Convective earrh coil

Abstract

The present invention relates to a method of heat rejection and extraction between a fluid and the earth, providing for a high efficiency convective heat exchanger located in ground water, a means for inducing flow of said ground water at its initial temperature from ground water pool through said heat exchanger, a means of inducing heat transfer from said ground water to said heat transfer fluid or gas, a means of discharging said ground water at a new temperature back into said ground water pool, and a piping system suitable to transport said heat transfer fluid from a thermal load at some remote location at a first temperature, though the said convective heat exchanger and transporting the heat transfer fluid at a new temperature to the location(s) where the thermal energy is utilized.

Description

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a method of heat rejection and extraction between a fluid and the earth.

BACKGROUND OF THE INVENTION

Traditionally, if the designer of a heating and/or cooling system for building wanted to substantially improve the energy efficiency of his building, he could invest in the installation of a ground-source (or earth-coupled) heat-pump system. This would require the installation of one or more water-source heat-pumps in the building and installing a dedicated piping system from the water-source heat-pumps to a ground coil. The ground coil heating and cooling systems use the earth as an energy source and heat sink. A series of pipes, commonly called a “loop,” are used to connect the heat pump system to the earth. In a few installations, refrigerant from the heat pump is circulated through the ground in a closed loop. However, the more common loops discussed here use only water or a water and antifreeze mixture. While the value of these systems in the savings of heating and cooling energy has been profound, the real world-building owners generally have not been able to justify the cost, complexity or size of the ground coil in the competitive environment they face.

Traditionally, these ground coils have been done in one of two ways.

• 1) Closed Loop Ground Coil Systems

Closed loop systems are becoming the most common. A fluid or refrigerant is circulated through a continuous buried pipe. The length of loop piping varies depending on ground temperature, thermal conductivity of the ground, soil moisture, and system design, or

• 2) Open Loop Ground Coil Systems

Used successfully for decades, ground water is drawn from an aquifer through one well and is pumped to the surface, passes through some fashion of heat exchanger, and is discharged sometimes to the surface but usually to the same aquifer it was drawn from, either through the same well or a second well at a distance from the first. A special case of open loop systems is available when a nearby pond or lake can be used as the water source instead of drilling wells.

Closed Loop Ground Coil Systems general come in three configurations: Horizontal, Vertical, and Pond.

Horizontal closed loop installations are generally most cost-effective for small installations, particularly for new construction where sufficient land area is available. These installations involve burying pipe in trenches dug with back-hoes or chain trenchers. Up to six pipes, usually in parallel connections, are buried in each trench, with minimum separations of one fourth of a meter between pipes and 3 to 5 meters between trenches. Often slinky shaped coils —overlapping coils of pipe—are used to increase the heat exchange per meter of trench, but require more pipe per ton of capacity. Two-pipe systems may require as much as 100 meters of trench per ton of nominal heat exchange capacity.

Vertical closed loops are preferred in many situations. For example, most large commercial buildings and schools use vertical loops because the land area required for horizontal loops would be prohibitive. Vertical loops are also used where the soil is too shallow for trenching. Vertical loops also minimize the disturbance to existing landscaping. For vertical closed loop systems, one or more U-tubes are installed in a well drilled 30 to 150 meters deep. Because conditions in the ground may vary greatly, loop lengths can range from 40 to 100 meters per ton of heat exchange. Multiple drill holes are required for most installations, where the pipes are generally joined in parallel or series-parallel configurations. Installation costs depend on geological conditions and local drilling industry experience.

Both horizontal and vertical closed loop ground coil systems can be relatively expensive compared with above ground air based systems due to the extensive size requirements. This large area is the result of the low thermal heat transfer rate of conduction from the pipe to the ground and by poor conduction through the ground.

Pond closed loops are a special kind of closed loop system. Where there is a pond or stream that is deep enough and with enough flow, closed loop coils can be placed on the pond bottom. Fluid is pumped just as for a conventional closed loop ground system where conditions are suitable, the economics are very attractive, and no aquatic system impacts have been shown. Unfortunately, over time, the exposed pipe coils become fouled with dirt and microbiological growth and lose their effectiveness.

Open loop systems are the simplest. Generally, two to three gallons per minute per ton of capacity are necessary for effective heat exchange. Since the temperature of ground water is nearly constant throughout the year, open loops are a popular option in areas where they are permitted. Open loop systems do have some associated challenges: (1) Local ground water chemical conditions can lead to fouling the heat pump's heat exchanger particularly if oxygen, carbon dioxide and/or other gases are introduced or disturbed in solution in the water. (2) Increasing environmental concerns mean that local officials often require permitting to assure compliance with regulations concerning water use and acceptable water discharge methods. (3) As the water is returned to the aquifer, challenges arise with re-injection flow rates, oxygenating the water, creating a vacuum at the high point of the loop, etc. (4) A open well system may not be practical where the water table is very deep, because pumping requirements would become prohibitive.

