Patent Application
20130087306
The field of the invention is the ground source heat pump system, and more specifically, the portion of that field that exchanges heat with the earth. Ground source heat pumps (GSHP) are well established as being efficient means to heat and cool buildings. Rather than use the ambient air as a source or sink for the heat required for building heat addition (in winter) and cooling (in summer), the GSHP relies on the fact that the underground is relatively constant in temperature year round. The main disadvantage has been the initial cost of the GSHP system, caused by the cumbersome, costly and detrimental means to install the in-ground Heat exchanger. Other parts of a GSHP system are similar in design to the conventional ambient air source heat pump and are not part of the present invention.
There are two general types of systems practiced for using the earth's heat as a source and a sink for heating and cooling buildings, open loop and closed loop. The open loop style withdraws water from the ground and uses that as the heat source and sink. The closed loop style circulates a heat exchange liquid medium such as water or water modified with an anti-freeze agent, through a Heat exchanger buried in the earth. There exist two main methods of providing closed loop ground coupled heat sources/sinks for a heat pump system: (1) Installation of piping in horizontal trenches; and, (2) Drilling of deep boreholes and grouting-in a vertical heat exchange pipe. The trenching and installation of underground heat exchange piping requires much space and the digging of wide trenches typically about 5 feet wide and 5 feet deep. If a leak develops the entire trench may have to be unearthed and replaced. The other main method of installation involves the drilling of deep wells, and the grouting-in of a heat exchange loop, which can also be very costly to install and difficult to repair. Today's invention regards only the closed loop style of GSHP system.
The subject invention is drawn toward solving the following list of problems in the existing art:
These above-listed disadvantages are solved or ameliorated by the subject invention, respectively as follows:
Currently, GSHP in-ground Heat exchangers are made of high density polyethylene (HDPE) which is known to have poor heat transfer capability when compared to metals. The specific new heat exchanger design utilized in the subject invention consists of a small diameter pipe, typically 1.25 to 2 inches diameter and 20 to 40 feet long, with pointed closed bottom ends, usually of a metal such as galvanized steel, stainless steel, or aluminum. In aggressive soils, it may be necessary to use passive or active electrode corrosion protection. Thick-walled or schedule 80 pipe is recommended. Once the pipe is inserted into the ground, a smaller flexible tube is inserted and contained within the pipe nearly to the depth of the metal pipe. This inner smaller diameter tube, is typically 0.5 to 0.75 inch diameter, and made of flexible polymer. The annular space created therewith contains the flowing heat exchange fluid while the heat passes from the ground through the outer pipe wall into the liquid, or the reverse in the summer. The inner tubing carries the heat exchange medium, usually water/glycol solution, from the bottom extremity of the outer tube where it flows up in the flexible inner tube and out, back to the building's heat pump system. The piping connecting the house to the exchangers is usually HDPE so that little heat is lost or gained while at shallow depths. Since the tubing heat exchange capacity is so much lower than the metal pipe wall, little heat short-circuits from the annulus to the center flow of liquid. Spacers may be used to center the tube in the pipe. A fitting at the top of this heat exchanger keeps the inlet and outlet separate. This general type of heat exchanger is known as a concentric flow heat exchanger. The current invention includes a novel specific design of the concentric flow heat exchanger, as described herein.
In the subject invention, three methods of insertion of this Heat exchanger into the ground are by means of
These methods are currently in service inserting pipes, wells, sampling devices, or poles into the ground.
Seven figures are provided.
Heat Exchanger Design:
The concentric tube ground source heat exchangers have been known as prior art for many years [Oliver, J., and H. Braud, 1981. Thermal exchange to earth with concentric well pipes. Transactions of ASAE. 24(4): 906-910]. Notes the use of concentric pipe Heat exchangers]. Also, in patent application Ser. No. 12/720052 by Lawless et al, the use of concentric Heat exchangers is noted. The specific designs for existing concentric Heat exchangers utilize complicated ribbed tubes and special head plumbing. Today's invention provides a much-simplified design, consisting of standard piping, tubing, and fittings (100). The invention provides a novel and inexpensive method of installing the inner concentric flow tube (106) into the pointed 20 to 40 foot long heat exchange pipe (101) by using standard materials arranged in a novel fashion to accomplish the objective. The novel means to provide the concentric annular flow is shown in
The actual heat exchange surface of the unit in contact with the soil (108) is a metal tube or pipe (101), typically 1.25 to 2 inches in diameter, approximately 20 to 40 feet long. The contact with the soil (108) is extremely tight due to the method of placement, described below in the Installation section. This very tight communication between the soil and the pipe enhances heat transfer and eliminates the need to grout the exchanger.
