MXPA00005692A - Thermoelectric cooling apparatus with dynamic switching to isolate heat transport mechanisms - Google Patents

Abstract

Apparatus and method for sub-ambient cooling using thermoelectric element dynamics in conjunction with pulsed electrical power and selectively enabled thermal coupling to the cold sink. In one form, Peltier devices (1) are dynamically enabled using pulses of electrical power while the thermal path between the cold side of the Peltier device (1) and the cold sink (4) is selectively switched in relative synchronism between conductive states responsive to the dynamics of the Peltier device temperatures. Switched coupling of the thermal connection between the cold sink (4) and the Peltier device materially improves efficiency by decoupling Joule heating and conductive heat transfer losses otherwise conveyed from the Peltier device. Preferable implementations utilize MEMS to accomplish the selective thermal switching, whereby sub-ambient cooling capacity is increased by parallel operation of multiple Peltier devices and MEMS switches.

Description

THERMOELECTRIC COOLING WITH SWITCHING DYNAMICS TO INSULATE THERMAL TRANSPORT MECHANISMS The present invention is generally related to cooling systems. More particularly, the invention is directed to systems that achieve thermoelectric cooling of high relative efficiency through the application of selectively switched electrical power and selectively switched thermal coupling concepts and configurations. Sub-ambient cooling is conventionally achieved through refrigeration cycles based on liquid vapor / gas compression using freon-type refrigerants to implement heat transfers. These refrigeration systems are widely used to cool human residencies, food and vehicles. Sub-ambient cooling is also often used with major electronic systems such as large computers. Although vapor compression cooling can be very efficient, it requires significant moving equipment or tooling, including at least one compressor, condenser, evaporator, and related refrigerant transfer plumbing. As a result of the complexity and high associated cost, vapor compression cooling has not found material acceptance in small cooling applications, for example personal computers. The fact that the CMOS logic can operate materially faster as the temperature decreases has been well known for at least ten years. For example, if the CMO logic devices are operated at -50 ° C, the performance is improved by 50% compared to the operation at room temperature. Operating temperatures of liquid nitrogen in the -197 ° C range have shown performance improvements of 200%. Similar benefits have been shown to accumulate for integrated circuit wiring, where the metal wiring resistance decreases by a factor of two for integrated circuits that operate at -50 ° C compared to operation at room temperature. This improvement rivals the recent technological development of using copper wiring in integrated circuits to reduce the interconnection resistance and thus effectively increase the operating frequencies that are reached. In this way, the sub-environment operation of integrated circuit logic devices, such as field effect transistors, as well as the interconnection wiring, can materially improve integrated circuit performance, leaving the question of how to achieve this cooling in the confines of an increasingly large and materially reduced cost environment. Thermoelectric cooling is an alternative that has found some use given the compact size of some predominantly used Peltier devices. The thermoelectric cooling of Peltier devices is also very reliable, since the cooling is totally solid state. The key negative aspect of thermoelectric cooling is inefficiency, where the efficiency of the cooling system of a common Peltier device is commonly only in the range of 20% for a relatively nominal temperature drop between the cold collector and the environment. For example, to cool at the rate of 1 watt at sub-ambient temperature of 0 °, the Peltier cooling system must be energized with 5 watts. As the amount of heat to be transferred increases, the total energy to dissipate in the environment forces large convection devices and high-performance power supply circuits. Therefore, the thermodynamic cooling of Peltier devices has not been considered as a widely applicable technology to improve the performance of integrated circuits. To understand how the present invention improves the thermoelectric cooling efficiency, it is necessary to understand why the thermoelectric cooling of the Peltier device is inefficient. A Peltier device is manufactured from semiconductor material such as bismuth telluride or lead telluride. Although now new materials are evaluated in different universities, they have yet to achieve their realization. The commonly used Peltier materials exhibit a very high electrical conductivity and relatively low thermal conductivity, in contrast to normal metals that have both high thermal and electrical conductivity. In operation, Peltier devices transport electrons from a