Thermal energy management system and method

A system, such as a thermal energy management system, is provided. The system can include an absorption module and an evaporation module. The absorption module can include at least two absorption chambers, each absorption chamber being configured to receive liquid absorbent. The evaporation module can be in independent selective fluid communication with each of the absorption chambers, and can be configured to receive and cause therein evaporation of a refrigerant.

BACKGROUND

In the U.S., conditioning of indoor environments is responsible for about 40% of all energy consumption, and for about 65% of all electricity consumption. Much of this conditioning involves space cooling. As such, efficient space cooling systems are desirable. Conventional methods of space cooling include absorption-based space cooling systems. However, the efficiency of absorption-based space cooling systems may be reduced when operating in a relatively warm ambient environment, and for this reason, the use of absorption-based space cooling systems may be limited.

BRIEF DESCRIPTION

In one aspect, a system, such as a thermal energy management system, is provided. The system can include an absorption module and an evaporation module. The absorption module can include at least two absorption chambers, each absorption chamber being configured to receive liquid absorbent (e.g., including one or more of LiBr, LiCl, LiClO3, CaCl2, ZnCl2, HnBr, and H2SO4). In some embodiments, the absorption module can be configured such that at least one of the absorption chambers is configured to selectively receive liquid absorbent while another of the absorption chambers is selectively prevented from receiving liquid absorbent.

The evaporation module can be in independent selective fluid communication with each of the absorption chambers, and can be configured to receive and cause therein evaporation of a refrigerant. In some embodiments, the evaporation module can include multiple evaporation chambers, and each of the absorption chambers can be in selective independent fluid communication with a respective evaporation chamber.

In some embodiments, the system may include a desorption module configured to exchange liquid absorbent with the absorption module. A condenser may be configured to receive refrigerant from the desorption module and to output refrigerant to be received by the evaporation module.

In some embodiments, the absorption chambers can be configured to receive liquid absorbent that includes at least a solution of an absorbent and the refrigerant. The system can include a refrigerant storage module in fluid communication with the evaporation module and configured to store the refrigerant. The evaporation and absorption modules can be configured such that refrigerant can selectively flow from the evaporation module to a first of the absorption chambers to combine with the liquid absorbent. Simultaneously, flow of the refrigerant from the evaporation module to a second of the absorption chambers can be selectively prevented to cause crystallization of the absorbent in the second of the absorption chambers and storage of a corresponding portion of the refrigerant in the refrigerant storage module. Flow of the refrigerant to the second absorption chamber can be selectively provided to cause the crystallized absorbent to decrystallize.

In another aspect, a method is provided. The method can include providing a system including an absorption module including at least two absorption chambers and an evaporation module in independent selective fluid communication with each of the absorption chambers. Absorbent can be flowed into the at least two absorption chambers. Refrigerant can be evaporated in the evaporation module. During a first interval, the evaporated refrigerant can be allowed to flow to a first of the absorption chambers and prevented from flowing to a second of the absorption chambers to cause absorbent to crystallise in the second of the absorption chambers. During a second interval subsequent to the first interval, evaporated refrigerant can be allowed to flow to the second of the absorption chambers to cause the absorbent to decrystallize.

In yet another aspect, a system, such as a thermal energy management system, is provided. The system can include an absorption module having at least two absorption chambers, with each absorption chamber being configured to receive a liquid absorbent. An evaporation module can be in independent selective fluid communication with each of the absorption chambers, the evaporation module being configured to receive and cause therein evaporation of a refrigerant.

DETAILED DESCRIPTION

Example embodiments are described below in detail with reference to the accompanying drawings, where the same reference numerals denote the same parts throughout the drawings. Some of these embodiments may address the above and other needs.

