Heat pump and method of operating a heat pump with a vapour compression system

Abstract

In a method for operating a heat pump with a vapor compression system, an at least partially gaseous refrigerant is compressed from a low pressure ND to a high pressure HD by a compressor controlled by a controller. The refrigerant is driven through a condensing heat exchanger operated downstream of the compressor, whereby the refrigerant is condensed. The refrigerant is then passed to an intermediate pressure throttle device controlled by the controller, with which the refrigerant is expanded to an intermediate pressure ZD. The refrigerant expanded to the intermediate pressure ZD is passed into a refrigerant collector and the refrigerant is led in liquid form from the collector to a low pressure throttle device controlled by the controller, with which the refrigerant is expanded to a low pressure ND. The refrigerant at the low pressure ND evaporates in an evaporating heat exchanger.In further method steps, a first manipulated variable ES for the intermediate pressure throttle element, through which the refrigerant flows after the condensing heat exchanger, is determined as a function of a subcooling deviation Ua of an actual subcooling value Ui from a target subcooling value Us of the refrigerant at an outlet of the condensing heat exchanger. Furthermore, a second manipulated variable ZS for the intermediate pressure throttle element, through which the refrigerant flows after the condensing heat exchanger, is determined as a function of at least one process value PW of the vapor compression system, which process value is processed in a stored calculation model to form the second manipulated variable ZS. The first manipulated variable ES is processed with the second manipulated variable ZS to determine a target manipulated value SST for adjusting the intermediate pressure throttle element through which the refrigerant flows after the condensing heat exchanger and setting it to the target manipulated value SST.

Description

[0001] The invention relates to a method for operating a heat pump with a vapor compression system and a device with a liquefying heat exchanger.

[0002] The method relates to the operation of a heat pump with a vapor compression system in which an at least partially gaseous refrigerant is compressed from a low pressure to a high pressure by a compressor controlled by a controller. The refrigerant is driven through a condensing heat exchanger operated downstream of the compressor, in which condensation of the refrigerant takes place. The refrigerant is then fed to an intermediate pressure throttle device controlled by the controller, in which the refrigerant is expanded to an intermediate pressure ZD. The refrigerant expanded to the intermediate pressure ZD is fed into a refrigerant collector, wherein the refrigerant is led in liquid form from the collector to a low pressure throttle device controlled by the controller, with which the refrigerant is expanded to a low pressure ND. The refrigerant at the low pressure ND is evaporated in an evaporating heat exchanger.

[0003] DE 101 03 150 B4 shows a ventilation system with a first heat exchanger supplied with an outside air flow. The first heat exchanger is an air-to-air heat exchanger in which heat energy is transferred from an exhaust air flow from rooms to be heated to the outside air flow. A second heat exchanger is provided, through which the outside air flow supplied to the first heat exchanger is guided. The second heat exchanger is supplied with the refrigerant of a heat pump in order to keep the first heat exchanger free of frost and / or ice. The second heat exchanger is supplied with condensed refrigerant from the heat pump circuit of the heat pump, which is heated by sensible heat of the condensed refrigerant.

[0004] EP 2 664 868 B1 shows a heat pump device comprising a compressor, a condenser, a first heat exchanger, an electronic expansion valve, and a four- / two-way valve arranged in a refrigeration circuit. The first heat exchanger has a first refrigerant line for absorbing heat through evaporation of the refrigerant and a second refrigerant line for releasing heat through subcooling of the liquid refrigerant. It also has a plurality of fins and a defrost tray. At least one of the fins has an extension at its ends, which serves to accommodate the second line, which is part of the refrigeration circuit and is designed as a defrost coil in which liquid refrigerant flows and is used to heat the defrost tray.

[0005] The object of the invention is to improve the coefficient of performance (COP) of the heat pump by making better use of the properties of the refrigerant. In particular, a further object of the invention is to achieve optimal use of environmental energy by using a flammable refrigerant such as R290.

[0006] The invention provides a solution for this by operating a heat pump with the features of claim 1. Preferred embodiments of the invention are defined in the dependent claims.

[0007] The method for operating the heat pump with a vapor compression system is carried out by determining a first manipulated variable ES for the intermediate pressure throttle element, through which the refrigerant flows after the condensing heat exchanger. The first manipulated variable ES is determined as a function of a subcooling deviation of an actual subcooling value from a target subcooling value of the refrigerant at an outlet of the condensing heat exchanger. A second manipulated variable ZS is determined for the intermediate pressure throttle element, through which the refrigerant flows after the condensing heat exchanger, as a function of at least one process value of the vapor compression system, which is processed in a stored calculation model to form the second manipulated variable ZS.The first manipulated variable ES is linked to the second manipulated variable ZS to determine a setpoint value for setting the intermediate pressure throttle element through which the flow passes after the condensing heat exchanger to the setpoint value S ST .

[0008] The refrigerant mass flow is also advantageously influenced by the low-pressure throttle valve. Changes in the opening degree of the low-pressure throttle valve influence the low pressure, which also affects the mass flow through the vapor compression system. The mass flow is taken into account when calculating the second manipulated variable, the model-based calculation.

[0009] Advantageously, the method is carried out by driving the refrigerant in a heating mode in a high-pressure flow direction S HD through the condensing heat exchanger, in which the refrigerant transfers heat Q h to a heat transfer medium during condensation. The refrigerant is then passed in the high-pressure flow direction S HD sequentially first through the intermediate-pressure throttle device before being passed to the low-pressure throttle device and then evaporating in the evaporating heat exchanger in an exchange with a source heat QQ.

[0010] Advantageously, the method is carried out by driving the refrigerant in a cooling mode in a high-pressure cooling flow direction S HDK through the condensing heat exchanger, in which the refrigerant transfers the source heat QQ to the heat transfer medium during condensation. Advantageously, in addition to the source heat, the energy input of the compressor is transferred to the refrigerant. The refrigerant is then directed in the high-pressure cooling flow direction S HDK to the intermediate-pressure throttle device, then to the low-pressure throttle device, and then into the evaporating heat exchanger, where the refrigerant evaporates upon exchange with the heat Q h.

[0011] The receiver advantageously stores a mass of liquid refrigerant that should not remain in the condensing heat exchanger. Active refrigerant, which participates in particular in thermal processes in the vapor compression system, is also located in the evaporating heat exchanger, the compressor, and any internal heat exchanger that may be provided. The receiver thus serves as a buffer storage for refrigerant not required for the thermal processes.

[0012] According to one concept of the invention, subcooling in the condenser is influenced or regulated by changing the refrigerant level, and in particular, refrigerant not required in the condensing heat exchanger is collected in the receiver. On the other hand, the refrigerant available in the receiver also serves as a reservoir to supply refrigerant to the condensing heat exchanger depending on the operating mode, in particular heating mode or cooling mode, with the level in the condensing heat exchanger being varied. In principle, the level in the receiver advantageously decreases when the level in the condensing heat exchanger rises, and vice versa.

[0013] According to a further idea of ​​the invention, the high pressure HD of the refrigerant is measured, a condensation temperature T Kd is calculated with the measured high pressure HD from a vapor pressure curve of the refrigerant, a refrigerant temperature T KA is measured at the outlet of the condensing heat exchanger and the actual subcooling value U i of the refrigerant is determined from a difference between the refrigerant temperature T KA and the condensation temperature T Kd.

[0014] Advantageously, the target subcooling value U s is determined, at least in heating mode, as a function of process values ​​PW of the vapor compression system, wherein the target subcooling value U s is set at least as a function of a heat transfer medium temperature difference. The heat transfer medium temperature difference is determined from a flow temperature and a return temperature of the heat transfer medium, wherein the target subcooling value U s is set to 50% to 110% of the heat transfer medium temperature difference, particularly advantageously between 70% and 90%, in particular approximately 80%.

