U.S. patent application number 12/811731 was filed with the patent office on 2011-01-13 for methods and apparatuses for operating heat pumps in hot water systems.
This patent application is currently assigned to DUX MANUFACTURING LIMITED. Invention is credited to Patrick Pussell.
Application Number | 20110005245 12/811731 |
Document ID | / |
Family ID | 40912151 |
Filed Date | 2011-01-13 |
United States Patent
Application |
20110005245 |
Kind Code |
A1 |
Pussell; Patrick |
January 13, 2011 |
METHODS AND APPARATUSES FOR OPERATING HEAT PUMPS IN HOT WATER
SYSTEMS
Abstract
A method for operating a heat pump (100) in low ambient air
temperatures comprises periodically or temporarily halting flow of
refrigerant through an evaporator (170) of the heat pump (100) and
providing forced airflow across the evaporator (170) while the
refrigerant flow is halted. The method enables operation of the
heat pump (100) at low ambient temperatures and provides a means
for de-icing the evaporator (170) when operating at low ambient
temperatures. The method is particularly applicable to heat pumps
having an evaporator located outdoors, such as domestic and
industrial water heating systems.
Inventors: |
Pussell; Patrick; (Pyrmont
New South Wales, AU) |
Correspondence
Address: |
LADAS & PARRY
5670 WILSHIRE BOULEVARD, SUITE 2100
LOS ANGELES
CA
90036-5679
US
|
Assignee: |
DUX MANUFACTURING LIMITED
Moss Vale New South Wales
AU
|
Family ID: |
40912151 |
Appl. No.: |
12/811731 |
Filed: |
December 19, 2008 |
PCT Filed: |
December 19, 2008 |
PCT NO: |
PCT/AU2008/001884 |
371 Date: |
September 27, 2010 |
Current U.S.
Class: |
62/89 ; 62/186;
62/228.1; 62/238.6 |
Current CPC
Class: |
Y02B 40/00 20130101;
Y02B 40/32 20130101; F25B 2600/112 20130101; F25B 2600/23 20130101;
F25B 2700/2106 20130101; F24D 11/0214 20130101; Y02B 30/70
20130101; F25B 2600/0251 20130101; F25B 2339/047 20130101; F25B
2500/31 20130101; F25D 21/125 20130101; Y02B 30/743 20130101; F24D
19/1039 20130101; F25B 30/02 20130101 |
Class at
Publication: |
62/89 ; 62/186;
62/228.1; 62/238.6 |
International
Class: |
F25D 17/06 20060101
F25D017/06; F25B 49/02 20060101 F25B049/02; F25B 27/00 20060101
F25B027/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 30, 2008 |
AU |
2008900409 |
Sep 8, 2008 |
AU |
2008904653 |
Claims
1. A method for operating a heat pump in low ambient air
temperatures, said method comprising the steps of: periodically
halting flow of refrigerant through an evaporator of said heat
pump; and providing forced airflow across said evaporator while
said refrigerant flow is halted.
2. The method of claim 1, wherein said step of periodically halting
flow of refrigerant through an evaporator comprises the step of
repeatedly turning a compressor of said heat pump off for a first
predetermined time period and on for a second predetermined time
period, said second predetermined time period greater than said
first predetermined time period.
3. The method of claim 1, wherein said method is performed when the
ambient air temperature falls below a predetermined temperature
value.
4. The method of claim 1, wherein said heat pump in used to heat
water in a hot water system and a condenser of said heat pump is
positioned in a heat exchanging relationship with a body of water
in said hot water system.
5. An apparatus comprising: a heat pump circuit comprising a
compressor, a condenser, a pressure-lowering device, and an
evaporator, said heat pump circuit adapted to hold a charge of
refrigerant; a fan adapted to generate airflow across said
evaporator; a temperature sensor adapted to measure ambient air
temperature; and an electronic controller coupled to said
compressor, said fan and said temperature sensor, said electronic
controller adapted to: obtain ambient air temperature values from
said temperature sensor; repeatedly turn said compressor on and off
while said ambient air temperature values are lower than a first
predetermined temperature value; and operate said fan to provide
forced airflow across said evaporator while said compressor is
turned off.
6. The apparatus of claim 5, wherein said electronic controller is
adapted to cyclically operate said compressor by repeatedly turning
said compressor off for a first predetermined time duration and on
for a second predetermined time duration, said second predetermined
time duration greater than said first predetermined time
duration.
