EP4686898A1

EP4686898A1 - Controller, method, computer program product and non transitory computer readable medium for monitoring leakage of refrigerant, heat pump comprsing the controller

Info

Publication number: EP4686898A1
Application number: EP24192550.2A
Authority: EP
Inventors: Miquel GUZMAN
Original assignee: BDR Thermea Group BV
Current assignee: BDR Thermea Group BV
Priority date: 2024-08-02
Filing date: 2024-08-02
Publication date: 2026-02-04

Abstract

A heat pump with malfunction detection is described, which improves protection for the compressor. Pressure is monitored on both high pressure and low-pressure sides of the refrigerant circuit and the compressor is stopped if any reading is above a respective threshold. A time period T is then started, and genuine pressure drop confirmed by acquiring further pressure readings. If N instances occur of either high pressure side or low-pressure side readings below their respective threshold value then the reset button for the heat pump is blocked. In further embodiments temperature at a discharge line may also be measured.

Description

The invention relates to heat pump with malfunction detection.
Heat pumps are complex devices with multiple components and there are a number of ways in which they may malfunction.
Of increasing importance is leak detection. Changes in environmental regulations have forced changes in the use of certain refrigerant classes, necessitating use of refrigerants with a low global warming potential (GWP). Even better is the use of a GWP no greater than 150 (GWP<150, the reference 1 being the global warming potential of CO2), compared with 2100 for previously used refrigerants such as R410a, 1430 for R134a and 675 for R32.
Manufacturers are therefore switching to fluids that meet these GWP conditions and in particular natural fluids such as propane R290 with a GWP of 3 or butane R600 with a GWP of 4 have become the preferred refrigerants of choice. However, these fluids are flammable, and it is therefore necessary to put in place measures to guarantee the safety of users.
If a flammable fluid is brought into contact with a potential source of ignition (PIS) there is a risk of fire or explosion. In particular, self-ignition can occur, which is a form of spontaneous combustion due to contact with a source of heat at or above the flammability point of the fluid, or due to contact with a source of sufficient energy, known as activation energy.
Heat pumps are systems powered by electrical energy, some of whose connections can generate electric arcs or sparks that can reach activation energy. They may also include additional heating elements that can reach the self-activation temperature or self-ignition temperature in particular an electrical resistor reaching a surface temperature of around 500 °C.
Heat pumps are designed to keep flammable refrigerants away from potential sources of ignition; however, it should never be assumed that any encompassing construction will never break down or leak. Therefore, the move to flammable refrigerants and other working fluids means leakage detection becomes critical in order to further control the risk of ignition of flammable refrigerants.
Additionally, elements external to the heat pump may also increase the risk due to leakage. Any activities normally undertaken in and around buildings and which involve use of heat sources or ignition points may create risk, for example cooking activities including stoves and barbecues, smoking, making a fire, connecting an electrical appliance which may spark or arc, connecting an electric vehicle, connection to any electrical socket particularly if damaged, or exposure to hot spots for example from a thermal vehicle.
In general, a leak of any fluid in a heat pump will only occur subsequent to some form of damage, but it could also occur over time due ageing, corrosion, fatigue, severe vibration, etc. In rare cases it could also be due to poor assembly. Additionally external events or actions may also lead to refrigerant circuit failure with associated leakage, for example accident or severe mechanical shock, and these can occur due to fire, building collapse, earthquake, etc.
A large proportion of heat pumps are used in residential applications, and it is impossible to control all these events, therefore refrigerant leakage is a risk, particularly now that manufacturers are moving to flammable refrigerants in order to significantly reduce the environmental impact of the previously used refrigerants. It is impossible to guarantee the total absence of leakage over the entire life of the product.
With this in mind it is impossible to completely remove all potential sources of ignition in and around the product. Residential installation is particularly high risk because of the numbers and type of people involved, in terms of age, skillset, and awareness of the risk, and the variation in precise installation position, for example communal areas, gardens, living rooms, technical rooms, balconies, etc. It is therefore impossible to control for all risk.
Manufacturers have implemented a range of countermeasures, particularly mechanical ones, to reduce the associated risks, however it is essential to be able to detect a leak in the first place in order to take action on the system to reduce the effects.