Referring toFIG. 1, therein is shown a system, such as a thermal energy management system100. The thermal energy management system100can include an absorption system101that has an evaporation module102and an absorption module104. The evaporation module102can be configured to receive and cause therein evaporation of a fluid (referred to as “refrigerant”). For example, the evaporation module102can include multiple evaporation chambers106a-dthat are each configured to receive liquid refrigerant. The evaporation chambers106a-dcan facilitate the transfer of thermal energy to the liquid refrigerant to cause evaporation of the refrigerant. The properties and function of the refrigerant are discussed in more detail below. The thermal energy transferred to the liquid refrigerant at the evaporation chambers106a-d, for example, may be heat from room air (cooling effect to the room), solar in origin and/or may be generated by industrial processes (such as exhaust heat from combustion-based processes and/or gas turbines).

The absorption module104can include at least two (in the illustrated embodiment, four) absorption chambers108a-d, and the evaporation module102can be in independent selective fluid communication with each of the absorption chambers. For example, each evaporation chambers106a-dcan be connected to a respective absorption chamber108a-dvia absorption conduits110a-d. The function of the absorption chambers108a-dis discussed below.

The thermal energy management system100can include a network of conduits112for directing fluid flow. As discussed below, during operation of the thermal energy management system100, the conduits112can carry one or both of absorbent and refrigerant (depending on where within the system a specific conduit is located). Each of the absorption chambers108can be configured to selectively receive liquid absorbent, which absorbent may be, for example, in combination (e.g., in solution) with liquid refrigerant (absorbent and/or refrigerant in vapor phase may also be received by the absorption chambers). Valves114,115may be included and individually controlled to selectively allow or prevent flow through each of the absorption chambers108. Each of the absorption chambers108can also be configured to facilitate the rejection of thermal energy from absorbent-refrigerant solution contained therein.

The thermal energy management system100can also include a desorption module116that is configured to exchange liquid absorbent with the absorption module104. The desorption module116can be configured to receive from the absorption module104liquid absorbent, say, combined with refrigerant. A pump118may be included to urge the absorbent-refrigerant combination to circulate between the desorption module116and the absorption module104. The desorption module116can be configured to facilitate thermal energy transfer to the absorbent/refrigerant combination to cause evaporation of at least some of the refrigerant. A valve119can be included between the desorption module116and the absorption module104to allow fluid passing therethrough to be throttled to a lower pressure. In some embodiments, the valve119can be excluded, and the valves114can act to reduce the pressure of fluid passing from the desorption module116to the absorption module104. A heat exchanger120can be included to allow thermal energy to be passed between the combined absorbent/refrigerant flowing from the absorption module104to the desorption module116and the combined absorbent/refrigerant flowing from the desorption module to the absorption module.

The system100can also include a condenser122, the condenser being configured to receive refrigerant (e.g., in vapor phase) from the desorption module116. The condenser122can be further configured to facilitate transfer of thermal energy from the refrigerant to cause condensation of the refrigerant, and to output the (condensed) refrigerant so as to be received by the evaporation module102. A refrigerant storage module124can be in fluid communication with the evaporation module102, e.g., disposed between and in fluid communication with the condenser122and the evaporation module. The storage module124(e.g., a storage tank) can be configured to store refrigerant outputted by the condenser122, which refrigerant can subsequently be outputted by the storage module, throttled to lower pressure through a valve126, and selectively supplied to the evaporation chambers106of the evaporation module102via the conduits112and the valves128. In some embodiments, the valve126can be excluded, and the valves128can act to reduce the pressure of fluid passing from the storage module124to the evaporation module102.

Operation of the system100is now described with reference toFIGS. 1 and 2. Combined (e.g., a solution of) absorbent-refrigerant130, can be discharged from the absorption chambers108and urged toward the desorption module116by the pump118. At the desorption module116, thermal energy can be transferred to the absorbent-refrigerant solution130to cause refrigerant to evaporate, thereby producing a concentrated absorbent-refrigerant solution132(the less-concentrated absorbent-refrigerant solution also being referred to as a “diluted absorbent-refrigerant solution”). The concentrated absorbent-refrigerant solution132can be throttled through the valve119to a lower pressure and directed to the absorption chambers108via the valves114. In order to increase the overall efficiency of the system100, both the concentrated and diluted absorbent-refrigerant solutions132,130can be passed through the heat exchanger120to allow thermal energy to be transferred from the concentrated solution to the diluted solution.

