Patent Application
20060174640
The present invention relates generally to a condenser arrangement for a heating, ventilation, and air conditioning (HVAC) system.
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 to be cooled 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 refrigeration cycle. The fluid to be cooled passes through the evaporator in a separate fluid channel and is cooled by the evaporation of the refrigerant. The cooled 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.
High capacity HVAC systems may include multiple refrigerant circuits or multiple compressors connected in the refrigerant loop. Air-cooled refrigeration systems that utilize multiple compressors, arranged in tandem (parallel), typically utilize a single condenser coil that is sized to handle the load of all of the compressors operating simultaneously. This results in a condenser that has excessive heat exchange capacity when less than all of the compressors in the system are operating, essentially making the condenser coils oversized for the system operating. Making this problem worse, condenser coils are often manufactured oversized, with corresponding increased airflows, with respect to the system full load requirements, in order to meet the ever-increasing efficiency requirements for modern refrigeration systems. The condensers present in these systems are typically installed outdoors and/or in locations 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. A decrease in suction pressure to the compressor results in a lowering of the temperature of the refrigerant at the evaporator. However, when the temperature of the refrigerant at the evaporator becomes too low, system performance suffers. If the suction pressure falls too low, the system may experience problems, such as evaporator freezing, liquid slugging at the compressor and/or system instability.
In addition to the problem of an oversized condenser coil, there is a need to decrease the condenser “capacity” in order to maintain proper system operation. One approach to provide good system control and offset the excessive cooling that may result from an oversized coil includes a variable speed condenser fan 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 evaporator to cool the heat transfer fluid without system performance problems. The use of the variable speed condenser fan has the drawback that it is expensive and requires complicated wiring and controls. An alternate method used for condenser airflow control is to utilize multiple small condenser fans that may be cycled on and off as necessary. However, the flow resulting from multiple small condensers is stepped and provides predetermined levels of cooling capacity at the condenser based upon the number of fans activated. To provide adequate control a very large number of fans and independent controls for each fan are required, which is expensive and requires complicated wiring and/or controls.
Air-cooled condensers that are oversized often result in a system performance that degrades rapidly as the ambient temperature of the condenser air decreases. In order for these types of systems to operate effectively and reliably, the amount of cooling taking place at the condenser has to be reduced as the ambient temperature decreases. As discussed above, a common way to vary the performance of the condenser coil at lower ambient temperatures is to use multiple condenser fans controlled in such a way as to decrease the number of fans that are operating. As the number of fans in operation decreases, the volume of air drawn through the condenser coil is likewise decreased. Unfortunately, to provide sufficient control, particularly at low ambient temperature conditions, there must be a large number of condenser fans used, or excessive fan cycling will occur. Excessive fan cycling increases the amount of energy required to operate the condenser and increases the wear on the fans, which increases maintenance costs. This excessive fan cycling is due to the fact that the operating ambient temperature range when a fan is activated versus when the same fan is deactivated can have a significant gap. For example, the operating ambient temperature range for one system having a single fan activated may be 20° F.-35° F. However, the same system may include an operating ambient temperature range of 45° F.-60° F. for two fans activated. Operational problems occur for this condenser system if the ambient temperature is between about 35° F. and 45° F. In this temperature range, the second condenser fan may be cycled repeatedly with relatively small changes in temperature.
Therefore, what is needed is a method and apparatus for improving low ambient temperature operation and reliability in a high efficiency condenser, while not sacrificing high ambient temperature performance and overall system efficiency.
The present invention includes a condenser arrangement for control of condenser temperature and condenser pressure and an HVAC system employing the condenser arrangement. The condenser arrangement includes a condenser coil and a plurality of fans disposed adjacent to the condenser coil. The plurality of fans are arranged and disposed to circulate air through the condenser coil. At least one baffle extending from a surface of the condenser coil is positioned between adjacent fans of the plurality of fans and forms a plurality of channels. The plurality of channels include a variable flow channel having a plurality of adjacent fans of the plurality of fans to control airflow through the channel. The condenser arrangement also includes a control system to control operation of the plurality of fans. The control system is configured to independently control each fan of the plurality of fans in response to a sensed condition.
The present invention also includes a method for controlling condenser pressure. The method includes providing a condenser arrangement having a condenser coil, a plurality of fans disposed adjacent to the condenser coil, and a plurality of channels extending from a surface of the condenser coil. The plurality of channels include a variable flow channel having a plurality of adjacent fans of the plurality of fans to control airflow through the channel. Air is circulated through the condenser coil by activating one or more of the plurality of fans. A condition of refrigerant in the condenser coil or a condition of inlet air to the condenser coil is sensed. At least one fan of the plurality of fans of the variable flow channel is deactivated in response to the sensed condition to lower airflow through the condenser coil. At least one active fan of the plurality of fans draws bypass air from an area adjacent to the at least one deactivated fan to further lower airflow through the condenser coil.