Most existing solutions for leakage detection utilise dedicated sensors placed in the spaces into which the refrigerant fluid could be expected to leak. One problem with this however is that gas detection is generally sensitive but not specific. In other words, many detectors can detect leaked gas at low levels but they cannot report where it comes from in the system. So in a case where there may be more than one heat pump unit, either because there is more than one separate heat pump in a particular area, or because the heat pump comprises multiple modules, a leak may be detected, but it may not be immediately obvious from where the leak emanates.
Sensors may also produce false positives, in that they make detect other gas that has not leaked from a heat pump.
In EP3764073A1 ultrasound is used to detect gas bubbles from a leakage in a second fluid.
In WO2020010082 a detection system for a heat pump is described which uses a first sensor situated in the space into which refrigerant might leak, and second and third sensors for confirmation.
Once a leak has been identified it is possible to take action, such as stopping the compressor to reduce propagation, ventilating the space to dilute the fluid as for example in WO2017183234 , confining the leakage, as for example in EP3875862 , triggering absorption of the fluid as for example in EP3805671 , or by utilizing fire-fighting measures as for example in EP3770520 .
False positives are a problem in any detection system, particularly when detection causes the stopping of the compressor, because a false positive means the compressor has been erroneously stopped. Manufacturers therefore introduced reset buttons to allow a user to re-start an automatically stopped heat pump. Typically, in the case of detection of a leak or some other malfunction the compressor would stop automatically and the heat pump owner or operator would be required to manually check the system to confirm a leak or other malfunction, and to determine action to be taken. If there was in fact no evidence of the event detected, the reset button could be pressed to restart the heat pump.
However, it was realised that owners and operators were inclined to press the restart button anyway, without thoroughly checking the stopped heat pump. In the event of a genuine leak this increases the risk of danger and moreover, in the event that refrigerant has leaked sufficiently, for example due to a long and slow leak, can actually damage the compressor, because when it is restarted by the reset button there may be insufficient refrigerant to allow correct and safe working.
Therefore, it is an object of the invention to provide a heat pump with improved malfunction detection.
The object is solved by a heat pump with malfunction detection, the heat pump comprising a compressor, a refrigerant circuit comprising a high pressure side and a low pressure side, a first pressure sensor S_PH situated on the high-pressure side of the refrigerant circuit and arranged to acquire first pressure readings P_PHn, a second pressure sensor S_PL situated on the low-pressure side of the refrigerant circuit and/or arranged to acquire second pressure readings P_PLn, a reset system to allow a user activated restart of the heat pump when the heat pump stops operating, and a controller coupled to the compressor, the first pressure sensor S_PH, the second pressure sensor S_PL and the reset system, whereby the controller is arranged to monitor the first and/or second pressure readings P_PHn and P_PLn while the compressor is in operation and if any first pressure reading P_PHn is below a threshold Th_PH, or if any second pressure reading P_PLn is below a threshold Th_PL, then the controller is arranged to stop operation of the compressor and start a time period T, and is further arranged during time period T to monitor further first and/or second pressure readings, wherein if first pressure readings P_PHn are below a threshold Th_PH with a frequency greater than N in the time period T, or if second pressure readings P_PLn are below a threshold Th_PL with a frequency greater than N in the time period T, then the controller is arranged to block the reset system, whereas if first pressure readings P_PHn are not below a threshold Th_PH with a frequency greater than N in the time period T, and/or if second pressure readings P_PLn are not below a threshold Th_PL with a frequency greater than N in the time period T, then the controller is arranged to restart the compressor.
This invention improves protection of the compressor by monitoring the pressure in both sides of the refrigerant circuit and stopping the compressor at the first sign of a drop in suitable pressure, on either the high-pressure side or low-pressure side, but by then allowing for a time period T to confirm if the drop in pressure is sustained, and if it is then by blocking the reset function. The reset function may be a button, controllable by panel or other input device, or a reset function controlled by an app. In a typical example reset can be performed directly with the service HMI or via modbus. This means that the owner or operator of the heat pump can no longer override compressor stop and must revert to more formal means of confirming the safety of the heat pump, for example by calling out a qualified engineer.
In an embodiment, further devices will also be stopped in addition to the compressor, for example water circulator, fan, EEV, etc. In an embodiment all devices can be stopped if the alarm is severe, and in a particular embodiment all devices except the pump for a less severe alarm. In these embodiments the controller will be arranged to restart all stopped components.
In an embodiment typical values of N and T are: N has the value 3, and/or T has the value 15 mins.
In another embodiment T may be 60 mins (or 1 hour).
In an embodiment typical threshold values are:

Th_PH < 4 absolute bar, and/or
Th_PL < 4 absolute bar.

