Refrigerant Detection for a Cooling System

The application is a continuation of U.S. patent application Ser. No. 18/156,112, filed Jan. 18, 2023, entitled “REFRIGERANT DETECTION FOR A COOLING SYSTEM,” which is incorporated herein by reference.

The present disclosure relates generally to heating, ventilation, and air conditioning (HVAC) system control, and more specifically to refrigerant detection for a cooling system.

Heating, ventilation, and air conditioning (HVAC) systems are used to regulate environmental conditions within an enclosed space. Air is cooled or heated via heat transfer with refrigerant flowing through the system and returned to the enclosed space as conditioned air. During operation, refrigerant may leak from the working-fluid conduit subsystem or from one or more components.

Regulations in the HVAC industry are pushing manufacturers to transition away from traditional refrigerants towards low global warming potential (GWP) refrigerants, particularly mildly flammable (A2L) refrigerants and flammable (A3) refrigerants. Currently, there is a need to develop HVAC systems that are optimized for low GWP refrigerants. Notably, in the case of flammable refrigerants, such as A2L and A3 refrigerants, there is a need to develop mitigation systems and methods that can detect the presence of leaked refrigerant and implement strategies for mitigating the leak. This disclosure addresses the aforementioned problems by providing an HVAC system that can detect the presence of a leak and discharge at least a portion or all of the refrigerant out from the HVAC system.

In one embodiment, the system comprises an evaporator coil configured to receive an airflow and to transfer heat from the received airflow to a flow of refrigerant. The system further comprises a compressor configured to receive the flow of refrigerant from the evaporator coil and to discharge the flow of refrigerant at a higher pressure. The system further comprises a refrigerant detection sensor disposed upstream of the evaporator coil and configured to detect a concentration of refrigerant in a volume. The system further comprises a controller operably coupled to the refrigerant detection sensor, comprising a memory and a processor. The memory is configured to store a threshold value associated with a lower flammability limit of the refrigerant, wherein the lower flammability limit corresponds to the concentration of the refrigerant. The processor is operably coupled to the memory and configured to operate the HVAC system in a first mode of operation, wherein the HVAC system is turned on and energized during the first mode of operation. The processor is further configured to receive a plurality of concentration measurements from the refrigerant detection sensor. The processor is further configured to determine if the concentration of refrigerant in the volume exceeds the stored threshold value based at least in part on the received plurality of concentration measurements. In response to determining that the concentration of refrigerant in the volume does exceed the stored threshold value, the processor is configured to operate the HVAC system in a second mode of operation. During the second mode of operation, the compressor is turned off and a blower disposed downstream of the evaporator coil is actuated to discharge the airflow.

Certain embodiments of the present disclosure may include some, all, or none of these advantages. These advantages and other features will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings and claims.

Cooling systems cycle refrigerant to cool various spaces. For example, a heating, ventilation, and air conditioning (HVAC) system cycles refrigerant to cool spaces near or around air conditioner loads. Refrigerant may leak from the working-fluid conduit subsystem or from one or more components at certain locations throughout the HVAC system. Depending on the refrigerant used, there is a risk that the concentration of leaked refrigerant accumulates to a threshold value indicative of flammability.

This disclosure contemplates an unconventional cooling system capable of detecting leaked refrigerant and discharging the refrigerant out of the HVAC system to reduce the accumulated concentration. This disclosure contemplates using a refrigerant detection sensor disposed within a housing near the drain pan underneath the evaporator coils. The cooling system will be described using, whereinwill describe the overall, improved cooling system, andwill describe the configuration and operation of the refrigerant detection sensor within the cooling system in further detail.

is a schematic diagram of an embodiment of a HVAC systemconfigured to detect a concentration of refrigerant leaking from a conduit subsystem during operations. The HVAC systemis generally configured to perform cooling and/or heat pump cycles. The HVAC systemconditions air for delivery to an interior space of a building or home. The HVAC systemis generally configured to control the temperature of a space. Examples of a suitable space may include, but are not limited to, a room, a home, an apartment, a mall, an office, a warehouse, or a building. In embodiments, the HVAC systemmay be a rooftop unit (RTU) that is positioned on the roof of a building and the conditioned air is delivered to the interior of the building. In other embodiments, portions of the system may be located within the building and a portion outside the building. The HVAC systemmay also include heating elements that are not shown here for convenience and clarity. The HVAC systemmay be configured as shown inor in any other suitable configuration. For example, the HVAC systemmay include additional components or may omit one or more components shown in. The HVAC systemmay comprise a controller or thermostat, compressors, blowers, evaporators, condensers, and/or any other suitable type of hardware for controlling the temperature of the space. Althoughillustrates a single HVAC system, a location or space may comprise a plurality of HVAC systemsthat are configured to work together. For example, a large building may comprise multiple HVAC systemsthat work cooperatively to control the temperature within the building.

