Abstract:
A system and method for measuring the airflow in an air handling unit, includes placing two sensor tubes having apertures along the thereof at specific locations within the air handling unit that, when attached to a manometer, measuring the differential pressure loss across the two locations and, by means of a special readout scale, providing the airflow through the air handling unit.

Description:
PRIORITY INFORMATION 
     This application is a continuation-in-part of U.S. non-provisional application Ser. No. 12/849,388, filed on Aug. 3, 2010 now U.S. Pat. No. 8,186,230 which in turn claims the benefit of U.S. provisional patent application Ser. No. 61/230,916, filed Aug. 3, 2009, and Ser. No. 61/354,807, filed Jun. 15, 2010, the entire contents of which are herein incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to heating, ventilating and air condition (“HVAC”) systems and more specifically to systems and methods for sensing, measuring, and monitoring airflow conditions within HVAC systems. 
     BACKGROUND OF THE INVENTION 
     Proper airflow is a critical component to assure maximum efficiency in forced-air ducted air conditioning (AC) systems. The Department of Energy sponsored Energy Star Survey determined that more than 50% of air-conditioning installations have low airflow. Low airflow reduces system efficiency (SEER), increases energy costs, results excessive maintenance and repair costs, and leads to premature failure of equipment. 
     Current methodology to measure and establish proper airflow is problematic and unreliable. Methods known in the art, such as placing an air velocity meter inside an AC duct and then estimating the cross-sectional area of the duct, are far too complex and prone to inaccuracy for field technician charged with effectively diagnosing problems with AC systems. More accurate and precise methods of measuring and establishing proper airflow typically require extensive technician training, and expensive instrumentation and installation costs. 
     One example of a known method of measuring airflow in HVAC systems includes the use of “flow hoods.” A flow hood typically consists of a large housing having a known area and an air velocity sensor placed therein. The hood is then placed over an intake grill or return grill of a given ducted AC system, and the air velocity is measured. The clear downside to these flow hoods is that the large housing often renders the flow hood useless in buildings where the grills are too close to other structural elements and therefore the flow hood, while accurate, simply cannot be used. 
     Other examples of known methods for measuring HVAC airflow include temperature-based methods. Typically, one first turns on the heating element within the system and then measures the temperature of the air going into the heater and the temperature of the air leaving the heater. Then, a series of calculations are carried out, resulting in a determination of the airflow velocity. However, this indirect method of calculating airflow velocity can be very imprecise and inaccurate due to the stratification of the temperature gradient across the system and therefore is not effective in diagnosing problems within the HVAC system, whether up-stream or down-stream from the air handling unit. 
     Known means for monitoring the performance and efficiency of an HVAC system have severe limitations. Typical thermostats known in the art do not monitor the actual airflow conditions in its attendant HVAC system. Rather, they simply measure the temperature of the room to be cooled/heated and provide a feedback-based switching system for the HVAC system. While some of these thermostats have the ability to inform the user whether a filter change is needed, this indication is usually based solely on the length of operation of the HVAC system between filter changes and does not take into account the actual airflow conditions within the system. 
     Consequently, there is a marked need in the art for an easy-to-operate, cost-effective, integrated system and method for sensing, measuring, and monitoring the airflow conditions within an HVAC system. 
     SUMMARY OF THE INVENTION 
     The present invention comprises several embodiments of a system and method for sensing, measuring, and monitoring the airflow in an HVAC system, and more specifically, the air handling unit thereof. One embodiment comprises the use of a pressure plate having a known free area which is placed in the filter rack of an air handling unit. The pressure loss across the plate is measured using a manometer attached to the plate by two leads, one on each side. The pressure loss is converted to an airflow velocity measurement using known airflow data for the particular air handling unit. Other embodiments comprise the use of sensor tubes placed at specific locations within the air handling unit that are attached to a manometer for determining the pressure differential across the two locations. 
     A comparison of the measured airflow velocity to the optimal airflow velocity can be determined in order to assess whether there is an obstruction in the system. Further, the disclosed systems can be used to monitor the actual performance of a given HVAC system over time and a visible or audible indicator can be employed to signal that a filter change is needed or that there is an obstruction or other problem within the system, such as a dirty evaporator coil. 
     Accordingly, it is an object of the present invention to eliminate the hurdles of known methods for measuring and monitoring HVAC airflow conditions and allow an HVAC technician of average skill to accurately and precisely determine the airflow conditions and correct airflow deficiencies for any HVAC system. It is a further objective of the present invention to provide the ability to monitor an HVAC system during its useful life to assure maximum energy efficiency and filtration effectiveness. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is side aspect view of one embodiment of the system of the present invention. 