In a further embodiment:

Th_PH < 2 absolute bar, and/or
Th_PL < 2 absolute bar.

In a further embodiment the heat pump further comprises a temperature sensor S_TD situated at a discharge line and arranged to acquire temperature readings T_TDn, whereby the controller is further arranged to monitor the temperature readings T_TDn and if any temperature reading T_TDn, is above a threshold Th_TD the controller is arranged to stop operation of the compressor and start the time period T, and in addition to readings P_PHn and P_PLn takes temperature readings T_TDn, wherein if temperature readings T_TDn, are above a threshold Th_TD. with a frequency greater than N in the time period T, then the controller is arranged to block the reset system, whereas if first pressure readings P_PHn are not also below a threshold Th_PH with a frequency greater than N in the time period T, and if second pressure readings P_PLn are not also below a threshold Th_PL with a frequency greater than N in the time period T, then the controller is arranged to restart the compressor.
This embodiment further improves protection for the compressor by including a monitoring of temperature at a discharge point. A discharge point could be any point or position in the system at which the heat in the refrigerant circuit is transferred to some form of load, for example in a domestic heat pump a domestic heating network which is heated by the heat pump. These high heat levels can occur in particular in the event of a leak. It is therefore an additional means of identifying a leak and confirming the hypothesis associated with the pressure measurement.
In an embodiment a typical threshold value is:
Th_TD is between 100°C and 140°C, and preferably between 110°C and 135°C. In a particular embodiment prevention is started at 115°C, and 120 °C is the threshold for the alarm.
In a further embodiment a second temperature sensor, at a suction point, may be used. In a further embodiment a choice may be made to use one or the other, or both.
In particular the invention takes advantages of a number of sensors, which may be operational sensors, including for example:

a pressure sensor arranged to detect pressure in the low-pressure section;
a pressure sensor arranged to detect pressure in the high-pressure section;
a temperature sensor arranged to detect temperature at a first heat exchanger or associated piping line
a temperature sensor arranged to detect temperature at a second heat exchanger or associated piping line.

