Patent Application
20130000347
The present application is based on U.S. Provisional Application Ser. No. 61/501,927, filed Jun. 28, 2011, which is incorporated herein by reference.
This application is directed to a hybrid heat exchanger, and more specifically to a hybrid heat exchanger that may be used in a heating and ventilation air conditioning (HVAC) system.
For decades, HVAC heat exchangers have been comprised primarily of copper. However, in recent years due to the increase in the cost of copper, HVAC manufacturers have begun seeking more cost effective solutions for the materials from which they manufacture heat exchangers. One such alternative material is aluminum, but since aluminum is not as strong a material as copper, manufacturers have had to compensate for this material difference by increasing the thickness of the aluminum tubing, which in turn, decreases internal volume.
In one embodiment there is provided a heat exchanger that comprises a header frame having end plates, a plurality of rows of finned hairpins, each extending through a cooling fin and each having ends extending through the end plates, and at least one finless hairpin having ends extending through the end plates.
In another embodiment, there is provided a HVAC system comprising, a compressor, an evaporator fluidly connected to the compressor and having a first fan associated therewith, and a condenser fluidly connected to the compressor and having a second fan associated therewith. At least one of the evaporator or condenser comprises; a header frame having end plates, a plurality of rows of finned hairpins, each extending through a cooling fin and each having ends extending through the end plates, and a plurality of finless hairpins having ends extending through the end plates.
Another embodiment provides a method of manufacturing the heat exchanger. This embodiment comprises providing a header frame having end plates, providing a plurality of hairpins, providing cooling fins have openings located therethrough, placing a portion of the plurality of hairpins through each of the openings, expanding each of the portion such that each expands against the circumference of the openings to form a plurality of rows of finned hairpins, placing opposing ends of the finned hairpins through a portions of openings in opposing end plates of the header frame, and placing opposing ends of finless hairpins through a remaining portion of the openings in opposing end plates of the header frame.
Reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
For an aluminum slab, composed of aluminum fins and aluminum hairpins (i.e. refrigerant tubes), the internal volume is smaller than that for a copper slab having the same number of hairpins with the same outside diameter as copper hairpins because of thicker walls that are required to achieve the requisite tensile strength need for a heat exchanger. This is due to the fact that aluminum has a lesser tensile strength than copper. As such, the wall must be made thicker in order to withstand the refrigerant pressure associated with a refrigeration cycle.
In order to increase the internal volume using conventional processes, especially for heat pump applications, manufacturers have typically added more hairpins with cooling fins by either increasing slab height or adding more row or rows. However, increasing slab height with the same number of rows and causes lower frontal velocity for the same air flow rate resulting in lower efficiency. Additionally, adding more row or rows for the same height slab causes higher air side pressure drop, which is an undesirable effect.
It has been presently found that an effective way of increasing the internal volume without a loss of cooling efficiency is to add one or more additional rows of finless hairpins, that is, hairpins that do not have any cooling fins attached to them. If hairpins are added by increasing slab height with the same number of rows resulting in a taller evaporator, this is a negative effect on the end user resulting in an evaporator that will not fit into the existing cooling chamber of the end user. The pressure drop associated with the extra row of finned hairpins is a negative outcome for the end user resulting in not achieving the correct airflow required for the system. Adding a finless row or rows will achieve the required internal volume, while maintain the desired height and airside pressure drop of the heat exchanger, without adding the negative results of increased height and additional finned row or rows. This technique can be used in both aluminum and copper heat exchangers. However, a “finless” hairpin is very counter intuitive to conventional practices that teach that cooling fins are highly desirable on all of the refrigerant tubes that make up the core of the slab of the heat exchanger to effect the desired amount of heat transfer. Moreover, the concepts as provided herein can be added on to either existing copper based or aluminum based heat exchangers.
It should be noted that the support sheet 125 is distinguished from cooling fins 130, illustrated by the horizontal lines, in that the primary purpose of the support sheet 125 is to provide support and not intended to provide a heat exchange function, even though heat transfer may take place between the hairpins 115 and the support sheet 125. The support sheet 125 is in contrast to a cooling fin 130 whose purpose is to transfer heat from the hairpin to which it is attached. Moreover, there is a distinguishable difference in dimensions between the support sheet 125 and a cooling fin 130. For example, in one embodiment, the support sheet 125 may have a surface to volume ratio of at most about 40/cm, whereas a cooling fin 130 will typically have a surface to volume ratio of at least about 200/cm. In one such embodiment, the thickness of a cooling fin 130 will be about 0.11 mm, while the thickness of the support sheet 125 may have a thickness that is about 0.5 mm to about 1.27 mm, or greater in other embodiments.
Also seen in this view are the coupling ends 120 to which return bends, not shown, can be attached to each pair of hairpins to close off the pair, such that they can serve as a sealed refrigeration loop within the heat exchanger 100.
The addition of one or more rows of finless hairpins 115 provides an increased internal volume of the heat exchanger 100 without increasing its overall size. This is particularly useful in heat exchangers that are comprised of aluminum.
With reference to
In one embodiment, the row of the plurality of finned hairpins includes one of the finless hairpins, and in another embodiment, only a portion of the plurality of the rows of finned hairpins includes a finless hairpin. Both finned and finless hairpins may be comprised of aluminum, which includes alloys thereof, or they may both be comprised of copper, which also includes alloys thereof. Alternatively, the finned hairpins may be comprised of copper, while the finless hairpins may be comprised of aluminum, or vice versa.
Those skilled in the art to which this application relates will appreciate that other and further additions, deletions, substitutions and modifications may be made to the described embodiments.
| Number | Date | Country | |
|---|---|---|---|
| 61501927 | Jun 2011 | US |
