Heat Exchanger Element and a Water Heater and Heat Pump Utilizing Same
A heat exchanger element (30) formed from an inner copper tube (32) and an outer copper tube (34). The entire outer surface of the inner tube (32) is substantially in contact with the entire inner surface of the outer tube (34).
The present invention relates to a heat exchanger element and a water heater and a heat pump utilising same.
The invention has been primarily developed for use in domestic hot water heaters and will be described hereinafter with reference to this application. However, the invention is not limited to this particular use and is also suitable for heating fluid other than water in numerous heat exchanger applications.
BACKGROUND OF THE INVENTIONRegulatory authorities in many jurisdictions, including Australia, Europe and the United States of America, require heat exchanger elements used in domestic hot water heaters to have two layers of metal separating the heated fluids circulating through the heat exchanger and the water being heated in the hot water tank. This is to ensure that even if one of the layers is compromised, there will be no mixing between the heat exchanger fluid and the water supplied to user.
One known ‘double walled’ hot water heater utilises a copper tube wrapped around the outside of a cylindrical steel water tank. Heat exchanger fluid is pumped through the copper tube. However, this arrangement is difficult and thus relatively expensive to produce, particularly the step of rolling the tube around the approximately 600 mm diameter tank. This arrangement also has relatively poor heat exchanging efficiency, as steel is almost 30 times less effective as a conductor than copper.
Another known ‘double walled’ hot water heater utilises a coil of copper tube positioned inside a tube within a water tank. This arrangement is also difficult and thus relatively expensive to produce. It is difficult to ensure the copper tube makes good surface to surface contact with the tube interior, which is required for good heat exchanging efficiency.
OBJECT OF THE INVENTIONIt is the object of the present invention to overcome or substantially ameliorate at least one or more of the above prior art deficiencies.
SUMMARY OF THE INVENTIONAccordingly, in a first aspect, the present invention provides a heat exchanger element formed from an inner copper tube and an outer copper tube, wherein the entire outer surface of the inner tube is substantially in contact with the entire inner surface of the outer tube.
In one form, the inner diameter of the outer tube is substantially equal to the outer diameter of the inner tube, such that approximately 100% of the inner surface of the outer tube is in contact with the outer surface of the inner tube.
In another form, the inner surface of the outer tube includes rifling or grooves having a minimum diameter substantially equal to the outer diameter of the inner tube, such that approximately 80% of the inner surface of the outer tube is in contact with the outer surface of the inner tube.
In an embodiment, the element is preferably substantially cylindrical in shape, and most preferably with cylindrical walls formed from spiralled inner and outer tubes.
In another embodiment, the element is preferably substantially cylindrical in shape, with cylindrical walls formed from spiralled inner and outer tubes, and includes an outer cylindrical wall attached to the exterior of the spiralled outer tubes.
In yet another embodiment, the element is preferably substantially cylindrical in shape, with cylindrical walls formed from spiralled inner and outer tubes, and includes an inner cylindrical wall attached to the interior of the spiralled outer tubes.
In yet another embodiment, the element is preferably substantially cylindrical in shape, with cylindrical walls formed from spiralled inner and outer tubes, and includes inner and outer cylindrical walls respectively attached to the interior and exterior of the spiralled outer tubes.
The element preferably has two substantially longitudinal inlet and outlet portions, one extending from a first end of the cylinder and the other extending from the second end of the cylinder through the cylinder interior to the first end of the cylinder.
In a second aspect, the present invention provides a water heater including a tank and a heat exchanger element according to the first aspect.
In a third aspect, the present invention provides a method of forming a heat exchanger element, the method comprising the following steps:
- a. drawing a first and a second copper tube, the first tube having an outer diameter less than the internal diameter of the second tube;
- b. inserting the first tube into the second tube;
- c. passing the tubes through a roll former adapted to crush the second tube onto the first tube, such that the entire outer surface of the first tube is substantially in contact with the entire inner surface of the second tube.
- d. annealing the crushed tubes;
- e. bending the tubes into a desired configuration; and
- f. annealing the bent tubes.
Step e. preferably includes bending the tubes into a generally cylindrical shape, most preferably with the cylindrical walls being formed from spiralled tubes.
Step a. preferably includes drawing the second tube with internal rifling or grooves.
In a fourth aspect, the present invention provides a hot water heat pump comprising:
- a heat pump circuit comprising an evaporator coil; a compressor, a condenser coil in a heat exchanging relationship with a body of water, and a thermostatic expansion valve (TX valve), the circuit adapted to hold a charge of refrigerant,
- wherein the condenser coil is in the form of a heat exchanger element according to the first aspect.