The heat transmission capability of metals is well known to be higher than plastic, plastic being the current primary art practiced in the GSHP industry for in-ground Heat exchangers. Because of the higher coefficient of heat transfer in the metal pipe, arrangements such as special finned or extended surface area pipes are not needed. And because of the low heat transfer coefficient of the polymer inner tubes, very little heat transfer by-passing takes place through the inner tube. [Oliver and Braud, cited above, notes that the energy short circuiting of heat in the liquid channels can be moderated by the use of a lower heat transfer center pipe.] Plastic spacers (103) may be used to keep the inner tube and outer tube separated physically. A novel fitting at the top of the pipe provides a separate inlet into the inner tube and outer tube. By the novel use of flexible tubing, the tubing can be inserted or removed easily from the outer pipes. It is recognized that the overall heat transfer coefficient will likely be influenced significantly by the soil characteristics.
Installation Method (I) Ballistically Launched
The pipes are installed vertically and at various angles to the ground to about 45 degrees. Typically the tubes are inserted from one central point splayed out at many different angles to encompass the maximum volume of soil. The result is similar to an “inverted pincushion.” The figures show fewer angles and tubes in order to simplify the comprehension of the method. The insertion of these Heat exchanger tubes extends the typical 5 foot depth (of trenched systems) to about 20 feet, typically into a much better and more temperature-stable stratum. Tests have shown that a 5 foot deep system [as used in the prior art] is impacted by changes in season and rainfall. [Burkhard Sanner, writing in the GHC Bulletin, June 2001, titled “Shallow Geothermal Energy”, noted that the variation within the top 2 meters of earth is as much as 10° C. from January to July (Wetzlar, Germany), but at a depth of 6 meters, the variation is only about 4° C.] Also, it is more likely that the 20 foot tubes will contact groundwater than a 5 foot deep trench. The groundwater will enhance heat exchange.
The intent is to push the Heat exchanger tube into the ground rather than trench or drill it. One of the methods utilized in this invention is the “Ballistic Launched Soil Nail.” [Soil Nail Launcher, Inc., 2841 North Avenue; Grand Junction, Colo. 81501] This technique is currently in use for other purposes. The Launched Soil Nailer is used for slope stabilization. (The “nails” referred to are approximately 20 feet long.) This “soil nailing” technique has not been used for heat exchange installation purposes in the past. By this insertion technique, there is a tight contact between the ground and the inserted pipe, which enhances heat exchange and eliminates the need for grouting. The force of the insertion causes the soil near the pipe to become compacted. No voids are created as may be the case in trenched/backfilled or drilled systems. Depending on the launcher used, it may be necessary to provide a specially formed gripping ring or ferrule on the nail.
Soil nail launchers are patented through a series of patents culminating in U.S. Pat. No. 7,654,775 B2 (Ruckman), which shows graphically in its
The soil nail launcher accelerates the 20 foot tubes to 250 miles per hour by means of a compressed air gun, driving the nail into the ground at any angle. The Soil Nail Launcher typically is mounted on a modified tracked excavator. However, it can be mounted on vehicles, long reach excavators, or crane basket frames. It is able to reach remote locations. The launcher unit has full articulation, allowing it to work around overhead wires, underground utilities, and guard rail.”
In the case of the “Launched Nails,” an array of variously angled insertions can be done from one position, allowing the individual heat exchange tubes to have their liquid connections close together, while splaying the array to encounter a larger conical body of soil. The typical installation would have a number (about 10 to 20) of the 20 foot heat exchange pipes “spiked” or “launched” from one small diameter shallow hole. This small chamber (which could be made from concrete or fiberglass with areas left open for the tubes) would provide a connection point for the ten to 20 heat exchange tubes. Alternately the connections could be made in a small aboveground fiberglass or other enclosure.
The size of the hole and chamber into which the heat exchange tubes are driven will depend on the specific requirements and size of the particular launching gun being used.
