FIELD OF THE INVENTION The present invention relates generally to heating, ventilation and air conditioner systems (HVAC), including systems that can dehumidify air.
BACKGROUND OF THE INVENTION An HVAC system generally includes a closed loop refrigeration system with at least one evaporator, at least one condenser and at least one compressor. As the refrigerant travels through the evaporator, it absorbs heat from a heat transfer fluid and changes from a liquid to a vapor phase. After exiting the evaporator, the refrigerant proceeds to a compressor, then a condenser, then an expansion valve, and back to the evaporator, repeating the loop. The heat transfer fluid to be cooled (e.g. air) passes through the evaporator in a separate fluid channel and is cooled by the evaporation of the refrigerant. The heat transfer fluid can then be sent to a distribution system for cooling the spaces to be conditioned, or it can be used for other refrigeration purposes.
Other refrigeration purposes may include dehumidification. Dehumidification of air in HVAC systems can occur through the use of the evaporator in the cooling mode. One drawback to using just an evaporator for dehumidification is an excess reduction in air temperature that results, which is commonly referred to as overcooling. Overcooling occurs when air that is subject to dehumidification is cooled to a temperature that is below the desired temperature of the air. Overcooling is a particular problem when dehumidification is required in a room that is already relatively cool and does not require additional cooling. Overcooling generally involves air temperatures of approximately 50° F. to 55° F. or lower.
The problem of overcooling has been addressed in one solution by utilization of a reheat coil in one solution. Air that is overcooled by the evaporator is passed over the reheat coil in order to increase the temperature of the overcooled, dehumidified air to a desired temperature. The reheat coil can be heated by diverting hot refrigerant through the reheat coil when dehumidification is required. Reheat may also be provided by alternate heat sources, such as electric heat or gas heat. The reheat coil system for providing heat to the dehumidified, overcooled air has several drawbacks including the requirement of additional equipment and/or piping and/or additional energy input.
Another dehumidification method known in the art is disclosed in U.S. Pat. No. 4,182,133 (the '133 patent). The '133 patent is directed to a dehumidification method that controls refrigerant flow through circuits within the indoor coil of an air conditioning/heat pump unit. The '133 patent system, when providing dehumidification, has a header that distributes the refrigerant across several circuits within the indoor coil. At the opposite end of the indoor coil, the outlets of the various circuits of the coil are allowed to flow into a single common vapor header. The header at the inlet of the indoor coil contains a solenoid valve that may be closed to prevent refrigerant flow to one or more of the circuits within the coil. The '133 patent system operates such that when humidity reaches a certain level, the valve in the inlet header is closed in order to limit the number of available circuits for refrigerant flow. The area of the indoor coil that remains in the active circuit and receives refrigerant flow, experiences an increase in refrigerant flow through a given heat transfer area. The increased flow of refrigerant results in a greater amount of moisture being removed from the air in that portion of the indoor coil. One drawback of the '133 patent system is that the dehumidified air is not reheated and may be overcooled. Another drawback of the '133 patent system is that the inlet header does not distribute flow across the circuits of the evaporator, leading to uneven phase distribution of refrigerant across the evaporator heat exchanger. Another drawback of the '133 patent system is that it is nearly impossible for a properly functioning system to deliver supply air that has not been sensibly cooled.
One type of HVAC system is a split system where there is an indoor unit or heat exchanger, which is generally the evaporator, and an outdoor unit or heat exchanger, which is generally the condenser. Often, the outdoor unit is placed outdoors and is subject to outdoor ambient conditions, particularly temperature. When the outdoor ambient temperature falls, the amount of heat being removed from the refrigerant in the condenser increases. The increased heat removal in the condenser can result in a decrease in the refrigerant pressure at the suction line to the compressor, commonly referred to as head pressure. The decrease in head pressure results in a lowering of the temperature of the refrigerant at the evaporator. When the temperature of the refrigerant at the evaporator becomes too low, icing of the evaporator can occur. Icing is a condition when the temperature at the exterior of the system is sufficiently low to freeze water present in the atmosphere. The ice formed by the water frozen on the surface reduces the available heat transfer surface and eventually prevents the proper operation of the HVAC system by inhibiting heat transfer and/or damaging system components.
Some attempts to address the problem of icing have utilized the control of system pressure. In one approach, a variable speed condenser fan or a plurality of condenser fans having independent controls are used to control airflow over the condenser coil. As the amount of air passing over the coil decreases, the amount of heat transfer taking place at the coil decreases. Therefore, the temperature of the refrigerant in the condenser and the pressure of the system increase to allow the indoor coil to cool the air without icing problems. The use of the variable speed condenser fan or a plurality of condenser fans having independent controls has the drawback that it is expensive and requires complicated wiring and controls.
An alternate approach for the problem of low system pressure or icing is a parallel set of condensers in the refrigerant cycle, as described in U.S. Pat. No. 3,631,686 (the '686 patent). In the '686 patent system a parallel set of refrigerant condensers allows for two modes of operation. One mode of operation allows refrigerant to flow from only one of the refrigerant condensers. During this mode of operation, the condenser that does not permit the flow of refrigerant fills with liquid refrigerant. Because of this flooding, there is a reduction in the effective surface area of the condenser. The reduced surface area thereby reduces the ability of the condenser to remove heat from the refrigerant. Therefore, the temperature of the refrigerant in the condenser and the head pressure of the system increase, allowing the indoor coil to cool the air without icing. The use of parallel refrigerant condensers has the drawback that it requires an additional condenser coil and additional piping, thereby increasing the space and cost required for installation. Another drawback associated with refrigerant flooding of the condenser coil is the resultant decrease in system capacity. Refrigerant normally available in a properly operating system is trapped in the condenser coil and not available to the compressor, thereby decreasing system capacity.
Therefore, what is needed is a method and system for dehumidification that dehumidifies air without overcooling, provides control of the refrigerant pressure and provides a system that can be retrofitted into existing systems without the drawbacks discussed above.
SUMMARY OF THE INVENTION The present invention is directed to a method for dehumidification and controlling system pressure in a refrigeration system. The method comprises the step of providing a refrigeration system having a compressor, a condenser and an evaporator connected in a closed refrigerant loop. Each of the condenser and evaporator have a plurality of refrigerant circuits. A first heat transfer fluid is flowed over the condenser. A second heat transfer fluid is flowed over the evaporator. The flow of refrigerant is controlled in the refrigerant circuits in the condenser to control the amount of heat transfer between refrigerant in the condenser and the first heat transfer fluid. The flow of refrigerant is controlled in the refrigerant circuits in the evaporator to control an amount of heat transfer between refrigerant in the evaporator and the second heat transfer fluid. At least one of the refrigerant circuits of the condenser is isolated to provide a decreased amount of heat transfer area within the condenser and to increase the refrigerant pressure within the refrigeration system when the refrigerant pressure within the refrigeration system is at or below a predetermined pressure. At least one of the refrigerant circuits of the evaporator is isolated to dehumidify the second heat transfer fluid and maintain the temperature of the second heat transfer fluid at or above a predetermined temperature when dehumidification is required.
Another embodiment of the invention includes a method for dehumidification and controlling refrigerant pressure in a heating, ventilation and air conditioning system. The method comprises providing a closed loop refrigerant system comprising a compressor, a condenser and an evaporator. Each of the condenser and evaporator having a plurality of refrigerant circuits configured and disposed to allow isolation of at least one of the refrigerant circuits from refrigerant flow. Pressure is measured at a predetermined location in the refrigeration system. An operational mode is determined for the refrigeration cycle. The operational mode is selected from the group consisting of cooling and dehumidification. At least one of the refrigeration circuits in the condenser is isolated from refrigerant flow when the measured pressure at the predetermined location is equal to or less than a predetermined pressure. A first set of refrigerant circuits in the evaporator is isolated from flow of refrigerant from the condenser when the operational mode is dehumidification. Flow of refrigerant is permitted from the condenser to both the first and second set of refrigerant circuits in the evaporator when the operational mode is cooling. The refrigerant pressure is increased by isolation of at least one of the refrigerant circuits in the condenser from refrigerant flow until the measured pressure is greater than the predetermined pressure.