Open Loop Ground Coil Systems general come in three configurations: Standing well, Multiple well and Pond.

Open Loops—Standing Wells

Standing wells, also called turbulent wells, may be as deep as 500 meters, withdraw water from the bottom of the well, circulate it through the heat pump's heat exchanger, and return it to the top of the water column in the same well. Some systems operate with less than 30 meters of well per ton of nominal capacity. Short circuiting of return water to supply and oxygenating the water are some of the concerns with this approach.

Multiple wells

By providing distance between supply and discharge wells, the short circuiting of return water to supply is usually avoided. However additional wells and piping will be required and the ability of the discharge well to accept the re-injection flow may be limited. In addition, there may be permitting issues.

Pond or lake water can be drawn out, pumped through a heat exchanger and returned to the pond. Debris, scaling and fouling of the piping system and heat exchanger are concerns with this approach.

While ground source systems provide energy savings, low maintenance, and minimum noise, the relatively high cost of constructing the ground coil reduces their popularity.

To avoid the high costs and problems associated with open and closed loop ground coils; this novel invention demonstrates a new means of thermally coupling heating and cooling systems with the earth.

Prior art in ground coil systems focused on either using vast array of pipes in the ground or pond as the heat exchanger (closed loop system) or ground water was brought above grade to an efficient heat exchanger using forced convection (open loop system).

This innovative invention combines the advantages of open systems (high heat transfer rates associated with convective heat transfer) with the advantages of closed loop systems (no removal of water from its location, with associated problems of permitting, re-injecting and aerating). This novel approach, locates a high efficiency, convection based, heat transfer coil in the aquifer or pond. Ground or pond water is forced to flow through one side of the heat exchanger either through the known principle of natural convection, or with the assistance of a mechanical means, providing forced convection. On the other side of the heat exchanger, a fluid or refrigerant transfers the thermal energy to where it is needed by a closed loop piping system. Since ground water is never removed from its natural location, concerns of contamination, aeration, permitting, and re-injection are avoided.

An additional unforeseen advantage of this unique invention is that it promotes the natural thermal stratification of the ground water. This means that cooler water settles below warmer water. This allows the system designer to treat the ground water as a huge thermal storage device. During times when heat is rejected to the ground water, cool water is drawn from lower levels (either by natural convection or a mechanical means), and heated and stored in upper levels. The poor thermal characteristics of the earth combined with the stratification effect prevent the thermal energy from warming the cooler water below. Then when heat is need by the building, the convection flow direction is reversed (either by natural convection or a mechanical means), and warm water is cooled and stored in the lower level of the ground water. Again, the poor thermal characteristics of the earth combined with the stratification effect prevent the thermal energy from cooling the warmer water above. This thermal storage feature could allow thermal energy stored during the day to be used for heat at night. It is possible that even heat energy stored over the summer could be used in the winter. Also with proper design of the distribution system within the building, the heating and cooling energy could be transferred to their needed uses by direct heat transfer, without the need of a heat pump. For example, the energy removed to cool a house in August, could be used to melt snow from a driveway in January, with only the power consumption of a small pump.

Additional benefits of this novel invention accrue from the substantially improved heat transfer rate of the heat exchanger compared to conventional closed loop. This allows for a closure approach between the temperature of the heat transfer fluid and the ground fluid. This of course improves the efficiency of the whole system and saves energy. This offers an addition advantage in cool climates (ground temperatures below 10 to 15 degrees C.) when the system is used to extract heat from the ground. Conventional ground coils may have as much as a 15 degree total temperature difference between the working fluid and the ground, meaning the fluid temperature drops below freezing and requires antifreeze. This new invention can provide an approach temperature of 5 degrees or less, avoiding the need for antifreeze and its associated cost, energy and pumping penalties, and ground water contamination concerns.

An additional unforeseen benefit of this novel invention is that the depth of the aquifer is no longer a deterrent to using an earth coil. Going down hundreds of meters to find an aquifer will not adversely affect pumping energy, since with a closed loop the return water going down pushes the supply water back up.