Connections among the Heat exchanger tubes could be made with flexible tubing, using manifolds (204, 205) to supply (109) and return (110) the fluid medium. The flow pattern may be either series or in parallel, or a combination of both. There may be one or more of these “nests” or “arrays” (300) of heat exchange pipes, connected by a shallow buried plastic pipeline between them, and the building being served. This gives obvious benefits to small plots, since the heat exchange tubes can be spiked or shot at angles that would go under driveways, trees, buildings, playgrounds, and the like. Whereas the cost of the ballistic launcher itself is expensive, it should be required for only a day or less at each site. The launcher reloads quickly and shoots the pipe into the ground as if from a gun. The entire field of heat exchange tubes should be installed in 2 or 3 hours, more or less. Then the workers would trim or cut any excess pipe and, using common threading machines, thread the ends of the pipes. The threaded pipe (101) would then receive the threaded Tee fitting (104), (either directly or with a coupling) and then the tubing assembly would be fed into the pipe. The pipe head assembly would then be tightened, pressure tested, and connected to the supply (204) and return (205) manifolds. These head fittings could be made up in advance to speed the final installation. The chamber (300) for the exchanger heads would have a bottom (302), and a sidewall (302) and a lid (303).
One of the benefits of the multi-tube inserted Heat exchanger is that if one tube were to fail or leak, it can simply be disconnected from the system, as the system will have been designed for excess capacity. Also, it would be possible to install several extra empty tubes for backup, but not use them unless needed. Obviously, the metallic pipe could be subject to corrosion in certain soils. In moderate conditions, the use of galvanized steel pipe would provide a long life. In severely corrosive soils, cathodic protection could be used. Stainless steel or aluminum tubes could be used but at a cost penalty.
Another benefit for the “launched nail” Heat exchanger is that it can be used on steep embankments, allowing the use of GSHP systems in hilly terrain. The use of launched nail Heat exchangers has the added benefit (not part of the claims of the instant invention) of stabilizing hillsides, its original function. If prior art “trenched” systems were installed in hilly terrain, possible destabilization effects could ensue.
Installation Method (II) Mechanical Direct Push
A second method of insertion of the Heat exchanger into the ground is “direct push.” Direct Push refers to rods, tools, pipes, and sensors that are “pushed” into the ground without the use of drilling to remove soil or to make a path for the tool. An insertion machine relies on a relatively small amount of vehicle weight combined with percussion as the energy for advancement of a rod or pipe. The insertion machine grasps the pipe or rod and drives it slowly into the ground percussively. One such direct push machine is made by Geoprobe, of Salina Kans.
Installation Method (III) Manual Direct Push
A variation of the direct push method is the manually driven “well point” insertion. Well point pipes (without the filter section) may be driven into the ground by a manual device such as a post driver, sledge hammer, or a jackhammer. Also, hydraulic rams, compressed air post drivers or propane powered percussive hammers may be used. The points of the Heat exchanger pipe may be either formed by commercially available machines or by fitting with a preformed point.
Many of the benefits of the ballistic soil nail launcher are to be had using the direct push method. The drawbacks are in the reduced range of angles of insertion, and the time for insertion of each pipe. On the positive side, the direct push may be used to provide deeper insertion, limited only by bedrock or very tight soils. By using two standard 20 foot pipe lengths and joining them with a coupling, a 40 foot Heat exchanger can be made.
The layout of a direct push installed system would be that of a 20 to 40 foot pipe, 1.25 to 2 inch diameter, installed vertically, with a small junction box at the top. A supply and return pipe would pass through the junction box as shown on
Supply and Return Piping
The supply and return piping is described as follows: The supply pipe would follow a path from the HVAC unit underground to the first Heat exchanger, then sequentially to the rest of the heat exchanger units. The supply pipe would be sized large enough to handle the flow to all the heat exchangers. Each supply and return connection would have a shut-off valve. The tops of the heat exchangers and the supply and return piping would be inside buried small plastic boxes, similarly to the use in irrigation systems. Manifolds would be designed to distribute flow evenly to the heat exchanger units, and to maintain turbulent flow for better heat exchange.
The return piping would be the reverse, that is, the pipe would start at the last heat exchanger and progress in reverse order to the first, then back to the HVAC unit. The supply and return pipe diameters may change as the supply and return piping progress.
For a typical residential system of 3 ton Air Conditioning capacity, the total flow rate of heat exchange fluid would be approximately 9 gallons per minute and the number of 40 foot exchangers would be about 20. Because of the deeper insertion into damper earth, it is possible that certain soils and locations may allow substantial reductions in quantity of flow and/or length of heat exchanger. Each individual system would be designed for soil conditions at the site by a HVAC professional.
Figure Details
| Number | Date | Country | |
|---|---|---|---|
| 61545191 | Oct 2011 | US |