Another embodiment of the invention includes a heating, ventilation and air conditioning system. The system comprises a compressor, a condenser arrangement and an evaporator arrangement. The condenser arrangement comprises a plurality of circuits arranged into a first and second set of circuits, and a valve arrangement configured and disposed to isolate the first set of circuits of the condenser arrangement when the refrigerant pressure is below a predetermined pressure. The evaporator arrangement comprises a plurality of circuits arranged into a first and second set of circuits, at least one distributor configured to distribute and deliver refrigerant to each circuit of the plurality of circuits in the evaporator, and a valve arrangement configured and disposed to isolate the first set of circuits of the evaporator arrangement from refrigerant flow in a dehumidification operation of the HVAC system.
The present invention provides an inexpensive method and system to control head pressure, while also being capable of reheating dehumidified air. The method and system requires little or no additional piping in order to implement the method and system in an existing HVAC unit. The system requires less in materials and therefore costs less than systems having separate components, such as separate reheat coils.
Another advantage of the present invention is that the air conditioning or heat pump unit can operate at lower outdoor ambient temperatures by providing an increase in system pressure to avoid icing of the system components.
Another advantage of the present invention is that the system and method distributes refrigerant substantially uniformly across the evaporator to provide substantially uniform refrigerant phase distribution and heat exchange across the evaporator.
Another advantage of the present invention is that the system can reheat air and control head pressure without the need for a separate airflow system.
Another advantage of the system is that the simultaneous control of the head pressure of the system and reheating of the air during dehumidification permits the system to be operated in a manner that increases the efficiency and reliability of the system, while maintaining greater control of the temperature and humidity of the conditioned air.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 schematically illustrates a refrigeration or HVAC system.
FIG. 2 schematically illustrates one embodiment of an evaporator and piping arrangement of the present invention.
FIG. 3 schematically illustrates another embodiment of an evaporator and piping arrangement of the present invention.
FIG. 4 schematically illustrates further embodiment of an evaporator and piping arrangement of the present invention.
FIG. 5 schematically illustrates one embodiment of a condenser and piping arrangement of the present invention.
FIG. 6 schematically illustrates another embodiment of a condenser and piping arrangement of the present invention.
FIG. 7 schematically illustrates one embodiment of a refrigeration or HVAC system according to the present invention.
FIG. 8 schematically illustrates another embodiment of a refrigeration or HVAC system according to the present invention.
FIG. 9 schematically illustrates a refrigeration or HVAC system of another embodiment of the present invention.
FIG. 10 schematically illustrates a refrigeration or HVAC system of a further embodiment of the present invention.
FIG. 11 illustrates a control method of the present invention.
FIG. 12 illustrates a control method of another embodiment of the present invention.
FIG. 13 illustrates a control method of a further embodiment of the present invention.
FIG. 14 illustrates a control method of a further embodiment of the present invention.
FIG. 15 illustrates a control method of a further embodiment of the present invention.
FIG. 16 illustrates a control method of a further embodiment of the present invention.
Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.
DETAILED DESCRIPTION OF THE INVENTION FIG. 1 illustrates a HVAC, refrigeration, or chiller system 100. Refrigeration system 100 includes a compressor 130, a condenser 120, and an evaporator 110. The compressor 130 compresses a refrigerant vapor and delivers it to the condenser 120 through compressor discharge line 135. The compressor 130 is preferably a reciprocating or scroll compressor, however, any other suitable type of compressor can be used, for example, screw compressor, rotary compressor, and centrifugal compressor. The refrigerant vapor delivered by the compressor 130 to the condenser 120 enters into a heat exchange relationship with a first heat transfer fluid 150, preferably air, and undergoes a phase change to a refrigerant liquid as a result of the heat exchange relationship with the first heat transfer fluid 150. The first heat transfer fluid 150 is moved by use of a fan 170, which moves the first heat transfer fluid 150 through the condenser 120 in a direction perpendicular the cross section of the condenser 120. In a preferred embodiment, the refrigerant vapor delivered to the condenser 120 enters into a heat exchange relationship with air as the first heat transfer fluid 150. The refrigerant leaves the condenser through the condenser discharge line 140 and is delivered to an evaporator 110 after passing through an expansion device (not shown). The evaporator 110 includes a heat-exchanger coil. The liquid refrigerant in the evaporator 110 enters into a heat exchange relationship with a second heat transfer fluid 155 to lower the temperature of the second heat transfer fluid 155. The second heat transfer fluid 155, preferably air, is moved by use of a blower 160, which moves the second heat transfer fluid 155 through evaporator 110 in a direction perpendicular the cross section of the evaporator 110. Although FIG. 1 depicts the use of a blower 160 and fan 170, any fluid moving means may be used to move fluid through the evaporator and condenser 120. In a preferred embodiment, the refrigerant vapor delivered to the evaporator 110 enters into a heat exchange relationship with air as the second heat transfer fluid 155. The refrigerant liquid in the evaporator 110 undergoes a phase change to a refrigerant vapor as a result of the heat exchange relationship with the second heat transfer fluid 155. The vapor refrigerant in the evaporator 110 exits the evaporator 110 and returns to the compressor 130 through a suction line 145 to complete the cycle. The conventional refrigerant system 100 includes many other features that are not shown in FIG. 1. These features have been purposely omitted to simplify the figure for ease of illustration.
FIG. 2 illustrates a partitioned evaporator 200 according to one embodiment of the present invention. The inlet of the partitioned evaporator 200 includes a condenser discharge line 140 from the partitioned condenser 500 (see FIG. 7), a first and second thermostatic expansion valve (TXV valve) 260 and 265, an isolation valve 250, and a first and second distributor 240 and 245. Although FIGS. 2-4 and 7-9 illustrate TXV valves, any suitable pressure reduction or expansion device may be used to control refrigerant flow, such as a fixed orifice. The first TXV valve 260 and the isolation valve 250 are positioned between condenser discharge line 140 and the first distributor 240. The second TXV valve 265 is positioned between the condenser discharge line 140 and the second distributor 245. The partitioned evaporator 200 includes refrigerant circuits 210. Although refrigerant circuits 210 are shown as curved lines in FIGS. 2-4, the shape shown is merely schematic and any suitable configuration of refrigerant circuit 210 can be used. Refrigerant circuits 210 can include any configuration of device capable of transferring heat. An example of a suitable device includes a finned tube. The number of refrigerant circuits 210 may be any number of refrigerant circuits 210 that provide sufficient heat transfer to maintain operation of the partitioned evaporator 200 within the refrigeration system 100. The partitioned evaporator 200 is preferably partitioned into a first and second evaporator portions 220 and 230. The first and second evaporator portion 220 and 230 may be sized in any proportion. For example, the first evaporator portion 220 may be 60% of the size of the partitioned evaporator 200 and the second evaporator portion 230 may be 40% of the size of the partitioned evaporator 200 or the first evaporator portion 220 may be 40% of the size of the partitioned evaporator 200 and the second evaporator portion 230 may be 60% of the size of the partitioned evaporator 200 or the first and second evaporator portions 220 and 230 may each represent 50% of the size of the partitioned evaporator 200.
Although FIG. 2 shows the partitioned evaporator 200 as only including two portions, any number of portions may be used in the present invention. Where more than two evaporator portions are present, the flow may be regulated to each of the portions. For example, in the embodiment where the evaporator is split into three portions, two of the three portions include valve arrangements that allow independent isolation of each of these portions. One or both of the two portions with valve arrangements may be isolated, dependent on a signal from a controller and/or sensor. The outlet of the partitioned evaporator 200 includes first and second discharge headers 270 and 275, first and second thermostatic expansion valve bulbs (TXV bulbs) 264 and 269, and an evaporator discharge line 145 to the compressor 130. The first discharge header 270 receives refrigerant from the refrigerant circuits 210 in the first evaporator portion 220. The second discharge header 275 receives refrigerant from the refrigerant circuits 210 present in the second evaporator portion 230. The first TXV bulb 264 is positioned between the first discharge header 270 and the evaporator discharge line 145. The first TXV bulb 264 senses the temperature of the refrigerant leaving the first discharge header 270 and compares the temperature of the refrigerant to the temperature of the refrigerant at the first TXV valve 260 through line 262. The flow of refrigerant through the first TXV valve 260 is increased as the temperature difference at the first TXV bulb 264 and the first TXV valve 260 increases. The flow of refrigerant through the first TXV valve 260 is decreased as the temperature difference at the first TXV bulb 264 and the first TXV valve 260 decreases. The second TXV valve 265 operates in the same manner with respect to the refrigerant discharge from the second discharge header 275 and communicates the temperature measurement to the second TXV valve 265 through line 267. The isolation valve 250 allows the first evaporator portion 220 of the partitioned evaporator 200 to be isolated from flow of refrigerant. In one embodiment, to accommodate an increased flow of refrigerant to the second evaporator portion 230, as discussed in detail below, the size of the second TXV valve 265 (i.e., the amount of flow permitted through the valve) is greater than the size of the first TXV valve 260.
