Patent Description:
The ability to maintain healthy environments in working and living spaces depends largely on the quality of air filtration. Filters may be either consumable or reusable and need to be changed/cleaned periodically to ensure optimal air quality and adequate system airflow. The drawback to many systems is that they rely on hours of operation (a timer) to signal a filter change. This results in suboptimal maintenance and system efficiency as the actual filter status is dependent on the cleanliness of the operating environment as much or more so than the hours of use.

Ideally, filter monitoring is implemented by measuring cleanliness of the filter directly, or by measuring a physical parameter that is more closely correlated to the cleanliness of the filter itself. One methodology that has been employed for filter measurement is based on the correlation between filter cleanliness and air resistance. As filter cleanliness decreases, the air resistance increases and results in higher differential pressure across the filter. Since differential pressure varies significantly depending on airspeed, satisfactory accuracy with this approach requires that the blower be operating, and an additional sensor be used to measure system airspeed. Manometers (differential pressure sensors) are also subject to measurement variation due to temperature/humidity changes, so temperature compensation using an additional thermal sensor is needed for accuracy. For these reasons, implementing a differential pressure technique for filter status can add complexity and cost to the air management system.

According to a first aspect of the present invention there is provided an acoustic monitoring system for detecting a condition of an air filter, the acoustic monitoring system including: a first acoustic transducer upstream with respect to airflow over the air filter; a second acoustic transducer upstream with respect to airflow over the air filter; a third acoustic transducer downstream with respect to airflow over the air filter; a fourth acoustic transducer downstream with respect to airflow over the air filter; a control unit in communication with the first acoustic transducer, the second acoustic transducer, the third acoustic transducer and the fourth acoustic transducer; wherein: the control unit is configured to generate an acoustic test signal from at least one of the first acoustic transducer, the second acoustic transducer, the third acoustic transducer and the fourth acoustic transducer; and the control unit is configured to determine a filter attenuation value in response to one or more sound pressure level (SPL) values measured by at least one of the first acoustic transducer, the second acoustic transducer, the third acoustic transducer and the fourth acoustic transducer from the acoustic test signal. The one or more SPL values includes a first direction cross-filter SPL value (c1) and a second direction cross-filter SPL value (c2), wherein the first direction is opposite the second direction. The one or more SPL values includes an upstream SPL value (u) in response to attenuation between the first transducer and the second transducer. The one or more SPL values includes a downstream SPL value (d) in response to attenuation between the third transducer and the fourth transducer.

Further embodiments may include wherein the filter attenuation value is determined as: Rfilter = [(u-c1)+(d-c2)]/<NUM>.

Further embodiments may include wherein the control unit is configured to determine a presence or absence of the air filter by comparing the filter attenuation value to a first threshold.

Further embodiments may include wherein the first threshold varies in response to a type of filter media in the air filter.

Further embodiments may include wherein the control unit is configured to determine the condition of the air filter by comparing the filter attenuation value to a second threshold.

Further embodiments may include wherein the second threshold varies in response to a type of filter media in the air filter.

According to a second aspect of the present invention there is provided a method for detecting a condition of an air filter, includes placing a first acoustic transducer upstream with respect to airflow over the air filter; placing a second acoustic transducer upstream with respect to airflow over the air filter; placing a third acoustic transducer downstream with respect to airflow over the air filter; placing a fourth acoustic transducer downstream with respect to airflow over the air filter; generating an acoustic test signal from at least one of the first acoustic transducer, the second acoustic transducer, the third acoustic transducer and the fourth acoustic transducer; and determining a filter attenuation value in response to one or more sound pressure level (SPL) values measured by at least one of the first acoustic transducer, the second acoustic transducer, the third acoustic transducer and the fourth acoustic transducer from the acoustic test signal. The one or more SPL values includes a first direction cross-filter SPL value (c1) and a second direction cross-filter SPL value (c2), wherein the first direction is opposite the second direction. The one or more SPL values includes an upstream SPL value (u) in response to attenuation between the first transducer and the second transducer. The one or more SPL values includes a downstream SPL value (d) in response to attenuation between the third transducer and the fourth transducer.

Further embodiments may include determining a presence or absence of the air filter by comparing the filter attenuation value to a first threshold.

Further embodiments may include wherein determining the condition of the air filter includes comparing the filter attenuation value to a second threshold.

Technical effects of embodiments of the present invention include the ability to detect air filter condition using a plurality of acoustic transducers.