The HVAC systemmay comprise a working-fluid conduit subsystemfor moving a working fluid, or refrigerant, through a cooling cycle. The working fluid may be any acceptable working fluid, or refrigerant, including, but not limited to, fluorocarbons (e.g. chlorofluorocarbons), ammonia, non-halogenated hydrocarbons (e.g. propane), hydrofluorocarbons (e.g. R-410A), A2L refrigerants, or any other suitable type of refrigerant. Without limitations, A2L refrigerants may include R-454b, R-32, R-1234yf, and R-1234ze.

The HVAC systemmay comprise one or more condensing units. In one embodiment, the condensing unitcomprises a compressor, a condenser coil, and a fan. The compressoris coupled to the working-fluid conduit subsystemthat compresses the working fluid. The condensing unitmay be configured with a single-stage or multi-stage compressoror with multiple compressors. In the configuration of one or more compressors, the one or more compressors can be turned on or off to adjust the cooling capacity of the HVAC system. In some embodiments, a compressormay be configured to operate at multiple speeds or as a variable speed compressor. For example, the compressormay be configured to operate at multiple predetermined speeds.

The condenseris configured to assist with moving the working fluid through the working-fluid conduit subsystem. The condenseris located downstream of the compressorfor rejecting heat. The fanis configured to move airacross the condenser. For example, the fanmay be configured to blow outside air through the heat exchanger to help cool the working fluid. The fanmay be coupled to a motor, wherein the motor may be configured to actuate the fan.

With reference back to the flow of the working fluid, the compressed, cooled working fluid flows downstream from the condenserto an expansion device, or a metering device. The expansion deviceis configured to remove pressure from the working fluid. The expansion deviceis coupled to the working-fluid conduit subsystemdownstream of the condenserfor removing pressure from the working fluid prior to flowing to an evaporator. The expansion devicemay be closely associated with the evaporator. In this way, the working fluid is delivered to the evaporatorand receives heat from airflowto produce a treated airflowthat is delivered by a duct subsystemto the desired space, for example, a room in the building.

In embodiments, refrigerant, such as an A2L refrigerant, flowing through the working-fluid conduit subsystemmay have an increased probability of leaking in an area proximate to the evaporator. To maintain compliance standards, the HVAC systemmay be configured to detect a concentration of leaking refrigerant and reduce the concentration within pre-determined periods of time. As illustrated, the HVAC systemmay further comprise a refrigerant detection sensordisposed in proximity to the evaporatorconfigured to detect a concentration of refrigerant in a volume. The refrigerant detection sensormay be disposed upstream or downstream of the evaporator. The refrigerant detection sensormay be any suitable sensor and/or collection of equipment operable to detect a concentration of refrigerant. Without limitations, the refrigerant detection sensormay be a gas sensor, speed of sound sensor, thermal conductivity sensor, heated diode leak detector, or any combination thereof.

In an embodiment, the refrigerant detection sensormay be in signal communication with a controllerusing a wired or wireless connection. The controllermay be configured to provide commands or signals to control the operation of the HVAC system. An example of the controllerin operation is described further below in. For example, the controlleris configured to send signals to turn on or off a blowerto facilitate airflow over the evaporator, wherein the blowermay be disposed upstream or downstream of the the evaporator. In another example, the controllermay be configured to receive a plurality of concentration measurements from the refrigerant detection sensor. In this example, the controllermay transmit instructions to the blowerbased on a determination that the the concentration of refrigerant in the HVAC systemexceeds a stored threshold value.

As an example, the controllermay comprise a processor, a memory, and a network interface. In embodiments, the controllermay further comprise a graphical user interface, a display, a touch screen, buttons, knobs, or any other suitable combination of components. The controllermay be configured as shown or in any other suitable configuration.