During operation of the refrigeration system 100 in cooling mode, refrigerant flows from the partitioned condenser 500 to the partitioned evaporator 200 through condenser discharge line 140. The flow is split into two refrigerant flow paths prior to entering the partitioned evaporator 200. Although FIG. 2 shows two paths leading to the first and second distributors 240 and 245, the refrigerant flow may be split into two or more paths. If the system is in a cooling only mode, isolation valve 250 is open and refrigerant is permitted to flow into both the first and second evaporator portions 220 and 230 of the partitioned evaporator 200. The two refrigerant flow paths are further split by a first and second distributor 240 and 245 into a plurality of lines, corresponding to the individual refrigerant circuits 210. The first and second distributors 240 and 245 may include any arrangement that distributes the refrigerant to the individual refrigerant circuits 210 within the partitioned evaporator 200. The first and second distributors 240 and 245 can preferably distribute the refrigerant to provide uniform phase distribution across the refrigerant circuits 210 of the partitioned evaporator 200 and, thus, provide substantially uniform heat transfer. The first and second distributors 240 and 245 also may include combinations of distributor tubes and orifices to provide the uniform refrigerant flow. The refrigerant flows into the refrigerant circuits 210 of first and second evaporator portions 220 and 230. The refrigerant circuits 210 permit the refrigerant to enter into a heat transfer relationship with the second heat transfer fluid 155 to cool the second heat transfer fluid 155. Due to the heat transfer with the second heat transfer fluid 155, the refrigerant entering the first and second discharge headers 270 and 275 has a higher temperature than the temperature of the refrigerant entering the partitioned evaporator 200. The refrigerant then travels from the first and second discharge headers 270 and 275 past the first and second TXV bulbs 264 and 269. The TXV bulbs 264 and 269 sense the temperature of the refrigerant leaving the partitioned evaporator 200 and communicate the temperature to the first and second TXV valves 260 and 265 in order to determine the appropriate refrigerant flow into the partitioned evaporator 200. After traveling past the first and second TXV bulbs 264 and 269, the refrigerant is delivered to the compressor 130 through evaporator discharge line 145.
If the system shown in FIG. 2 is operated in a dehumidification mode, isolation valve 250 is closed and refrigerant flow to the first evaporator portion 220 is prevented. The refrigerant flow in the second evaporator portion 230 occurs substantially as described above with respect to evaporator portion 220 in cooling mode. However, the flow of refrigerant to the first evaporator portion 220 is prevented. Since flow to the first evaporator portion 220 is prevented, the flow to the second evaporator portion 230 is increased. Due to the increased flow of the refrigerant through the second evaporator portion 230, the amount of heat transfer per unit area is increased and the dehumidification per unit area is likewise increased. Therefore, when the second heat transfer fluid 155 is passed through the second evaporator portion 230 the second heat transfer fluid 155 is cooled and dehumidified, and the second heat transfer fluid 155 passing through the first evaporator portion 220 remains substantially unchanged in temperature and humidity from inlet to outlet. The second heat transfer fluid 155 passed through the second evaporator portion 230 is generally overcooled and the second heat transfer fluid 155 passed through the first evaporator portion 220 is about ambient temperature. The ambient second heat transfer fluid 155 that passes though the first evaporator portion 220 mixes with the second heat transfer fluid 155 passing through the second evaporator portion 230 and produces an outlet heat transfer fluid, preferably air, that is dehumidified and not overcooled. As shown in FIG. 2, the flow of the second heat transfer fluid 155 is substantially perpendicular to the cross-section of the evaporator. The direction of the flow is such that the heat transfer fluid 155 flows simultaneously through first evaporator portion 220 and second evaporator portion 230. A single system for moving the second heat transfer fluid 155, such as an air blower 160, can be used to simultaneously move air through first evaporator portion 220 and second evaporator portion 230.
FIG. 3 illustrates a partitioned evaporator 200 according to another embodiment of the present invention. The inlet of the partitioned evaporator 200 includes substantially the same arrangement of components as FIG. 2, including a condenser discharge line 140 from the partitioned condenser 500, first and second TXV valves 260 and 265, and first and second distributors 240 and 245. FIG. 3 further includes check valve 255 that prevents flow of refrigerant into evaporator portion 220 and allows flow of refrigerant out of evaporator portion 220. The partitioned evaporator 200 includes substantially the same arrangement of refrigerant circuits 210 as FIG. 2. The outlet of the partitioned evaporator 200 shown in FIG. 3 includes the first and second discharge headers 270 and 275, first and second TXV bulbs 264 and 269, an evaporator discharge line 145 to the compressor 130 and a first discharge header discharge line 310 to a 3-way valve 910 (see FIG. 8). The first discharge header 270 receives refrigerant from the refrigerant circuits 210 present in the first evaporator portion 220. The second discharge header 275 receives refrigerant from the circuits 210 present in the second evaporator portion 230. The first TXV bulb 264 is positioned on the first discharge header discharge line 310. The first TXV bulb 264 senses the temperature of the refrigerant leaving the first discharge header 270 and compares the temperature of the refrigerant to the temperature of the refrigerant at the first TXV valve 260 through line 262. The flow of refrigerant through the first TXV valve 260 is increased as the temperature difference at the first TXV bulb 264 and the first TXV valve 260 increases. The flow of refrigerant through the first TXV valve 260 is decreased as the temperature difference at the first TXV bulb 264 and the first TXV valve 260 decreases. The second TXV valve 265 operates in the same manner with respect to the refrigerant discharge from the second discharge header 275 and communicates the temperature measurement to the second TXV valve 265 through line 267. The use of independent first and second TXV valves 260 and 265 allows independent control of the flow through each of the portions of the partitioned evaporator 200.
During operation in cooling mode, FIG. 3, like in the system shown in FIG. 2, refrigerant flows from the partitioned condenser 500 into the partitioned evaporator 200 through condenser discharge line 140, through the valve arrangement, including the first and second TXV valves 260 and 265, and into the first and second distributors 240 and 245. The refrigerant circuits 210 permit the refrigerant to enter into a heat transfer relationship with the second heat transfer fluid 155 that flows through the circuits perpendicular to the cross-section shown in FIG. 3. Due to the heat transfer with the second heat transfer fluid 155, the refrigerant entering the first and second discharge headers 270 and 275 has a higher temperature than the temperature of the refrigerant entering the partitioned evaporator 200. The refrigerant flow through discharge line 310 from the first discharge header 270 travels past the first TXV bulb 264 and travels to a 3-way valve 910, discussed in greater detail below. The refrigerant flow through evaporator discharge line 145 from the second discharge header 275 travels past the second TXV bulb 269 to the compressor 130.
