Heat Pump and Method of Heating Fluid
A heat pump comprising an evaporator, a compressor and a heat exchanger is provided. The evaporator transfers heat from taken in air to a first fluid and expels the taken in air at a temperature cooler than ambient temperature. The compressor compresses and pumps the first fluid. The heat exchanger comprises a first passage for the heated compressed first fluid driven by the compressor and a second passage for a second fluid driven by thermal convection. A heat pump comprising a second heat exchanger that receives heated compressed first fluid from the compressor which heats compressed first fluid from the heat exchanger is also provided. Additionally, methods and systems for heating a fluid are also provided.
The present invention relates to a heat pump and method of heating a fluid. In particular, but not exclusively, the present invention relates to a thermosiphonic heat pump and thermosiphonic method of heating water using heat from the atmosphere.
BACKGROUND TO THE INVENTIONHot water is costly to produce, a cost compounded by the high cost of water heaters. Electric, solar, gas and heat pump water heaters all have disadvantages. Electric hot water systems are undesirable as they have a comparatively high cost of operation and generate considerable pollutants. Solar hot water heaters are expensive, heavily regulated in many countries and they are unable to be used in some sites, such as boutique housing developments, for aesthetic reasons. Solar water heaters usually require a booster energy source such as the non-renewable energy sources of electricity and natural gas which produce pollutants.
Natural gas is another alternative to electric water heaters however these systems also produce harmful greenhouse gases and use a non-renewable energy source.
Another method of providing hot water is heat pumps which extract heat from the surrounding atmosphere using a refrigerant gas and a compressor. Prior art heat pumps are expensive and rely on electricity to power a pump. Further the utility of prior art heat pumps is reduced as they are not capable of operating when the ambient temperature is below 10° C. which makes them unsuitable for many sites or increases their reliance on booster energy sources such as the above-mentioned non-renewable energy sources, electricity and natural gas.
Many of the water heaters in use in homes and other buildings are electric, gas or solar powered, or a combination of these. Replacing all existing hot water tanks would be an enormous cost and would take a long time to gain a favourable energy and pollution cost/benefit ratio. With this in mind it is highly desirable that any alternative for providing less costly hot water has the capacity of fitting to existing water tanks.
In this specification, the terms “comprises”, “comprising” or similar terms are intended to mean a non-exclusive inclusion, such that an apparatus, method or system that comprises a list of elements does not include those elements solely, but may well include other elements not listed.
OBJECT OF THE INVENTIONIt is an object of the present invention to provide a heat pump comprising a thermosiphon which is a useful commercial alternative to existing heat pumps. Further objects will be evident from the foregoing description.
SUMMARY OF THE INVENTIONIn one form, although it need not be the only or indeed the broadest form, the invention resides in a heat pump comprising an evaporator that transfers heat from taken in air to a first fluid and expels the taken in air at a temperature cooler than ambient temperature, a compressor for compressing and pumping the first fluid and an improved heat exchanger, the improvement residing in the improved heat exchanger comprising a first passage for the heated compressed first fluid driven by the compressor and a second passage for a second fluid driven by thermal convection.
The inventors' novel utilization of thermosiphon technology to drive the passage of the second fluid eliminates the need for a pump to pump the second fluid which has the advantages of reducing cost, reducing energy usage and reducing both noise and green house gas pollution.
In one aspect the taken in air is heated above ambient temperature by heat generated by normal operation of the evaporator and heat is transferred from the heated taken in air to the first fluid.
In another aspect the heat pump also comprises a second heat exchanger comprising a third passage for heated compressed first fluid from the compressor and a fourth passage for compressed first fluid from the heat exchanger that has exchanged heat with the second fluid.
In still another aspect the invention further includes a storage tank filled with the second fluid.
Unlike prior art heat pumps the heat pump of the invention is capable of operating below 10° C. and even below 0° C.
In a second form the invention resides in a water heater comprising a tank and a heat pump, the heat pump comprising an evaporator that transfers heat from taken in air to a first fluid and expels the taken in air at a cooler temperature, a compressor for compressing and pumping the heated first fluid and an improved heat exchanger, the improvement residing in the heat exchanger comprising a first passage for the heated compressed first fluid driven by the compressor and a second passage for a second fluid driven by thermal convection.
