Heat pump with malfunction detection system

Abstract

A heat pump with malfunction detection is described, which improves protection for the compressor by mitigating the risk of diesel effect during or subsequent to refrigerant leak. A heat pump comprises a refrigerant circuit with high-pressure side and low-pressure side, and high-side and low-side pressure sensors, a counter, and controller arranged to control an alarm state, which can be activated. The controller monitors high-side and low-side pressure readings and if any high-side pressure reading is below a respective first high-side threshold, and / or any low-side pressure reading below a respective first low-side threshold, then the compressor is stopped, the counter increased and alarm state activated until a high-side pressure reading is above a respective second high-side threshold while also a low-side pressure reading is above a respective second low-side threshold. If there are more than N alarms in any period T the compressor is blocked.

Description

[0001] Heat Pump with Malfunction Detection System

[0002] The invention relates to heat pump with malfunction detection.

[0003] Heat pumps are complex devices with multiple components and there are a number of ways in which they may malfunction.

[0004] 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.

[0005] 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.

[0006] 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.

[0007] 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.

[0008] 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.

[0009] 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.

[0010] 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.

[0011] 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.

[0012] 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.

[0013] 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.

[0014] Sensors may also produce false positives, in that they make detect other gas that has not leaked from a heat pump.

[0015] In EP3764073A1 ultrasound is used to detect gas bubbles from a leakage in a second fluid.

[0016] In W02020010082 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.

[0017] 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.

[0018] 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.

[0019] However further to this there is an extra risk for the compressor following or during a refrigerant leakage. When a refrigerant leakage occurs, and the pressure drops below atmospheric pressure, air may be sucked into the refrigerant circuit. In particular this can occur if the compressor remains running during an undetected leakage. Once air has entered into the refrigerant circuit it may be sucked into the compressor where it poses an explosion risk if mingled with the oil in the compressor. This explosion risk is known as ‘diesel effect’.

[0020] Therefore, it is an object of the invention to provide a heat pump with improved malfunction detection.

[0021] 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 high-side pressure sensor SPHsituated on the high-pressure side of the refrigerant circuit and arranged to acquire high-side pressure readings PPHn, and a low- side pressure sensor SPLsituated on the low-pressure side of the refrigerant circuit and arranged to acquire low-side pressure readings PPLn, a counter, and a controller coupled to the compressor, the counter, the first pressure sensor SPHand, the second pressure sensor SPL, and wherein the controller is arranged to control an alarm state, which can be set in an activated state or a non-activated state, whereby the controller is arranged to monitor the high-side PPHn and low-side PPi_npressure readings and if any if high-side pressure reading PPHnis below a respective first high-side threshold Th1PH, and / or any low-side pressure reading PPLnis below a respective first low-side threshold Th1PL,.then the controller is arranged to stop the compressor, increase the counter by 1 , and activate the alarm state which remains activated until both a high-side pressure reading PPHn is above a respective second high-side threshold Th2PH, and a low-side pressure reading PPLnis above a respective second low-side threshold Th1PL, and where the second high- side threshold Th2PH> first high-side threshold Th1PH, and the second low-side threshold Th2PL> the first low-side threshold Th1PL, whereupon the alarm state is turned off and re-start of the compressor is allowed, and further wherein if the counter registers more than N in any time period T then the controller is arranged to block automatic restart of the compressor.

[0022] The invention solves the diesel effect in heat pumps by going one step back and detecting refrigerant leakage using an improved method, and by stopping the compressor and thereby avoiding the risk of explosion from any air that may have already entered the refrigerant circuit following the evolution of a leak. In other words the invention focuses on the detecting the conditions under which air might be sucked into the refrigerant circuit, rather than, say, attempting to manipulate, say, the point of air entry.

[0023] The arrangement uses two pressure sensors, one placed on the high-pressure side of the refrigerant circuit, the other placed on the low-pressure side, and readings from each are compared successively to two respective levels of threshold.

[0024] The improved arrangement and method of the invention allows for a dangerous leak to be detected with a degree of sensitivity because it enforces comparison of refrigerant circuit pressures to a higher threshold in order to leave the alarm state, which was entered into by comparison of previously measured refrigerant circuit pressures to a lower threshold.