         FIG. 2  is side cutaway view of one embodiment of the system of the present invention. 
         FIG. 3  is an exemplary chart determined in accordance with the method of the present invention, depicting the relationship between airflow and differential static pressure for a given air handling unit and pressure plate. 
         FIG. 4  is an exemplary graph employed in accordance with the method of the present invention, depicting the relationship between the percentage of air flow through a given air filter and the level of obstruction of the given air filter. 
         FIG. 5  is an exemplary chart employed in accordance with the method of the present invention, depicting various air filters with respect to cost and filter face velocity. 
         FIG. 6  is side view of another embodiment of the system of the present invention. 
         FIG. 7  is an expanded view of another embodiment of the system of the present invention, depicting sensor tubes mounted to an auxiliary heater, wherein the sensor tubes are disposed between the auxiliary heater and a blower (not shown). 
         FIG. 8  illustrates a manometer face with a readout scale in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     While the present invention will be described more fully hereinafter with reference to the accompanying drawings, in which one or more embodiments of the present invention are shown, it is to be understood at the outset of the description which follows that persons of skill in the appropriate arts may modify the invention herein described while still achieving the favorable results of this invention. Accordingly, the description which follows is to be understood as being a broad, teaching disclosure directed to persons of skill in the appropriate arts, and not as limiting upon the present invention. 
     Pressure Plate 
       FIG. 1  depicts one embodiment of the system of the present invention. Shown is air handling unit  10 , supply duct  11 , perforated pressure plate  12  containing a plurality of apertures  13 , and flexible leads  14  and  15 . Air flows into the system in the direction of arrow  17 . With reference to  FIG. 2 , also shown is filter rack  18 , blower  19 , and heating element  110 . The dimensions of the pressure plate  12  correspond to the dimensions of the particular filter rack  18  of the air handling unit  10 . In accordance with the method of the present invention, the combined area of the apertures  13  of the pressure plate  12  is calculated to represent an air pressure loss equal to the known nominal airflow rating, measured in cubic feet per minute (cfm), of the particular air handling unit  10  taking into account a standard low-pressure-loss air filter under slightly used (dirty) conditions. Accordingly, the pressure plate  12  provides a stable surface across which to measure the pressure loss with predictability and repeatability. 
     In order to determine the optimal airflow for a given air handling unit  10  in the field, an airflow/pressure loss relationship is first calculated under laboratory conditions. Accordingly, each specific air handling unit  10  (or self contained air conditioning unit) model for any given manufacturer may be tested according to the method of the present invention: 
     The published nominal airflow for the subject air handling unit  10  is reviewed and noted. If the air handling unit  10  has provisions for a mounted air filter, the filter is removed and a pressure plate  12  with a known free area opening is inserted in the filter rack. The pressure plate  12  is designed to equally distribute the air across the face area of the intake of air handling unit  10  in order to create sufficient pressure to provide repeatable differential static pressure readings at varying airflow rates. 
     The differential static pressure across plate  12  is measured and recorded using a differential pressure manometer  112  using two flexible leads  14  and  15  which are attached to either side of the pressure plate  12  and further to manometer  112 . Next, pressure plate  12  is removed and the nominal airflow is measured with a high accuracy flow meter, such as, without limitation, a flow hood or air velocity meter known in the art. Additional differential static pressure measurements are then performed at varying airflow rates which are created either by restricting the airflow at the inlet or outlet of the system and/or varying the blower  19  speed of the air handling unit  10 . Accordingly, by plotting the recorded data, an airflow/pressure loss table is generated, as shown by way of example in  FIG. 3 , for a particular air handling unit  10 . This plot depicts the relationship between the static differential pressure and the actual airflow. Additional plots can be generated which take into account air-filters of varying size and filtration capability. 
     Pressure Plate—Establishing and Monitoring Proper Airflow 
     In order to establish and monitor proper airflow according to the present invention, one first determines the current airflow of a particular air handling unit  10  in order to assess whether the airflow is sub-optimal, and secondly, determine the cause of the sub-optimal airflow and the location of the blockage (i.e. upstream or downstream). Accordingly, the airflow (without filter) for any specific air handling unit  10  or air handling unit/filter combination can be determined by measuring the differential static pressure across the pressure plate  12  and referring to the corresponding airflow/pressure loss plot (for example,  FIG. 3 ) for that specific air handling unit  10  or air handling unit/filter-grille combination. This procedure allows the technician to accurately determine the airflow with simple low cost devices where the use of laboratory instruments is not practical. 
