Controller for monitoring leakage of refrigerant

Abstract

In the event of a heat pump refrigerant leak operational sensors may detect readings varying outside expected normal limits and may therefore be used to detect refrigerant leakage using a leakage alarm, resettable only using manufacturer information. If a first reading from a pressure sensor is below a lower pressure pre-determined threshold value, Th3, then a time delay initiated, further readings are acquired and compared to a higher pressure pre-determined threshold value, Th4, where Th4 > Th3. If no further readings during the time delay are above the higher pressure pre-determined threshold value, Th4, then the compressor is stopped and the leakage alarm set.

Description

[0001] Controller for Monitoring Leakage of Refrigerant

[0002] The invention relates to heat pump with leakage detection, the heat pump arranged for performing a heating and / or cooling operation associated with a building.

[0003] Changes in environmental regulations are forcing changes in the use of refrigerant classes in heat pumps, 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.

[0004] Manufacturers are therefore finding ways to switch 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.

[0005] 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, with a particular fluid concentration, into contact with a potential source of ignition (PIS) there is a risk of fire or explosion. In particular, selfignition 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 spark that can reach activation energy. They may also include additional heating elements that can reach the self-activation temperature, in particular an electrical resistor reaching a surface temperature of more than 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. 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.

[0009] 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, 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.

[0010] 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.

[0011] 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 is precise installation position, for example communal areas, gardens, living rooms, technical rooms, balconies, etc. It is therefore impossible to control for all risk.

[0012] 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.

[0013] 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. Additionally, leakage sensors have a very limited range and a limited perimeter. As the system leak can occur throughout the whole refrigerant circuit and can go in all directions (depending on the geometry of the hole generating the leak), it is not possible to position a leak sensor adequately to effectively cover all potential leak zones. In addition, leakage sensors require regular maintenance because, since they are not used for standard operation, they need to be tested separately to confirm that they are working. This type of test is costly and is not always carried out, which can also affect the correct operation of this type of detection.

[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] It is also a known problem that even if a leak is detected and the compressor and / or heat pump stopped or even shut down, some form of reset is provided, originally as a button but more recently as a menu option on a HMI user interface, which allows for a user activated reset in the event that the stoppage is not caused by a leak. Typically once a leak is detected and stoppage occurs the user may be presented with a series of checks to perform to ensure reset is justified. However it has been found that many users simply hit, press or click reset, even in the event that stoppage is regular and therefore suggestive of actual refrigerant leak. Therefore it is an object of the invention to provide a heat pump with improved leakage detection.

[0019] The object is solved by a heat pump with leakage detection, the heat pump arranged for performing a heating and / or cooling operation associated with a building, and comprising a first sensor, Si, arranged to acquire pressure readings (sim) within the refrigerant circuit of the heat pump, a compressor, a leakage alarm, arranged to be resettable only by use of manufacturer information, and a controller coupled to the first sensor, Si, the compressor, and the leakage alarm. The controller is arranged to compare a first reading, S11, from the first sensor, Si, to a lower pressure pre-determined threshold value, Ths, and if the first reading, Sn, is not below the lower pressure pre-determined threshold value, Th3, then re-perform the first reading Sn, whereas if the first reading, Sn, is below the lower pressure pre-determined threshold value, Th3, then the controller is arranged to initiate a time delay T3and acquire further readings, sm, from the first sensor, Si, during elapse of the time period T3and further compare each further reading Sm to a higher pressure pre-determined threshold value, Th4, wherein Th4> Th3, whereby if no reading from further readings Sm, during time delay T3is above the higher pressure predetermined threshold value, Th4, then the controller is arranged to stop the compressor and set the leakage alarm, whereas if any reading, Sm, from further readings Sm, during time delay T3is above the higher pressure pre-determined threshold value, Th4, then the controller is arranged to stop the comparison of readings Sm to the higher pressure pre-determined threshold value, Th4, and re-perform the first reading Sn.

[0020] The invention uses two pre-determined threshold values, a lower pressure predetermined threshold value, in this case referred to as Th3, and a higher pressure predetermined threshold value, in this case referred to as Th4, and wherein the higher pressure pre-determined threshold value is greater than the lower pressure predetermined threshold value, i.e. Th4> Th3.

[0021] Pressure readings (Sim) are measured by the pressure sensor Si and by comparing pressure readings, Sim, to a lower pressure pre-determined threshold value Th3, the system can be put into a form of alert state in which subsequent pressure readings are compared to the higher pressure pre-determined threshold value, Th4. Once pressure readings reach or go above the higher pressure pre-determined threshold value, Th4, the system essentially moves out of the alert state and reverts to comparing all measurements to the lower pressure pre-determined threshold value Ths.

[0022] Typically pressure readings (sim) are measured on a continuous basis, in practice there may be some lag within the system meaning that readings are actually taken with a frequency of once every few hundred milliseconds. In a typical case this could be once every 500ms.

[0023] In a particular embodiment the pressure sensor is on the low pressure side of the refrigerant circuit, which ensures that the arrangement is more sensitive to refrigerant leaks, as a leak of a certain volume of refrigerant will have a more noticeable effect on the low pressure side of refrigerant circuit than on the high pressure side. This is because a pressure sensor placed on the low pressure side of the refrigerant circuit will be more sensitive to detecting leaks, and is likely to detect a leak faster. However, using measurements from a sensor on the high pressure side is possible, and in fact heat pumps typically comprise sensors on both their high- and low-pressure sides.

[0024] However, if the pressure drops for a certain amount of time, defined by a delay, and remains below the higher pressure pre-determined threshold value, Thu at the end of this delay period, then the leakage alarm is set.

[0025] The leakage alarm can only be reset using manufacturer information. In an embodiment this is by use of a manufacturer password, alternatively a code, which must be inputted into a hidden menu within the HMI user interface (which may itself require a possibly separate password) reserved for approved and trained installers and other specialized staff, for example manufacturer’s own staff. Alternatively a key may be used, which could be a digitally available encrypted key, or may even be an actual key, which fits a lock in the heat pump and it provided only to approved personnel. Typically such approved and specialized staff would follow a check list and / or other technical instructions (for example provided in a service manual) in order to physically check and / or fix the leak before resetting the leakage alarm, thereby allowing restart of the compressor.

[0026] The requirement of the use of manufacturer information in order to reset at this point overcomes the problem of the user continuously hitting reset and thereby overriding the heat pump’s own safety systems. In a particular embodiment the manufacturer password, code, or electronic key, is changed daily and may be provided internally to the heat pump and / or heat pump controller by remote connection, or alternatively can be pre-programmed in before installation so that on any given date the heat pump knows or can calculate the correct password for that day. The approved installer or staff would then access the password on the day from the manufacturer in order to input it correctly.

[0027] In particular the time delay T3may be 15 minutes, the reason being that if there is a leak then the amount of time it would typically take for the leak to have a noticeable physical effect on the heat experienced by the user, is about 15 to 30 minutes. This delay of heat effect occurs because the heating system includes a natural buffer in terms of heated fluids which retain heat for a certain amount of time once transfer of heat from the ultimate heat source has stopped. Heat pumps typically have user activatable reset buttons or a HMI menu-driven user reset function, which the user (and this might typically be a domestic user, therefore not necessarily technically untrained) can simply push or click to restart the compressor or heat pump if one or both are turned off. A problem that can therefore occur is that any unscheduled stoppage perceivable by the user in terms of a drop in heat is simply reset using the reset button or menu option. In the event of actual leakage this allows the user to override the mechanisms which have stopped the system in order to protect it and the user. Therefore by using a time delay T3of 15 minutes the system can detect a leakage within an amount of time before the compressor stoppage would be perceivable by the user in terms of heat output and thereby impose a hard shutdown, which cannot be overridden by the user because it requires manufacturer information to override.

[0028] Generally though it may be a time period defined in a range from 10 minutes to 20 minutes, or from 5 minutes to 30 minutes.

[0029] One advantage of the invention is that it uses the measurements from only one sensor, and this provides a simple, efficient and cost-effective way of detecting refrigerant leakage. In an embodiment the sensor may be an existing operational sensor which would be used for ongoing monitoring of the internal workings of the system.

[0030] The value of thresholds depends upon the design of the heat pump and compressor, the nature and identity of the particular refrigerant, and temperature range for which the heat pump is designed to operate within and to service. Typical thresholds for propane as a refrigerant may include:

[0031] Lower pressure pre-determined threshold, Th3= 0.4 bar

[0032] Higher pressure pre-determined threshold, Th4= 1.4 bar

[0033] Once design, refrigerant and temperature range are known the skilled person can select appropriate thresholds that allow the detection of leaks using this method.

[0034] Another advantage provided by the arrangement is that a refrigerant leak can be detected even if the compressor is not on, is not yet turned on, or has been on but has been turned off. The compressor is not required to be in an ON state for the invention to work.