[0025] The method places the heat pump system into an alarm state if one or other of the measured pressures is found to be below a first respective threshold, and in order to allow the heat pump to leave that alarm state subsequently measured pressures, from the same two sensors, are compared to second respective thresholds, and the alarm state is only cancelled (or reset) if BOTH subsequent measured pressures are, during the same measurement cycle, above their respective second threshold value.

[0026] Typically all threshold values are pre-determined before measurements begin.

[0027] The values of the threshold values can be chosen according to the design of the heat pump and refrigerant circuit, and of the identity of the refrigerant itself, e.g. propane. Typically all four threshold values would be different and would reflect the values of each side of the refrigerant circuit, the high-pressure side and low-pressure side, however in a particular embodiment: the first high-side threshold value Th1PH= the first low-side threshold value Th1PL, and / or the second high-side threshold value Th2PH= the second low-side threshold Th2PL

[0028] Whenever it is not true than both subsequently measured pressures are above their respective second threshold value then start is forbidden and pressure measurements are simply re-acquired until both fulfil the condition of being above the respective thresholds. This would normally occur unless there was a catastrophic refrigerant leak because refrigerant pressure normally increases within the refrigerant circuit whenever the compressor stops or is shut down. Therefore it would be expected that under normal conditions, even if there is some form of slight leak, the pressures in the circuit would eventually rise on both the high- and the low-pressure sides above the respective second threshold values.

[0029] So in a further embodiment, if both the high-side pressure reading PPHnis not above the respective second high-side threshold Th2PH, and / or the low-side pressure reading PPi_nis not above the respective second low-side threshold Th1PL,.then the controller is arranged to forbid restart of the compressor.

[0030] Each time the alarm is set a counter N is increased by one and measured against a time period T. Essentially the number of alarms N is measured within a shifting time window T.

[0031] In an embodiment:

[0032] N = 4, and

[0033] T = 24 hours.

[0034] In the event of a serious leak it might take much less than 24 hours to generate 4 alarms, therefore the time period T can be varied, in particular may be less than 24 hours. However 24 hours is a time period which allows for detection of a range of refrigerant leaks.

[0035] Eventually, if the number of alarms exceeds the limit N in time T, for example more than 4 in 24 hours, then compressor start is forbidden and must be reset to start again. Typically reset will be by, for example, pressing a button or entering a reset instruction on a HMI. In a particular embodiment reset may be performed by communication of a reset signal to the compressor or to a controller that controls the compressor.

[0036] So in a further embodiment if automatic restart of the compressor is blocked then the compressor can be re-started by communication, the counter is reset, and re-start of the compressor is allowed.

[0037] In a further embodiment of a heat pump with malfunction detection, the heat pump comprises a compressor, a refrigerant circuit comprising a high pressure side and a low pressure side, a first pressure sensor SPHsituated on the high-pressure side of the refrigerant circuit and arranged to acquire first pressure readings PPHn, a second pressure sensor SPL situated on the low-pressure side of the refrigerant circuit and / or arranged to acquire second pressure readings PPLn, 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 SPH, the second pressure sensor SPLand the reset system, whereby the controller is arranged to monitor the first and / or second pressure readings PPHnand PPLnwhile the compressor is in operation and if any first pressure reading PPHn is below a threshold Th™, or if any second pressure reading PPi_nis below a threshold ThPL, 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 PPHnare below a threshold Th™ with a frequency greater than N in the time period T, or if second pressure readings PPLnare below a threshold ThPLwith 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 PPHnare not below a threshold ThPHwith a frequency greater than N in the time period T, and / or if second pressure readings PPLnare not below a threshold ThPLwith a frequency greater than N in the time period T, then the controller is arranged to restart the compressor.

[0038] 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.

[0039] 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.

[0040] In an embodiment typical values of N and T are: N has the value 3, and / or T has the value 15 mins.

[0041] In another embodiment T may be 60 mins (or 1 hour).

[0042] In an embodiment typical threshold values are:

[0043] ThpH < 4 absolute bar, and / or

[0044] ThpL < 4 absolute bar.