[0015] In particular, the target subcooling value Us is changed by adding an offset subcooling value Uo.

[0016] Advantageously, the target subcooling value Us is applied within a specific range of the heat transfer medium temperature difference. Another advantageous embodiment is that the offset subcooling value Uo is non-linear and / or determined by a function.

[0017] A general target subcooling value is always advantageously calculated and regulated by the control system.

[0018] Advantageously, the setpoint control value SST is calculated from the first control variable ES and the second control variable ZS, wherein in a first step an offset opening degree is subtracted from the second control variable ZS, namely a theoretical opening degree of the expansion valve, to obtain an offset-adjusted theoretical opening degree. In a second step, the offset-adjusted theoretical opening degree from the first step is multiplied by the first control variable ES to obtain an offset-adjusted control value. In a third step, the offset-adjusted control value from the second step and the offset opening degree are added, thus achieving a constant control loop gain in the working range of the throttle element through which the flow flows after the condensing heat exchanger.

[0019] It is advantageous to set the heat transfer medium temperature difference to a predetermined range between 4 K and 15 K, particularly advantageously between 7 K and 13 K and especially between 9 K and 11 K.

[0020] The target subcooling value U s is set in particular between approximately 5 K and 10 K, in particular approximately 8 K and furthermore particularly advantageously between 6 K and 9 K.

[0021] For a given spread between 4 K and 15 K, the target subcooling value U s is set, in particular, between approximately 3 K and 13 K, in any case such that the target subcooling value U s is set at a ratio of less than 1 to the heat transfer medium temperature difference. For a heat transfer medium temperature difference of approximately 10 K, in particular, the target subcooling value U s is set to approximately 8 K. Thus, the target subcooling value Us is approximately 80% of the heat transfer medium temperature difference. Percentage values ​​of the target subcooling U s between 70% and 90% have also proven advantageous.

[0022] In an advantageous method, a filling quantity of refrigerant in the condensing heat exchanger, in particular in heating mode, is advantageously set between a minimum filling quantity of approximately 0.5% and a filling quantity of 80%, depending on a heating output, the target subcooling d TUKsoll , the high pressure HD and a contour of the condensing heat exchanger, in particular contours of internal heat transfer surfaces to which the refrigerant adheres.

[0023] Advantageously, the charge quantity takes into account the adhesion of refrigerant to the internal heat transfer surfaces of the condensing heat exchanger, which is particularly determined by the design of the respective first heat exchanger or second heat exchanger, depending on which of the heat exchangers operates as a condensing heat exchanger. This preferably records a quantity of refrigerant that accrues when liquid refrigerant drains or that adheres to the internal heat transfer surfaces of the evaporating heat exchanger when refrigerant condenses in the zone above a liquid level of the liquid refrigerant. These quantities are determined in particular through tests and then taken into account when determining a charge quantity according to process values ​​PW with a parameter for the adhesion of refrigerant.

[0024] According to one concept of the invention, experiments are conducted to determine how much refrigerant needs to be backed up at which operating point of the heat pump to achieve the desired target subcooling, and to what degree of opening of the intermediate pressure expansion valve this can be achieved. The dependence of this opening degree on the respective refrigerant circuit process values ​​is then taken into account in the model calculation.

[0025] According to a further aspect of the invention, the target subcooling value U s is changed depending on at least one operating limit of at least one component of the vapor compression system. In particular, the operating limit is monitored and maintained with respect to a minimum or maximum permissible operating pressure of the vapor compression system, whereby, in particular, an optimum efficiency is deviated from in order to maintain the operating limit. Operating limits are defined, in particular, by design values.

[0026] In particular, the permissible operating range of the compressor has limit temperatures and / or limit pressures that are specified to be adhered to as operating limits. Accordingly, the specified design ranges of the compressor's limit temperatures and / or limit pressures must not be exceeded. Therefore, the optimum efficiency of the vapor compression system is more important than preventing the compressor from being destroyed or impaired, or, advantageously, protecting other components of the vapor compression system.

[0027] Furthermore, there are advantageous specifications for maximum and minimum values ​​for compressor operation, such as a minimum temperature, in particular the minimum oil temperature, which advantageously correlates with the oil pan or housing temperature of the compressor, and also a minimum pressure. Maximum and minimum temperatures are also specified - design parameters and operating limits of the compressor. Especially with compressors, function is therefore permitted within a temperature and / or pressure range, in addition to minimum and maximum speed limits. The maximum and minimum design temperatures depend in particular on the design of the compressor and the oil used. For reliable operation of the compressor, especially of the valves or inlet and outlet devices, a minimum pressure on the low-pressure side and a minimum pressure on the high-pressure side are required.Maximum design pressures should not or must not be exceeded and minimum design pressures should not or must not be undercut.

[0028] The condensing and evaporating heat exchangers, or other components, also advantageously have design values ​​or design ranges that must or should be adhered to, and deviations from these design values ​​or design ranges should not be permitted. Just as with the compressor, the principle is to protect the entire vapor compression system and / or its components from overload beyond an optimum efficiency.

[0029] According to one idea of ​​the invention, the target subcooling value U s is increased when the refrigerant pressure in the high-pressure range approaches a minimum high pressure HD min, in particular approx. 1 bar, so that the minimum high pressure HD is definitely not undercut, wherein the high pressure is advantageously increased by approx. 1 bar or less at an HD min limit.

[0030] In particular, a minimum differential pressure of approximately 1 to 3 bar, and preferably approximately 2 bar, must be achieved across the compressor, especially so that a metal blade, an outlet valve of the compressor, is closed in a rotary piston compressor. In particular, the metal blade must reliably close the outlet opening with the minimum differential pressure after the compressed refrigerant has been expelled from the compression chamber.

[0031] In an advantageous embodiment of a rotary piston compressor, the inlet is open—the piston closes the opening. Rotary piston compressors typically do not use a conventional inlet valve, but rather a cavity whose position and volume are variable, sealed by the rotary piston position.

[0032] If the minimum differential pressure is not achieved with optimal subcooling or optimal actual subcooling U i, then according to one concept of the invention the target subcooling value U s is increased. Coordinating the high pressure HD and the subcooling U i advantageously leads to an optimum. If application limits such as the minimum or maximum operating pressure are reached or are in danger of being reached, then the efficiency optimum is deviated from. With regard to the maximum design pressure, it is monitored how much the pressure increases and / or whether there is a risk that the maximum design pressure will be reached or exceeded. On the other hand, with regard to the minimum design pressure, it is preferably monitored how far the pressure drops and whether there is a risk that the minimum design pressure will be reached or undercut.Advantageously, the target subcooling value U s is reduced when the refrigerant pressure in the high-pressure range approaches a maximum high pressure HD max, in particular approximately 1 bar, so that the high pressure HD remains safely below the high pressure HD max.

[0033] Furthermore, it is proposed to change or activate parameters for the heat pump's operation when the high pressure (HP) is within approximately 1 bar of the maximum high pressure. The parameters are then modified, particularly with a P controller, to contain, limit, or reduce the high pressure (HP).

[0034] According to a further aspect of the invention, the target subcooling value U s is increased when the refrigerant pressure in the high-pressure range approaches a minimum high pressure H Dmin, in particular in a range of less than approximately 1 bar, so that the high pressure HD remains safely above the minimum high pressure H Dmin.

[0035] It is advantageous to reduce the target subcooling value U s depending on a medium temperature difference, calculated from the flow temperature of the heating medium and the condensation temperature T Kd of the refrigerant. The target subcooling value U s is reduced if the flow-side temperature difference, calculated from the flow temperature and the condensation temperature T Kd, exceeds a specified value.

