Refrigeration system leak detection

A refrigeration system includes: a leak sensor disposed within a building and configured to measure an amount of refrigerant that has leaked from the refrigeration system within the building; an estimation module configured to determine an estimated amount of refrigerant that has leaked from the refrigeration system within the building based on the measured amount; and a leak module configured to: determine whether a leak is present in the refrigeration system within the building based on the estimated amount of refrigerant that has leaked from the refrigeration system; and take one or more remedial actions when a leak is present in the refrigeration system within the building.

FIELD

The present disclosure relates to heating ventilation and air conditioning (HVAC) and other types of refrigeration systems and more particularly to a refrigeration leak detection system and method for an HVAC or refrigeration system.

BACKGROUND

Refrigeration and air conditioning applications are under increased regulatory pressure to reduce the global warming potential of the refrigerants they use. In order to use lower global warming potential refrigerants, the flammability of the refrigerants may increase.

Several refrigerants have been developed that are considered low global warming potential options, and they have an ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) classification as A2L, meaning mildly flammable. The UL (Underwriters Laboratory) 60335-2-40 standard, and similar standards, specifies a predetermined (M1) level for A2L refrigerants and indicates that A2L refrigerant charge levels below the predetermined level do not require leak detection and mitigation.

SUMMARY

The standards for sensing and mitigation of A2L refrigerants limit the technologies available for refrigerant detection because of the time elapsed between leak release and identification and mitigation of the leak. Leak sensors require time to sense a refrigerant leak and to achieve a signal level representative of a predetermined leak level. Leak sensors have a decay curve upon initial detection of a refrigerant until the leak sensor achieves a signal level that is representative of the refrigerant's concentration level.

Using data from testing performed using a range of sensors, each measurement device has a representative decay curve. Decay curves can be quantified from three or more data points to identify the asymptote of the refrigerant concentration measurement.

The present application involves use of the representative decay curve to estimate the actual refrigerant concentration sooner to enable mitigation at an earlier time that enhances the safety of the system and permits more sensing technologies to meet the sensing requirements.

A refrigeration system includes a refrigeration cycle including a compressor, a condenser, an expansion valve and an evaporator. A refrigerant leak sensor is disposed adjacent to the evaporator and/or other components of the system. A control module receives signals from the refrigerant leak sensor and controls operation of the compressor. The control module stores a plurality of decay curves representative of different actual concentration values and upon receipt of data representing an increasing signal from the refrigerant leak sensor the control module matches the data to a stored decay curve and estimates an actual concentration. If the estimated actual concentration exceeds a predetermined value, the control module inhibits operation of the compressor and can activate additional mitigation devices including activation of isolation valves, a fan, a ventilation system, an air exchange system and lockout devices for preventing operation of any ignition devices in proximity to the refrigeration components.

In a feature, a refrigeration system includes: a leak sensor disposed within a building and configured to measure an amount of refrigerant that has leaked from the refrigeration system within the building; a estimation module configured to determine a estimated amount of refrigerant that has leaked from the refrigeration system within the building based on the measured amount; and a leak module configured to: determine whether a leak is present in the refrigeration system within the building based on the estimated amount of refrigerant that has leaked from the refrigeration system; and take one or more remedial actions when a leak is present in the refrigeration system within the building.

In further features, the estimation module is configured to determine the estimated amount of refrigerant that has leaked from the refrigeration system within the building using an equation that relates multiple of the measured amounts from the leak sensor to the estimated amount of refrigerant that has leaked.

In further features, the multiple measured amounts include at least three measured amounts from at least three different times, respectively.

In further features, the estimation module is configured to determine the estimated amount of refrigerant that has leaked from the refrigeration system within the building using a stored curve that relates at least one measured amount from the leak sensor to the estimated amount of refrigerant that has leaked.

In further features, a selection module is configured to select the stored curve from a plurality of different stored curves.

In further features, the selection module is configured to select the stored curve from the plurality of different stored curved based on an increase in the measured amount of refrigerant that has leaked from the refrigeration system within the building.

In further features, the leak module is configured to determine that a leak is present in the refrigeration system within the building when the estimated amount of refrigerant is greater than a predetermined amount.

In further features, the leak module is configured to turn on a fan disposed within the building when a leak is present in the refrigeration system within the building.

In further features, the leak module is configured to turn off a compressor of the refrigeration system when a leak is present in the refrigeration system within the building.

In further features, the leak module is configured to actuate an interlock device and inhibit ignition by one or more components when a leak is present in the refrigeration system within the building.

In further features, the refrigerant has an American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) classification of A2L.

In a feature, a refrigeration method includes: receiving, from a leak sensor disposed within a building, a measured amount of refrigerant that has leaked from a refrigeration system within the building; determining a estimated amount of refrigerant that has leaked from the refrigeration system within the building based on the measured amount; and determining whether a leak is present in the refrigeration system within the building based on the estimated amount of refrigerant that has leaked from the refrigeration system; and executing one or more remedial actions when a leak is present in the refrigeration system within the building.

