Patent Application
20240053064
In order to protect the global ozone layer, only zero ozone depletion potential (0 ODP) refrigerants are utilized globally in new commercial refrigeration systems. Due to global warming concerns, there is a global goal to set a top end threshold of 500 Global Warming Potential (GWP) for refrigerants utilized in mechanical cooling. Mechanical cooling applications are often categorized as high temperature, or air conditioning, and low temperature, or refrigeration. Some blend refrigerants are now available with GWP under the 500 threshold, but they have flammability or toxicity issues. These low GWP flammable refrigerants are not generally suitable for use in indoor refrigeration systems.
The natural refrigerants such as R717 (ammonia), R744 (CO2), and R290 (propane) are all below the 500 GWP line. These refrigerants all have technical issues that must be addressed for normal use in commercial refrigeration.
As commercial refrigeration solutions are sought in order to reach the sub 500 GWP refrigeration system goal, one can omit systems with refrigerant larger refrigerant charges, perhaps more than 10 lbs, for indoor use due to the code, or end user, mandated maximum indoor charge of A2 and A3 refrigerants. In low temperature refrigeration systems operating below −30° F., cascade refrigeration systems have been employed in order to meet the low temperature requirements. These cascade refrigeration systems utilize one refrigerant for a low stage refrigeration system. The −30° F. low stage refrigeration system rejects the high side heat, condenser heat, to the condenser side of a heat exchanger. The high stage refrigeration system removes the condenser heat through the evaporator side of the cascade heat exchanger. This design allows the refrigeration systems to have higher, efficiency, less horsepower, lower pressures and lower discharge temperatures.
In order to operate sub 500 GWP A1 refrigeration systems with indoor components the natural refrigerant R744 (CO2) appears to be a suitable choice. However, R744 based refrigeration systems have issues with high discharge pressures and operating envelopes above the critical point of the refrigerant. Operation of refrigeration systems in the supercritical domain adds significant complexity requiring added controls, valving, and high-pressure components. This complexity leads to a tripling or quadrupling of the cost of a low temperature refrigeration system. Additionally, if an R744 refrigeration system loses power, the refrigerant in the system gradually warms up. At a temperature of 85° F., R744 will be at a pressure 1,108 psi above the atmosphere. This pressure exceeds the operating pressure of most refrigeration system tanks, so the refrigerant charge has to be released to atmosphere through a pressure relief device if the power outage is long enough for the R744 refrigerant to warm up to 85° F. anywhere within the system. Thus, as described herein, certain improvements are provided to a cascade refrigeration system in order to provide for the use a sub 500 GWP A1 refrigerant.
Using a cascade refrigeration system it is possible to achieve sub 500 GWP using the A1 natural refrigerant R744 on all indoor components of the system. In order to minimize pressures, and therefore component cost, the R744 refrigeration cycle is limited to a saturated condensing temperature of 80° F., or less. This low condensing temperature is achieved by employing a cascade refrigeration design. Certain sub 500 GWP refrigerants are A2L flammable refrigerants. The high stage refrigeration system that employs a sub 500 GWP refrigerant that has a flammability rating of A2L is installed outdoors (i.e., outside an enclosed structure, contained facility or building) due to the flammability issues of A2L refrigerants. The high stage system can utilize certain newly developed sub 500 GWP A2L such as R454C and R455A in order to provide a suitable high stage solution in a cascade refrigeration system,
The majority of the commercial refrigeration market is made up of refrigeration systems with air cooled condensing units (ACCUs), 2 hp to 500 hp, with refrigerant charge from 10 lb to 300 lb, that operate stand alone with the exception of occasional contractor visits for preventative maintenance or repairs.
As described herein, an improved sub 500 GWP cascade refrigeration system utilizing air cooled condensing units (ACCU) for the commercial refrigeration market with sub 500 GWP A2L refrigerants may be employed. The preferred refrigeration system includes positioning the entire A2L refrigerant charge contained outdoors, in the high stage cycle, and positioning the R744 natural refrigerant indoors on the low stage for fluid connection to evaporators. In this design, the 500 GWP A2L refrigerant stays inside the outdoor ACCU cabinet, cooling a cascade heat exchanger through evaporation, compression, condensation and expansion. The low stage natural refrigerant R744 liquid flows out of the ACCU through an expansion device, to the evaporator to pick up a heat load, and then return back to the ACCU through a suction line for compression and condensation at lower temperature and pressures than a single stage ACCU.
