Patent ID: 12203680

REFERENCE NUMBERS100multi-circuit cooling system105first airflow110first coil115first fan120first fluid125compressor130pump135heat exchanger140phase change composite145second fluid150second airflow155condenser160second fan165expansion valve201first plurality of microchannels202second plurality of microchannels301module401thermal energy storage unit700multi-circuit heating and cooling710second coil715check valve730reversing valve735three-way valve805fluid heat exchanger815diverting valve915on/off valve925heat pump

DETAILED DESCRIPTION

The present disclosure may address one or more of the problems and deficiencies of the prior art discussed above. However, it is contemplated that some embodiments as disclosed herein may prove useful in addressing other problems and deficiencies in a number of technical areas. Therefore, the embodiments described herein should not necessarily be construed as limited to addressing any of the particular problems or deficiencies discussed herein.

Disclosed herein are multi-circuit thermal energy storage (TES) systems connected in heating, ventilation, and air conditioning (HVAC) systems. The two circuits (a refrigeration circuit and a secondary fluid circuit) are designed to work together, but they might contain separate units. In certain configurations, the TES system may use a phase change composite (PCC) with high thermal conductivity, which allows for efficient heat transfer within the PCC. Thus, the PCC itself may be used as the heat transfer media between a refrigerant and a secondary fluid, allowing the refrigerant/secondary fluid heat exchanger in typical configurations of HVAC systems to be removed. Operation may also be simplified, because the PCC may be charged using a fixed or variable speed compressor at a heat rate different than what is required to cool the process air stream and at a time coincident or not coincident with the need to cool the process air stream. To further simplify the system, mixing or diverting valves in the system to complicate control may be removed. The system may operate as a variable cooling load system by modulating a fluid pump and a process air fan in conjunction with one another. Alternatively, to save cost and be more energy efficient, a secondary fluid pump may be fixed speed while a process air fan can be variable speed.

The PCC may act as a buffer between a traditional mechanical refrigeration cycle and a secondary fluid. The vapor compression cycle may act as a traditional refrigeration cycle and the secondary fluid cycle may cool air in a building. The secondary fluid cycle may include a cooling coil which removes heat from the air in the building. The vapor compression cycle may include an evaporator to release heat outside of the system (i.e., outside of the building). The secondary fluid temperature exiting the PCC may be constant (within a few ° C.) regardless of the cooling load from the cooling coil. The vapor compression cycle's evaporator temperature (i.e., suction temperature) may respond to the PCC's state of charge. Thus, the compressor may be a fixed speed unit removing heat from the PCC at a constant rate regardless of the rate of heat removal from the secondary fluid. A single speed compressor may then be operated at its maximum efficiency rather than being tied to the cooling requirements of the building. The system can therefore provide significant energy savings similar to air conditioners with variable speed compressors. In some embodiments, the present disclosure integrates a PCC material with a vapor-compression air conditioner.

Exemplary secondary fluids may include water, brine, hydrocarbon (e.g. propylene or ethylene glycol), or a refrigerant (e.g. R410A, carbon dioxide—CO2). Use of a refrigerant may allow for enhanced heat transfer in the cooling coil and TES, thus improving system efficiency. Exemplary refrigerants may include R410A, carbon dioxide, propane, ammonia, or other fluids with high heat conductivity.

A PCC may consist of a graphite matrix made from expanded graphite flakes and a phase-change material embedded into the pores of the graphite matrix. Exemplary phase-change materials may be organic alkanes, inorganic alkanes, or fatty acids. The large heat capacity may maintain battery temperature and prevent thermal runaway. A refrigeration system using the TES containing a PCC may first involve a liquid refrigerant entering half of the tubes in a PCC, where the liquid refrigerant may evaporate and cool the PCC, solidifying the PCC. Next, a compressor may increase the pressure of the refrigerant vapor exiting the PCC. The refrigerant may then condense in a condenser, rejecting the heat of condensation to the ambient air, which may be directed outside of the building. Finally, an expansion valve may lower the pressure of the refrigerant back to the evaporator pressure.

Operating a multi-circuit phase change composite cooling system may have many benefits over existing air conditioning systems. First, the first circuit and second circuit do not need to have balanced heat rates. The lift of each compressor may be managed through the selection of the proper phase transition temperature of the PCC. Second, no intercooling is required. Third, the first fluid that charges the PCC will cool the second fluid down to the PCC's phase change transition temperature, which is colder than if the first fluid was returning from a process air stream. This allows the first fluid to extract more heat from the first airflow at the same compressor lift.

