Patent Description:
Gas sensors have been used in various applications such as process monitoring and control and safety monitoring. As the compounds can also be flammable or explosive, gas detection sensors have also been used for leak detection where such compounds are used or manufactured. Various types of sensors have been used or proposed, including but not limited to metal oxide semiconductor (MOS) sensors, non-dispersive infrared detector (NDIR) sensors, pellistor (pelletized resistor) sensors, ultrasonic sensors, high-temperature solid electrolytes that are permeable to oxygen ions, and electrochemical cells.

<CIT> discloses a method for leak detection of flammable refrigerants using a first sensing element and a second sensing element.

<CIT> discloses a method for determining a refrigerant leakage with either a temperature sensor, a first refrigerant sensor or a second refrigerant sensor.

<CIT>, a document falling under Art. <NUM>(<NUM>) EPC, discloses a refrigerant leak sensor configured to detect a refrigerant leak at the usage-side refrigeration circuit and a refrigerant state sensor near the compressor to determine erroneous detection.

Viewed from a first aspect, the invention provides a method for monitoring for leakage of flammable compounds according to claim <NUM>.

Viewed from a second aspect, the invention provides a monitoring system for detecting leakage of flammable compounds according to claim <NUM>.

Viewed from a third aspect, the invention provides an air conditioning or heat pump system according to claim <NUM>.

Optionally, the refrigerant has a class <NUM> or class <NUM> or class <NUM> flammability rating according to ASHRAE <NUM>-<NUM>.

Optionally, the sensors are disposed in a conduit on the conditioned air flow path comprising an inlet and an outlet, and the first and second sensors are disposed in the conduit with the second sensor downstream from the first sensor with respect to a direction of flow from the inlet to the outlet.

Optionally, measurements of the first parameter are indicative of the presence and concentration of a flammable compound.

Optionally, measurements of the first parameter are provided by a sensor selected from an ultrasound sensor, an infrared absorbance sensor, an electrochemical sensor, or a MOS sensor.

Optionally, the second parameter includes temperature.

Optionally, the second parameter includes humidity.

Optionally, the second parameter includes gas flow.

Optionally, the space around the potential leak source is an enclosed space.

The above types of sensors have been used with varying degrees of success in the industrial or laboratory settings where they have been employed. However, many such sensors have limitations that can impact their effectiveness in demanding new and existing applications. For example, pellistor sensors are prone to false alarms due to cross-sensitivity. NDIR sensors can provide good selectivity, but are expensive for high volume applications. Electrochemical sensors rely on redox reactions involving tested gas components at electrodes separated by an electrolyte that produce or affect electrical current in a circuit connecting the electrodes. However, solid state electrochemical sensors can be prone to nuisance alarms due to poor selectivity. Additionally, solid state electrochemical sensors testing for combustible hydrocarbons may utilize solid electrolytes formed from ceramics such as perovskite, which can require high temperatures (typically in excess of <NUM>) that render them impractical for many applications that require long lifetime. Some electrochemical sensors that operate at lower temperatures (e.g., carbon monoxide sensors, hydrogen sulfide sensors) are incapable of electrochemically oxidizing relatively stable organic compounds that nevertheless be flammable or mildly flammable, such as some hydrofluoro carbon refrigerants.

MOS sensors rely on interaction between gas test components such as hydrogen sulfide or hydrocarbons with adsorbed oxygen on the metal oxide semiconductor surface. In the absence of the gas test components, the metal oxide semiconductor adsorbs atmospheric oxygen at the surface, and this adsorbed oxygen captures free electrons from the metal oxide semiconductor material, resulting in a measurable level of base resistance of the semiconductor at a relatively high level. Upon exposure to reducing or combustible gas test components such as hydrocarbons or hydrofluorocarbons (HFCs), the gas test component interacts with the adsorbed oxygen, causing it to release free electrons back to the semiconductor material, resulting in a measurable decrease in resistance that can be correlated with a measured level of test gas component. Though MOS sensors are relatively inexpensive, the lack of selectivity can potentially cause false alarms.