One advantage of the present invention is that condenser fan cycling is significantly reduced or even eliminated at all but the lowest ambient temperatures.
Another advantage of the present invention is improved system control by improving the overlaps in condenser performance between condenser fan stages.
Still another advantage of the present invention is that fewer condenser fans can be used resulting in a lower system cost.
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.
Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.
A general system to which the invention can be applied is illustrated in
The first and second compressors 102 and 103 compress a refrigerant vapor and deliver it to the condenser arrangement 108 by discharge lines that are combined into a single line. In another embodiment of the present invention, separate discharge lines are used to deliver refrigerant vapor to the condenser arrangement 108, where the refrigerant vapor is combined. The first and second compressors 102 and 103 are preferably screw compressors or centrifugal compressors, however the compressors can be any suitable type of compressor including reciprocating compressors, scroll compressors, rotary compressors or other type of compressor. The refrigerant vapor delivered to the condenser 108 enters into a heat exchange relationship with a fluid, which is preferably air, and undergoes a phase change to a refrigerant liquid as a result of the heat exchange relationship with the fluid. The condensed liquid refrigerant from condenser arrangement 108 flows through corresponding expansion devices to an evaporator 110.
The refrigerant liquid delivered to the evaporator 110 enters into a heat exchange relationship with a fluid, e.g., air, water or secondary liquid, and undergoes a phase change to a refrigerant gas as a result of the heat exchange relationship with the fluid. The evaporator 110 can include connections for a supply line and a return line of the fluid. The fluid travels into the evaporator 110 via the return line and exits the evaporator 110 via the supply line. The liquid refrigerant in the evaporator 110 enters into a heat exchange relationship with the fluid to remove heat from the fluid. The vapor refrigerant in the evaporator 110 then returns to the first and second compressors 102 and 103 to complete the cycle. The vapor refrigerant in the evaporator 110 can be combined into a single line exiting the evaporator 110 that then splits or branches to deliver refrigerant vapor to the first and second compressors 102 and 103. In another embodiment of the present invention, the vapor refrigerant then returns to the first and second compressors 102 and 103 by separate suction lines to complete the cycle. It is to be understood that any suitable configuration of evaporator 110 can be used in the system 100, provided that the appropriate phase change of the refrigerant in the evaporator 110 is obtained.
To drive the first and second compressors 102 and 103, the system 100 includes a motor or drive mechanism for the first and second compressors 102 and 103. While the term “motor” is used with respect to the drive mechanism for the first and second compressors 102 and 103, it is to be understood that the term “motor” is not limited to a motor, but is intended to encompass any component that can be used in conjunction with the driving of motor, such as a variable speed drive and a motor starter. In a preferred embodiment of the present invention, the motor or drive mechanism is an electric motor and associated components. However, other drive mechanisms, such as steam or gas turbines or engines and associated components can be used to drive the first and second compressors 102 and 103.
The condenser arrangement 108 also includes a baffle 206 positioned between the fourth and fifth fans 237 and 239. “Baffle” as used herein includes a barrier having a structure configured to substantially prevent flow of air through the baffle and capable of channeling air in a direction from coil 202. Baffle 206 extends from the coil 202 towards the fourth and fifth fans 237 and 239 for a sufficient length to form a constant or fixed flow channel 210 for airflow between the baffle 206 and the housing 204. “Constant flow” as used herein indicates that the flow of air through channel 210 is substantially constant when the fifth fan 239 is operating, i.e., the flow of air in channel 210 is either occurring at a substantially constant rate based on operation of fifth fan 239 or no flow is occurring. Airflow through channel 210 and the channeled portion 242 of the condenser coil 202 corresponding to the channel 210 is isolated from the airflow through the remainder of the condenser arrangement 108, if any, by baffle 206. In addition, for channel 210, the flow of air through the channeled portion 242 of condenser coil 202 is substantially equal to the flow of air from the channel 210. In other words, the flow of air in channel 210 is limited to a single direction with a single entrance and single exit. The arrangement of channel 210 in this embodiment results in a substantially constant ratio of airflow to condenser coil surface area. For example, in the embodiment shown in
In addition to channel 210, the present invention further includes a variable flow channel 211, which draws air from mixed airflow portion 244 of the condenser coil 202. “Variable flow” as used herein indicates that flow in the channel 211 may be varied by selective activation and/or deactivation of one or more of the first through fourth fans 231, 233, 235 and 237 disposed in the channel 211. Unlike the constant flow channel 210, which provides a predetermined fraction or substantially constant ratio of airflow to condenser coil surface area, the variable flow channel 211 allows the fraction of airflow to be based upon the combination of fans activated or deactivated within the variable flow channel 211. Channel 211 includes the first through fourth fans 231, 233, 235 and 237, each of which are independently controlled and operated. Further, one or more of the first through fourth fans 231, 233, 235 and 237 may be deactivated, permitting air to enter channel 211 from the area of the deactivated fan(s) to provide a mixed airflow exiting channel 211. In an alternate embodiment of the invention, first through fourth fans 231, 233, 235 and 237 each include a plurality of fans, such as fan pairs, which may be dependently or independently activated and deactivated with the first through fourth fans 231, 233, 235 and 237. The mixed airflow includes a mixture of air drawn through the coil 202 and air drawn into channel 211 from the areas of the one or more deactivated fans (see e.g.