[0045] In a further embodiment:

[0046] ThpH < 2 absolute bar, and / or

[0047] ThpL < 2 absolute bar.

[0048] In a further embodiment the heat pump further comprises a temperature sensor STD situated at a discharge line and arranged to acquire temperature readings TTDn, whereby the controller is further arranged to monitor the temperature readings TTDn and if any temperature reading Tron is above a threshold ThTD the controller is arranged to stop operation of the compressor and start the time period T, and in addition to readings PPHn and PpLn takes temperature readings TTDn wherein if temperature readings TTDn are above a threshold ThTD. 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 PpHn are not also below a threshold ThPHwith a frequency greater than N in the time period T, and if second pressure readings PpLnare not also below a threshold ThPLwith 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.

[0049] In an embodiment a typical threshold value is:

[0050] ThTD 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.

[0051] 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.

[0052] In particular the invention takes advantages of a number of sensors, which may be operational sensors, including for example:

[0053] - a pressure sensor arranged to detect pressure in the low-pressure section;

[0054] - a pressure sensor arranged to detect pressure in the high-pressure section;

[0055] - a temperature sensor arranged to detect temperature at a first heat exchanger or associated piping line

[0056] - a temperature sensor arranged to detect temperature at a second heat exchanger or associated piping line.

[0057] However, dedicated sensors may also be provided.

[0058] In further embodiments values for N and / or the time period Tand / or the threshold values ThpL and / or ThpHand / or ThTD may be dependent on the mode of the heat pump, in other words whether it is in a cooling mode or a heating mode.

[0059] 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, wherein the heat pump comprises a compressor, a refrigerant circuit comprising a high-pressure side and a low pressure side, a high-side pressure sensor SPHsituated on the high-pressure side of the refrigerant circuit and arranged to acquire high-side pressure readings PPHn, a low-side pressure sensor SPL situated on the low-pressure side of the refrigerant circuit and arranged to acquire low-side pressure readings PpLn, a counter, and a controller coupled to the compressor, the counter, the high-side pressure sensor SPHand, the low-side pressure sensor SPL, and wherein the controller is arranged to control an alarm state, which can be set in an activated state or a non-activated state, wherein the method comprises, in the controller, monitoring the high-side PPHn and low- side PP^ pressure readings and if any if high-side pressure reading PPHn is below a respective first high-side threshold Th1PH, and / or any low-side pressure reading PpLnis below a respective first low-side threshold Th1PL,,then stopping the compressor, increasing the counter by 1 , and activating the alarm state which remains activated until both a high-side pressure reading PPHn is above a respective second high-side threshold Th2pH, and a low-side pressure reading PpLnis above a respective second low-side threshold Th1 pi_, and where the second high-side threshold Th2PH > first high-side threshold Th1PH, and the second low-side threshold Th2PL> the first low-side threshold Th1 pL, whereupon turning off the alarm state and allowing re-start of the compressor, and further wherein if the counter registers more than N in any time period T then blocking automatic restart of the compressor.

[0060] In a particular embodiment a method is also 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 SPHsituated on the high-pressure side of the refrigerant circuit and arranged to acquire first pressure readings PPHn, a second pressure sensor SPL situated on the low-pressure side of the refrigerant circuit and arranged to acquire second pressure readings PpLn, 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 SPH, the second pressure sensor SPLand the reset system, and wherein the method comprises, in the controller, monitoring the first and second pressure readings PPHn and PpLnwhile the compressor is in operation and if any first pressure reading PPHn is below a threshold ThPH, or if any second pressure reading PpLn is below a threshold ThPL,,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 PPHnare below a threshold ThPHwith a frequency greater than N in the time period T, or if second pressure readings PPi_nare below a threshold ThPLwith a frequency greater than N in the time period T, then performing the operation of blocking the reset system, whereas if first pressure readings PPHn are not below a threshold ThPHwith a frequency greater than N in the time period T, and if second pressure readings PPi_nare not below a threshold ThPi_with a frequency greater than N in the time period T, then restarting the compressor.

[0061] Monitoring of pressure readings may occur throughout the time period T.