However, dedicated sensors may also be provided.
In further embodiments values for N and/or the time period Tand/or the threshold values Th_PL and/or Th_PHand/or Th_TD may be dependent on the mode of the heat pump, in other words whether it is in a cooling mode or a heating mode.
In an embodiment, once the reset is blocked then this should ideally be communicated to the owner or operator of the heat pump, and this can be arranged by having the controller transmit an alert, and/or send a report. The alert or report may be in the form of a short service message, an email, a signal to light a warning lamp on the heat pump, an alert to an app (for example on a mobile device), or a signal to sound an audible alarm such as, for example, a klaxon on the heat pump.
In another aspect of the invention, a method is provided to detect malfunction in a heat pump comprising a compressor, a refrigerant circuit comprising a high pressure side and a low pressure side, a first pressure sensor S_PH situated on the high-pressure side of the refrigerant circuit and arranged to acquire first pressure readings P_PHn, a second pressure sensor S_PL situated on the low-pressure side of the refrigerant circuit and arranged to acquire second pressure readings P_PLn, a reset system to allow a user activated restart of the heat pump when the heat pump stops operating, and a controller coupled to the compressor, the first pressure sensor S_PH, the second pressure sensor S_PL and the reset system, and wherein the method comprises, in the controller, monitoring the first and second pressure readings P_PHn and P_PLn while the compressor is in operation and if any first pressure reading P_PHn is below a threshold Th_PH, or if any second pressure reading P_PLn is below a threshold Th_PL,_.then stopping operation of the compressor and starting a time period T, and during time period T, monitoring further first and second pressure readings, wherein if first pressure readings P_PHn are below a threshold Th_PH with a frequency greater than N in the time period T, or if second pressure readings P_PLn are below a threshold Th_PL with a frequency greater than N in the time period T, then performing the operation of blocking the reset system, whereas if first pressure readings P_PHn are not below a threshold Th_PH with a frequency greater than N in the time period T, and if second pressure readings P_PLn are not below a threshold Th_PL with a frequency greater than N in the time period T, then restarting the compressor.
Monitoring of pressure readings may occur throughout the time period T.
In a further embodiment of the method, and wherein the heat pump further comprises a temperature sensor S_TD situated at a discharge point and arranged to acquire temperature readings T_TDn, and/or optionally a second temperature sensor situated at the succion point, the method further comprises, in the controller, monitoring the temperature readings T_TDn and if any temperature reading T_TDn is above a threshold Th_TD then stopping operation of the compressor and starting the time period T, and in addition to readings P_PHn and P_PLn acquiring temperature readings T_TDn wherein if temperature readings T_TDn are above a threshold Th_TD. with a frequency greater than N in the time period T, then blocking the reset system, whereas if first pressure readings P_PHn are not also below a threshold Th_PH with a frequency greater than N in the time period T, and if second pressure readings P_PLn are not also below a threshold Th_PL with a frequency greater than N in the time period T, then restarting the compressor.
In a further embodiment the method includes sending a report, and/or sending an alert, in particular to an operator of the heat pump.
In additional embodiment a method may be provided for determining an error or malfunction in a heat pump, which heat pump comprises a plurality of sensors, S_n, for operational monitoring, an alert monitoring circuit, and wherein the method comprises providing a threshold value, Th_n, for each respective sensor S_n, taking or acquiring readings, S_n, from each sensor S_n, comparing each sensor reading s, to its respective threshold value Th_n, and arranging the sensors into groups G_m, wherein if all sensor readings, s_n, are below their respective threshold values Th, in a particular group G_m then performing the action of transmitting an alert to the alert monitoring circuit.
In an additional embodiments, the values for N and/or the time period T and/or threshold values Th_TD and/or Th_PH and/or Th_PL can be predefined fixed values and/or values which are dependent on one or more parameters, in particular dependent on changes of the one or more parameters, of the heat pump; said one or more parameters are in particular pressure and/or temperature.
In another aspect of the invention, a controller for a heat pump is provided, wherein the controller is configured to perform the method of the invention.
In another aspect of the invention, a computer program product is provided comprising program instructions operable to cause a processor to perform operations according to the method of the invention. The computer program product may be formulated as software, in any computer language or means of communication suitable for the respective heat pump and/or a heat pump controller, may be formulated as firmware, or may be formulated as hardware.
In another aspect of the invention, a non-transitory computer readable medium is provided, having stored thereupon the computer program product according to the invention. Such a non-transitory computer readable medium may be a computer hard disk, a computer floppy disk, a computer magnetic storage medium, a laser readable disk or any other form of non-transitory storage capable of storing a computer program and capable of being read or of delivering up the stored instructions for reading or for decompiling by another means.
In another aspect of the invention, a data carrier signal carrying the computer program product of the invention is provided. The data carrier signal may be a mobile telecommunications signal, for example a 2G, 3G, 4G or 5G signal, a radio signal, for example a short wave, medium wave or long wave signal, any electronic signal transmitted wirelessly or transmitted along wires, a light signal or any form of sonic signal.
In the figures, the subject-matter of the invention is schematically shown, wherein identical or similarly acting elements are usually provided with the same reference signs.

Figure 1: shows a heat pump according to aspects of the invention.
Figure 2: shows a flow diagram of a method according to the invention.
Figure 3: shows a heat pump according to aspects of the invention.
Figure 4: shows a flow diagram of a method according to the invention.
Figure 5: shows a heat pump with an arrangement of operational sensors that may be used in the invention.