In addition to the positioning of the first baffle 206, and/or second baffle 208, the first through fifth fans 231, 233, 235, 237 and 239 may be controlled by the control panel 112 to generate a desired condenser temperature and/or condenser pressure when the condenser arrangement is operated at lower ambient conditions and lower load conditions. A reduction in outdoor ambient temperature and/or a decrease in system load reduces the number of the first through fifth condenser fans 231, 233, 235, 237 and 239 that remain activated by the control panel 112.
In one embodiment of the invention, the control panel 112 executes a control system that preferably uses control algorithm(s) or software to control operation of the system 100 and to determine and implement an operating configuration for the first through fifth fans 231, 233, 235, 237 and/or 239 of the condenser arrangement 108 to control the condenser temperature and/or condenser pressure. The control algorithm(s) may include computer programs or software stored in the non-volatile memory of the control panel and can include a series of instructions executable by the microprocessor of the control panel. While it is preferred that the control algorithm be embodied in a computer program(s) and executed by the microprocessor, it is to be understood that the control algorithm may be implemented and executed using digital and/or analog hardware by those skilled in the art. If hardware is used to execute the control algorithm, the corresponding configuration of the control panel can be changed to incorporate the necessary components and to remove any components that may no longer be required.
The control algorithm may sense system parameters and/or system conditions to generate the appropriate control signals for the first through fifth fans 231, 233, 235, 237 and/or 239 to obtain a desired condenser temperature and/or condenser pressure. Conditions sensed may include, but are not limited to refrigerant pressure, refrigerant temperature, inlet air temperature, outlet air temperature, or combinations thereof. For example, a predetermined set of conditions may allow the control algorithm to determine that the fifth fan 239 should be operated and the remaining first through fourth fans 231, 233, 235 and 237 should not be operated because the airflow through the predetermined ratio of condenser coil 202 resulting from operation of the fifth fan 239 provides the desired condenser temperature and/or condenser pressure. However, for another set of inputs the control algorithm may determine that the first fan 231 should be operated and the second through fifth fans 233, 235, 237 and 239 should not be operated because the airflow resulting from operation of the first fan 231 through channel 211 of condenser coil 202 not isolated from airflow by first baffle 206 provides the desired condenser temperature and/or condenser pressure. The control algorithm is not limited to the combinations above and may include any combination of the first through fifth fans 231, 233, 235, 237 and /or 239 to obtain the desired condenser coil temperature and/or condenser pressure.
In one embodiment of the invention, the control of the condenser arrangement 108 may include sensing an ambient temperature and utilizing a lookup table or similar control scheme that contains a predetermined combination of fans that corresponds to the ambient temperature sensed. For example, if the ambient temperature is between 15° F. and 25° F., the control panel 112 may deactivate fifth fan 239 and activate first fan 231. In addition, for ambient temperatures between 25° F. and 35° F. the control panel 112 may activate fifth fan 239 and activate first fan 231.
In another embodiment of the present invention, the control of the condenser arrangement may include sensing condensing pressure with a pressure sensing device, such as a pressure transducer, and providing a predetermined combination of fans corresponding to a condensing pressure range for a lookup table or similar control scheme. For example, if the pressure falls below a minimum pressure in a particular capacity step range, the combination of fans corresponding to the lower capacity are activated. Likewise, if the pressure rises above a maximum pressure in a particular capacity step range, the combination of fans corresponding to the higher capacity are activated.
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.
| Number | Date | Country | |
|---|---|---|---|
| 60651723 | Feb 2005 | US |