[0062] In a further embodiment of the method, and wherein the heat pump further comprises a temperature sensor STD situated at a discharge point and arranged to acquire temperature readings TTDn, and / or optionally a second temperature sensor situated at the succion point, the method further comprises, in the controller, monitoring the temperature readings TTDn and if any temperature reading TTDn is above a threshold ThTD then stopping operation of the compressor and starting the time period T, and in addition to readings PPHnand PPLnacquiring temperature readings TTDn wherein if temperature readings TTDR are above a threshold ThTD. with a frequency greater than N in the time period T, then blocking the reset system, whereas if first pressure readings PPHnare not also below a threshold ThPHwith a frequency greater than N in the time period T, and if second pressure readings PPLnare not also below a threshold ThPLwith a frequency greater than N in the time period T, then restarting the compressor.

[0063] In a further embodiment the method includes sending a report, and / or sending an alert, in particular to an operator of the heat pump.

[0064] 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, Sn, for operational monitoring, an alert monitoring circuit, and wherein the method comprises providing a threshold value, Thn, for each respective sensor Sn, taking or acquiring readings, sn, from each sensor Sn, comparing each sensor reading snto its respective threshold value Thn, and arranging the sensors into groups Gm, wherein if all sensor readings, sn, are below their respective threshold values Thnin a particular group Gmthen 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 ThTD and / or ThpH and / or Thpi. 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] Figure 3 shows a flow diagram of a method according to the invention.

[0072] Figure 4 shows a heat pump according to aspects of the invention.

[0073] Figure 5 shows a flow diagram of a method according to the invention.

[0074] Figure 6 shows a heat pump with an arrangement of operational sensors that may be used in the invention.

[0075] 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.

[0076] Figure 2 shows a flow diagram of a method according to the invention which begins with acquiring pressure measurements on the high-pressure side 2a and acquiring pressure measurements on the low-pressure side 2b. In the following decision step 2c if the alarm is not already activated the method proceeds to comparison step 2d in which both pressure measurements are compared with respective threshold values. In the case depicted the threshold values are the same for both the high-side pressure reading and the low-side pressure reading. If both readings are above their respective first threshold values then the method loops back to pressure measurement steps 2a and 2b. In this example the first threshold values are equal to each other.

[0077] However if either the high-side or low-side pressure readings are lower than their respective threshold value then the method proceeds to stop the compressor 2b, and to set the alarm and increase the counter step, 2f.

[0078] The following step 2g interrogates the counter and if the number of alarms is not over a value N in a time period T, in this case not more than 4 in a 24 hour period, then the method loops back to the measurement of pressures 2a and 2b. At this point the method starts again, with acquisition of pressure readings, however this time at step 2c the alarm is already activated, therefore the method proceeds to comparison step 2h where the newly acquired pressure measurements are each compared to their respective second threshold values. At this point both pressure values must be above their respective second threshold value, i.e. the high-side pressure reading must be above the respective second high-side threshold value AND the low- side pressure reading must be above the respective second low-side threshold value for the method to proceed to step 2j at which the alarm is reset, and step 2k at which compressor start is allowed.

[0079] However if it is NOT TRUE that both the high-side pressure reading is above the respective second high-side threshold value AND the low-side pressure reading is above the respective second low-side threshold, then the method proceeds to step 2i and compressor restart is forbidden.

[0080] The method therefore allows a dangerous leak to be detected with a degree of sensitivity because it enforces comparison of refrigerant circuit pressures to a higher threshold in order to leave the alarm state, which was entered into by comparison of previously measured refrigerant circuit pressures to a lower threshold.

[0081] If the situation occurs that compressor restart is forbidden at step 2i then pressures are remeasured at 2a and 2b, the alarm is still set (because it has not been cancelled) and so acquired pressure readings are re-compared to the respective second thresholds at step 2h until eventually (since the compressor has stopped and refrigerant circuit pressure will typically rise when the compressor is stopped) both are above their respective threshold and the method proceeds to steps 2j and 2k, as described above.