[0035] In a further embodiment the heat pump with leakage detection further comprises an expansion valve, a counter, a low pressure alarm, a lock function which can only be cancelled by manual action, and the controller is further coupled to the expansion valve, the counter, the low pressure alarm and the lock function, wherein the controller is further arranged to compare the first reading, sn, from the first sensor, Si, to a first predetermined threshold value, Thi, and if the first reading, Sn, is not below the first predetermined threshold value, Thi, then re-perform the first reading sn, whereas if the first reading, Sn, is below the first pre-determined threshold value, Thi, then the compressor is arranged to initiate a time delay Tmdependent upon whether the compressor is in startup phase or no longer in start-up phase and acquire further readings, Sm, from the first sensor, Si, during elapse of the time period Tmand further compare each further reading s^ to a second pre-determined threshold value, Th2, wherein Th2> Thi, whereby if no reading from further readings Sm, during time delay Tmis above the second predetermined threshold value, Th2, then the controller is arranged to set the low pressure alarm, stop the compressor, open the expansion valve, and increase the counter by 1 , whereas if any reading, Sm, from further readings Sm, during time delay Tmis above the second pre-determined threshold value, Th2, then the controller is arranged to stop the comparison of readings Sm to the second pre-determined threshold value, Th2, and reperform the first reading Sn, and further wherein if the counter reaches more than a value N in one hour the controller is arranged to use the lock function to lock the heat pump, whereas if the counter does not reach more than a value N in one hour the controller is arranged to acquire further readings, Sm, from the first sensor, Si and compare each further reading Sm to the second pre-determined threshold value Th2, and when any reading from the further readings sm is not below the second pre-determined threshold value Th2then the controller is arranged to stop the comparison of readings Sm to the second pre-determined threshold value, Th2, and re-perform the first reading Sn.

[0036] This low pressure alarm embodiment can be run concurrently with the leakage alarm invention as described above, however in the event that the pressure stays below the second pre-determined threshold value, Th2, then the arrangement of the invention, above, allows the leakage alarm to be set, even if the compressor has been stopped.

[0037] In a particular embodiment:

[0038] N = 3; and

[0039] Tm= 180 seconds if the compressor is in start-up phase; whereas

[0040] Tm= 120 seconds if the compressor is no longer in start-up phase.

[0041] The period of time over which N is counted is a sliding window of time, typically one hour long.

[0042] Again, values of thresholds depends upon the design of the heat pump and compressor, the nature and identity of the particular refrigerant, and temperature range for which the heat pump is designed to operate within and to service. Typical thresholds for propane as a refrigerant may include:

[0043] First pre-determined threshold, Thi = 0.6 bar

[0044] Second pre-determined threshold, Th2= 1.4 bar

[0045] A compressor has a minimum ON time, defined by the compressor manufacturer, which may typically be of the order of 120s, varying by compressor design. Start-up phase is, in this case, defined as operation within a period of time equal to the minimum ON time. Once the compressor has run through a period of time equal to its minimum ON time it can then be thought of as running in steady state, i.e. out of start-up phase.

[0046] Typically the range is related to the minimum compressor off time, which is the minimum length of time that a compressor, once it has been stopped or turned off, must be kept off to allow for equalization and resetting. The expansion valve is opened in order to equalize the pressures in the refrigerant circuit, this ensures when using only one pressure sensor that any loss of pressure due to leakage is forced across the volume of the refrigerant circuit and thereby ensuring that the pressure drop detected due to leakage is a genuine pressure drop. It also ensures that leakage can be detected through pressure drop using only one sensor, because if the expansion valve was not opened an additional pressure sensor on the high pressure side of the refrigerant circuit would be required to detect leakage on the high pressure side.

[0047] Opening the expansion valve is only required in the low pressure alarm embodiment and is not required in the leakage alarm invention, because if upon turning the heat pump on the unit never starts, due to leakage, then the pressures on both sides of the refrigerant circuit will be equalised anyway, and if instead the compressor does start but then experiences significant pressure drop then the low pressure alarm will be activated and the expansion valve opened anyway, thereby equalizing pressures on both sides of the refrigerant circuit.

[0048] The low pressure alarm can only be reset manually, either by pushing a button, or by inputting instructions on a digital communication interface, for example a HMI screen used to interact on site with the heat pump. In other words, once the leakage alarm is set

[0049] In further examples the invention uses sensors already situated within the heat pump to monitor the operation and working of the heat pump for control purposes. Operational sensors already connected up within the heat pump to provide operational readings for internal heat pump control actually provide an ongoing information flow to the heat pump control system which is indicative of normal heat pump working. For example, in order to directly or indirectly monitor if a heat pump is working correctly it may include temperature sensors upstream and downstream of the expansion valve, an air temperature sensor at the air / refrigerant heat exchanger outlet (i.e. the evaporator of a ASHP in heating mode), temperature and pressure sensors at the compressor inlet and outlet, a safety pressure / temperature sensor on the compressor. Other sensors can also be added for finer control of the refrigeration circuit, e.g. to control the expansion valve. Signals provided by these sensors signals can be used to monitor the state of the heat pump system, whether they are imposed by the control system or received in response to external actions or events, such as compressor and / or network frequency, electrical power consumption, etc. Equally and in parallel, further sensors can be used to determine the temperature and / or pressure and / or flow rate of the heat pump's source and destination fluid circuits. The parameters detected by these sensors and monitored by the control system are used primarily to optimize product performance, for example control of compressor frequency, valves, consumption modes, etc., as well as to determine any major or minor system faults, which may be characteristic of nonstandard, non-compatible operating conditions of the product or which may be characteristic of a malfunction. Therefore if the heat pump is working normally, or properly, then the readings provided by the operational monitors will be within certain expected limits.

[0050] The use of these sensors, used for standard heat pump operation, also ensures that they are functional by default. In fact, they are used for the normal operation of the product. In the event of a fault, they will generate errors in the operation of the product and potentially lead to a preventive shutdown of the product. This is therefore an advantage over the use of dedicated sensors, such as leakage sensors, which can malfunction without being noticed and are therefore not as reliable.

[0051] Therefore in the event of a leak, either a fast leak or a slow leak, the readings taken by operational sensors can be expected to vary outside expected normal limits. Therefore these readings can be used to detect a leak of refrigerant. According to the invention a first reading is therefore taken from an operational sensor, say a pressure sensor arranged to detect pressure in the refrigerant, and compared to a pre-determined threshold value which would be indicative, in this case, of the lower end of normal working of the heat pump. In the event of a refrigerant leak the internal pressure of the refrigerant can be expected to decrease. Therefore if the pressure as detected by a normal operating pressure sensor falls below a certain pre-determined threshold value, then a leak may be one of several reasons. However if the reason is a refrigerant leak then the compressor is at risk so the compressor is halted or otherwise stopped from operation. This action protects the compressor from operating with possibly reduced refrigerant, which may result in damage. Most of the risks are thereby eliminated as the heat pump is stopped at first passage below the threshold and so most the potential ignition source (PIS) from the heat pump are stopped (sparking, hot point, etc.). Only the PIS from the environment can be still present, so with a lower probability of presence. A check is then made to ensure that the reading is not merely a stray or transitory reading, and this is performed by starting a time period T, for example 15 mins, and at the end of the time period re-sampling, or acquiring, a new reading from the same sensor and comparing this reading to the same pre-determined threshold value. If this reading is also below the threshold value then it suggests the problem is ongoing, which is more indicative of a leak of refrigerant. At this point an alert is transmitted to a monitoring circuit. The monitoring circuit may then transmit a leakage signal to the environment, for example an alarm, error code, sms, etc. to an operator, to a home owner, to the heat pump itself.

[0052] However if the second reading is above the threshold then it suggests the problem was temporary and the compressor can be restarted.

[0053] The invention has the advantage that it detects leakage at source, from within the refrigerant piping itself. The invention is therefore extremely specific, when a leak is detected, as to which heat pump is leaking. It can therefore be more reactive and therefore faster at leakage detection, because it takes sensor readings from within the refrigerant loop that may leak, and will therefore detect anomalies as soon as leakage occurs.

[0054] Detection at appropriate sensors can be arranged to fit in with the normal detection cycle within the heat pump, and in fact all readings from operational sensors can be additionally polled for abnormal readings out of range, i.e. above or below appropriate threshold values for the respective sensor. Alternatively, the heat pump controller can divert only specific instances of readings to analyse for their relationship to normal ranges on a per sensor basis.

[0055] Regardless of what value or values may be considered to be normal, in the event that a sensor will detect a lower reading if leakage occurs, some threshold value can always be found which a reading can be compared to and be found to be lower than. By the same logic in the event that a sensor will detect a higher reading if leakage occurs (for example in some cases refrigerant temperature may rise in the event of a refrigerant leak), some threshold value can always be found which a reading can be compared to and be found to be higher than. The threshold limit can be determined by measuring the lowest low-pressure of the refrigerant circuit in the extremum of use of the heat pump in nominal mode, in particular when the temperature of the source (air) is at its lowest value (for example -20°C).