[0036] On the one hand, the condensing heat exchanger should contain as much refrigerant as possible, but not too much liquid refrigerant, so that sufficient condensation surface is available. This resolves the discrepancy between, on the one hand, as much refrigerant as possible in the condensing heat exchanger, but, on the other hand, not too much liquid refrigerant in the condensing heat exchanger, so that sufficient condensation surface is available for the refrigerant in the condensing heat exchanger.

[0037] The discrepancy is advantageously achieved with a refrigerant quantity set for the respective operating point of the heat pump, which ensures an overall efficiency optimum through at least sufficient refrigerant to achieve a sufficiently high efficiency-promoting subcooling, but not too much refrigerant to increase a condensation temperature increase that reduces the efficiency.

[0038] When the condensing heat exchanger, vapor compression system, or compressor is at high performance, the surface area of ​​the condensing heat exchanger for condensation is increased by lowering the level. In an extreme case, it is advantageous to retain no, almost no, or as little liquid refrigerant as possible in the condensing heat exchanger in order to provide as much condensation surface area as possible for a high performance of the vapor compression system. The level is then particularly close to zero or zero. This undesirable increase in the condensation temperature is particularly detected when the condensation temperature T Kd rises significantly above the flow temperature. For physical reasons, liquid refrigerant components may remain adhering to the surfaces of the condensing heat exchanger, even when the level is zero or close to zero.

[0039] The heat transfer surface of the condensing heat exchanger is the heat transfer surface at which condensation of refrigerant can take place in the condensing heat exchanger.

[0040] This advantageously results in a high or increasing temperature difference between the flow temperature and the condensation temperature of the refrigerant due to a heat transfer surface where condensation occurs that is too small for the transferred power. The heat transfer surface where condensation can occur is advantageously increased by reducing the refrigerant level, thus lowering the condensation temperature of the refrigerant.

[0041] Advantageously, at least one of the following measured variables MG and / or process values ​​PW or control values, in particular the target subcooling U s as a control value, is included in the calculation model: the refrigerant mass flow, advantageously from the high pressure HD, the low pressure ND and the compressor speed determines the target subcooling U s an offset value of the throttle element a refrigeration circuit-specific constant at least one exponent as a refrigeration circuit-specific variable the high pressure HD the low pressure ND or the compressor speed VD.

[0042] Three genera are defined according to an idea of ​​the invention as follows: Control values ​​or controller values ​​are quantities calculated by the controller(s) and do not directly correspond to measured variables MG, which, for example, contain a proportional component, an integral component, and / or a pilot control component. Constants describe physical properties of the components, such as the refrigerant density, from which a volume flow can then be converted into a mass flow. Measured variables MG from the vapor compression circuit are process values ​​PW that are recorded directly by sensors in the vapor compression circuit, such as temperatures, pressures, or speeds.

[0043] The more refrigerant is backed up in the condensing heat exchanger acting as a condenser, the less condensation surface is available for the condensing refrigerant and as a result the high pressure HD increases and the subcooling U i increases and vice versa.

[0044] In an advantageous embodiment, the refrigerant mass flow is calculated from refrigerant circuit process values ​​PW, in particular from the low pressure ND, the high pressure HD and the compressor speed VD.

[0045] In particular, the high pressure HD is used to determine the subcooling value U i at the outlet of the condensing heat exchanger using a pressure drop compensation to produce a corrected high pressure HD k, particularly when the location of the high pressure detection is not located at the location of the measuring point for measuring the subcooling value U i. In heating mode, the refrigerant temperature is advantageously measured with the third temperature sensor downstream of the heat exchanger condensing in heating mode and in cooling mode with a fourth temperature sensor in the flow direction downstream of the heat exchanger condensing in cooling mode to calculate the actual subcooling.

[0046] If the subcooling of the refrigerant is to be measured and / or controlled during cooling operation, it is advantageous to use the fourth temperature sensor, downstream of the heat exchanger condensing during cooling operation.

[0047] In particular, between the second throttle device and the second heat exchanger, the subcooling temperature of the refrigerant, in particular that of the subcooled liquid refrigerant, is measured in cooling mode and the pressure drop compensation is calculated using a corresponding value.

[0048] With the help of the corrected high pressure HD k, a subcooling value U i is advantageously determined after the first or second condensing heat exchanger acting as a condenser.

[0049] According to a further consideration, a heating pressure drop compensation value is calculated when the vapor compression system is operated in heating mode, a cooling pressure drop compensation value is calculated when the vapor compression system is operated in cooling mode and with the heating pressure drop compensation value or the cooling pressure drop compensation value, the subcooling value U i is corrected after the condensing heat exchanger.

[0050] Advantageously, the subcooling value U i is thus indirectly corrected by first correcting the high pressure value and then calculating the actual subcooling value from the corrected high pressure value and the temperature of the subcooled refrigerant.

[0051] Advantageous process steps involve measuring the high pressure HD in the high pressure path of the vapor compression circuit, particularly in the high pressure flow direction downstream of the compressor. The condensation temperature TK d is calculated using the measured high pressure HD and a pressure drop correction value from a conveniently stored vapor pressure curve. The pressure drop correction value measures a pressure difference caused by a pressure drop in the condensing heat exchanger between the actual pressure measuring point and the point at which the temperature of the subcooled refrigerant is measured, advantageously directly downstream of the compressor. A corrected high pressure HD k is calculated based on the model, as it prevails in the high pressure flow direction downstream of the condensing heat exchanger.

[0052] In heating mode, a refrigerant temperature T KA is advantageously further measured between the condensing heat exchanger and the intermediate pressure throttle device, and the actual subcooling value U; of the refrigerant is determined from the difference between the refrigerant temperature T KA and the condensation temperature T Kd. In cooling mode, the refrigerant temperature T KA is advantageously further measured between the then condensing heat exchanger and the throttle device, which then functions as an intermediate pressure throttle device, and the actual subcooling value U i of the refrigerant is determined from the difference between the refrigerant temperature T KA and the condensation temperature T Kd.

[0053] Furthermore, a calculation model for the pressure drop correction value with at least one real process value PW of the vapor compression cycle is advantageously proposed as a possible embodiment.

[0054] The pressure drop correction value advantageously represents a model-based calculated pressure difference between the high pressure HD at the respective high pressure detection location and the high pressure present at the temperature detection location of the refrigerant temperature T KA. Furthermore, the actual subcooling value Ui of the refrigerant is advantageously determined from the difference between the refrigerant temperature T KA and the pressure difference-corrected condensation temperature T Kd.

[0055] In a first process step, a non-measured mass flow is calculated model-based, in particular from measurable variables of the vapor compression cycle, which are advantageously real process values ​​PW or measured variables MG.

[0056] A speed parameter advantageously determines the influence of the speed on the compressor's volumetric efficiency as a function of the compressor speed, thus taking into account a decrease in volumetric efficiency with increasing compressor speed, which allows a mass flow value to be calculated that is at least dependent on the compressor speed. A high-pressure parameter advantageously also takes into account the influence of the high pressure on the mass flow value, which can be linear or non-linear.

[0057] According to a further aspect of the invention, in a second method step, this calculated mass flow value is used for the model-based calculation of the pressure drop correction value. In particular, the pressure drop correction value refers to the pressure drop of the refrigerant between the high-pressure sensor, advantageously in the immediate vicinity of a refrigerant outlet from the compressor, and a location in the high-pressure flow direction upstream of the intermediate-pressure throttle device or downstream of the condensing heat exchanger.

[0058] According to one concept of the invention, the dependency can be mathematically linear or nonlinear. This takes into account the dependency of the pressure drop on the mass flow and, furthermore, advantageously also the dependency of the pressure drop on the high pressure (HD) itself.

[0059] According to a further advantageous idea, the first and second process steps are converted into a formula.