Thermal energy storage may be employed in a cascade refrigeration system. When a cascade refrigeration system is installed with a thermal energy storage reservoir surrounding cascade heat exchanger (CHX), then there is a passive buffer available to more evenly maintain condensing temperature for R744 (CO2) or R717 (ammonia) between 65 and 85° F. without the addition active valving or controls. In addition, in the event of a power outage, the thermal energy storage reservoir will maintain an R744 (CO2) system saturation temperature below 85° F. for a longer time, up to one week, during a power outage, preventing a release of the system refrigeration charge due to pressure increase.
Another cascade refrigeration system can be installed with a thermal energy storage reservoir surrounding cascade refrigerant receiver, or flash tank, for the benefit that in the event of a power outage, the thermal energy storage reservoir will maintain an R744 (CO2) system saturation temperature below 85° F. for a longer time, up to one week, during a power outage, preventing a release of the system refrigeration charge due to pressure increase.
The features, aspects, and advantages of the disclosed deliver system will become apparent from the following description, and the accompanying exemplary embodiments shown in the drawings, which are briefly described below.
An exemplary embodiment of a refrigeration system for an enclosed structure capable of sheltering personnel is disclosed herein. The refrigeration system includes a high stage refrigeration circuit including a high stage compressor, a condenser, a high stage expansion device, wherein the high stage refrigeration circuit circulates a high stage refrigerant having a GWP less than 500. The system further includes a low stage refrigeration circuit including a low stage compressor, a low stage expansion device, and an evaporator, wherein the low stage refrigeration circuit is configured to circulate a low stage refrigerant comprising R744. The evaporator is configured to be located within the enclosed structure and the condenser is configured to be located outside the structure. The system further includes a heat exchanger configured to transfer heat from the low stage refrigerant to the high stage refrigerant.
According to another embodiment, a refrigeration system for a building is disclosed. The refrigeration system includes a high stage refrigeration circuit including a high stage compressor, a condenser upstream of the high stage compressor, a high stage refrigerant receiver downstream of the condenser, a high stage expansion device downstream of the high stage refrigerant receiver. The high stage refrigeration circuit circulates a high stage refrigerant having a GWP less than 500 and a flammability classification of A2 or A2L. The system further includes a low stage refrigeration circuit including a low stage compressor, an evaporator upstream of the low stage compressor, a low stage expansion device upstream of the evaporator, and a low stage refrigerant receiver upstream of the low stage expansion device, wherein the low stage refrigeration circuit is configured to circulate a low stage refrigerant comprising R744. The evaporator is configured to be located within the building and the condenser is configured to be located outside the building. The system further includes a heat exchanger downstream of the low stage compressor and upstream of the high stage compressor configured to transfer heat from the low stage refrigerant to the high stage refrigerant.
Referring to
The CHX 30 may be surrounded by optional thermal energy storage reservoir 35. The reservoir may be included in order to extend the time until refrigerant will be vented through the pressure relief device during a power outage.
Referring to
Referring to
Referring to low) in btu/min. times a change in enthalpy of 142−55×
low×60=5,220
low btu/hr. The heat of rejection of this low stage system equals the compressor mass flow (
) in btu/min. times a change in enthalpy as H12 of 182−H63 of 55×
low×60=7,620
low btu/hr.
Referring to thigh) in btu/min. times a change in enthalpy of 113−45×
high×60=4,080
high btu/hr.
Since energy is conserved, this low stage heat of rejection is equal to the evaporation effect of the high stage refrigeration system. For low btu/hr=4,080
high btu/hr. Usually, the low stage refrigeration system is selected to match the mass flow required of the of the cold room cooling load. Then the high stage refrigeration system is then selected to match the mass flow required of the cascade heat exchanger CHX 30 cooling load coming from the low stage heat of rejection. In summary in this example
high=7,620±4,080=1.868
low.