In some embodiments, the first circuit and second circuit may operate independently, such that either circuit may be at a drastically different flow rate from the other. Likewise, one circuit may be inactive (or “shut down”) while the other operates. The two circuits may in some instances operate concurrently.

FIG.1illustrates an embodiment of the present disclosure, a multi-circuit cooling system100where a first airflow105is in contact with a first coil110, then via a first fan115returned to its source. A first fluid120is routed through the first coil110using a pump130. The first fluid120is directed into a heat exchanger135contained in a phase change composite140. Inside the phase change composite140, the first fluid120exchanges heat with a second fluid145. The second fluid145is directed through a compressor125then a condenser155. In the condenser155the second fluid145exchanges heat with a second airflow150. The second airflow150is then routed back to its source by a second fan160. The second fluid is then routed through an expansion valve165before returning to the phase change composite140.

Heat may be removed from the first airflow105by the first fluid120using the first coil110. That heat is then either absorbed by the phase change composite140or absorbed by the second fluid145. In some embodiments heat may be absorbed by both the phase change composite140and the second fluid145. If heat is absorbed by the second fluid145, then second fluid145is directed through a compressor150, which increases the pressure and temperature of the second fluid145. Second fluid145is then routed through an evaporator155where heat is absorbed by a second airflow150. The second airflow150is directed, via a fan160back to its source. Prior to returning to the phase change composite140the second fluid145is directed through a valve165, which decreases the temperature of the second fluid145.

A first circuit may include the first fluid120and the components through which it is directed (i.e., a coil100and pump130). A second circuit may include the second fluid145and the components through which is it directed (i.e., a valve165, evaporator155, and compressor150). When the first circuit delivers the same heat rate to the phase change composite as the second circuit removes from the phase change composite, the amount of thermal energy stored in the phase change composite will not change. When the second circuit has a higher heat rate than the first circuit, the thermal energy in the phase change composite will increase and the PCC is said to be “charged.” When the first circuit has a higher heat rate than the second circuit, the amount of thermal energy stored in the PCC will decrease and is said to be “discharged.”

In some embodiments, the first circuit and second circuit may be operated at the same time. In other embodiments, the second circuit may be stopped (meaning the compressor150is turned off and the flow rate is significantly decreased) while the first circuit continues to operate. In some embodiments the first circuit may be stopped (meaning the pump130is turned off and the flow rate is significantly decreased) while the second circuit continues to flow. The flow rates and heat rates of the two circuits need not be the same.

In some embodiments, the heat exchange between the refrigerant and secondary fluid through the PCC should be closely thermally coupled, meaning the heat transfer resistance between the two fluids should be minimized. In such an embodiment, the system may be designed with two fluid circuits that are thermally connected through a high conductivity material, such as metal. Thus, heat exchange is not hampered by a lower conductivity PCC because of the large heat transfer between the circuits. Having a PCC with lower conductivity allows for a PCC with higher heat capacity to be used. A larger heat capacity of the PCC results in a larger capacity for thermal energy storage.

FIGS.2A,2B,3,4,5A and5Bshow how the two circuits are thermally coupled within the PCC. As shown inFIGS.2Aand B, a heat exchanger135is produced by either extruding a micro-channel tube arrangement as shown or by stacking and thermally connecting two single row micro-channel tubes. A first plurality of microchannels201and a second plurality of microchannels202may be arranged in parallel- or counter-flow as shown inFIG.2Aor in cross-flow as shown inFIG.2B. Only a section of the tubes of the first plurality of microchannels201and the second plurality of microchannels202are shown inFIGS.2A and2B, however, these tubes can be extruded into other lengths. The first plurality of microchannels201belong to a first circuit, the second plurality of microchannels202belong to a second circuit. The two circuits through the microchannel heat exchanger135may be stacked as shown inFIGS.2A or2Bor in another pattern. The first plurality of microchannels201and the second plurality of microchannels202may each contain two or more fluids. The first plurality of microchannels201may contain the first fluid120and the second plurality of microchannels202may contain the second fluid145.

