Refrigeration – Refrigeration producer – Compressor-condenser-evaporator circuit
Reexamination Certificate
2002-08-19
2003-11-04
Norman, Marc (Department: 3744)
Refrigeration
Refrigeration producer
Compressor-condenser-evaporator circuit
C165S144000, C062S515000
Reexamination Certificate
active
06640583
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The subject invention generally pertains to a refrigerant system and more specifically to the coil configuration of a wound heat exchanger coil.
2. Description of Related Art
Many air conditioning systems, such as split-systems and/or heat pumps, fundamentally include an indoor heat exchanger, an outdoor heat exchanger, a compressor and an expansion device that are connected in series to comprise a refrigerant circuit. As the compressor forces refrigerant through the circuit, compression and expansion of the refrigerant respectively raises and lowers the temperature of the refrigerant. The refrigerant then absorbs or expels heat to the external surroundings of the heat exchangers. For example, in a cooling mode, relatively cool, lower pressure refrigerant passing through the indoor heat exchanger (operating as an evaporator) cools the indoor air (directly or via an intermediate fluid), while relatively hot, higher pressure refrigerant delivered to the outdoor heat exchanger (operating as a condenser) expels heat to the outside ambient air (or water). With some systems, generally reversing the direction of part or all of the refrigerant flow through the circuit places the system in a heating mode to warm the indoor air or temporarily places the system in a defrost mode. In the defrost mode, the circuit directs relatively hot, higher pressure refrigerant to the heat exchanger that was previously operating as the evaporator, and thus thaws frost that may have accumulated on that heat exchanger.
Outdoor heat exchangers often comprise several wound tubes to provide several coiled circuits that are arranged directly above each other so that the coiled tubes become the perimeter of a larger tubular assembly. Two vertical manifolds connecting the ends of each wound tube places the coiled circuits in parallel flow relationship with each other. The tubes usually have external fins (e.g., spine fins) to promote heat transfer and thus improve the overall efficiency of the air conditioning system.
However, as consumers demand higher efficiencies, the size of the outdoor coil (i.e., the tubular assembly) increases. To keep the overall size of the outdoor coil within a reasonably sized package, sometimes a second coil is added to the outdoor coil. The second coil can be wound around the first, as disclosed in U.S. Pat. No. 4,554,968, or the second coil can be slightly smaller than the first and slipped inside the outer one. Either way provides an outdoor heat exchanger with two rows of coils: an inner one and an outer one.
Although a conventional heat exchanger coil with two rows is quite efficient, several problems are associated with such a coil. First, some double-row coils require a tubing connection, or jumper, to connect an inner coil to an outer one. Such a connection is commonly made by cutting both coils, pulling part of the inner coil through the outer one, and then connecting the two with a U-shaped return bend. When the return bend is copper and the coil tubing is aluminum, a transition joint may also be necessary. Each connection adds assembly time and increases the likelihood of leaks. Moreover, wherever the coil is cut to attach either a manifold or a jumper, a hole is left through which air flows, bypassing the coil and avoiding heat exchange.
Second, inner coils are typically large and unwieldy, which make them difficult to insert into an outer coil.
Third, the coil configuration of conventional double-row coils tends to dictate the location of the manifolds (e.g., both on the inside, both on the outside, or one on each side), regardless of other design criteria. However, it may be preferable to have the manifold in another location for other reasons, such as ease of assembly (e.g., both manifold on the outside) or compactness (e.g., both manifolds on the inside).
Fourth, for many double-row coils most of the inner loops (i.e., inner passes) are closer to the vapor connections with respect to refrigerant flow than the liquid connections, as is the case with the U.S. Pat. No. 4,554,968. The terms, “vapor connection” and “liquid connection” are relative in that the refrigerant normally tends more toward the liquid state at the liquid connection than at the vapor connection. However, the refrigerant is not necessarily a liquid, gas, or any particular combination of the two at either connection. For example, an individual wound tube of the outdoor coil runs between a vapor connection at one manifold and a liquid connection at another manifold. When the outdoor coil functions as a condenser in a system operating in a cooling mode, the refrigerant tends to give off heat and condense as it flows from the vapor connection to the liquid connection. And for that same outdoor coil functioning as an evaporator when the system is in a heating mode, the refrigerant tends to a more gaseous or superheated state as the refrigerant absorbs heat upon flowing in reverse from the liquid connection to the vapor connection. With the system operating in the heating mode, the loops near the vapor connection typically convey superheated refrigerant. The problem here is that significantly more coil area is required to reach a given level of superheat if the superheating passes are on the inner row, since the difference between the refrigerant temperature and the outdoor air temperature here is slight. Also, since a large portion of the coil's refrigerant-side pressure drop occurs in the superheating region, more coil area in superheat means more refrigerant-side pressure drop and worse performance. Nonetheless, of the five circuits of the coil disclosed in the U.S. Pat. No. 4,554,968, only one (the bottom one) transits from an outer loop to an inner one, and then it only transits once.
Fifth, in manufacturing a multi-circuit, coiled heat exchanger, it is often preferable to first wrap the entire coil as a single circuit and later cut the continuous coil into smaller circuits. This avoids slowing the coiling process by having to repeatedly interrupt a power coiler, such as those similar to the one disclosed in U.S. Pat. No. 5,737,828. However such an approach is not always practical, especially when the coil configuration fails to position the liquid loop of a first circuit closer to the vapor loop of an adjacent circuit than to the vapor loop of the first circuit, as appears to be the case in the U.S. Pat. No. 4,554,968. Placing the liquid loop of a first circuit adjacent or near the vapor loop of an adjacent circuit allows two ends of each loop to be created with a single tube cut.
Just as the terms, “vapor connection” and “liquid connection,” are used in a relative sense, other terms such as “vapor loop,” “vapor manifold,” “vapor connection,” “liquid loop,” “liquid manifold,” “liquid connection,” etc., are also used relatively in that the refrigerant tends more toward the liquid state in the liquid manifold, liquid loop, and liquid connection than in the vapor manifold, vapor loop, and vapor connection respectively.
A sixth problem with many conventional double-coil heat exchangers is that most of the hot discharge refrigerant gas used for defrost cools significantly upon first passing through the inner coil before reaching the outer one. For example, the U.S. Pat. No. 4,554,968 appears to show refrigerant in a defrost cycle having to pass through at least three inner loops before transiting to an outer loop. But often most of the frost tends to accumulate on the outer coil where the outdoor air enters the coil. Consequently, hot defrost refrigerant having to first pass through several inner loops before reaching an outer one tends to extend the defrost cycle and degrade the heating efficiency of the system.
Seventh, the maximum outdoor air velocity across a heat exchanger having a uniform distribution of coils usually occurs near the fan inlet, somewhere between the top and bottom of the coil. The airflow velocity at the top and bottom of the coil is generally lower, and thus those areas are not used as effectively as the area near the fan
American Standard International Inc.
Beres William J.
Norman Marc
O'Driscoll William
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