the disadvantages of the prior art, or to provide a useful alternative.
It is an object of the invention in its preferred form to provide a heat pump
system with a compressor which can perform quasi-two-stage compression to
allow
operation in cold environments or environments with large variations in
ambient
temperature and which is simple and inexpensive.
SUMMARY OF THE INVENTION
According to one aspect of the invention, there is provided a heat pump system
1o for heating a fluid, said system including:
an evaporator for extracting heat from a heat source to vaporise a
refrigerant;
a compressor fluidly connected to said evaporator for compressing said
refrigerant vapour;
a condenser fluidly connected to said compressor for transferring heat from
said compressed refrigerant to said fluid;
a main expansion device fluidly connecting said condenser to said evaporator
for reducing the temperature of the refrigerant;
means for diverting and reducing the temperature of a portion of said
refrigerant from said condenser, and
means for fluidly injecting said temperature reduced refrigerant portion into
said compressor such that said temperature reduced refrigerant portion mixes
with
said refrigerant vapour at an intermediate pressure and induces at least quasi-
two-
stage compression of said refrigerant vapour and said refrigerant portion for
discharge
into said condenser.
According to another aspect of the invention, there is provided a method for
heating a fluid, said method including the steps of:
extracting heat from a heat source to vaporise a refrigerant;
compressing said refrigerant vapour to increase its temperature;
transferring heat from said compressed refrigerant vapour to said fluid;
diverting and reducing the temperature of a portion of said refrigerant after
said transferring step;
reducing the temperature of said refrigerant;

CA 02608688 2007-11-16
WO 2006/122367 PCT/AU2006/000663
-3-
introducing said temperature reduced refrigerant portion during said
compressing step such that said temperature reduced refrigerant portion mixes
with
said refrigerant vapour at an iintermediate pressure and induces at least
quasi-two-
stage compression of said refrigerant vapour and said refrigerant portion, and
discharging said compressed refrigerant to transfer heat to said fluid in said
transferring step.
Preferably, the diverting and temperature reducing.means includes an
expansion device fluidly -connected to the condenser and the compressor. The
expansion device preferably includes a capillary tube or an expansion valve.
The
expansion device may further include a heat-exchan.ger, such as an
intercooler.
It is preferred that the diverting and temperature reducing means includes a
bypass passage fluidly connecting the condenser and the expansion device.
The fluid injecting means preferably includes a fluid injection valve for
controlling the flow of the refrigerant portion into the expansion device. The
compressor preferably includes a fluid injection port connected to the fluid
injection
means. It is preferred that the fluid injection means includes a check valve
connected
to the fluid injection port.
The method preferably includes the step of returning said refrigerant from
said
temperature reducing step to said vaporising step.
The main expansion device is preferably fluidly connected to the condenser by
a first pipe. The first pipe is preferably connected to the bypass passage.
The main
expansion device may be an expansion valve.
The capillary tube is preferably in close proximity with the first pipe to
cool
the refrigerant passing through the first pipe to the main expansion device.
In one
preferred form, the capillary tube is helically wound around the first pipe. A
downstream end of the capillary tube may be connected to a section of pipe.
The pipe
section is preferably in contact with the first pipe to transfer heat between
the first
pipe and the pipe section. The pipe section may lie substantially parallel to
the first
pipe and may be fixed to the first pipe by metal clamps or other suitable
fastening
means. Heat transfer paste is preferably interposed between the pipe section
and the
first pipe to facilitate heat transfer. The pipe section is also preferably
deformed to
conform to the first pipe.

CA 02608688 2007-11-16
WO 2006/122367 PCT/AU2006/000663
-4-
Where the temperature reducing means includes an expansion device and an
intercooler, it is preferred that the intercooler is fluidly connected to the
condenser and
the main expansion device so that refrigerant passes through the intercooler
to the
main expansion device and exchanges heat with the refrigerant portion passing
through the intercooler.
The fluid that is to be heated is preferably water. The heat source may be
ambient air.
BRIEF DESCRIPTION OF THE DRAWINGS
A preferred embodiment of the invention will now be described, by way of
example only, with reference to the accompanying drawing, in which:
Figure 1 is a schematic diagram of a heat pump system for heating water
according to the iiivention; and
Figure 2 is a schematic diagram of another embodiment of the invention.
PREFERRED EMBODIMENT OF THE INVENTION
Referring to Figure 1, the heat pump system for heating water includes an
evaporator 1 for vaporising a refrigerant by transferring heat from an ambient
heat
source 3, a compressor 4 fluidly connected to the evaporator 1 for compressing
the
refrigerant vapour and a condenser 5 fluidly connected to the compressor 4 for
transferring heat from the compressed refrigerant to the water 6. The heat
source 3 is
the ambient air of a cold environment and the compressor 4 is a conventional
compressor for low temperature refrigeration with a liquid injection port 7.
An expansion device 8 in the form of a capillary tube is fluidly connected to
the condenser 5 and the compressor 4 to divert a small portion of the
condensed
refrigerant and reduce its temperature. A fluid injection means 9 fluidly
injects the
temperature reduced refrigerant portion into the compressor 4 from the
capillary tube
8. The temperature reduced refrigerant portion mixes with the refrigerant
vapour that
has been compressed to an intermediate pressure in the compressor 4 and
induces at
least quasi-two-stage compression. The combined refrigerant (the refrigerant
vapour
and the refrigerant portion) is then further compressed and discharged into
the
condenser 5.

