Abstract:
A method and/or apparatus for at least one of: protecting the sub-surface metal refrigerant transport tubing of a DX heat pump system from corrosive sub-surface environments via a specially designed protective coating; efficiently insulating the sub-surface liquid refrigerant transport line in a DX heat pump system; and enhancing at least one of the convective heat transfer rate and the efficiency of at least a DX heat pump system; and where the outside diameter (“OD”) of a central containment core upon which to roll a spool of sub-surface refrigerant transport tubing is specially sized so as not to damage any tubing insulation and so as to avoid any “S” bends during ground loop installation.

Description:
FIELD OF THE DISCLOSURE 
       [0001]    The present disclosure generally relates to geothermal “direct exchange” (“DX”) heating/cooling systems, which are also commonly referred to as “direct expansion” heating/cooling systems, comprising various design improvements for protecting metal refrigerant transport tubing in corrosive environments, for specially insulating select portions of the sub-surface ground loop used for conductive heat transfer, and for enhancing the convective heat transfer ability of refrigerant to air heat transfer in a DX geothermal heating/cooling system. 
       BACKGROUND OF THE DISCLOSURE 
       [0002]    Conventional geothermal ground source/water source heat exchange systems typically use liquid-filled closed loops of tubing (typically approximately ¼ inch wall polyethylene tubing) buried in the ground, or submerged in a body of water, so as to either absorb heat from, or to reject heat into, the naturally occurring geothermal mass and/or water surrounding the buried or submerged liquid transport tubing. The tubing loop, which is typically filled with water and optional antifreeze and rust inhibitors, is extended to the surface. A water pump is then used to circulate one of the naturally warmed and naturally cooled liquid to a liquid to refrigerant heat exchange means. 
         [0003]    The transfer of geothermal heat to or from the ground to the liquid in the plastic piping is a first heat exchange step. In a second heat exchange step, a refrigerant heat pump system transfers heat to or from the liquid in the plastic pipe to a refrigerant. Finally, via a third heat exchange step, an interior air handler (comprised of finned tubing and a fan) transfers heat to or from the refrigerant to heat or cool interior air space. 
         [0004]    More recent geothermal DX heat exchange systems have refrigerant fluid transport lines disposed in the sub-surface ground and/or water typically circulate a refrigerant fluid, such as R-22, R-410A, or the like, in sub-surface refrigerant lines, typically comprised of copper tubing, to transfer geothermal heat to or from the sub-surface elements via a first heat exchange step. DX systems only require a second heat exchange step to transfer heat to or from the interior air space, typically by means of an interior air handler. Consequently, DX systems are generally more efficient than water-source systems because less heat exchange steps are required and because no water pump energy expenditure is necessary. Further, since copper is a better heat conductor than most plastics, and since the refrigerant fluid circulating within the copper tubing of a DX system generally has a greater temperature differential with the surrounding ground than the water circulating within the plastic tubing of a water-source system, generally less excavation and drilling is required (and installation costs are typically lower) with a DX system than with a water-source system. 
         [0005]    While most in-ground/in-water DX heat exchange designs are feasible, various improvements may enhance overall system operational efficiencies. Several such design improvements, particularly in direct expansion/direct exchange geothermal heat pump systems, are taught in U.S. Pat. No. 5,623,986 to Wiggs; in U.S. Pat. No. 5,816,314 to Wiggs, et al.; in U.S. Pat. No. 5,946,928 to Wiggs; and in U.S. Pat. No. 6,615,601 B1 to Wiggs, the disclosures of which are incorporated herein by reference. Such disclosures encompass both horizontally and vertically oriented sub-surface heat geothermal heat exchange means, using historically conventional refrigerants, such as R-22, as well as using a newer design of refrigerant identified as R-410A. R-410A is an HFC azeotropic mixture of HFC-32 and HFC-125. 
         [0006]    DX heating/cooling systems have three primary objectives. The first is to provide the greatest possible operational efficiencies. This directly translates into providing the lowest possible heating/cooling operational costs, as well as other advantages, such as, for example, materially assisting in reducing peaking concerns for utility companies. The second is to operate in an environmentally safe manner with environmentally safe components and fluids. The third is to operate for long periods of time absent the need for any significant maintenance/repair, thereby materially reducing servicing and replacement costs over other conventional system designs. 
         [0007]    Historically, DX heating/cooling systems, even though more efficient than other conventional heating/cooling systems, have experienced practical installation limitations created by the relatively large surface land areas necessary to accommodate the sub-surface heat exchange tubing. For example, with horizontal “pit” systems, a typical land area of 500 square feet per ton of system design capacity was required in first generation designs to accommodate a shallow (within 10 feet of the surface) matrix of multiple, distributed, copper heat exchange tubes. Further, in various vertically oriented first generation DX system designs, about one to two 50 foot to 100 foot (maximum) depth wells/boreholes per ton of system design capacity, with each well spaced at least about 20 feet apart, and with each well containing an individual refrigerant transport tubing loop, were required. Such requisite surface areas effectively precluded system applications in many commercial and/or high density residential applications. An improvement over such predecessor designs was taught by Wiggs, which disclosed various DX system design features that enabled a DX system to operate within wells/boreholes that were about 300 deep, thereby materially reducing the necessary surface area land requirements for a DX system. 
         [0008]    Historically, copper tubing has been used for sub-surface refrigerant transport purposes in DX system applications. Copper has been used because of its general longevity in most underground applications, because of its modest cost, because of its ability to withstand typical refrigerant system operational pressures, because it is easily installed, and because it is easily brazed to various system component parts. However, in some sub-surface applications, such as where soil conditions are below a 5.5 ph, or above an 11 ph, and/or where high levels of chlorine and/or sulfur are present, the copper tubing is susceptible to corrosion and should be protected via cathodic protection and/or placement of the copper tubing within a separate and additional protective, and liquid filled, containment pipe, such as a protective polyethylene plastic pipe, which pipe typically has an approximate ¼ inch thick plastic wall. This all requires additional time and expense. Further, the provision of an additional and separate protective plastic containment pipe, particularly if comprised of polyethylene, can decrease system operational efficiencies by as much as 15%, or more, thereby necessitating additional drilling depths per ton of design capacity. 
       SUMMARY OF THE DISCLOSURE 
       [0009]    In view of the foregoing, a coating is provided for a sub-surface and/or other heat transfer refrigerant transport tubing that provides an excellent general longevity for such metal tubing in most corrosive underground applications, which has a reasonably modest cost, that is easily installed, and that does not require a separate and additional protective containment pipe. Additionally, the subject disclosures outline a means to actually enhance overall above-surface heat transfer rates for convective refrigerant to air heat transfer designs, and particularly within DX system operational temperature ranges. Further, the present disclosure provides a means for insulating the sub-surface liquid refrigerant transport line. Lastly, a ground loop interior central core size for a spool of fully or partially coated metal refrigerant transport tubing is disclosed that may materially assist in eliminating “S” bends in the sub-surface geothermal heat transfer tubing during field installation, and that will not impair any insulating and/or protective plastic coating on the exterior of the tubing. 