7. The apparatus of claim 5, wherein said electronic controller is
further adapted to turn said compressor off an said fan off when
said ambient air temperature values are less than a second
predetermined temperature value.
8. The apparatus of claim 5, wherein said electronic controller is
further adapted to operate said fan and said compressor
continuously while said ambient air temperature values are greater
than or equal to said first predetermined temperature value.
9. The apparatus of claim 5, wherein said pressure-lowering device
comprises a thermostatic expansion valve (TX valve).
10. A hot water system, comprising: a water tank for storing water;
a heat pump circuit comprising a compressor, a pressure-lowering
device, an evaporator, and a condenser in a heat exchanging
relationship with said water in said water tank; a fan adapted to
generate airflow across said evaporator; a first temperature sensor
adapted to determine ambient air temperature; and an electronic
controller coupled to said compressor, said fan and said first
temperature sensor, said electronic controller adapted to: obtain
ambient air temperature values from said temperature sensor;
repeatedly turn said compressor on and off while said ambient air
temperature values are lower than a first predetermined temperature
value; and operate said fan to provide forced airflow across said
evaporator while said compressor is turned off.
11. The hot water system of claim 10, further comprising a second
temperature sensor coupled to said electronic controller and
adapted to determine temperature of water in said water tank, and
wherein said electronic controller is further adapted to: obtain
water temperature values from said second temperature sensor; and
turn off said compressor and said fan when said water temperature
exceeds a third predetermined temperature.
12. The hot water system of claim 10, wherein said electronic
controller is adapted to cyclically operate aid compressor by
repeatedly turning said compressor off for a first predetermined
time duration and on for a second predetermined time duration, said
second predetermined time duration greater than said first
predetermined time duration.
13. The hot water system of claim 10, wherein aid electronic
controller is further adapted to turn said compressor off and said
fan off when said ambient air temperature values are less than a
second predetermined temperature value.
14. The hot water system of claim 10, wherein said electronic
controller is further adapted to operate said fan and said
compressor continuously while said ambient air temperature values
are greater than or equal to said first predetermined temperature
value.
15. The hot water system of claim 10, wherein said
pressure-lowering device comprises a thermostatic expansion valve
(TX valve).
16. A method for operating a heat pump in low ambient air
temperatures, said method comprising the steps of: temporarily
halting flow of refrigerant through an evaporator of said heat
pump; and providing forced airflow across said evaporator while
said refrigerant flow is halted.
17. The method of claim 1, wherein the step of providing forced
airflow comprises forcing airflow onto a side of said evaporator
that is less susceptible to icing.
18. The apparatus of claim 5, wherein said electronic controller is
adapted to control said fan to blow air onto a side of said
evaporator that is less susceptible to icing.
19. The hot water system of claim 10, wherein said electronic
controller is adapted to control said fan to blow air onto a side
of said evaporator that is less susceptible to icing.
20. A method for operating a heat pump in a hot water system, said
method comprising the steps of: providing forced airflow across an
evaporator of said heat pump while said heat pump is operational to
heat water in a tank of said hot water system; and temporarily
halting flow of refrigerant through said evaporator and reversing
the direction of said forced airflow across said evaporator while
ambient air temperature is lower than a predetermined temperature
value.
21. The method of claim 20, wherein said step of temporarily
halting flow of refrigerant through aid evaporator and reversing
the direction of said forced airflow across said evaporator is
performed periodically while said heat pump is operational to heat
water in said tank of said hot water system and ambient air
temperature is lower than a predetermined temperature value.
22. The method of claim 21, wherein said flow of refrigerant
through said evaporator is halted and the direction of said fan is
reversed for a period of approximately 30 minutes every 2
hours.
23. The method of claim 20, wherein the direction of said fan is
reversed to provide forced airflow onto a side of said evaporator
that is less susceptible to icing.
24. A hot water system, comprising: a water tank for storing water;
a heat pump circuit comprising a compressor, a pressure-lowering
device, and evaporator, and a condenser in a heat exchanging
relationship with said water in aid water tank; a fan adapted to
provide forced airflow across said evaporator; a temperature sensor
adapted to determine ambient air temperature; and an electronic
controller coupled to said compressor, aid fan and said temperature
sensor, said electronic controller adapted to: obtain ambient air
temperature values from said temperature sensor; operate said fan
to provide forced airflow across said evaporator while said heat
pump is operational to hot water in said water tank; and
temporarily halt flow of refrigerant through said evaporator and
reverse the direction of said forced airflow across said evaporator
while ambient air temperature is lower than a predetermined
temperature value.
