BACKGROUND OF THE INVENTION

Many systems rely on the transfer of heat into or out of liquid media. The transfer is often accomplished using a heat exchanger, in which two fluids are separated by a wall, and heat flows from the higher temperature fluid to the lower temperature fluid through the wall. The performance of a heat exchanger is dependent on many factors, including the surface area to which the fluids are exposed, the thermal conductivity of the wall, the flow rates of the fluids, and the thermal conductivity of the fluids themselves. In other systems, a fluid may exchange heat with a solid or composite substance.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the invention use nano fluids to enhance heat transfer in thermal systems.

Nanoparticles in the nanofluids increase the thermal conductivity of the fluid, as compared to a similar fluid without nanoparticles. The enhanced thermal conductivity enables more efficient heat transfer into and out of the fluid. Example embodiments relate to solar water heating, ground-coupled piping loops, and in-fioor heating and cooling.

According to one aspect, a system for heat transfer includes a piping loop and a heat transfer fluid that circulates within the piping loop such that heat is transferred into or out of the heat transfer fluid through the walls of the piping loop. The heat transfer fluid is a nano fluid containing nanoparticles, and the nanofiuid has enhanced thermal conductivity as compared with a similar fluid not containing the nanoparticles. In some embodiments, the heat transfer fluid contains ions of copper, ions of silver, or both ions of copper and ions of silver. In some embodiments, the system further comprises an ion generator, the ion generator including a pair of spaced apart electrodes in contact with the heat transfer fluid and circuitry arranged to impress an alternating voltage between the two electrodes such that ions of material from the electrodes are generated within the heat transfer fluid by electrolysis. In some embodiments, the electrodes comprise copper, silver, or both copper and silver. The electrodes may comprise sterling silver. In some embodiments, the alternating voltage has a frequency of at least 6 Hz. The alternating voltage may have a frequency greater than 20 kHz. The piping loop may comprise plastic pipe.

According to another aspect, a system for heating water comprises a solar collector, a tank of water to be heated, a heat exchanger within the tank, a fluid circuit coupling the solar collector with the heat exchanger, and a heat transfer fluid that circulates within the fluid circuit. The heat transfer fluid is a nanofluid containing nanoparticles, and the nanofluid has enhanced thermal conductivity as compared with a similar fluid not containing the nanoparticles. In some embodiments, the heat transfer fluid contains ions of copper, ions of silver, or both ions of copper and ions of silver. In some embodiments, the system further comprises an ion generator, the ion generator including a pair of spaced apart electrodes in contact with the heat transfer fluid, and circuitry arranged to impress an alternating voltage between the two electrodes such that ions of material from the electrodes are generated within the heat transfer fluid by electrolysis. In some embodiments, the electrodes comprise copper, silver, or both copper and silver. The electrodes may comprise sterling silver. In some embodiments, the alternating voltage has a frequency of at least 6 Hz. The alternating voltage may have a frequency greater than 20 kHz. In some embodiments, the solar collector comprises plastic tubes for carrying the heat transfer fluid through the solar collector. In some embodiments, the solar collector comprises polyethylene tubes for carrying the heat transfer fluid through the solar collector. The solar collector may comprise a flat panel solar collector. The solar collector may comprise a concentrating solar collector. In some embodiments, the system further comprises a pump for circulating the heat transfer fluid through the fluid circuit, and a controller that controls the operation of the pump.

According to another aspect, a thermal system comprises an environmental control system, a ground coupled piping loop coupled to the environmental control system, and a heat transfer fluid that circulates within the ground coupled piping loop. The heat transfer fluid is a nanofluid containing nanoparticles, and the nanofluid has enhanced thermal conductivity as compared with a similar fluid not containing the nanoparticles. In some embodiments, the heat transfer fluid contains ions of copper, ions of silver, or both ions of copper and ions of silver. In some embodiments, the system further comprises an ion generator, the ion generator including a pair of spaced apart electrodes in contact with the heat transfer fluid, and circuitry arranged to impress an alternating voltage between the two electrodes such that ions of material from the electrodes are generated within the heat transfer fluid by electrolysis. In some embodiments, the electrodes comprise copper, silver, or both copper and silver. The electrodes may comprise sterling silver. In some embodiments, the alternating voltage has a frequency of at least 6 Hz. The alternating voltage may have a frequency greater than 20 kHz. The ground coupled piping loop may comprise polymer pipe. The ground coupled piping loop may be buried underground in a trench, and embedded in sand. In some embodiments, the system further includes a mechanism for wetting the ground in the vicinity of the ground coupled piping loop. In some embodiments, the system further comprises a pump for circulating the heat transfer fluid through ground coupled piping loop, an ion generator that generates ions within the heat transfer fluid, and a photovoltaic solar panel that supplies power for operating the pump and the ion generator. In some embodiments, the ground coupled piping loop exhausts heat from the heat transfer fluid into the ground at least some of the time. In some embodiments, the ground coupled piping loop absorbs heat from the ground into the heat transfer fluid at least some of the time.