         [0010]    The protection of sub-surface metal tubing from corrosive sub-surface environments, thereby to improve longevity of the system, and the ability to increase overall DX system operational efficiencies are two primary issues in any DX system design. 
         [0011]    Historically, the sub-surface metal refrigerant transport tubing of a DX geothermal system has been protected by at least one of cathodic protection and imposing an electrical current on the sub-surface metal tubing (both of which are well understood by those skilled in the art). However, the sacrificial anode of a cathodic protection design will eventually wear out, and an imposed electrical current could be interrupted via a power outage, or the like. Thus, an improved and more permanent means of protecting the sub-surface metal refrigerant transport tubing of a DX geothermal system would be preferable. 
         [0012]    Corrugated stainless steel tubing is presently well known for the transportation of natural gas. However, such steel tubing is typically plastic coated with a PVC type, or the like, plastic, and is designed to transport gas at relatively low pressures and at relatively low temperatures, which are much lower than that of an operational DX refrigerant system within a home or building. For example, while PVC, or the like, plastic coated steel tubing is used to transport relatively low temperature gas at several hundred pounds of pressure, or more, through main transport lines to structures within developed areas, as well as to transport gas within the structures themselves, a regulator typically drops the pressure from the outside main line to only an ounce or so of pressure within the structure, with the pressure such as to raise a column of water only about ½ inch high, and with the gas temperature relatively close to that of the surrounding geology. Thus, the gas transport PVC plastic coated steel lines need only be thick enough to convey gas at relatively low pressures, to help guard against accidental damage, and to protect the steel from conditions that may be corrosive to steel (even to stainless steel), all while the gas is at a rather constant and relatively low temperature. This is why a PVC, or the like, coating is acceptable for gas transmission lines. 
         [0013]    To the contrary, issues that are important to a DX system, such as relatively high pressure (up to 600 psi) gas containment, all while conveying a refrigerant that widely fluctuates in temperatures, with both relatively high (up to around 200 degrees F. in the cooling mode) and relatively low (down to around 12 degrees F. in the heating mode) temperature fluctuations, can adversely affect the commonly used exterior plastic coating upon metal gas transport tubing, since widely fluctuating temperature stresses (inherent to operational DX heating/cooling systems), are not issues that are of any material concern to the gas transportation industry. For example, it has been reported that PVC can develop stress crack over a 10 year period when subjected to only no more than 15 to 30 degree F. temperature differentials. 
         [0014]    However, in a DX system application, the refrigerant transport tubing, whether within or without a structure, must be strong enough to withstand typical system operational pressures, which can periodically reach as high as 450 psi when an R-410A type refrigerant is used. Thus, a 600 psi safe working load is appropriate for any metal refrigerant transport tubing used in any R-410A refrigerant-based DX system application, as well as for any DX system using any refrigerant with similar operating pressures to R-410A. Refrigerant types and operating pressures are well understood by those skilled in the art. Further, while a PVC plastic coating can help to prevent damage to steel gas transport lines, in such a gas transport application, as mentioned, the PVC plastic coating is not subjected to materially varying temperature/pressure conditions. To the contrary, as explained, a plastic coating for DX system refrigerant transport lines would be subjected to materially varying temperature and pressure conditions in an operational geothermal heating/cooling system. When DX refrigerant transport tubing is subjected to varying high and low pressure situations (such as up to 450 psi in the cooling mode and down to 50 psi in the heating mode, as an example), the refrigerant transport tubing, when not in a confining material (such as cementitious Grout 111 for example) can tend to expand and contract, and thereby stress a plastic, or the like, coating. 
         [0015]    As mentioned, PVC, as commonly used in the gas industry for coating gas transport metal tubing, is factually not an acceptable plastic for coating operational heating/cooling DX system refrigerant transport lines, as PVC reportedly develops stress cracks over a period of years when subjected to materially varying temperature and/or pressure conditions. Such exterior PVC coating stress cracks, in a geothermal heating/cooling DX system, would result from the typical, and rather constant, expansion/contraction and changing temperature conditions of the interior metal (usually copper) refrigerant transport tubing, which tubing transports refrigerant under widely varying pressure and temperature conditions. Further, in a gas transport system, the effect of a plastic coating on the heat transfer ability of the metal gas transport tubing is generally immaterial and is not a significant consideration, which is not the case in a DX system application. 
         [0016]    The immateriality of heat transfer in metal gas transport lines is further evidenced by the fact that, to withstand relatively high, and relatively constant, operational pressures, corrugated stainless steel tubing must be braided on the exterior. Braiding corrugated stainless steel tubing can result in minute air gaps between the corrugated steel and the braiding, which air gaps are detrimental to heat transfer, but are of no consequence when simply transporting natural gas. To the contrary, in a DX geothermal heating/cooling system, where the sub-surface refrigerant transport tubing is used for primary geothermal heat transfer purposes, the effects of any plastic coating and/or air bubbles upon the sub-surface metal refrigerant transport tubing poses a primary concern and must be taken into account. 
         [0017]    Thus, for a DX system application, any plastic coating applied to the sub-surface metal refrigerant transport tubing should be carefully considered and analyzed, as DX system operating parameters materially differ from mere gas transportation applications and from other conventional water-source geothermal system applications where only water, or a water/antifreeze mixture, is transported at relatively low pressures, and with relative low temperature differentials. 
         [0018]    Regarding other conventional water-source geothermal system applications, the use of polyethylene plastic pipe, with typical approximate ¼ inch thick walls (down to about 300 feet deep), for both water conveyance and geothermal heat transfer purposes, in water-source geothermal systems has long been used, in lieu of PVC, because the industry discovered decades ago that PVC piping reportedly developed stress cracks and leaked after multiple years of service, resulting in system failures and in requisite, and expensive, sub-surface heat exchange loop replacements. 
         [0019]    Further, while the general heat transfer rate of polyethylene walled piping is relatively low, only about 0.225 BTUs/Ft.Hr. degrees F., since the temperature delta between the water circulated within the pipe and the surrounding ground is also relatively low (typically only about 10 to about 20 degrees F.), and since the typically bentonite clay, sand, and water grouting typically used to fill the annular space within the borehole of a closed-loop system typically has less than an approximate 0.7 to 1.0 BTUs/Ft.Hr. degrees F. heat transfer rate, even though the surrounding ground&#39;s heat transfer rate may be much higher (3.6 BTUs/Ft.Hr. degrees F. for typical limestone, dolomite, and marble, for example), polyethylene piping has still been widely used in the water-source heating/cooling industry because it is crack resistant and relatively cheap in the diameters, and wall thicknesses (thick enough to accommodate water pressure depending on depths of boreholes) necessary to accommodate the requisite large gallon per minute water-flow rates of about 8, plus or minus, gallons per minute per ton of system design capacity. Further, since the heat transfer rate of the polyethylene is so poor, the conventional water-source geothermal industry would typically prefer to have the entire sub-surface water heat exchange pool exposed, for extra geothermal heat absorption (in the heating mode) and rejection (in the cooling mode) capacities, without worrying about the “short-circuiting” effect of the warmer water in one side of the plastic loop being proximate to the cooler water on the other side of the loop within the same well/borehole. 