Refrigerant134, now separated from the absorbent-refrigerant solution130by the evaporation process facilitated by the desorption module116, can flow from the desorption module to the condenser122. At the condenser122, thermal energy can be removed from the refrigerant134to cause the refrigerant to condense. The condensed refrigerant134can then flow into the storage module124, from where it can flow to and be throttled through the valve126, thereafter being selectively supplied to each of the evaporation module102via the valves128.

At the evaporation module102, the evaporation chambers106can facilitate the transfer of thermal energy to the refrigerant134to cause evaporation of the refrigerant. The evaporated refrigerant134therefore accepts thermal energy and converts that thermal energy into latent heat of evaporation. The evaporated refrigerant134can propagate from each evaporation chamber106a-dto a respective absorption chamber108a-dvia the conduits110a-d, where at least some of the vapor phase refrigerant can be combined with the concentrated absorbent-refrigerant solution132, thereby forming the diluted absorbent-refrigerant solution130.

The absorbent and refrigerant may be chosen such that the act of combining the evaporated refrigerant134and the concentrated absorbent-refrigerant solution132causes a release of thermal energy. For example, the absorber104can be configured to combine evaporated refrigerant134and concentrated absorbent-refrigerant solution132so as to cause at least some evaporated refrigerant to become liquid, thereby causing a release of the latent heat of evaporation associated with the vapor. In some embodiments, the absorbent may be configured to form a liquid solution with the refrigerant, such that when vapor phase refrigerant134comes into contact with the concentrated absorbent-refrigerant solution132, the refrigerant tends to transform into a liquid component of the liquid solution with the absorbent, thereby causing a release of the heat of absorption. In other embodiments, a chemical reaction may occur between the vapor phase refrigerant134and the concentrated absorbent-refrigerant solution132, which reaction may be exothermic and/or may induce a transformation of the evaporated refrigerant to a liquid, thereby releasing heat of reaction and/or latent heat.

As refrigerant134evaporates in the evaporation module102to form vapor phase refrigerant, thermal energy is absorbed. As the vapor phase refrigerant134moves through the conduits110and is combined in the absorption module104with the concentrated absorbent-refrigerant solution132, thermal energy in the form of latent heat of evaporation and/or absorption can be released (as well as heat produced by any exothermic chemical reactions that may take place between the first and second working fluids). The overall result is a thermal energy transfer from the evaporation module102to the absorption module104, and the absorption system101can be thought of as a heat pump.

The absorbent and refrigerant can be chosen such that, when received at the absorption module104(under appropriate conditions), an equilibrium partial pressure of vapor phase refrigerant134in the evaporation module102is greater than a partial pressure of vapor phase refrigerant in absorption chambers108a-dwith which the evaporation module is in communication. For example, the absorbent and refrigerant can be chosen such that the absorbent (or the concentrated absorbent-refrigerant solution132) has a strong affinity for the refrigerant. In such a case, the equilibrium partial pressure of vapor phase refrigerant134in the vicinity of the concentrated absorbent-refrigerant solution132will tend to be low relative, say, to the partial pressure expected in the vicinity of liquid refrigerant. The difference in partial pressures of vapor phase refrigerant134in the evaporation module102and the absorption chambers108results in a driving force for diffusion of vapor phase refrigerant from the evaporation module102to the absorption chambers108. Examples of refrigerant-absorbent pairs that may be utilized in conjunction with embodiments of the above described system100include, but are not limited to, water and lithium bromide; NH3and water; water and LiCl; water and LiClO3; water and CaCl2, water and ZnCl2; water and HnBr; water and H2SO4; and SO2and organic solvents. For each refrigerant-absorbent pair including water as the refrigerant, the absorbent may include an aqueous solution of the listed composition.