According to another aspect, an underfloor environmental control system comprises a piping loop embedded within a floor, a heat transfer fluid that circulates within the piping loop. The heat transfer fluid is a nano fluid. The heat transfer fluid is a nano fluid containing nanoparticles, and the nanofluid has enhanced thermal conductivity as compared with a similar fluid not containing the nanoparticles. The system further comprise a device coupled to the piping loop, such that the device imparts heat to the heat transfer fluid or removes heat from the heat transfer fluid. In some embodiments, the device imparts heat to the heat transfer fluid. In some embodiments, the device removes heat from the heat transfer fluid. In some embodiments, the device imparts heat to the heat transfer fluid some of the time and removes heat from the heat transfer fluid some of the time. In some embodiments, the heat transfer fluid contains ions of copper, ions of silver, or both ions of copper and ions of silver. In some embodiments, the system further comprises an ion generator, the ion generator including, a pair of spaced apart electrodes in contact with the heat transfer fluid, and circuitry arranged to impress an alternating voltage between the two electrodes such that ions of material from the electrodes are generated within the heat transfer fluid by electrolysis. In some embodiments, the electrodes comprise copper, silver, or both copper and silver. The electrodes may comprise sterling silver. In some embodiments, the alternating voltage has a frequency of at least 6 Hz. The alternating voltage may have a frequency greater than 20 kHz. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a solar water heating system, in accordance with embodiments of the invention.

FIG. 2 illustrates the operation of example ion generator, in accordance with embodiments of the invention. FIG. 3 shows a simplified diagram of one example architecture of a part of the interior of the solar collector shown in FIG. 1.

FIG. 4 illustrates a thermal system including a ground coupled piping loop and associated other components in accordance with embodiments of the invention.

FIG. 5 illustrates an end view of the structure of an example trench, in which the ground coupled piping loop of FIG. 4 is installed.

FIG. 6 illustrates an example circuit for intermittently driving a pump, in accordance with embodiments of the invention.

FIG. 7 schematically illustrates an underfloor heating system, in accordance with embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Solar Water Heating Embodiments

FIG. 1 illustrates a solar water heating system 100, in accordance with embodiments of the invention. In system 100, solar radiation strikes a collector 101. Collector 101 may be of any suitable type. For example, in some embodiments collector 101 may be a flat panel collector comprising an insulated box with a transparent cover and a flat absorber from the transparent cover. The absorber may be a sheet of metal painted or otherwise coated to be black or another dark color. The absorber may be in contact with one or more tubes carrying a heat transfer fluid as discussed in more detail below. In some embodiments, the absorber may be one or more tubes surrounded by a transparent cylinder. The cylinder may be evacuated or partially evacuated. In other embodiments, solar collector 101 may be a concentrating solar collector, such as a parabolic trough that focuses incoming solar radiation on a tube at the focus of the parabolic cylinder. In a trough type solar collector, the absorber may be a tube through which the heat transfer fluid flows. The absorber may be surrounded by a larger transparent tube that admits solar radiation but reduces convective losses from the absorber. The annular space between the absorber and the transparent tube may be evacuated or partially evacuated. In prior systems, the tubes carrying heat transfer fluid through collectors have typically been made of metal, for example copper. A tank 102 holds a reservoir of water to be heated. In some systems, water from tank 102 may be circulated directly to collector 101 to be heated by conduction and convection from the absorber. More typically, though, a separate heat transfer fluid is circulated in fluid circuit 103 by a pump 104. The heat transfer fluid is heated by collector 101, and circulated to a heat exchanger 105 within tank 102 to heat the water in tank 102. Heat exchanger 105 may be a coil of tubing through which the heat transfer fluid circulates, or may have another shape. In any event, when the heat transfer fluid is at a higher temperature than the water in tank 102, heat from the heat transfer fluid flows by conduction and convection into and through the walls of the tubing of heat exchanger 105 and into the water in tank 102. In the process, the heat transfer fluid is cooled to near the temperature of the water in tank 102, and is then recirculated to collector 101 to be reheated.

A controller 106 may optimize operation of the system, for example by operating pump 104 only when the heat transfer fluid exiting collector 101 is hotter than the water in tank 102. A backup heater 107 may be provided for heating the water in tank 102 during long periods of inclement weather, or to supplement the ability of the system to heat the water using solar energy alone. Typically, collector 101 is placed outdoors, for example on a rooftop, and tank 102 is indoors, for example in a basement or utility room. In some climates, the outdoor portion of fluid circuit 103 may be subject to freezing temperatures, and the system may handle cold weather in various ways. For example, if the heat transfer fluid in fluid circuit 103 is water, controller 106 may recognize the threat of freezing, and drain the water from collector 101 and the outdoor portion of fluid circuit 103 until the risk of freezing has passed. In other systems, the heat transfer fluid circulating through fluid circuit 103 may be a fluid that will not freeze, such as a mixture of water and ethylene glycol or other anti-freeze treatment.

