The disclosed embodiments relate generally to dehumidification systems, and more particularly to systems directed at removing moisture from agricultural or other moisture-laden products.
It is often necessary or advantageous to lower the moisture content of certain products, including agricultural commodities. Corn, soybeans, wheat, oats, and even leafcutter bees are examples of products that require moisture removal for shipping, storing, and processing. The process of removing moisture from such commodities may be accomplished by closed-loop refrigeration methods. This involves forcing air over or through the subject product—i.e., the product from which moisture is to be removed—and then extracting moisture from the circulating air. The employed refrigeration systems typically include a heat pump, which comprises a condensing coil and an evaporator coil. Moisture from the circulating air adheres to the evaporator coil, thus lowering the relative humidity of the circulating air. After some time of operation, the moisture content of the subject product is reduced to a desired amount.
One problem with heat pump-based systems, however, is that the evaporator coil accumulates frost; and, at some point, the coil becomes so frosted that the evaporator coil no longer functions to remove moisture from the air. The typical solution to this frost issue is to cease operation of the heat pump in order to defrost the coil. This, of course, limits the effective operating time of the heat pump.
Disclosed here is a moisture removal system with a heat pump that employs alternating cycles of operation, reversing functions of the condenser coil and the evaporator coil at certain intervals or when specified conditions are present. This allows the heat pump to continue operating while simultaneously thawing the frosted coil. In this way, the moisture removal process is sped up because there is no need to cease operation of the system to defrost a coil.
In accordance with some embodiments of the disclosed technology, a moisture removal system employs a dual evaporator. Air is forced through or over the subject product and circulated through a drying enclosure. Within the drying enclosure, the air travels over or through several coils, at least one of which is operated as a condenser and one an evaporator. Moist air enters the removal, or evaporator coil, which is operated at temperature below freezing. The moisture from the air adheres to the coil, which drops the relative humidity of the air. Then, when the evaporator coils is frosted, the system is cycled such that the functions of at least two coils are reversed: at least one coil that initially operated as a condenser changes to an evaporator, and at least one coil the initially operated as an evaporator changes to a condenser. The process continues until the subject product reaches desired moisture content.
Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the disclosed concepts. It will, however, be apparent to one of ordinary skill in the art that the disclosed concepts may be practiced without these specific details. Well-known methods, procedures, components, circuits, and networks have not been described in detail so as not to unnecessarily obscure aspects of the embodiments.
The moisture removal system 10 has one or more sections of duct for conveying air through the system. In a preferred embodiment, there is a first section of duct 38 that is connected between the exhaust side 16 of the product container 12 and the inlet side 20 of the drying enclosure 18. There is a second section of duct 40 which is connected between the outlet side 22 of the drying enclosure 18 and the intake side 14 of the product container 12. At least one blower 42, which, in
The heat pump 24 may be equipped with a third coil 44 and a second expansion valve 45. Additionally, it may be equipped with a four-way valve 46 and a plurality of flow control devices 48.
In one embodiment, in which the heat pump 24 comprises three coils, there is a first coil 28 having a condenser inlet 50, an evaporator inlet 52, and a valve outlet 54. There is also a second coil 30 having a first outlet 56, a second outlet 58, and a valve inlet 60. There is a third coil 44 having a condenser inlet 62, an evaporator inlet 64, and a valve outlet 66. In such an arrangement, the first coil 28 and the third coil 44 are each capable of operating as either a condenser or evaporator. The compressor 26 has a suction inlet 68 and a discharge outlet 70. The four-way valve 46 has a first coil inlet 72, a second coil outlet 74, a third coil inlet 76, and a compressor outlet 78. The first expansion valve 32 has an inlet 80 and an outlet 82, and the second expansion valve 45 has an inlet 84 and outlet 86.
In this embodiment, the heat pump 24 is operated in either of two cycles.
