Patent Application
20070033957
This application relates to a variable speed drive provided for a fluid-moving device such as a fan operated within a refrigerant system, wherein the variable speed is achieved by an automated mechanical control for the fan drive.
Refrigerant systems are utilized in many applications to condition an environment. In particular, air conditioners and heat pumps are employed to cool and/or heat a secondary fluid such as air entering an environment. The cooling or heating load of the environment may vary with ambient conditions, occupancy level, other changes in sensible and latent load demands, and as the temperature and/or humidity set points are adjusted by an occupant of the environment.
It would be desirable to have a variable speed control for fluid-moving devices, such as the fans moving air over indoor and outdoor heat exchangers. As an example, a fan speed change may be desirable when there is a change in the compressor speed or mode of operation. As known, the compressor speed may need to be adjusted to accommodate internal and external thermal load demands. Further, to have an ability to operate in various modes, a refrigerant system may be provided with an economizer cycle, and a compressor may be equipped with an unloading function. When the compressor is run unloaded or economized, it may be desirable to change the fan speed accordingly to maintain operational parameters, such as temperature and humidity, within the environment to be conditioned. Additionally, the fan speed may be required to be adjusted with a change in occupancy level or to maintain desired sensible heat ratios to provide a certain level of comfort for an occupant of the environment. Also, it may be desirable to decrease the fan speed to improve the system efficiency by minimizing fan power draw.
In another example, it may also be desirable to adjust the fan speed in response to changes of ambient conditions or variations in cooling requirements. For instance, to provide safe and reliable refrigerant system operation a condenser fan speed may be increased at high ambient temperatures to reduce discharge pressure (an opposite functionality may be required at low ambient temperatures), or an evaporator fan speed may need to be raised to prevent coil frosting.
In the past, if variable speed fan operation was desired, a variable frequency drive needed to be provided. However, variable speed drives are expensive, and are challenging to integrate with conventional system controls. Also, variable speed drives carry additional efficiency losses and reliability issues for a refrigerant system.
In the past, to vary the fan speed, mechanical drives for the fans have been adjusted manually. As an example, such fans are typically driven by a mechanical pulley, and a mechanic would manually adjust the setting on the pulley to set the fan speed. However, such technology does not change the fan speed on the fly, and has typically been performed only at initial set-up/installation. Thus, this option does not allow a fan speed change in response to constantly changing operating conditions and cooling demands.
Thus, there is a need exists for automated mechanical variable speed drive for air moving devices provided within a refrigerant system.
In a disclosed embodiment of this invention, a drive for a fan incorporates an automated variable diameter pulley system. In a disclosed embodiment, two plates of a conical shape (two adjustable pulley halves) driven by a belt (or to drive a belt) are movable toward and away from each other to vary the diameter of the contact surface between the belt and the plates. As this diameter varies, the speed at which the fan will be operated will also vary.
In a disclosed embodiment, a hydraulic fluid may be injected into chambers associated with the pulley plates to drive these plates toward and away from each other. A spring biases the plates in opposition to the force exerted hydraulic fluid.
In another embodiment, an electric current may be provided to the electric coil to create an electromagnetic force to drive the pulley plates toward and away from each other.
In still another embodiment, a permanent magnet may be used to replace the spring.
The present invention may also be utilized in refrigerant systems incorporating an unloader function, an economizer function, and other optional controls and features. The fan speed may be varied dependent upon whether these functions are actuated. Also, a desired fan speed may change based upon the thermal load or system operating conditions, such as the condenser or evaporator refrigerant pressures. A worker in this art would recognize when a fan speed should change. The present invention provides a simple way to change the fan speed.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.
A refrigerant system 20 is illustrated in
Downstream of the economizer heat exchanger 100 is a main expansion device 30, and downstream of the main expansion device 30 is an evaporator or in this case an indoor heat exchanger 32. A fan 34 is provided with a motor drive 36 and blows air over the evaporator 32. A system control 38 controls the speed of the fan motor drive 36, as will be explained below. Similar control 38 may also be associated with the fan motor drive 28 (not shown) but in reality it would be used less frequently than the control 38. The controls 38 may communicate to, or be integrated with, a refrigerant system control 18. The system control 38 can also control other components within the refrigerant system 20.
A suction line 110 returns refrigerant to the compressor 22 from the evaporator 32. A bypass line 106 allows at least a portion of partially compressed refrigerant to be selectively bypassed from the compressor 22 back to the suction line 110. An unloader valve 108 opens or closes this bypass line. Of course, the single compressor 22 can be replaced with two compressor stages and the unloader function can bypass refrigerant from a point intermediate the two stages.
As shown in
A center core 46 carries springs 48 that bias the plates 40 away from each other. Chambers 50 selectively receive hydraulic fluid from a pump and reservoir 52 to force the plates 40 back toward each other. A control 38 controls the flow of hydraulic fluid to the cambers 50 that in turn controls the position of the plates. By adjusting the position of the plates toward and away from each other, and as is clearly shown between
The adjustment for the pulley 39 is shown schematically in this application. However, automated pulley drive systems are well known. A worker of ordinary skill in the art, given the teachings of this application, would be able to provide a suitable drive system.
Also, while
A control 18 for the refrigerant system 20 determines a desired fan speed, and adjusts the position of the plates to achieve that desired fan speed. A worker of ordinary skill in the art would recognize when and how a desired fan speed change would be determined.
As shown in
It is understood that the present invention may equally benefit belt-driven applications outside of the air conditioning, heating, ventilation and refrigeration field. Also, it is understood that although the present invention was explained in relation to the fans blowing air across the heat exchangers, it can be equally applied to belt-driven pumps utilized in chiller applications for pumping secondary loop liquid through these heat exchangers. Further, the present invention can be used with an open drive belt-driven compressors.
A worker of ordinary skill in the art would understand that various modifications of the disclosed embodiment would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.
