Integrating Room Space Pressure Measurements with Hvac Controls

This application claims the benefit of U.S. Provisional Application No. 63/639,815, filed Apr. 29, 2024, and titled “Integrating Room Pressure with HVAC Controls,” which is herein incorporated by reference in its entirety.

The ability to monitor individual rooms with an understanding of pressure changes relative to outside air pressure provides an opportunity to determine whether windows or doors are open while trying to cool or heat the room. According to some methods, sensors can be installed to detect if a window or door is open. In some examples, a thermostat receives the sensor information from the door and window sensors and then, based on this sensor data, reacts to ambient conditions by turning the air conditioning or heating off as needed. However, each sensor is costly and needs to be installed and integrated with the thermostat so as to permit easy removal and ready battery replacement.

These and other challenges are addressed by a substantially tubeless and wireless system that accurately measures differential air pressures at several different indoor points relative to outside air. In some embodiments, individual units (e.g., receivers and/or zone transmitters) apply an algorithm to derive the air pressure in the space in which the unit is installed. If the derived pressure is at or near the outside pressure, the unit starts a counter to measure the length of time the equalized pressure condition exists. If the condition persists longer than the time it takes to egress or ingress through a door or to open and close a window, a flag signal is sent to the unit. The unit then takes action to halt cooling or heating in the space. In some embodiments, the unit may be a thermostat, or HVAC controlling device or cloud acting as a HVAC controller. Notification to the end user of the action taken may be provided on the thermostat panel or through a mobile application or other available source.

Disclosed here are embodiments of an automated tubeless communicating pressure system that may continuously, periodically, or aperiodically determine air pressure of an indoor space relative to outdoor air pressure (differential pressure) and take action through a unit to turn heating or cooling OFF if the pressure system determines windows or doors are open. The system may include, among other elements, one or more zone transmitting devices capable of Pascal resolution pressure measurement, communication components, a receiver, which may be a thermostat, with a communications component and the ability to influence HVAC climate controls directly through relays or indirectly through cloud based APIs. An outdoor air transmitter is present to measure outside barometric pressure. Each individual receive or zone device receives outside air pressure measurements and resolves individual indoor space pressures independently. The receiving device aggregates the pressure information from the multiple zone transmitters. Action performed by the thermostat is based on if the thermostat is actively cooling or heating the space. The supply fan control, typically the G relay, acts as a trigger to begin monitoring pressure and, if required, take action.

The receiving device may have a visual display component that alerts users to the condition. In some embodiments, system alerts may be generated and sent to a mobile app or text message. Pre- and post-processing algorithms may be integrated into both transmitters and receivers to determine if the condition is temporary such as a door opening and closing, or if the condition is persistent (e.g., a window is opened and remains so). The receiver device may obtain outside air barometric pressure from a wired sensor, a wireless sensor or an external source such as a cloud interface, for example. This information may be continuously transmitted to all elements in the pressure measurement system. A differential pressure reading is derived from the two absolute pressure readings (indoor and outdoor) to determine if the space is pressurized or at a neutral pressure with respect to the outside air, indicating a door or window is open and causing the space pressure to neutralize. Post processing algorithms and filters may be applied to increase pressure resolution to address noise, prior to being sent to a receiver.

In some embodiments, an automatic calibration process may be trigged when the space is non-occupied. This can be determined by the schedule in the thermostat or if the CO2 level indicates that there are no people present. Calibration is performed during unoccupied periods. Calibration uses an offset zeroization algorithm introduce to calculate variables into the final derived pressure values. Variables determined during the zeroization process include: production offsets between two sensors, drift introduced over time and altitude differences between the physical placement of the two absolute sensors. Temperature of the sensor membranes is controlled at all times through a modulating pulse width signal with feedback driving a heating element.

In at least one embodiment, multiple (indoor) zone and outside transmitting devices may communicate wirelessly with a receiver device. Although described as a “wireless transmission” this phrase or word is not intended to be limiting, but would encompass, for example, any signal transmission method including but not limited to Wi-Fi, Lo-Ra, Cellular, BlueTooth, RF in any MHZ, Zigbee, cable,C bus, serial and/or directly to an application programming interface for cloud based calculations.

