Cooling system with low temperature load

A system includes a flash tank, a load, a first compressor, a second compressor, a refrigerant routing line, and a flash gas bypass line. The flash tank stores a refrigerant. The load uses the refrigerant from the flash tank to remove heat from a space proximate the load. The first compressor compresses the refrigerant from the load. The refrigerant routing line routes the refrigerant from the first compressor to the flash tank below a liquid level line of the flash tank. The flash gas bypass line is coupled to the flash tank and sends the refrigerant as a flash gas from the flash tank to the second compressor. The second compressor compresses the refrigerant.

TECHNICAL FIELD

This disclosure relates generally to a cooling system, specifically a refrigeration system with a low temperature load.

BACKGROUND

Refrigeration systems may be configured in a carbon dioxide booster system. This system may cycle CO2refrigerant to cool a space using refrigeration. The refrigerant may be cycled through a low temperature load, low temperature compressor(s), a medium temperature load, and medium temperature compressor(s).

SUMMARY OF THE DISCLOSURE

According to one embodiment, a system includes a high side heat exchanger, a flash tank, a load, a first compressor, a second compressor, a refrigerant routing line, and a flash gas bypass line. The high side heat exchanger removes heat from a refrigerant. The flash tank stores the refrigerant from the high side heat exchanger. The load uses the refrigerant from the flash tank to remove heat from a space proximate the load. The first compressor compresses the refrigerant from the load. The refrigerant routing line routes the refrigerant from the first compressor to the flash tank below a liquid level line of the flash tank. The flash gas bypass line is coupled to the flash tank and sends the refrigerant as a flash gas from the flash tank to the second compressor. The second compressor compresses the refrigerant and sends the refrigerant to the high side heat exchanger.

According to another embodiment, a method includes removing, by a high side heat exchanger, heat from a refrigerant and storing, by a flash tank, the refrigerant from the high side heat exchanger. The method also includes using, by a load, the refrigerant from the flash tank to remove heat from a space proximate the load and compressing, by a first compressor, the refrigerant from the load. The method further includes routing, by a refrigerant routing line, the refrigerant from the first compressor to the flash tank below a liquid level line of the flash tank and sending, by a flash gas bypass line coupled to the flash tank, the refrigerant as a flash gas from the flash tank to a second compressor. The method also includes compressing, by the second compressor, the refrigerant and sending, by the second compressor, the refrigerant to the high side heat exchanger.

According to yet another embodiment, a system includes a flash tank, a load, a first compressor, a second compressor, a refrigerant routing line, and a flash gas bypass line. The flash tank stores a refrigerant. The load uses the refrigerant from the flash tank to remove heat from a space proximate the load. The first compressor compresses the refrigerant from the load. The refrigerant routing line routes the refrigerant from the first compressor to the flash tank below a liquid level line of the flash tank. The flash gas bypass line is coupled to the flash tank and sends the refrigerant as a flash gas from the flash tank to the second compressor. The second compressor compresses the refrigerant.

Certain embodiments may provide one or more technical advantages. For example, an embodiment allows for the safe operation of a medium temperature compressor when a medium temperature load is not present in a CO2booster system by routing refrigerant from a low temperature compressor to a flash tank below a liquid level line of the flash tank and then sending flash gas from the flash tank to the medium temperature compressor. As another example, an embodiment reduces the temperature and/or pressure of a superheated refrigerant by routing the superheated refrigerant to a flash tank below the liquid level line of the flash tank. Certain embodiments may include none, some, or all of the above technical advantages. One or more other technical advantages may be readily apparent to one skilled in the art from the figures, descriptions, and claims included herein.

DETAILED DESCRIPTION

Embodiments of the present disclosure and its advantages are best understood by referring toFIGS. 1 through 4of the drawings, like numerals being used for like and corresponding parts of the various drawings.

Cooling systems, such as for example refrigeration systems, may be configured in a CO2booster configuration. These systems may cycle refrigerant from a flash tank through low temperature loads and medium temperature loads to cool spaces corresponding to those loads. For example, in a grocery store, the low temperature loads may be freezers used to store frozen foods and the medium temperature loads may be refrigerated shelves used to store fresh produce. The refrigerant from the low temperature load is sent through low temperature compressors, and then that compressed refrigerant is mixed with refrigerant from the medium temperature load and refrigerant from the flash tank. That mixture is then sent through medium temperature compressors and then cycled back to the condenser.