The present invention solves the problems, reduces the initial cost and improves the performance of conventional earth coil systems. The proper design and engineering, a single well could provide heating and cooling for a large building. Moreover, because the systems is simple and can require only one well, it is readily fit for existing buildings. In addition, this single well can serve multiple functions, such as housing a conventional well pump providing water for domestic irrigation or fire fighting. It can be appreciated that the cost of installing such an earth coil system is relatively low, making it more enticing to the existing building owner and building developers.

SUMMARY OF THE INVENTION

Thus and in accordance with a first aspect of the present invention, there is provided a system for heat rejection and extraction between a heat transfer fluid or gas and the earth, providing for a high efficiency convective heat exchanger located in ground water, a means for inducing flow of said ground water at its initial temperature from ground water pool through said heat exchanger, a means of inducing heat transfer from said ground water to said heat transfer fluid or gas, a means of discharging said ground water at a new temperature back into said ground water pool, and a piping system suitable to transport said heat transfer fluid from a thermal load at some remote location at a first temperature, though the said convective heat exchanger and transporting the heat transfer fluid at a new temperature to the location(s) where the thermal energy is utilized.

Preferably said ground water can be below ground surface water in a well or cave, or above ground surface water in a pond, lake, stream or ocean.

Preferably said heat transfer fluid is a substance that would not harm or deteriorate the quality of the said ground water if it were to leak into the ground water, including potable water, water with non-toxic additives, or other environmentally friendly fluid or gases.

Preferably said convective heat exchanger utilizes the efficiencies of convective heat transfer to thermally link the said ground water to the said heat transfer fluid.

Preferably said convective heat exchanger utilizes efficient heat exchanger design, including tube-in-tube, spiral tubing, finned or enhanced tubing, or a rectangular or circular plate design.

Preferably said convective heat exchanger utilizes thermally conductive materials that are suitable for contact with the said ground water and said heat transfer fluid, such as copper, cupronickel, stainless steel, or plastic.

Preferably said means for inducing flow of said ground water at its initial temperature from said ground water pool through said heat exchanger is an enclosed vertical chamber of sufficient length to generate natural fluid flow forces due to the difference in temperature and density of said ground water entering the said heat exchanger at its initial temperature with the said ground water leaving the said heat exchanger at its said new temperature.

Advantageously said means for inducing flow of said ground water through said heat exchanger could be a mechanical pump. Preferably said mechanical pump could be electrically driven or could be driven by the flow of the heat transfer fluid acting upon an impeller, which drives said pump. The said impeller could be mechanically coupled via a sealed shaft, or preferably, could be magnetically coupled.

Preferably said means for inducing flow of said ground water at its initial temperature from said ground water pool includes a means of filtering out particles that would foul said convective heat transfer means, and a means of eliminating or back flushing said particles.

Preferably said heat transfer fluid piping system utilizes materials that are suitable for contact with the said ground water and said heat transfer fluid, such as copper, cupronickel, stainless steel, or plastic.

Advantageously, the said means for inducing flow of said ground water may also promote the natural stratification of the ground water into thermal layers, allowing for storage of thermal energy. Preferably said system for heat rejection and extraction between a heat transfer fluid or gas and the earth water cooling means is connected to other heat sinks or heat sources, such as a hydronic snowmelt system (a series of tubes buried in or beneath sidewalks and driveways near the said building) or solar energy panels, or waste heat collection system and controls are provided to allow for the optimum storage and removal of thermal energy on a daily and seasonal basis.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantage of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawing, wherein:

FIG. 1 is a section view of the present invention for an underground aquifer incorporating the present invention using ground water directly as accessed through a deep well.

FIG. 2 is a section view of the present invention for a lake incorporating the present invention using ground water and incorporating a heat transfer driven pump to induce ground water flow.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, a portion of an aquifer some depths below the earth surface 1 is generally shown by reference numeral 2. A well 3 is drilled from the earth surface 1 until it reaches the desired aquifer 2. Pipes 4 and 5 for supplying and returning the heat transfer fluid from the thermal load 6 to the convective earth coil 7 are run below the earth's surface 1 (preferably below the frost line 8) to the well 3, and down the well 3 to the convective earth coil 7. In FIG. 1, the convective earth coil 7 is generally comprised of inlet 9, a vertical chamber 10, a convective heat exchanger 11, and a discharge outlet 12. In FIG. 1 the convective heat exchanger 11 is represented as a spiral tube within a tube.