     Specifically, the airflow is determined by removing the filter from the filter rack and inserting the appropriate pressure plate  12  that corresponds to the particular air handling unit  10 . The technician then measures the pressure loss across the plate  12  using a differential pressure manometer  112  and determines the corresponding airflow by using the known airflow/pressure loss plot (for example,  FIG. 3 ) for the air handling unit  10 . With reference to  FIGS. 4 and 5 , the technician can then determine the optimal airflow, taking into account airflow loss due to the type of air filter being used by referring to the airflow/filter degradation relationship, which provides a reference for most standard filter types and filter-rack size combinations. 
     Once the airflow has been assessed and adjustments and/or corrections have been made to achieve the optimum airflow, the corresponding suction pressure of the blower  19  (shown in  FIGS. 1 and 2 ) may be measured and recorded in real time at point  16 . This establishes the reference point of optimum airflow for the system regardless of variations caused by dirty filters, dirty coils, closed registers, and the like. A number of visible or audible devices may be used to monitor airflow and conditions and signal deviation from the reference point. Such devices may be as simple as a visual indicator gage  111  or an audible alarm that may be incorporated into an electronic thermostat. The monitoring data may be used to calculate cost/benefit analysis for system efficiency and filtration effectiveness by using the airflow/filter degradation relationship shown in  FIG. 4  and  FIG. 5 . 
     Sensor Tubes 
       FIG. 6  depicts an alternative embodiment of the system of the present invention. Shown is air handling unit  20 , supply duct  21  with air flowing in the direction of arrow  27 , auxiliary heater assembly  22 , air velocity pressure sensor tubes  24  and  25 , heating/cooling coil  28 , blower  29 , motor  210 , heating element  211 , and differential pressure manometer  212 . 
     With reference to  FIG. 7 , in one embodiment, the sensor tubes  24  and  25  are mounted directly in the auxiliary heater assembly  22 , or on a mounting plate (not shown) disposed within supply duct  21  when the electric heater is not integrated into the air handling unit  20 . Each of sensor tubes  24  and  25  contain one or more apertures  23  located substantially toward the distal end of the tubes through which air ejected from the blower  29  is sensed. In some embodiments, sensor tubes  24  and  25  are stacked one upon the other such that the corresponding apertures  23  of the tubes are substantially co-incident. 
     As shown in  FIG. 7 , tube  25  is disposed between the blower  19  and tube  24 , with both sensor tubes  24  and  25  disposed between the blower  19  and heating element  211 , such that tube  25  measures the total pressure and tube  24  measures the static pressure. The two sensor tubes  24  and  25  are attached to manometer  212 , at their proximal ends. Air velocity pressure is determined by subtracting the static pressure from the total pressure. Accordingly, with air flowing in the direction of arrow  213 , the manometer  212  measures the air velocity pressure by sensing the difference between the total pressure at sensor tube  25  and static pressure at sensor tube  24 . 
     With reference again to  FIG. 6 , in an alternative embodiment, sensor tubes  24  and  25  may be located at the outlet  32  and inlet  31 , respectively, of the blower  29 . In this configuration, the manometer  212  measures the pressure differential across the blower  29 , which can be used to effectively determine obstructions or problems in the system, i.e. whether it is up-stream or down-stream of the blower. The advantage of this configuration is that there is typically a greater pressure differential across the blower than is typically found within the auxiliary heater assembly or, if omitted, within the supply duct  21 . 
     As with the pressure plate embodiment, in order to determine the optimal airflow for a given air handling unit  20  in the field, an airflow/pressure loss relationship is first calculated under laboratory conditions. Accordingly, each specific air handling unit  20  (or self contained air conditioning unit) model for any given manufacturer may be tested according to the method of the present invention. The published nominal airflow for the subject air handling unit  20  is reviewed and noted. Sensor tubes  24  and  25  with a known free area opening (i.e. combined surface area of one or more apertures  23 ) are inserted between the auxiliary heater  22  (if used) and blower  19 . Alternatively, sensor tubes  24  and  25  may be located at the outlet  32  and inlet  31 , respectively, of the blower  29 . 