cold collector, at a cold temperature, to a hot collector, at a Tcal temperature, in response to an electric field formed through the Peltier device. However, there are other mechanisms that affect the efficiency of the Peltier device, these mechanisms degrade the net transport of thermal energy from the cold collector to the hot collector. Figure 1 schematically illustrates a conventional Peltier type (TE) 1 thermoelectric element with power supply CD 2 that creates the electric field through TE 1 while being at a charging current 3. The desired heat transfer is from the cold collector 4, at the cold temperature, to the hot collector 6, at the temperature T hot. As indicated in the equation of Figure 1, the net thermal energy transported is constituted by three elements, the first represents the contribution to the Peltier effect (thermoelectric), the second defines the negative Joule heating effects, and the third defines the effects of negative conductivity. The thermoelectric component is a function of the Seebeck coefficient a, the operating temperature (T £ r? O) and the current applied. The Joule heating component reflects that approximately half of the Joule heating goes to the cold collector and the rest to the hot collector. Finally, the negative component that is attributed to the thermal conduction represents the thermal flux through the Peltier device, as defined by the thermal conductivity of the Peltier device, from the hot collector to the cold collector. See equation 1 (1) q = aTfrxo I - I2R -? T _ Since the thermoelectric component of thermal transport increases in direct proportion to the current, while Joule heating increases in proportion to the square of the current, and The thermal conduction is in direct proportion to the difference of temperature from hot collector to cold collector, the equation clearly reflects how quickly the Peltier device becomes inefficient. Equation (2) defines a performance coefficient for the Peltier device. The coefficient is the ratio of the net thermal energy transported at low temperature to the energy consumed by the Peltier device. For a Peltier device, of typical bismuth telluride material, the performance coefficient is less than 0.3. (2) a Tfrío JÍI ^ R K? T FR + l? T It should be noted that the numerator of equation (2) represents the net cooling capacity of the Peltier device. The denominator of equation (2) represents the total energy that is provided by the external energy source 2. The individual elements of the numerator were previously described. The first term is the denominator is the total Joule heating, while the second term is the thermal energy transport work performed by the Peltier device to move the energy from the collector to the collector tcaiene • Based on this relationship, the maximum possible coefficient of performance in the configuration of Figure 1 is given by equation (3). - T - hot () \ áx = ifrío Y- ~ 3-cold? T? +1 The parameter? can it be expressed in terms of the Seebeck coefficient, the electrical conductivity s and the thermal conductivity? as established in equation (4). Y ^ - hot "1" - * • hot I heard O (4)? = 1+ = 1 + T RK 2? = 1 + ZT It should be noted that the first factor in equation (3) is the Carnot efficiency, which is the maximum possible efficiency for any thermal pump that operates between two T cold and T hot temperature collectors. The second factor represents non-ideal thermoelectric cooling that can also be characterized by a Merit Figure ZT. Note that n ^ * - - > (Tfrio /? T) how? - > 8. To date it has been very difficult to develop a thermoelectric material that produces high values of ZT. The predominant materials for thermoelectric coolers have been bismuth telluride (Bi2Te3) and lead telluride (PbTe). These materials have ZT values of approximately 0.3 at room temperature. Recent work in universities has shown that ZT values approach one may be possible in multiredes and quantum wells of lead telluride. However, even with these materials, thermoelectric cooling is not competitive with mechanical vapor compression cooling systems. Another restriction of the Peltier device cooling is the limited temperature excursion below the ambient that is reached. That limitation arises from the fact that temperature extension is restricted by efficiency, a parameter that degrades rapidly as the temperature differential increases. The maximum possible temperature differential Tmax is given by equation (5). (5)? Tmax = / L? For bismuth telluride having a ZT of about 0.3, TmAlí is 45 ° K at 300 ° K. In this way, there are a number of very fundamental restrictions for efficiency and differential temperature that limit the use of conventional thermoelectric elements for sub-ambient cooling applications. The present invention overcomes the fundamental restrictions of cooling of conventional thermoelectric element through the application of dynamic modulation to electrical energy and thermally conductive paths that connect the thermoelectric element to the power supply and thermal collector, respectively.