The transmitters can be battery and/or line voltage operated, and support a visual method to test the communication link and confirm operation. In some embodiments, this testing capability can be installed through an embedded web server running on the transmitter that is accessible through a browser, for example, allowing the testing device to be remote from the transmitter device. However, incorporating the testing capability directly into the transmitter is an example and testing is not limited to such embodiments. In the case that the unit is battery operated, the transmitting device may also contains an audio method to notify the user of low battery or other alert conditions.

The receiver can be battery and/or line voltage operated. A visual method for an installer to configure the system may be provided by an embedded web server that is accessible through a standard browser, allowing the configuration to be remote from the receiver. Alternatively, or in addition, the configuration device may be incorporated directly into the receiver. In some embodiments, the receiver may provide a visual display to the user that a window or door has been opened or is open.

Advantages of certain embodiments described herein are numerous and include, without limitation, providing differential pressure measurements between any two points independently and at a low cost by using separate micro-electromechanical (MEMS)-based absolute pressure sensor data to perform the algorithms associated with determining the pressure difference between the areas of interest. A visual indicator of individual space pressure/ventilation characteristics may include both air molecules present based on CO2 molecules and the flow of these air molecules into or out of the space based on positive or negative pressurization. Updating the firmware over the wireless link to provide future capabilities and bug fixes is also possible.

shows an example of a communications systemthat includes a plurality of transmitting units (here, represented by transmitters,, and) controlled by a receiving unit (represented by a receiver), although no limit on the number of transmitters or receiversshould be inferred. The receivermay be or include a thermostat or an HVAC controller, for example. In some embodiments, the transmitters,, and/ormay be located in different respective indoor spaces or zones, for example in different rooms, with the same receiveracting as a receiver for multiple transmitters. The receivermay receive information regarding outdoor air pressure sensed by a sensor or sensorsand communicated to the receiver. The outside air pressure may be a reference used by the transmitters to derive differential pressure in the zones in which the transmitters are respectively installed and resolve zone differential pressure relative to the outside. In at least some embodiments, the receivermay be responsible for the retransmission of outside pressure information to one or more of the transmitters,, and. This information can be transmitted to the receivervia a direct wired input or wirelessly over Wi-Fi or other method using UDP broadcast packets, for example.

The transmitters,andmay capture transmissions from the receiverto receive outside air information and also the calibration state. In this schematic, each of the individual zones monitored by the transmitters,, andmay transmit their resolved differential pressures in their respective zones. This data may be transmitted in the form of UDP packets over Wi-Fi to the receiver. In such embodiments, the receivermay have an internal antenna and be under line power operations. Data received from the transmitters are then used in the control determination algorithm described elsewhere herein.

shows an example transmitterin block diagram form according to at least one embodiment. This figure identifies the breakout of hardware logic elements that can perform various functions of the transmitter. The transmittermay correspond to one or more of the transmitter devices,, andof.

The transmittermay include a power management unit, die temperature control logic, an ambient noise (fast Fourier transform) filter, a differential pressure derivation algorithm unit, a zeroization algorithm unit, and a visual display filter. The transmittermay be operably coupled to receive AC power from a commercial power source via a line conditioning unit, and/or DC power from another power source, such as a battery. In case the power is received from an AC power source, the line conditioning may include an AC/DC converter, not shown.

The transmittermay further be operably coupled to one or more sensors related to air quality, examples of which may include one or more of an absolute pressure sensor(which may include or be coupled with a die temperature sensor to adjust for a pressure offset proportional to the temperature of the sensor die), a CO2 sensor, and one or more other indoor air quality sensors. In some embodiments, output of the absolute pressure sensor(as adjusted according to the die temperature, in some examples) is received by the transmittervia the ambient noise FFT filter.