     The differential static pressure between sensor tube  24  and sensor tube  25  is measured and recorded using the aforementioned manometer  212 . Next, sensor tube  24  and sensor tube  25  are removed and the nominal airflow is measured with a high accuracy flow meter. Additional air velocity pressure measurements are then performed at varying airflow rates which are created by restricting the airflow inlet or outlet; and/or varying the fan speed of the blower  19  of the air handling unit  20  (or self contained air conditioning unit). Accordingly, an airflow/air velocity pressure table is generated as shown by way of example in  FIG. 3 , for a particular air handling unit  20 , and auxiliary electric heater (if used) combination. Additional plots can be generated which take into account airflow losses from various air filter models of various manufacturers. 
     Sensor Tubes—Establishing and Monitoring Proper Airflow 
     In order to establish and monitor proper airflow in an air conditioning system according to the second embodiment of the method of the present invention, one first determines the actual airflow to assess whether the airflow is sub-optimal, and make adjustments to fan speeds, dampers, duct sizing, etc. to attain optimal airflow. The sensor tube embodiment of the present invention allows the airflow to be measured for any system, regardless of airflow restrictions (air filters, size of ductwork, dampers, etc.) and for each specific air handling unit  20  that is used in the system that has been laboratory tested with the present invention. This allows the technician to use simple low cost devices to quickly and accurately determine airflow if the use of laboratory instruments is not practical. 
     The technician measures the pressure loss across the sensor tubes  24  and  25  manometer  212  and determines the corresponding airflow by using the known airflow/pressure loss plot (for example,  FIG. 3 ) for the air handling unit  20 . With reference to  FIGS. 4 and 5 , the technician can then determine the optimal airflow, taking into account airflow loss due to the type of air filter being used by referring to the airflow/filter degradation relationship, which provides a reference for most standard filter types and filter-rack size combinations. 
     In comparison to the pressure plate embodiment described herein, the sensor tube embodiments have additional benefits in that the sensor tube arrangement can be permanently installed for continuous monitoring and adjustment of the airflow. Accordingly, once the airflow has been assessed and adjustments and/or corrections have been made to achieve the optimum airflow, the corresponding pressures may be measured and recorded in real time with the use of manometer  212 . If the optimal airflow falls below a given threshold value, a warning can be activated which advises the operator of the AC unit to check the unit for obstructions or to change a dirty filter. In cases where the airflow drop is drastic, a secondary warning can be delivered which instructs the operator to contact a technician to service the unit or an automated shutdown of the AC system may be initiated. 
     In a third embodiment of the method of the present invention, the known airflow/pressure loss plot (for example,  FIG. 3 ) for the air handling unit  20  may be directly incorporated into the scale readout on the faceplate of manometer  212  making it unnecessary for the user to make note of the pressure differential and refer to a separate table such as the one shown in  FIG. 3 . 
     With this third embodiment, the user need only refer to the manometer  212  itself to directly determine the airflow without reference to an external chart. An example of the scale readout on the face of a manometer  212  to be used with this third embodiment is shown in  FIG. 8 . 
     Referring to  FIG. 8 , the shown, scale readout  300  can be incorporated by imprinting the information directly on the face of the manometer  212  or on a removable card insert that is overlaid over an existing manometer  212  readout scale. The scale readout  300  can also be printed on an overlay that can be applied externally to the manometer  212 . 
     As shown in  FIG. 8 , in addition to the traditional WC (inches, water column) scale  310 , the scale readout  300  includes one or more additional scales ( 301 ,  302 ) specifically applicable to particular AC units. In this case there is a scale for a 2.0 TON unit,  301 ; and a separate scale for a 2.5 TON unit  302 . In addition, each scale includes one or more sub-scales ( 303 - 305 ,  306 - 308 ) each of which can correspond to a different fan speed for its respective unit. Each of the sub-scales, in turn, includes a lower and upper range corresponding to the measured airflow. 
     In the example shown, the sub-scale  304  corresponding to a 2.0 TON AC unit with a fan setting of “2” would indicate a high airflow of 800 CFM when pointer  309  (shown for reference only) indicates approximately 0.41 WC and a low airflow of 700 CFM when pointer  309  indicates approximately 0.70 WC. The specific correlation of the scale would, of course, vary from unit to unit as determined experimentally in accordance with the methods detailed above. 
     In the foregoing description, the present invention has been described with reference to specific exemplary embodiments thereof. However, it will be apparent to those skilled in the art that a person understanding this invention may conceive of changes or other embodiments or variations, which utilize the principles of this invention without departing from the broader spirit and scope of the invention. The specification and drawings are, therefore, to be regarded in an illustrative rather than a restrictive sense.