In one form, the invention relates to a thermoelectric cooling apparatus according to claim 1. In a still further form, the invention relates to a method for operating a thermoelectric cooling apparatus in accordance with claim 16. In a Particularized form of the invention, thermoelectric elements of complementary impurity type are connected in electrical series and energized by switched voltage pulses. The thermoelectric elements are thermally coupled to individual electrically insulated thermal collectors on one side, and thermally coupled to a common connection of their respective cold sides to a thermal switch that selectively establishes a thermal path to the cold collector. A selective but synchronized operation of the electric switch and the thermal switch provides thermal energy transport, from the cold collector through the thermal switch and through the pair of thermoelectric elements to respective thermal collectors, at an efficiency that exceeds the static operation mode of these thermoelectric elements. The use of transitory principles allows the relative isolation of the thermoelectric thermal transport mechanism from the Joule heating mechanisms and thermal conduction. The performance effect is expected to approximate the Carnot efficiency. Modes of the invention will now be described with reference to the accompanying drawings in which: Figure 1 illustrates schematically a cooling system with conventional statically operable Peltier device. Figure 2 schematically illustrates one embodiment of the invention of a single switch, a single thermoelectric element. Figure 3 illustrates schematically one embodiment of the invention of double thermoelectric element of simple thermal switch. Figure 4 schematically illustrates relative time traces of electric power and thermal energy transports according to the embodiment of Figure 3. Figure 5 illustrates schematically a closed loop implementation of the simple thermal switch configuration of Figure 3. Figure 6 schematically illustrates a microelectromechanical system (MEMS) device. Figure 7 illustrates by schematic cross section a set of MEMS devices and thermoelectric elements of the Peltier type.

