Refrigerant Circuits For HVAC Units

This application claims priority to EP Application Serial No. 24182293.1 filed Jun. 14, 2024, the contents of which are hereby incorporated by reference in their entirety.

The present disclosure deals with HVAC systems. Various embodiments of the teachings herein include systems and methods for addressing fluctuations of pressure in closed circuits for heating and/or ventilation and/or air-conditioning (HVAC).

Installations for heating and/or ventilation and/or air-conditioning are commonly made up of a plurality of circuits. Each circuit comprises one or more terminal units to provide cooling and/or heating to various parts of a building. Terminal units can comprise cooling devices and/or heating devices. A terminal unit of a domestic heating system can be a thermal energy exchanger such as a radiator, a condenser or an evaporator.

HVAC installations such as installations for air-conditioning can also comprise one or more refrigerant circuits. These refrigerant circuits are made up of compressors, evaporators, (expansion) valves, and condensers. A compressor, an evaporator, an expansion valve such as an electronic expansion valve, and a condenser connect in series to form a refrigerant circuit. The circuit can provide additional sensors such as temperature sensors, pressure sensors, and/or power meters to monitor and to control operation of the circuit.

Fluctuations of pressure and of temperature can be caused by changes of the configuration of a HVAC circuit. In operation, refrigerant circuits are also prone to refrigerant loss. Those changes can impact on pressure and on temperature as well as on nominal flow through a circuit. A loss of refrigerant from an installation for heating and/or ventilation air- and/or conditioning does not only harm the environment in terms of global warming. A loss of refrigerant can decrease process efficiency (COP).

What's more, a loss of refrigerant can cause additional wear of and/or damage to mechanical components such as compressors of the refrigerant circuit. For example, fluctuations and/or changes in pressure can impact on the boiling point of a refrigerant in a circuit. Ultimately, a refrigerant in liquid form can enter a compressor and cause the compressor to fail. To prevent such failures, the system operates with a safety margin and the refrigerant is typically superheated as it enters the compressor. That said, a superheated refrigerant lowers process efficiency.

The issue is further exacerbated because refrigeration systems leaking refrigerant can incur a risk of personnel injury. Certain refrigerants are known to be explosive especially when mixed with air. Systems leaking refrigerant can also affect a person's respiratory system and can cause suffocation and/or chemical burn.

Various approaches exist to control the flow of a medium regardless of pressure. In mechanical pressure-independent control valves, a pressure regulator comprises a valve that moves as a function of a differential pressure. The dependence of flow on differential pressure is thereby mitigated. Flow through this type of control valve is essentially constant so long as the differential pressure exceeds a threshold. The patent U.S. Pat. No. 9,784,375B2 discloses a pressure-independent control valve.

Pressure independent flow can also be achieved by means of closed-loop control. For example, the utility model CN201093671Y discloses a configuration having a flow sensor of the ultrasonic type, a control valve and a control unit. The control unit reads a signal from the flow sensor and adjusts the valve in accordance with this signal. However, flow sensors such as ultrasonic flow sensors have shortcomings. Ultrasonic flow sensors tend to be unpredictable in the regime between laminar flow and turbulent flow. Also, a concentration of solids or of bubbles above a lower limit is required for a Doppler flowmeter to ensure reliable, accurate operation.

Instead of ultrasonic flow meters, a signal related to flow can also be recorded using a pair of pressure nozzles. For example, the patent application CN1837996A discloses a first pressure nozzle upstream of a butterfly valve and a second pressure nozzle downstream of the butterfly valve. A differential pressure ΔP is recorded using the pair of pressure nozzles and an opening degree of the butterfly valve is adjusted in accordingly. Flow Q through the valve of CN1837996A can be calculated using Bernoulli's equation

This presupposes that Bernoulli's equations is applicable.

A solution harnessing a plurality of sensors to detect refrigerant loss is also known from the European patent EP4006454B1. A sensor such as a temperature sensor is arranged upstream of or downstream of an expansion valve of the system of EP4006454B1. Another sensor records a pressure at or near the outlet of the evaporator. The sensors are used to estimate a maximum capacity of the refrigerant circuit. An alarm will be generated whenever a ratio between a current capacity of the system and a maximum capacity of the system exceeds a threshold.