25. The hot water system of claim 24, wherein said electronic
controller adapted to periodically halt flow of refrigerant through
said evaporator and reverse the direction of said forced airflow
across said evaporator while said heat pump is operational to heat
water in said water tank and ambient air temperature is lower than
a predetermined temperature value.
26. The hot water system of claim 25, wherein said flow of
refrigerant through said evaporator is halted and the direction of
said fan is reversed for a period of approximately 30 minutes every
2 hours.
27. The hot water system of claim 24, wherein the direction of said
fan is reversed to provide forced airflow onto a side of said
evaporator that is less susceptible to icing.
Description
RELATED APPLICATIONS
[0001] The present application claims priority from Australian
Provisional Patent Application No. 2008900409, filed on 30 Jan.
2008, and Australian Provisional Patent Application No. 2008904653,
filed on 8 Sep. 2008. The contents of Australian Provisional Patent
Application No. 2008900409 and Australian Provisional Patent
Application No. 2008904653 are incorporated herein by
reference.
FIELD OF THE INVENTION
[0002] The present invention relates to the operation of heat pumps
that may be used in hot water systems and more particularly to the
operation of such heat pumps under low ambient temperature
conditions.
BACKGROUND
[0003] Heat pumps are devices or systems that move heat from a
`source` location to a `sink` location using work. Heat pumps
operate by exploiting the physical properties of an evaporating and
condensing fluid known as a refrigerant. The refrigerant, in a
pressurised gaseous state, is circulated through the heat pump
circuit by a compressor. On the discharge side of the compressor,
hot and highly pressurised gas is cooled in a heat exchanger known
as a condenser until the gas condenses into a high pressure liquid
at a relatively more moderate temperature. The condensed
refrigerant then passes through a pressure-lowering device such as
a thermostatic expansion valve or capillary tube, which passes the
low pressure, barely liquid, refrigerant to another heat exchanger,
known as an evaporator, where the refrigerant evaporates into a gas
via heat absorption. The refrigerant is then returned to the
compressor and the cycle is repeated.
[0004] In a hot water system that employs a heat pump to heat a
body of water, the greater the difference between the water
temperature and the ambient air temperature, the greater the
pressure difference and amount of energy required to compress the
refrigerant fluid. Coefficient of Performance (COP) is a measure
used to describe energy efficiency, that is, the amount of heat
moved per unit of work. COP values are thus relatively higher when
the ambient air temperature is much less or much greater than the
water temperature in a hot water system. When the ambient air
temperature is substantially lower or substantially higher than the
actual or demanded water temperature (i.e., at relatively higher
COP values), the heat pump becomes subject to excessive strain. One
conventional method of operating under such temperature conditions
is to turn off the heat pump and employ a booster (e.g., an
auxiliary electric heating element) to heat the water.
[0005] Another disadvantageous effect that is manifested when the
ambient air temperature is substantially lower than the water
temperature is that moisture in the air condenses and forms ice on
the evaporator. This is particularly significant in hot water
systems on account of the evaporator typically being located
outdoors. Switching to boosted operation, as described above,
ameliorates this problem However, boosters require continuous power
and are contrary to the environmental motivation for using a heat
pump in the first place. Furthermore, electric heating elements are
susceptible to corrosion when installed in the water tank of a hot
water system.
[0006] A need thus exists to provide alternative and/or improved
methods and apparatuses for operating heat pumps under extreme
ambient temperature conditions and particularly under low ambient
temperature conditions.
SUMMARY
[0007] According to one aspect of the present invention, there is
provided a method for operating a heat pump in low ambient air
temperatures. The method comprises the steps of: periodically or
temporarily halting flow of refrigerant through an evaporator of
the heat pump; and providing forced airflow across the evaporator
while the refrigerant flow is halted.
[0008] The step of periodically or temporarily halting flow of
refrigerant through an evaporator may comprise the step of
repeatedly turning a compressor of the heat pump off for a first
predetermined time period and on for a second predetermined time
period. The second predetermined time period is greater than the
first predetermined time period.
[0009] Another aspect of the present invention provides an
apparatus comprising: a heat pump circuit comprising a compressor,
a condenser, a pressure-lowering device, and an evaporator; a fan
adapted to generate airflow across the evaporator; a temperature
sensor adapted to measure ambient air temperature; and an
electronic controller coupled to the compressor, the fan and the
temperature sensor. The heat pump circuit is adapted to hold a
charge of refrigerant. The electronic controller is adapted to:
obtain ambient air temperature values from the temperature sensor;
repeatedly turn the compressor on and off while the ambient air
temperature values are lower than a first predetermined temperature
value; and operate the fan to provide forced airflow across the
evaporator while the compressor is turned off.