A designer of a system such as system 100 may strive to provide good performance at low cost, and may trade off design variables in pursuit of this goal. For example, a larger collector 101 may permit faster heating of the water in tank 102, but will also likely be more expensive, so the designer will trade off the improved performance against the increased cost and choose a collector size according to his or her cost and performance goals.

The performance of system 100 is dependent on may factors, including the size of collector 101, the amount of sunlight falling on collector 101, the effectiveness of heat transfer from collector 101 to the heat transfer fluid, amount of heat lost from the system once collected, and the effectiveness of heat transfer from the heat transfer fluid to the water in tank 102. The effectiveness of heat transfer into and out of the heat transfer fluid at collector 101 and heat exchanger 105 will depend in part on the thermal conductivity and convective heat transfer properties of the heat transfer fluid itself. The higher the thermal conductivity and the more effective the fluid is in convective heat transfer, the better the performance of system 100.

According to embodiments of the invention, the heat transfer performance of the heat transfer fluid in system is improved by using a nanofluid as the heat transfer fluid. A nanofluid is a fluid containing particles of a size conveniently expressed in nanometers, typically between 1 and 100 nanometers. The particles are called nanoparticles. The particles may be colloidal, or may be atomic in size. The addition of nanoparticles to a fluid, for example water or ethylene glycol, can increase both the thermal conductivity of the fluid and the effectiveness of convective heat transfer between the fluid and surrounding structures. Although the physical mechanism accounting for the increases may not be fully understood, the increases may be affected by the size and concentration of the nanoparticles, the material of the nanoparticles, the temperature at which the fluid characteristics are measured, and other factors. The increases may be surprisingly large, and not predicted by conventional theory. A review of thermal properties of some nano fluids may be found in X.-Q. Wang, A.S. Mujumdar, Heat transfer characteristics of nanofluids: A review, International Journal of Thermal Sciences 46 (2007) pp. 1-19.

In some embodiments, the nanoparticles may be supplied to the heat transfer fluid in fluid circuit 103 at the time system 100 is manufactured or installed. However, in other embodiments, the nanoparticles may be generated by an ion generator 108 that is part of system 100. Nanoparticle generator 108 may be, for example, of the type described in co-pending U.S. Patent Application No. 13/035,479 filed February 25, 2011 and titled "Thermoelectric Generator", the entire disclosure of which is hereby incorporated by reference herein for all purposes. FIG. 2 illustrates the operation of example ion generator 108, in accordance with embodiments of the invention. Ion generator 108 includes two electrodes 201 and 202, in contact with heat transfer fluid 214 in fluid circuit 103. For example, electrodes 201 and 202 may penetrate the wall of a pipe defining fluid circuit 103 to reach heat transfer fluid 214. In some embodiments, electrodes 201 and 202 are made of sterling silver, which comprises nominally 92.5% silver and 7.5%) copper, and thus ion generator 108 produces silver and copper ions 213 in heat transfer fluid 214. Example ion generator 108 impresses a voltage between electrodes 201 and 202, so that ions 213 are generated by electrolysis. As heat transfer fluid 214 circulates, ions 213 are dispersed throughout heat transfer fluid 214. Preferably, the voltage impressed between electrodes 201 and 202 is an alternating voltage. In one example method of producing the alternating voltage, an oscillator 203 produces a train of pulses 204. Oscillator 203 may be, for example, a well-known 555 timer integrated circuit, or another kind of oscillator. Pulse train 204 may be a train of digital pulses, alternating between 0 and 5 nominal volts. Pulse train 204 may be provided to a D flip-flop 205, which has the effect of halving the frequency of pulse train 204 and producing a second pulse train having a 50%> duty cycle, regardless of the duty cycle of pulse train 204. The two complementary outputs of D flip-flop 205 are further conditioned by AND gates 206, producing complementary pulse trains 207 and 208, each having a frequency half that of pulse train 204, and a 50%> duty cycle.

Complementary pulse trains 207 and 208 may be fed to an H-bridge circuit 209, which may be for example a TA7291SG Bridge Driver available from Toshiba America, Inc., of New York, New York. Control circuitry 210 within H-bridge circuit 209 utilizes complementary pulse trains 207 and 208 to switch a set of transistors to alternately impress the voltage on electrodes 201 and 202. For example, when pulse train 207 is at a high level and pulse train 208 is at a low level, transistors 211 may be switched on and transistors 212 may be switched off. Conversely, when pulse train 207 is at a low level and pulse train 208 is at a high level, transistors 211 may be switched off and transistors 212 may be switched on. As a result, electrodes 201 and 202 alternately plate and disperse ions. Ion generator 108 may be operated whenever pump 104 is in operation, or may be operated intermittently, may be operated only upon startup to build up a concentration of ions 213 in heat transfer fluid 214, or may be operated based on some other scheme.