Figure 1 shows a heat pump 1 according to aspects of the invention and comprising a refrigerant circuit 2, a compressor 3, a controller 4, an expansion device 5, two heat exchangers 6, 7, a first pressure sensor 8' situated on the high-pressure side of the refrigerant circuit, a second pressure sensor 8" on the low pressure side of the refrigerant circuit, and a reset system 9. Controller 4 is coupled to the compressor 3, the first pressure sensor 8', second pressure sensor 8" and reset system 9.
Figure 2 shows a flow diagram of a method according to the invention in which first pressure readings P_PHn are acquired 10 and second pressure readings P_PLn are acquired 20 and each is compared to a respective threshold value. If any first pressure reading P_PHn is below a threshold Th_PH 11 or if any second pressure reading P_PLn is below a threshold Th_PL 21 then the controller stops operation of the compressor and starts a time period T 25. As long as readings remain above the threshold the method proceeds no further, and the controller simply waits to acquire or be sent the next reading.
During time period T both first and second pressure sensors continue to acquire readings and the controller monitors these. If N or more instances of a first pressure reading P_PHn below respective threshold Th_PH occur, or, if N or more instances of a second pressure reading P_PLn below respective threshold Th_PL occur 26, then the controller blocks the reset system 27. If not, then the controller restarts the compressor.
Figure 3 shows a heat pump according to a further embodiment of the invention. The heat pump 1 is essentially the same as that depicted in Figure 1 and comprises a refrigerant circuit 2, a compressor 3, a controller 4, an expansion device 5, two heat exchangers 6, 7, a first pressure sensor 8' situated on the high-pressure side of the refrigerant circuit, a second pressure sensor 8" on the low-pressure side of the refrigerant circuit, and a reset system 9. Controller 4 is coupled to the compressor 3, the first pressure sensor 8', second pressure sensor 8" and reset system 9. Additionally, it comprises a temperature sensor 29 at a discharge point, i.e. situated in a position by which it can measure the temperature delivered to the system being fed by the heat pump. In a further embodiment temperature sensor 29 could also be situated at a discharge line.
Figure 4 shows a flow diagram of a method according to the invention in which temperature readings T_TDn are acquired 30. If any temperature reading T_TDn is above a threshold Th_TD 31 then the compressor is stopped, and a time period T is started 25. This method takes place in parallel to the main method of the invention, in other words in parallel to the acquisition of pressure readings P_PHn and P_PLn. During time period T further temperature readings may be taken and if N or more instances of temperature readings T_TDn, are above a threshold Th_TD during time period T 26' , then the controller blocks the reset system. If not, and there are no N or more instances of either of the pressure readings being below their respective thresholds during the same time period T, then the compressor is restarted.
Figure 5 shows a heat pump with an arrangement of operational sensors that may be used in the invention. An outdoor unit 50 is connected to an indoor unit or heat network or further domestic or building network of fluid pipes 51 and comprises a fan 52 arranged to create an airflow over a heat exchanger 53 in a heat pump circuit with a compressor 54, a second heat exchanger 55 and an expansion device 56. Various operational sensors, including pressure sensors 57, PCS situated in the low pressure section and PCD situated in the high pressure section, and temperature sensors 58 are arranged around the circuit and may be used in the arrangements and methods of the invention.

Reference Signs

1: heat pump
2: refrigerant circuit
3: compressor
4: controller
5: expansion valve
6: heat exchanger
7: heat exchanger
8': first pressure sensor
8": second pressure sensor
9: reset system
10: data acquisition step
11: comparison step
20: acquisition step
21: comparison step
25: action step of stopping compressor, starting T
26: comparison step
26': comparison step
27: action step of blocking reset system
28: action step of restarting compressor
29: temperature sensor
30: acquisition step
31: comparison step
50: outdoor unit of heat pump
51: indoor unit or heat network
52: fan
53: heat exchanger
54: compressor
55: heat exchanger
56: expansion valve
57: pressure sensors
58: temperature sensors

Claims

A heat pump with malfunction detection, the heat pump comprising:
- a compressor,

- a refrigerant circuit comprising a high-pressure side and a low-pressure side,

- a first pressure sensor S_PH situated on the high-pressure side of the refrigerant circuit and arranged to acquire first pressure readings P_PHn, and/or a second pressure sensor S_PL situated on the low-pressure side of the refrigerant circuit and arranged to acquire second pressure readings P_PLn ,

- a reset system to allow a user activated restart of the heat pump when the heat pump stops operating, and

- a controller coupled to the compressor, the first pressure sensor S_PH and/or the second pressure sensor S_PL and the reset system, whereby

- the controller is arranged to monitor the first and/or second pressure readings P_PHn and P_PLn while the compressor is in operation and if:

- any first pressure reading P_PHn is below a threshold Th_PH, or if

- any second pressure reading P_PLn is below a threshold Th_PL,then

- the controller is arranged to stop operation of the compressor and start a time period T, and is further arranged during time period T:

- to monitor further first and/or second pressure readings, wherein if

- first pressure readings P_PHn are below a threshold Th_PH with a frequency greater than N in the time period T; and/or if

- second pressure readings P_PLn are below a threshold Th_PL with a frequency greater than N in the time period T; then

- the controller is arranged to block the reset system, whereas

- if first pressure readings P_PHn are not below a threshold Th_PH with a frequency greater than N in the time period T; and

- if second pressure readings P_PLn are not below a threshold Th_PL with a frequency greater than N in the time period T; then the controller is arranged to

