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Probe for collecting thermal energy from the ground for a heat pump, and a collection network equipped with such probesProbe for collecting thermal energy from the ground for a heat pump, and a collection network equipped with such probes description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20090025902, Probe for collecting thermal energy from the ground for a heat pump, and a collection network equipped with such probes. Brief Patent Description - Full Patent Description - Patent Application Claims
The invention relates to a probe for collecting thermal energy from the ground for heat pumps, which pumps may be of the so-called “water/water” type or of the “gas/water” type. Such equipment serves to collect the thermal energy available in the upper layers of the earth's crust, to concentrate said energy (raise it to a higher temperature), and to deliver it in said concentrated form to feed a heater circuit. The core of the pump comprises a compressor and two heat exchangers connected respectively to the collection network and to the heat delivery network, together with a refrigerant fluid circuit comprising a condenser, an expander, and an evaporator. The compressor concentrates the energy collected from the ground at the evaporator and delivers the energy for delivering to the heater circuit at the condenser. In the collection network, there is provided a “collector probe” constituted by a circuit for a heat-conveying fluid, generally a liquid such as water having ethylene glycol added thereto, but which could equally well be a gaseous fluid. This collector fluid or heat-conveying fluid is cooled by the evaporator of the heat pump, and is then sent into the ground in order to be heated by coming into contact with the surrounding medium, thereby extracting heat energy therefrom. Each linear meter of the probe buried in the surrounding medium in question can thus bring a few joules of thermal energy to the heat pump when the circuit is in operation, and the fluid as heated in this way then returns to the heat pump which concentrates and delivers the thermal energy as collected in this way. The technique described above should be distinguished from the technique described for example in U.S. Pat. No. 5,561,985 which does not make use of a “collector probe” in the meaning of the invention, i.e. a circuit in which a heat-conveying fluid circulates (and not a refrigerant fluid), without changing phase. That document proposes burying an evaporator, i.e. a heat exchanger in which the refrigerant fluid coming from the compressor is taken to the evaporator while in the liquid phase and leaves the evaporator in the vapor phase. DE-A-103 27 602 describes a comparable technique in which a tube receives a CO2 condensate that flows downwards in the form of a film along the walls of the tube to a deep zone at higher temperature where the CO2 vaporizes and is returned under pressure by rising up the tube. In contrast, a “collector probe” is never directly connected to the compressor, the heat-conveying fluid that circulates therein being different from the refrigerant fluid of the circuit including the compressor. Collector probes are generally implemented in the form of a tube constituting a loop connected at each of its ends to a respective terminal of the heat pump. The nature of the tube, and most particularly the thermal conductivity of its wall, determines its heat exchange characteristics with the surrounding medium. Furthermore, the diameter of the tube and the longer or shorter length of the loop determine the heat exchange area, and thus the mass of the surrounding medium from which heat is collected. A first technique known as “horizontal” collection consists in burying the tube in the ground to a shallow depth (about 50 centimeters (cm) to 70 cm), causing it to follow a sinuous path so as to occupy a maximum area of ground in order to engage a sufficient mass of the surrounding medium. For the purposes of burying the probe, said technique requires the ground to be stripped over a large extent, or else it requires trenches to be dug, with various constraints that stem therefrom: earth-moving costs; impossibility of placing the collection network under a house; and restrictions on how the ground can be used after the tube has been buried, for example no possibility of planting trees therein. A second technique known as “vertical” collection consists in drilling a vertical borehole to a depth that may be as much as 100 meters (m), and then burying over the entire depth one or more looped tubes. Given the depth that is to be reached, this technique requires a borehole of relatively large diameter, of the order of 200 millimeters (mm), thus requiring specialist equipment that is heavy and bulky in use. It can indeed be deployed from a small area of ground, but it suffers from other drawbacks: cost and duration of drilling; poorly-controlled heat exchange; the medium is involved only in the form of a single cylindrical mass surrounding the borehole. U.S. Pat. No. 5,339,890 describes a “collector probe” embodied in the form of a flexible tubular element provided at one of its ends with both the fluid inlet and the fluid outlet, and in which the other end is a free end. That configuration enables the tubular element to be inserted by means of its free portion into a gallery that opens out to the surface via a single point. The buriable tubular element is strong enough to be capable of being pushed along said gallery over its entire length from only one of its ends. However, no presently-proposed solution for burying a collector probe for a heat pump has been found to be genuinely satisfactory, neither economically speaking nor in terms of the effectiveness of heat exchange. One of the objects of the invention is to propose a collector probe, which probe is capable specifically of being optimized from the point of view of heat exchange effectiveness compared with previously-proposed solutions. The starting point of the invention lies in noticing the importance of controlling the flow conditions by a particular configuration of the respective inside surfaces of the fluid return tube and of the fluid admission tube, to obtain a noticeable increase in thermal efficiency. The probe proposed by the invention is a probe of the type known in U.S. Pat. No. 5,339,890, that is to say comprising a circuit for circulating a heat-conveying fluid, the circuit having a fluid inlet and a fluid outlet suitable for being connected to respective terminals of a heat pump. The circuit comprises at least two tubes extending in parallel, with a fluid admission tube connected to the fluid inlet and a fluid return tube connected to the fluid outlet. The fluid admission and return tubes are in communication with each other at their distal ends, and they are made with a wall in common over their entire length, thus forming a single tubular element for burying having a proximal end with the fluid inlet and outlet, and a distal end that is free. In a manner characteristic of the invention, the inside surface of the wall of the fluid return tube is provided with portions in relief suitable for creating turbulence in the fluid flowing in said tube, and the inside surface of the wall of the fluid admission tube is a smooth surface suitable for encouraging laminar flow of the fluid flowing in said tube. The portions in relief in the fluid return tube provide a return flow that is slow and turbulent, encouraging heat exchange with the surrounding medium, unlike the smooth surface of the admission tube that, on the contrary, encourages a fast flow minimizing heat losses. U.S. Pat. No. 5,339,890 does not describe any configuration of a probe of this type: the only portions in relief that are present are to be found on the outside surface of the fluid tube, and therefore have no effect on the flow conditions of the fluid circulating inside that tube. On the contrary, that document is of the opinion (column 5, lines 44 to 50) that “there is no need for spacers or fins to control annular spacing between the internal tube 60 and the external tube 42 or to create turbulence because positioning of the internal tube 60 in relation to the external tube 42 is unimportant and fluid flow patterns are controlled by other factors including diameter, lumen, and flow rate”. In contrast, the present invention proposes controlling the respective flow regimes in the fluid admission and return tubes by giving the inside surfaces of these tubes configurations that are suitable for encouraging the looked-for type of flow. According to various preferred and advantageous characteristics:
the common wall is an isothermal wall and/or enclosing the insulating cavities;
the fluid flow section of the return tube is greater than the fluid flow section of the admission tube;
the outside section of said single tubular element for burying is uniform, in particular circular, over the entire length of said element;
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