As shown inFIG.3, the first plurality of microchannels201and the second plurality of microchannels202may then be thermally connected to a phase change composite (PCC)140to form a module301. In this embodiment, the PCC140has a high thermal conductivity normal to the plane of the first plurality of microchannels201or second plurality of microchannels202. This arrangement allows heat to flow from the first plurality of microchannels201and the second plurality of microchannels202to the PCC140, or vice versa. Because the first plurality of microchannels201and the second plurality of microchannels202are closely coupled, the heat transfer resistance from the PCC140to the first plurality of microchannels201and the second plurality of microchannels202is small. Thus, the first plurality of microchannels201may have little to no fluid flow and the second plurality of microchannels202may have a significant fluid flow, or vice versa. InFIG.3, the thermal resistance from the first plurality of microchannels201to the PCC140is small because of the high conductivity of the microchannel material. The first plurality of microchannels201and the second plurality of microchannels202themselves may also be made of a high conductivity material.

As shown inFIG.4, stacked modules301may be repeated to become a thermal energy storage (TES) unit401. Each module301comprises the first plurality of microchannels201and the second plurality of microchannels202and PCC140, as shown inFIG.3. Stacking the modules may result in the PCC140being in thermal communication channels201and202in the adjacent module301.

Because the first plurality of microchannels201and the second plurality of microchannels202may be bent, they may wrap around the PCC140layers of the TES unit401, as shown inFIGS.5A and5B.FIG.5Ashows the first plurality of microchannels201and the second plurality of microchannels202arranged in a cross-flow configuration and wrapping around the PCC140.FIG.5Bshows the first plurality of microchannels201and the second plurality of microchannels202arranged in a parallel- or counter-flow configuration and wrapping around the PCC140. Additional channels may be added to make a larger multi-circuit TES unit401. In some embodiments, the first plurality of microchannels201and the second plurality of microchannels202need not be closely coupled as long as each channel has PCC140on both sides.

It may be beneficial to reuse thermal energy storage during periods when a building requires heating. Through a series of valves, pipes, and controls the system may use the compressor to provide three modes of operation. The first is a discharging mode, wherein heat is drawn from the PCC and delivered to a heating coil to heat the building. This occurs when the heat being removed from the PCC is greater than the heat being added to the PCC. Thus, the heat rate of the secondary fluid is greater than the heat rate of the refrigerant. During this discharging mode the PCC may undergo a phase change and may solidify. The second mode is a heating only mode without the use of the PCC, and thus without the use of TES. In this second mode heat is drawn from the outdoor coil and delivered to the heating coil. Thus, the heat rate of the secondary fluid is equal to the heat rate of the refrigerant. The third mode is a charging mode of the PCC material. During this third mode heat is drawn from the outdoor coil and delivered to the PCC material. During this third mode the PCC material may undergo a phase change and may liquify or melt.

The charging and discharging modes may be independent and may occur at different times or simultaneously. This decouples the energy use of the refrigeration system from the cooling or heating load of the building, enabling improved flexibility and efficiency. The flexibility comes from the decoupling of energy use with the delivered service, which allows the system to be responsive to the grid without compromising thermal comfort. System efficiency gains may be the result of operating the refrigeration system during cooler ambient conditions or operating the system with less cycling.

Operating using these three modes is beneficial because extracting heat from the TES when the ambient temperature is much colder than the TES's phase transition temperature is much more efficient than traditional air conditioning processes. This arrangement also enables the compressor to pump the necessary heat from the ambient in two steps: first from the ambient to the TES, then from the TES to the process air. This allows the lift to be broken into two steps, which may be performed by two compressors, reducing the lift on each individual compressor and keeping the lift within the optimum range of most compressors. Additionally, the liquid refrigerant will be colder exiting the PCC material (during the charging mode, while melting the PCC material) which feeds colder refrigerant to the outdoor coil. This allows for a higher extraction of heat from the ambient without additional refrigerant flow from the compressor. More thermal energy may be extracted without additional electronic power to the compressor. This enables the use of a lower capacity compressor for heating, which helps in balancing the compressors capacity during cooling and heating months. Because the compressor requires the most electrical energy to operate, reducing its power requirements can reduce the electrical energy needs of the system. A variable-speed fan may enable capacity control without the need for a variable-speed compressor because heat can be transferred to the PCC material at a variable rate.

Additionally, the refrigeration system may interact with the PCC material and not the building. A secondary fluid may be cooled in a first plurality of microchannels in the PCC material by adding heat to the PCC material and then removing heat from the supplied airstream. The refrigerant may absorb heat from the PCC via a second plurality of microchannels in the PCC and release heat to the ambient. This enables the use of non-traditional refrigerants, such as propane, which are generally avoided because of concerns about air quality.