The processorcomprises one or more processors operably coupled to the memory. The processoris any electronic circuitry including, but not limited to, state machines, one or more central processing unit (CPU) chips, logic units, cores (e.g. a multi-core processor), field-programmable gate array (FPGAs), application-specific integrated circuits (ASICs), or digital signal processors (DSPs). The processormay be a programmable logic device, a microcontroller, a microprocessor, or any suitable combination of the preceding. The processoris communicatively coupled to and in signal communication with the memoryand the network interface. The one or more processors may be configured to process data and may be implemented in hardware or software. For example, the processormay be 8-bit, 16-bit, 32-bit, 64-bit, or of any other suitable architecture. The processormay include an arithmetic logic unit (ALU) for performing arithmetic and logic operations, processor registers that supply operands to the ALU and store the results of ALU operations, and a control unit that fetches instructions from memory and executes them by directing the coordinated operations of the ALU, registers and other components. The one or more processors are configured to implement and execute various instructions. The instructions may comprise any suitable set of instructions, logic, rules, or code operable to be executed. In this way, processormay be a special-purpose computer designed to implement the functions disclosed herein.

The memoryis operable to store any of the information described with respect toalong with any other data, instructions, logic, rules, or code operable to implement the function(s) described herein when executed by the processor. The memorycomprises one or more disks, tape drives, or solid-state drives, and may be used as an over-flow data storage device, to store programs when such programs are selected for execution, and to store instructions and data that are read during program execution. The memorymay be volatile or non-volatile and may comprise a read-only memory (ROM), random-access memory (RAM), ternary content-addressable memory (TCAM), dynamic random-access memory (DRAM), and static random-access memory (SRAM).

The network interfaceis configured to enable wired and/or wireless communications. The network interfaceis configured to communicate data between the controllerand other devices (e.g. sensors and the HVAC system), systems, or domains. For example, the network interfacemay comprise an NFC interface, a Bluetooth interface, a Zigbee interface, a Z-wave interface, an RFID interface, a WIFI interface, a LAN interface, a WAN interface, a PAN interface, a modem, a switch, or a router. The processormay be configured to send and receive data using the network interface. The network interfacemay be configured to use any suitable type of communication protocol as would be appreciated by one of ordinary skill in the art.

In further embodiments, controllermay include a display that is a graphical user interface configured to present visual information to a user using graphical objects.

Examples of a display include, but are not limited to, a liquid crystal display (LCD), a liquid crystal on silicon (LCOS) display, a light-emitting diode (LED) display, an active-matrix OLED (AMOLED), an organic LED (OLED) display, a projector display, or any other suitable type of display as would be appreciated by one of ordinary skill in the art.

A portion of the HVAC systemmay be configured to move air across the evaporatorand out of the duct sub-system. Return air, which may be air returning from the building, fresh air from outside, or some combination, is pulled into a return duct. A variable-speed blower, such as blower, may pull the return airinto the return ductwhere the airflowcrosses the evaporatoror heating elements (not shown) to produce the treated airflow. In these embodiments, the return airmay be the same airflow as airflowor may be discharged as airflowby blower.

The HVAC systemmay comprise one or more sensorsin signal communication with the controller. The sensorsmay comprise any suitable type of sensor for measuring the air temperature. The sensorsmay be positioned anywhere within a conditioned space (e.g. a room or building) and/or the HVAC system. For example, the HVAC systemmay comprise a sensorpositioned and configured to measure an outdoor air temperature. As another example, the HVAC systemmay comprise a sensorpositioned and configured to measure a supply or treated air temperature and/or a return air temperature. In other examples, the HVAC systemmay comprise sensorspositioned and configured to measure any other suitable type of air temperature, pressure, humidity, or any other suitable parameter.

The HVAC systemmay comprise one or more thermostats, for example, located within a conditioned space (e.g. a room or building). The thermostat may be a single-stage thermostat, a multi-stage thermostat, or any suitable type of thermostat as would be appreciated by one of ordinary skill in the art. The thermostat may be configured to allow a user to input a desired temperature or temperature set point for a designated space or zone such as the room.

is a cross-sectional side-view of the HVAC systemas an RTU. In embodiments, the HVAC systemmay be positioned on the roof of a building and the conditioned air, such as treated airflow, is delivered to the interior of the building. In other embodiments, portions of the HVAC systemmay be located within the building and a portion outside the building. As illustrated, return airmay be received by the HVAC systemfor treatment and enter the RTU through an inletfluidly coupled to return duct(reference to). The blowermay be actuated to pull in the return airinto and through the RTU. As illustrated, the blowermay be disposed downstream of the evaporatorand on top of a blower stand. The blower standmay comprise any suitable size, height, shape, and any combinations thereof. Further, the blower standmay comprise any suitable materials, such as metals, nonmetals, polymers, composites, and any combinations thereof. The blower standmay be at least partially hollow, wherein the blowermay discharge the return airas treated airflowthrough the blower standand out of the RTU via an outlet.