         [0020]    A water-source system would generally never use metal sub-surface water transport piping for geothermal heat transfer purposes because the price of 1 inch interior diameter, or larger, metal tubing (such as copper, for example), to accommodate the requisite gallon per minute water flow rate in both the supply and return sub-surface heat transfer lines, would likely be prohibitive, and therefore usually never realistically considered. Further, yet another disadvantage in conventional closed-loop water-source system designs is that the deeper one places a plastic polyethylene walled water containment/transport loop, the thicker the wall needs to be to withstand the increased water pressure, and the thicker the wall, the more the inhibition of the geothermal heat transfer rate via the plastic (which is not a good heat conductor). 
         [0021]    Regarding the insulating of portions of metal refrigerant transport tubing designed for geothermal heat transfer, there is basis for the general and widely held belief that plastic is an insulator and that plastic coating metal refrigerant transport tubing will impair system operational efficiencies. In fact, common refrigerant transport line insulation is comprised of expanded (foam) polyethylene plastic, or the like. Thus, historically, there has been legitimate basis for the general DX system industry perception that coating refrigerant transport lines with plastic will inhibit heat transfer. Consequently, plastic coated refrigerant transport tubing has not been used for DX system geothermal heat transfer enhancement purposes. 
         [0022]    Some plastic coated copper refrigerant transport lines have reportedly been used for hydronic heating purposes, where the plastic coated copper tubing is embedded in concrete or cement. However, this is because of the general industry misconception that concrete or cement is always corrosive to copper. 
         [0023]    For example, metal (typically copper) water transport lines have historically been coated with plastic for a number of years, particularly in Europe, to protect the metal water transport lines against alleged corrosive effects of surrounding concrete. However, such prior applications were based upon misinformation. Extensive testing via The Copper Development Association, with offices in New York, N.Y., and/or various expert consultants cited by The Development Association, have evidenced that concrete is not corrosive to copper, unless it has exceptionally high sulfur content, which is not the norm. More often, damage to copper tubing, historically incorrectly attributed to the concrete the copper tubing was surrounded by, usually resulted from corrosive elements within the water the copper tubing was transporting, or resulted from uninsulated entry/exit points from the concrete, where the copper tubing would naturally expand/contract longitudinally under changing temperature/pressure conditions, or would otherwise be subjected to external wear and tear forces (not the fault of the concrete&#39;s composition). 
         [0024]    Further, just as in the natural gas transportation industry, the application of a plastic coating to copper tubing for heating purposes only (typical operational temperature ranges of around freezing to only 70 degrees F.) does not expose the plastic coating to the extreme temperatures encountered via a reverse-cycle DX heat pump system operating in both the heating mode and the cooling mode, where temperatures well below freezing can be encountered in the heating mode, and where temperatures as high as around 200 degrees F. can be encountered in the cooling mode. In fact, since plastic coated copper tubing, used for hydronic heating purposes in concrete, is historically operated only in the heating mode, only a common polyethylene coating, with a melting point typically around 140 degrees to 180 degrees F., is typically used, and only the effects of modest temperature/pressure changes upon the plastic, which coats the copper, have historically been considered. 
         [0025]    Regardless, due to the generally incorrect perception that concrete is corrosive to copper tubing, many various in-floor heating systems, called hydronic heating systems (hydronic heating systems are well understood by those skilled in the art), as well other industry applications where copper is embedded within concrete or cement, now require copper tubing within concrete to be coated with a protective plastic covering. Such a plastic coating is typically comprised of a standard polyethylene plastic covering, even though the plastic cover is generally perceived as detrimental to heat transfer and/or to initial system costs (as coating copper tubing with plastic incurs additional expenses) under most all common heating purpose applications. Further, due to the fact that such a polyethylene plastic coating is generally perceived as detrimental, or at least of no significant value, to heat transfer in most all common and historical heating purpose applications (such as hydronic system applications, for example), the heating/cooling industry, just as the DX system industry, has generally assumed any plastic coating applied to copper refrigerant transport tubing, used for heat transfer purposes, would be detrimental to heat transfer and/or of not enough positive value to offset the additional request cost, and therefore generally undesirable. 
         [0026]    In fact, for traditional hydronic heating purposes, where relatively low temperature differentials (about 20 degrees F., more or less) are employed via the circulation of heated water within typical ½ inch to 1 inch, or larger, I.D. tubing (plastic tubing and/or plastic coated copper tubing, or the like), the heat transfer rate differential through copper tubing versus plastic coated copper tubing is virtually the same (because of the relatively low temperature differentials), and is relatively insignificant at best. Thus, the additional cost to plastic coat such copper tubing is viewed as a burden occasioned by the misconception that normal concrete (normal concrete as opposed to concrete with a known high sulfur and/or other known corrosive element content) is corrosive to copper. 
         [0027]    Further, in support of such a general belief that coating copper tubing inhibits heat transfer, testing has indicated that even in a DX system operating in the cooling mode, where the copper refrigerant transport tubing is installed within a water-filled polyethylene pipe, to protect the copper tubing from corrosive soil/water conditions (typically below a 5.5 ph, or above an 11 ph, or in other conditions corrosive to copper), geothermal heat transfer abilities are inhibited about 17%, or more, in a ¼ inch walled polyethylene pipe installed within limestone to a depth of about 300 feet. 
         [0028]    Regarding air-source heat pumps, a primary design feature of air-source heat pumps is to abstract heat from the air during the winter without having to burn a fossil fuel, and to reject heat into the air during the summer season. An air-source heat pump system (which is well understood by those skilled in the art) operates with reasonable efficiencies when the outside air is about 55 degrees F. in the winter, and when the outside air is about 70 degrees F. in the summer. However, when the outside air becomes colder during the winter or warmer during the summer, the operational efficiencies drop, and when heating or cooling is most needed during periods of outside air temperature extremes, air-source heat pumps are at their worst operational efficiencies. Even when operating under good conditions, the temperature differentials between the refrigerant circulating within the exterior air heat exchange tubing and the air itself is typically relatively low, and may only be in the approximate 15 to 20 degree F. range. 
         [0029]    Again, for reasons as outlined above, because of the wide-spread belief that a plastic coating has a negative effect on the heat transfer ability of copper tubing, and/or that a plastic coating, at best, does not have enough positive effect to offset the additional cost, the finned copper tubing portion, designed for heat transfer, of air-source heat pumps, generally, and most certainly at least the refrigerant to air heat transfer finned tubing portion of DX geothermal heating/cooling systems, have historically not been plastic coated. As explained, since DX systems usually operate with higher temperature differentials than conventional water-source geothermal heat pump systems, and also usually operate with higher temperature differentials than conventional air-source heat pump systems, the coatings disclosed herein for the finned tubing portion of any segment of a DX geothermal heating/cooling system designed for convective heat transfer may be coated as disclosed so as to increase system operational efficiencies. Finned tubing segments of a DX geothermal heating/cooling system designed for refrigerant to air convective heat transfer are well understood by those skilled in the art, and typically consist of the finned tubing inside at least one of an interior air handler, or the like, although DX systems can also periodically utilize an array of finned tubing designed for exterior convective heat transfer so as to reduce the cooling load on the well/borehole when operating in the cooling mode. Interior air handlers and arrays of finned tubing designed for refrigerant to air convective heat transfer are well understood by those skilled in the art. 