[0056] In a further embodiment the heat pump also comprises a second sensor, S2, arranged to acquire readings (s2n) for operational monitoring and wherein the controller is further coupled to the second sensor and is further arranged to compare a first reading, s2i, from the second sensor to a second pre-determined threshold value, Th2, and if the first reading, s2i, is below the second pre-determined threshold value, Th2, then regardless of the state of readings, (sim) , from the first sensor, Si, perform the action of stop operation of the compressor and initiate a time period T, acquire a second reading, s22, from the second sensor, S2, after elapse of time period T and if the second reading, s22, is below the second pre-determined threshold value, Th2, perform the action of transmitting an alert to the alert monitoring circuit; whereas if the second reading is above the second pre-determined threshold value performing the action of restarting the compressor if and only if a reading from the first sensor Sn or Si2is also above the first pre-determined threshold value, Thi.

[0057] This embodiment provides an alternative, or second, route through which the heat pump may monitor for leakage. This embodiment uses a second sensor, in addition to the first, comparing the readings from this sensor to a threshold value appropriate to the range of values normally associated with the parameter read by this second sensor. Again if the reading is out of range for that sensor then the controller stops operation of the compressor and initiates the time period. If at the end of the time period a second reading from the second sensor is also out of range then an alert is transmitted, sent, or passed, to the alert monitoring circuit. If the second reading is within range than the compressor may be restarted, but as this embodiment runs essentially in parallel to the invention, the compressor is only re-started if readings from the first sensor do not indicate a leak.

[0058] Typically the heat pump refrigerant circuit comprises a low-pressure section and a high- pressure section, and the heat pump includes at least one heat exchanger, and in any of the above embodiments the first and second sensors may be selected from the group of a pressure or temperature sensor arranged to detect pressure or temperature in the low-pressure section, a pressure or temperature sensor arranged to detect pressure or temperature in the high-pressure section, a temperature sensor arranged to detect temperature at a heat exchanger. In a particular embodiment refrigerant pressure on both high pressure and low-pressure side of a heat pump may be used, in which case if one and / or the other pressure drops below a threshold value, it is indicative of a very strong risk of major leakage. For example, if a pressure drops below a value, say, between 1.1 and 1.4 absolute bars, in particular below 1.3 or 1.4 absolute bar for certain manufactured heat pumps, it is considered that there is a major leakage. Indeed, in normal operation mode, many propane heat pump have the low pressure between 1.4 bar and 12 bars (dependent on parameters like source temperature, medium temperature, and frequency of compressor). If pressure falls to, for example, less than 1.3 absolute bar, it is not necessary to countercheck with additional parameters to launch remedial action because the leakage risk would be deemed to be so great that immediate or at least imminent action needs to be taken, like switching off the compressor and / or send a signal alarm to installer and / or customer.

[0059] In a particular embodiment, the threshold values of the refrigerant can be between 1 and 3 absolute bar, preferably between 1 ,1 and 2 absolute bar, even preferably between 1 ,2 and 1 ,5 absolute bar.

[0060] In a particular embodiment, the threshold values of the refrigerant are determined based on the measurement of pressure and / or temperature of a fluid in the system.

[0061] There are a number of advantages to using only one or two parameters to evaluate the risk of leaks, in particular large leaks. Firstly the limited number of parameters makes it possible to limit the number of determination components (e.g. the number of sensors), and therefore the number of faults associated with each of them. This limits the risk of errors and false positives due to sensor faults (for example incorrect positioning, internal fault, disconnection, etc.). Secondly, use of a limited number of parameters simplifies the control logic and therefore the possible processing errors, speeds up the processing response and simplifies its technical validation. Having a simple system therefore offers greater reliability and speed of execution. Thirdly, the fact of having one or more errors specific to the detection of a large leak and in a flammable fluid context, which are different from the generic errors that enable the system to be validated, means that the system is more reliable and faster. Fourthly, the invention requires no additional resources over and above the current product architecture. It uses sensors already in use for other purposes, and a control interface already in use for other purposes. So there are no additional costs, either for the product itself or for installation and maintenance (unlike for example the installation of a dedicated leak detector). Moreover, such sensors or determination means do not require additional maintenance or regular check to be realized to ensure a proper functioning. Indeed, as these sensors are also used for regulation purpose, if a failure of such component happens, it will be identified quickly due to a failure in the regulation (no more heating / cooling for example). Fifthly, unlike with the use of a leak detector, the measurement is not local, but takes place directly within the system itself. This means it can measure an internal error and is not dependent on the position of the leak sensor, or on false positives arising from the presence of similar refrigerant in the vicinity. Sixthly, the availability of one or more specific errors for the detection of large leaks in the context of flammable fluids, which are different from the generic errors used to identify large-scale faults, makes it possible to characterize a particular leak. This enables specific triggers and specific actions, which are particularly more restrictive than generic errors.

[0062] With this last point in mind two levels of error and action are therefore possible. In the first use of at most two parameters allows detection of major leaks and makes it possible to distinguish with a high probability the occurrence of a major leak and to implement very restrictive actions (no or little relighting, major warning, etc.). This also makes it easy for the repairer to identify the fault and implement the associated direct actions. In the second the specific forms of the inventions may be used to provide a more general level of fault detection, for which the causes may be multiple and for which there is a low probability of occurrence of, say, a small leak (low probability because of a range of possible causes, and small leak because the major leak error is not reached). The safety risk is low, and it is therefore possible to implement less restrictive actions (restarting, waiting for a delay to recheck if the error is present, etc.). It is possible to keep standard operation, without precise definition of the cause, a solution which is currently satisfactory, as it limits the cost of error determination components.

[0063] In fact there are in some instances advantages to the use of two sensors instead of one. In theory, in most of configurations, both should detect the leak independently and so one could be enough. However, having two sensors improves the safety and speed of the system. On the other hand, it may happen, due to whatever event generates or causes the leak, that one of the two sensors becomes unable to identify the leak, for example due to sensor fault, part of the circuit being blocked that delays the measurable drop in pressure on a section, etc. In a further embodiment the heat pump further comprises a third sensor, S3, arranged to acquire readings (s3p) for operational monitoring of the compressor, and wherein the controller is further coupled to the third sensor S3and is further arranged to compare the first reading, Sn, from the first sensor, Si, to a first dependent threshold value, Th3i, where Th3iis dependent on a reading, S31, from the third sensor, S3, and which reading,

[0064] 531, is performed within a time period Dt of the first reading, Sn, and if the first reading, Sn, is below the first dependent threshold value, Th3i, then perform the action of stop operation of the compressor and initiate a time period T, acquire a second reading, S12, from the first sensor, Si, after elapse of time period T and if the second reading, S12, is below a second dependent threshold value, Th32, where Th32 is dependent on a reading,

[0065] 532, from the third sensor, S3, which reading, S32, is performed within a time period Dt of the second reading, S12, perform the action of transmitting an alert to the alert monitoring circuit; whereas if the second reading, S12, is above the second dependent threshold value, Th32, perform the action of restarting the compressor.

[0066] This embodiment allows for a more advanced comparison check to detect leakage. Here, the reading from the first sensor are compared to a threshold reading which itself is dependent upon contemporary operational parameters of the compressor. This allows for greater accuracy in leakage detection, because the appropriate range of normal values that may occur for parameters within a heat pump may vary with operation of the compressor. Therefore in this embodiment the readings from the first sensor are compared to a threshold value calculated from, or dependent from, a third sensor which detects parameters concerned with operational monitoring of the compressor.

[0067] Operation of the compressor may increase or decrease the rate of leakage in the refrigerant and therefore use of a threshold value derived from compressor operation itself may provide a significantly more accurate way to detect refrigerant leakage. The reading from the third sensor is taken within a time period Dt of the first reading, which creates a connection in time between the first reading and the dependent threshold reading. Appropriate values of Dt may be less than 30 seconds, preferably less than 1 second.

[0068] Again, if the first sensor reading falls outside of an appropriate range of dependent readings, or below a dependent threshold reading (in certain embodiments it may be above a dependent threshold) then the compressor is stopped, a time period started, at the end of which a second reading is taken and a new reading dependent threshold value calculated for comparison with the newly acquired second reading from the first sensor. Again, this allows for a check to ensure that any erroneous comparison is not transitory. If the extreme sensor reading persists, i.e. if the second reading is also outside of the appropriate range of dependent readings, or below the dependent threshold reading, then an alert is sent or transmitted to the alert monitoring circuit. If not, then the compressor is re-started.

[0069] In the above embodiment the third sensor may be selected from the following: a sensor arranged to detect compressor operating status, a sensor arranged to detect if the compressor is operating or not operating, a sensor arranged to detect compressor frequency, a sensor arranged to detect compressor power consumption, a sensor arranged to detect temperature of a source or destination fluid, a sensor arranged to detect flow of a source or destination fluid, a sensor arranged to detect operating status or power of a means of propelling the source or destination fluid (i.e. a pump or a fan).