Properly sizing the TES module (and therefore the PCC material) is important for the TES system to function properly and remain cost competitive. An objective of the TES as it relates to size is to not require the compressor to operate for longer than fifteen (15) minutes. If the compressor operates for longer than fifteen minutes, then it will contribute to the building's overall whole energy demand. A goal of the TES system is to reduce the electrical energy required for heating and cooling a building.

In some embodiments, during peak cooling hours (i.e., during the day) the compressor may operate continuously for ten (10) minutes, then the TES system will operate in a discharging mode (wherein heat is removed from the process air and heat is added to the PCC material) continuously for five (5) minutes. This operation of the compressor then operation of the TES system in the discharging mode may be repeated during peak air conditioning hours. During non-peak hours (i.e., in the evening and night) the compressor may cool the air and the TES system may be operated in the charging mode (wherein heat is removed from the PCC material and released to the outside air).

In some embodiments, a staged compressor or set of tandem compressors may be used at part load during the peak air conditioning hours. A variable speed compressor may also be used at reduced speed. Using these configurations of compressors may reduce the electrical needs of the system and prevent the system from significantly contributing to the electrical load of the building.

The measure of the charge of the PCC may be stated as the state-of-charge (SOC). The SOC indicates how much thermal energy the PCC contains or can absorb. The relationship between the state of charge for a heating application and a cooling application is shown in Equation 1 below.
SOCheating=100% −SOCcooling(Equation 1)

Where SOCheatingis the state of charge for when the building requires heating and SOCcoolingis the state of charge when the building requires cooling. The two SOCs sum to 100% because as the building is heated, the PCC gains the ability to absorb heat from the building should cooling be necessary. And as the building is cooled, the PCC gains the ability to release heat to the building should heating be necessary. As used herein, “charging” refers to adding thermal energy to the PCC, and therefore SOC is the SOCheating, unless otherwise indicated.

To effectively use the TES system to reduce energy consumption and thus costs, controlling the SOC of the PCC material may be important. During high volume days (such as week days in non-residential buildings), the SOC of the PCC material may be near zero (meaning it can hold no more heat) by the end of the day (approximately 6:00 PM). On lower volume days (such as weekend days in non-residential buildings), the SOC of the PCC material may be used for cycles of more than ten minutes, so the PCC material may have a SOC of zero by the end of the day.

In some embodiments, the SOC may be controlled by comparing the current SOC to the target SOC and discharging the TES system to result in the TES system being fully discharged by the end of the day. This may allow a greater TES system discharge (and therefore less compressor runtime) per timestep. This system may be used only for low volume days, as during high volume days the TES system may be operated for ten minutes then the compressor may be run for five minutes. On low volume days the control scheme may ensure that the TES system is used to its fullest capacity and saving as much compressor energy as possible during the day (approximately 12:00 PM to 6:00 PM).

FIG.6illustrates a state of charge (SOC) graph for a PCC in a cooling application. At 100% SOCcooling, the bulk average temperature of the PCC is approximately −2° C. At 0% SOCcooling, the bulk average temperature of the PCC is approximately 15° C. The phase change temperature used in this example is approximately 6.5° C. Therefore, the SOCcoolingincludes both the latent heat of fusion (i.e., the energy released during the phase transition at 6° C.) and the sensible heat to cool from approximately 15° C. to approximately −2° C. The latent heat of fusion may be approximately 85% of the total heat content of the PCC.

Examples

The foregoing discussion and examples have been presented for purposes of illustration and description. The foregoing is not intended to limit the aspects, embodiments, or configurations to the form or forms disclosed herein. In the foregoing Detailed Description for example, various features of the aspects, embodiments, or configurations are grouped together in one or more embodiments, configurations, or aspects for the purpose of streamlining the disclosure. The features of the aspects, embodiments, or configurations may be combined in alternate aspects, embodiments, or configurations other than those discussed above. This method of disclosure is not to be interpreted as reflecting an invention that the aspects, embodiments, or configurations require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment, configuration, or aspect. While certain aspects of conventional technology have been discussed to facilitate disclosure of some embodiments of the present invention, the Applicants in no way disclaim these technical aspects, and it is contemplated that the claimed invention may encompass one or more of the conventional technical aspects discussed herein. Thus, the following claims are hereby incorporated into this Detailed Description, with each claim standing on its own as a separate aspect, embodiment, or configuration.

