Patent Application
20200352356
The present disclosure relates generally to refrigerated display cabinets, and more specifically to a cabinet utilizing a radial cross-flow fan for driving the refrigerated air.
In practice, the grocery stores and supermarkets use refrigerated merchandisers of different types, which may be open or with doors, for displaying and presenting fresh food and beverages to the customers while maintaining a temperature of the products below a predefined threshold. In order to maintain the low temperature, cold air is circulated to the product display area of the cabinet by passing airflow over a heat exchanger surface of an evaporator. A cold refrigerant is pumped through the internal passages of the tubes which absorb the heat from the air via fins and tube surfaces and changes from a liquid phase to a vapor phase in the process. As a result the temperature of the air passing through the evaporator is lowered. One or more fans are typically included in the base of the refrigerated display cabinet and drive cold air through the heat exchanger and into the product display area of the merchandiser.
In addition to the increased operating costs and high first cost due required sizes of the heat exchangers, frost buildup and need for defrost cycles negatively impacts fan performance and energy efficiency of the merchandiser.
In one exemplary embodiment a refrigerated display case includes a housing surrounding a plurality of shelves, an air distribution gap defined behind the plurality of shelves, an air return passage defined below the plurality of shelves, a radial cross-flow fan disposed in a fan region of the air return passage, the radial cross-flow fan having an output connected to the air distribution gap, a primary cooling microchannel heat exchanger disposed in the fan region downstream of the radial cross-flow fan such that air output from the radial cross-flow fan to the air distribution gap passes through the primary cooling microchannel heat exchanger, and a pre-cooler microchannel heat exchanger disposed upstream of the primary cooling microchannel heat exchanger.
In another example of the above described refrigerated display case the pre-cooler microchannel heat exchanger is disposed downstream of the cross-flow fan.
In another example of any of the above described refrigerated display cases the pre-cooler microchannel heat exchanger connects the output of the radial cross-flow fan to the air distribution gap.
In another example of any of the above described refrigerated display cases the primary cooling microchannel heat exchanger is disposed immediately downstream of the pre-cooler microchannel heat exchanger.
In another example of any of the above described refrigerated display cases the pre-cooler microchannel heat exchanger is disposed upstream of the radial cross-flow fan.
In another example of any of the above described refrigerated display cases the pre-cooler microchannel heat exchanger includes a cooled air output connected to an input of the radial cross-flow fan.
In another example of any of the above described refrigerated display cases the pre-cooler microchannel heat exchanger has a first saturation temperature and the primary cooling microchannel heat exchanger has a second saturation cooling temperature, and where the second saturation temperature is lower than the first saturation temperature.
In another example of any of the above described refrigerated display cases the first saturation temperature is below a temperature required to extract moisture from the return air and above a minimum cooling temperature for the plurality of shelves.
In another example of any of the above described refrigerated display cases the second saturation temperature is above a frost temperature.
Another example of any of the above described refrigerated display cases further includes a top duct define above the plurality of shelves and connecting the air distribution gap to an air curtain fan and a third microchannel heat exchanger connected to the air curtain fan such that cooled air is provided to the air curtain fan.
In another example of any of the above described refrigerated display cases the fan region is at a downstream end of the air return passage.
An exemplary method of cooling shelves in a refrigerated display cabinet includes driving air through a cooling circuit using a radial cross-flow fan, passing the air through a primary microchannel heat exchanger, thereby cooling the air below a minimum cooling temperature of at least one shelf, and extracting moisture from the air using a pre-cooler microchannel heat exchanger prior to passing the air through the primary microchannel heat exchanger.
In another example of the above described method of cooling shelves in a refrigerated display cabinet the pre-cooler microchannel heat exchanger is downstream of the radial cross-flow fan and upstream of the primary microchannel heat exchanger.
In another example of any of the above described methods of cooling shelves in a refrigerated display cabinet the pre-cooler microchannel heat exchanger is upstream of the radial cross-flow fan.
Another example of any of the above described methods of cooling shelves in a refrigerated display cabinet further includes driving at least a portion of the air to create a downward flowing air curtain using an air curtain fan.
Another example of any of the above described methods of cooling shelves in a refrigerated display cabinet further includes cooling the at least the portion of the air immediately prior to the air curtain fan using a micro-channel heat exchanger.
Another example of any of the above described methods of cooling shelves in a refrigerated display cabinet further includes operating the primary microchannel heat exchanger at a saturation temperature below a frost point and operating the pre-cooler microchannel heat exchanger at a temperature above the frost point and below a condensation point.
Another example of any of the above described methods of cooling shelves in a refrigerated display cabinet further includes deactivating the pre-cooler microchannel heat exchanger in response to a controller determining a low load period.
Another example of any of the above described methods of cooling shelves in a refrigerated display cabinet further includes reactivating the pre-cooler microchannel heat exchanger in response to a controller detecting a door opening.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.
Also included within the gap 30 is a round-tube plate-fin heat exchanger 50 for cooling the air being provided to the shelves 12. A fan 52 is positioned immediately downstream of the heat exchanger 50 at an aft end of a return cavity 54 below the bottom most shelf 12. The fan 52 drives all of the air from the return cavity 54 to pass through the heat exchanger 50, thereby causing all of the air to be cooled. An aft end 51 of the heat exchanger 50 expels cooled air into the gap 30. A portion of the air flows upward through the gap 30 to the top gap 40 and the top shelves 12. A redirection feature 32 alters a flow direction of another portion of the cooled air by 180 degrees such that the redirected cooled air is provided to the lower shelves 12.