Figure 8 illustrates schematically a thermoelectric cooler that can be used for sub-ambient cooling of integrated circuits and electronic modules. Figure 9 illustrates schematically the extended use of the invention in a food refrigeration system. Figure 10 illustrates schematically potential applications and benefits of the invention applied to various residences of humans and means of transport. Figure 11 illustrates schematically the application of a small thermoelectric cooler to locally cool a selected part of an integrated circuit chip. -. The fundamental conceptual work for the present invention involves a separation of the dependence between thermal conductivity and electrical conductivity, a dependence that to date has limited the temperature differential and efficiency of thermal transfers of conventional thermoelectric elements. Mathematically, the objective is to effectively isolate the elements that contribute to the net thermal transfer ratio specified in Figure 1, through the use of thermoelectric switches to dynamically maximize thermoelectric thermal transfer while minimizing Joule heating and transfer thermal driving. The transient effects of thermoelectric elements are used to increase the efficiency by synchronizing the pulsed voltage that is applied through the thermoelectric element and the switched thermal conductivity coupling between the cold side of the thermal electric element and the cold collector. In a preferred implementation, thermal conductivity switching is achieved using thermal switches of microelectromechanical systems (MEMS) where sets of multiple miniature thermoelectric elements and thermal conductivity switches Related MEMS are used to increase the thermal transfer capacity. Figure 2 schematically illustrates a configuration of minimum elements of the invention. The thermoelectric element 1 is continuously coupled to the hot collector 6 through a thermal path having a thermal transfer q. The opposite end of thermoelectric element 1, from the perspective of the application of voltage and response heat transfers, is thermally coupled through the thermal switch 7 to the cold collector 4. As incorporated in Figure 2, the switch 7 also conducts current electrical, allowing the application of the voltage 2 through the thermoelectric element 1 when the switch 7 is closed. At the beginning of a cycle, the thermoelectric element 1 is Tcally by virtue of the thermal coupling with the hot collector 6. Upon pulsed closure of the switch 7, the thermoelectric element 1 quickly establishes a relative temperature differential between the hot end 8 and the cold end 9, the temperature differential allows thermal transfer from the cold collector 4 through the thermal switch 7. Over time however, Joule heating effects within the thermoelectric element 1 raise the average temperature of the thermoelectric element 1 in such a way that the net heat transfer through the thermoelectric element 1 begins to decrease. At this point, the switch opens, disconnecting both the electrical energy and the thermal coupling. The residual thermal energy in the thermoelectric element 1 at the switch-off time, raises the temperature enough to provide a thermal transfer of exponential deterioration between the thermoelectric element 1 and the hot collector 6. When the temperature of the thermoelectric element 1 has deteriorated the one that approaches the hot collector 6, repeats the cycle. The transient nature of the operation is linked to the fact that thermoelectric thermal transfer occurs immediately upon receiving a relative voltage while the Joule heating and the conduction loss of the subsequent thermoelectric element are delayed effects. In this way, the invention is based on different time scales and electric and thermal conduction time constants. The basic concept for improving efficiency, as described with reference to Figure 2, exhibits somewhat less pronounced but still significantly inefficient contributors. The most pronounced are the Joule heating in the switch 7 when the switch closes, the thermal conductance losses through the switch 7 when the switch is in an open state, and the heat loss due to the thermal capacity of the thermoelectric element 1 A detailed analysis of the transient effects provides that the heat loss due to the thermal capacity of the thermoelectric element is approximately equal to the Fourier conductance term. Here, the expression for the performance coefficient previously established in equation 2 is more fully described by equation (6). (6) al Friction FR "K, -K? T l? T + I2 (R + R In equation 6, the terms Rs and Ks are the electric ignition resistance and the thermal conductance gives both sides of the commutator. ON (ON) Rs of the switch can be made commonly small at the cost of increasing the thermal conductance of OFF (Kg). A focus on improving the performance coefficient is illustrated by the mode of Figure 3, where the electrical switch is placed in the thermal collector through the judicious placement and connection of the thermoelectric elements of type-n and type-p In this way, the heating associated with the electric switch is eliminated as a contributor to the performance coefficient. this allows the performance coefficient to be rewritten as stated in equation (7). (7) aIT r rio - K? T? 2 = I2R + a? T The effect is that the maximum performance coefficient is slightly higher, typically 20%, than that associated with the single switch implementation of Figure 2, as mathematically described by equation (3). See equation (8). (8) Y-? T Y + 1 Although the improvement in performance coefficient is not dramatic, the difference is particularly significant for point cooling applications. In this regard, it should be noted that the net cooling energy of the thermoelectric refrigerant as represented by the numerator of equation (9), indicates that the maximum temperature is effectively unlinked. O) aTfrlo? T = I K Therefore, the maximum temperature differential can be significantly increased by increasing the current and in this context making the thermoelectric cooling practical for small detectors and specialized circuits in a silicon matrix. These localized or spot cooling applications are particularly useful in controlled voltage oscillators, phase detectors, mixers, low-interference amplifiers, lasers, photodiodes, and various optoelectronic circuit type materials. In theory at least, cooling to cryogenic point may be possible in limited applications. The use of multiple impurity-type thermoelectric elements and a separate electric switch provides significant potential in terms of efficiency and temperature range. The modality in Figure 3 introduces a number of interrelated refinements. First, multiple thermoelectric elements are used. Second, the synchronization of the electrical energy as applied to the thermoelectric elements is separated from the synchronization of the thermal switch that couples the cold end of the thermoelectric elements to the fluid collector. Finally, the switch that connects the empty end of the thermoelectric elements to the cold collector is only a thermal switch, eliminating any electrical conduction requirements and Joule losses associated with a current flow through the commutator. The embodiment in Figure 3 utilizes two thermoelectric elements, a thermoelectric element of the impurity-n type 11, and a thermoelectric element je type impurity-p 12. This configuration