The return airmay engage with the evaporatoras the return airflows through the RTU. For example, during a refrigeration cycle, heat may transfer from the return airto the refrigerant flowing through the evaporatoras the return airflows through and/or around evaporator. The removal of heat from return airmay reduce the temperature of the return air, thereby treating the return airand producing treated airflow. Before flowing through the evaporator, the return airmay engage with an air filterdisposed upstream of the evaporator. The air filtermay be any suitable filter configured to remove at least a portion of particles or particulate matter present within an airflow. The air filtermay be configured to remove particles from the return airprior to the HVAC systemdischarging the return airafter treatment (i.e., as treated airflow).

The HVAC systemmay further comprise a drain pandisposed underneath the evaporator. The drain panmay be configured to collect condensation or any fluids that may be produced and find their way to the drain pan. For example, operation of evaporatormay produce water condensate from return airas heat is removed from the return air. In another example, ice and/or frost build-up present on the coils of the evaporatormay melt and produce water condensate during a defrost cycle. The drain panmay comprise any suitable size, height, shape, and any combinations thereof. Further, the drain panmay comprise any suitable materials, such as metals, nonmetals, polymers, composites, and any combinations thereof. The drain panmay be flat and/or angled to help direct liquids to a drain aperture, or drain, and an associated drain line to discharge the collected condensate out of the RTU. As illustrated, the drain panmay be disposed under the evaporatorand between the air filterand the blower stand.

The blower standmay comprise at least one sidethat is angled with respect to a vertical axis, wherein the angle of the at least one sideprovides for the blower standto direct a fluid down and towards the drain pan. For example, if refrigerant is leaking from evaporatorduring operations, gravity may pull the refrigerant in a downward direction toward the drain panas the refrigerant may weigh more than the surrounding air. However, air may be flowing through the RTU and may force the falling refrigerant in a lateral direction vertically offset from the drain pan. In this example, the refrigerant may encounter the at least one sideof the blower standand may be directed to flow back towards the drain pan.

each illustrate cross-sectional embodiments of a portion of the HVAC system. As illustrated, the evaporatormay be disposed above the drain pan, wherein the drain panmay be configured to collect condensate and any other suitable fluid (for example, refrigerant leaking from evaporator). The drain panmay comprise a base, a first side, and a second side. The basemay be disposed along the bottom of the HVAC system, wherein both the first sideand the second sidemay extend vertically upward and away from the base.

The first sidemay be disposed at one side of the base, and the second sidemay be disposed at another side of the baseopposite from the first side. Both the first sideand the second sidemay comprise the same dimensions, such as having an equivalent height. In other embodiments, first sidemay have a height less than the height of second side. As illustrated, the base, first side, and second sidemay define a channel, wherein any suitable condensate or fluids may flow into and be partially contained by the channel. The drain panmay have an open side, opposite from the base, wherein condensate or fluids may flow into and be received by the channel. In certain embodiments, there may be a drain (not shown) disposed at a suitable location along the basewhere condensate or fluids contained within the channelmay be directed for discharge.

The HVAC systemmay comprise a flangedisposed adjacent to the drain panand at the bottom of the HVAC system. The flangemay be configured to section off a portion of HVAC systemand prevent condensate or fluids overflowing from the drain panto spread upstream from the evaporator. The flangemay be disposed between the air filterand the drain pan. In embodiments, the flangemay have approximately an equivalent length as the RTU (i.e., the HVAC system). The flangemay have a length equal to or greater than the drain pan. The flangemay comprise any suitable size, height, shape, and any combinations thereof. Further, the flangemay comprise any suitable materials, such as metals, nonmetals, polymers, composites, and any combinations thereof. The flangemay comprise a main supportand a lateral side. The main supportmay extend vertically upwards from the bottom of the HVAC system. The lateral sidemay be disposed perpendicular to the main supportand may extend towards the drain pan. The lateral sidemay extend to an area at least partially below the evaporator. As illustrated, the lateral sidemay be disposed at a height greater than the first sideof drain pan, wherein there may be a clearance of any suitable distance between the lateral sideand first side.