The size of the gap 30 is dictated by the size of the heat exchanger 50, and the space between the heat exchanger 50 and the distribution plate 20 required to allow sufficient air to be provided to each shelf 12. Further, as all of the air is cooled by the single heat exchanger 50, the heat exchanger 50 must be sufficiently sized to cool all of the air to a temperature that remains below the required temperature until it reaches the farthest shelf 12 from the heat exchanger 50. This can result in overcooling the middle shelves in order to achieve the desired cooling at the top and/or bottom shelves 12. Even further still, the travel from the output of the heat exchanger 50 to each of the shelves 12 where the cooling is required causes the temperature of the air provided to the shelves 12 to be higher than the outlet temperature of the heat exchanger 50.
With continued reference to prior art
The shelves 112 are supported within the cabinet by a distribution plate 120 positioned at the rear of the shelves 112. An air distribution gap 130 is disposed behind the shelves 112. The air distribution gap 130 transmits air from a primary microchannel heat exchanger 150 to each of the shelves 112. An air return passage 154 is disposed beneath all of the shelves 112, and provides a route for spent air to return from the shelves 112 to the cooling system. A fan 152 is disposed in a fan region 151 of the air return passage 152. The fan 152 is a radial cross flow fan, and drives air through the microchannel heat exchanger 150, and into the air distribution gap 130. As used herein, a radial cross-flow fan refers to a fan that includes a cylindrical bladed rotor mounted for rotation about its axis in a predetermined direction and defining an interior space. The fan includes a guide means defining with the rotor a suction region and a pressure region. The guide means and the rotor co-operate on rotation of the latter in the predetermined direction to induce a flow of fluid from the suction region through the path of the rotating blades on the rotor to the interior space and again through the path of the rotating blades to the pressure region. The guide means and rotor co-operate to set up a vortex having a core region eccentric of the rotor axis and a field region which guides the fluid so that flow through the rotor is strongly curved about the vortex core. Radial cross-flow flow fans can alternatively be referred to as “tangential” or “transverse” fans. Likewise, as used herein, a microchannel heat exchanger refers to a heat exchanger that primarily utilizes flat-tube constructions. A flat tube heat exchanger 102 includes an inlet manifold and an outlet manifold fluidly connected by multiple flat tubes. The flat tubes may be formed to include multiple channels, or internal passageways that are much smaller than the internal passageways of the tubes in the conventional round-tube plate-fin heat exchanger 50.
As used herein, the flat tubes may also include mini size multi-port channels, or micro size multi-port channels (otherwise known as microchannel tubes). The flat tube heat exchangers using small size multi-port channels are alternately known as microchannel heat exchanger 102. In alternative constructions the flat tubes may include one channel, or internal passageway. The microchannel heat exchanger 102 includes a plurality of secondary heat transfer surfaces in the form of serpentine-shape fins with louvers. The fins encompasses the width of the tube which also defines the minor dimension of the microchannel heat exchanger 102 and through which the air flows. The fins are positioned along the flat tubes and solidly coupled to two adjacent flat tubes by a brazing or welding process. While it is appreciated that the cooling air circulates in a loop, as used herein the upstream end of the air return passage 154 is referred to as the beginning of the cycle.
It is appreciated that microchannel heat exchangers, such as the primary microchannel heat exchanger 150 frost at relatively high refrigerant saturation temperatures, and that it is difficult to maintain low enough shelf 112 temperatures when the microchannel heat exchanger has a higher saturation temperature. In order to ameliorate this, a second microchannel heat exchanger 156 (referred to as the pre-cooler microchannel heat exchanger 156) is incorporated upstream of the primary microchannel heat exchanger 150. Additionally the second microchannel heat exchanger allow sufficient time to remove enough heat from the airflow to cool the air to the requisite temperature needed.
In the example of
The pre-cooler microchannel heat exchanger 156 is maintained at high enough saturation temperature that no frost is formed on the pre-cooler microchannel heat exchanger 156, but at a low enough saturation temperature that the pre-cooler microchannel heat exchanger 156 operates as a de-humidifier and extracts moisture from the air prior to providing the air to the radial cross-flow fan 152. The primary microchannel heat exchanger 150 is disposed downstream of the fan 152 and is maintained at a cool enough saturation temperature that the air exiting the primary microchannel heat exchanger 150 is cooled to low enough temperatures to maintain the shelf 112 temperatures below a required cooling threshold.
In order to reduce costs and/or minimize energy expenditures, a controller 101 can be incorporated within the refrigerated display case 100 and can be configured to deactivate (not operate) the pre-cooler 156 during times when there is a low load, such as night time or other times when the door 102 is not frequently opened and closed. During such times, the evaporator function of the pre-cooler microchannel heat exchanger 156 may be unnecessary as the air with the refrigerated display case is a closed system, and new moisture is not introduced until the door 102 is opened.
In order to prevent any moisture that may not have been removed from the air from dripping into the radial cross-flow fan 152 from the primary microchannel heat exchanger 150, the primary microchannel heat exchanger 150 is angled, relative to gravity, and drips into a drip pan 153 upstream of the radial cross-flow fan 152.
Disposed above the top end of the refrigerated case 100 is a top gap 140 connected to the air distribution gap 130. The top gap 140 provides air that has not been distributed to one of the shelves 112 to an air curtain generating fan 160. The air curtain generating fan 160 blows the air downward in front of the shelves 112 to create an air curtain. The air curtain helps prevent outside air from mixing with the cooled air on the shelves 112, as well as draws air through the shelves 112, further increasing the cooling able to be achieved on a given shelf 112.
In the illustrated example of
With continued reference to
It is further understood that any of the above described concepts can be used alone or in combination with any or all of the other above described concepts. Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.