During dehumidification mode, refrigerant flow in the first evaporator portion 220 is received from the 3-way valve 910 through the discharge line 310, as discussed in greater detail below. The flow from the 3-way valve 910 is hot refrigerant gas taken from the compressor discharge. The flow from the 3-way valve 910 travels through the discharge line 310 in the direction of the first discharge header 270. From the first discharge header 270, the hot refrigerant gas enters the first evaporator portion 220 and travels through circuits 210 to the first distributor 240. The refrigerant in refrigerant circuits 210 of the first evaporator portion 220 can heat the second heat transfer fluid 155 as the fluid passes over the refrigerant circuits 210. The hot refrigerant gas is at least partially condensed to a liquid in the first evaporator portion 220. The refrigerant, which is at least partially condensed to a liquid, then bypasses the TXV valve 260 by traveling through check valve 255. The flow through check valve 255 combines with the condenser discharge line 140 and enters the second evaporator portion 230 through the second distributor 245. Due to the increased flow of the refrigerant through the second evaporator portion 230, the amount of heat transfer per unit area is increased and the dehumidification per unit area is likewise increased. Simultaneously, hot gas refrigerant entering the first evaporator portion 220 of the partitioned evaporator 200 provides an increase in the temperature of the first evaporator portion 220 due to the at least partial condensing of the hot gas. Therefore, the second heat transfer fluid 155 passing through the second evaporator portion 230 is cooled and dehumidified, while the second heat transfer fluid 155 passing through the first evaporator portion 220 is heated by the hot gas refrigerant from the compressor discharge. This second heat transfer fluid 155 simultaneously is circulated through first and second evaporator portions 220 and 230 by a fluid moving system, such as an air blower 160, when the second heat transfer fluid 155 is air. The warmer second heat transfer fluid 155 that passes though the first evaporator portion 220 mixes with the second heat transfer fluid 155 passing through the second evaporator portion 230 and produces an outlet heat transfer fluid, preferably air, that is dehumidified and not overcooled.
FIG. 4 illustrates a partitioned evaporator 200 according to a further embodiment of the present invention. The inlet of the partitioned evaporator 200 includes a condenser discharge line 140 from the partitioned condenser 500, a bypass line 410 (see FIG. 9) from the discharge of the compressor 130, first and second TXV valves 260 and 265, isolation valve 250, and first and second distributors 240 and 245. The first TXV valve 260 and the isolation valve 250 are positioned between condenser discharge line 140 and the first distributor 240. The bypass line 410 connects to the line between the first TXV valve 260 and the first distributor 240. Bypass line 410 is from the discharge of the compressor 130 and includes a flow restriction valve 430 and a bypass valve 440. While FIG. 4 shows both a flow restriction valve 430 and a bypass valve 440, either one or both of valves 430 and 440 may be present. The isolation valve 250 is positioned between the condenser discharge line 140 and the first TXV valve 260. The second TXV valve 265 is positioned between the condenser discharge line 140 and the second distributor 245. The partitioned evaporator 200 includes substantially the same arrangement of refrigerant circuits 210 as shown in FIG. 2. The outlet of the partitioned evaporator 200 includes first and second discharge headers 270 and 275, first and second TXV bulbs 264 and 269, and evaporator discharge line 145 to the compressor 130. The first discharge header 270 receives refrigerant from the refrigerant circuits 210 present in the first evaporator portion 220. The second discharge header 275 receives refrigerant from the refrigerant circuits 210 present in the second evaporator portion 230. The first TXV bulb 264 is positioned between the first discharge header 270 and the evaporator discharge line 145. The first TXV bulb 264 senses the temperature of the refrigerant leaving the first discharge header 270 and compares the temperature of the refrigerant to the temperature of the refrigerant at the first TXV valve 260 through line 262. The flow of refrigerant through the first TXV valve 260 is increased as the temperature difference at the first TXV bulb 264 and the first TXV valve 260 increases. The flow of refrigerant through the first TXV valve 260 is decreased as the temperature difference at the first TXV bulb 264 and the first TXV valve 260 decreases. The second TXV valve 265 operates in the same manner with respect to the refrigerant discharge from the second discharge header 275 and communicates the temperature measurement to the second TXV valve 265 through line 267. The isolation valve 250 allows the first evaporator portion 220 of the partitioned evaporator 200 to be isolated from flow of refrigerant. In one embodiment, to accommodate the increased flow of refrigerant to the second evaporator portion 230, the size of the second TXV valve 265 (i.e., the amount of flow permitted through the valve) is greater than the size of the first TXV valve 260.
During operation in cooling mode, FIG. 4, like in the system shown in FIG. 2, refrigerant flows from the partitioned condenser 500 into the refrigerant circuits 210 of the partitioned evaporator 200 through the condenser discharge line 140, through the valve arrangement, including the first and second TXV valves 260 and 265, and the isolation valve 250, and into the first and second distributors 240 and 245. In cooling mode, substantially no flow of refrigerant takes place into or out of the bypass line 410 because the bypass valve 440 is closed. The operation of the refrigerant circuits 210 and the outlet of the partitioned evaporator 200, including the first and second headers 270 and 275, the first and second TXV bulbs 264 and 269 and the evaporator discharge line 145 to the compressor is substantially similar to the operation described above with respect to FIG. 2.
However, if the system shown in FIG. 4 is in dehumidification mode, isolation valve 250 is closed and refrigerant flow to the first TXV valve 260 is prevented. Refrigerant flow from the discharge of the compressor 130 through bypass line 410 flows into the first distributor 240 and into the first evaporator portion 220. The hot gas refrigerant entering the first evaporator portion 220 of the partitioned evaporator 200 provides an increase in the temperature of the first evaporator portion 220. Due to the increased flow of the refrigerant through the second evaporator portion 230 by closing isolation valve 250, the amount of heat transfer per unit area is increased and the dehumidification per unit area is likewise increased. Therefore, the second heat transfer fluid 155 passing through the second evaporator portion 230 is cooled and dehumidified, while the second heat transfer fluid 155 passing through the first evaporator portion 220 is warmed by the hot gas refrigerant from the compressor discharge. The second heat transfer fluid 155 simultaneously is circulated through first and second evaporator portions 220 and 230 by a fluid moving system, such as a blower 160. The warmer second heat transfer fluid 155 that passes though the first evaporator portion 220 mixes with the second heat transfer fluid 155 passing through the second evaporator portion 230 and produces an outlet heat transfer fluid, preferably air, that is dehumidified and not overcooled.
Although the partitioned evaporator 200 has been illustrated as containing two evaporator portions 220 and 230, the partitioned evaporator 200 is not limited to two portions. Any number of portions may be used, so long as one or more of the portions includes valving to isolate the respective portion from refrigerant flow.
In another embodiment, refrigerant circuits 210 may also be isolated individually within the first and/or second distributor. The refrigerant circuits 210 may be isolated with flow blocking means or flow restriction means on first and second distributors 240 and 245. In this embodiment, a controller is used to determine the number of circuits isolated. The number of refrigerant circuits 210 isolated relates to the amount of cooling and/or heating of dehumidified air required and may be adjusted by the controller.
FIG. 5 illustrates a partitioned condenser 500 according to one embodiment of the invention. Partitioned condenser 500 includes a plurality of heat transfer circuits 510. The heat transfer circuits 510 are preferably partitioned into a first condenser portion 520 and a second condenser portion 530. Although heat transfer circuits 510 in the partitioned condenser 500 are shown as lines in FIGS. 5-6, the shape shown is merely schematic. Heat transfer circuits 510 are preferably of any suitable configuration capable of transferring heat. An example of a suitable device includes a finned tube. The first and second condenser portions 520 and 530 may be sized in any proportion. For example, the first condenser portion 520 may be 60% of the size of the partitioned condenser 500 and the second condenser portion 530 may be 40% of the size of the partitioned condenser 500 or the first condenser portion 520 may be 40% of the size of the partitioned condenser 500 and the second condenser portion 530 may be 60% of the size of the partitioned condenser 500 or the first and second condenser portions 520 and 530 may each represent 50% of the size of the partitioned condenser 500. When the first and second condenser portions 520 and 530 are different sizes, e.g., 60%/40% split, the refrigerant flow may be directed in any manner that provides efficient condenser 500 operation. For example, the first condenser portion 520 may constitute 60% of the size of the partitioned condenser 500 and the second condenser portion 530 may constitute 40% of the partitioned condenser 500. When desirable, the flow may be directed to either the 60% portion or the 40% portion and the designation of the first and second condenser portions 520 and 530 may be alternated to the isolated portion that provides the desired condenser 500 operation.