Many variations in the operation of ion generator 108 are possible, for example in the voltage used, the frequency of operation, and other parameters. In one embodiment, oscillator 203 produces a pulse train 204 having a frequency of about 14 Hz, resulting in a frequency of switching of the voltage between electrodes 201 and 202 of about 7 Hz. Because exemplary ion generator 108 uses digital circuitry, the voltage between electrodes 201 and 202 may switch essentially instantaneously between its extremes. For the purposes of this disclosure, this kind of alternating voltage will be referred to as a "chopped" alternating voltage. A chopped alternating voltage may also be known as a square wave. Using other drive schemes, the alternating voltage may transition smoothly, for example sinusoidally.

Other frequencies may be used, for example 10 Hz, 60 Hz, 120 Hz, 1 kHz, 5 kHz, 10 kHz, 20 kHz, or another suitable frequency. For example, in some embodiments, the alternating voltage between electrodes 201 and 202 may have a frequency of more than 20 kHz. In some embodiments, the alternating voltage between electrodes 201 and 202 maybe about 5 volts, but other voltages may be used, for example 3 volts, 12 volts, 24 volts, or another suitable voltage. The use of an alternating voltage may have the beneficial effect of preventing the buildup of scale on electrodes 201 and 202, as during operation, each electrode is a donor of material at least some of the time, so that the surface of each electrode is routinely at least partially shed. This cleaning action may serve to maintain good electrical contact between the electrodes and the fluid.

The presence of nanoparticles in heat transfer fluid 214, for example copper and silver ions as described above, increases the thermal conductivity of heat transfer fluid 214, and may also improve the effectiveness of convective heat transfer between heat transfer fluid 214 and other structures such as heat exchanger 105 and internal parts of collector 101. This improved heat transfer effectiveness can be exploited by a system designer to improve the performance of the system, to reduce the cost of the system, to adjust the cost/performance balance, or to provide other benefits.

For example, because the improved heat transfer characteristics of heat transfer fluid 214 improve the performance of heat exchanger 105, the size of heat exchanger 105 may be reduced, because less surface area in contact with water in tank 102 and with heat transfer fluid 214 may be needed to maintain the performance of the system as compared with a system that does not utilize a nanofluid. The change in size may include a shorter length of tubing in heat exchanger 105, a smaller diameter of tubing, or other changes in dimensions or combinations of

dimensions. Thus, the cost of heat exchanger 105 may be reduced. In another example, the number of tubes within collector 101 may be reduced, resulting in cost savings. It may even be possible to reduce the size of collector 101 itself, resulting in significant cost savings. In another example, the materials used in the system may be reduced in cost or weight. FIG. 3 shows a simplified diagram of one example architecture of a part of the interior of collector 101. In this example, incoming solar radiation 301 passes through glass cover 302 and strikes absorber 303. Absorber 303 may be, for example a metal sheet painted black for good absorption characteristics. Tubes 304 are in intimate contact with absorber 303 and carry heat transfer fluid 214. In prior systems, tubes 304 would typically be made of copper or another metal. While tubes 304 may absorb some solar radiation directly, they also collect heat from plate 303 by conduction, and from the surrounding air by conduction and convection. Heat conducts through the walls of tubes 304 and is transferred to heat transfer fluid 214 by conduction and convection. The path of heat from absorber 303 to heat transfer fluid 214 may be thought of as a series of thermal resistances. Reducing any of the thermal resistances will improve the performance of collector 101, and increasing any of the thermal resistances will decrease the performance of collector 101.

The nanofluid improves the transfer of heat between tubes 304 and heat transfer fluid 214. This improvement in performance may enable material savings in collector 101. For example, the number of tubes 304 in collector 101 may be reduced. In another example, the dimensions of tubes 304 may be modified, for example to use smaller diameter tubing. In some embodiments, the improved heat transfer characteristics may enable use of materials with poorer heat transfer characteristics but other desirable qualities, while maintaining acceptable or even improved system performance. For example, rather than being made of copper, in some embodiments tubes 304 may be made a material that is lighter than copper, cheaper than copper, or both, for example aluminum or a plastic such as polypropylene. Additionally, the lighter weight of collector 101 may result in savings in shipping costs, and improvements in the ease of installation of collector 101. Ground Coupled Heating and Cooling Embodiments

FIG. 4 illustrates a thermal system 400 including a ground coupled piping loop 401 in accordance with embodiments of the invention, and associated other components that combine to condition the space 402 within building 403. Ground coupled piping loop 401 uses the earth as a heat source or heat sink, to exhaust heat to or receive heat from the ground as needed to facilitate the performance of environmental control unit 404. In some embodiments, environmental control unit 404 may be a heat pump capable of heating space 402 in the winter by extracting heat from a fluid flowing in ground coupled piping loop 401, or cooling space 402 in the summer by exhausting heat from space 402 into the fluid flowing in ground coupled piping loop 401. The efficiency of a heat pump depends on the temperature differential the heat pump must overcome. Some heat pumps provide heat by extracting it from outdoor air, but in very cold weather, this results in a very large temperature differential.