Example 1

FIG.7illustrates one possible embodiment of a multi-circuit heating and cooling system700, wherein a first fluid120and a second fluid145are routed through a phase change composite140to form a heat exchanger135. In this embodiment, the second fluid145may be routed through a second coil710to exchange heat with the first airflow105. The second fluid145may be directed to the heat exchanger135inside PCC140by way of an expansion valve165and check valve715. After exchanging heat with the PCC140in the heat exchanger135, the second fluid145may be directed through a reversing valve730. The reversing valve730may change the direction of flow of the second fluid145. In this embodiment the second fluid145may add or remove heat from the phase change composite140.

In this embodiment, the second fluid145removes heat from the first airflow105by use of a first coil110and deposits heat in the PCC140(i.e., the PCC140is discharged). Heat is removed from the PCC140(i.e., the PCC140is charged) by a second fluid145. In some embodiments the second fluid145may be refrigerant. The second fluid145may be routed through a reversing valve730, compressor125, and a three-way valve735on its way to a second coil710. When the second fluid145flows through the second coil710it may heat the first airflow105. After leaving the second coil710the second fluid145is either returned to the PCC140by way of an expansion valve165or routed through a condenser155.

By operating the embodiment described inFIG.7in three different modes of operation, the process may be made more efficient. During the first operation, heat is removed from the PCC140by the second fluid145and delivered to a second coil610. In this operation the PCC140is “discharged” as the amount of thermal energy in the PCC140is decreased. During the second operation, heat is added to the PCC140by the first fluid120, which removed heat from the first airflow105. In this operation the PCC140is “charged” as the amount of thermal energy in the PCC140is increased. During the third operation, heat is added to the second fluid145by the first fluid120. In this operation the thermal energy storage in the PCC remains unchanged.

In this embodiment, the first airflow105may be simultaneously heated (by the second fluid145in the second coil610) and cooled (by the first fluid120in the first coil110). The first airflow105may also be independently heated or cooled by the multi-circuit heating and cooling system700. The direction of flow of the first fluid120and the second fluid145may be switched as needed based on whether the multi-circuit heating and cooling system700is heating the first airflow105or cooling the second airflow105.

Example II

FIG.8illustrates one embodiment of the present disclosure, a multi-circuit heating and cooling system700. In this embodiment, the first fluid120may exchange heat with the second fluid145both in the heat exchanger135inside the PCC140and in a fluid heat exchanger805. In this embodiment, the second fluid145does not add heat to the first airflow105via the second coil710(as inFIG.7), but instead exchanges heat with the first fluid120in fluid heat exchanger805. In this embodiment, the first fluid120may be used to heat and cool the first airflow105, rather than using the first fluid120for cooling the first airflow105and the second fluid145to heat the first airflow105(as shown inFIG.7). A distinction from the embodiment shown inFIG.7is that in the embodiment shown inFIG.8, simultaneous cool and reheat of the first airflow105is not possible.

In this embodiment, the second fluid145may be a refrigerant. Additionally, because the second fluid145is exchanging heat with the first fluid120and not the first airflow105, the second fluid145may be more highly flammable than traditional refrigerants. For example, the second fluid145may be propane.

Example III

FIG.9illustrates one embodiment of the present disclosure, a multi-circuit heating and cooling system700. In this embodiment, the PCC140is integrated with a heat pump925that provides both heating and cooling to a first airflow105. The flow of the first fluid120to the heat pump925may be controlled by an on/off valve915. The first fluid120and second fluid145may operate independently such that the first fluid120may operate at a drastically different fluid flow rates from the second fluid145. Likewise, one circuit may be shut down while the other one operates. This is advantageous, because heat may be added to the PCC140during the warmest part of the day, then heat may be pumped to the first airflow105later. This may save energy by reducing the lift of compressor125. This operation may also help in scheduling electric load on the grid. Compressor125may operate when electricity is abundant or cheap, and shut down when electricity is scarce. Compressor925may operate to meet the first airflow105's heating load as required. Operating in this manner, nearly half of the power for heating a first airflow105may be shifted to periods with cheap electricity.

In this embodiment, the PCC140may be used as an intermediary heat exchanger between the first fluid120and the second fluid145. This enables simultaneous heat addition and subtraction to the PCC140when operating the system to heat the first airflow105. In this embodiment the first airflow105may be simultaneously heated and cooled by the multi-circuit heating and cooling system700. The pump130may be used to heat the PCC140when operating the system to cool the first airflow105.

FIG.10shows a system that builds upon a cooling system comprising a multi-circuited phase-change composite heat exchanger by adding hot thermal energy storage to the cold storage.