Inlet flow 550 includes vaporous refrigerant from the compressor 130. Inlet flow 550 enters the partitioned condenser 500 and travels through the heat transfer circuits 510, where the heat transfer circuits 510 can enter into a heat exchange relationship with a heat transfer fluid such as air. The partitioned condenser 500 preferably has two condenser portions; however, the present invention is not limited to two condenser portions. The present invention may include more than two condenser portions. Where more than two condenser portions are present, the flow may be regulated to each of the portions. For example, in an embodiment where the condenser is split into three portions, two of the three portions include valve arrangements that allow independent isolation of each of these portions. One or both of the two portions with valve arrangements may be isolated, dependent on a signal from a controller and/or sensor. In FIG. 5, isolation valves 540 are positioned in the vapor header 590 and liquid header 592 of the partitioned condenser 500. When isolation valves 540 are closed, the refrigerant is prevented from flowing into the second condenser portion 530. When isolation valves 540 are open, refrigerant is permitted to flow to both the first condenser portion 520 and the second condenser portion 530. The outlet flow 560 leaving the partitioned condenser 500 comprises liquid refrigerant resulting from the heat exchange relationship with the heat transfer fluid and the resultant phase change. The outlet flow 560 is then circulated to the partitioned evaporator 200.
FIG. 6 illustrates a partitioned condenser 500 according to an alternate embodiment of the invention. Partitioned condenser 500 includes a plurality of heat transfer circuits 510. The heat transfer circuits 510 are partitioned into a first condenser portion 520 and a second condenser portion 530. Although FIG. 6 shows two condenser portions, the present invention is not limited to two condenser portions. The present invention may include more than two condenser portions. Inlet flow 550 is vaporous refrigerant from the compressor 130 that is split into two refrigerant streams. The two refrigerant streams enter the partitioned condenser 500 through two vapor headers 593 and 594 and travel into the heat transfer circuits 510. Heat transfer circuits 510 can enter into a heat exchange relationship with a heat transfer fluid such as air. The two refrigerant streams then exit the partitioned condenser 500 through two liquid headers 595 and 596. Isolation valves 540 are positioned on the piping to the vapor header 594 and on the piping from the liquid header 596 of the partitioned condenser 500. When isolation valves 540 are closed, the refrigerant is prevented from flowing into the second condenser portion 530. When isolation valves 540 are open, refrigerant is permitted to flow to both the first condenser portion 520 and the second condenser portion 530. The outlet flow 560 leaving the partitioned condenser 500 includes liquid refrigerant that is circulated to the partitioned evaporator 200.
The system for controlling the refrigerant pressure of an air conditioning or heat pump unit according to the present invention includes an HVAC unit that can operate at lower ambient temperatures. The present invention involves a piping arrangement that partitions the circuits within the condenser of a refrigeration system. The piping arrangement includes valves positioned so that one or more of the circuits within the condenser may be isolated from flow of refrigerant. The piping arrangement may be applied to a new system or may be applied to an existing system. Applying the piping arrangement to the existing system has the advantage that it allows control of the refrigerant pressure without the addition of expensive piping, equipment and/or controls.
When the temperature around the partitioned condenser 500 decreases (e.g., when the outdoor temperature decreases), the system refrigerant pressure also decreases. To help increase refrigerant head pressure, the present invention uses the valves connected to the refrigerant circuits 510 of the partitioned condenser 500 to isolate a portion of the partitioned condenser 500 from flow of refrigerant. The portion of the partitioned condenser 500 that is not isolated remains in the active circuit and receives refrigerant. Because the refrigerant is only permitted to flow into a portion of the partitioned condenser 500, the heat transfer area and the corresponding amount of heat transfer is reduced. Therefore, less heat is removed from the refrigerant. Likewise, less heat is transferred to the first heat transfer fluid 150, thereby maintaining a higher refrigerant temperature. Additionally, because the temperature of the refrigerant is higher, the corresponding pressure of the refrigerant is also higher. Therefore, the refrigerant pressure of the system is increased.
The piping arrangement of the partitioned condenser 500 of the present invention includes piping sufficient to isolate the one or more heat transfer circuits 510 within the condenser. In one embodiment, the isolation valves 540 are positioned inside the vapor header 590 of the partitioned condenser 500. In an alternate embodiment, the isolation valves 540 are positioned on piping upstream from the vapor headers 594 of the partitioned condenser 500.
The lack of additional piping for both the partitioned evaporator 200 and the partitioned condenser 500 also allows retrofitting of the system of the present invention into existing systems. Because the system utilizes the same components as existing systems, the system takes up approximately the same volume as existing HVAC systems. Therefore, the method and system of the present invention may be used in existing systems whose piping is arranged according to the present invention.
FIG. 7 shows a refrigeration system 100 incorporating a partitioned evaporator 200 and a partitioned condenser 500 according to the present invention. FIG. 7 shows the refrigeration system 100, including evaporator discharge line 145, blower 160, compressor 130, compressor discharge line 135, partitioned condenser 500, fan 170, condenser discharge line 140, and first heat transfer fluid 150, substantially as described above in the description of FIG. 1. FIG. 7 also shows the partitioned evaporator 200, including first and second TXV valves 260 and 265, isolation valve 250, check valve 255, first and second distributors 240 and 245, first and second discharge headers 270 and 275, arranged as discussed above in the description of FIG. 2. For illustration purposes, FIGS. 7-10 divides second heat transfer fluid 155 flow into an inlet flow 710 and an outlet flow 715. The inlet flow 710, preferably air, flows into the partitioned evaporator 200 substantially evenly across the first and second evaporator portions 220 and 230. Blower 160 moves inlet flow 710. Although FIG. 7 depicts a blower, any fluid moving means is suitable for moving the fluid across the first and second evaporator portions 220 and 230. The heat transfer fluid enters into a heat exchange relationship with the first and second evaporator portions 220 and 230 and exits the partitioned evaporator as outlet flow 715. During cooling mode, refrigerant is circulated from the partitioned condenser 500 to the partitioned evaporator 200, through the first and second evaporator portions 220 and 230 and to the compressor 130 through evaporator discharge line 145. The inlet flow 710 of heat transfer fluid is cooled by both the first and second evaporator portions 220 and 230, providing outlet flow 715 of heat transfer fluid that has been cooled. During dehumidification mode, isolation valve 250 is closed, preventing flow of refrigerant into the first evaporator portion 220. The inlet flow 710 is cooled and dehumidified by the second evaporator portion 230 and is substantially untreated by the isolated first evaporator portion 220. The outlet flow 715 is a mixture of the cooled, dehumidified air that flowed through the second evaporator portion 230 and the substantially untreated air that flowed though the first evaporator portion 220. The resultant outlet flow 715 is dehumidified air that is not overcooled.
The partitioned condenser 500 shown in FIG. 7 is a partitioned condenser having two partitions, shown as the first and second condenser portions 520 and 530. Although FIG. 7 shows two condenser portions, the present invention is not limited to two condenser portions. The present invention may include more than two condenser portions. The piping to the partitioned condenser 500 includes isolation valves 540 on the inlet side and the outlet side of the second condenser portion 530 inside the partitioned condenser 500. Closing the isolation valves 540 prevents the flow of refrigerant to the second condenser portion 530. The isolation valves 540 may be operated by a controller 720. One or more controllers 720 facilitates the closing of isolation valves 540. The controller 720 may receive inputs from pressure measuring or temperature measuring devices and position the isolation valves 540, e.g., open or closed. When the pressure on the compressor suction line 145 from the partitioned evaporator 200 to the compressor 130 reaches a predetermined level, the isolation valves 540 can be closed to the second condenser portion 530. Once isolation valves 540 are closed, the refrigerant is only permitted to flow through the first condenser portion 520. Because the refrigerant is only permitted to flow into first condenser portion 520, the heat transfer area and the corresponding amount of heat transfer occurring in the partitioned condenser 500 is reduced. Therefore, less heat is removed from the refrigerant. Likewise, less heat is transferred to the first heat transfer fluid 150, thereby maintaining a higher refrigerant temperature. Additionally, because the temperature of the refrigerant is higher, the corresponding pressure of the refrigerant is also higher. Therefore, the refrigerant pressure of the system is increased.