[0070] From a technical point of view, all chosen parameters are measured and fed back to the control software. Each manufacturer has their own particular methodologies, but in principle the invention concerns the identification, or gathering, of a useful set of operational parameters and an arrangement to ensure that detected values of these parameters may be compared them with nominal values.

[0071] In further embodiments of the inventive arrangement other forms of faults may be detected. Here the aim is not to determine the specific origin of the fault, but to identify any abnormal operation that could pose a risk to the product, its environment or reduce its service life (premature ageing or damage of the compressor if liquids enters into if for example). In fact, it is the effects that are determined through the parameters, not the causes. It is not possible to discriminate the exact origin of a fault, as the same effect may be associated with several potential faults. For example, using several temperature sensors, it may be determined that the heat exchange between the energy source and the refrigerant is not satisfactory. This can be achieved by evaluating joint measurements of the source temperature at the heat exchanger inlet and outlet, measurements of the refrigerant temperature and pressure at the exchanger inlet and outlet or at other points in the circuit, evaluation of the operating signal from electronic components (compressor, electronic expansion valve, fan, etc.). It may be determined that the operation is abnormal and that there is a fault to be rectified. However, it will not be possible to determine the origin of the fault reliably and efficiently, as there may be many different causes, for example clogged exchanger (dust, icing, leaves, etc.); faulty fan or pump (damage, blades stuck, dust, rust, etc.); valve / expansion valve totally or partially blocked; abnormal refrigerant charge; defective compressor; faulty sensor etc.

[0072] It may also be possible to use a single parameter alone to determine an error, without the need to combine them, for example in the leak detection embodiments as described above. Here again, it is not possible to determine the origin of the error as such, it is only possible to determine which criterion is not met and to identify a list of probable causes. For example, a pressure measured below or above a known threshold can have several causes: sensor fault; problem in the circuit network (partially or totally obstructed, more or less clean break, pinch, etc.); valve / expansion valve out of nominal status (partially or totally closed, for example); compressor faulty or not supplied; incorrect refrigerant charge; fault in the wiring between the sensor and the control board, etc.

[0073] After all embodiments if a second reading is still outside the normal range the controller transmits an alert to an alert monitoring circuit. The alert monitoring circuit is input for various actions that may be taken within the wider control of the heat pump. For example the system can then shut down the entire heat pump; it can wait and reboot after a shutdown or transition period; it may perform several fault detection iterations to check for other faults within the system; it may alert a homeowner, other operator of the system or other professional, for example an installer, in each case advising, via message, email or otherwise, that professional examination or assessment is now appropriate.

[0074] The invention allows for the determination of a fault, or faults, or example leakage of refrigerant, by measured effect.

[0075] In the case of large refrigerant leaks it is not possible to discriminate them from other probable causes of fault with the prior art solutions currently in use. With the use of flammable fluids, this poses a serious safety problem, as it is important and necessary for different actions to be taken when a major refrigerant leak is identified compared with other possible causes. For example, in the event of a major leak being identified, it is wise not to attempt to restart the system several times, at the risk of igniting the refrigerant, and it is wise to issue a stronger warning message to users and people in the surrounding area to exercise greater vigilance. The invention allows for an improved detection of leakage. In the case of a smaller leak, involving a gradual reduction in the refrigerant charge, for example by a few grams a year, the risk is virtually non-existent. This is because a flammable fluid can only catch fire if its concentration in the air is between the upper and lower flammability limits. For example, the lower flammability limit for R290 (propane) is 0.038 kg / m3. Below this concentration threshold, there is no risk of flammability or explosion. As a result, a small refrigerant leak will not entail any substantial risk because the flammable refrigerant will be diluted in the environment and the lower concentration threshold will not be reached. This is even more true in the case of a heat pump unit installed outdoor or in a ventilated space, since the refrigerant will be diluted even more quickly due to air movement.

[0076] The invention therefore allows the implementation of a simple, cheap means of leakage determination, using few components (which thereby reduces the number of potential errors) which makes it possible to characterize a significant refrigerant leak in a very probable manner compared to actual situation. The means of determination, that is the operational sensors, are already included in a standard heat pump installation for regulation purpose and current error identification and therefore does not create additional cost for the manufacturer.

[0077] In effect the invention uses a single parameter or a combination of two parameters to identify a very high probability of a major refrigerant leak, where the one or two parameters used may be chosen from among: pressure or temperature on the high- pressure side of the refrigerant circuit (after compression and before expansion); pressure or temperature on the low-pressure side of the refrigerant circuit (before compression and before expansion); compressor operating status (running, stopped or frequency of operation); refrigerant circuit temperature at the heat exchanger(s).

[0078] In another aspect of the invention, a method of determining refrigerant leakage in a heat pump arranged for performing a heating and / or cooling operation associated with a building in provided, in which the heat pump comprises a first sensor, Si, for acquiring pressure readings (sim) in the refrigerant circuit of the heat pump, a compressor, a leakage alarm, arranged to be resettable only by the manufacturer, and a controller coupled to the first Sensor, Si, the compressor, and the leakage alarm, and wherein the method comprises, in the controller, comparing a first reading, sn, from the first sensor, Si, to a lower pressure pre-determined threshold value, Th3, and if the first reading, Sn, is not below the lower pressure pre-determined threshold value, Th3, then re-performing the first reading, sn, whereas if the first reading, sn, is below the lower pressure predetermined threshold value, Th3, then performing the action of initiating a time delay T3, acquiring further readings, Sm, from the first sensor, Si, during elapse of time delay T3and further comparing each further reading Sm to a higher pressure pre-determined threshold value, Th4, where Th4> Th3and whereby if no reading from further readings , s^, during time delay T3is above the second pre-determined threshold value, Th4, then the controller is arranged to stop the compressor and set the leakage alarm; whereas if any reading from further readings, sm, , acquired during time delay T3is above the higher pressure pre-determined threshold value, Th4, then the controller is arranged to stop the comparison of readings sm to the higher pressure pre-determined threshold value, Th4, and re-perform the first reading Sn.

[0079] In a further aspect of the invention, a method is providing to determine refrigerant leakage in a heat pump arranged for performing a heating and / or cooling operation associated with a building, which heat pump comprises a first sensor, Si, for acquiring readings (sim) for operational monitoring of the heat pump, a compressor, an alert monitoring circuit, a controller coupled to the first Sensor, Si, the compressor, and the alert monitoring circuit, wherein the method comprises, in the controller, comparing a first reading, Sn, from the first sensor, S1 , to a first pre-determined threshold value, Thi, and if the first reading, sn, is below the first pre-determined threshold value, Thi, performing the action of stopping operation of the compressor and initiating a time period T, taking a second reading, Si2, from the first sensor, S1 , after elapse of time period T and if the second reading, Si2, is below the first pre-determined threshold value, Thi, performing the action of transmitting an alert to the alert monitoring circuit; whereas if the second reading, Si2, is above the first pre-determined threshold value, Thi, performing the action of restarting the compressor.

[0080] The method is particularly suitable to detect the leakage of a flammable or dangerous refrigerant.

[0081] In a further embodiment of a method, the heat pump further comprises a second sensor, S2, for acquiring readings (s2n) for operational monitoring and the method further comprises, in the controller, comparing a first reading, s2i, from the second sensor to a second pre-determined threshold value, Th2, and if the first reading, s2i, is below the second pre-determined threshold value, Th2, then regardless of the state of readings, (Sim) , from the first sensor, Si, performing the action of stopping the compressor and initiating a time period T, taking a second reading, S22, from the second sensor, S2, after elapse of time period T and if the second reading, S22, is below the second predetermined threshold value, Th2, performing the action of transmitting an alert to the alert monitoring circuit, whereas if the second reading is above the second predetermined threshold value performing the action of restarting the compressor if and only if a reading from the first sensor Sn or S12 is also above the first pre-determined threshold value, Thi.

[0082] In a further embodiment of a method, the heat pump comprises a third sensor, S3, for acquiring readings (s3p) for operational monitoring of the compressor, and wherein the method comprises comparing the first reading, Sn, from the first sensor, Si, to a first dependent threshold value, Th3i, where Th3iis dependent on a reading, S31, from the third sensor, S3, and which reading, S31, is performed within a time period Dt of the first reading, sn, and if the first reading, sn, is below the first dependent threshold value, Th3i, performing the action of stopping the compressor and initiating a time period T, taking a second reading, S12, from the first sensor, Si, after elapse of time period T and if the second reading, S12, is below a second dependent threshold value, Th32, where Th32 is dependent on a reading, s32, from the third sensor, S3, which reading, s32, is performed within a time period Dt of the first reading, Sn, performing the action of transmitting an alert to the alert monitoring circuit, whereas if the second reading, S12, is above the second dependent threshold value, Th32, performing the action of restarting the compressor.

[0083] This allows leakage detection to be based on operational monitoring of the compressor itself.