CA 02608688 2007-11-16
WO 2006/122367 PCT/AU2006/000663
-5-
A main expansion valve 10 is fluidly connected to the condenser 5 by a pipe
11 and to the evaporator 1. A bypass passage 12 diverts the refrigerant
portion from
the pipe 11 to the capillary tube 8.
The fluid injection means 9 includes a fluid injection solenoid valve 13 for
turning liquid injection of the refrigerant portion on and off, and a pipe
section 15 for
delivering the temperature reduced refrigerant portion through a check valve
17 to the
injection port 7 at the compressor 4. The check valve 17 ensures that only the
temperature reduced refrigerant portion enters the compressor 4 and prevents
any
backflow of refrigerant from the compressor 4 through pipe section 15 to the
capillary
tube 8 and the fluid injection solenoid valve 13.
The capillary tube 8 is helically wound around the pipe 11 to cool down the
refrigerant passing through the pipe 11 as it flows towards the main expansion
valve
10. The pipe section 15 is also fixed to a portion 21 of the pipe 11 by metal
clamps
and lies substantial parallel to and in contact with the, pipe portion 21 to
facilitate heat
transfer between the pipe section 15 and the pipe portion 21. Heat transfer
paste is
also applied between the pipe section 15 and the pipe portion 21. The pipe
section 15
can be deformed to conform to the pipe portion 21 to improve heat transfer.
Other elements of the heat pump system include a liquid solenoid valve 23 for
turning the flow of condensed refrigerant on and off and a filter/drier 25
located
between the condenser 5 and the-capillary tube 8. A sight glass 27 is provided
on the
pipe 11 for observing the refrigerant prior to entering the main expansion
valve 10. A
de-ice solenoid valve 29 is also provided in a subsidiary line 31.
The operation of the heat pump system will now be described. Refrigerant in
the evaporator 1 is vaporised using heat extracted from the ambient air 3. The
compressor 4 draws the refrigerant vapour from the evaporator 1 and compresses
it
from a low pressure, low temperature vapour state to a high pressure, high
temperature vapour state. The high pressure, high temperature refrigerant
vapour is
then exhausted to the condenser 5, which acts as a heat exchanger to pass heat
from
the refrigerant vapour to the water 6. As a result of this process, the
refrigerant is
condensed into a liquid and subcooled.
The liquid refrigerant then passes through the liquid solenoid valve 23 and
filter/drier 25 to remove moisture and contaminants from the refrigerant.
After

CA 02608688 2007-11-16
WO 2006/122367 PCT/AU2006/000663
-6-
passing through the filter/drier 25, the majority of the liquid refrigerant
flows through
the pipe 11 to the main expansion valve 10. The liquid refrigerant expands
through
the main expansion valve 10, causing its pressure and temperature to drop. The
temperature of the refrigerant is now below the temperature of the ambient air
3. The
refrigerant then enters the evaporator 1 where heat is again transferred from
the
ambient air 3 to the refrigerant. The vaporised refrigerant is subsequently
drawn into
the compressor 4 and the cycle repeats.
While most of the liquid refrigerant enters the main expansion valve 10, a
small portion of the liquid refrigerant (which may be about 10% of the total
refrigerant) enters the bypass passage 12 from the pipe 11 and passes through
the
liquid injection solenoid valve 13 to capillary tube 8. The capillary tube 8
expands the
refrigerant portion, causing its pressure and temperature to drop. The
temperature
reduced refrigerant portion then passes through the pipe section 15 and the
check
valve 17 to the injection port 7. The refrigerant portion in liquid/vapour
form is then
injected to the compressor 4 to mix with, and cool down, the superheated
refrigerant
vapour in the compressor 4 after quasi-first-stage compression (that is, the
refrigerant
portion is injected into the compressor after the refrigerant vapour has been
compressed to an intermediate pressure). As a result, quasi-second stage
compression
takes place and the combined refrigerant vapour and refrigerant portion is
compressed
to a final pressure. The compressed refrigerant is then discharged into
condenser 5.
Since the refrigerant in the compressor 4 has undergone at least quasi-first-
stage compression, introducing the temperature reduced refrigeration portion
into the
compressor 4 to mix with the superheated refrigerant reduces the temperature
of the
refrigerant prior to the next stage of compression and thus reduces the
temperature in
the compressor for subsequent compressions. This results in the pressure ratio
for
each stage of compression being reduced to the desired level for quasi-two-
stage
coinpression, and thus improves the efficiencies for each compression. Quasi-
two-
stage compression, combined with intercooling in the compressor due to fluid
injection of the refrigerant portion, also reduces the power drawn by the heat
pump
system (compared to single-stage compression). The fluid injection valve 13
and the
check valve 17 controls the timing and direction of the temperature reduced
refrigerant portion that is injected into the compressor 4. Thus, at least
quasi-two-