Ultrasonic sensors can detect for the presence of gas components based on the dependence of speed of sound on gas compositions, but can be susceptible to false alarms because environment conditions such as temperature and moisture content can also affect the output as do gas compositions. More importantly, the speed-of-sound based detection can be relatively non-selective, hence can potentially lead to false alarms.

In the HVAC/R industry, more environmentally friendly refrigerants are being developed and used to replace refrigerants with high global warming potentials (GWP) such as R134A and R410A. Many of the low GWP refrigerants are flammable (A3 refrigerants such as R290 i.e. propane) or mildly flammable (A2L refrigerants such as R32, R1234ze etc.). In refrigerant leak detection applications involving testing for compounds foreign to ambient air, false alarms can be a problem, potentially interrupting system operations. Various leak detection technologies have been proposed to address potential fire hazards from flammable refrigerants in interior building spaces; however, there continues to be a need to provide scalable cost-effective detection technologies capable of discerning refrigerant leaks.

The systems and methods described herein include first and second sensors, and additional sensors. The sensors can be disposed as separate sensor assemblies or can be combined into a unitary sensor assembly with multiple sensor components. One of the sensors, or a constituent component in a sensor, measures a parameter indicative of a presence of flammable gas. Such a sensor or a sensing mechanism can include, but is not limited to, conductance measurement e.g., metal oxide sensors or speed of sound measurement, e.g. ultrasonic sensors. The architecture of the core elements of a detection system <NUM> with multiple indicators is illustrated schematically in <FIG>. As shown in <FIG>, the system <NUM> includes a first sensing element <NUM> for monitoring a primary condition parameter or parameters of a sample from the surrounding atmosphere indicative of the presence of flammable compounds in a space <NUM> around a potential leak source of a flammable compound. In some embodiments, the first sensing element <NUM> can measure a primary parameter that is also indicative of a concentration of flammable compounds or indicative of a change in concentration of flammable compounds. In some embodiments, the first sensing element <NUM> for measuring the primary parameter(s) can be selected from ultrasound sensors, infrared absorbance sensors, electrochemical sensors, or MOS sensors. As further shown in <FIG>, the system <NUM> also includes one or more sensing elements to measure multiple 'second' parameters, which can also be referred to as secondary and tertiary, etc. parameters (in this case a second sensing element <NUM> and a third sensing element <NUM>), and which operates on a different sensing mechanism from that of the primary parameter. Secondary or tertiary parameters can include any of the above primary parameters that can directly or indirectly measure gas phase composition, or parameters such as environmental parameters (e.g., temperature and humidity) that may not be sufficiently selective by themselves for detection of flammable compounds. Secondary environmental parameters can be examined for a rate of change. The output of the system is pertinent to whether flammable gas is present, and hence that a system leak has occurred. This decision is made by a controller, e.g., an electronic control unit (ECU) <NUM>, which can utilize software and/or firmware logic to examine the primary and auxiliary indicators physically measured by the aforementioned sensing components. Specifically, a primary parameter is based the detection of gas compositions or the change in gas compositions and the auxiliary parameters are related to environment conditions that indirectly reflect leaks, particularly those involves phase changes such as liquid refrigerant vaporization.

An example embodiment of an ultrasonic sensor <NUM> is shown in <FIG>. As shown in <FIG>, a sound emitter/receiver <NUM> directs sound waves <NUM> through a test gas sample <NUM> to another emitter/receiver <NUM>. The ultrasound transceivers can be mounted at two ends of a gas sampling conduit <NUM>. Gas ports <NUM> and <NUM> are provided on the conduit <NUM> to allow gas to transport into the space for determining the change in atmosphere composition. A measured speed of sound through the gas can be calculated based on elapsed time for the signal, and compared to stored data such as a look-up table based for example on calibrated test data from samples of known flammable gas concentrations, and a determination made of flammable gas concentration in the sample. In some embodiments, a sensing element for a secondary indicator can be mounted inside the conduit <NUM>, or exterior to the conduit <NUM> to detect concomitant evidence associated with a leak, or located on other system components such as on a printed circuit board assembly (PCBA).