[0084] In yet another embodiment the first reading, Sn, from the first sensor, Si, may be compared to a first dependent threshold value, Th3i, where Th3iis dependent on at least the reading, s3i, from the third sensor, S3. In this embodiment Th3imay be dependent on combinations of sensor readings. For example, the threshold value could be defined based on different sensors. In a particular example it could be dependent upon frequency of compressor and a temperature of the source. For example it may be dependent on values, for examples on tables of values stored in the software, enabling threshold values to be adjusted as a function of measured values. For example, it could be a table with the frequency of the compressor and the temperature of the source as input data. Depending on these values, threshold values are defined in the software memory and are used for the elements of the preceding claims.

[0085] In a further embodiment the method further comprises, in the controller, taking a sensor reading Sn after every interval Ts. In this case Tscan be preferably from a few milliseconds to a few seconds.

[0086] In a further embodiment, and if an alert is transmitted to the alert monitoring circuit, the method further comprises, in the alert monitoring circuit, sending a report and / or, sending an alert, in particular to the operator of the heat pump, which operator may be a homeowner or other home resident. Other possibilities include: sounding an alarm; sending an alarm sound to a device, for example a mobile telephone; sending a message to the heat pump or heat pump controller with instructions to make alight a light visible on the heat pump; send a signal to the heat pump or heat pump controller giving instructions to display of an error code on the HMI of the heat pump; send a short message service text or other message text to a phone registered to an operator of the heat pump, which operator may be a homeowner or other home resident, or to an installer of the heat pump, or to a distributer of the heat pump; send a message to an application run and monitored by the operator of the heat pump, which operator may be a homeowner or other home resident, or by an installer of the heat pump, or by a distributer of the heat pump. Combinations of the listed alert options and messages may also be used. For example a message may be sent to the home owner owning the heat pump and also a message sent to the heat pump or heat pump controller to lit a warning light on the heat pump.

[0087] In an additional aspect of the invention, a controller for a heat pump is provided, which controller is configured to perform the method of the invention.

[0088] In a further embodiment the controller comprises the alert monitoring circuit. The alert monitoring circuit may be integrated into the controller of the heating unit, the heating system or the installation's home automation system. It can also be a remote solution supported by a Cloud-type network.

[0089] In an additional aspect of the invention a heat pump is provided comprising a controller according to the invention. The heat pump may be in all other respects a standard heat pump as is known in the art. In an additional 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.

[0090] In an additional 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.

[0091] In an additional aspect of the invention a data carrier signal is provided carrying the computer program product according to the invention. 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.

[0092] 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.

[0093] Figure 1A shows a heat pump according to aspects of the invention.

[0094] Figure 2A shows a flow diagram showing aspects of the invention

[0095] Figure 2B shows hysteresis in the invention

[0096] Figure 3A shows a further flow diagram showing aspects of the invention

[0097] Figure 3B shows hysteresis in the invention Figure 4A shows the working of the invention

[0098] Figure 4B shows the working of the invention

[0099] Figure 4C shows the working of the invention

[0100] Figure 5 shows a flow diagram of a method according to the invention.

[0101] Figure 6A shows a heat pump according to aspects of the invention.

[0102] Figure 6B shows a flow diagram of a method according to the invention.

[0103] Figure 7A shows a heat pump according to aspects of the invention.

[0104] Figure 7B shows a flow diagram of a method according to the invention.

[0105] Figure 8 shows a heat pump with an arrangement of operational sensors that may be used in the invention.

[0106] Figure 9 shows a particular embodiment of the invention.

[0107] Figure 10 shows a particular embodiment of the invention.

[0108] Figure 1A shows a heat pump 1 according to aspects of the invention and includes a refrigerant circuit 2 with heat exchangers 2’ and 2”, expansion device 2”’, compressor 3, a controller 4, an alert monitoring circuit 5 and a first sensor 6. Controller 4 is coupled to the compressor 3, alert monitoring circuit 5 and first sensor 6.

[0109] Figure 2A shows a flow diagram showing aspects of the invention. In first step 2a a pressure measurement PLP is acquired and compared 2b to lower pressure predetermined threshold Th3. If PLP is not lower than Th3the method ends and reverts to the beginning and the next acquisition of pressure measurement PLP.

[0110] However if PLP is lower than Th3then in step 2c PLP is compared to higher pressure pre-determined threshold value Th4, As Th4is greater than Th3the measurement PLP, having been lower than Th3will also be lower than Th4, therefore the method will advance at least initially to step 2e which it is determined if or not a time delay has been completed. The time delay may be set at step 2b, comparison with Th3, or at step 2c, comparison with Th4, or at step 2e itself. If the time delay has not yet completed the system will loop back through step 2c until the time delay is completed 2e, and at some point during the loop a further pressure measurement 2d is taken. This may be taken after step 2e but before the following comparison with Th4at 2c as shown, or alternatively immediately before step 2e once the first comparison with Th4at 2c has failed. If at any point PLP as remeasured is not lower than Th4then the method will exit and revert to the beginning.

[0111] However upon completion of the time delay 2e the leakage alarm will be set, which can only be reset either by the manufacturer or on site by a user or installation expert using manufacturer supplied information, such as a code, or key.

[0112] There is a hysteresis incorporated into the system, as shown in Fig. 2B, by way of the use of different values for the lower pressure pre-determined threshold Th3, 2h, and the higher pressure pre-determined threshold Th4, 2i. The variation in value of the two thresholds means that the system has to clear a higher threshold to leave an alarm state than it is adjudged by in order to enter the alarm state.

[0113] Figure 3A shows a flow diagram showing further aspects of the invention. In first step 3a a pressure measurement PLP and in the next step 3b if the compressor is not in an ON state the method loops with acquisition of pressure measurement 3a. Even though the compressor may be in an OFF state the remainder of the heat pump may be ON and therefore the controller will be operative and pressure measurements may be acquired. However, if in step 3b the compressor is ON then a comparison is made 3c to a first predetermined threshold Thi. If PLP is not lower than Thi the method ends and reverts to the beginning and the next acquisition of pressure measurement PLP.

[0114] However if PLP is lower than Thi then in step 3d PLP is compared to second predetermined threshold value Th2, As Th2is greater than Thi the measurement PLP, having been lower than Thi will also be lower than Th2, therefore the method will advance at least initially to step 3f where, again, it is determined if or not a time delay has been completed. The time delay may be set at step 3c, comparison with Thi, or at step 3d, comparison with Th2, or at step 3f itself. The length of the time delay will depend on whether the heat pump is in start-up phase or out of start-up phase and therefore running in steady state.

[0115] If the time delay has not yet completed the system will loop back through step 3d until the time delay is completed 3f, and at some point during the loop a further pressure measurement 3e is taken. This may be taken after step 3f but before the following comparison with Th2at 3d as shown, or alternatively immediately before step 3f once the first comparison with Th2at 3d has failed. If at any point PLP as remeasured is not lower than Th2then the method will exit and revert to the beginning.

[0116] However upon completion of the time delay 3f a number of actions 3g will take place: a low pressure alarm will be set; the compressor will be stopped; the expansion valve will be opened; and a counter will be increased by 1.

[0117] Following actions 3g the counter is interrogated 3h and if there have been more than N instances of the counter in an hour, then the heat pump is locked 3i. This lock can be reset by the user 3j. Typically reset is allowed upon a check as advised or prescribed by the manufacturer. However if in step 3h there have not been more than N instances within an hour then further measurements are acquired 3k and compared to the second pre-determined threshold value Th2, 3I, and if the measured pressure is greater than the second pre-determined threshold value Th2, the method will exit and revert to the beginning.

[0118] Again, there is a hysteresis incorporated into the system, as shown in Fig. 3B, by way of the use of different values for the first pre-determined threshold Thi, 3m, and the second pre-determined threshold Th2, 3n. The variation in value of the two thresholds means that the system has to clear a higher threshold to leave an alarm state than it is adjudged by in order to enter the alarm state.

[0119] Figure 4A shows the imposition of low pressure alarms 4a over a typical evolution of a refrigerant leak, culminating in the imposition of leakage alarm 4a’. Each low pressure alarm 4a can be reset by the user, however leakage alarm 4a’ can only be reset by the manufacturer, or by a user or installation expert using manufacturer information. In the case shown in Figure 4A there have been 3 low pressure alarms 4a over or within a one hour period, therefore the heat pump is locked. This can be reset by the user, however this is followed by a continual decrease in measured pressure therefore leakage alarm 4a’ is triggered, at which point the compressor can no longer be simply reset by the user without extra input from the manufacturer.

[0120] Figure 4B shows the compressor ON states 4b during the same evolution of time. In each case the compressor is shut down by the method as described, and must remain off during a subsequent period of time know as its minimum off time. This time allows for the compressor to be equalised and reset before re-commencing operation.