A ground coupled heat pump takes advantage of the fact that subsoil temperatures are typically nearly constant year round— typically about 54-57 °F (12-14 °C) in many parts of the United States. By circulating a heat transfer fluid through an underground loop, the heat transfer fluid can be cooled or heated to about the underground soil temperature, and serve as a source or sink for the heat pump. The resulting temperature differential may be significantly less than for a heat pump that sources heat from outdoor air, resulting in improved performance of the heat pump. The system may benefit throughout the year, as the heat transfer fluid may be warmer than outdoor air in the winter, and cooler than outdoor air in the summer.

A major component of the cost of a ground couple heat pump system is the cost of the underground piping loop and its installation. In conventional systems, it is estimated that the ground loop accounts for about one third of the system cost. The ground loop is sized to provide sufficient heat transfer between the heat transfer fluid and the ground, given the thermal properties of the heat transfer fluid, the piping material, and the surrounding soil.

In embodiments of the invention, heat transfer between the heat transfer fluid in ground coupled piping loop 401 and the surrounding soil is enhanced as compared with a conventional system. This enables use of a smaller piping loop, and reduced system cost.

In some embodiments, the heat transfer fluid in ground coupled piping loop 401 is a nano fluid with enhanced heat transfer properties as described above. For example, an ion generator 108 may supply silver and copper ions to the fluid in ground coupled piping loop 401, although other kinds of nanoparticles may also be used. The heat transfer fluid may be any suitable fluid, for example water, a mixture of water and an anti-freeze additive, or another fluid.

In some embodiments, environmental control unit 404 may be a hydronic cooling unit, in which room air is circulated by a fan over a heat exchanger, to be cooled by coming in contact with tubes containing the cooled heat transfer fluid from ground coupled piping loop 401. Power for environmental control unit 404, ion generator 108, and a small pump 405 may be supplied by a photovoltaic panel 406, so that the ongoing energy cost of the system is nearly zero.

Other techniques may be used to enhance the transfer of heat between the heat transfer fluid in ground coupled piping loop 401 and the ground. For example, it has been recognized that packed sand, especially quartz sand, has a higher thermal conductivity than typical soils. In some embodiments, ground coupled piping loop 401 is embedded in sand rather than being backfilled with soil. FIG. 5 illustrates an end view of the structure of an example trench 501 with ground coupled piping loop 401 installed in it. Trench 501 is dug preferably more than three feet deep and up to 12 inches or more in width. Deeper trenches tend to result in more stable temperatures for the heat transfer fluid. Ground coupled piping loop 401 is then inserted in the trench in "slinky" fashion, in a series of loops extending one from the next lengthways in the trench. Piping loop 401 may be made, for example, from coiled polyethylene pipe, another kind of polymer pipe, or another suitable material. The ends 502 of the tube may be brought to the same end of the trench, preferably near building 403. Once the pipe is in place, sand 503 is added to the trench to embed the pipe and provide enhanced thermal conductivity to the surrounding soil 504. A layer of topsoil 505 may be placed on top of the sand, so that grass or other plants can be grown above trench 501.

Thermal conductivity to surrounding soil 504 may be further enhanced by keeping sand 503 and soil 504 area wet. This may be accomplished by actively soaking trench 501, for example using a soaker hose. In other embodiments, a downspout 407 (shown in FIG. 4) may be routed to drain over trench 501, so that at least some moisture is delivered to trench 501 passively.

In some embodiments, the heat transfer fluid in ground coupled piping loop is treated with an anti-freeze additive, but in other embodiments, no anti-freeze may be provided. Some parts of the piping loop may be exposed to ambient air (preferably with insulation), so that there is some risk of freezing of the heat transfer fluid. In some embodiments, pump 405 may be run intermittently in cold weather so that the heat transfer fluid does not remain stationary in the areas where freezing is a risk, but periodically cycles through ground coupled piping loop 401 to be warmed by heat transfer from the ground.

FIG. 6 illustrates an example circuit for intermittently driving pump 405, in accordance with embodiments of the invention. The circuit of FIG. 6 will drive pump 405 for about 120 seconds about once each hour, in the absence of an overriding control signal from environmental control system 404. In other embodiments, different duty cycles may be used. For example pump 405 may be run for 60 seconds every 30 minutes, or on any other suitable schedule.