There may be a holedefined in the main support. The holemay be any suitable size and shape. The holemay be disposed at a height greater than the first sideof the drain pan. In other embodiments, holemay be disposed at a height less than the first side. The holemay be configured to direct refrigerant having leaked from HVAC systeminto a housingcontaining the refrigerant detection sensor. The housingmay comprise any suitable size, height, shape, and any combinations thereof. As shown, the housingmay generally be rectangular, but the housingis not limited to such a shape. Further, the housingmay comprise any suitable materials, such as metals, nonmetals, polymers, composites, and any combinations thereof. The housingmay be defined by a plurality of closed sides disposed against the main supportof the flange. In embodiments, the housingmay be sealed against the main support. The housingmay define an internal volumeused for detecting a concentration of refrigerant by the refrigerant detection sensor. The housingmay be disposed between the flangeand the air filter. In embodiments, the housingmay be disposed in proximity to an internal access point for the HVAC system(for example, within 30inches from an access door to an RTU) for ease of maintenance and field servicing.

The housingmay be configured to contain the refrigerant detection sensorwithin the internal volume. The housingmay be configured to prevent leaked refrigerant from diffusing away from the internal volumeand protect the refrigerant detection sensorfrom an external environment. The refrigerant detection sensormay be disposed at a bottom of the housing. In other embodiments, the refrigerant detection sensormay be elevated within the housingas long as the holemaintains a greater height (i.e., the refrigerant detection sensoris not disposed along a parallel plane in-line with the hole). In these embodiments, the height difference may prevent fluid from splashing against the refrigerant detection sensoras fluid enters the housingthrough the hole.

During operation of HVAC system, refrigerant may leak and be collected in drain pan. In embodiments, the collected refrigerant may start to overflow and spill over first sidebetween the first sideand the main supportof flange. The refrigerant may then encounter holeand flow into the housingvia the hole. As the refrigerant flows into the housing, the refrigerant may be contained in the housing, and the refrigerant detection sensormay measure a concentration of that refrigerant with respect to the internal volumeover a period of time. The refrigerant detection sensormay be configured to transmit a plurality of concentration measurements of the refrigerant to the controller(referring to) for further operations.

illustrates a graphcomparing performance of the refrigerant detection sensor(referring to) within the housing(referring to) against the refrigerant detection sensorwithout the housing. In embodiments, the refrigerant may be classified as an A2L refrigerant. Certain properties of A2L refrigerants, such as flammability, may be related to how concentrated a given refrigerant is within a volume. To meet compliance standards, the HVAC systemmay be configured to determine when a lower flammability limit (LFL) of a refrigerant exceeds a threshold value within a specified period of time. The HVAC systemmay further be configured to reduce the LFL of the refrigerant if there is a determination that the LFL exceeds the threshold value within a second period of time.

Graphdepicts a first lineillustrating performance of refrigerant detection sensorwith the housingand a second lineillustrating performance of refrigerant sensorwithout the housing. In these embodiments, performance is measured as % LFL over time. As illustrated at a first point, the HVAC systemwas able to determine that the % LFL of refrigerant present within the internal volume(referring to) of housingwas 12% at 60 seconds based on measurements received by the refrigerant detection sensorwithin the housing. At a second point, the graphillustrates the HVAC systemdetermining that the % LFL of refrigerant present within a volume defined by the RTU was 12% at 82 seconds, wherein the refrigerant detection sensorwas not within the housingand open to the interior of the RTU. In these embodiments, the relevant compliance standards may have required detection of a refrigerant at 12% LFL to occur withinseconds. Graphillustrates both first lineand second linesatisfying this standard, but first lineshows that having the refrigerant detection sensorwithin the housinghaving an internal volumeis faster and more efficient than not having the refrigerant detection sensordisposed within the housing.

is a flowchart of an embodiment of a processfor the HVAC system. The HVAC systemmay employ processfor operating refrigerant detection sensor(referring to) and the HVAC system. At operation, processor(referring to) of the controller(referring to) may operate the HVAC systemin a first mode of operation. For example, the first mode of operation may be an energized status after being turned on for a refrigeration cycle or a heat pump cycle. In an example, the HVAC systemmay be energized to idle in anticipation of a demand. The processormay then transmit instructions to turn on the blower(referring to), the compressor(referring to), the fan(referring to), and any combination thereof for either the refrigeration cycle or heat pump cycle. Operation of the aforementioned components may enable heat transfer between the refrigerant flowing within the working-fluid conduit subsystem(referring to) and either the condenser(referring to) or the evaporator(referring to).