In another form, the invention resides in a method of heating water including the steps of:
taking ambient air in through an evaporator;
heating a first fluid in the evaporator with the taken in air;
expelling the taken in air as relatively cool air;
compressing the heated first fluid;
pumping the heated compressed first fluid through a heat exchanger; and
heating water in the heat exchanger by exchanging heat from the heated compressed first fluid to the water whereby passage of the water is driven by thermal convection.
Further features of the present invention will become apparent from the following detailed description.
By way of example only, preferred embodiments of the invention will be described more fully hereinafter with reference to the accompanying drawings in which like reference numerals refer to like elements, wherein:
Referring to
The evaporator 2 as best seen in
Advantageously, in one embodiment, like that shown in
The compressor 3 compresses the heated first fluid which has the effect of further heating the first fluid. The heated compressed first fluid is then pumped, by compressor 3, from the compressor 3 to the heat exchanger 4.
It is understood that the first fluid may be gas or liquid and phase depends on pressure and temperature. Therefore the phase of the first fluid is dependent on the temperature and pressure at each point in the heat pump 1. However, for ease of description, from exiting the compressor 3 until entering the evaporator 2 the first fluid will be referred to as “compressed first fluid” and from exiting the evaporator 2, where it is decompressed, until entry into the compressor 3 the first fluid will be referred to as “first fluid”. In a preferred embodiment the first fluid is a refrigerant.
The coaxial arrangement of the outer tube 7 and the inner tube 8 depicted in
The heated compressed first fluid entering the outer tube 7 exchanges heat with the second fluid and exits the outer tube 7 as cool compressed first fluid. The second fluid enters the inner tube 8 as relatively cool second fluid and exits the inner tube 8 as heated second fluid.
The cool compressed first fluid is pumped out of the outer tube 7 and returns to the evaporator 2 where it is decompressed. After decompression the cool first fluid is again heated in the evaporator 2 by taken in air and the above-described heat-exchange process continues in a cycle with the cycling of the first fluid driven by the compressor 3 and the passage of the second fluid driven by convection.
Like the taken in air, any vapour produced during decompression of the heated relatively cool first fluid is expelled through the air exhaust 10.
The heat pump 1 of the invention functions to heat a pump-driven first fluid, for example a refrigerant, through extracting heat from ambient air and in turn heating a thermosiphon-driven second fluid, for example water, by exchanging heat from the first fluid to the second fluid. In one form the heat pump 1 is a refrigerant heating system. The pumping force required to pump the first fluid through the heat pump 1 is provided by the compressor 3. However, beneficially in one embodiment the heat pump 1 can also comprise a pump, not shown, to provide additional pumping force.
The coaxial arrangement of the first passage 5 and second passage 6 described above and illustrated in
The above refrigerant heating cycle has been described with reference to the first fluid being pumped through the first passage 5 of the heat exchanger 4 and the second fluid passing through the second passage 6 of the heat exchanger 4 driven by a thermosiphon. It is understood that the passage of the first and second fluids could be swapped, with the first fluid being pumped through the second passage 6 of the heat exchanger 4 and the second fluid passing through the first passage 5 of the heat exchanger 4 driven by thermal convection. In this alternate configuration the flow of the first fluid and second fluids must be designed with regard to the second fluid rising when heated as driven by thermal convection. Likewise, the alternate coaxial arrangement wherein the first passage 5 of the heat exchanger 4 is the inner tube 8 and the second passage 6 of the heat exchanger 4 is an outer tube 7 is also encompassed in coaxial embodiments of the heat exchanger 4.
The coaxial arrangement of the outer tube 7 and the inner tube 8 depicted in
Another suitable arrangement is depicted in
To further increase the efficiency of heat exchange in some embodiments the surface(s) across which heat exchange takes place are in direct contact. Such an embodiment is shown in
To still further increase the efficiency of heat exchange the first passage 5 and second passage 6 in some embodiments share a wall, as depicted in FIGS. 2 and 5-7.