FIG. 8 shows a refrigeration system according to an alternate embodiment. FIG. 8 includes substantially the same piping arrangement as FIG. 7. In addition, FIG. 8 has a line with a drain valve connecting the condenser portion 530 to the suction of compressor 130. The refrigerant remaining in the second condenser portion 530 after isolation valves 540 are closed may be stored in the second condenser portion 530 or may be drawn into the refrigeration system 100 by opening drain valve 840 and permitting the refrigerant in condenser portion 530 to be drawn into the active system. Because the refrigerant from the isolated portion of the partitioned condenser 500 adds to the amount of refrigerant per unit volume of the refrigeration system 100, the pressure of the refrigerant in increased. Therefore, this addition of refrigerant into the system from the isolated portion of the partitioned condenser 500 further assists in raising the system pressure.
FIG. 9 shows a refrigeration system 100 incorporating a partitioned evaporator 200 and a partitioned condenser 500 according to the present invention. FIG. 9 shows the refrigeration system including evaporator discharge line 145, blower 160, compressor 130, compressor discharge line 135, partitioned condenser 500, fan 170, condenser discharge line 140, and first heat transfer fluid 150, substantially as described above in the description of FIG. 7. In addition, FIG. 9 includes a 3-way valve 910 and a discharge line 310. The 3-way valve 910 connects to the first discharge header 270 of the first evaporator portion 220, to the evaporator discharge line 145 and to the compressor discharge line 135. FIG. 9 also shows the partitioned evaporator 200 including first and second TXV valves 260 and 265, check valve 255, first and second distributors 240 and 245, first and second discharge headers 270 and 275, arranged as discussed above in the description of FIG. 3. Heat transfer fluid flow 710, preferably air, flows into the partitioned evaporator 200 substantially evenly across the first and second evaporator portions 220 and 230. A blower 160 moves heat transfer fluid flow 710. Although, FIG. 9 depicts a blower, any fluid moving system is suitable for moving the fluid across the first and second evaporator portions 220 and 230. The inlet flow 710 enters into a heat exchange relationship with the first and second evaporator portions 220 and 230 and exits the partitioned evaporator as outlet flow 715. During cooling mode, the refrigerant is circulated from the partitioned condenser 500 to the partitioned evaporator 200, through the first and second evaporator portions 220 and 230 and to the compressor through evaporator discharge line 145 and 3-way valve 910. The inlet flow 710 of heat transfer fluid is cooled by both the first and second evaporator portions 220 and 230, providing outlet flow 715 of heat transfer fluid that has been cooled. During dehumidification mode, hot gas refrigerant from the discharge of the compressor flows into the 3-way valve 910, which is opened to allow flow through the first discharge header discharge line 310 and into the first discharge header 270 of the first evaporator portion 220. One or more controllers 720 facilitate the positioning of 3-way valve 910. The controller 720 may receive inputs from pressure measuring or temperature measuring devices and position the 3-way valve 910. The hot gas refrigerant from the discharge of the compressor 130 enters the refrigerant circuits 210 of the first evaporator portion 220 and at least partially condenses to a liquid. The condensing refrigerant heats the first evaporator portion 220 and warms the inlet flow 710 to produce a higher temperature outlet flow 715. The refrigerant, which is at least partially condensed, travels through the check valve 255 and combines with line 140 into the second evaporator portion 230. The inlet flow 710 of heat transfer fluid is cooled and dehumidified by the second evaporator portion 230 and is heated by the isolated first evaporator portion 220, as the refrigerant gas is at least partially condensed. The outlet flow 715 is a mixture of the cooled, dehumidified air that flowed through the second evaporator portion 230 and the heated air that flowed though the first evaporator portion 220. To summarize, the resultant outlet flow 715 is dehumidified air that is not overcooled. In cooling mode, first evaporator portion 220 and second evaporator portion 230 of partitioned evaporator 200, act as evaporators. However, in dehumidification mode, first evaporator portion 220 acts as a condenser, while second evaporator portion 230 acts as an evaporator. The partitioned condenser 500 shown in FIG. 9 operates substantially as described above in the discussion of FIG. 7.
FIG. 10 shows a refrigeration system 100 incorporating a partitioned evaporator 200 according to the present invention. FIG. 10 further shows the refrigeration system 100 including evaporator discharge line 145, blower 160, compressor 130, compressor discharge line 135, partitioned condenser 500, fan 170, condenser discharge line 140, and first heat transfer fluid 150, substantially as described above in the description of FIG. 7. In addition, FIG. 10 includes one or both of a bypass valve 440, and a flow restriction valve 430 on bypass line 410. Bypass line 410 connects the compressor discharge line 135 of the compressor 130 to the inlet of the first evaporator portion 220 between the first TXV valve 260 and the first distributor 240. One or more controllers 720 facilitate the positioning of isolation valves 540 and of the bypass valve 440. The controller 720 may receive inputs from pressure measuring or temperature measuring devices and position the isolation valves 540 and bypass valve 440, e.g., open or closed. FIG. 10 shows the partitioned evaporator 200, including first and second TXV valves 260 and 265, isolation valve 250, first and second distributors 240 and 245, and first and second discharge headers 270 and 275, arranged as discussed above in the description of FIG. 4. Inlet flow 710, preferably air, flows into the partitioned evaporator 200 substantially evenly across the first and second portions 220 and 230. The inlet flow 710 enters into a heat exchange relationship with the first and second evaporator portions 220 and 230 and exits the partitioned evaporator as outlet flow 715. During cooling mode, the refrigerant is circulated from the partitioned condenser 500 to the partitioned evaporator 200, through the first and second evaporator portions 220 and 230 and to the compressor 130 through evaporator discharge line 145. The bypass valve 440 and the flow restriction valve 430 are set to prevent flow of refrigerant through the bypass line 410. The inlet flow 710 of heat transfer fluid is cooled by both the first and second evaporator portions 220 and 230, providing outlet flow 715 of heat transfer fluid that has been cooled. During dehumidification mode, isolation valve 250 is closed, preventing flow of refrigerant into the first evaporator portion 220. The bypass valve 440 is opened and the flow restriction valve 430 is set to allow flow of refrigerant. Although FIG. 10 is shown with both a bypass valve 440 and a flow restriction valve 430, either the bypass valve 440 or flow restriction valve 430 may be removed from the bypass line 410, so long as the flow of the refrigerant may be stopped during cooling mode and permitted during dehumidification mode. Hot gas refrigerant from the discharge of the compressor 130 is then allowed to flow from the compressor discharge line 135 through the bypass line 410 into the first distributor 240 and the first evaporator portion 220. The hot gas refrigerant from the discharge of the compressor 130 heats the first evaporator portion 220 and combines with the outlet flow from the second evaporator portion 230 into the evaporator discharge line 145. The inlet flow 710 of heat transfer fluid is cooled and dehumidified by the second evaporator portion 230 and is heated by the hot gas from the discharge of the compressor in the isolated first evaporator portion 220. The outlet flow 715 is a mixture of the cooled, dehumidified air that flowed through the second evaporator portion 230 and the heated air that flowed though the first evaporator portion 220. The resultant outlet flow 715 is dehumidified air that is not overcooled. The partitioned condenser 500 shown in FIG. 10 operates substantially as described above in the discussion of FIG. 7.