- restart the compressor.
A heat pump with malfunction detection system according to claim 1, whereby N has the value 3, and/or T has the value 15 min.
A heat pump with a malfunction detection system according to claim 1, whereby Th_PH and/or Th_PL is below 4 absolute bar, preferably below 2 absolute bar.
A heat pump with malfunction detection according to claim 1, the heat pump further comprising:
- a temperature sensor S_TD situated at a discharge line and arranged to acquire temperature readings T_TDn, whereby

- the controller is further arranged to monitor the temperature readings T_TDn and if any temperature reading T_TDn is above a threshold Th_TD the controller is arranged to stop operation of the compressor and start the time period T, and in addition to readings P_PHn and P_PLn takes temperature readings T_TDn wherein

- if any temperature reading T_TDn is above a threshold Th_TD with a frequency greater than N in the time period T, then

- the controller is arranged to block the reset system, whereas

- if first pressure readings P_PHn are not also below a threshold Th_PH with a frequency greater than N in the time period T; and

- if second pressure readings P_PLn are not also below a threshold Th_PL with a frequency greater than N in the time period T; then the controller is arranged to.

- restart the compressor.
A heat pump with malfunction detection according to claim 4, whereby Th_TD is between 100°C and 140°C, and preferably between 110°C and 135°C.
A heat pump with malfunction detection according to claim 1 wherein if the reset system is blocked the controller is further arranged to:
- transmit an alert, and/or

- send a report.
A method to detect malfunction in a heat pump comprising:
- a compressor,

- a refrigerant circuit comprising a high-pressure side and a low pressure side,

- a first pressure sensor S_PH situated on the high-pressure side of the refrigerant circuit and arranged to acquire first pressure readings P_PHn,

- a second pressure sensor S_PL situated on the low-pressure side of the refrigerant circuit and arranged to acquire second pressure readings P_PLn,

- a reset system to allow a user activated restart of the heat pump when the heat pump stops operating, and

- a controller coupled to the compressor, the first pressure sensor S_PH, the second pressure sensor S_PL and the reset system,
wherein the method comprises:
- in the controller, monitoring the first and second pressure readings P_PHn and P_PLn while the compressor is in operation and if:

- any first pressure reading P_PHn is below a threshold Th_PH, or if

- any second pressure reading P_PLn is below a threshold Th_PL,_,then

- stopping operation of the compressor and starting a time period T, and during time period T:

- monitoring further first and second pressure readings, wherein if

- first pressure readings P_PHn are below a threshold Th_PH with a frequency greater than N in the time period T; or if

- second pressure readings P_PLn are below a threshold Th_PL with a frequency greater than N in the time period T; then performing the operation of

- blocking the reset system, whereas

- if first pressure readings P_PHn are not below a threshold Th_PH with a frequency greater than N in the time period T; and

- if second pressure readings P_PLn are not below a threshold Th_PL with a frequency greater than N in the time period T; then

- restarting the compressor.
A method to detect malfunction in a heat pump, according to claim 7, wherein the heat pump further comprises:
- a temperature sensor S_TD situated at a discharge point and arranged to acquire temperature readings T_TDn, whereby the method further comprises:

- in the controller, monitoring the temperature readings T_TDn and if any temperature reading T_TDn is above a threshold Th_TD then

- stopping operation of the compressor and starting the time period T, and in addition to readings P_PHn and P_PLn acquiring temperature readings T_TDn wherein

- if temperature readings T_TDn are above a threshold Th_TD with a frequency greater than N in the time period T, then

- blocking the reset system, whereas

- if first pressure readings P_PHn are not also below a threshold Th_PH with a frequency greater than N in the time period T; and

- if second pressure readings P_PLn are not also below a threshold Th_PL with a frequency greater than N in the time period T; then

- restarting the compressor.
A method to detect malfunction in a heat pump according to claim 7 or 8, wherein if the method further comprises:
- sending a report and/or

- sending an alert, in particular to an operator of the heat pump.
A method to to detect malfunction in a heat pump according to any of the preceding claims, the values for N and/or the time period T and/or threshold values Th_TD and/or Th_PH and/or Th_PL are be predefined fixed values and/or values which are dependent on one or more parameters, in particular dependent on changes of the one or more parameters, of the heat pump, wherein said one or more parameters are in particular pressure and/or temperature.
A controller for a heat pump, wherein the controller is configured to perform the method of any of claims 7 to 10.
A computer program product comprising program instructions operable to cause a processor to perform operations according to the method of any one of claims 7 to 10.
Non transitory computer readable medium having stored thereupon the computer program product according to claim 12.
Data carrier signal carrying the computer program product of claim 12.