The convective earth coil can be used to inject heat into the ground or extract heat energy from the ground. In the illustrated embodiment, in operation in the heat injection mode, warm heat transfer fluid flows from the thermal load 6 through pipe 4 into the top portion of the convective heat exchanger 11. Thermal energy is transferred from the heat transfer fluid through the convective heat exchanger 11 to the ground water 2. The thermal energy increases the temperature of the ground water 2 that is in contact with the convective heat exchanger 11. The increase in temperature causes the warmer water to expand in volume, proportionately decreasing its density. The warmer, lower density water 13 will rise to the top of the aquifer 2 and cooler, denser ground water 14 will be drawn in from below the ground coil to replace it. This upward flow action within the convective earth coil 7 will produce a flow of warm water 13 filling and stratifying in the upper layers of the aquifer 2. The layers of warm water will gradually work their way down to replace the cool water 14 being drawn in at the base of the convective earth coil 7.

In the illustrated embodiment, in operation in the heat extraction mode, cool heat transfer fluid flows from the thermal load 6 through pipe 5 into the bottom portion of the convective heat exchanger 11. Thermal energy is transferred from ground water 2 through the convective heat exchanger 11 to the cool heat transfer fluid. The thermal energy loss decreases the temperature of the ground water 2 that is in contact with the convective heat exchanger 11. The decrease in temperature causes the cooler water to contact in volume, proportionately increasing its density. The cooler, higher density water 14 will drop to the bottom of the aquifer 2 and warmer ground water 13 will be drawn in from above the ground coil to replace it. This downward flow action within the convective earth coil 7 will produce a flow of cool water 14 filling and stratifying in the lower layers of the aquifer 2. The layers of cool water will gradually work their way up to replace the warm water 14 being drawn in at the top of the convective earth coil 7.

Referring to FIG. 2, a lake is generally shown by reference numeral 2. Pipes 4 and 5 for supplying and returning the heat transfer fluid from the thermal load (not shown) to the convective earth coil 7 are run below the earth's surface 1 (preferably below the frost line 8) to the lake 2, and to the convective earth coil 7. In FIG. 2, the convective earth coil 7 is generally comprised of inlet 9, a vertical chamber 10, a convective heat exchanger 11, a discharge outlet 12, and a means of anchoring and support the assembly 3.

In FIG. 2 the convective heat exchanger 10 is represented as a plate type heat exchanger. The illustrated embodiment includes screens at the inlet 9 and discharge 12 to keep debris and fish out of the heat exchanger. The illustrated embodiment includes an impeller 15 in the heat transfer stream that is magnetically coupled to a pump 16 in the lake water stream 14.

The convective earth coil can be used to inject heat into the lake or extract heat energy from the lake. In the illustrated embodiment, in operation in the heat injection mode, warm heat transfer fluid flows from the thermal load through pipe 4 into the top portion of the convective heat exchanger 12. Thermal energy is transferred from the heat transfer fluid through the convective heat exchanger 12 to the lake water 2. The thermal energy increases the temperature of the lake water 2 that is in contact with the convective heat exchanger 12. The increase in temperature causes the warmer water to expand in volume, proportionately decreasing its density. The warmer, lower density water 13 will rise to the top of the lake 2 and cooler, denser lake water 14 will be drawn in from below the convective earth coil 7 through the filter screen 9 to replace it. This upward flow action within the convective earth coil 7 will produce a flow of warm water 13 filling and stratifying in the upper layers of the lake 2. The layers of warm water will gradually work their way down to replace the cool water 14 being drawn in at the base of the convective earth coil 7. The heat transfer fluid leaving the heat exchanger acts on impeller 15, which is magnetically coupled to pump 16. Pump 16 assists the natural convective flow, and increase the flow of lake water 2.

In the illustrated embodiment, in operation in the heat extraction mode, cool heat transfer fluid flows from the thermal load through pipe 5 into the bottom portion of the convective heat exchanger 12. Thermal energy is transferred from the heat transfer fluid through the convective heat exchanger 12 to the lake water 2. The thermal energy decreases the temperature of the lake water 2 that is in contact with the convective heat exchanger 12. The decrease in temperature causes the cooler water to contact in volume, proportionately increasing its density. The cooler, higher density water 13 will sink to the bottom of the lake 2 and cooler, denser lake water 14 will be drawn in from above the convective earth coil 7 through the filter screen 12 to replace it. This downward flow action within the convective earth coil 7 will produce a flow of cool water 13 filling and stratifying in the lower layers of the lake 2. The layers of cool water will gradually work their way up to replace the warm water 14 being drawn in at the top of the convective earth coil 7. The heat transfer fluid entering the heat exchanger acts on impeller 15, which is magnetically coupled to pump 16. Pump 16 assists the natural convective flow, and increase the flow of lake water 2.