<FIG> depicts an example environment for implementing embodiments of the present invention. An air handler <NUM> includes a blower <NUM> for generating an airflow over a heat exchanger <NUM>. The air handler may be part of an HVAC system that provides heating and/or cooling. Return air <NUM> is provided to the blower <NUM>, which is blown over the heat exchanger <NUM> and directed by a supply duct as supply air <NUM>. The return air <NUM> flows through an air filter assembly <NUM>. The air filter assembly <NUM> includes an air filter <NUM> (<FIG>) that filters particulates (e.g., dust, pollen, fibers, etc.) from the return air <NUM> prior to the return air <NUM> being directed to an area to be conditioned. The air filter assembly <NUM> includes mechanical structure to support the air filter <NUM>. An acoustic monitoring system <NUM> is in communication with the air filter assembly <NUM> and provides for detection of a condition of the air filter <NUM>, as described in further detail herein.

<FIG> depicts the acoustic monitoring system <NUM>. The acoustic monitoring system <NUM> includes a control unit <NUM> and a plurality of acoustic transducers <NUM>. The acoustic transducers <NUM> may operate as transmitters and/or receivers. As used herein, a transducer may be a transmitter only, a receiver only, or a transmitter/receiver. The acoustic transducers <NUM> may be implemented using one or more of a piezoelectric device, MEMs microphone, or similar technology. One advantage of a piezoelectric transducer is that it can be operated as either a transmitter or receiver allowing multidirectional testing of the system. Hydrophobic coatings can be applied to the acoustic transducers <NUM> as a dust deterrent to minimize build up on the acoustic transducers <NUM> embedded in the airflow.

The control unit <NUM> includes a controller <NUM> which may be implemented using known devices, such as a field programmable gate array (FPGA), central processing unit (CPU), application specific integrated circuits (ASIC), etc. A signal generator <NUM> is used to generate test signals to be emitted by one or more of the transducers <NUM>. A multiplexer <NUM> directs signals to and from the various transducers <NUM>. A preamplifier <NUM> receives an analog output signal from one or more of the transducers <NUM> and increases the amplitude of the analog output signal. An analog-to-digital converter <NUM> converts the output signal from the preamplifier <NUM> into a digital format usable by the controller <NUM>. A memory <NUM> is coupled to, or integrated within, the controller <NUM> and provides for storage of calibration data, measured data, air filter characteristics, executable programs, alarm limits, etc. An indicator <NUM> is coupled to the controller <NUM> and may be used to indicate that an air filter <NUM> needs to be changed. The indicator <NUM> may be a visual indicator, audible indicator or a combination thereof.

<FIG> depicts the acoustic monitoring system <NUM> and air filter assembly <NUM>. Transducers <NUM> are located both upstream and downstream of the air filter <NUM> with respect to airflow, A, across the air filter <NUM>. As shown in <FIG>, a first transducer 140A and a second transducer 140B are located upstream of air filter <NUM>. A third transducer 140C and a fourth transducer 140D are located downstream of air filter <NUM>. The arrangement of transducers 140A-140D allows the acoustic monitoring system <NUM> to compensate for degradation of the transducers 140A-140D due to accumulation of particulates (e.g., dust) on one or more of transducers or other factors, such as decreased transducer efficiency over time.

<FIG> depicts a flowchart of a process for determining a condition of an air filter <NUM>. The process begins at <NUM>, where a periodic filter test is initiated based on a selectable interval controlled by the controller <NUM>.

At <NUM>, an upstream measurement value is obtained by generating an acoustic test signal from transducer 140A. The value of the acoustic signal is controlled by the controller <NUM> and the signal generator <NUM>. Transducer 140B receives the sound pressure level (SPL) from the first acoustic test signal and stores this value in memory as the upstream SPL value (u). In many cases, the attenuation of the upstream value will be small, but can be significant due to accumulation of dust and dirt on transducers 140A and 140B. The upstream SPL value can also vary based on environmental conditions (humidity, temperature, etc.).

At <NUM>, a first direction (upstream-downstream) cross-filter SPL value is obtained by measuring the same acoustic test signal from transducer 140A as generated in <NUM>. Transducer 140D receives the acoustic test signal and generates an output signal representing the magnitude of the received acoustic test signal and stores this value in memory as the first direction cross-filter SPL value (c1). The first direction may be downstream, i.e., across the air filter <NUM> in the same direction as air flow, A.

At <NUM>, a downstream SPL value is obtained by sending an acoustic test signal from transducer 140C. The value of the acoustic test signal is controlled by the controller <NUM> and the signal generator <NUM>. Transducer 140D receives the acoustic test signal and generates an output signal representing the magnitude of the received acoustic test signal and stores this value in memory as the downstream SPL value (d). In many cases, the downstream baseline attenuation value will be small, but can be significant due to accumulation of dust and dirt on transducers 140C and 140D. The downstream SPL value can also vary based on environmental conditions (humidity, temperature, etc.).

At <NUM>, a second direction (downstream-upstream) cross-filter attenuation test is initiated. The second cross-filter value is obtained by measuring the same acoustic test signal from transducer 140C as generated in <NUM>. Transducer 140B receives the acoustic test signal and generates an output signal representing magnitude of the received acoustic test signal and stores this value in memory as the second direction cross-filter SPL value (c2). The second direction may be upstream, i.e., across the air filter <NUM> in the opposite direction as air flow, A.