At operation, the processorof the controllermay receive a plurality of concentration measurements of a refrigerant leaking from the working-fluid conduit subsystem. For example, during operation of HVAC systemin a first mode of operation, refrigerant may leak and be collected in the drain pan(referring to). The collected refrigerant may overflow and spill over the first side(referring to) of drain panbetween the first sideand the main support(referring to) of the flange(referring to). The refrigerant may then encounter hole(referring to) and flow into the housing(referring to) via the hole. As the refrigerant flows into the housing, the refrigerant detection sensormay measure a concentration of that refrigerant with respect to the internal volume(referring to) of the housingover a period of time. The refrigerant detection sensormay transmit the plurality of concentration measurements to the controller.

At operation, the processorof the controllermay determine whether or not the concentration of refrigerant in the internal volumeexceeds a threshold value. For example, the memory(referring to) may store the threshold value for a refrigerant associated with a lower flammability limit (LFL), wherein the LFL corresponds to the concentration of the refrigerant. In embodiments, the LFL may refer to the lowest concentration of a substance in the air capable of igniting in the presence of an ignition source. If the processordetermines that the concentration of refrigerant in the internal volumedoes not exceed the stored threshold value, the processproceeds back to operation. Otherwise, the processproceeds to operation.

At operation, the processorof the controllermay transmit a notification indicating that the HVAC systemhas detected a leak of refrigerant. Transmission of the notification may occur in conjunction with, before, or after the HVAC systemtransitions from the first mode of operation to a second mode of operation to reduce the concentration of refrigerant leaking into the HVAC system.

At operation, the processorof the controllermay actuate the HVAC systemto transition to the second mode of operation. During the second mode of operation, the processormay transmit an instruction to turn off the compressorand to actuate the blowerto discharge an airflow. In these embodiments, the airflow may comprise a concentration of refrigerant exceeding the stored threshold value. Discharging the airflow may reduce the concentration of refrigerant present within the HVAC system.

At operation, the processorof the controllermay terminate operation of the HVAC systemfor maintenance when the concentration of refrigerant decreases to a value below the stored threshold value in the memoryas a result, for example, of discharging the airflow in conjunction with operation. For example, after the HVAC systemtransitions to the second mode of operation, the concentration of refrigerant leaking within the HVAC systemdecreases due to the discharge of the leaked refrigerant mixed with the air. There may be a certain volume of leaked refrigerant remaining within one or more components in the HVAC system, such as in the drain panand/or housing. The HVAC systemmay terminate operations in order for an operator to access and service the interior of the HVAC system, wherein the processmay then proceed to end.

While several embodiments have been provided in the present disclosure, it should be understood that the disclosed systems and methods might be embodied in many other specific forms without departing from the spirit or scope of the present disclosure. The present examples are to be considered as illustrative and not restrictive, and the intention is not to be limited to the details given herein. For example, the various elements or components may be combined or integrated with another system or certain features may be omitted, or not implemented.

In addition, techniques, systems, subsystems, and methods described and illustrated in the various embodiments as discrete or separate may be combined or integrated with other systems, modules, techniques, or methods without departing from the scope of the present disclosure. Other items shown or discussed as coupled or directly coupled or communicating with each other may be indirectly coupled or communicating through some interface, device, or intermediate component whether electrically, mechanically, or otherwise. Other examples of changes, substitutions, and alterations are ascertainable by one skilled in the art and could be made without departing from the spirit and scope disclosed herein.

To aid the Patent Office, and any readers of any patent issued on this application in interpreting the claims appended hereto, applicants note that they do not intend any of the appended claims to invoke 35 U.S.C. § 112 (f) as it exists on the date of filing hereof unless the words “means for” or “step for” are explicitly used in the particular claim.