By mixing the refrigerant from the low temperature compressor with refrigerant from the medium temperature load and from the flash tank, the temperature of the refrigerant from the low temperature compressor may be reduced before being sent to the medium temperature compressor. However, when the medium temperature load is not present and/or removed from the refrigeration system, the refrigerant from the medium temperature load is not included in the mixture. As a result, the temperature of the mixture may be too high for the medium temperature compressors to handle safely. Unsafe operating conditions may result if that mixture is sent to the medium temperature compressors (e.g., overheating the medium temperature compressors and/or causing the medium temperature compressors to fail or compressor protection mechanisms to trip with loss of refrigeration to the system owner).

This problem also occurs when the medium temperature load and the low temperature load are imbalanced. For example, the low temperature load could be operating much more actively than the medium temperature load. As a result, the medium temperature load may not send enough refrigerant to mix with the refrigerant from the low temperature compressor. The temperature of the refrigerant received by the medium temperature compressor would then be too high for the medium temperature compressor to safely compress.

This disclosure contemplates a configuration of the refrigeration system that lowers the temperature of the unsafe mixture and avoids such unsafe operating conditions. In the configuration, the refrigerant from the low temperature compressor is routed through the flash tank before being received by the medium temperature compressor. In this manner, the refrigerant may be cooled by the liquid refrigerant in the flash tank before being sent to the medium temperature compressor.

Cooling systems and the contemplated configuration will be discussed in more detail usingFIGS. 1 through 4.FIG. 1shows a cooling system with a medium temperature load and a low temperature load.FIG. 2shows the cooling system ofFIG. 1configured without a medium temperature load.FIG. 3shows the cooling system ofFIG. 1with imbalanced loads.FIG. 4describes the operation of the system ofFIGS. 2 and 3.

As provided inFIG. 1, system100includes a high side heat exchanger105, an expansion valve110, a flash tank115, an expansion valve120, a low temperature load125, expansion valve130, a medium temperature load135, a low temperature compressor140, a medium temperature compressor145, and a flash gas bypass line150. System100may circulate a refrigerant to remove heat from spaces proximate low temperature load125and medium temperature load135.

High side heat exchanger105may remove heat from the refrigerant. When heat is removed from the refrigerant, the refrigerant is cooled. This disclosure contemplates high side heat exchanger105being operated as a condenser and/or a gas cooler. When operating as a condenser, high side heat exchanger105cools the refrigerant such that the state of the refrigerant changes from a gas to a liquid. When operating as a gas cooler, high side heat exchanger105cools the refrigerant but the refrigerant remains a gas. In certain configurations, high side heat exchanger105is positioned such that heat removed from the refrigerant may be discharged into the air. For example, high side heat exchanger105may be positioned on a rooftop so that heat removed from the refrigerant may be discharged into the air. As another example, high side heat exchanger105may be positioned external to a building and/or on the side of a building.

Expansion valves110,120, and130reduce the pressure and therefore the temperature of the refrigerant. Expansion valves110,120, and130reduce pressure from the refrigerant flowing into the expansion valves110,120, and130. The temperature of the refrigerant may then drop as pressure is reduced. As a result, warm or hot refrigerant entering expansion valves110,120, and130may be cooler when leaving expansion valves110,120, and130. The refrigerant leaving expansion valve110is fed into flash tank115. Expansion valves120and130feed low temperature load125and medium temperature load135respectively.

Flash tank115may store refrigerant received from high side heat exchanger105through expansion valve110. This disclosure contemplates flash tank115storing refrigerant in any state such as, for example, a liquid state and/or a gaseous state. Refrigerant leaving flash tank115is fed to low temperature load125and medium temperature load135through expansion valves120and130. Flash tank115is referred to as a receiving vessel in certain embodiments.

System100may include a low temperature portion and a medium temperature portion. The low temperature portion may operate at a lower temperature than the medium temperature portion. In some refrigeration systems, the low temperature portion may be a freezer system and the medium temperature system may be a regular refrigeration system. In a grocery store setting, the low temperature portion may include freezers used to hold frozen foods and the medium temperature portion may include refrigerated shelves used to hold produce. Refrigerant may flow from flash tank115to both the low temperature and medium temperature portions of the refrigeration system. For example, the refrigerant may flow to low temperature load125and medium temperature load135. When the refrigerant reaches low temperature load125or medium temperature load135, the refrigerant removes heat from the air around low temperature load125or medium temperature load135. As a result, the air is cooled. The cooled air may then be circulated such as, for example, by a fan to cool a space such as, for example, a freezer and/or a refrigerated shelf. As refrigerant passes through low temperature load125and medium temperature load135the refrigerant may change from a liquid state to a gaseous state.

Refrigerant may flow from low temperature load125and medium temperature load135to compressors140and145. This disclosure contemplates system100including any number of low temperature compressors140and medium temperature compressors145. Both the low temperature compressor140and medium temperature compressor145may be configured to increase the pressure of the refrigerant. As a result, the heat in the refrigerant may become concentrated and the refrigerant may become a high pressure gas. Low temperature compressor140may compress refrigerant from low temperature load125and send the compressed refrigerant to medium temperature compressor145. Medium temperature compressor145may compress refrigerant from low temperature compressor140and medium temperature load135. Medium temperature compressor145may then send the compressed refrigerant to high side heat exchanger105.