The techniques described above, for example the use of nanofluid in ground coupled piping loop 401, enable flexibility in design, and may result in improved performance of an environmental control system, reduced cost, or both, as compared with a system that does not use nanofluid. For example, because the effectiveness of heat transfer to the soil is improved, a shorter piping loop may be used, resulting in savings in material and installation costs. In another example, it may be possible to use smaller diameter piping for a ground coupled piping loop installed according to embodiments of the invention, resulting in further material cost savings. Further, the enhanced heat transfer may enable the use of lower cost materials for the ground coupled piping loop, for example low cost plastic tubing where copper or other metals may have been used in a conventional system.

Another advantage of a system according to embodiments of the invention is that the ability to use a shorter piping loop may enable installation of a ground coupled system in a smaller area than was previously possible. Accordingly, homeowners or others who would otherwise be constrained by property size limitations may be able to take advantage of a ground coupled system.

In-Floor Heating and Cooling Embodiments

Underfloor heating and cooling is a form of central heating and cooling which achieves indoor climate control for thermal comfort using conduction, radiation, and convection.

FIG. 7 schematically illustrates and underfloor heating system 700, in accordance with embodiments of the invention. A piping loop 701 is embedded in floor 702 of room 703, and arranged in a serpentine pattern. It will be recognized that system 700 as shown is highly simplified. Floor 702 may include various layers of differing materials such as concrete and polystyrene insulation. Many different serpentine patterns are possible, and a particular pattern may be selected to try to achieve uniform heating of floor 702.

In a heating mode, piping loop 701 is coupled to a boiler or other heating device 704, which heats a heat transfer fluid and circulates the heat transfer fluid through piping loop 701. Heating device 704 may use any suitable technology for heating the heat transfer fluid, for example burning a fossil fuel such as natural gas, or heating the heat transfer fluid via electric resistance heating. Heating device 704 may be a heat pump.

As the heated fluid flows through piping loop 701, heat from the fluid is transferred through the walls of piping loop 701, conducts through floor 702, and warms room 703 by radiation and convection from floor 702. In some embodiments, cooling of room 703 can be accomplished by cooling the heat transfer fluid rather than heating it.

The effectiveness of heat transfer from the heat transfer fluid to room 703 depends on several factors, including for example, the thermal conductivity of floor 702, the kind of floor coverings on floor 702, the material from which piping loop 701 is made, and the heat transfer properties of the heat transfer fluid within piping loop 701.

According to embodiments of the invention, the heat transfer fluid used in piping loop 701 is a nanofluid. In some embodiments, the nanofluid includes silver and copper ions, which may be generated using an ion generator 108 as described above, although other kinds of nanoparticles may be used. The nanofluid has an increased thermal conductivity as compared with a similar fluid not including nanoparticles, and may also be more effective in transferring heat via convection. This improved heat transfer capability may enable performance improvements, cost savings, or both.

For example, because heat can be delivered to room 703 more effectively by a system utilizing a nanofluid, the total length of embedded pipe in piping loop 701 may be reduced, resulting in savings in material and installation costs. In another example, it may be possible to reduce the diameter or other dimensions of the pipe used to construct piping loop 701, also resulting in material cost savings.

EXPERIMENT ONE

A solar collector panel was constructed having six receiver tubes, two each made of copper, aluminum, and polypropylene. Other than being made of different materials, the receivers were as nearly identical in other aspects as could be arranged, for example in diameter and length of receiver within the panel. Each receiver was connected in a closed loop with a respective water tank and a heat transfer fluid was pumped continuously in a closed loop between the respective tank and receiver pipe. For each pair of receiver tubes of similar material, one used plain water as the heat transfer fluid, and one used water with nanoparticles in the form of silver and copper ions generated with a device as described above and shown in FIG. 2.

The panel was placed in direct sunlight and the pumps were activated. After one hour of solar collection and circulation of the heat transfer fluids, the circuit using a polypropylene receiver tube and nano fluid had delivered 2733 BTUs to its water tank as measured by the temperature and mass of the water, while the circuit using a copper receiver tube and plain water had delivered only 2123 BTUs. Thus, the addition of the nanoparticles provided improved performance with lighter and cheaper collector materials.