[0010] The electronic controller may be adapted to cyclically
operate the compressor by repeatedly turning the compressor off for
a first predetermined time duration and on for a second
predetermined time duration. The second predetermined time duration
is greater than the first predetermined time duration.
[0011] Another aspect of the present invention provides a hot water
system, comprising: a water tank for storing water; a heat pump
circuit comprising a compressor, a pressure-lowering device, an
evaporator, and a condenser in a heat exchanging relationship with
the water in the water tank; a fan adapted to generate airflow
across the evaporator; a first temperature sensor adapted to
determine ambient air temperature; and an electronic controller
coupled to the compressor, the fan and the first temperature
sensor. The electronic controller is adapted to: obtain ambient air
temperature values from the temperature sensor; repeatedly turn the
compressor on and off while the ambient air temperature values are
lower than a first predetermined temperature value; and operate the
fan to provide forced airflow across the evaporator while the
compressor is turned off.
[0012] The hot water system may further comprise a second
temperature sensor coupled to the electronic controller and adapted
to determine temperature of water in the water tank. In this
instance, the electronic controller is further adapted to: obtain
water temperature values from the second temperature sensor; and
turn off the compressor and the fan when the water temperature
exceeds a third predetermined temperature.
[0013] The electronic controller may be adapted to cyclically
operate the compressor by repeatedly turning the compressor off for
a first predetermined time duration and on for a second
predetermined time duration. The second predetermined time duration
is greater than the first predetermined time duration.
[0014] Another aspect of the present invention provides a method
for operating a heat pump in a hot water system. The method
comprises the steps of: providing forced airflow across an
evaporator of the heat pump while the heat pump is operational to
heat water in a tank of the hot water system; and temporarily
halting flow of refrigerant through the evaporator and reversing
the direction of the forced airflow across the evaporator while
ambient air temperature is lower than a predetermined temperature
value. The step of temporarily halting flow of refrigerant through
the evaporator and reversing the direction of the forced airflow
across the evaporator may be performed periodically while the heat
pump is operational to heat water in the tank of the hot water
system and ambient air temperature is lower than a predetermined
temperature value. The flow of refrigerant through the evaporator
may be halted and the direction of the fan reversed for a period of
approximately 30 minutes every 2 hours. The direction of the fan
may be reversed to provide forced airflow onto a side of the
evaporator that is less susceptible to icing.
[0015] Another aspect of the present invention provides a hot water
system comprising: a water tank for storing water; a heat pump
circuit comprising a compressor, a pressure-lowering device, an
evaporator, and a condenser in a heat exchanging relationship with
said water in the water tank; a fan adapted to provide forced
airflow across the evaporator; a temperature sensor adapted to
determine ambient air temperature; and an electronic controller
coupled to the compressor, the fan and the temperature sensor. The
electronic controller is adapted to: obtain ambient air temperature
values from the temperature sensor; operate the fan to provide
forced airflow across the evaporator while the heat pump is
operational to heat water in the water tank; and temporarily halt
flow of refrigerant through the evaporator and reverse the
direction of the forced airflow across the evaporator while ambient
air temperature is lower than a predetermined temperature
value.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] Embodiments are described hereinafter, by way of example
only, with reference to the accompanying drawings in which:
[0017] FIG. 1 is a schematic block diagram of an embodiment of a
heat pump;
[0018] FIG. 2 is a flow diagram of a method for operating a heat
pump, such as the heat pump of FIG. 1, in a hot water system;
[0019] FIG. 3 is a schematic block diagram of an electronic
controller for operating a heat pump, such as the heat pump of FIG.
1; and
[0020] FIG. 4 is a schematic block diagram of another embodiment of
a heat pump.
DETAILED DESCRIPTION
[0021] Embodiments of methods and apparatuses are described
hereinafter for operating a heat pump under low ambient temperature
conditions. Although the embodiments are described with reference
to a heat pump used to heat water in a hot water system, it is not
intended to limit the present invention in this manner. For
example, the embodiments described hereinafter may have application
for operating heat pumps used for other purposes such as heating
systems for buildings (e.g., reverse cycle air conditioning).
[0022] References to hot water systems in this specification are
intended to include both domestic and industrial water heating
systems.