In further features, the determining the estimated amount includes determining the estimated amount of refrigerant that has leaked from the refrigeration system within the building using an equation that relates multiple of the measured amounts from the leak sensor to the estimated amount of refrigerant that has leaked.

In further features, the multiple measured amounts include at least three measured amounts from at least three different times, respectively.

In further features, the determining the estimated amount includes determining the estimated amount of refrigerant that has leaked from the refrigeration system within the building using a stored curve that relates at least one measured amount from the leak sensor to the estimated amount of refrigerant that has leaked.

In further features, the refrigeration method further includes selecting the stored curve from a plurality of different stored curves.

In further features, the selecting includes selecting the stored curve from the plurality of different stored curved based on an increase in the measured amount of refrigerant that has leaked from the refrigeration system within the building.

In further features, the determining whether a leak is present includes determining that a leak is present in the refrigeration system within the building when the estimated amount of refrigerant is greater than a predetermined amount.

In further features, the executing one or more remedial actions includes turning on a fan disposed within the building when a leak is present in the refrigeration system within the building.

In further features, the executing one or more remedial actions includes at least one of: turning off a compressor of the refrigeration system when a leak is present in the refrigeration system within the building; and actuating an interlock device and inhibit ignition by one or more components when a leak is present in the refrigeration system within the building.

DETAILED DESCRIPTION

With reference toFIG. 1, a schematic view of an example refrigeration (e.g., air conditioning) system10is shown including a compressor12, a condenser14, an expansion valve16, and an evaporator18disposed inside of relative to the building.

A fan (or blower)24is provided adjacent to the evaporator18and blows air across the evaporator18. A control module26controls operation (e.g., on, off, speed) of the fan24. In various implementations, the building may additionally include a whole house fan, a ventilation system fan, an air exchange system fan, or another type of fan. The control module26also controls operation (e.g., on, off, speed, capacity) of the compressor12.

The control module26can communicate with the compressor12, the fan24, and various sensors by wired or wireless communication directly or indirectly through another device or control module. The control module26can include one or more modules that can be in communication with one another and can be implemented as part of a control board, furnace board, thermostat, air handler board, contactor, or in another suitable manner.

The control module26may include power conditioning circuitry and supply power to electronic devices using 24 volts (V) alternating current (AC), 120-240 V AC, 5 V direct current (DC) etc. The control module26may include a bidirectional communication port which can be wired, wireless, or both, for example, for system debugging, programming, updating, monitoring, parameter value/state transmission, etc.

A refrigerant leak sensor30is provided adjacent to the evaporator18(e.g., at or near a midpoint of the evaporator18or at or near a bottom (lowest vertical point) of the evaporator18). The refrigerant leak sensor30may be located in another suitable location. The leak sensor30, as discussed in the present disclosure can be an infrared leak sensor, an optical leak sensor, a chemical leak sensor, a thermal conductivity leak sensor, an acoustic leak sensor, an ultrasonic leak sensor, or another suitable type of leak sensor.

In the example ofFIG. 1, the control module26receives signals from the leak sensor30and determines if a leak is detected. The refrigeration system can further include additional mitigation devices such as a lockout device32that stop and lock out (e.g., prevent) operation of one or more ignition devices that are in the building when a leak is detected. Examples of ignition devices may include furnace and water heater igniters and pilot lights or other electronic devices that can create an electrical arc or ignite fire. The locking out of any ignition devices can be performed, for example, by the control module26deactivating electronic circuitry controlling the ignition device.

The leak sensor30may have a response lag between when an actual value changes and when the value measured by the leak sensor30changes. According to the present disclosure, leak sensors like the leak sensor30are tested to determine decay curves (e.g., equations corresponding to the decay curves) for the leak sensor30and is stored in the control module26.

The control module26stores a plurality of decay curves representative of different actual concentration values. Example decay curves are provided inFIG. 2. Upon receiving an increasing measurement (e.g., an increase from a first measurement to a second measurement taken after the first measurement) from the leak sensor30, the control module26matches the increase to a stored decay curve. In other words, the control module26selects a stored decay curve based on the increase (e.g., the one of the decay curves that increases most closely with the increase in the measurements).

The control module26estimates (determines) an actual concentration based on the increase and the selected stored decay curve. For example, the control module26may estimate the actual concentration by solving the equation for the selected decay curve with the (e.g., second) measurement or the increase.

Alternatively, the control module can store a decay calculation including, for example, the equation EQ-1:
Actual concentration=(c(t)−c(t−1))/(1−(c(t)−c(t−1))/(c(t−1)−c(t−2))+c(t),

where actual concentration is the actual concentration, c(t) is the measured concentration at time t, c(t−1) is the measured concentration at time t−1 (one time step before time t), and c(t−2) is the measured concentration at time t−1 (two time steps before time t).

