Method for operating a compression refrigeration system and associated compression refrigeration system
Patent Information
- Authority / Receiving Office
- DE · DE
- Patent Type
- Patents
- Current Assignee / Owner
- STIEBEL ELTRON GMBH & CO KG
- Filing Date
- 2020-06-09
- Publication Date
- 2026-07-23
AI Technical Summary
Existing compression refrigeration systems face issues with condensation formation due to refrigerant overheating, leading to potential corrosion and damage to components, particularly in areas where the dew point of ambient air is lower than the refrigerant temperature.
A control method and system that detects overheating by defining superheat as the difference between the dew point temperature and refrigerant temperature, regulating the throttle body to maintain a permissible superheat range, ensuring the refrigerant temperature exceeds the dew point to prevent condensation.
Prevents condensation on refrigeration system components, maintaining efficient operation and protecting components from corrosion while optimizing efficiency by keeping the refrigerant temperature above the dew point.
Smart Images
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Abstract
Description
[0001] The invention relates to a method for operating a compression refrigeration system and an associated compression refrigeration system comprising a refrigerant, an evaporator, a compressor, a condenser, an throttling device, an internal heat exchanger for transferring heat energy of the refrigerant before entering the throttling device to the refrigerant before entering the compressor, and a control unit for detecting superheating of the refrigerant upon entry into the compressor, wherein superheating is defined as a difference between a dew point temperature and a temperature of the refrigerant, and a control of the throttling device based on the superheating.
[0002] Such compression refrigeration systems, for example in the form of heat pumps, with a vapor compression system in which a gaseous refrigerant is compressed from a low pressure to a high pressure by a compressor controlled by a control unit, which for example has a regulator, are known.
[0003] The refrigerant is forced through the condenser, where it releases heat to a heating medium in a heat sink system. Internal heat is transferred in an internal heat exchanger, for example in the form of a recuperator, between the refrigerant flowing under high pressure from the condenser to the expansion valve and the refrigerant flowing under low pressure from the evaporator to the compressor.
[0004] The refrigerant is then guided in a high-pressure flow direction to an expansion valve controlled by the regulator, where the refrigerant is expanded from high pressure to low pressure according to a set control value. The refrigerant, now at low pressure, evaporates in the evaporator, absorbing heat from the surrounding environment.
[0005] From DE 101 59 892 A1, it is known to use a recuperator in a refrigeration machine, particularly in a heat pump, to increase the heating capacity in a structurally simple manner at low outside temperatures. For this purpose, the recuperator is dimensioned such that at low evaporation temperatures it transfers at least approximately 15% of the heat pump's heating capacity from the liquid refrigerant to the gaseous refrigerant. An injection valve injects liquid refrigerant into the compressor so that the final compression temperature remains below 120 °C.
[0006] A heat pump system with a refrigerant circuit is known from DE 10 2005 061 480 B3. It is equipped with a compressor, a first heat exchanger, an throttling device, an evaporator, and a 4-2-way valve unit for switching between a first (heating) and a second (cooling) operating mode. The flow direction of the refrigerant in the refrigerant circuit can be reversed such that the first heat exchanger serves to condense the refrigerant in the first operating mode and to evaporate it in the second operating mode, and the second heat exchanger serves to evaporate the refrigerant in the first operating mode and to condense it in the second operating mode, wherein the first heat exchanger in the refrigerant circuit is configured to operate as a counterflow heat exchanger in both heating and cooling modes.
[0007] During operation, the heat extracted from the refrigerant can cause the dew point of the moisture contained in the ambient air to be undershot in the area of the refrigerant path between the internal heat exchanger and the compressor inlet, so that moisture from the ambient air can condense and settle on the components.
[0008] The object of the invention is to propose a control method for the aforementioned compression refrigeration system, with which the precipitation of condensate is effectively prevented.
[0009] The problem is solved by the method features of claim 1 and the device features of claim 7.