Medium temperature compressor145may not be able to safely compress the refrigerant if the temperature of that refrigerant is too high. To regulate the temperature of the refrigerant received by medium temperature compressor145, the refrigerant from low temperature compressor140may be mixed with a cooler refrigerant coming from medium temperature load135before being received by medium temperature compressor145. The refrigerant from low temperature compressor140may further be mixed with a cooler flash gas from flash tank115via flash gas bypass line150. By cooling the refrigerant from low temperature compressor140before it is received by medium temperature compressor145may allow medium temperature compressor145to safely compress the received refrigerant.

Flash gas bypass line150may be used to mix flash gas from flash tank115with the refrigerant from low temperature compressor140and medium temperature load135before that refrigerant is received by medium temperature compressor145. The flash gas supplied by flash gas bypass line150cools the refrigerant before the refrigerant is received by medium temperature compressor145. Flash gas bypass line150includes expansion valve155. Expansion valve155may further cool the flash gas coming from flash tank115.

In particular embodiments, the refrigerant from low temperature compressor140(125° F.-140° F.) is cooled by both the refrigerant from medium temperature load135(25° F.-35° F.) and the refrigerant from flash gas line150(21° F.) at a ratio of about 10%-15% from low temperature load140, 45%-50% from medium temperature load135, and 30%-40% from flash gas bypass line150. This allows medium temperature compressor145to operate safely.

The operation of system100as illustrated inFIG. 1may depend on medium temperature load135providing enough refrigerant to mix with the refrigerant from low temperature compressor140. If medium temperature load135is not present or is not providing enough refrigerant, then the refrigerant received by medium temperature compressor145may be too high a temperature for medium temperature compressor145to safely compress. This disclosure contemplates configurations of system100that may allow medium temperature compressor145to safely compress a received refrigerant when medium temperature load135is not present and/or is not providing enough refrigerant.FIGS. 2 and 3illustrate the alternative configurations.FIG. 4describes the operation of the alternative configurations.

FIG. 2illustrates the example cooling system100ofFIG. 1with the medium temperature load removed. As illustrated inFIG. 2, system100may be configured with a refrigerant routing line200when the medium temperature load is removed. As a result of removing the medium temperature load, it is not possible to mix the refrigerant from low temperature compressor140with the refrigerant from the low temperature load. As a result, the refrigerant received by medium temperature compressor145may be too hot for medium temperature compressor145to safely compress. Using the example of a previous embodiment, because the medium temperature load is not present in system100, the refrigerant from low temperature compressor140is not mixed with the refrigerant from the medium temperature load. As a result, the resulting mixture (at around 71° F.) may include about 60% of high temperature gas from the low temperature compressor140at around 140° F. and about 40% of the vapor from the flash tank through flash gas bypass line150at around 21° F. Because medium temperature compressor145may not safely handle refrigerant above 65° F., this mixture may be unsafe to pass to medium temperature compressor145. Refrigerant routing line200allows for the refrigerant from low temperature compressor140to be further cooled so that medium temperature compressor145can safely compress the refrigerant.

Refrigerant routing line200is coupled to low temperature compressor140and flash tank115. Refrigerant routing line200routes refrigerant from low temperature compressor140to flash tank115. The refrigerant is routed to a portion of flash tank115that is below a liquid level line205of flash tank115. Because the refrigerant routed by refrigerant routing line200is typically in the gaseous state, the refrigerant will rise through the liquid refrigerant in flash tank115. As the refrigerant travels through the liquid refrigerant, the refrigerant is cooled although the refrigerant may remain in the gaseous state. The refrigerant may further mix with the flash gas inside flash tank115and/or flash gas bypass line150, which further cools the refrigerant. After being cooled, the refrigerant may enter flash gas bypass line150and travel to medium temperature compressor145. By routing the refrigerant through flash tank115, the refrigerant may be cooled sufficiently for medium temperature compressor145to safely compress the refrigerant. In this manner, the refrigerant may be sufficiently cooled even though it is not mixed with refrigerant from a medium temperature load.

As illustrated inFIG. 2, flash gas bypass valve155is removed from system100. It is understood however that system100may still operate as intended even with flash gas bypass valve155included.