Knowing the relationship between measured and actual concentration allows the control module26to react quicker (and actuate the lockout device32to disable and inhibit ignition) when a leak is detected. One or more remedial actions may also be taken more quickly. For example, the control module26may turn the fan on24sooner than it otherwise would have. When the control module26detects a rising (increasing) measurement from the leak sensor30, the control module26matches the data to a stored decay curve and estimates an actual concentration.

In HVAC systems, a fast response is important to help minimize the amount of and duration of refrigerant leaks. The response time of the sensor30is enhanced by using previously established data about the time response and measurement error decay of the sensor30in measurement processing to estimate the asymptote to quickly estimate the actual concentration from three or more measurements. In this regard, the control module26observes values or changes to the output of the leak sensor30. The post-processed result of the sensed concentration is the estimated actual concentration.

If the estimated actual concentration exceeds a predetermined value, the control module26disables and inhibits operation of the compressor12. In the example architecture as provided, when a leak is detected by the control module26, the control module26can turn off the compressor12and maintain the compressor12off until the leak is remediated. The control module26may additionally turn ON the fan24for a predetermined period of time or until it is turned off. In addition, the control module26can also turn on any other mitigation devices in order to dissipate any leaked refrigerant and prevent/lockout operation of any ignition sources until they are reset.

FIG. 3is a flowchart depicting an example method of refrigerant leak detection and mitigation. Control begins with S100and proceeds to S102. At S102, the control module26determines whether a measurement has been received from the leak sensor30. The leak sensor30may take measurements at a predetermined rate (once every predetermined period, such as once per second or at another suitable rate).

If S102is true, control continues with S104. If S102is false, control may return to S100. At S104, the control module26estimates an actual concentration of refrigerant based on multiple measurements from the leak sensor30using a selected stored decay curve (e.g. and interpolation) or an equation (e.g., the equation provided above). Control proceeds to S106.

At S106, the control module26determines whether the estimated actual concentration is greater than a predetermined concentration. The predetermined concentration is calibrated and may be greater than zero. If S106is true, the control module26determines that a leak is present, and control continues with S108.

At S108, the control module26turns off the compressor12. The control module26may also take one or more other remedial actions, such as actuating the lockout device32to disable and inhibit ignition, turn on the fan24, and generate one or more outputs (e.g., alerts). Control ends at S112.

FIG. 4is a functional block diagram of an example control system. A fan module404controls operation (e.g., on, off, speed) of the fan24. A compressor module408controls operation (e.g., on, off, speed, capacity, etc.) of the compressor12. A lockout module412controls actuation of the lockout device32.

A buffer module416stores measurements from the leak sensor30. The buffer module416may also store timestamps indicative of when the measurements were received (or taken). An increase module420determines an increase in the measurements, such as the most recently received measurement (c(t)) and the measurement received immediately before the most recently received measurement (c(t−1)). For example, the increase module420may subtract the measurement received immediately before the most recently received measurement (c(t−1)) from the most recently received measurement (c(t)) to determine the increase.

When the increase is positive, a selection module424may select one of a plurality of stored curves428that has an increase that most closely matches the increase in the measurements. A estimation module432may estimate the actual concentration (at time t) based on the increase using the selected one of the stored curves428(e.g., using interpolation).

In various implementations, when the increase is positive, the estimation module432may estimate actual concentration using a stored equation and multiple of the measurements (e.g., c(t), c(t−1), and c(t−2)) as inputs. An example equation is provided above.

A leak module436determines whether a leak is present (i.e., refrigerant is leaking from the refrigeration system within the building) based on the estimated actual concentration. Using the estimated actual concentration as opposed to the measurements from the leak sensor30may allow the leak module436to detect the presence of a leak more quickly than if the measurements were used. The leak module436may determine that a leak is present when the estimated actual concentration is greater than a predetermined concentration.

The leak module436generates a signal that indicates whether a leak is present. For example, the leak module436may set the signal to a first state when a leak is present and set the signal to a second state when a leak is not present.

One or more remedial actions may be taken when a leak is present. For example, the fan module404may turn on the fan24when a leak is present. Additionally, the compressor module408may turn off the compressor12and maintain the compressor12off until the leak is remediated (e.g., as indicated by the system being reset, such as by disconnecting the control module26from power for at least a predetermined period). Additionally, the lockout module412may actuate the lockout device32to prevent ignition by one or more ignition devices within the building. The lockout module412may maintain the state of the lockout device32for a predetermined period, such as to allow the refrigerant leak to dissipate.

Additionally, an alert module440may generate one or more indicators when a leak is present. For example, the alert module440may transmit an indicator to one or more external devices444, generate one or more visual indicators448(e.g., turn on one or more lights, display information on one or more displays, etc.), and/or generate one or more audible indicators, such as via one or more speakers452.