A German patent application DE102004019929A1 deals with an air conditioning system having an acoustic sensor coupled to a refrigerant circuit. The acoustic sensor records a signal indicative of loss of a carbon dioxide refrigerant from the circuit. The acoustic sensor sends its signal to a signal processing circuit. The signal processing circuit employs a band-pass filter to extract frequencies that indicate leakages from the circuit. The filtered signal is then integrated, rectified, and compared to a threshold. If the experimentally determined threshold is exceeded, a signal indicative of a leakage will be produced.

A European patent application EP2499435A2 deals with refrigerant leak detection. A receiver is arranged in between the condenser and the evaporator. The receiver provides a refrigerant level indicator such as an ultrasonic sensor that detects a refrigerant level using an ultrasonic beam. The system also provides temperature and pressure sensors associated with a compressor rack. A model is selected based on data gathered from the temperature and pressure sensors and is employed to predict a level of refrigerant. The predicted level of refrigerant is compared to a reading obtained from the refrigerant level indicator. An alarm will be generated as soon as a deviation between the predicted level of refrigerant and the refrigerant level as indicated exceeds a threshold.

The instant disclosure deals with disturbances in a refrigerant circuit. The present disclosure describes systems and/or methods for use with a wide range of fluids such as perfect liquids, perfect gases, flashing liquids, single-phase fluids, and two-phase fluids. For example, some embodiments of the teachings herein include a method of detecting and/or compensating a disturbance in a refrigerant circuit (), the refrigerant circuit () comprising at least one valve () having an inlet port and an outlet port, the refrigerant circuit () also comprising a first sensor () for recording a signal indicative of a thermodynamic state of a refrigerant at the inlet port of the at least one valve (), and a second sensor () for recording a signal indicative of a thermodynamic state of the refrigerant at the outlet port of the at least one valve (), the method comprising: recording a first signal using the first sensor (); recording a second signal using the second sensor (); receiving a position signal indicative of a position () of the at least one valve (); processing the first signal to determine an upstream pressure p; processing the second signal to determine a downstream pressure p; processing the position signal to determine the position () of the at least one valve (); determining a discharge coefficient cbased on the upstream pressure pand based on the downstream pressure p, wherein the discharge coefficient crelates actual flow {dot over (m)} at the determined position () of the at least one valve () to maximum flow {circumflex over ({dot over (m)})} at the determined position () of the at least one valve (); using a valve curve (,) of the at least one valve () and the discharge coefficient cand the determined position () to estimate a flow through the at least one valve () at a predetermined position of the at least one valve (); calculating a deviation measure as a function of the estimated flow through the at least one valve () at the predetermined position and as a function of a value of expected flow at the predetermined position; comparing the deviation measure to a threshold value; and if the deviation measure is greater than the threshold value: producing a signal indicative of a disturbance in the refrigerant circuit ().

In some embodiments, the method comprises determining the discharge coefficient cas an exclusive function of the upstream pressure pand of the downstream pressure p.

In some embodiments, refrigerant circuit () includes a third sensor () for recording a signal indicative of a thermodynamic state of the refrigerant at the inlet port of the at least one valve (), the method comprising: recording a third signal using the third sensor (); processing the third signal to determine an upstream temperature t; and determining the discharge coefficient cbased on the upstream pressure pand based on the downstream pressure pand based on the upstream temperature t.

In some embodiments, method further comprises: receiving a choice signal indicative of a choice of a refrigerant; processing the choice signal to determine the refrigerant; determining a back pressure ratio ras a function of the downstream pressure pand of the upstream pressure p; determining a critical pressure ratio ras a function of the upstream pressure p, of the upstream temperature t, and of the determined refrigerant; comparing the back pressure ratio rand the critical pressure ratio rto one another; determining an application pressure ratio ras a maximum value of the back pressure ratio rand of the critical pressure ratio re; and determining the discharge coefficient cbased on the application pressure ratio r.