[0023] FIG. 1 shows an embodiment of a heat pump 100. Referring to
FIG. 1, the heat pump 100 has a heat pump circuit comprising an
evaporator 170, a compressor 150, a condenser 140 and a pressure
reducing device 130 such as a thermostatic expansion valve (TX
valve). The heat pump circuit is configured such that the outlet of
the compressor 150 is coupled to an inlet of the condenser 140, an
outlet of the condenser 140 is coupled to the inlet of the pressure
reducing device 130, the outlet of the pressure reducing device 130
is coupled to an inlet of the evaporator 170, and an outlet of the
evaporator 170 is coupled to an inlet of the compressor 150. The
heat pump circuit is adapted to hold a charge of refrigerant that
is circulated through the heat pump circuit by the compressor 150
in a direction shown by the arrows 190. The foregoing components of
the heat pump 100 operate to produce a refrigeration cycle, as is
well known to persons skilled in the art.
[0024] A fan 160 is used to generate airflow 180 across the
evaporator 170. The fan 160 may comprise a single, multi or
variable speed fan. Operation of the compressor 150 and the fan 160
is controlled by an electronic controller 120, which is coupled to
a source of electricity (not shown), typically mains power. A
temperature sensor 110 is also coupled to the electronic controller
120, for determining and providing the electronic controller 120
with ambient temperature values. When the heat pump 100 is used in
a hot water system, the condenser 140 is typically positioned in a
heat exchanging relationship with a body of water contained in a
tank 145 of the hot water system.
[0025] As described hereinbefore, the heat pump 100 may become
subject to excessive strain when the ambient air temperature is
substantially lower or substantially higher than the actual or
demanded water temperature. Furthermore, when the ambient air
temperature is substantially lower than the water temperature,
moisture in the air condenses and forms ice on the evaporator and
other refrigerant bearing components used to couple the evaporator
to the heat pump circuit.
[0026] An embodiment of the present invention provides a method for
operating the heat pump 100 in low ambient air temperatures. The
method comprises temporarily or periodically halting the flow of
refrigerant through the evaporator 170 of the heat pump 100 and
providing forced airflow from the fan 160 across the evaporator 170
while the refrigerant flow is halted. Forced airflow from the fan
160 is preferably provided for the entire duration the refrigerant
flow is halted. However, this is not essential as the forced
airflow may only need to be maintained for a substantial portion of
the time the refrigerant flow is halted. The refrigerant flow
through the evaporator 170 may be halted by switching off the
compressor 150. An effect of halting the flow of refrigerant is
that the forced airflow from the fan 160 causes the static
refrigerant in the evaporator 170 to heat up. This causes the
difference in temperature between the refrigerant and the ambient
air to reduce significantly, which in turn causes any ice build-up
on the evaporator 170 and associated coupling components to melt.
De-icing is assisted by the use of a single wall evaporator
structure.
[0027] In the embodiment described hereinbefore with reference to
FIG. 1, the fan 160 is adapted to draw air to heat the refrigerant
in the evaporator 170. In other words, the direction of forced
airflow as indicated by arrow 180 in FIG. 1 is across the
evaporator 170 towards the fan 160. In this configuration, the
forced airflow first strikes the side of the evaporator 170 that is
most susceptible to icing as a consequence of low ambient
temperature conditions.
[0028] However, the inventor has discovered that operating the fan
160 in the reverse direction to cause forced airflow from the fan
160 towards the side of the evaporator 170 less susceptible to
icing (i.e., forced airflow in a direction opposite to that
indicated by the arrow 180 in FIG. 1) while the flow of refrigerant
through the evaporator 170 is temporarily halted, substantially
improves the efficiency of de-icing as opposed to operating the fan
160 in the direction indicated by the arrow 180 in FIG. 1. This, in
turn, improves the overall heating efficiency of the heat pump
100.
[0029] In one embodiment, the fan 160 is adapted to provide forced
air flow in the direction of arrow 180 during normal (i.e.,
non-de-icing) operation and is reversed during de-icing operation
to provide forced air flow in the direction opposite to arrow
180.
[0030] In another embodiment, the fan 160 may be adapted to always
provide forced airflow in the direction opposite to arrow 180
(i.e., during both normal and de-icing operation). Although the
effect of the moving refrigerant during normal operation (i.e.,
compressor 150 operating) may result in increased icing of the
evaporator 170, the forced airflow may additionally be caused to
pass in close proximity to the compressor 150, thereby providing
forced airflow at an increased temperature which will assist
de-icing.