FIG. 3illustrates the example cooling system100ofFIG. 1with imbalanced loads. When low temperature load125and medium temperature load135are imbalanced, medium temperature load135may not provide enough refrigerant to mix with the refrigerant from low temperature compressor140. As a result, the refrigerant received by medium temperature compressor145may be too hot to be safely compressed. As illustrated inFIG. 3, system100can be configured according to the same guiding principles used in the configuration ofFIG. 2to cool the refrigerant received by medium temperature compressor145. Refrigerant routing line200routes the refrigerant from low temperature compressor140to flash tank115below a liquid level line205of flash tank115. The refrigerant is then cooled by the refrigerant in flash tank115and leaves flash tank115through flash gas bypass line150. Furthermore, the refrigerant from medium temperature load135is mixed with the refrigerant in flash gas bypass line150before the refrigerant is received by medium temperature compressor145. As a result, the refrigerant received by medium temperature compressor145is at a low enough temperature such that medium temperature compressor145can safely compress the refrigerant. In this manner, system100may operate safely even if medium temperature load135and low temperature load125are imbalanced.

In some embodiments, system100includes a heat exchanger300coupled to flash gas bypass line150and refrigerant routing line200. The heat exchanger transfers heat from the refrigerant in refrigerant routing line200to the refrigerant in flash gas bypass line150. In this manner, the temperature of the refrigerant received by medium temperature compressor145may be further regulated to be above a minimum temperature. As a result, the heat exchanger may offset any over cooling resulting from routing the refrigerant through flash tank115and/or flash gas bypass valve155. Furthermore, any liquid refrigerant may be evaporated before reaching medium temperature compressor145so that medium temperature compressor145does not malfunction. Although this disclosure illustrates heat exchanger300inFIG. 3, it is understood that heat exchanger300can also be included in the configuration ofFIG. 2.

In particular embodiments, system100may include a second high side heat exchanger that removes heat from the refrigerant. The second high side heat exchanger is positioned along refrigerant routing line200between low temperature compressor140and flash tank115. The second high side heat exchanger may operate as a gas cooler or as a condenser. The second high side heat exchanger may receive refrigerant from low temperature compressor140, remove heat from that refrigerant, and then send the refrigerant to flash tank115. In this manner, additional heat may be removed from the refrigerant before it is received by medium temperature compressor145.

In certain embodiments, a portion of refrigerant routing line200may extend into flash tank115. The portion extending into flash tank115may include a plurality of pipes. The refrigerant may travel through these pipes into the liquid refrigerant in flash tank115. For example, one or more of these pipes may be perforated which allows the gaseous refrigerant to escape through holes in the pipe into the liquid refrigerant in flash tank115. The gaseous refrigerant may then bubble up through the liquid refrigerant into flash gas bypass line150. Perforating these pipes may increase the bubbling surface area, which improves heat removal from the refrigerant.

This disclosure contemplates refrigerant routing line200and flash tank115being configured in any appropriate manner. For example, a baffle may be positioned between refrigerant routing line200and flash gas bypass line150. As another example, the baffle may be positioned at the entrance of flash gash bypass line150. The baffle may restrain the flow of gaseous refrigerant from refrigerant routing line200to flash gas bypass line150. In this manner, the gaseous refrigerant may spend more time in flash tank115thereby further reducing the temperature of the gaseous refrigerant.

Modifications, additions, or omissions may be made to the present disclosure without departing from the scope of the invention. For example, the components of system100may be integrated or separated.

FIG. 4is a flowchart illustrating a method400of operating the example cooling system ofFIG. 2. Various components of the cooling system perform the steps of method400. In particular embodiments, by performing method400the temperature of a refrigerant may be reduced before the refrigerant is received by a medium temperature compressor.

Method400may begin by a high side heat exchanger removing heat from a refrigerant in step405. The high side heat exchanger sends the refrigerant to a flash tank. In step410, the flash tank stores the refrigerant. The flash tank sends the refrigerant to a load. In step415, the load uses the refrigerant to remove heat from a space proximate the load. The load then sends the refrigerant to a first compressor.

In step420, the first compressor compresses the refrigerant. The first compressor sends the compressed refrigerant to a refrigerant routing line. In step425, the refrigerant routing line routes the refrigerant to the flash tank below a liquid level line of the flash tank. In this manner, the refrigerant may be cooled by the liquid refrigerant in the flash tank. After being cooled the refrigerant leaves the flash tank through a flash gas bypass line. In step430, the flash gas bypass line sends the refrigerant as a flash gas to a second compressor. The second compressor compresses the refrigerant in step435. Then in step440, the second compressor sends the refrigerant back to the high side heat exchanger.

Modifications, additions, or omissions may be made to method400depicted inFIG. 4. Method400may include more, fewer, or other steps. For example, steps may be performed in parallel or in any suitable order. While discussed as various components of cooling system100performing the steps, any suitable component or combination of components of system100may perform one or more steps of the method.