To still further increase the efficiency of heat exchange the first passage 5 and second passage 6 of the heat exchanger 4 are constructed in one-piece and the surfaces of the first passage 5 and the second passage 6 across which heat exchange occurs are constructed in a shape that increases the surface area of the surface(s) across which heat exchange takes place. Suitable shapes for increasing the surface area of the first passage 5 and the second passage 6 are the ribbed shape 27 depicted in
For efficient thermosiphoning the second passage 6 is positioned so that the second passage 6 runs vertically, or close to vertical. Such a vertical embodiment is shown in
In preferable embodiments to increase the heat exchange between the first fluid and the second fluid the fluids flow in opposite directions, i.e. the flows of the first and second fluid are counter-current. In this counter-current embodiment the second passage 6 must be positioned in an orientation that allows the second fluid to be driven by thermal convection alone.
A disadvantage of prior art heat pumps is that they cannot operate effectively below 10° C. where the heat pump evaporator develops ice. The conventional solution to eliminate ice, like that adopted in air conditioners, is to commence a reverse cycle. This however is undesirable in water heating as it would cool the water and in embodiments where the heat pump is fitted to a tank, such as described below, would cycle cold water into the water storage tank.
The ice management system 129 comprises a second heat exchanger 130 which comprises a third passage 131 through which heated compressed first fluid that has exited the compressor 103 passes as driven by the pumping action of the compressor 103. The second heat exchanger 130 also comprises a fourth passage 132 through which cool compressed first fluid that has exited the heat exchanger 104 passes and is also pumped by compressor 103.
In the second heat exchanger 130 the heated compressed first fluid exchanges heat with the cool compressed first fluid. Therefore the first fluid exiting the third passage 131 is relatively cool heated compressed first fluid and the first fluid exiting the fourth passage 132 is relatively warm cool compressed first fluid. It is to be understood that the relatively cool heated compressed first fluid is not cool per se and is only relatively cool compared to the heated compressed first fluid. The relatively cool heated compressed first fluid can function in the heat exchanger 104 to exchange heat with the second fluid to produce heated second fluid.
The heating in the third passage 131 of the cool compressed first fluid to relatively warm cool compressed first fluid reduces the incidence of ice production and has the significant effect of allowing the heat pump 101 to operate effectively at temperatures as low as 0° C. to 4° C.
In another embodiment the ice management system 129 further comprises a constant pressure/temperature valve (not shown) that detects the temperature of the first fluid at entry to the evaporator 102. The constant pressure/temperature valve functions to operate the ice management system 129 when the temperature of the circulating first fluid entering the evaporator 102 falls below a set pressure/temperature. In one embodiment the constant pressure/temperature valve functions to operate the ice management system 129 when the compressed first fluid entering the evaporator 102 is at a pressure between about 300-25000 kpa. In another embodiment the constant pressure/temperature valve functions to operate the ice management system 129 when the compressed first fluid entering the evaporator 102 is at a temperature less than 10° C., or at a temperature between about 0 and 10° C.
The efficiency and the low temperature operability of the heat pump 1, 101, and heat pumps described below can be further increased by utilizing a low boiling point refrigerant as the first fluid. Prior art heat pumps use air conditioning refrigerant as the first fluid giving hot water at about 55° C. The heat pump 1, 101 and heat pumps described below, are designed to use either conventional refrigerants, such as air conditioning refrigerants, or to use a lower boiling point refrigerant. Utilization of a lower boiling point refrigerant produces higher condensing temperatures and generates the benefit of hotter water.
The heat pump 1 has an expected average coefficient of performance (COP) at 55° C. of 3 to 3.2 which is equivalent to other domestic hot water heat pumps. At 65° C. the expected COP of the heat pump 1 is about 2.
A further important advance made by the present inventors is the circumvention of superheating of the first fluid which occurs in prior art heat pumps. Prior art heat pumps when fitted to a water tank return the first fluid from the heat exchanger to the compressor directly adjacent to the hottest second fluid which sends the first fluid to the evaporator hotter than is desirable and is inefficient. The inventors prevent superheating of the first fluid by advantageously locating the heat pump 1, 101 and the heat pumps described below, external to the tank and by insulating the path of the first fluid.
A feature of the heat pump 1, 101 and the heat pumps described below of great benefit is that they are suitable for easy retrofit installation on existing water storage tanks, such as domestic water tanks and including domestic water tanks with a capacity of, for example, 80, 125, 160, 180, and 250 litres or greater. The heat pump 1, 101 and those described below are easily retrofitted, via for example T-pieces, to water tanks with a separate flow outlet and return inlets. Additionally, the heat pump 1, 101 and those described below are suitable for installation onto existing water tanks that do not comprise a separate flow outlet and return inlet.