Overall, the system100may operate so as to form a continuous cycle in which refrigerant134is caused to evaporate at the evaporation module102, combines with the concentrated absorbent-refrigerant solution132at the absorption module104, and then is separated from the diluted absorbent-refrigerant solution130at the desorption module116to allow refrigerant and diluted absorbent-refrigerant solution to repeat the cycle, thereby affecting a transfer of thermal energy from the evaporation module102to the absorption module104. This will be referred to as the “heat-pumping mode” of operation of the system100. As discussed below, the system100can also be operated so as to store energy (referred to as “energy storage mode” of operation) that can be subsequently retrieved and utilised to drive thermal energy transfer. The system100may be configured to selectively operate in heat-pumping mode, in energy storage mode, or simultaneously in heat-pumping mode and energy storage mode.

Referring toFIGS. 1-8, the system100may at an initial time be operating as described above, that is, in purely heat-pumping mode (this situation is depicted inFIGS. 2 and 3). Subsequently, a valve128acan be closed to prevent the flow of refrigerant134to one of the evaporation chambers106a(referred to as the “first evaporation chamber”); flow may continue to the remaining evaporation chambers106b-d(seeFIG. 4). Evaporation of the refrigerant134therefore only occurs in the evaporation chambers to which refrigerant is supplied (in the figure, chambers106b-d), and evaporated refrigerant is not supplied to the absorption chamber108a(referred to as the “first absorption chamber”) associated with the non-operative evaporation chamber106a; evaporated refrigerant continues to be supplied to the remaining absorption chambers108b-d. The first evaporation and absorption chambers106a,108acan now be referred to as operating in energy storage mode.

With the flow of evaporated refrigerant134halted to the first absorption chamber108a, the temperature of the concentrated absorbent-refrigerant solution132in residence in the first absorption chamber108atends to decrease. The absorbent composition and concentration in the concentrated absorbent-refrigerant solution132can be chosen such that the temperature decrease of the concentrated absorbent-refrigerant solution induces crystallization of the absorbent. For example, in one embodiment, the absorbent-refrigerant solution130,132can include lithium bromide and water, and upon leaving the desorption module116, the concentrated absorbent-refrigerant solution132can have a concentration of 66.5% lithium bromide (by weight). For such a solution, crystallization of the lithium bromide will tend to initiate when temperature is at or below about 71° C. (the crystallization temperature being relatively insensitive to pressure). In order to allow the concentrated absorbent-refrigerant solution132sufficient time in residence in the first absorption chamber108ato experience the temperature decrease necessary for crystallization, the valves114a,115acan be closed, thereby preventing flow through the first absorption chamber.

As thermal energy continues to be rejected by the partially crystallized absorbent, crystallization of the absorbent progresses (seeFIG. 4). Also, as crystallization proceeds, corresponding portions of refrigerant134(that is, refrigerant quantities sufficient to dissolve the now crystallized absorbent) can be stored in the storage module124. Eventually, crystallization of the absorbent136is complete, with a corresponding amount of refrigerant being stored in the storage module124. The separation of refrigerant from the crystallized absorbent serves to store energy in the form of a chemical potential.

At any time, energy storage mode of operation can be initiated for other evaporation and absorption chamber pairs. For example, the valves114b,115b,128bcan be closed to initiate energy storage mode operation for the evaporation chamber106b(the “second evaporation chamber”) and absorption chamber108b(the “second absorption chamber”) (seeFIG. 5). Crystallisation of the absorbent is thereby induced in the second absorption chamber108b, with a corresponding amount of refrigerant134being stored in the storage module124. It is noted that, for evaporation and absorption chambers106,108that are not operating in energy storage mode, these chambers can continue to operate in heat-pumping mode (for example, simultaneously with other chambers operating in energy storage mode).