In some embodiments, method further comprises: determining an isentropic expansion coefficient k as a function of the upstream pressure p, of the upstream temperature t, and of the determined refrigerant; determining the critical pressure ratio ras a function of the isentropic expansion coefficient k; comparing the back pressure ratio rand the critical pressure ratio rto one another; determining the application pressure ratio ras the maximum value of the back pressure ratio rand of the critical pressure ratio r; and determining the discharge coefficient cbased on the application pressure ratio rand based on the isentropic expansion coefficient k.

In some embodiments, the method further comprises: receiving a numeric signal; processing the numeric signal to determine a liquid pressure recovery factor Fsuch that the liquid pressure recovery factor Fis less than unity or equals unity; determining a critical pressure pbased on the determined refrigerant; determining a saturation pressure ratio ras a function of the upstream pressure p, of the upstream temperature t, and of the determined refrigerant; and using the liquid pressure recovery factor Fand the critical pressure pand the saturation pressure ratio rand the upstream pressure pto determine the critical pressure ratio r.

In some embodiments, the method further comprises: determining a saturation pressure pbased on the upstream temperature tand based on the determined refrigerant; and determining the saturation pressure ratio ras a function of the saturation pressure pand of the upstream pressure p.

In some embodiments, the method further comprises: determining a liquid pressure ratio factor Fas a function of the saturation pressure pand of the critical pressure p; and using the liquid pressure recovery factor Fand the liquid pressure ratio factor Fand the saturation pressure ratio rto determine the critical pressure ratio r.

In some embodiments, the method further comprises: receiving a choice signal indicative of a choice of a refrigerant; receiving a numeric signal; processing the choice signal to determine the refrigerant; processing the numeric signal to determine a liquid pressure recovery factor Fsuch that the liquid pressure recovery factor Fis less than unity or equals unity; determining a back pressure ratio ras a function of the downstream pressure pand of the upstream pressure p; determining a critical pressure pbased on the determined refrigerant; determining a saturation pressure ratio ras a function of the upstream pressure p, of the upstream temperature t, and of the determined refrigerant; using the liquid pressure recovery factor Fand the critical pressure pand the saturation pressure ratio rand the upstream pressure pto determine a liquid critical pressure ratio r; determining an isentropic expansion coefficient k as a function of the upstream pressure p, of the upstream temperature t, and of the determined refrigerant; using the isentropic expansion coefficient k to determine a gaseous critical pressure ratio r; comparing the back pressure ratio rand the liquid critical pressure ratio rand the gaseous critical pressure ratio rto one another; determining an application pressure ratio ras a maximum value of the back pressure ratio r, of the liquid critical pressure ratio r, and of the gaseous critical pressure ratio r; and determining the discharge coefficient cbased on the application pressure ratio rand based on the isentropic expansion coefficient k.

In some embodiments, the method further comprises: determining a saturation pressure pbased on the upstream temperature tand based on the determined refrigerant; and determining the saturation pressure ratio ras a function of the saturation pressure pand of the upstream pressure p.

In some embodiments, the method further comprises: determining a liquid pressure ratio factor Fas a function of the saturation pressure pand of the critical pressure p; and using the liquid pressure recovery factor Fand the liquid pressure ratio factor Fand the saturation pressure ratio rto determine the liquid critical pressure ratio r.

In some embodiments, the refrigerant circuit () also comprises a fourth sensor () for recording a signal indicative of a thermodynamic state of the refrigerant at the inlet port of the at least one valve (), and the method comprises: recording a fourth signal using the fourth sensor (); receiving a choice signal indicative of a choice of a refrigerant; receiving a numeric signal; processing the fourth signal to determine a vapour quality q; processing the choice signal to determine the refrigerant; processing the numeric signal to determine a liquid pressure recovery factor Fsuch that the liquid pressure recovery factor Fis less than unity or equals unity; determining a specific volume vof a liquid fraction of the refrigerant based on the upstream pressure pand based on the upstream temperature tand based on the determined refrigerant; determining a specific volume vof a gaseous fraction of the refrigerant based on the upstream pressure pand based on the upstream temperature tand based on the determined refrigerant; determining a critical pressure pbased on the determined refrigerant; determining a saturation pressure ratio ras a function of the upstream pressure p, of the upstream temperature t, and of the determined refrigerant; using the liquid pressure recovery factor Fand the critical pressure pand the saturation pressure ratio rand the upstream pressure pto determine a liquid critical pressure ratio r; determining an isentropic expansion coefficient k as a function of the upstream pressure p, of the upstream temperature t, and of the determined refrigerant; using the isentropic expansion coefficient k to determine a gaseous critical pressure ratio r; and determining the discharge coefficient cbased on the vapour quality qand based on the specific volume vof the liquid fraction and based on the specific volume vof the gaseous fraction and based on the liquid critical pressure ratio rand based on the gaseous critical pressure ratio r.