allows the shared use of the single voltage source 13, as it is activated to through the electric switch 14, while having the fluid ends 16 and 17 of respective thermoelectric elements 11 and 12, thermally coupled through the thermal switch 18 to the cold collector 4. The hot ends 19 and 21 of respective thermoelectric elements 11 and 12 are thermally and electrically connected to respective hot collectors 22 and 23, these hot collectors are electrically separated to effect the use of the shared voltage source 13. Although the operation of the mode of two thermoelectric elements in Figure 3 is analogous to that of the mode of a single thermoelectric element of Figure 2, the insulation of the thermal switch and the commutation Electricity provides greater flexibility to define the respective service cycles and switching synchronizations. Although the electric switch 14 and the thermal switch 18 both operate with very short service cycles, and exhibit a synchronous operation relative to each other, the synchronization of the closing and opening cycles is likely to differ depending on the transient characteristics of the thermoelectric elements. and conductive path couplings with hot and cold collectors. For example, the improved thermal coupling will suggest that the electrical switch 14 close first, the thermal switch 18 momentarily close later, the electrical switch 14 open somewhat later and the thermal switch 18 open somewhat after the opening of the electrical switch 14. The underlying objective of the switching operations is to maximize the efficiency of the heat transfer from the cold collector 4 to the hot collectors 23 and 24. Figure 4 schematically illustrates illustrative traces of waveforms for energy transport thermal and voltage associated with the operation of the embodiment of Figure 3. The first trace shows the pulsed nature of the voltage applied through the thermoelectric elements. The second trace illustrates the transient thermal effect 11 and the associated deterioration of the thermal energy dissipated in the hot collector. The last trace illustrates the absorption of thermal energy from the cold collector through the thermal switch. The lines in Figure 4 are schematic since they are intended to illustrate general concepts instead of presenting particular time-related magnitudes. Figure 5 illustrates schematically an extension of the preferred embodiment of Figure 3, wherein the activations of the electric switch 14 and the thermal switch 18 are performed in response to feeds of the temperature sensor 24. The temperature sensor 24 provides a power to the synchronization control 26 to operate the switches 14 and 18, in response to the current temperatures at the hot, cold or both ends of the thermoelectric elements. Although the synchrony and duty cycle characteristics of switches 14 and 18 remain relatively similar with those for the mode in Figure 3, the use of detected temperature optimizes efficiency by employing current thermal characteristics rather than estimated to operate the switches 14 and 18. The implementation in Figure 5 allows adjustment in the switching synchronization to compensate for effects such as higher hot collector temperatures or lower cold collector temperatures within the context of the same cooling apparatus. Figure 6 illustrates schematically the thermal switching structure of representative microelectromechanical systems (MEMS) of the type particularly suitable for the present invention. Since the MEMS technology is still in its infancy, the switch illustrated in Figure 6 simply illustrates one of many potential thermal switching configurations suitable to provide a selective thermal coupling between the thermoelectric element and the cold collector. The thermal switch illustrated in Figure 6 is manufactured using conventional integrated circuit techniques in order to form on a silicon chip surface 27 a set of nickel magnets 28 susceptible to slight movement by movement in thin flexible membranes 29. introduction of an electric current in the spiral coil 29 produces the adequate force to translate the magnetic structure in a direction perpendicular to the plane of the silicon flake. The MEMS switch in Figure 6 should have a relatively low thermal conductivity when opened, however a relatively high thermal conductivity when closed by actuation. If the MEMS device of Figure 6 is to achieve both electrical and thermal switching, refinements are probably necessary to reduce the "endangered" resistance of the switch. Figure 7 illustrates the use of a set of MEMS devices to selectively establish thermal connections between Peltier type thermoelectric devices and a cold collector. The Peltier devices 32 and 33 are electrically interconnected by the copper conductor 34 to replicate the functions associated with the illustration of Figure 3. The spacing between the copper layer 34 and the magnetic assemblies 28 of the MEMS switches 36 and 37 is expected that is in the nominal range of half of a miera. This dimension is expected to allow an electric coil of nominal size 31 (Figure 6) that initiates the actuation of the switching structures. Since switching cycles are expected to occur in the order of seconds, the reliability associated with the frequency switching in kilohertz of MEMS devices should not be a problem. The MEMS type thermal switch described with reference to the illustrations of Figures 6 and 7 is simply one of many potential thermal switching configurations. For example, it is fully contemplated that the electrostatic forces generated in the capacitive switch structures can be used to achieve similar objectives. The underlying goal for all switches is to maximize the thermal conductivity extremes for switching positions, such that when the switch closes, the thermal path between the thermoelectric element and the cold collector has a maximum thermal conductance, while for the open switch, thermal conductance is the minimum achievable. The illustration of Figure 7, discloses that the thermoelectric cooling system of the present invention is preferably composed of multiple thermoelectric elements and MEMS switches configured in the structure. The multiplicity of thermoelectric elements and switches ensures that the transient characteristics underlying the present invention can be achieved within the dimensions of the thermoelectric element and switching materials. In other words, it is expected that the thermal transfer insulation of the Joule conduction and heating components will be more effectively achieved with relatively small thermal capacity thermoelectric elements, commonly Peltier devices, and corresponding small MEMS type thermal switches. Figure 8 illustrates schematically an application for the thermoelectric coolant of the present invention. In this case, the refrigerant is located between a thermal collector that dissipates energy in an air environment and a cold collector that has electronic modules and integrated circuits connected to it. Figure 9 schematically illustrates the use of the thermoelectric refrigerant in the form of an extended structure, to operate efficiently and clean a food refrigerator. The high efficiency and lack of major moving parts that characterize the present invention facilitates the migration of thermoelectric cooling from limited and highly sensitive applications, such as small portable refrigerants, to main articles substantially throughout the home.