The absolute pressure sensorand die temperature control logicmay be coupled via an ABS temperature control circuit. The ABS temperature control circuitmay receive output from the absolute pressure sensorand provide the same to the die temperature control logicwhich operates to adjust the temperature of the die via a heating element to bring the temperature of the die sensor into conformity with a desired temperature programmed into the ABS temperature control sensor. An objective of this circuit is to maintain a predetermined die temperature between both the transmitting and receiving sensor membranes, resulting in a more accurate pressure calculation. The die temperature control logicmay operate a pulse width modulated control loop that maintains a known and fixed temperature at the sensor membrane. Software filters such as the FFTmay be applied to the output of the absolute pressure sensor. For example, pressure reading samples between the two disparate sensors are aligned in time to synchronize the measurements, resulting in comparing pressure differences within the sample period. These sample adjustments may take into consideration, for example, any communications delay incurred between getting the readings from the transmitting unit to the receiving unit. Rate of change filters applied to the output “slow” down any transients effects seen in the data from rapid noise injection.

The transmittermay receive measurements from one or more sensors integrated into the transmitting unit and/or made by a local sensor or sensors associated with the transmitter(e.g., at a site local to the transmitter and in communication with the transmitter), including but not limited to pressure, temperature, and/or humidity, and may wirelessly transmit the data to the receiver. The transmittermay have an internal or external antenna, and may be battery or line powered.

Outside air information, e.g., the outside air pressure, may be re-transmitted from one transmitter to another transmitter or transmitters. For example, in the illustration of, the transmittermay be configured to act as a micro access point for one or more of the transmitters,,. This allows the transmitter(s) to listen for re-transmission packets specifically from the transmitterover, e.g., a wireless link, and obtain the data being transmitted substantially at the same time as received by the transmitter.

The primary control logic executed by one or more processor(s) may apply the differential pressure derivation algorithmto the received measurement data, store the measurement data in local data storage, and compare the measurement data with its own measurements taken by the absolute pressure sensor, the CO2 sensor, and/or the other indoor air quality sensors according to a time vector to establish a differential pressure between the zone in which the transmitteris located and the outside air. One or more filters may be employed for the user to apply, for example via the user interface, rate of change limits to the output of the pressure sensor data via the communication interface and/or user interface, transmitter sensor data, and derived differential pressure value output. Optionally in accordance with a data averaging filter applied to the space pressure displayed via the visual display filter, a value for the differential pressure may be determined and the value may be output and/or transmitted via the user interface or communication interface.

The power management unitmay be embedded in the transmitter, and may determine the unit power source—the AC/DC line (via the line conditioning unit) or the battery, for example—and adapt communications and control operations based on the power configuration. During battery operations, a real-time clock may be used in some embodiments to wake up the transmitterwhen powered down to save energy, and to anticipate data packets at transmitting unit-based pre-configured time intervals.

In the case of the transmitter, wireless datamay be received from the receiverto synchronize calibration of the units and receive outside air pressure readings. Primary control stores measurements and compares the measurements with its own measurementsusing a differential pressure derivation algorithm based on a time vector to establish a differential between sensors. Several filters are available for the user to apply rate of change limits to the output of the pressure sensor data, transmitter sensor data and derived differential pressure value output. Once a value is determined, this can be transmittedto the visual display via the visual display filter.

A control and sensor management module manages the sensor temperature, reliability and data integrity. These functions are performed through the sensor interface hardware and software logicthat is operating a pulse width modulated control loop to maintain a known and fixed temperature at the sensor membrane. One or more additional software filters(e.g., an ambient noise filter) may be applied to the derived output from the sensors for out of band readings, rate of change dampening, sample timing filters for data integrity.

A CO2 sensorand other relevant indoor air quality sensorsmay be provided to measure, e.g., ambient temperature, humidity, particulates, etc. This data is available to expand the visual display and further refine the algorithms used for the display of ventilation and air quality, for example using machine learning techniques.

The transmitter embeds a power management moduleto detect the unit power source—e.g., batteryor line—and adapt communications and control operations based on the power configuration. For example, during battery operation, a real time clock may be used to wake up the transmitter.

illustrates an example of a receiveraccording to at least one embodiment. The receivermay correspond to the receiver. The receivermay function at least in part to receive data from one or more of the transmitting devices over a communications link, decode the protocol, and send commands to a control system in the receiverfor modifying ambient conditions such as temperature. For example, the control system may turn on or off a heating unit or air conditioning unit to conserve energy when an open door and/or open window is determined based on the pressure differential.

