Patent ID: 12228314

DETAILED DESCRIPTION OF THE INVENTION

A thermoelectric cooler (TEC) device utilizes electric power to cause a thermal gradient across the device causing one side to become cold and the other hot. Solid-state TECs operate in accordance with the Peltier effect, creating a temperature difference by transferring heat between two electrical junctions. When a voltage is applied across joined conductors, an electric current is generated, which flows through the junctions of the two conductors. Heat is thereby removed at one junction, resulting in cooling, while the heat is deposited at the other junction, resulting in heating.

TEC devices are relatively high in cost relative to cooling capacity, and they have relatively low power efficiency, i.e., a low coefficient of performance (COP). But TECs have no moving parts, conferring durability and resistance to stress, as well as enjoying a long lifespan. They generally do not rely on circulating liquid as used in conventional heat exchange units, and thus are not prone to leaks or potentially hazardous refrigerant liquids. TECs are also generally small in size, and adaptable in shape.

The temperature performance of a TEC varies with voltage, current, and heat flow, and different embodiments of the invention may utilize different TECs depending on the desired specifications and characteristics. In some embodiments, for example, a Marlow TR060-6.5-040 single-stage thermoelectric cooler (Marlow TEC) may be used. Such a Marlow TEC physically measures about a 1.5 inch square with one edge extended for electrical connections, and with a thickness of about 4 mm. The temperature difference versus current and heat flow from this particular Marlow TEC is shown inFIG.1, drawn from its Technical Data Sheet. The temperature difference (ΔT) reflects the difference between the device's hot side temperature and its cold side temperature. While the Marlow TEC is just one example of TEC modules useful in the heat pump of the invention, those of skill in the art will understand that many other TECs available on the market would be as easily useful in the invention.

The performance of a TEC may be characterized by the following equation
ΔT=75−1.15Q−1.78(6.5−I)2

where ΔT is the temperature difference in ° C., I is the electrical current in amps, and Q is the heat flow in watts.

Rearranging the equation to determine heat load based on temperature difference produces:
Q=65.2−0.87ΔT−1.55(6.5−I)2

FIG.2shows a Marlow TEC1, and a schematic side view of a TEC2, where the heat load is transferred from the cold side to the hot side in response to electrical current flow in the thermoelectric material. Multiple TECs2(which may be Marlow TECs1or other TECs) are placed sandwiched between thermally conductive cold plates3. The TECs are electrically connected such that an electric current may be delivered to all the TECs simultaneously. Cold plates3have channels14running through them, in which tubes may be situated for carrying fluid streams. InFIG.2, one such cold plate is shown with a copper tube15looping therethrough. Cold plates3permit fluid streams to pass through tubes15therein and thereby exchange heat. As shown inFIG.2, for example, one cold plate3has cooler supply water4being cooled by the cold side of the TECs2, and the other cold plate3has warmer return water5being heated by the hot side of the TECs2.

The voltage for the Marlow TEC is equal to V=2.5/and the power is P=2.512. The coefficient of performance (COPTEC) of a single thermoelectric cooler is given by the following equation and shown inFIG.4.

COPTEC=QTECPTEC=65.2-0.8⁢7⁢Δ⁢T-1.5⁢5⁢(6.5-I)22.5I2

The temperature difference ranges from 7° F. (3.9° C.) to 11.1° F. (6.1° C.) at a 1 A current design.

The cold plates3with TEC2units arranged therebetween allow for progressive cooling and heating of water streams, thereby allowing a 67° F. water supply to be cooled, for example to 44° F. for use in an air conditioning cooling coil, while at the same time warming the returning water from the cooling coil from for example 51° F. to 80° F. for use in heating or for disposing of excess heat. For example, as shown schematically (not to scale) inFIG.3, a stack of two cold plates sandwiching a series of TECs2illustrates these heating/cooling effects on a water stream. The supply water4at 67° F. enters a cold plate at the upper left at the first TEC2, which cools the 67° F. supply water to 66° F. while heating the 79° F. return water to 80° F., and the last TEC2cools the 45° F. supply water to 44° F. supply water while heating the 51° F. incoming return water to 52° F. The series of TECs thereby cools and warms water simultaneously by heat exchange with the cool cold plate on one side and the hot cold plate on the other. Each TEC in the series is capable of contributing a temperature difference, and the series of TECs shown inFIG.3combine to cumulatively yield desirable temperature differences output to the outflowing streams.

Such cold plates3may be stacked into an array allowing for progressive cooling and heating of water streams on a much larger scale, effectively generating a cascading thermoelectric heat pump13of the invention, as shown in the different perspectives inFIGS.4-6for a stack of 16 cold plates3.FIG.7illustrates the design layout of such a stack, with three cold plates3removed from the left side allowing observation of the TECs2sandwiched between the cold plates3, and the layout of the water streams passing alternately through the cold and hot plates in a staggered fashion.

The design shown inFIGS.4-7has TECs2sandwiched between cold plates3, such that the TECs2are situate on both sides of each cold plate (except for the end of the stack cold plates). This design uses McMaster Carr 35035K42 cold plates3with dimensions of about 12 inches long by 3.5 inches wide×0.5 inches thick. As shown inFIG.4, the cold plates3are modified with a slit6in the middle, extending from one end through the majority of the cold plate3toward the other end, to inhibit heat transfer from the bottom of the cold plate7to the top8.