FIG. 11 illustrates a flow chart detailing a method of the present invention relating to head pressure control in a HVAC system for use with the systems shown in FIGS. 7-10. The method includes a determination of the minimum system head pressure, Pf, at step 1101. The minimum head pressure is set to the desired operating pressure of the refrigeration system 100. The minimum head pressure is preferably greater than the pressure corresponding to temperature of evaporator icing. Evaporator icing may occur when the surface temperature of the evaporator and suction piping is less than 32° F. Pf is preferably the system high side pressure that results in saturated suction temperatures above freezing under most load conditions. For R22 refrigerant, a typical value of Pf is 180 psig. Subsequent to determining the minimum system head pressure, Pf, the actual system head pressure, Pm, is measured at step 1103. Any suitable pressure measurement method can be used for determining Pm. Preferably, the measurement takes place on a line between the TXV valve 265 and the compressor 130. Subsequent to the measurement taken at step 1103, a determination of whether the measured refrigerant pressure is less than the minimum system head pressure, Pf, at step 1105. If the measured pressure of the refrigerant, Pm, is less than the pressure for evaporator freezing, which corresponds to Pf, (i.e., “YES” on the flowchart show in FIG. 11), isolation valve(s) 540 are closed and refrigerant flow is blocked to one or more of the refrigerant circuits inside of the partitioned condenser 500 in step 1107. If the measured pressure of the refrigerant, Pm, is greater than the minimum system head pressure, Pf, (i.e., “NO” on the flowchart shown in FIG. 11), a determination of whether the measure head pressure, Pm, is less than the system reset pressure, Pr as shown in step 1110. If the measured pressure, Pm, is greater than the system reset Pressure, Pr, (i.e., “YES” on the flowchart shown in FIG. 11), the isolation valves 540, if closed, will be opened. If the measured pressure, Pm, is less than the system reset pressure, Pr, (i.e. “NO” on the flowchart shown in FIG. 11), then no action will be taken regarding the isolation valves 540. If open, the isolation valves 540 will remain open. If closed, the isolation valves 540 will remain closed. The value Pr−Pf represents a pressure buffer for the system so that the isolation valves 540 will not be inclined to open and close rapidly. The opening of the isolation valves 540 in step 1109 allows refrigerant to flow to all refrigerant circuits within the condenser. When the refrigerant flows through all the refrigerant circuits 510 of the condenser, the heat transfer to the first heat transfer fluid 150 from the refrigerant is at a maximum. If the isolation valves 540 are closed in step 1107, the refrigerant is only permitted to flow through a portion of the partitioned condenser 500. Each portion has a predetermined heat transfer surface area. Because the refrigerant is only permitted to flow into a portion of the condenser and some portions are isolated, the heat transfer area and the corresponding amount of heat transfer is reduced. Therefore, less heat is removed from the refrigerant. Likewise, less heat is transferred to the first heat transfer fluid 150, thereby maintaining a higher refrigerant temperature. Additionally, because the temperature of the refrigerant is higher, the corresponding pressure of the refrigerant is also higher. Therefore, the refrigerant pressure of the system is increased.
In the HVAC system according to the present invention, when the head pressure in the suction line 145 to the compressor 130 decreases, the temperature of the refrigerant in the evaporator 110 likewise decreases. When the head pressure has decreased to a certain level, the partitioned evaporator 200 operates at temperatures that may result in icing of the partitioned evaporator 200. Icing is a condition when the temperature at the exterior of the refrigerant circuits of the evaporator is sufficiently low to freeze water present in the heat transfer fluid. In particular, in a residential system, the heat transfer fluid is typically air and the water that freezes is humidity present in the air. The ice formed by the water frozen on the surface of the refrigerant circuits eventually prevents the proper operation of the HVAC system by inhibiting heat transfer and/or damaging system components. This icing generally begins at refrigerant saturated suction temperatures from about 25° F. to about 32° F. In order to prevent the freezing of the evaporator, the pressure in the suction line 145 is preferably maintained above the temperature that corresponds to the freezing point of the partitioned evaporator 200.
In one method according to the invention, the pressure of the refrigerant is measured and compared to a predetermined pressure. The pressure measurement may be taken from any point in the refrigeration system 100. However, the preferred point of measurement of refrigerant pressure is on the evaporator discharge line 145 to the compressor. The evaporator discharge line 145 to the compressor also corresponds to the outlet of the partitioned evaporator 200. The outlet of the partitioned evaporator 200 represents a low pressure point in the refrigeration system 100, due to the phase change of the refrigerant to a vapor resulting from the heat exchange relationship existing between the refrigerant and the second heat transfer fluid 155 in the partitioned evaporator 200. The predetermined pressure is preferably a pressure that is greater than or equal to the pressure that corresponds to a temperature that results in icing at the partitioned evaporator 200.
FIG. 12 shows a control method according to one embodiment of the present invention for use with the system shown in FIGS. 7-8. The method includes a mode determination step 1210 where the operational mode of the system is determined or selected. The operational mode can be provided by the controller and/or user, where the mode can either be cooling only or require dehumidification. Examples of control systems for determination of the operational mode are described in further detail below in the discussion of FIGS. 15 and 16. The method then includes a decisional step 1220 wherein it is determined whether dehumidification is required or not. If the determination in step 1220 is “NO” (i.e., no dehumidification required), then the method proceeds to opening step 1230 wherein the valve to the first evaporator portion 220 is opened or remains open in step 1230. The opening of the first evaporator portion 220 to the flow of refrigerant permits both the first and second evaporator portions 220 and 230 to provide cooling to the inlet flow 710. If the decisional step 1220 is a “YES” (i.e., dehumidification is required), then the valve to the first evaporator portion 220 is closed or remains closed in step 1240. The closing of the first evaporator portion 220 to the flow of refrigerant allows the first evaporator portion 220 to equilibrate at a temperature substantially equal to the temperature of the heat transfer fluid entering the partitioned evaporator 200. After either the opening step 1230 or the closing step 1240, the method returns to the determination step 1210 and the method repeats.
Although FIG. 12 shows that the decisional step 1220 provides a “YES” or “NO” to steps 1230 or 1240, the method is not limited to an open or closed isolation valve 250. A flow-restricting valve may also be used. The use of a flow-restricting valve allows the amount of flow into the first evaporator portion 220 to be varied. For example, the flow restricting valve may be used in an operational mode that is open to full flow, partially restricted flow or closed to flow, depending on the signal from a controller. Controller 720, using inputs, such as refrigerant temperature, heat transfer fluid temperatures, and humidity readings, provides a signal to the restricting valve to determine the amount of refrigerant flow permitted through the isolation valve 250.
FIG. 13 shows another control method according to the present invention for use with the system shown in FIG. 9. The method includes a mode determination step 1310 where the operational mode of the system is determined. As in the method shown in FIG. 12, the operational mode can be provided by the controller and/or user, where the mode can either be cooling only or dehumidification. Examples of control systems for determination of the operational mode are described in further detail below in the discussion of FIGS. 15 and 16. The method then includes a decisional step 1320 wherein it is determined whether dehumidification is required or not. If the determination in step 1320 is “NO” (i.e., no dehumidification required), then the method proceeds to step 1330 wherein the 3-way valve 910 is set to provide refrigerant flow from the discharge line 310 of the evaporator portion 220 to the compressor suction line 145. The setting of the 3-way valve 910 allows the flow of refrigerant to both the first and second evaporator portions 220 and 230 to provide cooling to the inlet flow 710. If the decisional step 1320 is a “YES” (i.e., dehumidification is required), then the 3-way valve 910 is set to provide refrigerant flow from the discharge of the compressor to the discharge line 310 of the evaporator portion 220. The hot gas refrigerant from the discharge of the compressor 130 flows into the first evaporator portion 220 and provides heat to the first evaporator portion 220. The directing of hot gas refrigerant to the first evaporator portion 220 allows the first evaporator portion 220 to exchange heat with the heat transfer fluid 155 entering the partitioned evaporator 200. The inlet flow 155 of heat transfer fluid is cooled and dehumidified by the second evaporator portion 230 and is heated by heat exchange with the hot gas from the discharge of the compressor 130 in the isolated first evaporator portion 220. The outlet flow 715 is a mixture of the cooled, dehumidified air that flowed through the second evaporator portion 230 and the heated air that flowed though the first evaporator portion 220. The resultant outlet flow 715 is dehumidified air that is not overcooled. After either the 3-way valve 910 directing steps 1330 or 1340, the method returns to the determination step 1310 and the method repeats.
Although FIG. 13 shows that the decisional step 1320 provides a “YES” or “NO” to steps 1330 or 1340, the method is not limited to an open or closed isolation valve 250. A flow restriction valve may also be used. The use of a flow restriction valve allows the amount of flow into the first evaporator portion 220 to be varied. For example, the flow restriction valve may be used in an operational mode that is open to full flow, partially restricted flow or closed to flow, depending on the signal from controller 720. Alternatively, the flow into the first evaporator portion 220 from the discharge of the compressor 130 in dehumidification mode may be varied through use of the 3-way valve 910, depending on the signal from a controller. The 3-way valve 910 may also include flow restriction abilities that allow the flow of refrigerant to be varied. A controller, using inputs, such as refrigerant temperature, heat transfer fluid temperatures, and humidity readings, provides a signal to the restriction valve or the 3-way valve 910 to determine the amount of refrigerant flow permitted through the isolation valve 250 or the amount of hot gas refrigerant permitted through the first evaporator portion 220.