Still further applications are illustrated schematically in Figure 10, as the concepts underlying the present invention are further refined and extended in size to encompass the majority of thermal transfer applications comprising residential and office cooling, food transport systems and cooling of personal vehicles. Figure 11 illustrates schematically an application at some point at the other end of the spectrum, where micro-sized thermoelectric refrigerants are selectively bonded to parts of an integrated circuit flake for selective cooling purposes of these selected regions, to control integrated circuit parameters . The present invention has very broad applicability in part because it is not restricted to thermoelectric materials or specific electronic configurations. The invention uses the thermal dynamics of pulse-operated thermoelectric elements in combination with miniature thermal switches to isolate thermal transfer characteristics and achieve superior cooling efficiency. It will be seen that while the embodiments of the invention describe the thermoelectric element continuously connected to the hot collector, it is within the scope of the invention that the thermoelectric element is connected to the collector, heated with a switch or structure similar to the thermal switch 18.

Claims (20)

1. CLAIMS 1.- A thermoelectric cooling apparatus, comprising t a first thermal collector of a first nominal temperature; a second thermal collector of a second nominal temperature, the second temperature is relatively greater than the first temperature; a thermoelectric element; second means for connecting the thermoelectric element to the second thermal collector; and means for activating the thermoelectric element; characterized by 10 first means for selectively switching a thermal coupling of the thermoelectric element with the first thermal collector. 2. - The apparatus according to claim 1, characterized in that the second means
2. 15 comprise a continuous thermal coupling between the thermoelectric element and the second thermal collector. 3. The apparatus according to claim 1, characterized in that the activation means comprise means for selectively switching
3. 20 an electrical voltage through the thermoelectric element. . - The apparatus according to claim 3, characterized in that the second thermal collector is constituted by first and second electrically separated sections.
4. *?
5. 5. - The apparatus according to claim 4, characterized in that the first and second electrically separated sections are coupled to a power source through means for selectively switching an electric voltage.
6. 6. - The apparatus according to claims 3 to 5, characterized in that the service cycle of the means for selectively switching an electrical voltage is similar to the duty cycle of the means for selectively switching a thermal coupling.
7. 7. - The apparatus according to claims 1 to 6, characterized in that the means for selectively switching a thermal coupling comprise a micro-electromechanical system device (E S).
8. 8. The apparatus according to claim 2, characterized in that it further comprises: a third thermal collector of the second nominal temperature, the third thermal collector is electrically separated from the second thermal collector; a second thermoelectric element thermally coupled with the third thermal collector; wherein the means for selectively commutating a thermal coupling comprises means for selectively switching a thermal coupling of the first mentioned thermoelectric elements and second with the first thermal collector; and the activation means comprise means for selectively switching an electrical voltage across the first mentioned thermoelectric elements 5 and second.
9. 9. - The apparatus according to claims 3 to 6 or 8, characterized in that the means for selectively switching a thermal coupling and the means for selectively switching an electrical voltage is
10. 10 adapted to operate in functional synchrony 10. - The apparatus according to claim 8, characterized in that the first and second thermoelectric elements are Peltier devices.
11. 11 - - The device in accordance with

    15 claim 10, characterized in that the first and second thermoelectric elements are of opposite impurity type.
12. 12. - The apparatus according to claim 2, characterized in that the apparatus is operable in an environment, the first collector means

    Thermal sensors are adapted to absorb thermal energy at a temperature below ambient, the second thermal collector means are adapted to dissipate thermal energy at a temperature above the environment, the thermoelectric element is adapted to transport thermal energy

    25 among them; the means for selective switching is

    **) adapted to switch the thermal conductance of the coupling between the first thermoelectric element and the second thermal collector; and the means for activating the thermoelectric element are adapted to do so in functional relative synchrony with the means for selectively switching the thermal conductance.
13. 13. - The apparatus according to claim 12, characterized in that the duty cycle of the means for activating is small with respect to the duty cycle of the means for selective switching.
14. 14. - The confrmidad apparatus with claim 4, characterized in that it also comprises a second thermoelectric element, the first thermoelectric element is coupled to the first section of the second thermal collector means and the second thermoelectric element is coupled to the second section of the second thermoelectric element and the second thermoelectric element is also coupled to the means for selective switching of the thermal coupling.
15. 15. The apparatus according to claim 14, characterized in that the means for activation are adapted to selectively switch a power supply or a power source connected through the first and second sections of the first thermal collector.
16. 16. - The apparatus according to claim 12, characterized in that the dissipation of the thermal energy is to the environment and the absorption of thermal energy is one of a group of a system of
17. 5 refrigeration of food or a vehicle occupant cooling system or an electronic integrated circuit device. 17. - Method for operating a thermoelectric cooling apparatus that has a first collector
18. 10 thermal that operates at a first nominal temperature, a second thermal collector that operates at a. second nominal temperature relatively greater than the first nominal temperature, and a thermoelectric element coupled to the second thermal collector, comprising the steps of:
19. 15 transmitting thermal energy from the thermoelectric element to the second thermal collector through a coupling; and activate the thermoelectric element; characterized by selectively switching the transmission of thermal energy between the thermoelectric element and the first collector
20. 20 thermal.

    (