As another example, some embodiments include a refrigerant circuit () comprising at least one condenser (), at least one compressor (), at least one evaporator (), and at least one valve () having an inlet port and an outlet port, the refrigerant circuit () also comprising a first sensor () for recording a signal indicative of a pressure of a refrigerant at the inlet port of the at least one valve (), a second sensor () for recording a signal indicative of a pressure of the refrigerant at the outlet port of the at least one valve (), a third sensor () for recording a signal indicative of a temperature of the refrigerant at the inlet port of the at least one valve (), a fourth sensor () for recording a signal indicative of a vapour quality at the inlet port of the at least one valve (), and a controller () communicatively connected to the at least one valve (), to the first sensor (), to the second sensor (), to the third sensor (), and to the fourth sensor (), wherein the controller () is configured to execute one or more of the methods described herein.

As another example, some embodiments include a computer program comprising instructions to cause the controller () of one of the refrigerant circuits described herein to execute one or more of the methods described herein.

As another example, some embodiments include a computer-readable medium having stored thereon a computer program as described herein.

Various embodiments of the instant disclosure define a discharge coefficient cto estimate actual mass flow {dot over (m)} through at least one valve. Actual mass flow {dot over (m)} is estimated as a percentage of maximum achievable mass flow {circumflex over ({dot over (m)})}. The maximum achievable flow {circumflex over ({dot over (m)})} is the flow that can be achieved at a given position of the at least one valve.

The discharge coefficient ccan be estimated and/or determined for various types of fluids such as perfect liquids, perfect gases, flashing liquids, single-phase fluids, and two-phase fluids. To that end, various sensors such as pressure sensors downstream and upstream of the at least one valve can be used. A temperature sensor and/or a vapour quality sensor can also be used to estimate and/or determine discharge coefficient c.

A characteristic curve of the at least one valve is then employed to estimate flow at a predetermined position. This characteristic curve describes flow through the at least one valve as a function of its opening degree. For example, a discharge coefficient cas estimated or determined at an opening degree of ten percent will lead to different value of flow when the at least one valve is fully open. In other words, the flow {dot over (m)} as indicated by the discharge coefficient cis rescaled using the characteristic curve of the at least one valve. The flow {dot over (m)} as indicated by the discharge coefficient cis rescaled to a predetermined position. The predetermined position can, by way of non-limiting example, be a maximum position of the at least one valve.

The value of flow at the predetermined position can then be compared to an expected value. A difference between the expected value and the flow at the predetermined position can, by way of non-limiting example, be determined. A ratio between the expected value and the flow at the predetermined position can, by way of another non-limiting example, be determined.

In some embodiments, the expected value of flow is a nominal value of flow. In some embodiments, the expected value of flow is a rated value of flow. The expected value of flow can depend on the type of fluid circulating inside the HVAC circuit. If the deviation is bigger than a threshold value, the deviation will be considered as an indication of an anomaly and/or of a disturbance. For example, a deviation between the expected value and the flow at the predetermined position of more than ten percent can point to a disturbance. The anomaly and/or the disturbance can, by way of non-limiting example, be a loss of refrigerant or a change of the configuration of a HVAC circuit.

shows an example refrigerant circuitincorporating teachings of the present disclosure. The refrigerant circuitcan, by way of non-limiting example, be a refrigerant circuit of an air-conditioning installation or system. The refrigerant circuitcan, by way of another non-limiting example, also be a refrigerant circuit of a HVAC installation or system.

