Measuring and testing – Volume or rate of flow – Using differential pressure
Reexamination Certificate
2000-03-30
2002-08-27
Noori, Max (Department: 2855)
Measuring and testing
Volume or rate of flow
Using differential pressure
Reexamination Certificate
active
06439061
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to airflow measuring assemblies and particularly to airflow measuring assemblies and methods to measure airflow in air handling equipment. The assemblies of the invention are constructed and arranged for placement in an air handling system and to condition or direct the airflow of the system into a controlled fluid stream for analysis. The measuring assemblies and methods provide accurate and reproducible airflow measurements for the air handling equipment being monitored or tested. More particularly, the assemblies of this invention are constructed and arranged for use in forced air HVAC distribution systems. The airflow measuring assembly is constructed to be placed in a predetermined location of a forced air distribution system, for example, in a slot proximate the air handler unit.
It is important for air handling equipment, such as furnaces, heat pumps and air conditioners to have proper airflow to insure efficient operation of the HVAC systems. Specified airflow or air volume rates are required to be within specified airflow ranges for particular air handling systems. The flow of air is typically measured to insure that a forced air distribution system, for example, was properly designed and installed, and is operating according to the specification. For example, it is important to avoid low airflow in heat pumps, furnaces and air conditioners because reduced airflow results in performance inefficiency and can damage the compressor. Determining an unusually low or high airflow may indicate that a leak in the system or insufficient ventilation exists.
A forced air distribution system typically includes an air handler unit, ductwork, registers, dampers, filters, etc. Although the airflow measuring assembly may be utilized in connection with any air handler unit, which contains the blower, the assembly may also be utilized at any location within the air distribution system. Preferably, the assembly is used in the filter position of the air distribution system. Depending upon the similarity of flow resistance between the assembly and the filter typically installed in the air distribution system, a correction factor is calculated and used in the method of the invention.
Airflow is preferably measured, however, proximate the air handler unit of the air handling assembly, where proper airflow is important for efficient operation of the equipment. Although the airflow measuring assembly may be positioned, permanently or removably, at a number of locations in an air handling assembly, it has been found that the air filter slot typically provided in air handling equipment provides an efficient, easy and convenient place for such airflow measurement. However, it is within the purview of the invention to utilize other positions or specified slots in an air handling assembly to make such airflow measurements. Thus, the airflow measuring assembly of the invention may be pre-installed in a furnace proximate the blower, may be positioned for use in a specified slot across the airstream, may be positioned in the filter slot of air handling equipment and in the filter slot of a forced air distribution system, whether proximate the blower unit or remote therefrom.
In residential furnaces, for example, a specified volume of air is heated and distributed throughout a house and is returned to the furnace by the air return duct system. It is desirable to measure the flow of air through the furnace, in order to insure airflow within the specified operating range of a furnace. The airflow measuring assemblies of this invention measure airflow in a furnace, such as at the filter position, and are constructed to be placed into the furnace filter slot or a similar position in the furnace. This placement has been found to provide a convenient, accessible location for the accurate air volume flow rate measurements. The airflow measuring assemblies are constructed and arranged to condition and direct the airflow therethrough and to measure the airflow via the use of an anemometer, for example, or by measuring a pressure signal generated by the assembly. In the latter assembly, a differential pressure signal generated from single or multiple designed pressure signal locations within the controlled fluid stream can be obtained and converted into volumetric airflow utilizing mathematical relationships. The assemblies of the invention may also be constructed and arranged to simulate the resistance of a typical filter for accuracy and reproducibility of the airflow measurements. Furthermore, a correction factor based on air handler system pressures measured with a typical filter, and again, with the assembly can be derived for improved accuracy. The correction factor accounts for the difference in airflow resistance between the test assembly and filter and is used to correct the measured airflow of the system by the test assembly.
Although the utilization of the airflow measuring assembly of the invention at or near the air handler may be preferred, the assembly may also be used at other locations of an air handler assembly. For example, filter holders may be built into ductwork or positioned at the return grille of the system. If the assembly is installed remotely from the furnace or air handler, duct leakage between the assembly and the air handler may exist and needs to be taken into consideration. Further, if the pressure drop across the filter is significantly different from that of the airflow measuring assembly, this difference is taken into consideration by calculating a correction factor.
Various airflow measuring assemblies and methods to estimate volumetric airflow have been proposed and used in the past, however, these prior art assemblies and methods have drawbacks and difficulties. Prior art methods and devices have often been found to be burdensome, difficult to use and yield inaccurate and unrepeatable results for purposes of measuring airflow in air handling equipment. For example, prior art devices typically require more care in proper use to obtain accurate results than installers or others have time to provide. Prior art assemblies and techniques include the utilization of heating elements in an air stream and a calibrated fan assembly used to deliver air to the return side of the air handler. However, accuracy in result and the time consumption required, to utilize these prior art techniques are undesirable for general testing usage. Other prior art assemblies use pitot tubes or like devices to measure air velocity pressures at various locations in a system and convert the measurement to volumetric airflow. Other prior art assemblies measure airflow at air outlets by trapping air in large capture hood devices. Capture hood devices are often difficult to seal over registers and return grilles due to obstructions and their respective locations, i.e., due to furniture, under cabinet locations, etc. And, because capture hood devices measure airflow at the registers and return grilles, any duct leakage is not accounted for when airflow at the air handler is desired.
Still other prior art devices attempt to have as little effect as possible on air flow by minimizing the pressure loss through the measuring device. The latter devices tend to be very sensitive to upstream conditions and require long lengths of straight duct to be accurate. Such lengths of straight duct often do not exist in actual installed systems. On the other hand, the assembly and method of this invention have been found through experimentation to be insensitive to upstream conditions. In summary, known prior art assemblies and methods are difficult and cumbersome to use and do not necessarily provide accurate airflow measurement at the air handler, where such measurement is most useful and yield more accurate and reproducible results.
Prior art assemblies, as far as is known, have not been developed to measure airflow at the air filter location of an air handler, for example. The airflow measuring assembly of the present invention overcomes the difficulties in u
Nelson Gary D.
Palmiter Larry
Rothman Ronald C.
Eggink Anthony G.
Noori Max
The Energy Conservatory
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