An example embodiment of a heat transfer system with integrated sensors for monitoring for accidentally leaked heat transfer fluid is shown in <FIG>. As shown in <FIG>, a heat transfer system includes a compressor <NUM> which pressurizes the refrigerant or heat transfer fluid in its gaseous state, which both heats the fluid and provides pressure to circulate it throughout the system. The hot pressurized gaseous heat transfer fluid exiting from the compressor <NUM> flows through conduit <NUM> to heat rejection heat exchanger <NUM>, which functions as a heat exchanger to transfer heat from the heat transfer fluid to the surrounding environment, resulting in condensation of the hot gaseous heat transfer fluid to a pressurized moderate temperature liquid. The liquid heat transfer fluid exiting from the heat rejection heat exchanger <NUM> (e.g., a condenser <NUM>) flows through conduit <NUM> to expansion valve <NUM>, where the pressure is reduced. The reduced pressure liquid heat transfer fluid exiting the expansion valve <NUM> flows to fan coil unit <NUM> inside the building <NUM>, which includes fan <NUM> and heat absorption heat exchanger <NUM> (e.g., an evaporator), which functions as a heat exchanger to absorb heat from the surrounding environment and boil the heat transfer fluid. In the heat absorption heat exchanger <NUM>, heat is absorbed by the refrigerant from a conditioned air flow path that includes a return air conduit <NUM> that returns air from the conditioned air space inside the building <NUM> and a supply air conduit <NUM> that supplies conditioned air to the conditioned air space inside the building <NUM>. Gaseous heat transfer fluid exiting the heat rejection heat exchanger <NUM> flows through conduit <NUM> to the compressor <NUM>, thus completing the heat transfer fluid loop. The heat transfer system can transfer heat from the environment surrounding to the evaporator <NUM> to the environment surrounding the heat rejection heat exchanger <NUM>. The thermodynamic properties of the heat transfer fluid allow it to reach a high enough temperature when compressed so that it is greater than the environment surrounding the condenser <NUM>, allowing heat to be transferred to the surrounding environment. The thermodynamic properties of the heat transfer fluid should also have a boiling point at its post-expansion pressure that allows the environment surrounding the heat rejection heat exchanger <NUM> to provide heat at a temperature to vaporize the liquid heat transfer fluid.

As further shown in <FIG>, the heat transfer system further includes sensor pack <NUM>, which is placed in the indoor section of the system to detect refrigerant leaks that can potential pose risks to the building and occupants. The sensor with auxiliary sensing elements besides the primary leak detection sensor is place in the unit to allow for monitoring the gas phase composition and environment conditions. As mentioned above a sensor in the sensor pack <NUM> can be operated to measure a primary parameter indicative of presence of a flammable gas. The other sensing element(s) in the sensor pack <NUM> can be operated to measure a secondary parameter(s) such as temperature, and/or humidity, and/or gas flow in the enclosed space. In the event of an actual leak of flammable vapor, physical changes to the surrounding space such as changes in temperature, and/or humidity, and/or gas flow are believed to result from the leakage and vaporization of refrigerant from the system. More specifically, leaking refrigerant in a substantial rate can cause temperature to drop, relative humidity to drop compared to normal conditions. Although these parameters may not be dispositive by themselves of a flammable gas leak, they can be used to identify false positive alarms from the primary sensor such as a MOS or ultrasonic sensor by comparing observed measurements to normal measurements or to criteria indicative of a gas leak during a time period proximate to the positive signal produced by the primary sensor.