         [0030]    In the heating mode, a Deep Well (herein defined as greater than approximately 100 feet deep) DX system typically extracts geothermal heat from surrounding approximate 55 degree (plus or minus depending on geographic location) ground, regardless of the outdoor ambient air temperature. Thus, in the heating mode, a DX system typically operates similarly to an air-source system when the exterior air is 55 degrees F., except that a DX system does not require the power draw of an exterior fan. Of course, the farther the exterior air temperature drops below 55 degrees F., the heat transfer ability of a DX system becomes increasingly superior to that of an air-source system in the heating mode. Further, at exterior air temperatures below about 40 degrees F., unlike an air-source heat pump, a DX system does not require an energy-consuming and extremely inefficient defrost cycle. 
         [0031]    During the cooling mode, a DX system is rejecting heat into approximate 55 degree F. ground, instead of into 80 to 90 degree F. air, as with an air-source heat pump. Thus, the temperature differential between the refrigerant entering the exterior, sub-surface, heat exchange portion of a DX system, and exiting same, is typically much greater than that of the entering/exiting refrigerant temperature differential of an air-source heat pump. This is because an air-source system is limited to the exterior air temperature for its low temperature point in the exterior finned tubing heat exchanger (an air-source exterior finned tubing heat exchanger is well understood by those skilled in the art). Thus, this greater temperature differential of a DX system, which is typically in the 25 degree F. to 80 degree F. range (as opposed to only an approximate 15 to 20 degree F. range via other conventional air-source system designs/applications), provides greatly enhanced operational efficiencies over an air-source heat pump, and also provides colder refrigerant with significantly enhanced humidity removal abilities (since the refrigerant is further below the dew-point). 
         [0032]    Because of the significant advantages of a DX heating/cooling system over other conventional designs, and because of the desire to protect the metal (typically copper) tubing of a DX system in a sub-surface environment that may be corrosive to the metal refrigerant transport tubing used, heat transfer testing with various coated and uncoated copper tubing designs was performed to ascertain the heat transfer ability of copper tubing in a DX system, with its typically much higher temperature differentials than other conventional system designs. In this regard, the value of the various coatings was first evaluated in the air for heat transfer purposes, and then next in a sub-surface environment. In a sub-surface heat transfer application in a DX heat pump system, heat transfer is via conductive heat transfer with the surrounding geology. In an above-surface heat transfer application in a DX heat pumps system, heat transfer is via convective heat transfer with the surrounding air (typically interior air, but exterior air can sometimes be utilized when one is decreasing the cooling load on the well). 
         [0033]    DX system sub-surface conductive heat transfer is typically effected by sub-surface metal heat exchange tubing (usually copper tubing) placed within ground and/or water and/or a heat conductive grout fill material. DX system above-ground heat transfer is typically effected by above-surface finned metal heat exchange tubing exposed to the air (usually interior air). DX systems are unique from conventional heat pump system designs in their operational pressures and temperatures, all of which is further distinguished via DX systems operating on R-410A refrigerant, in lieu of the more conventional R-22, or the like, refrigerants. The use of more conventional refrigerants, such as R-22 or R-407C for example, result in DX systems operating at lower pressures, and are clearly distinguishable from DX systems operating on a higher pressure (typically at least a 33.3% higher pressure) refrigerant, such as R-410A, or the like, as is well understood by those skilled in the art. 
         [0034]    Of great interest and importance was the following unanticipated fact disclosed via the subject testing: Namely, testing reflected that a special very thin plastic coating applied to the above-surface portion of the metal, refrigerant transport, heat transfer tubing segments of a DX system, exposed to the air for convective heat transfer purposes, actually enhanced the heat transfer ability of the above surface heat exchange tubing by about 25%, or more, with the typical greater entering/exiting operational refrigerant temperature differentials unique to a DX system, and particularly unique to a Deep Well DX system. 
         [0035]    Specifically, testing has shown that, in the heating mode, a very thin plastic, or the like, coating improves the convective heat transfer in a DX system by approximately 25% when the temperature of the fluid within the plastic coated metal tubing is raised from 43 degrees F. to 59 degrees F., as an example. Further, testing has shown that, in the cooling mode, a very thin plastic, or the like, coating provides an approximate 25% advantage when the temperature of the fluid within the plastic coated metal tubing is lowered from 156 degrees F. to 88 degrees F., as an example. Thus, in a DX system application, there is a distinct positive heat transfer efficiency advantage in coating the above surface metal heat transfer tubing with a very thin plastic, or the like, coating. The very thin coating may be less than about 0.017 inches thick, and may have an approximate 0.009 inch thick, or less, wall, for example. Further, testing has shown that coating the above-ground portion of the heat transfer tubing in a DX system with a very thin paint, such as a high gloss paint, will also similarly increase the convective heat transfer ability. 
         [0036]    These test results, for convective heat transfer purposes in a DX system application, run contra to generally anticipated results that a plastic coating would be detrimental and/or not worth the additional cost. 
         [0037]    In addition to providing an overall significant system operational heat transfer advantage of about 25% in the refrigerant to air exchange side of a reverse-cycle DX system, which operates during both the heating season and the cooling season, such a special very thin plastic, or the like, coating, as herein explained, provides protection against most all common above-surface naturally occurring potentially corrosive air related environments. Further, the approximate 25% enhanced heat transfer capacity for the above-referenced above-ground heat exchange portions (typically comprised of a refrigerant to air heat exchanger, comprised of finned metal tubing and a fan, which are all well understood by those skilled in the art) of a DX system, when coated with at least one of a very thin paint and a very thin plastic, or the like, coating, no more than about 0.17 inches thick and preferably about 0.009 inches, or less, thick, would at least one of further enhance overall DX system operational efficiencies and decrease interior air handler sizing requirements and costs. Also, in such an application, the very thin coating may be able to withstand at least 200 degree F. heat without impairment. 
         [0038]    As disclosed, a very thin paint coating, or the like, may alternately be used, in lieu of a thin plastic, or the like, coating, for use in coating the refrigerant transport tubing of any refrigerant to air heat transfer system and/or unit, although such a very thin coating is particularly useful in a DX system application because of the advantages produced in the operational ranges of a DX system, particularly when operating on an R-410A refrigerant. Thus, one could also optionally paint refrigerant transport tubing (commonly metal tubing and commonly used for convective heat transfer) with a very thin paint, or the like, which may be capable of withstanding at least 200 degree F. operational temperatures (which paint may be comprised of a high gloss paint) and obtain enhanced operational performance similar in nature to that afforded by a very thin plastic, or the like, coating as described herein. The very thin paint coating, or the like, would be virtually (for enhanced heat transfer purposes) identical to the very thin plastic, or the like, coating, except being comprised of a thinner, non-plastic, wall of paint. 