[0082] Once through steps 2j and 2k the alarm will be re-set therefore the next time pressures are measured at 2a and 2b the method will proceed again to step 2d and comparison to the respective first threshold values. The next time one or other or both measured pressures are below their respective first threshold values the compressor is again stopped at 2e, and at 2f the alarm is set again and the counter increased by 1. Therefore eventually, if there are sufficient loops though the steps of the method, decision 2g which queries the number of alarms in a time period (in the example given considers if there are more than 4 alarms in 24 hours) will return a YES. At this point the method proceeds to 2I which is a FORBID START step. At this the controller forbids the restart and / or automatic restart of the compressor, and this ensures that if there is a leak in the refrigerant circuit that it does not damage the compressor or cause diesel effect.

[0083] At the point the compressor would be checked by qualified personnel and following remedial action would be reset, 2m, possibly by communication or by other means. Following this reset the counter is now reset 2n and start is allowed 2p.

[0084] Figure 3 shows a flow diagram of a further possible method according to the invention in which a heat pump with malfunction detection is provided, the heat pump comprising a compressor, a refrigerant circuit comprising a high-pressure side and a low-pressure side, a first pressure sensor SPHsituated on the high-pressure side of the refrigerant circuit and arranged to acquire first pressure readings PPHn, and / or a second pressure sensor SPLsituated on the low-pressure side of the refrigerant circuit and arranged to acquire second pressure readings PPLn, 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 SPH and / or the second pressure sensor SPL and the reset system, and whereby the controller is arranged to monitor the first and / or second pressure readings PPHn and PPi_nwhile the compressor is in operation and if any first pressure reading PPHnis below a threshold ThPH, or if any second pressure reading PPLnis below a threshold ThPL,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 PPHn are below a threshold ThPHwith a frequency greater than N in the time period T and / or if second pressure readings PPLnare below a threshold ThPLwith 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 PPHnare not below a threshold ThPHwith a frequency greater than N in the time period T, and if second pressure readings PPLnare not below a threshold ThPi_with a frequency greater than N in the time period T, then the controller is arranged to restart the compressor. In particular N may have the value 3, and / or T may have the value of 15 min. In particular ThPHand / or ThPLmay be below 4 absolute bar, preferably below 2 absolute bar. In particular if the reset system is blocked the controller is further arranged to transmit an alert, and / or send a report. In this version first pressure readings PPHnare acquired 10 and second pressure readings PPLnare acquired 20 and each is compared to a respective threshold value. If any first pressure reading PPHnis below a threshold ThPH11 or if any second pressure reading PPLnis below a threshold ThPL21 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.

[0085] 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 PpHn below respective threshold ThPHoccur, or, if N or more instances of a second pressure reading Ppi_nbelow respective threshold ThPi_ occur 26, then the controller blocks the reset system 27. If not, then the controller restarts the compressor.

[0086] Figure 4 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.

[0087] Figure 5 shows a flow diagram of a further possible method according to the invention in which a heat pump with malfunction detection is provided, and which further comprises a temperature sensor STD situated at a discharge line and arranged to acquire temperature readings TTDn, whereby the controller is further arranged to monitor the temperature readings TTDn and if any temperature reading TTDn is above a threshold ThTD the controller is arranged to stop operation of the compressor and start the time period T, and in addition to readings PPHn and PpLntakes temperature readings TTDn wherein if any temperature reading TTDn is above a threshold ThTD 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 PpHn are not also below a threshold ThPH with a frequency greater than N in the time period T, and if second pressure readings PpLnare not also below a threshold ThPLwith a frequency greater than N in the time period T, then the controller is arranged to restart the compressor. In this particular example ThTD may be between 100°C and 140°C, and preferably between 1 10°C and 135°C. In this version temperature readings TTDn are acquired 30. If any temperature reading TTDn is above a threshold ThTD 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 PPHnand PPLn. During time period T further temperature readings may be taken and if N or more instances of temperature readings TTDn are above a threshold ThTD 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.

[0088] Figure 6 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.