When used in conjunction with a tank the heat pump 1, 101 and those described below, will draw the second fluid, for example water, from the tank. As shown in
The circular heating motion of the second fluid from the tank 34 through the heat exchanger 4 and back to the tank 34 is driven by thermal convection so that the greater the difference in temperature between the water in the heat exchanger 4 and the water in the storage tank 34, the faster the flow between them.
As shown in
After exchanging heat with the second fluid in heat exchanger 204, the first fluid is cooled in a cooling loop 240 of evaporator 202. To efficiently cool the second fluid the cooling loop 240 may be positioned so that the relatively cooler air that has exchanged its heat with the first fluid flows over it. This cooling of the first gas draws heat out of heat pump 201 and increases the efficiency of the heating of the first fluid in the evaporator 202.
After exiting the evaporator 202 the first fluid passes through ice management system 229, which functions similarly to ice management system 29 and can also be turned on and off with fluctuations in ambient temperature. When ice management system 229 is functioning the first fluid that has exited the evaporator 202 will be heated in the ice management system 229 by the first fluid that has exited compressor 203.
The first fluid exits the ice management system 229, is heated in heating loop 242 of evaporator 202 by taken in ambient air and is then pumped through compressor 203.
Next if the ice management system is operating hot gas bypass valve 245 will direct a portion of the heated compressed first fluid through the ice management system 229 to mix with and heat the first fluid that has exited the cooling loop 240. The heated mixed first fluid then proceeds into the heating loop 242. A person of skill in the art is readily able to select an appropriate portion of the heated compressed first fluid to direct through the ice management system 229. The portion may be, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 30%, 40% or 50% In one embodiment the portion is up to 20% is used.
The heated compressed first fluid that is not directed by the valve 245 to the ice management system 229 passes through the heat exchanger 204 where it heats the second fluid from tank 234.
The cooling loop 240 and heating loop 242 are shown to comprise two and four longitudinal segments respectively. A person of skill in the art is readily able to choose an appropriate number of longitudinal and lateral segments.
The ice management system 329 shown in
In one embodiment the presence of electrical element 350 allows the elimination of bypass valve 245.
At temperatures ≦5° C. the speed of the fan (not shown) in the evaporator 302 may also be increased.
The heat pump 201 shown in
The inventors have shown that heat pump 201 operates effectively at −1° C.
Other tests by the inventors have also shown that an electrical element 350 drawing only 300 watts operates effectively in heat pump 301. This compares favourably with prior art heat pumps which require 3 000-3 600 watts to operate.
The invention also encompasses a method of heating water using the heat pump 1, 101, 201 described above to heat water.
In addition to encompassing a method of heating water the invention encompasses a system for heating water comprising a means for taking in ambient air, heating a first fluid with the taken in air and expelling the taken in air as relatively cooler air, a means for compressing the heated first fluid and for pumping the heated compressed first fluid through a heat exchanger, and an improved means for heating water wherein the improvement resides in the water being propelled through the improved heat exchanger by thermal convection and the water is heated by the heated compressed first fluid.
Hence, the heat pump 1, 101, 201, method and system of using the heat pump 1, 101, 201 provide a solution to the problems of reducing reliance on non-renewable energy resources, reducing pollution and providing low cost hot water by virtue of the inventors novel utilization of the natural thermal convection of thermosiphon technology to passage fluids such as water.
Further, the heat pump 1, 101, 201 and method and system of the invention are operable at lower temperatures than prior art heat pumps which extends the use of heat pumps into hitherto unworkable locations.
The retrofittable aspect of the invention has the further advantages of reducing cost of replacement as storage tanks are not required to be replaced and space is saved as the heat pump 1, 101, 201 of the invention can be mounted on existing tanks.
Throughout the specification the aim has been to describe the invention without limiting the invention to any one embodiment or specific collection of features. Persons skilled in the relevant art may realize variations from the specific embodiments that will nonetheless fall within the scope of the invention.