         [0039]    Optional very thin coatings may coat the refrigerant transfer tubing used for refrigerant to air heat DX system heat exchange via convective heat transfer would be comprised of a polyethylene (“PE”), a polycarbonate, a tetrafluoroethylene resin (PTFE) Teflon®, such as DuPont Teflon12 PFA, a fluoropolymer dip coating, plasma-polymerizing a fluoroethylene monomer, such as tetrafluoroethylene, in the presence of the desired exterior surface and depositing a fluoropolymer coating on the exterior surface, a triazine-dithiol derivative, a nylon, a tetrafluoroethylene resin (PTFE) Teflon 12, such as DuPont Teflon® PFA, having a thickness coating of only about 0.003 to 0.004 inches, a fluroropolymer dip coating, a plasma-polymerizing a fluoroethylene monomer, such as tetrafluoroethylene, in the presence of the desired exterior surface and depositing a fluoropolymer coating of about 1/10,000 inch or less on the exterior surface, and a triazine-dithiol derivative, All such additionally optional very thin coatings may be able to withstand at least 200 degree temperatures without any impairment. When rugged enough not to easily be scratched off during insertion into a well/borehole, at least one of the said optional coatings may also be utilized to protect sub-surface metal refrigerant transport tubing in a sub-surface environment that is corrosive to the metal refrigerant transport tubing. 
         [0040]    To the contrary of convective heat transfer, testing has shown that in a conductive heat transfer application, where the sub-surface portion of the DX system is exposed to at least one of a grout fill material and the naturally occurring surrounding geology, a plastic coating is detrimental to heat transfer. For example, when the DX system&#39;s typical copper tubing is positioned within a fluid filled polyethylene pipe with an approximate ¼ inch plastic wall thickness, the heat transfer ability is reduced by as much as about 17%. Testing has also shown that the thinner the plastic wall, the less the inhibitive effect upon the desired heat transfer rate. 
         [0041]    However, if such a plastic, or the like, coating is used to protect metal refrigerant transport tubing against elements corrosive to metal, if the coating wall is too thin, the coating is easily damaged and the integrity of the coating is easily impaired. Thus, when used for the purpose of protecting metal tubing from corrosive elements, the coating needs to be thick enough for the integrity not to be easily compromised, but thin enough so as not to materially impair the desired sub-surface geothermal heat transfer. Specifically, testing has demonstrated that such a coating would be comprised of a moderately thin polyethylene coating, or the like, with a wall thickness between about 0.01 and 0.03 inches thick, plus or minus about 20%. Such a moderately thin thickness is ample to protect the heat transfer tubing without undue integrity impairment risk, while typically only impairing sub-surface conductive heat transfer abilities by only about 5%, or less. 
         [0042]    Regarding protection of the sub-surface metal refrigerant transport tubing in a DX system, one solution to the potential of negative effects, of sub-surface corrosive conditions upon sub-surface copper tubing in a DX system, has been to fully surround the copper tubing with a heat conductive cementitious grout fill material that is not corrosive to copper tubing, and that can withstand temperatures of at least about 200 degrees F. Such a cementitious grout, for example, is a Grout 111 mix developed by the USA&#39;s Brookhaven National Laboratory in New York State, as is well known by those skilled in the art. Grout 111 is highly heat conductive (about 1.4 BTUs/Ft.Hr. degrees F.), and is far more heat conductive than commonly used bentonite clay based grouts. Clay based grouts are water permeable, and therefore, in addition to their poor heat conductivity, are also capable of corrosive element infiltration, However, if a cementitious grout does not completely surround the tubing within a deep well/borehole in a corrosive sub-surface environment, which may be difficult to always ascertain, the risk of damage to refrigerant transport copper tubing would still be present. Thus, an improved protective means, such as incorporating a moderately thin plastic, or the like, coating, for the sub-surface heat transfer portion of the refrigerant transport tubing, may be advantageous in a corrosive environment where a cementitious grout fill material is used. 
         [0043]    Another way to protect sub-surface refrigerant transport tubing in a DX system application from corrosive sub-surface environments would be to use a metal other than commonly used copper, such as stainless steel tubing, or the like, that is not affected by most naturally occurring elements. However, stainless steel tubing and/or flexible, corrugated stainless steel tubing, is typically far more expensive than copper tubing, and, if installed in salt water applications, can still be subject to damage from certain micro-organisms that eat stainless steel. Thus, even if another metal, other than copper, is used, a thin plastic coating still generally provides enhanced protective qualities in a DX system application. 
         [0044]    More specifically regarding the thickness of a moderately thin plastic coating, such as polyethylene coating for example, testing has shown that there is less than a 1.5% difference in using a heavier and more protective and rugged approximate 0.03 inch thick wall polyethylene plastic coating rather than a thinner and less protective approximate 0.017 inch thick wall polyethylene plastic coating. 
         [0045]    However, in a DX system application, an additional factor still needs to be considered. This additional factor is the melting point of the plastic used for a coating. A standard polyethylene (“PE”) plastic, for example, generally only has a temperature resistance level (prior to melting) of about 140 degrees F. to 180 degrees F. Thus, in a DX system application, where operational temperatures can periodically approach the 190 degrees F., or greater, temperature ranges, a special polyethylene raised temperature (“PERT”) type plastic may be used which has a melting point of at least 200 degrees C., as opposed to the more common standard polyethylene coating with a lower melting point. 
         [0046]    Additionally, testing has shown that an approximate 0.01 inch thick coating, plus or minus about 20%, of a normal/standard, solid-state, polyethylene coating (typically only rated to withstand about 180 degrees F.), as opposed to high temperature polyethylene coating capable of withstanding about 200 degree C. temperatures, is a better insulator, and a worse heat conductor, than a PERT type plastic, by about 5%, or less. Thus, when a greater heat conductivity rate is desired (such as for a moderately thin coating on sub-surface metal refrigerant transport tubing to protect against elements corrosive to metal, and/or such as to enhance convective heat transfer), a PERT type plastic may be used. However, if one is using a solid-state polyethylene plastic to insulate the liquid refrigerant transport line of a DX system, for example, a thicker normal/standard polyethylene coating may be used, unless the coating is applied in areas where temperature protection over about 180 degrees F. is preferred, in which case the PERT type plastic may be used so the integrity of the plastic is not compromised. 
         [0047]    Regarding additional practical considerations in a sub-surface DX system application, a thinner plastic coating, such as about 0.01 inches thick for example, can more easily get nicked off and compromised in rugged sub-surface conditions, such as jagged rock or the like. However, a heavier coating, beyond about 0.03 inches has too much of a negative impairment on heat transfer for highly efficient use in a DX system application. Thus, an approximate 0.02 inch, plus or minus about 20%, moderately thin PERT coating, or the like, on the sub-surface metal refrigerant transport tubing of a DX system may be preferable, for protective purposes only, in actually and/or potentially corrosive environments. Such a moderately thin coating thickness provides rather rugged protection against corrosive elements, while not impairing heat transfer to an excessive extent. 
         [0048]    Further, in the sea, such a special moderately thin plastic coating will help to protect sub-surface copper refrigerant transport tubing against the abrasive effects of the salt water and sand currents, and will even help to protect stainless steel refrigerant transport tubing against the small micro-organisms that actually eat and deteriorate stainless steel. 