Although described above are types of convective earth coils, it can be appreciated by those skilled in the art that other methods of heat exchange may be utilised.

Additional options include: 1) Transferring the heat energy via a heat exchanger to a series of tubes buried in or beneath sidewalks and driveways, thereby providing both building heat rejection and a snow melt system, 2) Storing thermal energy from a solar collector during the day and transfer the energy to domestic hot water the following morning.

As can be seen in the description above, earth heat extraction, injection and storage may be accomplished by utilizing convective heat exchange devices within the ground water. Moreover, in contrast to the prior art, the convective heat coil 7 is relatively simple in manufacture as compared with closed loop earth coils. As can be appreciated by those skilled in the art, the improved heat transfer characteristics of the convective earth coil may provide cool enough cold water temperatures, or warm enough hot water temperatures that eliminate the need for a complex heat exchanger including an evaporator and compressor in order to generate cooling or heating from a more moderate temperature fluid.

Additionally, the compressor type heat exchangers require large amounts of power and are relatively noisy. In contrast, the circulating pumps require only a small amount of power.

It is, of course, to be understood that the invention is not intended to be restricted to the details of the above embodiments which are described by way of example only.

Claims

1. A system for heat rejection and extraction between a heat transfer fluid or gas and the earth, providing for a high efficiency convective heat exchanger located in ground water, a means for inducing flow of said ground water at its initial temperature from said ground water through said heat exchanger, a means of inducing heat transfer from said ground water to said heat transfer fluid or gas, a means of discharging said ground water at a new temperature back into said ground water, and a piping system suitable to transport said heat transfer fluid from a thermal load at some remote location at a first temperature, though the said convective heat exchanger and transporting the heat transfer fluid at a new temperature to the location(s) where the thermal energy is utilized.

2. The heat rejection and extraction system in claim 1 wherein said ground water can be below ground surface water in a well or cave, or above ground surface water in a pond, lake, stream or ocean.

3. The heat rejection and extraction system in claim 1 wherein said heat transfer fluid is a substance that would not harm or deteriorate the quality of the said ground water if it were to leak into the ground water, including water, water with non-toxic additives, or other environmentally friendly fluid or gases.

4. The heat rejection and extraction system in claim 1 wherein said convective heat exchanger utilizes the efficiencies of convective heat transfer to thermally link the said ground water to the said heat transfer fluid.

5. The heat rejection and extraction system in claim 1 wherein said convective heat exchanger utilizes efficient heat exchanger design, including tube-in-tube, spiral tubing, finned tubing, or a rectangular or circular plate design.

6. The heat rejection and extraction system in claim 1 wherein said convective heat exchanger utilizes thermally conductive materials that are suitable for contact with the said ground water and said heat transfer fluid, such as copper, cupronickel, stainless steel, or plastic.

7. The heat rejection and extraction system in claim 1 wherein said means for inducing flow of said ground water at its initial temperature from said ground water pool through said heat exchanger is an enclosed vertical chamber of sufficient length to generate natural fluid flow forces due to the difference in temperature and density of said ground water entering the said heat exchanger at its initial temperature with the said ground water leaving the said heat exchanger at its said new temperature.

8. The heat rejection and extraction system in claim 1 wherein said means for inducing flow of said ground water through said heat exchanger could be a mechanical pump.

9. The mechanical pump in claim 8 could be electrically driven or could be driven by the flow of the heat transfer fluid acting upon an impeller, which drives said pump, the said impeller could be mechanically coupled via a sealed shaft, or could be magnetically coupled.

10. The mechanical pump in claim 8 use centrifugal, displacement or other known pumping strategies.

11. The heat rejection and extraction system in claim 1 wherein said heat transfer fluid piping system utilizes materials that are suitable for contact with the said ground water and said heat transfer fluid, such as copper, cupronickel, stainless steel, or plastic.

12. The heat rejection and extraction system in claim 1 wherein the said means for inducing flow of said ground water may also promote the natural stratification of the ground water into thermal layers, allowing for storage of thermal energy.

13. The heat rejection and extraction system in claim 1 wherein said system for heat rejection and extraction between a heat transfer fluid or gas and the earth water cooling means is connected to other heat sinks or heat sources, such as space heating or cooling system, a potable water heating system, a hydronic snowmelt system (a series of tubes buried in or beneath sidewalks and driveways near the said building) or solar energy panels, or waste heat collection system and controls are provided to allow for the optimum storage and removal of thermal energy on a daily and seasonal basis.