Claims
1. A heat pump comprising an evaporator that transfers heat from taken in air to a first fluid and expels the taken in air that has exchanged heat at a temperature cooler than ambient temperature, a compressor for compressing and pumping the first fluid and an improved heat exchanger, the improvement residing in the improved heat exchanger comprising a first passage for the heated compressed first fluid driven by the compressor and a second passage for a second fluid driven by thermal convection.
2. The heat pump according to claim 1 wherein the taken in air is heated above ambient temperature by heat generated by normal operation of the evaporator and heat is transferred from the heated taken in air to the first fluid.
3. The heat pump according to claim 1 wherein the first passage and second passage are coaxial.
4. The heat pump according to claim 1 wherein the first passage and second passage are side by side.
5. The heat pump according to claim 1 wherein the first passage and second passage share a common wall.
6. The heat pump according to claim 5 wherein the common wall is ribbed.
7. The heat pump according to claim 5 wherein the common wall comprises a raised spiral.
8. The heat pump according to claim 1 wherein the evaporator further comprises a cooling loop.
9. The heat pump according to claim 8 wherein the cooling loop is positioned to be exposed to the air that has exchanged heat.
10. The heat pump according to claim 1 further comprising a second heat exchanger that receives heated compressed first fluid from the compressor and compressed first fluid from the heat exchanger.
11. The heat pump according to claim 10 wherein a valve controls flow of the first fluid from the compressor to the second heat exchanger.
12. The heat pump according to claim 10 wherein the second heat exchanger further comprises a third passage for heated compressed first fluid from the compressor and a fourth passage for compressed first fluid from the heat exchanger that has exchanged heat with the second fluid.
13. The heat pump according to claim 10 wherein the heated compressed first fluid from the compressor and the compressed first fluid from the heat exchanger mix in the second heat exchanger.
14. The heat pump according to claim 10 wherein the second heat exchanger further comprises an electrical element.
15. The heat pump according to claim 10 wherein a valve is positioned between the first heat exchanger and the evaporator to allow pressure of the first fluid to be reduced.
16. The heat pump according to claim 15 wherein the valve is a Tx valve.
17. The heat pump according to claim 10 wherein a capillary tube is positioned between the first heat exchanger and the evaporator to allow pressure of the first fluid to be reduce.
18. The heat pump according to claim 1 further comprising a storage tank filled with the second fluid.
19. A water heater comprising a tank and a heat pump, the heat pump comprising an evaporator that transfers heat from taken in air to a first fluid and expels the taken in air that has exchanged heat at a cooler temperature, a compressor for compressing and pumping the heated first fluid and an improved heat exchanger, the improvement residing in the heat exchanger comprising a first passage for the heated compressed first fluid driven by the compressor and a second passage for a second fluid driven by thermal convection.
20. A method of heating water including the steps of:
- taking ambient air in through an evaporator;
- heating a first fluid in the evaporator with the taken in air;
- expelling the taken in air as relatively cool air;
- compressing the heated first fluid;
- pumping the heated compressed first fluid through a heat exchanger; and
- heating the water in the heat exchanger by exchanging heat from the heated compressed first fluid to the water whereby passage of the water is driven by thermal convection.
21. The method of claim 20 further including the step of heating the first fluid with the heated compressed first fluid.
22. The method of claim 21 further comprising reducing the pressure of the first fluid.
23. A system for heating water comprising: wherein the water is heated by the heated compressed first fluid and the water is propelled by thermal convection.
- a means for taking in ambient air, heating a first fluid with the taken in air and expelling the taken in air as relatively cooler air;
- a means for compressing the heated first fluid and for pumping the heated compressed first fluid through a heat exchanger; and
- a means for heating water;
24. The system of claim 23 further comprising a means for heating the first fluid with the heated compressed first fluid.
25. The system of claim 23 further comprising a means for reducing the pressure of the first fluid.
Type: Application
Filed: Aug 2, 2006
Publication Date: Feb 25, 2010
Applicant: Solacoil Pty Ltd (Kingston, Queensland)
Inventors: Murray McNeil (Sinnamon Park), Scott Michael Rawlinson (Carbrook), Steven Jeffrey Fitch (East Brisbane)
Application Number: 11/997,694
International Classification: F25B 41/00 (20060101); F25B 13/00 (20060101); F25D 13/00 (20060101); F25B 39/02 (20060101); F25B 27/00 (20060101);