         [0049]    However, the best protective coating design for the sub-surface tubing of a geothermal DX heating/cooling system in an environment that is corrosive to metal refrigerant transport tubing would be to both coat all of the sub-surface metal tubing with an approximate 0.02 inch, plus or minus about 20%, moderately thin PERT coating, or the like, and to surround the coated metal tubing with a protective grout fill material, such as a cementitious grout 111, or the like, that is virtually water impermeable (and therefore cannot be attacked by corrosive elements in the surrounding geology). 
         [0050]    Regarding convective heat transfer, as DX system testing has evidenced an unanticipated approximate 25% enhanced convective heat transfer capacity for a refrigerant to air heat exchanger when the metal refrigerant transport tubing is coated with at least one of a very thin plastic and paint, or the like, coating, additional testing has evidenced the finned metal tubing of any traditional interior and/or exterior convective heat exchange refrigerant to air heat transfer tubing (finned or otherwise) may also be coated with at least one of a very thin plastic, or the like, and a very thin paint coating, with the thin plastic, or the like, no more than about 0.017 inches thick, and preferably no more than about 0.009 inches thick. This would at least one of enhance overall DX system operational efficiencies and decrease interior air handler and/or other convective heat transfer apparatus sizing and costs. Due to the operational pressures and temperatures unique to a DX system, operating with an R410A refrigerant, such a thin coating of at least one of plastic, or the like, and paint would be of exceptional value in a DX system application. 
         [0051]    It may be advantageous for the coating material to be crack resistant. The transport tubing is subject to expansion and contraction over time, which may develop stress cracks in certain coatings (such as some PVC materials). PE materials are generally known to resist such stress cracks due to temperature and/or pressure fluctuations, and therefore may be advantageous in certain applications. 
         [0052]    U.S. Pat. No. 6,932,149 to Wiggs discloses the advantage of fully insulating a sub-surface liquid refrigerant transport line. However, as the result of expanded and more detailed testing, using five  300  foot deep test wells, which were simultaneously tested with differing insulation designs, an improved insulation design has been found for vertically oriented heat transfer tubing used in a DX system. Namely, about one-third of the upper top portion of the smaller sized liquid transport line should be insulated with at least an approximate 0.10 inch thick, plus or minus about 20% of the upper approximate one-third portion, heavy coating of a solid polyethylene, or the like, coating. Such a coating may be able to withstand at least a 200 degree F. minimum heat without any impairment. 
         [0053]    Additionally, an upper portion of the liquid transport line may have an additional thickness of coating to improve performance. The upper portion may be approximately fifteen percent of the overall tubing depth, plus or minus about 20% of that upper portion. The upper portion may already have an initial coating of approximately 0.10 inch thick, plus or minus about 20%. It may further be coated with an additional and/or thicker coating of polyethylene, or the like, to provide a wall thickness of at least approximately 0.20 inch thick, plus or minus about 20%. The upper portion of each liquid transport line may be coated with a PERT type polyethylene insulation, or the like, so as not to encounter problems with temperatures in excess of 200 degrees F., as herein more fully explained. 
         [0054]    An acceptable alternative, in wells of an approximate 300 foot, or less, depth, would be for the upper portion of the liquid transport line (up to a maximum of approximately 50 feet) to have the initial coating of approximately 0.10 inches and further to have an expanded foam polyethylene type insulation, or the like, with at least about a ½ inch thick wall. While the thicker the plastic and/or foam insulation wall, to a point, the better the insulation value, other factors in a unique DX system application are relevant and should be considered, such as cost and fabrication/installation time. Testing has indicated that with a primary plastic, or the like, heavily coated liquid refrigerant transport line in a DX system, an approximate ½ inch thick expanded foam insulation wall provides about 93% as much heat transfer impediment as does a ¾ inch thick insulation wall. Therefore, when the borehole diameter size warrants, at least a ¾ inch thick wall expanded foam insulation may be used, but if the borehole diameter is too small, at least a ½ inch thick wall expanded foam insulation may be alternatively used. Such an expanded plastic foam, or the like, may also be able to withstand at least a 200 degree F. heat level without incurring any impairment. 
         [0055]    Further, such a plastic foam, or the like, may be comprised of a rigid type foam, such as Tubolite, or the like, as a softer foam is susceptible to crushing by the surrounding geology and/or fill material. If the foam is crushed due to pressures of the surrounding geology or grout, it will lose its design insulation properties. At depths beyond about 45 to 50 feet, the double thick walled 0.2 inch thick, plus or minus 20%, solid state polyethylene insulation may be used as a heavy insulation coating for the liquid refrigerant transport line, as field trials have shown that the psi pressure of the borehole fill material (typically water and/or grout) will crush an expanded foam type insulation to an unacceptable level beyond an approximate 45 to 50 foot depth. 
         [0056]    However, when using a ¾ inch thick insulation wall material, boreholes may need to be wider, meaning at least one of more drilling time/expense and more drilling debris to remove. Additionally, pre-assembled spools of sub-surface DX system refrigerant transport tubing, with an un-insulated larger diameter vapor refrigerant transport line, and with at least a partially insulated smaller diameter liquid refrigerant transport line (as taught herein), may need to be larger, which increases shipping and storage costs. 
         [0057]    Thus, as testing has indicated that using an approximate ½ inch thick walled expanded foam insulation material still impedes the heat transfer rate by about 240% when a heavily plastic, or the like, coated sub-surface liquid refrigerant transport line is also utilized, and as there is only an approximate 7% heat transfer impediment when using an approximate ½ inch thick walled insulation instead of an approximate ¾ inch thick walled insulation, in conjunction with a heavily plastic coated liquid refrigerant transport line, the reduction in actual and potential sub-surface refrigerant transport tubing installation costs typically warrant the use of an approximate ½ inch walled insulation in a DX system application. The expanded foam insulation may be comprised of an expanded polyethylene foam, or the like, which is non-corrosive to copper tubing and which foam is resistant to most sub-surface environments. As mentioned, the foam may be of a rigid foam design as opposed to a soft foam design, so as to be able to better withstand moderate psi water/grout pressures in the 20 to 50 foot depth ranges. Thus, the actual borehole diameter and depth conditions will typically dictate the insulation type to be used on the liquid refrigerant transport line in the upper 15%, plus or minus 20% of the upper 15%, segment in a vertically oriented sub-surface DX system heat exchange loop. In such a system, the smaller liquid refrigerant transport line would be coupled to the larger vapor refrigerant transport line at or near the bottom of the well, as would be well understood by those skilled in the art. 
         [0058]    All of the preceding disclosures herein, due to the operational pressures and temperatures unique to a DX system operating with an R410A refrigerant (which operational pressures and temperatures are well understood by those skilled in the art) would be of exceptional positive value in a DX system application, when the DX system is operating with an R-410A refrigerant. In fact, all of the testing leading to the subject disclosures was based upon the unique factors of a DX system operating on an R-410A refrigerant. 