EXPERIMENT TWO To test the effectiveness of a ground coupled piping loop according to embodiments, a small loop was installed underground, and linked via a liquid-to-liquid heat exchanger to a 100 gallon reservoir of water. The reservoir was heated to approximately 98 °F, and the heat exchange fluid circulated to draw heat from the reservoir and reject it to the ground. In a first run, the heat transfer fluid was plain water, and in one hour of operation, 8830 BTUs were removed from the reservoir, based on measurements of the reservoir temperature and capacity. In a second test run on a different day, a nanofluid comprising water with silver and copper ions as described above was used as the heat transfer fluid. In one hour, 11,829 BTUs were removed from the reservoir. A baseline test run without circulating the heat transfer fluid showed only a loss of about 800 BTUs from the reservoir. EXPERIMENT THREE

In an example hydronic cooling installation, a ground coupled piping loop including about 364 feet of 1/2 inch diameter polyethylene pipe was installed in overlapping loops in a trench 67 feet long. The ground coupled piping loop was installed about three feet below the surface of the ground, and coupled to heat exchanger inside an enclosed garage workshop of about 588 square feet. The installation is located in Colorado. The ground coupled piping loop was filled with a heat transfer fluid made up of water with silver and copper ions generated by an ion generator as described above. A small electrical pump circulates the heat transfer fluid through the ground coupled piping loop and the heat exchanger, so that heat drawn from the interior space is exhausted into the ground, and the cooled heat transfer fluid is returned to the heat exchanger to carry away additional heat. Air is passed through the heat exchanger using a small fan. The system maintained the indoor temperature of the workshop at about 72 °F while the outdoor temperature ranged into the low 90s °F.

The invention has now been described in detail for the purposes of clarity and understanding. However, it will be appreciated that certain changes and modifications may be practiced within the scope of the appended claims.

EMBODIMENTS

Embodiment 1 : A system for heat transfer, the system comprising: a piping loop; and a heat transfer fluid that circulates within the piping loop such that heat is transferred into or out of the heat transfer fluid through the walls of the piping loop; wherein the heat transfer fluid is a nano fluid containing nanoparticles, the nano fluid having enhanced thermal conductivity as compared with a similar fluid not containing the nanoparticles.

Embodiment 2: The system of embodiment 1, wherein the heat transfer fluid contains ions of copper, ions of silver, or both ions of copper and ions of silver.

Embodiment 3: The system of any one of the embodiments 1 and 2, further comprising an ion generator, the ion generator including: a pair of spaced apart electrodes in contact with the heat transfer fluid; and circuitry arranged to impress an alternating voltage between the two electrodes such that ions of material from the electrodes are generated within the heat transfer fluid by electrolysis.

Embodiment 4: The system of any one of the embodiments 1-3, wherein the electrodes comprise copper, silver, or both copper and silver.

Embodiment 5: The system of any one of the embodiments 1-4, wherein the electrodes comprise sterling silver.

Embodiment 6: The system of any one of the embodiments 1-5, wherein the alternating voltage has a frequency of at least 6 Hz. Embodiment 7: The system of any one of the embodiments 1-6, wherein the alternating voltage has a frequency greater than 20 kHz.

Embodiment 8: The system of any one of the embodiments 1-7, wherein the piping loop comprises plastic pipe. Embodiment 9: The system of any one of the embodiments 1-8, further comprising a solar collector; a tank of water to be heated; and a heat exchanger within the tank; wherein the heat transfer fluid flows, via the piping loop, through the solar collector to be heated by solar energy and through the heat exchanger to heat the water in the tank. Embodiment 10: The system of any one of the embodiments 1-9, wherein the piping loop comprises a ground coupled piping loop, and wherein heat is exchanged between the heat transfer fluid and the ground through the walls of the ground coupled piping loop.

Embodiment 11 : The system of any one of the embodiments 1-10, wherein at least part of the piping loop is embedded within a floor, and wherein heat is exchanged between the heat transfer fluid and the floor to heat or cool a space above the floor.

Embodiment 12: A system for heating water, the system comprising: a solar collector; a tank of water to be heated; a heat exchanger within the tank; a fluid circuit coupling the solar collector with the heat exchanger; and a heat transfer fluid that circulates within the fluid circuit, wherein the heat transfer fluid is a nanofluid containing nanoparticles, the nanofluid having enhanced thermal conductivity as compared with a similar fluid not containing the nanoparticles.

Embodiment 13: The system of embodiment 12, wherein the heat transfer fluid contains ions of copper, ions of silver, or both ions of copper and ions of silver.

Embodiment 14: The system of any one of the embodiments 12 and 13, further comprising an ion generator, the ion generator including: a pair of spaced apart electrodes in contact with the heat transfer fluid; and circuitry arranged to impress an alternating voltage between the two electrodes such that ions of material from the electrodes are generated within the heat transfer fluid by electrolysis.

Embodiment 15: The system of any one of the embodiments 12-14, wherein the electrodes comprise copper, silver, or both copper and silver. Embodiment 16: The system of any one of the embodiments 12-15, wherein the electrodes comprise sterling silver.

Embodiment 17: The system of any one of the embodiments 12-16, wherein the alternating voltage has a frequency of at least 6 Hz. Embodiment 18: The system of any one of the embodiments 12-17, wherein the alternating voltage has a frequency greater than 20 kHz.

Embodiment 19: The system of any one of the embodiments 12-18, wherein the solar collector comprises plastic tubes for carrying the heat transfer fluid through the solar collector. Embodiment 20: The system of any one of the embodiments 12-19, wherein the solar collector comprises polyethylene tubes for carrying the heat transfer fluid through the solar collector.