[0060] It is also advantageous to represent the process steps in a computer program, in particular supported by a system with artificial intelligence.

[0061] In an advantageous implementation, three process values ​​PW such as the low pressure ND, the high pressure HD and the compressor speed VD are used to calculate the pressure drop correction value.

[0062] To reduce the number of process values ​​PW that flow into the first and second method steps or into the formula, according to another concept of the invention, individual process values ​​are replaced by representative constants, at least partially, or at least one process value is replaced. These are advantageously selected such that, within a possible operating condition value range, they approximately correspond to an average process value or a statistically frequently occurring process value. However, the calculation error increases, particularly when replacing process values ​​PW with one or more constants, which is acceptable as long as the accuracy is sufficient.

[0063] The operating condition value range refers to a process value PW and the range of values ​​this process value can assume during heat pump operation. For a process value, an operating condition value range is a selected process value or a favorable range of values ​​that can be continuously determined or determined in advance from tests and empirical values, e.g., in the laboratory or during operation.

[0064] According to a further idea of ​​the invention, the first manipulated variable ES is calculated as a factor which is influenced by a control component such as a proportional component and / or an integral component and / or a differential component as a function of the subcooling deviation Ua.

[0065] A method comprising the method steps of calculating the setpoint control value SST from the first control variable ES and the second control variable ZS is also advantageous. In a first step, an offset opening degree is subtracted from the second control variable ZS, namely advantageously a theoretical opening degree of the intermediate pressure throttle element, to obtain an offset-adjusted result. In a second step, the offset-adjusted result from the first method step is multiplied by the first control variable ES to obtain a corrected result and is also used to calculate the setpoint control value SST.

[0066] In a third step, the corrected result from the second process step is advantageously added to the offset opening degree and the setpoint value SST is calculated, whereby a constant control loop gain is achieved in the working range after the condensing heat exchanger.

[0067] Advantageously, a device is equipped with the first heat exchanger, the compressor, the evaporating heat exchanger and at least the intermediate pressure throttle device, the refrigerant collector, the low pressure throttle device and the regulator.

[0068] According to one concept of the invention, the controller is equipped with a first determination unit for determining the first manipulated variable ES for the one or at least one intermediate-pressure throttle element as a function of the deviation of an actual subcooling value U i of the refrigerant from a target subcooling value U s of the refrigerant when the refrigerant exits the condensing heat exchanger. The controller further comprises, or is connected to, a unit for determining measured variables MG for feeding into a calculation model for the second manipulated variable ZS for the intermediate-pressure throttle element.

[0069] A controller computing unit is advantageously provided for model-based calculation of the second manipulated variable ZS for the intermediate pressure throttle element using the calculation model from the determined measured variables MG and vapor compression system-specific variables. In one advantageous embodiment, specific variables are the density of the refrigerant at a specific refrigerant pressure, also called volumetric data. For propane, a specific volumetric value of 2.02 kg / m 3 at 1 bar and 0 °C is advantageously included in the calculation when determining the compressor mass flow.

[0070] A second determination unit of the controller is advantageously provided for determining a third control value DS for the first throttle element by linking the first control value ES with the second control value ZS and an actuating unit for setting the first throttle element to the third control value DS.

[0071] The vapor compression system can optionally be equipped with a changeover valve, as a four-way valve or with a changeover device consisting of several valves or actuating units, as described in the Figure 1 , 2 , 3 and 4 The switching valve switches the vapor compression system between a heating mode and a cooling mode. The switching valve is located downstream of the compressor in the high-pressure flow direction.

[0072] It is also advantageous to have a switching path of the switching valve connected on the suction side after the compressor and a switching path is advantageously connected on the pressure side of the compressor.

[0073] In heating mode, it is advantageous to set a switching position of the switching valve in which the switching valve is switched so that the first heat exchanger, which operates as a condensing heat exchanger in heating mode, is connected to the compressor in the flow direction. The high-pressure refrigerant therefore flows from the compressor to the first heat exchanger in heating mode. In this circuit, the first throttle element serves as an intermediate-pressure throttle element, and the second throttle element serves as a low-pressure throttle element. The second heat exchanger follows the second throttle element and operates as an evaporating heat exchanger in heating mode.

[0074] Furthermore, it is advantageous to switch the switching valve from heating mode to cooling mode when defrosting of the second heat exchanger is required. In heating mode, the second heat exchanger can become icy at temperatures below approximately 7°C. When icing is detected, the switching valve is moved to the cooling mode position, and the second heat exchanger, which operates as an evaporating heat exchanger in heating mode, is defrosted in defrost mode, which corresponds to the cooling mode circuit. Defrosting is advantageously determined by a defrost requirement signal and a defrost end signal, in which the system is operated in cooling mode for defrosting.

[0075] In cooling mode, it is also advantageous to set a switching position of the switching valve in which the switching valve is switched so that the second heat exchanger, which operates as a condensing heat exchanger in cooling mode, is connected to the compressor in the direction of refrigerant flow. The high-pressure refrigerant then flows from the compressor to the second heat exchanger. In this circuit, the second throttling element is used as an intermediate pressure throttling element and the first throttling element as a low pressure throttling element. The first heat exchanger follows the first throttling element in the direction of refrigerant flow and operates as an evaporating heat exchanger in cooling mode. The controller is suitable for selecting the switching position for cooling mode or heating mode.

[0076] According to one concept of the invention, the controller is suitable for operating the first throttle valve as an intermediate pressure throttle valve in heating mode and also for using the temperature or pressure sensors as described for heating mode. In particular, the controller uses the third temperature sensor in heating mode to measure the refrigerant temperature at the high pressure (HD). The second throttle valve is operated by the controller as a low-pressure throttle valve in heating mode. The controller sets the changeover valve to the heating mode position.

[0077] In cooling mode, the controller is advantageously designed to operate the second throttle as an intermediate pressure throttle and also uses the corresponding temperature or pressure sensors, as described for cooling mode. In cooling mode, the controller uses the fourth temperature sensor to measure the refrigerant temperature at the high pressure (HD). The first throttle is operated by the controller as a low pressure throttle. The controller sets the changeover valve to the cooling mode position.

[0078] The same operation as in cooling mode is advantageously carried out by the controller when a defrost operation is used, especially with a circuit reversal.

[0079] In defrosting mode, according to one idea of ​​the invention, the valves are not controlled for overheating or subcooling, but are operated to maintain a minimum pressure difference in the high pressure and / or in the low pressure to maintain a minimum low pressure value.

[0080] According to one idea of ​​the invention, in order to ensure the minimum differential pressure required to protect the outlet valve of the rotary piston compressor, the target subcooling value Us is increased compared to the default value calculated with regard to an efficiency optimum.

[0081] The figures show in Figure 1 shows the vapor compression system with the collector and the intermediate heat exchanger, with the switching valve switched to a "heating" operating mode. Figure 2 shows the vapor compression system with the collector and the intermediate heat exchanger, with the switching valve switched to a "cooling" operating mode. Figure 3 shows the vapor compression system with an intermediate heat exchanger integrated in the collector, with the switching valve switched to the "heating" operating mode. Figure 4 shows the vapor compression system with the collector, with the switching valve switched to the "heating" operating mode. Figure 5 shows the vapor compression system with the collector in the "heating" operating mode. Figure 6 shows a block diagram with units of the controller. Figure 7 shows a state diagram of a refrigerant. Figure 8 shows a diagram of the target subcooling relative to a temperature difference. Figure 9 shows a diagram of the target subcooling relative to a temperature difference.