         [0059]    In summary therefore, testing has indicated, especially in a DX system application with vertically oriented sub-surface heat exchange tubing: that the upper approximate one-third portion, plus or minus about 20% of the upper one-third portion of the sub-surface liquid refrigerant transport line, may be insulated with a solid-state insulation material, such as a polyethylene, or the like material, that is at least about 0.10 inch thick, plus or minus about 20%; that the upper approximate 15% portion, plus or minus about 20% of the upper 15% portion, of the liquid refrigerant transport line may be insulated with at least one of an expanded foam type insulation material, such as an expanded polyethylene foam, or the like, material, that has at least about a ½ inch thick wall (but not exceeding an approximate 50 foot depth for the expanded foam), and a solid-state material, such as a plastic (a polyethylene plastic for example), or the like, with a wall thickness of at least about 0.2 inches (such as a solid-state polyethylene, as an example); that the entire refrigerant to air heat exchanger&#39;s refrigerant transport heat exchange tubing (finned or otherwise) may be coated with at least one of a thin plastic coating, where the plastic coating is no more than about 0.017 inches thick, and a paint; and that all the sub-surface tubing of the DX system, that is exposed to a corrosive environment, may be at least one of fully surrounded by a protective grout material, such as Grout 111 or the like (Grout 111 is well understood by those skilled in the art, and is a cementitious grout that does not transfer water and, thus, prevents corrosive elements from reaching the refrigerant transport tubing), and fully coated with a protective coating of a solid-state plastic coating, or the like, such as polyethylene, as an example, that has a thickness of only about 0.02 inches thick, plus or minus about 20%. 
         [0060]    Lastly, in a vertically oriented geothermal heat transfer DX system design, the sub-surface refrigerant transport loop may be built at a factory, wound onto a containment core/spool, and shipped to the jobsite for installation, via rolling the tubing loop spool off the containment core into the well/borehole. Thus, the subject liquid and vapor refrigerant transport tubing spool may arrive at a job site in a mostly pre-built condition and already leak checked, wound into a spool onto on a central containment core, so that the metal (typically soft copper) tubing loop can be easily lowered into the well/borehole, as is well understood by those skilled in the art. However, field trials have indicated that the sizing of the central containment core of the copper spool is very critical so for at least a partially plastic coated ground loop spool, so as to avoid “S” bends in the copper tubing loop, and/or so as not to impair the plastic coating, during ground loop installation. In fact, field trials have evidenced the interior diameter of the central containment core of the spool, onto which the refrigerant transport tubing is rolled during assembly, may be at least 33 inches in diameter, so as to at least one of not overly stress any portions of the refrigerant tubing&#39;s plastic coating and to avoid “S” bends in any portions of the copper tubing during field installation. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0061]    For a more complete understanding of this disclosure, reference should be made to the embodiments illustrated in greater detail on the accompanying drawings, wherein: 
           [0062]      FIG. 1  is a side view of a metal refrigerant transport tube segment, with a thin plastic, or the like, exterior coating applied in accordance with the present disclosure. 
           [0063]      FIG. 2  is a top view of a metal refrigerant transport tube view with a plastic exterior coating applied in accordance with the present disclosure. 
           [0064]      FIG. 3  is a side view of a finned metal refrigerant transport tube of a refrigerant to air heat exchanger with at least one of a thin plastic exterior coating and a thin paint applied in accordance with the present disclosure. 
           [0065]      FIG. 4  is a top view of a finned metal refrigerant transport tube of a refrigerant to air heat exchanger with at least one of a thin plastic and a thin paint exterior coating applied in accordance with the present disclosure. 
           [0066]      FIG. 5  is a side view of a coil of plastic coated refrigerant transport tubing used for sub-surface refrigerant transport in a DX system. 
           [0067]      FIG. 6  is a side view of a plastic coated liquid refrigerant transport tube surrounded by insulation with a ½ inch thick wall. 
           [0068]      FIG. 7  is a side view, not necessarily drawn to scale, of a liquid refrigerant transport line, where the top one-third of the line is coated with a solid-state plastic coating, and where the top fifteen percent is additionally surrounded by an expanded foam insulation. 
       
    
    
       [0069]    It should be understood that the drawings are not necessarily to scale and that the disclosed embodiments are sometimes illustrated diagrammatical and in partial views. In certain instances, details which are not necessary for an understanding of this disclosure or which render other details difficult to perceive may have been omitted. It should be understood, of course, that this disclosure is not limited to the particular embodiments illustrated herein. 
       DETAILED DESCRIPTION 
       [0070]    The following detailed description is of the best presently contemplated mode of carrying out the disclosure. The description is not intended in a limiting sense, and is made solely for the purpose of illustrating the general principles of the disclosure. The various features and advantages of the present disclosure may be more readily understood with reference to the following detailed description taken in conjunction with the accompanying drawings. 
         [0071]    In one embodiment of the disclosure, as shown via a side view in  FIG. 1 , not drawn to scale, is a segment of a sub-surface refrigerant fluid transport tube  1  of a DX heat pump system (not shown in full herein as same is well understood by those skilled in the art). The sub-surface tube  1  segment is such as is typically found in refrigerant-based DX heating and cooling systems, which are well understood by those skilled in the art. A thin plastic, or the like, protective coating  2  may be applied to the exterior heat exchange surface of the sub-surface refrigerant transport tubing  1 . The coating  2  may be no more than about 0.02 and about 0.03 inches, plus or minus about 20%, thick for a DX system sub-surface refrigerant transport tubing  1  application, and is comprised of a material that resists developing stress cracks via at least one of temperature and pressure changes. The coating  2  has a melting point temperature that will withstand at least 200 degrees F. without impairment, such as a PERT plastic coating  2  for example. 
         [0072]    Additionally, when rugged enough to resist being scratched off during insertion into a well/borehole (not shown herein, but well understood by those skilled in the art), the coating  2  may comprise at least one of a polyethylene (“PE”), a polycarbonate, a tetrafluoroethylene resin (PTFE) Teflon®, such as DuPont Teflon® PFA, a fluoropolymer dip coating  2 , plasma-polymerizing a fluoroethylene monomer, such as tetrafluoroethylene, in the presence of the desired exterior surface and depositing a fluoropolymer coating  2  on the exterior surface, a triazine-dithiol derivative, and a nylon, or the like, as opposed to a PVC (polyvinylchloride) coating  2 , for example, that might develop stress cracks over time. The moderately thin coating  2  would be applied to the exterior surface of the metal refrigerant transport tubing  1  to protect the metal tubing  1  from actually and/or potentially corrosive sub-surface elements (not shown). 
         [0073]      FIG. 2 , not drawn to scale, is a top view of a sub-surface heat exchange component of a DX heat pump system sub-surface heat exchange system (not shown in full herein as same is well understood by those skilled in the art) is shown. The sub-surface heat exchange component is a segment of refrigerant transport tubing  1 , as conventionally found in refrigerant-based DX heating and cooling systems, which are well understood by those skilled in the art. A moderately thin plastic, or the like, coating  2  may be applied to the exterior heat exchange surfaces of the sub-surface refrigerant transport tubing  1 . The coating  2  may be no more than about 0.02 and 0.03 inches, plus or minus 20%, thick for a DX system sub-surface refrigerant transport tubing  1  application, and is comprised of a plastic, or the like, that is resistant to developing stress cracks via at least one of temperature and pressure changes. Additionally, the coating  2  may be optionally comprised of a coating  2  such as at least one of a plastic and a paint and an alternative material as described in  FIG. 1  above, or the like, that has a melting point temperature of at least about 200 degrees F., such as a PERT plastic for example. 