[0031] FIG. 2 is a flow diagram of a method for operating a heat
pump, such as the heat pump 100 of FIG. 1. The method of FIG. 2 may
be practiced as a computer program executed by the electronic
controller 120 of FIG. 1.
[0032] The method begins at step 210, during which hardware and/or
software of the electronic controller 120 is initialised. For
example, a counter may be initialised for time duration measurement
purposes.
[0033] The main program loop includes step 270 and is executed
approximately once per minute. However, those skilled in the art
will appreciate that other main program loop delay intervals may
alternatively be practiced.
[0034] At step 212, a determination is made whether the ambient air
temperature is less than a predetermined temperature value of
4.degree. C., below which de-icing is performed. If not (N), the
de-icing is not required and normal operation of the heat pump
proceeds at step 220.
[0035] At step 220, a determination is made whether the compressor
is on. If not (N), a determination is made at step 222 whether the
temperature of the water in the water tank of the hot water system
is less than a predetermined value of 53.degree. C. As a
temperature differential typically exists across the water tank and
hot water is drawn off the top of the water tank for consumption
purposes, the water temperature used for the determination in step
222 is preferably the temperature of water near the top of tank
(T.sub.t).
[0036] If the temperature of the water in the water tank of the hot
water system is less than a predetermined value of 53.degree. C.
(Y), the water in the tank requires heating and the compressor and
the fan are both turned on at step 224. Step 224 effectively turns
on the heat pump. The method then proceeds to step 270 of the main
loop. If the water in the tank does not require heating (N), at
step 222, the method proceeds directly to step 270 of the main loop
without turning the heat pump on.
[0037] If the compressor is on (Y), at step 220, a determination is
made at step 226 whether the water temperature at the top of the
water tank of the hot water system (T.sub.t) is greater than a
predetermined value of 58.degree. C. If so (Y), the water in the
tank does not require further heating and the compressor, fan and
counter are turned off at step 228. Step 228 effectively turns off
the heat pump. The method then proceeds to step 270 of the main
loop. If the water in the tank does require further heating (Y), at
step 226, the method proceeds directly to step 270 of the main loop
without turning the heat pump off.
[0038] Returning now to step 212, if the ambient air temperature is
less than a predetermined value of 4.degree. C., de-icing is
required and the method proceeds at step 230. At step 230, a
determination is made whether the ambient air temperature is less
than a predetermined value of -5.degree. C. If so (Y), the heat
pump is effectively turned off from step 232 onwards. A
determination is made, at step 232, whether the compressor is on.
If so (Y), the compressor is turned off at step 234. After waiting
for a delay of 30 minutes at step 236, the counter is turned off at
step 238 and the fan is turned off at step 240. Thereafter, the
method proceeds to step 270 of the main loop. If the compressor is
already off (N), at step 232, the method proceeds directly to step
270 of the main loop.
[0039] If the ambient temperature is not less than the
predetermined value of -5.degree. C. (N), at step 230, de-icing is
performed. A determination is made at step 250 whether the counter
is on. If not (N), the counter is turned on at step 252 and
processing continues at step 220 as described hereinbefore.
However, if the counter is on (Y), at step 250, a determination is
made, at step 254, whether the counter indicates that more than 2
hours has elapsed since last being turned on. If more than 2 hours
have not elapsed (N), processing continues from step 220 as
described hereinbefore. On the other hand, if more than 2 hours
have elapsed (Y), the compressor is turned off at step 256. After
waiting for a delay of 30 minutes at step 258, the counter is
turned off at step 260 and the compressor is turned on again at
step 262. Thereafter, the method proceeds to step 270 of the main
loop.
[0040] As described hereinbefore with reference to FIG. 2, the
compressor is turned on for 2 hours and off for 30 minutes in a
repeating cycle when de-icing is performed (i.e., when the ambient
air temperature is less than 4.degree. C. and greater than or equal
to -5.degree. C. The fan is, however, kept turned on during the
entire de-icing cycle. In ambient air temperatures of 4.degree. C.
or greater, de-icing is not required. In ambient air temperatures
below -5.degree. C., the heat pump is completely turned off (i.e.,
both the compressor and the fan), as heat pump operation in such
low temperatures is not viable.
[0041] Those skilled in the art will appreciate that the values and
ranges (e.g., of temperatures and times) referred to in the
description hereinbefore relating to FIG. 2 are for purposes of
describing a particular embodiment of the present invention only
and that other predetermined values and/or ranges may alternatively
be practiced. For example, de-icing may be performed over a
different range of ambient air temperatures. Furthermore, those
skilled in the art will appreciate that the on and off times for
operating the compressor during de-icing operation may vary from
the 2 hours and 30 minutes, respectively, used in the embodiment of
FIG. 2. Times for de-icing (i.e., compressor on and off times)
depend on humidity and typically range from 15 to 30 minutes.