[0082] A heat pump 100 includes a vapor compression system 200 as shown in Figure 1and is operated here in a heating mode. The vapor compression system 200 includes a compressor 210, a first heat exchanger 220, a first throttle element 230, a second throttle element 235, a second heat exchanger 240, an intermediate heat exchanger 250, a refrigerant collector 260, and a changeover valve 270. The compressor 210 has a compressor inlet 211 and a compressor outlet 212. The first heat exchanger 220 is operated as a condensing heat exchanger in heating mode and is designed as a condenser in which the refrigerant can be liquefied and preferably subcooled. It is further equipped with a first refrigerant connection 221 and a second refrigerant connection 222. The first heat exchanger 220 is connected to a heat sink system 400 with a heating medium inlet 401 and a heating medium outlet 402.The heat sink system 400 further comprises a heating medium pump 410, with which a heating medium is circulated in a heating medium flow direction S w.

[0083] In the heating mode shown, the first throttle element 230 is configured as an intermediate pressure throttle element, in which the refrigerant is expanded from the high pressure HD to the intermediate pressure ZD. A first throttle connection 231 and a second throttle connection 232 are provided on the first throttle element 230.

[0084] A third refrigerant connection 241 and a fourth refrigerant connection 242 are provided on the second heat exchanger 240. The second heat exchanger 240 is operated as an evaporating heat exchanger in heating mode and is designed as an evaporator in which the refrigerant is evaporated.

[0085] A first recuperator port 251 and a second recuperator port 252 are included on the intermediate heat exchanger 250. A first intermediate heat exchanger port 253 and a second intermediate heat exchanger port 254 are further attached to the intermediate heat exchanger 250. "Recuperator" and "intermediate heat exchanger" are different terms for the functionally identical component 250.

[0086] In heating mode and cooling mode, and advantageously also in defrosting mode, an intermediate pressure path is formed between the first recuperator connection 251 and the recuperator connection 252. A low-pressure path is then formed between the first intermediate heat exchanger connection 253 and the second intermediate heat exchanger connection 254.

[0087] In the exemplary embodiment, a fourth temperature sensor 510 is provided and suitable for measuring the temperature of the refrigerant at a high pressure (HD) during cooling operation as it exits the heat exchanger condensing during cooling operation and transmitting it to the controller. The controller is suitable for using the fourth temperature sensor during cooling operation to measure the temperature of the refrigerant at a high pressure (HD).

[0088] In addition to these components or parts of the vapor compression system 200, a heat source system 300 is provided. The heat source system 300, with a source medium inlet 320 and a source medium outlet 310, serves to exchange heat from a source medium with the refrigerant, whereby energy from the heat source system 300 is exchanged with the vapor compression system 200. In the case of air as a source medium, a fan serves to drive the source medium in a source medium flow direction SQ through the second heat exchanger 240. In the case of brine or water in particular, a brine pump 330 is provided.

[0089] In heating mode, energy is transferred from the source medium to the refrigerant in the second heat exchanger, thus evaporating the refrigerant in the second heat exchanger, which operates as an evaporating heat exchanger in heating mode. The controller treats the first heat exchanger as a condensing heat exchanger in heating mode.

[0090] In cooling mode, energy is transferred from the refrigerant to the source medium, thus condensing the refrigerant in the second heat exchanger, which operates as a condensing heat exchanger in cooling mode. The controller treats the second heat exchanger as a condensing heat exchanger in cooling mode.

[0091] If the changeover valve 270 is in the operating position "Heating" - heating mode - as shown in Figure 1As shown, the vapor compression system 200 absorbs source energy QQ from the heat source system 300. The refrigerant evaporates in the second heat exchanger 240, which is operated as an evaporating heat exchanger in heating mode, and is then passed on to the intermediate heat exchanger 250 before the refrigerant flows into the compressor 210 or is sucked in by it. On the way from the second heat exchanger 240, the evaporating heat exchanger in heating mode, to the compressor 210, the temperature of the refrigerant is determined using a second temperature sensor 508 upstream of the intermediate heat exchanger 250. In the exemplary embodiment, temperature data and pressure data of the refrigerant are transmitted via a bus system 560 or wirelessly.

[0092] Analog measured variables MG, or also called measured values, can also advantageously be fed to the controller 500, in particular by means of individual lines assigned to the respective sensor / actuator.

[0093] In the intermediate heat exchanger 250, heat is transferred from the refrigerant in its high-pressure path to the refrigerant in its low-pressure path. Before the refrigerant enters the compressor 210, downstream of the intermediate heat exchanger 250, the temperature of the refrigerant is measured with a compressor inlet temperature sensor 501, and the pressure of the refrigerant is determined upstream of the compressor 210 with a low-pressure sensor 502. In the compressor 210, the refrigerant is then increased in pressure, or compressed, to high pressure (HD).

[0094] The condition of the refrigerant is measured in the flow direction S HD downstream of the compressor 210 using a high-pressure sensor 503 and a hot-gas temperature sensor 504. This refrigerant data is also preferably transmitted to the controller 500 via the bus system 560. The refrigerant flows in the high-pressure flow direction S HD via the switching valve 270 to the first heat exchanger 220, which is operated as a condensing heat exchanger, and releases heat to a heat sink system 400 in the "heating" operating mode through hot-gas desuperheating, condensation, and preferably subcooling.

[0095] The heat sink system 400 can, in particular, be a hot water system via an apartment station, a hot water tank, or even a conventional building heating system. In the first heat exchanger 220, the temperature of the refrigerant is significantly reduced. The first heat exchanger 220 used here is designed as a condensing heat exchanger such that it can accommodate liquefied refrigerant, which can also be further subcooled in the first heat exchanger 220, i.e., brought to temperatures below the condensation temperature. Thus, the first heat exchanger 220 is suitable for accommodating liquid refrigerant at different levels or different masses or volumes of liquid refrigerant.

[0096] In heating mode, the liquefied and preferably subcooled refrigerant flows from the first heat exchanger 220 through the second refrigerant connection 222 to the first throttle device 230. The refrigerant temperature at high pressure HD is measured or detected between the second refrigerant connection 222 and the first throttle connection 231 using the third temperature sensor 509. The first throttle device 230, which operates as an intermediate pressure throttle device in heating mode, expands the refrigerant to the intermediate pressure ZD.

[0097] Further, in an intermediate-pressure flow direction S ZD , the refrigerant at the intermediate pressure ZD flows past the first throttle element 230 to the refrigerant collector 260 and enters the refrigerant collector 260 through a first collector connection 261. There, a liquid volume 264 or a mass of refrigerant can accumulate at a variable level 263. Refrigerant collects or remains in the refrigerant collector 260, preferably with a liquid phase and an associated volume or mass and / or a partially gaseous phase above the liquid phase. Through a second collector connection 262, the liquid refrigerant flows out of the refrigerant collector 260 again through the recuperator 250.Before the recuperator 250, a first intermediate pressure refrigerant temperature T ZDeZD is measured with a fifth temperature sensor 505 and after the recuperator 250, a second intermediate pressure refrigerant temperature T ZDz is measured with a sixth temperature sensor 506 and sent to the controller 500 via bus 560.

[0098] The refrigerant, still at the intermediate pressure ZD, now flows into the second throttle element 235, which is operated as a low-pressure throttle element in heating mode. The second throttle element 235 has a third throttle connection 236 and a fourth throttle connection 237. In the second throttle element 235, the refrigerant is expanded to the low pressure ND in heating mode, flows further in a low-pressure flow direction S ND into the second heat exchanger 240, which is operated as an evaporating heat exchanger in heating mode, absorbs energy, and evaporates—a cycle in the vapor compression system 200 is closed.