         [0074]      FIG. 3 , not drawn to scale, is a side view of a segment of a heat exchange component of an refrigerant to air heat exchange system that is used for convective heat transfer from refrigerant to air and vice versa. An refrigerant to air heat exchange system (typically an interior air handler, or the like) is not shown in its entirety as same is well understood by those skilled in the art. The segment of a heat exchange component shown herein is comprised of a segment of refrigerant fluid transport tube  1  with at least two exterior expanded surface area heat transfer fins  3  in thermal contact with, and arranged in a vertical position parallel to, the longitudinal axis of the tubing  1 , as conventionally found in a DX refrigerant to air heating and cooling system. A very thin plastic, or the like, coating  2  may be applied to the exterior heat exchange surfaces of the transport tubing  1  and the heat transfer fins  3 . The coating  2  is no more than approximately 0.017 inches thick (and may be no more than about 0.009 inches thick), and is comprised of at least one of a plastic, or the like, and a paint, or the like, that may have a melting point of at least about 200 degrees F., such as a PERT plastic for example. Additionally, the very thin coating  2  may be comprised of a material that will not readily develop stress cracks via at least one of temperature and pressure changes. 
         [0075]    Such a very thin plastic, or the like, coating  2  for a refrigerant to air heat exchanger (which is not shown herein in its entirety as same is well understood by those skilled in the art) may also alternatively and optionally be composed of a substance, for example, such as a polyethylene (“PE”), a polycarbonate, a tetrafluoroethylene resin (PTFE) Teflon®, such as DuPont Teflon12 PFA, a fluoropolymer dip coating  2 , plasma-polymerizing a fluoroethylene monomer, such as tetrafluoroethylene, in the presence of the desired exterior surface and depositing a fluoropolymer coating  2  on the exterior surface, a triazine-dithiol derivative, a nylon, a tetrafluoroethylene resin (PTFE) Teflon 12, such as DuPont Teflon® PFA, having a thickness coating  2  of only about 0.003 to 0.004 inches, a fluroropolymer dip coating  2 , a plasma-polymerizing a fluoroethylene monomer, such as tetrafluoroethylene, in the presence of the desired exterior surface and depositing a fluoropolymer coating  2  of about 1/10,000 inch or less on the exterior surface, and a triazine-dithiol derivative coating  2 . 
         [0076]      FIG. 4 , not drawn to scale, is a top view of a heat exchange component of a refrigerant to air heat exchange system (a refrigerant to air heat exchange system is not shown in its entirety as same is well understood by those skilled in the art). The heat exchange component is herein shown as a segment of refrigerant fluid transport tubing  1 , with at least two exterior expanded surface area heat transfer fins  3  in thermal contact with, and arranged in a vertical position parallel to the longitudinal axis of, the tubing  1 , as conventionally found in a refrigerant to air DX system heating and cooling system. At least one of a very thin plastic and a paint, or the like, coating  2  may be applied to the exterior heat exchange surfaces of the refrigerant transport tubing  1  and the heat transfer fins  3 . The very thin plastic, or the like, coating  2  may be no more than approximately 0.017 inches thick (and may be no more than about 0.009 inches thick), and may be comprised of a very thin plastic, or the like, and may have a melting point temperature of at least about 200 degrees F., such as a PERT plastic for example. 
         [0077]    Additionally, the very thin plastic coating  2  may comprise a plastic coating  2  that will not readily develop stress cracks via at least one of temperature and pressure changes. An optional very thin paint coating  2  could also be used with similar advantageous heat transfer results, and would may comprise a high gloss paint type, that also could withstand at least about 200 degree F. temperatures without impairment. 
         [0078]    Such a very thin coating  2  for a refrigerant to air heat exchanger (which is not shown herein in its entirety as same is well understood by those skilled in the art) may also be composed of a substance such as a tetrafluoroethylene resin (PTFE) Teflon®, such as DuPont Teflon® PFA, having a thickness coating  2  of only about 0.003 to 0.004 inches, or such as a fluroropolymer dip coating  2 . Another example of such a very thin coating  2  may consist of plasma-polymerizing a fluoroethylene monomer, such as tetrafluoroethylene, in the presence of the desired exterior surface and depositing a fluoropolymer coating  2  of about 1/10,000 inch or less on the exterior surface. Another example of such a very thin coating  2  may be a triazine-dithiol derivative, or the like, coating  2 . 
         [0079]      FIG. 5  is a top view of a coil  4  of thin plastic, or the like, coated  2  refrigerant transport tubing  1  used for sub-surface refrigerant transport in a DX system (a DX system is not shown in full herein as same is well understood by those skilled in the art). The coil  4  is shown as wrapped around a central containment core  7  that has at least an approximate 33 inch (not drawn to scale) interior diameter (evidenced by an arrow  5 ), so as not to impair the thin coating  2  on the tubing  1 , and so as not to otherwise result in “S” bends in the tubing  1  during installation into a well/borehole (not shown) if the central containment core  7  had an interior diameter  5  less than about 33 inches. 
         [0080]      FIG. 6  is a side view, not drawn to scale, of a moderately thin plastic, or the like, coated  2  refrigerant transport tube  1 , where the tube  1  is comprised of a smaller diameter liquid refrigerant transport line (smaller diameter liquid lines and larger diameter vapor lines are well understood by those skilled in the DX system art), as opposed to a larger diameter vapor refrigerant transport line (not shown herein, and which is also well understood by those skilled in the art), and where the tube  1  and coating  2  are both surrounded by at least an approximate ½ inch thick (not drawn to scale) walled expanded foam insulation  6 , which foam insulation  6  may comprise expanded polyethylene foam insulation  6 , or the like, which foam insulation  6  is non-corrosive to copper tubing  1 , which foam insulation  6  can withstand at least 200 degree F. temperatures without impairment, and which foam insulation  6  may have a rigid texture as opposed to a soft texture that would be more easily crushed. 
         [0081]      FIG. 7  is a side view, not necessarily drawn to scale, of a liquid refrigerant transport line  8 , where the top one-third  9  (the top one-third  9  is not necessarily drawn to scale) of the liquid line  8  is coated  2  with a solid-state plastic, or the like, heavy coating  2  that is at least about 0.1 inches, plus or minus about 20%, thick, and where at least one of the top approximate fifteen percent and the top approximate forty-five feet  10  is additionally surrounded by at least one of a 0.2 inch, plus or minus 20%, double thick solid-state coating  11  and an expanded foam insulation  6  with at least an approximate one-half inch wall thickness. 
         [0082]    While only certain embodiments have been set forth, alternatives and modifications will be apparent from the above description to those skilled in the art. These and other alternatives are considered equivalents and within the spirit and scope of this disclosure and the appended claims.