A protocol for operating a sensing device with multiple indicators to detect flammable gas leaks and to avoid false alarms is shown in <FIG>. The determination of refrigerant leaks is enhanced by the method based on multiple indicators as illustrated in the architecture of the sensing system such as shown in <FIG>, and related logic as shown in <FIG>. The embodiment of <FIG> shows logic based on the sensing system of <FIG>. As shown in <FIG>, a sensing system in detection mode <NUM> generates sensing output from the first sensing element <NUM> that is examined at decision block <NUM> to assess whether the primary parameter or indicator (e.g., a parameter related to gas phase composition flammable content) has exceeded a first or lower limit. If the primary parameter has exceeded the first limit, the routine proceeds to decision block <NUM> where output from a second sensing element <NUM> and/or third sensing element <NUM> is examined for a rate of change. The rate of change of a secondary indicator can in some cases manifest the effects of refrigerant leaks such as sudden temperature decreases and/or humidity variations due to displacement of moisture. If the rate of change of the secondary indicator(s) does not show sufficient changes to warrant determination of leak at block <NUM>, then the routine proceeds to block <NUM> where the primary indicator is examined against a second or upper limit. If the primary indicator is below this second or upper limit, then a false alarm is registered at block <NUM> and the system returns to sensor detection mode at block <NUM>. If the primary indicator is not below the second or upper limit at block <NUM>, or if the rate of change of the secondary indicator at block <NUM> confirmed the leak prospectively determined by the primary indicator at block <NUM>, then the routine proceeds to block <NUM>, where leak mitigation actions (e.g., introduce airflow by a fan) are taken by the system, followed by a system check at decision block <NUM> in which the primary indicator is measured and compared to a third limit (e.g., a safety limit). If the primary indicator is below the third limit, the mitigation actions are deemed effective and the sensor is reset at block <NUM> and returned to detection mode at block <NUM>. If the primary indicator is above the third limit, then the system is put into a safe mode at block <NUM> in which mitigation actions are continued, and a sensor fault is registered at block <NUM>. The leak mitigation actions are taken by the system at block <NUM> where primary indicator will be continually monitored until it drops below the lowest (safe) limit, namely the third limit. If the primary indicator confirms that the flammable gas concentration has decreased to a safe level, and sensor will be reset at block <NUM>. However, if the primary indicator fails to indicate expected trend resulting from flammable gas dissipation, a sensor fault likely has occurred and a notification on sensor fault will be registered in the system at block <NUM>. If the primary indicator does not exceed the upper (third) limit expected from more dramatic leaks, a false alarm can be registered at block <NUM> and sensor detection mode can continue.

An example output of a sensor device incorporating a primary, a secondary, and a tertiary sensing element is shown in <FIG> plots flammable mass concentration (primary indicator), temperature (secondary indicator), and relative humidity (tertiary indicator) versus time, under conditions of a controlled introduction of a flammable compound in a simulated leak. As shown in <FIG>, both the secondary and the tertiary indicators exhibited correlation with the primary indicator when a sudden atmosphere composition change was detected as manifested by the primary indicator. In this experiment, a leak was positively confirmed by examining the concomitant changes of either the secondary or the tertiary indicator.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting on the scope of the invention, which is defined by the claims.

Claim 1:
A method for monitoring for leakage of flammable compounds, comprising:
measuring a first parameter indicative of the presence of flammable compounds in a space around a potential leak source of a flammable compound;
determining a prospective presence of the flammable compound based on measurement of the first parameter exceeding a first limit (<NUM>); and
measuring a second parameter in the space around the potential leak source, wherein the second parameter is a physical property of gas in the space (<NUM>) around the potential leak source, and wherein the second parameter is selected from a temperature, humidity, pressure, or gas flow;
characterized by:
measuring a third parameter or a plurality of additional parameters, wherein the third or plurality of additional parameters is/are selected from temperature, humidity level, pressure, or gas flow; and
characterizing the prospective presence of the flammable compound determined by measurement of the first parameter, in conjunction with the measurement of the second parameter and the third parameter or plurality of additional parameters, as an actual presence of the flammable compound (<NUM>) or as a false alarm (<NUM>),
wherein the characterizing comprises characterizing the prospective presence as an actual presence of the flammable compound when a rate of change of the second parameter and/or the third parameter or plurality of additional parameters exceeds a fourth limit (<NUM>),
wherein the characterizing comprises characterizing the prospective presence as an actual presence of the flammable compound when the measurement of the first parameter is above a second limit (<NUM>), and
wherein the characterizing comprises characterizing the prospective presence as a false alarm when both of the following criteria are true: a) the rate of change of the second parameter and/or the third parameter or plurality of additional parameters does not exceed the fourth limit (<NUM>), and b) the measurement of the first parameter is below the second limit (<NUM>).