The refrigerant circuithas a condenser. The condenserprovides an outlet that leads to an inlet of the at least one valve. The at least one valvecan, by way of non-limiting example, be or comprise at least one expansion valve. A conduit can connect the outlet of the condenserto the inlet of the at least one valve, thereby enabling fluid communication between the condenserand the at least one valve. More specifically, a conduit can connect the outlet of the condenserto the inlet of the at least one expansion valve, thereby enabling fluid communication between the condenserand the at least one expansion valve.

In some embodiments, the expansion valvecomprises an electronic expansion valve. More specifically, the expansion valvecan be an electronic expansion valve. In some embodiments, the expansion valvecomprises a control valve. More specifically, the expansion valvecan be a control valve. The expansion valvecan comprise an electronic expansion valve and a control valve. The expansion valvecan still be an electronic expansion valve and a control valve.

Refrigerant leaves the at least one expansion valvevia its outlet and flows toward an inlet of the at least one evaporator. To that end, another conduit can be provided between the outlet of the at least one expansion valveand the inlet of the at least one evaporator.

The at least one evaporatoris in fluid communication with at least one compressorvia an outlet of the at least one evaporator. The at least one evaporatoris also in fluid communication with at least one compressorvia an inlet of the at least one compressor. Yet another conduit can connect the outlet of the at least one evaporatorto the inlet of the at least one compressor. The refrigerant can thus flow from the at least one evaporatorto the at least one compressor.

The refrigerant when leaving the at least one compressorvia an outlet of the at least one compressorflows toward the condenser. To that end, still another conduit connects the outlet of the at least one compressorto an inlet of the at least one condenser. That conduit closes the circuit. It affords flow from the condenserthrough the at least one valveand through the at least one evaporatorand back to the condenser.

Disturbances such as fluctuations of pressure as described herein can be handled by a controllerof the at least one valve. Those disturbances can also be handled by a controllerof at least one expansion valve. In some embodiments, the controllercomprises a microcontroller and/or a microprocessor. In some embodiments, the controlleris a microcontroller and/or is a microprocessor.

In some embodiments, the controllercomprises a memory such as a non-volatile memory. That is, the controllercan comprise a microcontroller and a non-volatile memory. The controllercan also comprise a microprocessor and a non-volatile memory. The controllercan still be a microcontroller having a non-volatile memory. The controllercan also be a microprocessor having a non-volatile memory.

In some embodiments, the controlleris separate from the at least one valve. The controllercan still be separate from at least one expansion valve.

In some embodiments, the at least one expansion valvehas a housing such as a metallic housing. The controlleris secured relative to the housing of the at least one expansion valve. In some embodiments, the controlleris arranged inside the housing of the at least one expansion valve.

In some embodiments, the controllercomprises a local controller such as a controllerof the at least one expansion valve. The local controller is or comprises an inexpensive, low-power system on a chip microcontroller having integrated wireless connectivity.

In some embodiments, the chip microcontroller has a memory not exceeding one mebibyte. The controlleralso comprises a remote controller such as a cloud computer. The local controller and the remote controller are in operative communication.

The controlleris in operative communication with sensors,arranged upstream of and downstream of the at least one valve.shows such sensors,. The sensors,record signals indicative of thermodynamic states of the refrigerant at or near the inlet and at or near the outlet. The sensors,advantageously are sensors,of the refrigerant circuit. In a special embodiment, the sensors,are sensors,of the at least one expansion valve.

In some embodiments, the sensorupstream of the at least one valvecomprises a pressure sensor. The pressure sensor is configured to sense a pressure of the refrigerant upstream of the at least one valve. In some embodiments, the sensorat or near the inlet of the at least one expansion valvecomprises a pressure transducer. In some embodiments, the sensorat or near the inlet of the at least one expansion valvecomprises a pressure nozzle.

In some embodiments, the sensorupstream of the at least one valveis a pressure sensor. The pressure sensor is configured to sense a pressure of the refrigerant upstream of the at least one valve. In some embodiments, the sensorat or near the inlet of the at least one expansion valveis a pressure transducer. In some embodiments, the sensorat or near the inlet of the at least one expansion valveis a pressure nozzle.