Preferred embodiments of the present invention will now be described, by way of examples only, with reference to the accompanying drawings, wherein:
The tank 12 also has a first hot water outlet 22 within the upper domed end 14 and a first cold water inlet 24 in the lower domed end 16. The outlet 22 is, in operation, connected to household plumbing. The inlet 24 is, in operation, connected to mains water supply. The tank 12 also has a second hot water outlet 26 and a second cold water inlet 20 which, for example, can be used to connect to the tank 12 in parallel to a solar hot water heater.
A first embodiment of a heat exchanger element 30 is inserted into the tank interior through the opening 18. As best shown
The construction of the heating element 30 involves the following steps. Firstly, two copper tubes are drawn to approximately 19 metres in length. The smaller diameter tube 32 has an internal diameter of 5.0 mm and an external diameter of 5.5 mm. The large diameter outer tube 34 has an internal diameter of 5.7 mm and an external diameter of 6.3 mm. The difference between the outer diameter of the inner tube 32 and the inner diameter of the outer tube 34 allows the inner tube 32 to be inserted within the outer tube 34. At this stage, there is a small gap between the outer surface of the inner tube 32 and the inner surface of the outer tube 34. The two tubes 42 and 34 are then fed through a roll former which crushes the outer tube 34 into contact with the inner tube 32 to eliminate the gap. The roll forming also slightly extends the length of the outer tube 34 and, if desired, it can initially be made slightly shorter than the inner tube 32 so that it expands to a common length. Alternatively, the excess of the outer tube 34 can be trimmed. The roll forming also hardens the tubes 32 and 34. The (roll formed/crushed) tubes 32 and 34 are then annealed for softening, so they can then be bent and spiral wound into the shape shown in
The advantage of the double walled heat exchanger element as the condenser coil 146 in the heat pump application is it provides the most direct, and thus efficient, transfer path of energy by conduction into the water. More particularly, as the condenser coil 146 is suspended in the water, there is no air gap around it. This results in a minimum coefficient of heat transfer from the refrigerant to the water.
This is in contrast to existing refrigerant systems which use copper piping systems to contain the refrigerant, such as existing heat pump configurations in which the copper pipe is wound on an external face of the water tank.
Further, the double walled construction of the condenser coil 146 provides a safety feature (being an internal refrigerant escape path between the inner and the outer tubes) that is only actuated when there is a failure in the inner tube. This safety feature is only possible due to the nature of the manufacturing process and the suspension of the condenser coil in water contained within a tank at a lower pressure than the refrigerant in the condenser coil.
Normal “tube in tube” designs have this safety feature permanently in place in the form of an air gap between the tubes, which results in poor heat transfer.
Although the invention has been described with reference to preferred embodiments, it would be appreciated by those persons skilled in the art that the invention may be embodied in many other forms.
Claims
1. A method of forming a heat exchanger element, the method comprising the following steps:
- a. drawing a first and a second copper tube, the first tube having an outer diameter less than the internal diameter of the second tube;
- b. inserting the first tube into the second tube;
- c. passing the tubes through a roll former adapted to crush the second tube onto the first tube, such that the entire outer surface of the first tube is substantially in contact with the entire inner surface of the second tube.
- d. annealing the crushed tubes;
- e. bending the tubes into a desired configuration; and
- f. annealing the bent tubes.
2. The method as claimed in claim 1, wherein step e. includes bending the tubes into a generally cylindrical shape.
3. The method as claimed in claim 2, including the step of forming the cylindrical walls from spiraled tubes.
4. The method as claimed in claim 1, wherein step a. includes drawing the second tube with internal rifling or grooves.
5. A heat exchanger clement formed by the method as defined in claim 1.
6. A water heater including a tank and a heat exchanger element according to claim 5.
7. A heat pump circuit comprising an evaporator coil; a compressor, a condenser coil in a heat exchanging relationship with a body of water, and a thermostatic expansion valve (TX valve), the circuit adapted to hold a charge of refrigerant,
- wherein the condenser coil is in the form of a heat exchanger element according to claim 5.
Type: Application
Filed: Aug 1, 2006
Publication Date: Oct 29, 2009
Inventor: Patrick Pussell (New South Wales)
Application Number: 11/992,034
International Classification: F24H 4/02 (20060101); B21D 53/02 (20060101); F25B 1/00 (20060101); F28D 7/10 (20060101);