[0089] In particular a method to detect malfunction in a heat pump may comprises a compressor, a refrigerant circuit comprising a high-pressure side and a low pressure side, a first pressure sensor SPHsituated on the high-pressure side of the refrigerant circuit and arranged to acquire first pressure readings PPHn, a second pressure sensor SPLsituated on the low-pressure side of the refrigerant circuit and arranged to acquire second pressure readings PPLn, 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 SPH, the second pressure sensor SPLand the reset system, wherein the method comprises in the controller, monitoring the first and second pressure readings PPHnand PPLnwhile the compressor is in operation and if any first pressure reading PPHn is below a threshold Th™, or if any second pressure reading PPi_nis below a threshold ThPL,.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 PPHnare below a threshold ThPHwith a frequency greater than N in the time period T, or if second pressure readings PPLnare below a threshold ThPLwith a frequency greater than N in the time period T; then performing the operation of blocking the reset system, whereas if first pressure readings PPHn are not below a threshold ThPHwith a frequency greater than N in the time period T, and if second pressure readings PPLnare not below a threshold ThPLwith a frequency greater than N in the time period T, then restarting the compressor.

[0090] Further, wherein the heat pump further comprises a temperature sensor STD situated at a discharge point and arranged to acquire temperature readings TTDR, the method may further comprise in the controller, monitoring the temperature readings TTDn and if any temperature reading TTDn is above a threshold ThTD then stopping operation of the compressor and starting the time period T, and in addition to readings PPHnand PPLnacquiring temperature readings I ron wherein if temperature readings Tron are above a threshold ThTD with a frequency greater than N in the time period T, then blocking the reset system, whereas if first pressure readings PPHnare not also below a threshold ThPHwith a frequency greater than N in the time period T, and if second pressure readings PPLn are not also below a threshold ThPi_ with a frequency greater than N in the time period T then restarting the compressor.

[0091] In particular the method may further comprise sending a report and / or sending an alert, in particular to an operator of the heat pump.

[0092] In particular in the method the values for N and / or the time period T and / or threshold values ThTD and / or ThPHand / or ThPLmay 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.

[0093] A controller for a heat pump may be configured to perform any of the described methods.

[0094] A computer program product may be provided comprising program instructions operable to cause a processor to perform operations according to any described method.

[0095] A non-transitory computer readable medium may be provided having stored thereupon any computer program product as described. A data carrier signal may be provided carrying the computer program product as described.

[0096] Reference Signs

[0097] 1 heat pump

[0098] 2 refrigerant circuit

[0099] 2a measuring step

[0100] 2b measuring step

[0101] 2c alarm activated comparison step

[0102] 2d comparison step

[0103] 2e stop compressor step

[0104] 2f set alarm + increase counter step

[0105] 2g number alarms over time period step

[0106] 2h comparison step

[0107] 2i FORBID START

[0108] 2j reset alarm step

[0109] 2k allow start step

[0110] 2I FORBID START

[0111] 2m reset by communication step

[0112] 2n reset counter step

[0113] 2p allow start step

[0114] 3 compressor

[0115] 4 controller

[0116] 5 expansion valve

[0117] 6 heat exchanger

[0118] 7 heat exchanger

[0119] 8’ first pressure sensor

[0120] 8” second pressure sensor

[0121] 9 reset system

[0122] 10 data acquisition step

[0123] 11 comparison step

[0124] 20 acquisition step

[0125] 21 comparison step 25 action step of stopping compressor, starting T

[0126] 26 comparison step

[0127] 26’ comparison step

[0128] 27 action step of blocking reset system 28 action step of restarting compressor