[0099] In Figure 2the vapor compression system 200 is switched to a cooling mode by means of the switching valve 270. The refrigerant at high pressure HD flows in the high pressure flow direction S HD from the compressor 210 to the switching valve 270 and from there in a high pressure cooling flow direction S HDK to the second heat exchanger 240, which is operated as a condensing heat exchanger in the cooling mode. Heat, in this cooling mode this is the source energy QQ, is transferred from the refrigerant to the heat source system 300 in the second heat exchanger 240. In an air-water heat pump, energy is thus transferred to the air, and in a brine-water heat pump, energy is transferred to the brine. Furthermore, the refrigerant is expanded from the high pressure HD to the intermediate pressure ZD in the second throttle element 235, which is operated as an intermediate pressure throttle element by the controller 500 in the cooling mode.After the second throttle element 235, the refrigerant at the intermediate pressure ZD flows through the high-pressure path of the intermediate heat exchanger 250 and then through the refrigerant collector 260 to the first throttle element 230, which in cooling mode is operated by the controller 500 as a low-pressure throttle element and where the refrigerant is further expanded to the low pressure ND. In a low-pressure cooling flow direction S NDK, the refrigerant flows on to the first heat exchanger 220, which in cooling mode is operated as an evaporating heat exchanger, and heat energy QH is absorbed by the heat sink system 400. In cooling mode, the heat energy Qh is transferred from the refrigerant to the heat source medium. It should be noted that the heat source medium is more advantageously referred to as the medium from which energy is transferred to the refrigerant circuit as a heat source.What is meant here in particular is that in cooling mode, heat is extracted from the house's heating system and transferred to the refrigerant.

[0100] In the low-pressure cooling flow direction S NDK, the switching valve 270 is also connected through which the refrigerant flows to the compressor 210, wherein the intermediate heat exchanger 250 is connected between the first heat exchanger 220, which operates as an evaporating heat exchanger in the cooling mode, and the compressor 210.

[0101] A first opening of a first tube 265 and a second opening 266 of a second tube are arranged at the same level in the collector. Thus, refrigerant is introduced and discharged at the same level in both cooling and heating modes.

[0102] It is important that the discharge of liquid refrigerant can take place even at low levels and therefore the openings of the pipes are preferably arranged at a low height

[0103] Fig. 3 shows one, largely to the in Fig. 1 The vapor compression cycle 200 described in the heating mode is similar to the one described above, with the intermediate heat exchanger 250 integrated into the refrigerant receiver 260. The intermediate heat exchanger 250 is surrounded by liquid refrigerant in the refrigerant receiver 260 corresponding to the level 263. Thus, the recuperator 250 is advantageously immersed in the liquid refrigerant to the same level as the refrigerant level 263. The intermediate heat exchanger 250 here is the low-pressure refrigerant path of the "recuperator" or intermediate heat exchanger 250.

[0104] The immersion depth of the low-pressure path of the intermediate heat exchanger 250 advantageously approximately equals the level of the high-pressure side of the intermediate heat exchanger 250, in particular if the low-pressure refrigerant path reaches to the bottom of the heat exchanger.

[0105] In the vapor compression system 200, as in Fig. 4As shown, the changeover valve 270 is set to heating. The possible option for a cooling mode is indicated by dashed arrows. This vapor compression system 200 is basically like the Figure 1 The vapor compression system 200 shown is constructed, but without an intermediate heat exchanger. Accordingly, a refrigerant collector 260 is arranged between the second throttle element 235 and the first throttle element 230, but no intermediate heat exchanger.

[0106] The vapor compression system 200 can also be constructed without a switching valve 270. In this case, switching from a heating mode to a cooling mode is not possible, nor vice versa. The embodiment according to Fig. 5shows the heating operating mode. Nevertheless, the vapor compression system 200 has a first throttle element 230, acting as an intermediate pressure throttle element, and a second throttle element 235, acting as a low pressure throttle element. Between the two throttle elements 230, 235, the refrigerant is maintained at the intermediate pressure ZD, a refrigerant pressure that is lower than the high pressure HD and higher than the low pressure ND. A reservoir, particularly for liquid refrigerant, is provided in a collector 260 at a level 263.

[0107] Not shown is the vapor compression system 200 without a switching valve 270 as a cooling system, i.e., in a non-reversible cooling mode. Switching from a cooling mode to a heating mode is not possible, nor vice versa. In such a cooling system, the vapor compression system 200 has a first throttle element 230, as a low-pressure throttle element, and a second throttle element 235, as an intermediate-pressure throttle element. Between the two throttle elements 230, 235, the refrigerant is maintained at the intermediate pressure ZD, a refrigerant pressure that is lower than the high pressure HD and higher than the low pressure ND. The compressor is then connected "inverted" in terms of flow direction relative to the existing figures, and the assignment of the sensors must also be inverted or, equivalently, offset accordingly.

[0108] Figure 6relates to the method for operating a heat pump (100) in heating mode with a vapor compression system (200) in which an at least partially gaseous refrigerant is compressed from the low pressure ND to the high pressure HD by a compressor (210) controlled by a controller (500). The first manipulated variable ES is determined for the first throttle element 230, which is flowed through in the high pressure flow direction S HD downstream of the first heat exchanger 220 and is designed and advantageously operated as an intermediate pressure throttle element, as a function of a subcooling deviation Ua of an actual subcooling value Ui from a target subcooling value Us of the refrigerant at an outlet of the first heat exchanger 220.The subcooling value Ui is determined at least with the aid of the third temperature sensor 509, wherein a temperature measurement value measured with the third temperature sensor 509 is at least one input variable for measuring or determining the subcooling value Ui and advantageously a further input variable is a boiling temperature T HD calculated from the high pressure. A second manipulated variable ZS for the first throttle element 230, through which flow takes place downstream of the first heat exchanger 220 as a liquefied heat exchanger in the refrigerant flow direction, is determined as a function of at least one process value PW of the vapor compression system 200, which is processed in a stored calculation model to form the second manipulated variable ZS.The first manipulated variable ES is linked to the second manipulated variable ZS to determine a setpoint S ST for adjusting the first throttle element 230, through which the refrigerant flows downstream of the first heat exchanger 220, as an intermediate pressure throttle element. The intermediate pressure throttle element is set to the setpoint S ST.

[0109] Figure 6 shows a unit 530 of the controller 500, which records measured variables MG such as the high pressure HD, a low pressure ND, a compressor speed, or another measured variable MG by means of a determination device EP for measured variables MG or process values ​​PW, which are then fed into a computing unit 540 via a feed device ER. Furthermore, in the exemplary embodiment, the target subcooling Us is advantageously transmitted to the computing unit 540.

[0110] In a computing unit 540, the second manipulated variable ZS is determined from the fed-in measured values ​​or measured variables MG and advantageously also the target subcooling.

[0111] The second manipulated variable is forwarded from the computing unit 540 to a control unit 550 of the controller.

[0112] A first determination unit 520 receives data of the target subcooling value Us and data of the actual subcooling value Ui, measured at the outlet of the condensing heat exchanger, or calculates these from temperature difference data, whereby a subcooling deviation Ua is advantageously determined in the determination unit 520.

[0113] From the subcooling deviation Ua, the first control value ES is derived or calculated in the first determination unit 520 and provided by the first determination unit 520 or transmitted to the control unit 550 of the controller.

[0114] The actuating unit 550 detects the first actuating value ES and the second actuating value ZS, which is used to determine a third actuating value DS in the actuating unit. The third actuating value DS is transmitted via a controller output RA to an actuating unit 560, in which a control signal is transmitted from the third actuating value to the intermediate pressure throttle element via a valve control output VA. In a throttle valve controlled by a stepper motor, for example, four control paths of the stepper motor are energized by the valve control output VA. The controller 500 thus controls the intermediate pressure throttle element with the third actuating value DS.