Embodiment 21 : The system of any one of the embodiments 12-20, wherein the solar collector comprises a flat panel solar collector.

Embodiment 22: The system of any one of the embodiments 12-21, wherein the solar collector comprises a concentrating solar collector.

Embodiment 23: The system of any one of the embodiments 12-22, further comprising: a pump for circulating the heat transfer fluid through the fluid circuit; and a controller that controls the operation of the pump.

Embodiment 24: A thermal system, comprising: an environmental control system; a ground coupled piping loop coupled to the environmental control system; and a heat transfer fluid that circulates within the ground coupled piping loop, wherein the heat transfer fluid is a nanofluid containing nanoparticles, the nanofluid having enhanced thermal conductivity as compared with a similar fluid not containing the nanoparticles.

Embodiment 25: The system of embodiment 24, wherein the heat transfer fluid contains ions of copper, ions of silver, or both ions of copper and ions of silver.

Embodiment 26: The system of any one of the embodiments 24 and 25, further comprising an ion generator, the ion generator including: a pair of spaced apart electrodes in contact with the heat transfer fluid; and circuitry arranged to impress an alternating voltage between the two electrodes such that ions of material from the electrodes are generated within the heat transfer fluid by electrolysis.

Embodiment 27: The system of any one of the embodiments 24-26, wherein the electrodes comprise copper, silver, or both copper and silver. Embodiment 28: The system of any one of the embodiments 24-27, wherein the electrodes comprise sterling silver.

Embodiment 29: The system of any one of the embodiments 24-28, wherein the alternating voltage has a frequency of at least 6 Hz. Embodiment 30: The system of any one of the embodiments 24-29, wherein the alternating voltage has a frequency greater than 20 kHz.

Embodiment 31 : The system of any one of the embodiments 24-30, wherein the ground coupled piping loop comprises polymer pipe.

Embodiment 32: The system of any one of the embodiments 24-31, wherein the ground coupled piping loop is buried underground in a trench, and embedded in sand.

Embodiment 33: The system of any one of the embodiments 24-32, further including a mechanism for wetting the ground in the vicinity of the ground coupled piping loop.

Embodiment 34: The system of any one of the embodiments 24-33, further comprising: a pump for circulating the heat transfer fluid through ground coupled piping loop; an ion generator that generates ions within the heat transfer fluid; and a photovoltaic solar panel that supplies power for operating the pump and the ion generator.

Embodiment 35: The system of any one of the embodiments 24-34, wherein the ground coupled piping loop exhausts heat from the heat transfer fluid into the ground at least some of the time.

Embodiment 36: The system of any one of the embodiments 24-35, wherein the ground coupled piping loop absorbs heat from the ground into the heat transfer fluid at least some of the time.

Embodiment 37: An underfloor environmental control system, comprising: a piping loop embedded within a floor; a heat transfer fluid that circulates within the piping loop, wherein the heat transfer fluid is a nanofluid containing nanoparticles, the nanofluid having enhanced thermal conductivity as compared with a similar fluid not containing the nanoparticles; and a device coupled to the piping loop, such that the device imparts heat to the heat transfer fluid or removes heat from the heat transfer fluid.

Embodiment 38: The underfloor environmental control system of embodiment 37, wherein the device imparts heat to the heat transfer fluid. Embodiment 39: The underfloor environmental control system of any one of the embodiments 37 and 38, wherein the device removes heat from the heat transfer fluid.

Embodiment 40: The underfloor environmental control system of any one of the embodiments 37-39, wherein the device imparts heat to the heat transfer fluid some of the time and removes heat from the heat transfer fluid some of the time.

Embodiment 41 : The underfloor environmental control system of any one of the embodiments 37-40, wherein the heat transfer fluid contains ions of copper, ions of silver, or both ions of copper and ions of silver.

Embodiment 42: The underfloor environmental control system of any one of the embodiments 37-41, further comprising an ion generator, the ion generator including: a pair of spaced apart electrodes in contact with the heat transfer fluid; and circuitry arranged to impress an alternating voltage between the two electrodes such that ions of material from the electrodes are generated within the heat transfer fluid by electrolysis.

Embodiment 43 : The underfloor environmental control system of any one of the embodiments 37-42, wherein the electrodes comprise copper, silver, or both copper and silver.

Embodiment 44: The underfloor environmental control system of any one of the embodiments 37-43, wherein the electrodes comprise sterling silver.

Embodiment 45 : The underfloor environmental control system of any one of the embodiments 37-44, wherein the alternating voltage has a frequency of at least 6 Hz. Embodiment 46: The underfloor environmental control system of any one of the embodiments 37-45, wherein the alternating voltage has a frequency greater than 20 kHz.