De-icing can be accelerated by increasing airflow across the
evaporator, which can be implemented by use of a multi-speed fan. A
multi-speed fan may also be used to assist heat pump performance at
high ambient or water temperatures by decreasing airflow and
consequently reducing refrigerant pressure. Forced airflow from the
fan is preferably maintained for the entire duration the compressor
is turned off. However, this is not essential as the forced airflow
may only need to be maintained for a substantial portion of the
time the compressor is turned off.
[0042] As described hereinbefore, the fan may be adapted to blow
air onto the side of the evaporator most susceptible to icing
during de-icing to improve the efficiency of de-icing. This may be
achieved by reversing the direction of the fan during de-icing or
by having the fan blow air onto the inside surface of the
evaporator during normal operation and de-icing.
[0043] FIG. 3 is a schematic block diagram of an embodiment of the
electronic controller 120 in FIG. 1. Control of the heat pump 100
is performed by a software control program resident in the memory
of the microcontroller 310. In one particular embodiment, the
microcontroller 310 comprises a Microchip PIC16F676 CMOS 8-bit
microcontroller. The PIC16F676 has 1,792 bytes of flash-based
program memory, 64 bytes of RAM and 128 bytes of EEPROM and also
includes an on-board 10-bit analog-to-digital (A/D) converter.
However, as would readily be appreciated by those skilled in the
art, other microcontrollers or microprocessors may alternatively be
practiced in the controller 310. Various memory and peripheral
configurations may also be practiced, such as a combination of
on-board and off-board memory.
[0044] The microcontroller 310 controls components of the heat pump
100 via output ports that are interfaced to the devices by means of
input/output interface circuitry 320. In one embodiment, the
compressor 150 and the fan 160 are controlled via relays, which
form part of the input/output interface circuitry 320. However,
alternative control elements may also be practiced, including solid
state switches such as thyristors and triacs. In certain
embodiments, the relays or control elements for the fan enable
reversing of the direction of the fan.
[0045] The microcontroller 310 obtains data from components of the
heat pump 100 and/or hot water system via input ports that are
interfaced to the devices by means of input/output interface
circuitry 320. For example, ambient air temperature data is
obtained from the temperature sensor 110 of FIG. 1. Furthermore,
the microcontroller 310 may also obtain data relating to the
temperature of the water at the top and/or bottom of the hot water
tank 145 (T.sub.t and T.sub.b, respectively) from temperature
sensors (not shown in FIG. 1) coupled via the input/output
interface circuitry to input ports of the microcontroller 310.
Thus, the microcontroller 310 is able to control the compressor 150
and the fan 160 in accordance with external variables such as water
temperature, ambient air temperature, etc.
[0046] The microcontroller 310 may also be coupled to an RF
transceiver 350 via an RF communications interface 340 for
receiving information from and/or transmitting information to a
remote entity. Such information may, for example, be used to
remotely monitor system performance (e.g., hot water temperature)
and/or hot water consumption. The RF transceiver 350 may comprise a
communications module for cellular telephone type communication
(e.g., GSM, GPRS or CDMA). Other types of communications
transceivers may alternatively be practiced, which may use
communications channels such as the ultra-high frequency (UHF),
very-high frequency (VHF) or microwave bands. Still further, a
receiver only may be practiced in place of the RF transceiver 350.
The RF transceiver may be used to communicate with fixed or mobile,
hand-held RF communication devices.
[0047] The microcontroller 310 may also be coupled to an RS-232
communications interface 330 to provide a communication link to a
computer apparatus (not shown). Various other types of
communications interfaces may be practiced in place of the RS-232
interface, such as a RS-485 interface, a parallel interface, an
infra-red interface, a Universal Serial Bus (USB) interface, or any
other commonly available or proprietary communications interfaces.
The computer apparatus may comprise a Personal Computer (PC), a
Personal Digital Assistant (PDA), a mobile telephone, or any other
off-the-shelf or proprietary computer apparatus. Parameters for
operation of the controller 310 may be adjusted by, and/or
downloaded to, the controller 310 from such a computer apparatus
via the RS-232 communications interface 330. In certain
embodiments, bootstrap loader software installed in the program
memory of the microcontroller 310 enables downloading of new and/or
revised control software to the controller 310 via the RS-232
communications interface 330.