[0115] An isobar is in Figure 7between refrigerant state "2" and refrigerant state "3". Here, the refrigerant is cooled in heating mode at high pressure (HD) from a first high-pressure temperature to a second high-pressure temperature. This occurs in the first heat exchanger 220, the heat exchanger that condenses in heating mode and is operated in a condensing manner. The term "high-pressure temperature" refers to the refrigerant temperature in the high-pressure path. The cooling of the refrigerant occurs in the first heat exchanger 220, initially during desuperheating of the gaseous refrigerant and then during condensation. In the high-pressure flow direction of the refrigerant through the first heat exchanger 220, the refrigerant continuously condenses after desuperheating. In high-pressure (HD) mode, the refrigerant is continuously condensed at the condensation point or at the condensation temperature (TK).Further energy release from the refrigerant then occurs by cooling the liquid refrigerant below the condensation temperature TK, whereby the refrigerant is subcooled in the condensing heat exchanger, which in heating mode is the first heat exchanger 220. The already liquefied refrigerant is further cooled, thus subcooled, by heat transfer to "colder" heat transfer surfaces in thermal contact with the return temperature. This process, known as subcooling, occurs by retaining a quantity of liquid refrigerant down to a certain level in the condenser, the first heat exchanger 220, which is essentially achieved by the first throttle device 230, the intermediate pressure throttle device. According to one concept of the invention, subcooling also occurs simply by heat transfer at the heat transfer surfaces without backflow through the first throttle device 230.In the event of back pressure and an increase in the level, the heat transfer increases and thus the subcooling increases. The degree of this heat transfer to subcool the refrigerant depends on the level of liquid refrigerant in the condensing heat exchanger, because this influences the heat transfer surface between the liquid refrigerant and the heat transfer medium. The desired subcooling is set by a degree of back pressure of the refrigerant in the condensing heat exchanger, which is done in particular with the intermediate pressure throttle element, which in heating mode is advantageously the first throttle element 230 and in cooling mode advantageously the second throttle element 235. In . Figure 7The enthalpy of the refrigerant at the condensation temperature is defined at the point TK where the dashed line meets the high-pressure line HD, which represents the boundary between condensation and subcooling, i.e., the phase transition between wet vapor and liquid. Between "2" and "TK," the first heat exchanger 220 contains gaseous and liquid refrigerant components. Between "TK" and "3," the refrigerant at the high-pressure HD is liquid and remains at the level in the first heat exchanger 220.

[0116] Then, according to the method with the first throttle element 230, the refrigerant is expanded to the intermediate pressure ZD, whereby the refrigerant reaches a refrigerant state "4" and a location of pressure and enthalpy of the KM located in the intermediate pressure circuit is achieved.

[0117] In the case of a refrigerant, its internal state is "located" or defined by pressure (temperature) and enthalpy. In particular, this means that the constellation of pressure and enthalpy represents a refrigerant state during the phase transition between "liquid" and "wet vapor."

[0118] The intermediate pressure ZD is lower than the high pressure HD, and the refrigerant at the intermediate pressure ZD is fed to the refrigerant collector 260. From here, i.e., from the refrigerant state "4," further expansion to the low pressure ND occurs in the second throttle element 235. The refrigerant is then fed at the low pressure ND to the second heat exchanger 240, the evaporating heat exchanger, where the refrigerant evaporates approximately isobarically and is advantageously superheated, from "5" to "1." Ideal, complete isobaric evaporation is rarely achieved in reality, since a pressure drop of up to one bar in the evaporator can sometimes occur due to undesired throttling.

[0119] The level of liquid refrigerant in the condensing heat exchanger, which in heating mode is the first heat exchanger 220, is advantageously determined essentially by the intermediate pressure throttle element, which in heating mode is the first throttle element 230. According to the method, the first throttle element 230 is controlled such that a desired level or mass of liquid refrigerant remains in the condensing heat exchanger, which in heating mode is the first heat exchanger 220.

[0120] The level of liquid refrigerant in the condensing heat exchanger, which is advantageously the second heat exchanger 240 in cooling mode, is advantageously determined essentially by the intermediate pressure throttle element, which is the second throttle element 235 in cooling mode. According to the method, the second throttle element 230 is then controlled by the controller 500 in cooling mode such that a desired level or mass of liquid refrigerant remains in the condensing heat exchanger, which is the second heat exchanger 240 in cooling mode.

[0121] In Fig. 8 The x-axis shows a temperature difference of the heat sink medium, i.e., the heat transfer medium temperature difference delta T, and the y-axis shows the calculated target subcooling Us. Furthermore, an offset subcooling value U offs is shown as an advantageous parallel shift.

[0122] In Fig. 9In addition, a minimum limitation for the target subcooling, thus a minimum offset subcooling value U offsmin, is provided, which in the exemplary embodiment is advantageously limited to 1 K.

Claims

1. A method for operating a heat pump (100) with a vapor compression system (200) in which an at least partially gaseous refrigerant is compressed from a low pressure ND to a high pressure HD by a compressor (210) controlled by a controller (500), the refrigerant is driven through a liquefied heat exchanger operated downstream of the compressor (210), whereby liquefaction of the refrigerant takes place, the refrigerant is fed to an intermediate pressure throttle device controlled by the controller (500), with which the refrigerant is expanded to an intermediate pressure ZD, the refrigerant expanded to the intermediate pressure ZD is fed into a collector (260) for the refrigerant, the refrigerant is fed in liquid form from the collector (260) to a low pressure throttle device controlled by the controller (500), with which the refrigerant is expanded to a low pressure ND,the refrigerant at the low pressure ND is evaporated in an evaporating heat exchanger, comprising the method steps of determining a first control variable ES for the intermediate pressure throttle element through which the refrigerant flows after the condensing heat exchanger, depending on a subcooling deviation U, a an actual subcooling value U i from a target subcooling value U sof the refrigerant at an outlet of the condensing heat exchanger, determining a second control variable ZS for the intermediate pressure throttle element through which the refrigerant flows after the condensing heat exchanger, depending on at least one process value PW of the vapor compression system (200) which is processed in a stored calculation model to the second control variable ZS, linking the first control variable ES with the second control variable ZS to determine a setpoint control value SST, for setting the intermediate pressure throttle element through which the refrigerant flows after the condensing heat exchanger to the setpoint control value S ST .

2. The method according to claim 1, wherein the refrigerant in a heating mode in a high pressure flow direction S HD is driven through the condensing heat exchanger, in which the refrigerant releases heat Q during condensation hwith a heat transfer medium, the refrigerant continues in the high pressure flow direction S HD in sequence is first passed through the intermediate pressure throttle before being passed to the low pressure throttle and then in the evaporating heat exchanger in an exchange with a source heat Q Q evaporated.

3. The method according to claim 1, wherein the refrigerant is in a cooling mode in a high pressure cooling flow direction S HDK is driven through the condensing heat exchanger, in which the refrigerant during condensation releases the source heat Q Q exchanges with the heat transfer medium, the refrigerant in the high-pressure cooling flow direction S HDK is passed to the intermediate pressure throttle device before it is passed to the low pressure throttle device and evaporates in the evaporating heat exchanger in an exchange with the heat Qh.

4. Method according to one of the preceding claims, comprising the following method steps: that the high pressure HD of the refrigerant is measured, a condensation temperature T Kd with the measured high pressure HD is calculated from a vapor pressure curve of the refrigerant, a refrigerant temperature T KA is measured at the outlet of the evaporating heat exchanger and the actual subcooling value U i of the refrigerant from the difference in the refrigerant temperature T KA and the condensation temperature T Kd is determined.

5. Method according to one of the preceding claims, comprising the following method steps: that the target subcooling value U s is determined depending on process values PW of the vapor compression system, whereby the target subcooling value U sat least in heating mode is set depending on a heat transfer medium temperature difference delta T, wherein the heat transfer medium temperature difference delta T is determined from a flow temperature and a return temperature of the heat transfer medium, wherein the target subcooling value U s is set to 50% to 110% of the heat transfer medium temperature difference delta T, particularly advantageously between 70% and 90%, in particular approx. 80%.