The refrigerant leaves the first coil 28 at valve outlet 54 and moves to the second coil 30, which acts as a secondary condenser, via the four-way valve 46. The second coil outlet 74 of the four-way valve 46 is connected to the valve inlet 60 of the second coil 30 via conduit means 36. Next, the refrigerant moves from the second coil 30 to the third coil 44, which operates as an evaporator, via a second expansion valve 45. The second outlet 58 of the second coil 30 is connected to inlet 84 of the second expansion valve 45 via a conduit means 36. Within the conduit means 36 is a flow-controlling device 48 which, again, could be either a solenoid or a check valve, or any other similar means of controlling the flow in a conduit or pipe. The outlet 86 of the second expansion valve 45 is connected to the evaporator inlet 64 of the third coil 44 via a conduit means 36.
The refrigerant is then circulated back to the compressor 26 by way of the four-way valve 46 and the accumulator 88. The valve outlet 66 of the third coil 44 is connected to the third coil inlet 76 of the four-way valve 46. The compressor outlet 78 of the four-way valve 46 is connected to the valve inlet 90 of the accumulator 88 via conduit means 36; and the compressor outlet 92 of the accumulator 88 is connected to the suction inlet 68 of the compressor 26 via conduit means 36. The preferred embodiment includes an accumulator 88; however, those skilled in the art will recognize that a compressor with an internal or integral accumulator may also be used.
The refrigerant leaves the third coil 44 at valve outlet 66 and moves to the second coil 30, which acts as a secondary condenser, via the conduit means 36 and the four-way valve 46. The second coil outlet 74 of the four-way valve 46 is connected to the valve inlet 60 of the second coil 30 via conduit means 36. Next, the refrigerant moves from the second coil 30 to the first coil 28, which operates as an evaporator, via a first expansion valve 32. The first outlet 56 of the second coil 30 is connected to inlet 80 of the first expansion valve 32 via a conduit means 36. Within the conduit means 36 is a flow-controlling device 48, which, again, could be either a solenoid or a check valve, or any other similar means of controlling the flow in a conduit or pipe. The outlet 82 of the first expansion valve 32 is connected to the evaporator inlet 52 of the first coil 28 via a conduit means 36.
The refrigerant is then circulated back to the compressor 26 by way of the four-way valve 46, and the accumulator 88. The valve outlet 54 of the first coil 28 is connected to the first coil inlet 72 of the four-way valve 46. The compressor outlet 78 of the four-way valve 46 is connected to the valve inlet 90 of the accumulator 88 via conduit means 36; and the compressor outlet 92 of the accumulator 88 is connected to the suction inlet 68 of the compressor 26 via conduit means 36.
Referring again to
In the preferred embodiment, the switching means comprises a timer that operates the flow-controlling devices to alternate the function of the first coil 28 and the third coil 44 in set increments. In the best mode presently known, the switching means comprises a timer set to fifteen-minute increments. The switching means could, however, comprise a temperature gauge and the cycling of the first coil 28 and the third coil 44 could be based on the temperature at a given point in the system. In one embodiment, the temperature gauge could reference refrigerant temperature at the outlet 82 of the first expansion valve 32 or the outlet 86 of the second expansion valve 45. (Whether to measure at the first expansion valve 32 or the second expansion valve 44 of course depends in which cycle the heat pump is operating.) Or, a switching means comprising a pressure gauge that could measure pressure at a given point in the system and switch the functionality of the first coil 28 and the third coil 44 when the pressure reaches a certain limit.
As the circulating air 43 travels through the coils, moisture adheres to the coil operating as an evaporator and the relative humidity of the circulating air 43 is reduced. This moisture removal occurs because the temperature of the refrigerant in the coil, and thus the coil itself, is below freezing. In one embodiment, the temperature of the system refrigerant is about −11 degrees Fahrenheit, as measured at outlet 82 or outlet 86, depending on the cycle of operation. But those skilled in the art will recognize that a range of temperatures will be suitable for moisture removal.
The disclosed technology may be operated using a method with the following. First, provide a moisture removal system 10, as described above. Then, circulate air through the system with the blower 42. Next, run the heat pump in a first cycle, as depicted in
The foregoing description, for purpose of explanation, has been described with reference to specific embodiments. The illustrative discussion above, however, is not intended to be exhaustive or to limit the disclosed concepts to any particular form. The embodiments were chosen and described in order to best explain the principles of the disclosed concepts in order to enable others skilled in the art.