The above process can be continued, for example, until all of the evaporation and absorption chambers106,108are operating in energy storage mode, that is, until the absorption chambers all contain crystallized absorbent (seeFIG. 6). Thereafter, one of the valves128, say, the valve128a, can be opened to allow refrigerant to be evaporated in the first evaporation chamber106aand provided to the first absorption chamber108a(seeFIG. 7). This introduction of evaporated refrigerant into the absorption chamber108acan induce decrystallization of the crystallized absorbent in the absorption chamber, with the refrigerant changing from vapor to liquid and dissolving a portion of the crystallized absorbent. Through the evaporation-absorption/decrystallization process, thermal energy is transferred from the first evaporation chamber106ato the first absorption chamber108a. Some of this thermal energy may be rejected from the absorption chamber108ato ambient, as discussed previously. However, some of the thermal energy can be absorbed by, and serve to raise the temperature of, the still crystallized absorbent in the absorption chamber108a, which crystallized absorbent can have a relatively low temperature and a relatively high heat capacity. Still more of the thermal energy can be dissipated in breaking the bonds of the previously crystallized absorbent as the absorbent dissolves into the liquid refrigerant to form the absorbent-refrigerant solution130. The valve114acan also be opened to facilitate the flow of concentrated absorbent-refrigerant solution132, and the valve115acan be opened to facilitate the flow of diluted absorbent-refrigerant solution130out of the absorption chamber108a. Thereafter, the first evaporation and absorption chambers106a,108acan again be seen to operate in heat-pumping mode.

At any time, the valves114,115,128can be opened to allow the evaporation and absorption chambers106a-d,108a-dto transition from operating in energy storage mode to operating in heat-pumping mode. For example, in some embodiments, once the first evaporation and absorption chambers106a,108ahave transitioned from energy storage mode to heat-pumping mode, the valves114b,115b,128bcan be opened to transition the second evaporation and absorption chambers106b,108b. The remaining evaporation and absorption chambers106c-d,108c-dcan be sequentially transitioned thereafter. In other embodiments, the evaporation and absorption chambers106,108can all be transitioned together from energy storage mode to energy recovery mode to heat-pumping mode.

Thermal energy management systems consistent with the above-described system100may demonstrate enhanced performance relative to existing thermal energy management systems. For example, the thermal energy management system100may be operated in heat-pumping/energy storage mode during periods of lower ambient temperature (e.g., at night), thereby producing crystallized absorbent in one or more of the absorption chambers108. During periods of higher ambient temperature (e.g., during the day), the absorbent in the absorption chambers108can be decrystallized, thereby facilitating the transfer of thermal energy from the evaporation chambers106to the absorption chambers with reduced requirement to reject thermal energy to ambient to continue the process. Instead, as discussed above, the thermal energy may be absorbed by the crystallized absorbent to raise the temperature and break solid bonds of the crystallized absorbent. Stored refrigerant and crystallized absorbent may, in some cases, be stored at ambient temperatures, thereby avoiding the need to expend energy to heat or cool these components.

Because the system100can be configured to allow crystallization of the absorbent in the absorption chambers108, relatively high concentrations of absorbent in the absorbent-refrigerant solution130,132(compared to existing absorption chillers) can be utilized while reducing concerns about system inoperability during heat-pumping due to unintended crystallization of the absorbent. This elevated absorbent concentration may be expected to improve the overall performance of the thermal energy management system100when operating in heat-pumping mode. Further, efficiency of the system100may be improved by the added energy storage capacity provided by the phase change associated with crystallization of the absorbent.

While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. For example, while thermal energy management systems have been described that incorporate an equal number of evaporation and absorption chambers, referring toFIG. 9, in some embodiments, the thermal energy management system200may include a single evaporation chamber206that is independently coupled to multiple absorption chambers208. The flow of evaporated refrigerant to each of the absorption chambers208may then be independently controlled by opening and closing a series of valves228. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.