In some embodiments, the receiverreceives measurements, including but not limited to pressure, temperature, humidity, and outside air pressure, from sensors in and/or local to the receiver, which may retransmit at least the outside air pressure, e.g., wirelessly, to the transmitters,, and. The receivermay also transmit information, in the form of a UDP packet for example, during a calibration, as described elsewhere herein.

Because the receiverincludes many of the same components as are included in the transmitterand are discussed above (such as the communication interface, user interface, processor(s), memory, and device hardware), such overlapping components will not be described further except to the extent there may be non-negligible differences.identifies the break out of example hardware logic elements associated with the pressure determination according to at least one embodiment. In some embodiments, the climate control logic in the receiveroperates as in the industry standard. The receiverreceives power from the Controller chassis.

In addition to these components, the receivermay include die temperature control logic, an ambient noise FFT filter, a differential pressure derivation algorithm unit, a zeroization algorithm unit, a visual display filter, and an air quality (AQ) control algorithm unit. The receivermay be operably coupled to receive AC power from a commercial power source, e.g., via a line conditioning unit, and/or DC power from another power source, such as a battery. In case the power is received from an AC power source, the line conditioning may include an AC/DC converter.

The receivermay further be operably coupled to one or more sensors related to air quality, examples of which may include one or more of an absolute pressure sensor (which may include or be coupled with a die temperature sensor to adjust for a pressure offset proportional to the temperature of the sensor die), a CO2 sensor, and one or more other indoor air quality sensors. In some embodiments, output of the absolute pressure sensor (as adjusted according to the die temperature, in some examples) may be received by the receivervia the ambient noise FFT filter.

As illustrated in, the absolute pressure sensor and die temperature control logic may be coupled via an ABS temperature control circuit. The ABS temperature control circuit may receive output from the absolute pressure sensor and provide the same to the die temperature control logic which operates to adjust the temperature of the die via a heating element to bring the temperature of the die sensor into conformity with a desired temperature programmed into the ABS temperature control sensor. An objective of this circuit is to maintain a predetermined die temperature between both the transmitting and receiving sensor membranes, resulting in a more accurate pressure calculation. More particularly, the control and sensor management unit is configured to manage the sensor power of the absolute pressure sensor, reliability and data integrity. These functions are performed through the die temperature control logic on the receiveroperating a pulse width modulated control loop that maintains a known and fixed temperature at the sensor membrane.

Software filters such as the FFT may be applied to the output of the absolute pressure sensor. In particular, pressure reading samples between the two disparate sensors may be aligned in time to assure that the measurements are synchronized, resulting in comparing pressure differences within a sample period. These sample adjustments may take into consideration, for example, any communications delay incurred between getting the readings from the transmitting unit to the receiving unit. Rate of change filters applied to the output “slow” down any transients effects seen in the data from rapid noise injection.

As further illustrated in, the primary control logic executed by the processor(s) of the receivermay apply the differential pressure derivation algorithmto the received measurement data, store the measurement data in local data storage, and compare the measurement data with its own measurements taken by the absolute pressure sensor, the CO2 sensor, and/or the other indoor air quality sensors according to a time vector to establish a differential pressure between sensors located in the compared spaces. One or more filters may be employed for the user to apply, for example via the user interface, rate of change limits to the output of the pressure sensor data via the communication interface and/or user interface, transmitting unit sensor data, and derived differential pressure value output. Optionally in accordance with a data averaging filter applied to the space pressure displayed by the visual display filter, a value for the differential pressure may be determined and the value may be output and/or transmitted via the user interface or communication interface.

A visual display can also be provided to indicate measurements and related analysis, including without limitation temperature, real-time space pressure, and CO2 molecule parts per million levels at the sensor site, which could be the location of the transmitter(s),, and/oror the receiver, or the location of a sensor remote from but in communication with either of these, for example. The visual display may also display differential pressure, e.g., the difference between absolute pressures measured outside and at the transmitter(s) and/or receiver.