FIG. 14 shows a control method according to the present invention for use with the system shown in FIG. 10. The method includes a mode determination step 1410 where the operational mode of the system is determined. As in the method shown in FIGS. 12 and 13, the operational mode can be provided by controller 720 and/or user, where the mode can either be cooling only or dehumidification. The method then includes a decisional step 1420 wherein it is determined whether dehumidification is required or not. If the determination in step 1420 is “NO” (i.e., no dehumidification required), then the method proceeds to step 1430 wherein the valve 250 to the first evaporator portion 220 is opened or remains open. After or concurrently with step 1430, a bypass line 410 is closed from refrigerant flow in step 1340. The opening of the first evaporator portion 220 and the closing of the bypass line 410 allow the flow of refrigerant to both the first and second evaporator portions 220 and 230 to provide cooling to the inlet flow 710. If the decisional step 1420 is a “YES” (i.e., dehumidification is required), then the valve to the first evaporator portion 220 is closed or remains closed. After or concurrently with step 1450, the bypass line 410 is opened to flow of refrigerant in step 1460. Hot gas refrigerant from the discharge of the compressor 130 flows through the bypass 410 and into the first evaporator portion 220 and provides heat to the first evaporator portion 220. The closing of the first evaporator portion 220 to the flow of refrigerant from the condenser 130 and the directing of hot gas refrigerant to the first evaporator portion 220 allows the first evaporator portion 220 to exchange heat with the refrigerant circuits 510 entering the partitioned evaporator 200. The inlet flow 710 of heat transfer fluid is cooled and dehumidified by the second evaporator portion 230 and is heated by heat exchange with the hot gas from the discharge of the compressor in the isolated first evaporator portion 220. The outlet flow 715 is a mixture of the cooled, dehumidified air that flowed through the second evaporator portion 230 and the heated air that flowed though the first evaporator portion 220. The resultant outlet flow 715 is dehumidified air that is not overcooled. After either the bypass-closing step 1440 or the bypass-opening step 1460, the method returns to the determination step 1410 and the method repeats.
Although FIG. 14 shows that the decisional step 1420 provides a “YES” or “NO” to steps 1430 or 1450, the method is not limited to an open or closed isolation valve 250. A flow restriction valve may also be used. The use of a flow restriction valve allows the amount of flow into the first evaporator portion 220 to be varied. For example, the flow restriction valve may be used in an operational mode that is open to full flow, partially restricted flow or closed to flow, depending on the signal from controller 720. Additionally, the flow through the bypass line 410 may be varied through use of the bypass valve 440 and/or flow restriction valve 430, depending on the signal from controller 720. Controller 720, using inputs, such as refrigerant temperature, heat transfer fluid temperatures, and humidity readings, provides a signal to isolation valve 250, bypass valve 440 and flow restriction valve 430 to determine the amount of refrigerant flow permitted through the flow restriction valve 430 in place of isolation valve 250 and the amount of hot gas refrigerant permitted through the first evaporator portion 220.
FIG. 15 illustrates a control method according to the present invention that determines the operation mode of the partitioned evaporator 200. The determination of the operational mode is made through the use of controller 720. This determination may be used in steps 1210, 1310 and 1410 of FIGS. 12, 13 and 14, respectively. The determination takes place by first sensing temperature and/or humidity in an enclosed space in step 1510. The temperature and/or humidity measurements are made for a controller to determine whether the enclosed space requires cooling or dehumidification. The inputs from temperature sensors and humidity sensors are provided to controller 720 in step 1520, where the controller uses the sensed temperatures and/or humidity to determine the operational mode. In step 1520, the controller determines whether cooling is required and whether dehumidification is required. In a first decisional step 1530, it is determined whether the controller has determined that cooling is required. If the first decisional step 1530 determines “YES”, cooling mode is required, the partitioned evaporator 200 in the refrigeration system 100 is set to allow flow into all of the refrigerant circuits 210 in the partition evaporator 200 and cool across both the first and second evaporator portions 220 and 230 in step 1540. In addition to cooling, cooling mode also performs dehumidification. However, in a cooling mode, the second heat transfer fluid is only cooled and is not heated to increase the temperature of the second heat transfer fluid 155 once the second heat transfer fluid 155 travels through the partitioned evaporator 200. If the first decisional step 1530 determines “NO”, then a second decisional step 1550 is made. The second decisional step 1550 determines whether the controller has determined that dehumidification mode (i.e., dehumidification without overcooling) is required. If the second decisional step 1550 determines “YES”, dehumidification mode is required, the operational mode is set to dehumidification in step 1560. If the second decisional step 1550 determines “NO”, dehumidification mode is not required, the operational mode is set to inactive and the system operates neither a cooling nor a dehumidification cycle in step 1570.
FIG. 16 shows an alternate control method according to the present invention that determines the operation mode of a multiple refrigerant circuit system. In the system controlled in FIG. 16, multiple refrigerant systems 100 are utilized and one or more of the refrigerant systems 100 include a partitioned evaporator 200 according to the invention. The control method shown in FIG. 16 operates in a similar manner to FIG. 15 in that the controller receives inputs from temperature and/or humidity sensors in step 1610 and determines the operational mode of the system in step 1620. Likewise, if the first decisional step 1630 determines “NO”, then a second decisional step 1650 is performed. The second decisional step 1670 determines whether the controller has determined that a dehumidification mode (i.e., dehumidification without overcooling) is required. If the second decisional step 1670 determines “YES”, dehumidification mode is required, the operational mode is set to dehumidification in step 1680. If multiple refrigerant systems 100 are present, the controller 720 independently determines which of the refrigerant systems 100 are active or inactive, based upon temperature and/or humidity measurements. When multiple refrigeration systems 100 are present, at least one refrigerant system 100 includes a partitioned evaporator 200. The controller 720 independently determines which partitioned evaporator 200 is subject to isolation of the first evaporator portion 220, based upon temperature and/or humidity measurements. However, if the second decisional step 1670 determines “NO”, dehumidification is not required, the operational mode is set to inactive and the system operates neither a cooling nor a dehumidification cycle in step 1690. If the first decisional step 1630 determines “YES”, cooling is required, a third decisional step 1640 is performed. In the third decisional step 1640, a determination is made as to the number of stages to be activated in order to provide the cooling. Each stage has an evaporator capable of providing cooling to the second heat transfer fluid 155. The greater the number of stages activated, the greater the amount of cooling provided. At least one of the multiple refrigerant circuits includes a partitioned evaporator 200. If the controller determines that the cooling demand only requires one refrigerant system 100 to be active, one refrigerant system 100 will be used to cool second heat transfer fluid 155 in step 1650. When the partitioned evaporator 200 is used to operate in cooling mode, the partitioned evaporator 200 is configured to allow flow into all of the refrigerant circuits 210 in the partition evaporator 200 and cool across both the first and second evaporator portions 220 and 230 in step 1660. If multiple partitioned evaporators 200 are present, all of the refrigerant circuits 210 in each of the partition evaporators 200 allow flow of refrigerant into both the first and second evaporator portions 220 and 230 and cool the second heat transfer fluid 155.
The present invention is not limited to the control methods shown in FIGS. 11-16. The partitioned evaporator 200 and the partitioned condenser 500 may be used in one or more refrigerant circuits of multiple refrigerant circuit systems, where the control of the reheating capabilities within the first evaporator portion 220 of the partitioned evaporator 200 and the head pressure control within the first condenser portion 520 may each be independently controlled to provide the desired temperature and/or humidity within the conditioned space and the desired refrigerant pressure within the system. Any combination of cooling, reheating, or modulation of combinations of cooling and reheating may be used with the present invention. In addition, operational modes controlling the refrigerant pressure may be used in conjunction with the cooling and dehumidification modes of operation.
While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