[0121] Figure 4C shows a series of pressure measurements PLP over time. At 4c a measurement PLP is made which is just below the first pre-determined threshold value, in this case 0.6 bar. A delay 1 is applied if the compressor is in steady state, in this case of 120 seconds, or a delay 2 is applied if the compressor is still in start-up phase, in this case of 180 seconds, at the end of which if the measured pressure 4c’” is not above the second pre-determined threshold value, the low pressure alarm is set. In this case delay 1 was applied, and it can be seen from the graph that at the end of 120 seconds the measured pressure is still below the second pre-determined threshold value, which in this case is 1.4 bar. Therefore a low pressure alarm 4a is set. It can be seen by comparison of Figures 4C with 4A that the low pressure alarms are only set during the period in which the second pre-determined threshold value is not exceeded.

[0122] During the application of the above method the measured pressures are also compared with the lower pressure pre-determined threshold value and the higher pressure predetermined threshold value, and if comparison of measured pressures to the higher pressure pre-determined threshold value has been triggered, following comparison to the lower pressure pre-determined threshold value, and measured pressures are still below the higher pressure pre-determined threshold value after expiry of the respective time delay, the leakage alarm 4a’ is set. In this case the respective time delay is 15 minutes.

[0123] In Figure 4C 3 separate incidents, 4d, 4d’ and 4d”, are shown in the which a measured pressure lower than the first pre-determined threshold value are shown, each necessitating the measured pressure to climb above the second pre-determined threshold value in order for the low pressure alarm to be cleared. However in this case during the third low pressure alarm the measured pressure stays below the second pre- determined threshold value and also the higher pressure pre-determined threshold value, with the result that after the respective delay the leakage alarm is set.

[0124] Figure 5 shows a flow diagram of a method according to an embodiment of the invention in which a heat pump with leakage detection is provided, the heat pump arranged for performing a heating and / or cooling operation associated with a building, and comprising a first sensor, Si, arranged to acquire readings (sim) for operational monitoring of the heat pump, a compressor, an alert monitoring circuit, a controller coupled to the first Sensor, Si, the compressor, and the alert monitoring circuit; and whereby the controller is arranged to compare a first reading, Sn, from the first sensor, Si, to a first predetermined threshold value, Thi, and if the first reading, sn, is below the first predetermined threshold value, Thi, perform the action of stopping operation of the compressor and initiating a time period T, acquiring a second reading, Si2, from the first sensor, Si, after elapse of the time period T and if the second reading, Si2, is below the first pre-determined threshold value, Thi, performing the action of transmitting an alert to the alert monitoring circuit, whereas if the second reading, Si2, is above the first predetermined threshold value, Thi, then performing the action of restarting the compressor. Here, a reading Sn is acquired 10 from the first sensor, and a comparison 11 made in the controller between sn and a threshold value Thi If sn is not less than Thi then the method essentially stops, or resets ready for the next acquisition of a reading from the sensor. However if sn is less than Thi then the controller performs the actions 12 of stopping the compressor and starting a time period T. At the end of time period T the compressor acquires 13 a second reading Si2from the sensor and makes a second comparison 14 between Si2and Thi If Si2is not less than Thi then the controller restarts the compressor 15. If however if si2is less than Thi then the controller transmits an alert 16 to the alert monitoring circuit.

[0125] Figure 6A shows the same heat pump 1 with refrigerant circuit 2 with heat exchangers 2’ and 2”, expansion device 2”’, compressor 3, a controller 4, an alert monitoring circuit 5 and a first sensor 6, and additionally a second sensor 7. Controller 4 is coupled to the compressor 3, alert monitoring circuit 5, first sensor 6 and second sensor 7.

[0126] Figure 6B shows a flow diagram of a method according to a further embodiment of the invention, similar in form to that shown in Fig. 6A, in which the heat pump with leakage detection may further comprise a second sensor, S2, arranged to acquire readings (s2n) for operational monitoring, and wherein the controller is further coupled to the second sensor S2and is further arranged to compare a first reading, s2i, from the second sensor to a second pre-determined threshold value, Th2, and if the first reading, s2i, is below the second pre-determined threshold value, Th2, then regardless of the state of readings, (Sim) , from the first sensor, Si, perform the action of stopping operation of the compressor and initiating a time period T, acquiring a second reading, s22, from the second sensor, S2, after elapse of time period T and if the second reading, s22, is below the second predetermined threshold value, Th2, performing the action of transmitting an alert to the alert monitoring circuit, whereas if the second reading is above the second predetermined threshold value performing the action of restarting the compressor if and only if a reading from the first sensor Sn or Si2is also above the first pre-determined threshold value, Thi. Here, a reading s2iis acquired 20 from the second sensor, and a comparison 21 made in the controller between s2iand a threshold value Th2If s2iis not less than Th2then the method essentially stops, or resets ready for the next acquisition of a reading from the sensor. However if s2iis less than Th2then the controller performs the actions 22 of stopping the compressor and starting a time period T. At the end of time period T the compressor acquires 23 a second reading s22from the sensor and makes a second comparison 24 between s22and Th2If s22is not less than Th2and if Si2is not less than Thi (item 14 from Fig. 1) then the controller restarts the compressor 25. If however if s22is less than Th2then the controller transmits an alert 26 to the alert monitoring circuit.

[0127] Figure 7A the same heat pump 1 with refrigerant circuit 2 with heat exchangers 2’ and 2”, expansion device 2”’, compressor 3, a controller 4, an alert monitoring circuit 5 and a first sensor 6, second sensor 7, and additionally a third sensor 8. Controller 4 is coupled to the compressor 3, alert monitoring circuit 5, first sensor 6, second sensor 7 and third sensor 8.

[0128] Figure 7B shows a flow diagram of a method according to a further embodiment of the invention in which the heat pump with leakage detection may further comprise a third sensor, S3, arranged to acquire readings (s3p) for operational monitoring of the compressor, and wherein the controller is further coupled to the third sensor S3and is further arranged to compare the first reading, Sn, from the first sensor, Si, to a first dependent threshold value, Th3i, where Th3iis dependent on a reading, s3-i, from the third sensor, S3, and which reading, s3-i, is performed within a time period Dt of the first reading, sn, and if the first reading, sn, is below the first dependent threshold value, Th3i, then perform the action of stopping operation of the compressor and initiating a time period T, acquiring a second reading, Si2, from the first sensor, Si, after elapse of time period T and if the second reading, S12, is below a second dependent threshold value, Th32, where Th32 is dependent on a reading, s32, from the third sensor, S3, which reading, s32, is performed within a time period Dt of the second reading, Si2, perform the action of transmitting an alert to the alert monitoring circuit, whereas if the second reading, Si2, is above the second dependent threshold value, Th32, performing the action of restarting the compressor. Here, reading Sn is acquired 10 from the first sensor, and a comparison 31 made in the controller between Sn and a threshold value Th3i, where Th3iis derived 30’ from reading s3iacquired 30 from a sensor arranged for operational monitoring of the compressor. If s3iis not less than Th3ithen the method essentially stops, or resets ready for the next acquisition of a reading from the sensor. However if s3iis less than Th3ithen the controller performs the actions 32 of stopping the compressor and starting a time period T. At the end of time period T the compressor acquires 13 a second reading S12 from the sensor and makes a second comparison 34 between S12 and a second value Th32, where Th32 is derived 30”’ from reading s32 acquired 30” from a sensor arranged for operational monitoring of the compressor If S12 is not less than Th3ithen the controller restarts the compressor 35. If however if S12 is less than Th3ithen the controller transmits an alert 36 to the alert monitoring circuit. Both readings sn and s3iare acquired within a time Dt of each other 30iv. Also both readings S12 and s32are acquired within a time Dt of each other 30v.

[0129] Figure 8 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 valve 56. Various operational sensors, including pressure sensors 57 and temperature sensors 58 are arranged around the circuit and may be used in the arrangements and methods of the invention.

[0130] Figure 9 shows a particular embodiment of the invention appropriate to for example one of Applicant’s air source heat pump product . In this case the invention may use pressure sensors on the low-side pressure only (referred as PCS for Pressure Compressor Suction, being shown in figure 4), and if pressure readings drop below 1.4 absolute bar there is a risk of leakage, due to any relevant cause or internal error. This particular embodiment of the invention is also appropriate to for example another model of Applicant’s air source heat pump product, in which case pressure sensors are used on both the low-side (PCS) and high-side pressure (PCD for Pressure Compressor Discharge, being shown in figure 4). In this case if at least one of the pressure values falls below 1 .3 absolute bar for the duration of the time period there is a risk of leakage, due to any relevant cause or internal error.

[0131] By using such “levels of error”, the first kind is characteristic of a major leakage, but it is not possible to ensure that it cannot be arise due to other causes. For example, a defective pressure sensor (mispositioned for example or having a default value below the threshold value) or an electronic error can also lead to a “first kind” error. So it can still be necessary to define that other causes can be associated to this error in a maintenance or repair manual. In an application, it may be implemented two steps of errors: a first kind of error 60 related to high probability of major refrigerant leakage, will be activated if one of the low-pressure side and / or high pressure side drops below the threshold value of 1.3 absolute bar. It will be called “Low pressure Error” and the main cause identified in the maintenance manual will be the refrigerant leak. Few other possible reasons which could lead to such low pressure will also be identified.