CA 02608688 2007-11-16
WO 2006/122367 PCT/AU2006/000663
-7-
stage compression can be controllably achieved by a single compressor.
Consequently, there is a significant increase in the difference between the
condensing
temperature and the evaporating temperature, increasing the operating ambient
temperature range of the heat pump system.
In its preferred form, the expansion device 8 is a capillary tube to simplify
the
heat pump system. The capillary tube 8 also permits the temperature reduced
refrigerant portion to be used simply after expansion to absorb heat from the
liquid
refrigerant in the pipe 11 before it enters the main expansion valve 10. As
described
above, the capillary tube 8 is helically wound around the pipe 11 and the pipe
section
15 located substantially parallel to and in contact with the pipe 11. In this
way,
additional subcooling of the refrigerant in the pipe 11 takes place, which
reduces the
risk of the liquid refrigerant flashing prior to entry into the main expansion
valve 10.
While an approximate amount of 10% of the total refrigerant is diverted to the
capillary tube 8 in the embodiment, the amount of the refrigerant portion that
is
diverted depends on the temperature of the ambient heat source and the water
temperature that is required.
While the above description represents a preferred configuration of the
invention, it will be appreciated that components of the system can be varied
in otlier
embodiments.
A second embodiment is illustrated in Figure 2, where corresponding features
have been given the same reference numerals. In the second embodiment, the
expansion device 8 is an expansion valve 33 with an intercooler 35. The
intercooler
35 is fluidly connected to the condenser 5 and the main expansion valve 10.
The
bypass passage 12 is located downstream of the intercooler 35. Liquid
refrigerant
from the condenser 5 enters the intercooler 35. The intercooler 35 initially
cools
down the liquid refrigerant before the refrigerant portion is extracted via
the bypass
passage 12 to the liquid injection valve 13. The refrigerant portion passes
througll
expansion valve 33 to further reduce its temperature and pressure. The
temperature
reduced refrigerant portion is then returned to the intercooler 35 to exchange
heat with
the liquid refrigerant from the condenser 5 passing through the intercooler 35
before
being delivered to the compressor 4. As in the first embodiment, the
refrigerant
portion mixes with the refrigerant vapour in the compressor to induce at least
quasi-

CA 02608688 2007-11-16
WO 2006/122367 PCT/AU2006/000663
-8-
two-stage compression. The liquid refrigerant portion is extracted after
the'intercooler
35 so that the probability of flashing of the refrigerant in both the
expansion valve 33
and the main expansion valve 9 will be reduced.
In other embodiments, multi-stage compression can be induced if required by
injecting additional temperature reduced refrigerant portion(s) after quasi-
second stage
compression.
The compressor may be a refrigeration compressor with one or more liquid
injection ports built in, or any compressor modified to be equipped with
liquid
injection port(s).
The description of the heat pump system has been simplified to assist
understanding of the invention. It will be appreciated that there are other
parts and
control and safety mechanisms in the heat pump system which have been omitted
from the description but do not affect the basic operation of the system in
its preferred
form.
The invention in its preferred form as described above provides an energy
efficient and practical system of water heating, particularly for an air
sourced heat
pump system delivering heat from a cold temperature environment. The invention
in
its preferred form replaces current fossil fuel burning boilers, thereby
reducing any
adverse impact on the environment.
Although the invention has been described with reference to a specific
example it will be appreciated by those skilled in the art that the invention
may be
embodied in many other forms.

Representative Drawing