[0129] 29 temperature sensor

[0130] 30 acquisition step

[0131] 31 comparison step

[0132] 50 outdoor unit of heat pump 51 indoor unit or heat network

[0133] 52 fan

[0134] 53 heat exchanger

[0135] 54 compressor

[0136] 55 heat exchanger 56 expansion valve

[0137] 57 pressure sensors

[0138] 58 temperature sensors

Claims

CLAIMS1 . 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 high-side pressure sensor SPHsituated on the high-pressure side of the refrigerant circuit and arranged to acquire high-side pressure readings PPHn, and- a low-side pressure sensor SPLsituated on the low-pressure side of the refrigerant circuit and arranged to acquire low-side pressure readings PPLn,- a counter, and- a controller coupled to the compressor, the counter, the first pressure sensor SPHand, the second pressure sensor SPL, and- wherein the controller is arranged to control an alarm state, which can be set in an activated state or a non-activated state, whereby- the controller is arranged to monitor the high-side PPHnand low-side PPLnpressure readings and if: o any high-side pressure reading PPHn is below a respective first high- side threshold Th1PH, and / or o any low-side pressure reading PPi_nis below a respective first low-side threshold Th1PL,.then- the controller is arranged to: o stop the compressor, o increase the counter by 1 , and o activate the alarm state which remains activated until both:■ a high-side pressure reading PPHnis above a respective second high-side threshold Th2PH, and■ a low-side pressure reading PPi_nis above a respective second low-side threshold Th1PL,■ and where• the second high-side threshold Th2PH > first high-side threshold Th1PH, and• the second low-side threshold Th2PL> the first low-side threshold Th1PL, o whereupon the alarm state is turned off and re-start of the compressor is allowed, and further wherein:if the counter registers more than N in any time period T then: the controller is arranged to block automatic restart of the compressor.

2. A heat pump with malfunction detection according to claim 1 , wherein:- N = 4, and- T = 24 hours.

3. A heat pump with a malfunction detection system according to claim 1 or 2, wherein if both: o the high-side pressure reading PPHnis not above the respective second high-side threshold Th2PH, and / or o the low-side pressure reading PPi_nis not above the respective second low-side threshold Th1PL,.then- the controller is arranged to forbid restart of the compressor.

4. A heat pump with malfunction detection according to any of claims 1-2, wherein if automatic restart of the compressor is blocked then :- the compressor can be re-started by communication;- the counter is reset, and- re-start of the compressor is allowed.

5. A heat pump with malfunction detection according to claim 1 , wherein the heat pump further comprises: a reset system to allow a user activated restart of the heat pump when the heat pump stops operating, and whereby alternatively if :- any first pressure reading PPHnis below a threshold ThPH, or if- any second pressure reading PPLnis below a threshold ThPL,.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 PPHnare below a threshold ThPHwith a frequency greater than N in the time period T; and / or if- second pressure readings PPi_nare below a threshold ThPi_ 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 PPHnare not below a threshold ThPHwith a frequency greater than N in the time period T ; andif second pressure readings PPLnare not below a threshold ThPLwith a frequency greater than N in the time period T; then the controller is arranged to restart the compressor.

6. A method to detect malfunction in a heat pump, wherein the heat pump comprises:- a compressor,- a refrigerant circuit comprising a high-pressure side and a low pressure side,- a high-side pressure sensor SPHsituated on the high-pressure side of the refrigerant circuit and arranged to acquire high-side pressure readings PPHn,- a low-side pressure sensor SPL situated on the low-pressure side of the refrigerant circuit and arranged to acquire low-side pressure readings PPLn,- a counter, and- a controller coupled to the compressor, the counter, the high-side pressure sensor SPH and, the low-side pressure sensor SPL, and wherein the controller is arranged to control an alarm state, which can be set in an activated state or a non-activated state, wherein the method comprises, in the controller: monitoring the high-side PPHnand low-side PPLnpressure readings and if: o any if high-side pressure reading PPHnis below a respective first high- side threshold Th1PH, and / or o any low-side pressure reading PPi_nis below a respective first low-side threshold Th1PL,.then: o stopping the compressor, o increasing the counter by 1 , and o activating the alarm state which remains activated until both:■ a high-side pressure reading PPHnis above a respective second high-side threshold Th2PH, and■ a low-side pressure reading PPLnis above a respective second low-side threshold Th1PL,■ and where• the second high-side threshold Th2PH > first high-side threshold Th1PH, and• the second low-side threshold Th2PL> the first low-side threshold Th1Pi_,o whereupon turning off the alarm state and allowing re-start of the compressor, and further wherein: if the counter registers more than N in any time period T then: blocking automatic restart of the compressor.

7. A controller for a heat pump, wherein the controller is configured to perform the method of claim 6.

8. A computer program product comprising program instructions operable to cause a processor to perform operations according to the method of claim 6.

9. Non transitory computer readable medium having stored thereupon the computer program product according to claim 8.

10. Data carrier signal carrying the computer program product of claim 8.

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