[0132] Figure 10 shows a particular embodiment of the invention in which a second kind or error 61 , related to generic errors for which it is not possible to identify a likely relevant cause, will be activated by a set of parameters (whateverthe number). There will be for example 13 groups possible (13 different errors) based on different parameter or set of parameters being outside the normal range. For each group, a large list of causes will be determined, without possibility to focus on a specific one. For most of them, one of the possible causes is a non-compliant refrigerant load (too much or too low) or a tightness of the refrigerant circuit compromised (pressure drop due to a restriction or bend; porosity; minor leaks, etc.), both being equivalent. A lot of possible causes are possible and will also be described in detail in the maintenance manual depending on the group error. Among them: defective compressor, defective fan, defective valve, defective sensors, clogged heat exchanger, 4-way valve stuck, defective expansion valve, etc.

[0133] This generic error can be understood as a second level of error, complementary with the first level of error, that can be implemented. It can be realized for example with a comparison between one of the pressure measured in the system and one other threshold value, this threshold having a value higher than the one used for the “Low pressure Error” and being for example 3 absolute bar. Such kind of error can be due to several causes, for example due to bad assembly, (partial) obstruction of an air duct, not compliant rotational speed of a pump or a compressor, incorrect refrigerant charge, etc.

[0134] As a result, the methodology can effectively distinguish between a major leak that poses a risk to the user (first level) and a more common or generic fault (second level or generic error) that may have multiple causes and does not pose a significant risk to the user or the environment.

[0135] In such a case a method of determining an error in a heat pump may be used, wherein the 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 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.

[0136] In a particular embodiment the heat pump with leakage detection may further comprise a refrigerant circuit comprising a low-pressure section and a high-pressure section, and at least one heat exchanger, and wherein the first and second sensors may be separately selected from the group of a pressure sensor arranged to detect pressure in the low- pressure section, or, a pressure sensor arranged to detect pressure in the high-pressure section, or, a temperature sensor arranged to detect temperature at a heat exchanger.

[0137] In a further embodiment the third sensor may be selected from the group of a sensor arranged to detect compressor operating status, or, a sensor arranged to detect if the compressor is operating or not operating, or, a sensor arranged to detect compressor frequency, or, a sensor arranged to detect compressor power consumption, or, a sensor arranged to detect temperature of a source or destination fluid, or, a sensor arranged to detect flow of a source or destination fluid.

[0138] Further a method of determining refrigerant leakage in a heat pump, arranged for performing a heating and / or cooling operation associated with a building, is provided, and wherein the heat pump comprises a first sensor, Si, for acquiring readings (sim) for operational monitoring of the heat pump, a compressor, an alert monitoring circuit, a controller coupled to the first Sensor, Si , the compressor, and the alert monitoring circuit, and wherein the method comprises: in the controller, comparing a first reading, Sn, from the first sensor, S1 , to a first pre-determined threshold value, Thi, and if the first reading, Sn, is below the first pre-determined threshold value, Thi, performing the action of:

[0139] - stopping operation of the compressor and initiating a time period T;

[0140] - taking a second reading, Si2, from the first sensor, S1 , after elapse of time period T and: if the second reading, si2, is below the first pre-determined threshold value, Thi, performing the action of transmitting an alert to the alert monitoring circuit; whereas if the second reading, Si2, is above the first pre-determined threshold value, Thi, performing the action of restarting the compressor.

[0141] A further method of determining refrigerant leakage in a heat pump is provided, wherein the heat pump may further comprise a second sensor, S2, for acquiring readings (s2n) for operational monitoring, wherein the method comprises: in the controller, comparing a first reading, s2i, from the second sensor to a second pre-determined threshold value, Th2, and if the first reading, s2i, is below the second pre-determined threshold value, Th2, then regardless of the state of readings, (sim) , from the first sensor, Si, performing the action of:

[0142] - stopping the compressor and initiating a time period T;

[0143] - taking a second reading, s22, from the second sensor, S2, after elapse of time period T and: if the second reading, s22, is below the second pre-determined threshold value, Th2, performing the action of transmitting an alert to the alert monitoring circuit; whereas if the second reading is above the second pre-determined threshold value performing the action of restarting the compressor if and only if a reading from the first sensor Sn or Si2is also above the first pre-determined threshold value, Thi.

[0144] The further method of determining refrigerant leakage in a heat pump may be provided, wherein the heat pump may comprise a third sensor, S3, for acquiring readings (s3p) for operational monitoring of the compressor, and wherein the method comprises: - comparing the first reading, Sn, from the first sensor, Si, to a first dependent threshold value, Th3i, where Th3iis dependent on a reading, S31, from the third sensor, S3, and which reading, S31, is performed within a time period Dt of the first reading, Sn;

[0145] - -and if the first reading, Sn, is below the first dependent threshold value, Th3i , performing the action of:

[0146] - stopping the compressor and initiating a time period T;

[0147] - taking a second reading, S12, from the first sensor, Si, after elapse of time period T and: if the second reading, S12, is below a second dependent threshold value, Th32, where Th32is dependent on a reading, s32, from the third sensor, S3, which reading, s32, is performed within a time period Dt of the first reading, Sn; performing the action of transmitting an alert to the alert monitoring circuit; whereas if the second reading, si2, is above the second dependent threshold value, Th32, performing the action of restarting the compressor.

[0148] The method of determining refrigerant leakage in a heat pump may further comprise: in the controller, taking a sensor reading sn after every interval Ts.

[0149] The method of determining refrigerant leakage in a heat pump, wherein if an alert is transmitted to the alert monitoring circuit, the method further comprises: in the alert monitoring circuit:

[0150] - sending a report and / or

[0151] - sending an alert, in particular to an operator of the heat pump.

[0152] A controller for a heat pump may also be provided, wherein the controller is configured to perform the method as described.

[0153] A controller for a heat pump may also be provided, wherein the controller comprises the alert monitoring circuit.

[0154] A heat pump may be provided comprising a controller as described.

[0155] A computer program product comprising program instructions operable to cause a processorto perform operations according to any method as described may be provided. A non-transitory computer readable medium having stored thereupon a computer program product as described may be provided. A data carrier signal may be provided, carrying the computer program product as described.