In the case of the receiver, air pressure information may be received wirelessly or via a wired bus from one or more of the transmitters,, andand input as part of the AQ control algorithm. Outside air pressure may be received by the receiverfrom the air pressure sensoreither wirelessly or via a wired bus. To synchronize calibration of all air pressure calculating units, the receivermay broadcast the outside air pressure readings to the transmitters,, and. In accordance with a calibration process described elsewhere herein, a calibration command (e.g., flag) can likewise be broadcast by the receiverto the transmitters,, andduring UNOCCUPIED periods of time.

The outputfrom the receivermay be integrated with standard thermostat, relay, or other HVAC controls to turn off the cooling or heating elements in the thermostat through a control bus or other thermostat control method available. The diagram inshows the integration to the thermostat chassis over an internal communications bus that controls the standard climate control functions of the thermostat. The internal communications can take other forms suitable to the system design.

In some embodiments, the visual display on or associated with the receivermay indicate real time indoor space pressure and CO2 molecule content of the various zones in which the transmitters,, andare located. This visual display may also be used to indicate to the user if action is taken to turn the heat/cool off when pressure conditions indicate an open air situation.

illustrates an example of a zeroization method that may be performed by the receiverto calibrate between or among individual absolute pressure sensors to realize a zeroized pressure differential value. The absolute pressures may include absolute outdoor air pressure measurementreceived from the air pressure sensorand absolute indoor air pressure measurementsensed by the absolute pressure sensor of the receiver. A periodic zeroization may be performed by the receiverbased on ambient and quiescent environmental-UNOCCUPIED-conditions. The zeroization algorithm measures the differences in absolute pressuresandduring this time and determines a pressure offset term. This offset value is constantly calculated during quiet or unoccupied times based on the required values that result in a 0 Pascal set point. A rate of change filter may be applied to the derivation of this term. When the receivertransfers into occupied mode, the last offset termis used in the derived pressure calculation to account for product, outside pressure and altitude differences. During OCCUPIED time, the offset termis fixed during all derived pressure calculations.

Zeroization cycles may be triggered by the CO2 sensor system during an UNOCCUPIED state or at an UNOCCUPIED time. The zeroization method may account for production offsets in the individual sensors, altitude differences between the absolute pressure sensors, and/or drift over time that may occur in a sensor, resulting in a corresponding differential drift between the two differentiated sensors. To counter this, a zeroization may be performed by the receiverwhen the UNOCCUPIED state of the space being monitored by the receiverhas been sensed, at some predetermined time set for the UNOCCUPIED state, or on demand.

In some embodiments, the zeroization algorithm may receive input of the air pressure values and a calculation is executed by the processor(s) in the receiverto determine one or more offset termsthat bring the difference between the two air pressure values at that time to a zero value. This offset value(s)(collectively, offset term or offset value) may be based on various factors including, without limitation, production, altitude, and drift offset values, and may be determined in some embodiments according to a machine learning model trained on empirical values. The offset valuesmay be re-calculated during UNOCCUPIED times. In some embodiments, a rate of change filter may be applied to this derivation of this term. When the receiverrecognizes a transition into an OCCUPIED state by one of the triggers described herein, the last offset termmay be used in the derived pressure calculation to account for production, altitude differences, and drift. During OCCUPIED times, the offset termmay be fixed because environmental changes within the occupied space may be so frequent as to likely make calibration ineffective or at least inefficient.