6. Method according to one of the preceding claims, comprising the following method step that the target subcooling value U s in a specific range of the heat transfer medium temperature difference delta T to a specific target subcooling value U ss which is determined from the target subcooling value U s deviates, whereby the target subcooling value U s an offset subcooling value U o is added, the target subcooling value U sto an offset subcooling amount U offs is set or the target subcooling value U s with a special offset value U ow is modified .

7. Method according to one of the preceding claims 5 or 6, comprising the following method step that the heat transfer medium temperature difference delta T is set to a predetermined spread between 4 K and 15 K, particularly advantageously between 7 K and 13 K and especially between 9 K and 11 K.

8. Method according to claim 5, comprising the following method step that the desired subcooling value Us is set between approximately 5 K and 10 K, by approximately 7 K and in particular between 6 K and 9 K.

9. Method according to one of the preceding claims, comprising the following method step that a filling quantity of refrigerant in the liquefied heat exchanger is set between a minimum filling quantity of approximately 0.5% and a filling quantity of 80% depending on a heating output, the target subcooling U Ksoll , the high pressure HD and a contour of the liquefying heat exchanger (220, 240), in particular contours of internal heat transfer surfaces to which the refrigerant adheres.

10. Method according to one of the preceding claims, comprising the following method steps: that the target subcooling value U s is changed depending on at least one operating limit of at least one refrigeration circuit component, in particular the operating limit with regard to a minimum or maximum permissible operating pressure of the components contained in the refrigerant circuit, wherein an optimum efficiency is deviated from in order to comply with the operating limit.

11. Method according to claim 10, comprising the following method steps: that the target subcooling value U s is reduced when the refrigerant pressure in the high pressure range reaches a maximum high pressure HD max close to, in particular approximately 1 bar, whereby the high pressure HD remains safely below the high pressure HDmax, whereby it is advantageous to set how close the high pressure HD to the maximum high pressure HD max may occur, whereby in particular maximum pressure parameters are set so that the maximum high pressure HD max can be set to values of approximately 1 bar and less and is preferably limited to a P-regulator of the high pressure HD for safety reasons.

12. Method according to claim 10, comprising the following method steps: that the target subcooling value U s is increased when the refrigerant pressure in the high pressure area is at a minimum high pressure HD minclose to, especially close to approximately 1 bar, so that the minimum high pressure HD is not undercut, whereby it is advantageous to have an HD min -Limit of high pressure is increased by approximately 1 bar or less.

13. The method according to claim 10, 11 or 12, wherein at least approximately 2 bar differential pressure is achieved at the compressor so that a metal blade of the rotary piston compressor, in particular an outlet valve, is closed, wherein during operation with optimal subcooling the minimum differential pressure is not achieved, advantageously the target subcooling value U s is increased and it is particularly advantageous to coordinate high pressure HD and subcooling U i leads to an optimum and at application limits around the minimum or maximum operating pressure there is a deviation from the optimum efficiency.

14. Method according to claim 5 or 6, comprising the following method steps, wherein a reduction of the target subcooling value Us depending on a temperature difference formed by the flow temperature with the condensation temperature T Kd takes place, whereby the target subcooling value U s is reduced if the flow-side temperature difference, which is determined by calculating the difference between the condensation temperature T Kd formed with the flow temperature, exceeds a predetermined value, which resolves a discrepancy between, on the one hand, as much refrigerant as possible in the condensing heat exchanger, but, on the other hand, not too much liquid refrigerant in the condensing heat exchanger, so that enough condensation surface is available.

15. The method according to claim 14, wherein at a high power, the heat transfer surface of the condensing heat exchanger, at which heat transfer surface in the condensing heat exchanger condensation of refrigerant can take place, is increased for improved condensation, wherein in an extreme case there is no level of refrigerant in the condensing heat exchanger, which is determined when the condensation temperature T Kd rises significantly above the flow temperature.

16. Method according to one of the preceding claims, wherein at least one or more of the following values are included in the calculation model: - the refrigerant mass flow, in particular calculated from the high pressure HD, the low pressure ND and compressor speed VD - the target subcooling U s, - an offset value of the throttle element, - a refrigeration circuit-specific constant, - at least one exponent as a refrigeration circuit-specific variable, - the high pressure HD, - the low pressure ND or - the compressor speed VD.

17. Method according to claim 16, comprising the method steps of calculating the refrigerant mass flow from refrigerant circuit process values PW, in particular from the low pressure ND, the high pressure HD and compressor speed VD.

18. Method according to one of the preceding claims, comprising the method steps of determining the subcooling value U j at the outlet of the respective condensing heat exchanger with a pressure drop compensation to a corrected high pressure H Dk and with this corrected high pressure H Dk a subcooling value U i after the condensing heat exchanger is determined.

19. Method according to one of the preceding claims, comprising the method steps of calculating a heating pressure drop compensation value when the vapor compression system is operated in heating mode, calculating a cooling pressure drop compensation value when the vapor compression system is operated in cooling mode, and using the heating pressure drop compensation value or the cooling pressure drop compensation value to determine the subcooling value U i after the condensing heat exchanger is corrected.

20. Method according to claim 8 or 9, comprising the following method steps: that the high pressure HD is measured in a high pressure path of the refrigeration circuit, the condensation temperature T Kd with the measured high pressure HD and a pressure drop correction value calculated from a vapor pressure curve, whereby the pressure drop correction value is a model-based calculated pressure difference between the high pressure HD and the refrigerant temperature T KArepresents the refrigerant temperature T KA between the condensing heat exchanger and the intermediate pressure throttle device and the actual subcooling value Ui of the refrigerant is calculated from the difference between the refrigerant temperature TKA and the condensation temperature T corrected in particular for the pressure difference Kd is determined.

21. Method according to one of the preceding claims, comprising the following method steps: the first manipulated variable ES is calculated as a factor which is determined by a control component such as a proportional component and / or an integral component and / or a differential component as a function of the subcooling deviation U a is influenced.

22. Method according to one of the preceding claims, comprising the following method steps: the setpoint control value SST is calculated from the first control variable ES and the second control variable ZS, wherein in a first step an offset opening degree is subtracted from the second control variable ZS, namely a theoretical opening degree of the expansion valve, to obtain an offset-adjusted theoretical opening degree, in a second step the offset-adjusted theoretical opening degree from the first step is multiplied by the first control variable ES to obtain an offset-adjusted control value, wherein in a third step the offset-adjusted control value from the second step and the offset opening degree are added, whereby a constant control loop gain of the throttle element through which the flow passes after the liquefied heat exchanger is achieved in its operating range.

23. Heat pump (100) comprising a vapor compression system with a liquefied heat exchanger, suitable for operation according to one of the preceding methods, with a compressor (210), an evaporating heat exchanger, a first throttle element, a refrigerant collector (260), a second throttle element, a control (500) with a first determination unit (520) for determining a first manipulated variable ES for the at least one intermediate pressure throttle element, which in dependence on the deviation of an actual subcooling value U i of the refrigerant from a target subcooling value U sof the refrigerant at an outlet of the condensing heat exchanger is regulated, a unit (530) for determining measured variables MG for feeding into a calculation model for a second manipulated variable ZS for the intermediate pressure throttle element, a computing unit (540) for model-based calculation of the second manipulated variable ZS for the intermediate pressure throttle element using the calculation model from the determined measured variables MG and specific variables of the vapor compression circuit or process values PW, a second determination unit (550) for determining a third manipulated value DS for the intermediate pressure throttle element by linking the first manipulated value with the second manipulated value and an actuating unit (560) for setting the intermediate pressure throttle element to the third manipulated value DS.

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