Disclosed herein is an air-cooled condensing unit with a stationary cascade refrigeration system that operates on natural refrigerants that have a global warming potential (GWP) under 500. The low stage refrigeration cycle operates partially indoors preferably utilizing a natural refrigerant R744 (CO2) with an A1 non-flammable and non-toxic safety rating. Although R744 is preferred, other non-flammable low GWP refrigerants may be employed in the low stage cycle. The high stage outdoor refrigeration cycle operates on a sub 500 GWP refrigerant blend with a flammability of A1, A2, or A2L.
The stationary refrigeration system may use R454C, GWP 148 as the high stage refrigerant. Alternatively, the stationary refrigeration system may use R455A, GWP 146 as the high stage refrigerant. In another embodiment, the stationary refrigeration system may use R-471A, GWP<150 as the high stage refrigerant. The stationary refrigeration system may include a configuration wherein the high stage refrigerant is R1234YF, GWP 4. In another embodiment, the stationary refrigeration system may use R290, GWP 4 as the high stage refrigerant. In still another embodiment, the stationary refrigeration system may use a blend of R-32 and R-1234yf with a GWP less than or equal to 500, but with a flammability of A1 or A2L as the high stage refrigerant. Alternatively, the stationary refrigeration system may use a blend of some or all of R-32, CO2, R277, R-1234zeE and R-1234yf with a GWP less than or equal to 500, but with a flammability of A1 or A2L as the high stage refrigerant.
In one embodiment, the stationary refrigeration system may use R744 (CO2) as the low stage refrigerant and include a thermal energy storage reservoir surrounding the refrigerant receiver or flash tank to extend the time until refrigerant will be vented through the pressure relief device during a power outage. This embodiment utilizes coconut oil in the reservoir. The oil has a melting point of 76 to 79° F. and may be employed as a thermal energy storage medium with an intention of extending the time until the refrigerant in the powerless system rises above 85 F.
In another embodiment, the stationary refrigeration system may use R744 (CO2) as the low stage refrigerant and include a thermal energy storage reservoir surrounding the refrigerant receiver or flash tank to extend the time until refrigerant will be vented through the pressure relief device during a power outage. This embodiment utilizes a blend of fats or oils with a melting point of 65 to 79° F. as a thermal energy storage medium in the reservoir with an intention of extending the time until the refrigerant in the powerless system rises above 85 F.
In yet another embodiment, the stationary refrigeration system may use R744 (CO2) as the low stage refrigerant and include a thermal energy storage reservoir surrounding the cascade heat exchanger (CHX) to extend the time until refrigerant will be vented through the pressure relief device during a power outage. This embodiment utilizes coconut oil with a melting point of 76 to 79° F. as the a thermal energy storage medium with an intention of extending the time until the refrigerant in the powerless system rises above 85° F.
Alternatively, the stationary refrigeration system may use R744 (CO2) low stage refrigerant and include a thermal energy storage reservoir surrounding the cascade heat exchanger (CHX) to extend the time until refrigerant will be vented through the pressure relief device during a power outage. This embodiment utilizes a blend of fats or oils with a melting point of 65 to 79° F. as the a thermal energy storage medium with an intention of extending the time until the refrigerant in the powerless system rises above 85° F.
It should be noted that the term “exemplary” as used herein to describe various embodiments is intended to indicate that such embodiments are possible examples, representations, and/or illustrations of possible embodiments (and such term is not intended to connote that such embodiments are necessarily extraordinary or superlative examples).
It is important to note that refrigeration system shown in the various exemplary embodiments is illustrative only. Although several embodiments have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that other embodiments are possible and are contained within the scope of the invention. For example, modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter described herein. For example, elements shown as integrally formed may be constructed of multiple parts or elements, the position of elements may be reversed or otherwise varied, and the nature or number of discrete elements or positions may be altered or varied. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. Other substitutions, modifications, changes and omissions may also be made in the design, operating conditions and arrangement of the various exemplary embodiments without departing from the scope of the present disclosure.
This application claims priority to and the benefit of U.S. Provisional Patent Application No. 63/397,801, filed Aug. 12, 2022, which is incorporated by reference herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 63397801 | Aug 2022 | US |