The detection and adaptation of the algorithm to a crossover condition between, e.g., outdoor air pressure changes from positive to negative relative to the indoor air pressure. This condition can be seen when a low pressure weather event is in the vicinity of the building. The derived differential pressure calculation may be affected, causing the calculation to adjust for this pressure inversion between the independent sensors. This and other embodiments may detect these relative pressure inversions and reflect the same in the measurements set to the display.

illustrates an example of a machine learning algorithm embedded in the receiverthat uses CO2 values (ppm) to determine unoccupied periods of time and to provide a zeroization trigger to begin the process of self-calibration by the receiver. When the receivertransitions from UNOCCUPIED to an OCCUPIED state, the pressure differential derived at the transition time may be used to set the OCCUPIED pressure baseline. The system supply fan (G relay) must also be energized during determination of this value. After the system transitions to OCCUPIED, the occupied pressure baseline is monitored to verify that it is not trending towards a 0 Pascals difference. If this occurs, it will trigger the action condition (e.g., turn on or off the heat or air conditioning). The action taken is based on the thermostat settings.

The receiverthat has the CO2 sensor may continuously monitor CO2 ppm values. During times of stable and lower ppm readings, the receivermay record and average this value to determine a non-occupied CO2 baseline. The receivermay send the UNOCCUPIED signal to some or all of the transmitters,, andduring these baselines periods. Self-calibration is to be performed during UNOCCUPIED periods in the space(s) of concern; this process enables the zeroization functions during those periods. In fact, the calibration method of zeroization can be triggered upon determining that the space is UNOCCUPIED. Initial calibration assumes a baseline of 400 ppm in at least one embodiment.

The UNOCCUPIED state can be based on several factors, taken individually or in combination. For example, an UNOCCUPIED state may be determined on the basis of the CO2 level in the space, a schedule during which time periods are specified or expected to be UNOCCUPIED, observation of the space, and/or other measurables associated with the absence of people. CO2 and/or other levels may be derived directly from a stand-alone CO2 sensor, a CO2 sensor integrated with a thermostat, or received from a cloud or BMS system.

The trigger may be output in response to a reading by one or more of the other air quality sensors shown in. For example, a CO2 parts per million value may be received from an on-board CO2 sensor (e.g., integral with the receiver) or a CO2 sensor coupled to the receiver. During times when the CO2 ppm indicates that the space is UNOCCUPIED, as at the shaded region under the baseline, the receivermay calibrate using the zeroization method, continuously, periodically, aperiodically, or on demand.

illustrates an example state machine for the control logic to the receiver functions for OCCUPIED times.

In Block, the receiver may receive a differential pressure measurement from one or more transmitters. A G relay and/or supply fan are generally active during heating or cooling times. For example, the receivermay receive (continuously or otherwise) derived differential pressures from one or more of the transmitters,, and/orbased on the absolute outside and (indoor) space air pressures as described elsewhere herein. This is received over the wireless communication system as also described elsewhere herein.

In Block, which may occur during block, the receivermay calculate its own space pressure (this flow assumes that the receiverand transmitter(s) are in different rooms).

In Decision Block, the processor(s) of the receivermay determine whether any absolute pressure values measured by the receiverand/or transmitter(s) are within a predetermined value of the outside air pressure. For example, the receivermay determine this from the derived differential pressures received from the transmitter(s) (i.e., if any of the derived differential pressures are below a predetermined threshold), or from absolute pressure values that may be received from the transmitter(s) and subtracted from the outside air pressure are processed to determine if they are below the baseline pressure recorded at the transition from OCCUPIED or UNOCCUPIED. If they are at or approaching a neutral or 0 pascal reading, the receivermay transition to Decision Block; if not, then the flow may return to Block.

In Decision Block, the receivermay determine whether the space HVAC is pressurizing the space. This may be determined by the state of the G relay. If the pressure is at the baseline and not near the baseline within a predetermined value, the receivermay cycle back to Block. Pressure measurements may be performed, for example, at a minimum of once every second. If the derived pressure in any of the (indoor) zones or at the receiveris within the deadband for 0 Pascals, the receivermay transition to Decision Block.

In Decision Block, the receivermay determine whether cooling or heating is active. This may include determining whether the space is being pressurized by the supply fan and the unit is set to heat or cool. For example, the receivermay determine the state of the Y, Yrelays for cooling and the W, Wrelays for heating. In the case of a heat pump, the O or B relays may be used in this determination. If the HVAC is not actively cooling or heating, the flow may cycle back to Block.