[0156] Reference Signs

[0157] 1 heat pump

[0158] 2 refrigerant circuit

[0159] 2’ heat exchanger

[0160] 2” heat exchanger

[0161] 2”’ expansion device

[0162] 2a measurement step

[0163] 2b comparison step

[0164] 2c comparison step

[0165] 2d measurement step

[0166] 2e delay completion

[0167] 2f set leakage alarm

[0168] 2g manufacturer reset

[0169] 2h lower pressure pre-determined threshold value

[0170] 2i higher pressure pre-determined threshold value

[0171] 3 compressor

[0172] 3a measurement step

[0173] 3b comparison step

[0174] 3c comparison step

[0175] 3d comparison step

[0176] 3e measurement step

[0177] 3f delay completion

[0178] 3g actions

[0179] 3h counter comparison step

[0180] 3i lock heat pump

[0181] 3j reset alarm step

[0182] 3k measurement step

[0183] 3I comparison step

[0184] 3m first pre-determined threshold value

[0185] 3n second pre-determined threshold value

[0186] 4 controller

[0187] 4a low pressure alarm

[0188] 4a’ leakage alarm

[0189] 4b compressor ON state 4c pressure measurement

[0190] 5 alert monitoring circuit

[0191] 6 first sensor

[0192] 7 second sensor

[0193] 8 third sensor

[0194] 10 acquisition step

[0195] 11 comparison step

[0196] 12 action step of stopping compressor, starting T

[0197] 13 acquisition step

[0198] 14 comparison step

[0199] 15 action step of restarting compressor

[0200] 16 action step of transmitting alert

[0201] 20 acquisition step

[0202] 21 comparison step

[0203] 22 action step of stopping compressor, starting T

[0204] 23 acquisition step

[0205] 44 comparison step

[0206] 25 action step of restarting compressor

[0207] 26 action step of transmitting alert

[0208] 30 acquisition step

[0209] 30’ threshold value creation step

[0210] 30” acquisition step

[0211] 30’” threshold value creation step

[0212] 30ivtime duration Dt

[0213] 30vtime duration Dt

[0214] 31 comparison step

[0215] 32 action step of stopping compressor, starting T

[0216] 34 comparison step

[0217] 35 action step of restarting compressor

[0218] 36 action step of transmitting alert

[0219] 50 outdoor unit of heat pump

[0220] 51 indoor unit or heat network

[0221] 52 fan

[0222] 53 heat exchanger

[0223] 54 compressor

[0224] 55 heat exchanger 56 expansion valve

[0225] 57 pressure sensors

[0226] 58 temperature sensors

[0227] 60 first kind of error

[0228] 61 second kind of error

Claims

CLAIMS1. A heat pump with leakage detection, the heat pump arranged for performing a heating and / or cooling operation associated with a building, and comprising:- a first sensor, Si, arranged to acquire pressure readings (sim) within the refrigerant circuit of the heat pump;- a compressor;- a leakage alarm, arranged to be resettable only by use of manufacturer information;- a controller coupled to the first sensor, Si, the compressor, and the leakage alarm; and whereby the controller is arranged to:- compare a first reading, sn, from the first sensor, Si, to a lower pressure predetermined threshold value, Th3, and if the first reading, Sn, is not below the lower pressure pre-determined threshold value, Ths, then re-perform the first reading S11, whereas: if the first reading, Sn, is below the lower pressure pre-determined threshold value, Th3, then the controller is arranged to: initiate a time delay T3; and- acquire further readings, Sm, from the first sensor, Si, during elapse of the time period T3and further- compare each further reading sm to a higher pressure pre-determined threshold value, Th4, wherein Th4> Th3; whereby if no reading from further readings sm, during time delay T3is above the higher pressure pre-determined threshold value, Th4, then the controller is arranged to:- stop the compressor and set the leakage alarm; whereas if any reading, Sm, from further readings Sm, during time delay T3is above the higher pressure pre-determined threshold value, Th4, then the controller is arranged to stop the comparison of readings Sm to the higher pressure predetermined threshold value, Th4, and re-perform the first reading Sn.

2. A heat pump with leakage detection according to claim 1 , wherein time delay T3is 15 minutes.

3. A heat pump with leakage detection according to claim 1 or 2, and further comprising: an expansion valve;- a counter;- a low pressure alarm;- a lock function which can only be cancelled by manual action; and- where the controller is further coupled to the expansion valve, the counter, the low pressure alarm and the lock function; and- wherein the controller is further arranged to:- compare the first reading, Sn, from the first sensor, Si, to a first pre-determined threshold value, Thi, and if the first reading, Sn, is not below the first predetermined threshold value, Thi, then re-perform the first reading sn, whereas: if the first reading, Sn, is below the first pre-determined threshold value, Thi, then the compressor is arranged to: initiate a time delay Tmdependent upon whether the compressor is in start-up phase or no longer in start-up phase; and- acquire further readings, Sm, from the first sensor, Si, during elapse of the time period Tmand further- compare each further reading Sm to a second pre-determined threshold value, Th2, wherein Th2> Thi; whereby if no reading from further readings Sm, during time delay Tmis above the second pre-determined threshold value, Th2, then the controller is arranged to: o set the low pressure alarm; o stop the compressor; o open the expansion valve; o increase the counter by 1 ; whereas if any reading, Sm, from further readings Sm, during time delay Tmis above the second pre-determined threshold value, Th2, then the controller is arranged to stop the comparison of readings Sm to the second pre-determined threshold value, Th2, and re-perform the first reading Sn; and- further wherein: if the counter reaches more than a value N in one hour the controller is arranged to use the lock function to lock the heat pump, whereas if the counter does not reach more than a value N in one hour the controller is arranged to acquire further readings, Sm, from the first sensor, Si and compare each further reading Sm to the second pre-determined threshold value Th2, and when any reading from the further readings Sm is not below the second predetermined threshold value Th2then the controller is arranged to stop thecomparison of readings Sm to the second pre-determined threshold value, Th2, and re-perform the first reading sn.

4. A heat pump with leakage detection according to claim 3 wherein:N = 3; andTm= 180 seconds if the compressor is in start-up phase; whereasTm= 120 seconds if the compressor is no longer in start-up phase.

5. A heat pump with leakage detection according to claim 1 , and wherein- the first sensor, Si, is arranged to acquire the readings (sim) for operational monitoring of the heat pump; and further comprising:- an alert monitoring circuit coupled to the controller; and- whereby the controller is arranged to:- compare a first reading, Sn, from the first sensor, Si, to a first initial predetermined threshold value, Thia, and if the first reading, Sn, is below the first initial pre-determined threshold value, Thia, perform the action of:- stop operation of the compressor and initiate a time period Ta;- acquire a second reading, Si2, from the first sensor, Si, after elapse of time period Taand: if the second reading, Si2, is below the first initial pre-determined threshold value, Thia, perform the action of transmitting an alert to the alert monitoring circuit; whereas if the second reading, si2, is above the first initial pre-determined threshold value, Thia, perform the action of restarting the compressor.

6. A heat pump with leakage detection according to claim 5, wherein the heat pump further comprises:- a second sensor, S2, arranged to acquire readings (s2n) for operational monitoring:- and wherein the controller is further coupled to the second sensor S2and is further arranged to:- compare a first reading, s2-i, from the second sensor to a second initial predetermined threshold value, Th2a, and if the first reading, s2-i , is below the secondinitial pre-determined threshold value, Th2, then regardless of the state of readings, (sim) , from the first sensor, Si, perform the action of:- stop operation of the compressor and initiate a time period T ;- acquire a second reading, s22, from the second sensor, S2, after elapse of time period T and: if the second reading, s22, is below the second initial pre-determined threshold value, Th2a, perform the action of transmitting an alert to the alert monitoring circuit; whereas if the second reading is above the second initial pre-determined threshold value performing the action of restarting the compressor if and only if a reading from the first sensor sn or si2is also above the first initial pre-determined threshold value, Thia.

7. A heat pump with leakage detection according to claim 6, wherein the heat pump further comprises:- a third sensor, S3, arranged to acquire readings (s3p) for operational monitoring of the compressor, and wherein the controller is further coupled to the third sensor S3and is further arranged to:- compare the first reading, sn, from the first sensor, Si, to a first dependent threshold value, Th3i, where Th3iis dependent on a reading, s3-i , from the third sensor, S3, and which reading, s3i, is performed within a time period Dt of the first reading, Sn;- and ifthe first reading, Sn, is below the first dependent threshold value, Th3i, then perform the action of:- stop operation of the compressor and initiate a time period T ;- acquire a second reading, Si2, from the first sensor, Si, after elapse of time period T and: if the second reading, Si2, is below a second dependent threshold value, Th32, where Th32is dependent on a reading, s32, from the third sensor, S3, which reading, s32, is performed within a time period Dt of the second reading, Si2; perform the action of transmitting an alert to the alert monitoring circuit; whereas if the second reading, Si2, is above the second dependent threshold value, Th32, perform the action of restarting the compressor.

8. A heat pump with leakage detection according to claim 5 or 6, wherein the heat pump further comprises a refrigerant circuit comprising a low-pressure section and a high-pressure section, and at least one heat exchanger, and wherein the first and second sensors are each separately selected from the group of:- 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 heat exchanger.

9. A heat pump with leakage detection according to claim 7, wherein the third sensor is selected from the group of:- a sensor arranged to detect compressor operating status;- a sensor arranged to detect if the compressor is operating or not operating;- a sensor arranged to detect compressor frequency;- a sensor arranged to detect compressor power consumption;- a sensor arranged to detect temperature of a source or destination fluid- a sensor arranged to detect flow of a source or destination fluid.

10. Method of determining refrigerant leakage in a heat pump arranged for performing a heating and / or cooling operation associated with a building, which heat pump comprises:- a first sensor, Si, for acquiring pressure readings (sim) in the refrigerant circuit of the heat pump;- a compressor;- a leakage alarm, arranged to be resettable only by the manufacturer;- a controller coupled to the first Sensor, Si, the compressor, and the leakage alarm; wherein the method comprises: in the controller, comparing a first reading, Sn, from the first sensor, Si, to a lower pressure pre-determined threshold value, Th3, and if the first reading, Sn, is not below the lower pressure pre-determined threshold value, Th3, then reperforming the first reading, sn, whereas if the first reading, sn, is below the lower pressure pre-determined threshold value, Th3, then performing the action of: initiating a time delay T3;- acquiring further readings, Sm, from the first sensor, Si, during elapse of time delay T3and further:- comparing each further reading Sm to a higher pressure pre-determined threshold value, Th4, where Thu > Ths; whereby if no reading from further readings , Sm, during time delay T3is above the second pre-determined threshold value, Th4, then the controller is arranged to- stop the compressor and set the leakage alarm; whereas if any reading from further readings, Sm,, acquired during time delay T3is above the higher pressure pre-determined threshold value, Th4, then the controller is arranged to stop the comparison of readings Sm to the higher pressure predetermined threshold value, Th4, and re-perform the first reading sn.

11. A controller for a heat pump, wherein the controller is configured to perform the method of claim 10.12 A controller for a heat pump according to claim 11 , wherein the controller comprises the alert monitoring circuit.

13. Heat pump comprising a controller according to claim 11 .

14. A computer program product comprising program instructions operable to cause a processor to perform operations according to the method of claim 10.

15. Non transitory computer readable medium having stored thereupon the computer program product according to claim 14.

16. Data carrier signal carrying the computer program product of claim 14.

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