[0048] The microcontroller 310, RF communications interface 340,
the RF transceiver 350 and the RS-232 communications interface 330
are powered by a power supply 360, which typically receives input
power from the mains supply.
[0049] Those skilled in the art will appreciate that electronic
controller described hereinbefore with reference to FIG. 3 is an
example of an electronic controller that may be used to practice
embodiments of the present invention. Various other types of
electronic controllers may alternatively be practiced, including an
electronic circuit that does not include a microprocessor or
microcontroller.
[0050] FIG. 4 shows another embodiment of a heat pump 400. The heat
pump 400 is similar to the heat pump 100 of FIG. 1 in that
components having the same reference designators in FIGS. 1 and 4
are similar or substantially identical. For example, the evaporator
170, the fan 160, the compressor 150, the condenser 140 and the
pressure reducing device 130 in FIGS. 1 and 4 are equivalent or
similar in functionality. However, the fan 160 in the embodiment of
FIG. 4 is adapted to blow air in the direction of the arrow 480
towards the evaporator 170. The evaporator 170 comprises two main
operational sides or surfaces for heat exchanging, namely sides 172
and 174. One of the sides is generally more susceptible to icing,
for example, on account of being exposed to lower ambient
temperatures. The forced airflow from the fan 160 strikes the side
174 of the evaporator 170 that is less susceptible to icing. That
is, the side 172 of the evaporator 170 is more susceptible to
icing.
[0051] In a particular embodiment, the fan 1670 is operated to blow
air in the direction of the arrow 480 for a 0.5 hour period every 2
hours to perform de-icing. However, those skilled in the art will
appreciate that other periods and/or values may alternatively be
practiced.
[0052] In certain embodiments of the present invention, the fan 160
is typically only turned on to provide forced airflow across the
evaporator 170 during water heating to heat the refrigerant in the
evaporator 170. However, when the ambient air temperature drops
lower than a predetermined temperature value (e.g., 8.degree. C.),
icing of the evaporator 170 becomes possible. As a consequence, the
flow of refrigerant through the evaporator 170 is temporarily
halted (e.g., the compressor 150 is turned off) and the direction
of the fan 160 is temporarily reversed (e.g., to provide or direct
forced airflow in the direction of arrow 480 in FIG. 4). Halting
the flow of refrigerant through the evaporator 170 and reversing
the direction of the fan 160 (i.e., the direction of forced airflow
across the evaporator 170) is typically performed periodically
while the heat pump is operational to heat water in the tank of the
hot water system and the ambient air temperature is lower than the
predetermined temperature value.
[0053] In a particular embodiment, flow of refrigerant through the
evaporator 170 is halted and the direction of the fan 160 is
reversed for a period of approximately 30 minutes every 2
hours.
[0054] During the period in which the direction of the fan 160 is
reversed, forced airflow is provided or directed onto a side of the
evaporator 170 that is less susceptible to icing (e.g., with
reference to FIG. 4, the direction of forced airflow indicated by
the arrow 480 onto the side 174 of the evaporator 170 that is less
susceptible to icing, compared to the side 172 of the evaporator
170 that is more susceptible to icing).
[0055] Embodiments described hereinbefore advantageously enable
operation of a heat pump at low ambient temperatures. Embodiments
described hereinbefore also provide a means for de-icing components
of a heat pump (e.g., an evaporator), when operating at low ambient
temperatures. A significant advantage of the embodiments described
is that no supplementary de-icing equipment or energy is required.
The embodiments are particularly applicable to heat pumps having an
evaporator located outdoors, such as domestic and industrial water
heating systems.
[0056] The foregoing detailed description provides exemplary
embodiments only, and is not intended to limit the scope,
applicability or configurations of the invention. Rather, the
description of the exemplary embodiments provides those skilled in
the art with enabling descriptions for implementing an embodiment
of the invention. Various changes may be made in the function and
arrangement of elements without departing from the spirit and scope
of the invention as set forth in the claims hereinafter. Where
specific features, elements and steps referred to herein have known
equivalents in the art to which the invention relates, such known
equivalents are deemed to be incorporated herein as if individually
set forth. Furthermore, features, elements and steps referred to in
respect of particular embodiments may optionally form part of any
of the other embodiments unless specifically stated to the
contrary.
[0057] In the context of this specification, the word "comprising"
means "including principally but not necessarily solely" or
"having" or "including", and not "consisting only of". Variations
of the word "comprising", such as "comprise" and "comprises" have
correspondingly varied meanings.
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