FIG.4illustrates a cold plate3at one end of a stack, in an edge-on view of the heat pump13with the length and width of the cold plate3at the right side of the stack facing toward the viewer. Conduits9-12for fluid streams are shown, which connect to the cold plates'3internal tubes15; however, in this perspective, the viewer sees the conduits for the cold supply4streams for the cold plate3shown and also the conduit for the hot stream5of the next cold plate3in the stack, that of the next, etc., superimposed. In each of the “cool” cold plates3, the cold supply stream4flows into the inflowing cool conduit9, passes through the cold plate tubes15in a loop, and out the outflowing cool conduit10. In each of the “hot” cold plates3, the hot supply stream5flows into the inflowing hot conduit11, passes through the cold plate tubes15in a loop, and out the outflowing hot conduit12. The conduits (9,10or11,12) respectively of each alternate cold plate3in the stack are joined to each other to make a continuous stream through the stack, as further illustrated inFIGS.5,6, and7.

FIG.5illustrates a top-down view of the heat pump13showing the upper edges of the cold plates3, the TECs2sandwiched therebetween, and the conduits9-12carrying water from and to the heat pump13.FIG.6illustrates a face-on view of the “front” of the heat pump13in which the viewer can see the stack of cold plates3with the slits6in each of the cold plates3, the TECs2sandwiched between the cold plates3, and the conduit9-12lines carrying the water streams. The alternate cold plates3are labeled “Cool” and “Hot” to show the staggered alternating structure of the stack of cold plates3making the heat pump13.

FIG.7illustrates the construction of the heat pump13stack of cold plates3. The incoming cool water stream4feeds and empties the conduits9-10feeding and emptying the cool cold plates3respectively, while the hot water stream5feeds and empties the conduits11-12feeding and emptying the hot cold plates3, respectively.

Combining the views inFIGS.4-7, the path of the cool water stream4through the heat pump13begins as it enters the inflowing cool conduit9, enters the inflow ends of the tubes15of the cold plates3, flows through the upper side8of each cold plate3around the loop defined by the slit6and the tube15, back through the lower sides7of each cold plate3, and finally flows out the outflow ends of the tubes15of the lower sides of the cold plates3into the outflowing cool conduit10. Likewise, the path of the hot water stream5through the heat pump13begins as it enters the inflowing hot conduit11, enters the inflow ends of the tubes15of the cold plates3, flows through the lower side7of each cold plate3around the loop defined by the slit6and the tube15, back through the upper sides8of each cold plate3, and finally flows out the outflow ends of the tubes15of the lower sides of the cold plates3into the outflowing hot conduit10. During the water streams' journeys through the stack of cold plates3, the streams are cooled and warmed, respectively, by virtue of heat exchange with the cold and hot sides of the cold plates3which were cooled and heated by the sandwiched TECs2.

A model heat pump13of the design was constructed using the McMaster cold plates described above, each of which accommodate 32 Marlow TECs (16per side) on each cool cold plate. Table 1 provides a comparison of the results for different operating and design conditions with estimates of performance, weight, volume, and power consumption.

The coefficient of performance of the system (COP) is the ratio of heat absorbed in the cooling coil (Qcc) to the power (P) utilized to reduce the chilled water from 67° F. to 44° F. N is the number of TECs per ton. As the number of TECs increase, the system weight and volume increase, and the total system power and COP decrease.

COP=QCCP=3500⁢W2.5I2⁢N

TABLE 1Per 1 TonRVolumePowerCurrent(cubicWeight(Watts)(Amps)inches/ton)(lb/1 ton)COP6640.547711605.39450.7528221054109912016803.215991.51277602.2

The COP is an indicator of the amount of heat being transferred compared to the amount of power being put in. A COP of 5, for example, means 5 kW of heat are transferred from low to higher temperature for every 1 kW of power input to the system.FIG.8shows the how the relationship between the COP for TEC-based heat pumps of the invention vary with current and temperature differences.

FIG.9illustrates use of the invention during the summer when cooling air conditioning is desired.FIG.10illustrates use of the invention during the fall, winter, and spring when distributed conditioning is needed.

While future efforts will undoubtedly expand the SWAP of the TEC-based heat hump of the invention, it is plainly evident that the TEC-based solution is not only viable but superior in many ways to existing chillers. Importantly, the TEC module mean time before failure (MTBF) is greater than 250,000 hours (28.5 years). This is the typical lifetime of a naval vessel, suggesting that such TEC chillers will not require costly and time-consuming service and maintenance. Conventional vapor compression chilling systems, on the other hand, require regular maintenance for continued operation.

While a standard heat pump may appear to be more energy efficient than the heat pump of the invention, standard heat pumps have several noteworthy disadvantages including noise hazards, and refrigerant hazards that can cause serious injury for sailors in the confined spaces of a ship. The heat pump of the invention does reduce the electrical power used for heating and cooling on a Navy ship. With no moving parts, the heat pump of the invention also has an advantage in that it produces no noise.

Heat pumps of the invention can heat water from a 67° F. supply to as high as 95° F., and can chill water from a 67° F. supply to as low as 40° F. The heat pumps of the invention are far smaller in size than conventional heat pumps, and can be provisioned at the desired points of service, for example, where water enters HVAC equipment. The heat pumps of the invention is also useful in other applications. For example, they may be used for replenishment air entry into buildings or vessels, without the hazards posed by refrigerant-based heat pumps.

Those of skill in the art will readily appreciate that the heat pumps of the invention may be constructed using a variety of TEC modules and a variety of cold plates depending on the user's particular application and particular desired results. Likewise, those of skill in the art will readily appreciate that a variety of materials may be used for conduits, connections, and the like.

The present invention is not to be limited in scope by the specific embodiments described above, which are intended as illustrations of aspects of the invention. Functionally equivalent methods and components are within the scope of the invention. Various modifications of the invention, in addition to those shown and described herein, will be readily apparent to those skilled in the art from the foregoing description. Such modifications are intended to fall within the scope of the appended claims. All cited documents are incorporated herein by reference.