At <NUM>, a filter attenuation value is calculated using the stored values captured in the previous steps using the following formula: Rfilter = [(u-c1)+(d-c2)]/<NUM>. The averaging of the relative cross-filter and common side measurements accounts for variation due to environmental conditions (humidity, temperature, etc.), as well as the asymmetric accumulation of dust and dirt buildup on upstream and downstream sides of the filter.

At <NUM> the calculated filter attenuation value is compared with a stored first threshold value that represents the value of a clean, installed filter of similar composition and type. If the calculated value is below the minimum level, then the control moves to <NUM> where an "Install Filter" message can be annunciated to indicate that the system does not detect the presence of a filter. The "Install Filter" warning will clear when a value above the stored minimum value is detected. If the calculated filter attenuation value is higher than the stored minimum threshold value, then the control moves to <NUM>.

At <NUM> the calculated filter attenuation value is compared with a stored second threshold value that represents the value of an installed filter of similar composition and type that has reached the recommend lifetime based on the attenuation value. If the calculated value is above second threshold, then the control moves to <NUM> where a "Replace Filter" message can be annunciated to indicate that the system filter should be exchanged for a new unit to maintain proper operating efficiency. The "Replace Filter" warning will clear when a value above the second threshold value is detected. The second threshold is greater than the first threshold.

The first threshold used at <NUM> and the second threshold used in <NUM> may vary based on the type of air filter <NUM> installed. The user may enter the type of air filter <NUM> (e.g., model number, filter media, thickness) through a user interface on control unit <NUM>, or through a QR code on the filter via a mobile phone application. The type of air filter <NUM> may be used to establish condition thresholds in the control unit <NUM>.

In <NUM> the next filter test is scheduled to initiate on a periodic basis based on a timed interval controlled by the controller <NUM> that can a variable, selectable setting (e.g. once every <NUM> hour period).

The process of <FIG> be initiated periodically (e.g., daily, weekly, monthly) under control of the control unit <NUM>. The controller <NUM> may confirm that certain operational conditions are met (e.g., blower <NUM> is off or has been off for a period of time). The cross-filter attenuation test may also be initiated manually, by a user interacting with the control unit <NUM> (e.g., pressing a test button or some other user interface).

Transducers 140A-140D may operate at various frequencies, including ultrasonic frequencies. The test acoustic signal may have a frequency adjusted based on the type of filter media used in air filter <NUM>, or use multiple signal amplitudes to calculate a filter attenuation value. The thresholds used at <NUM> and <NUM> to determine the presence and condition of the air filter <NUM> may vary based on the type of filter media used in air filter <NUM>. The type of filter media used in the air filter <NUM> may be entered via user interface at the control unit <NUM>. The control unit <NUM> may also detect the type of filter media used in the air filter <NUM> by reading indicia on the air filter <NUM> (e.g., a bar code). The controller <NUM> may also detect when the air filter <NUM> is removed (e.g., based on a significant drop in cross-filter attenuation value) and restart the entire process of <FIG>.

Claim 1:
An acoustic monitoring system (<NUM>) for detecting a condition of an air filter (<NUM>), the acoustic monitoring system (<NUM>) comprising:
a first acoustic transducer (140A) upstream with respect to airflow (A) over the air filter (<NUM>);
a second acoustic transducer (140B) upstream with respect to airflow (A) over the air filter (<NUM>);
a third acoustic transducer (140C) downstream with respect to airflow (A) over the air filter (<NUM>);
a fourth acoustic transducer (140D) downstream with respect to airflow (A) over the air filter (<NUM>);
a control unit (<NUM>) in communication with the first acoustic transducer (140A), the second acoustic transducer (140B), the third acoustic transducer (140C) and the fourth acoustic transducer (140D);
characterized in that:
the control unit (<NUM>) is configured to generate an acoustic test signal from at least one of the first acoustic transducer (140A), the second acoustic transducer (140B), the third acoustic transducer (140C) and the fourth acoustic transducer (140D); and
the control unit (<NUM>) is configured to determine a filter attenuation value in response to one or more sound pressure level, SPL, values measured by at least one of the first acoustic transducer (140A), the second acoustic transducer (140B), the third acoustic transducer (140C) and the fourth acoustic transducer (140D) from the acoustic test signal;
wherein the one or more SPL values includes a first direction cross-filter SPL value (c1) and a second direction cross-filter SPL value (c2);
wherein the first direction is opposite the second direction;
wherein the one or more SPL values includes an upstream SPL value (u) in response to attenuation between the first transducer (140A) and the second transducer (140B); and
wherein the one or more SPL values includes a downstream SPL value (d) in response to attenuation between the third transducer (140C) and the fourth transducer (140D).