[0010] According to a first aspect, a method for controlling a compression refrigeration system is being developed. - a refrigerant, - an evaporator, - a compressor, - a liquefier, - a thoracic organ, - an internal heat exchanger for transferring heat energy from the refrigerant before it enters the throttling device to the refrigerant before it enters the compressor, and - a control unit a) for detecting superheating of the refrigerant upon entry into the compressor, wherein superheating is defined as a difference between a dew point temperature and a temperature of the refrigerant, and b) for regulating the throttle device based on overheating, proposed. The procedure comprises the following steps: - Measurement of a temperature that is representative of a surface temperature of a component of the refrigeration circuit, which during operation of the refrigeration circuit can fall below a dew point temperature of the air surrounding the refrigeration circuit containing water vapor, - Calculation of a minimum temperature to ensure that the surface temperature of the component does not exceed the dew point, based on a recorded environmental parameter, - Calculation of a minimum refrigerant superheat value from a) the minimum temperature to ensure that the dew point is not exceeded and b) a corresponding evaporation temperature of the refrigerant underlying the superheat calculation, which would result in the dew point being exceeded on the surfaces of low-pressure-side components of the refrigeration circuit, - Determining the maximum from a) a provided setpoint for the superheat of the refrigerant for regular operation of the compression refrigeration system and b) the calculated minimum value of the refrigerant superheat, and - Control of the throttling device to the maximum determined value for the superheating of the refrigerant.
[0011] Superheat control therefore corresponds to a control of the superheat, particularly at the compressor inlet, which is defined as the difference between the dew point temperature and a refrigerant temperature. Control here means that the throttling device is controlled using a superheat setpoint in such a way that the difference between the actual superheat value and the superheat setpoint approaches zero.
[0012] For example, the superheat for the compressor may be permissible in a range between just over 0K and 30-40K, whereby the optimal coefficient of performance depends on the operating point and is between 0K and 30K, so that for regular operation a target superheat is preferably set for this operation.
[0013] When operating according to this target value, the refrigerant temperature, particularly between the internal heat exchanger and the compressor inlet, can fall below the ambient condensation temperature during normal operation. Consequently, humidity can condense, potentially freeze, run down the refrigeration circuit, etc., and cause corrosion.
[0014] The present application counteracts this undesirable effect by ensuring that the surfaces of the refrigeration circuit are kept sufficiently warm, even in the area between the internal heat exchanger and the compressor inlet, to prevent condensation of ambient air. This is achieved through a specific type of superheat control.
[0015] The first step is to determine how the superheat is to be controlled so that the surface temperature meets this condition. Superheat control is implemented primarily through the opening position of the throttling device, for example, a throttle valve, and exists alongside capacity control, which is usually implemented via compressor speed control. As already mentioned, refrigerant with a wet vapor component drawn into the compressor can damage it, corresponding to insufficient superheat, or conversely, excessive superheat of the refrigerant drawn into the compressor can lead to excessive superheat. This means that an excessively high compressor inlet temperature can result in an excessively high compressor outlet temperature, potentially causing oil damage and / or thermal damage to compressor components. For each operating point, there is an efficiency-optimized superheat setting, which can vary between operating points.
[0016] The temperature that can be measured, and is representative of the surface temperature of a component of the refrigeration circuit (which, during operation, can fall below the dew point temperature of the surrounding air containing water vapor), is preferably the compressor inlet temperature of the refrigerant. The surface temperature for which this temperature is representative is therefore that of the refrigeration circuit components exposed to this temperature, such as refrigerant pipes, internal heat exchangers, or refrigerant separators. The thermal conductivity of such components is sufficient to approximate the refrigerant temperature on the surface of the associated components.
[0017] The minimum temperature required to ensure that the dew point is not exceeded is preferably set to the dew point temperature of the water vapor content of the air surrounding the refrigeration circuit, plus a buffer to account for inaccuracies in measuring the ambient parameter. For example, the buffer can be in the range of at least 2-3 K, particularly in the range of 2-3 K.
[0018] The measured environmental parameter preferably includes room temperature, measured by a room temperature sensor, and / or room humidity, measured by a room humidity sensor. If no room humidity sensor is available, a relative humidity of 100% must be assumed; that is, the measured room temperature is considered the condensation temperature. Room temperature and / or room humidity are particularly suitable for indoor heat pumps.
[0019] In the case of externally installed heat pumps, an outside temperature and / or outside humidity is particularly advantageous.
[0020] Alternatively or additionally, the environmental parameter can include a temperature inside the housing, for example, measured using an air sensor. Preferably, the sensor that determines the temperature inside the housing is not in contact with components such as parts of the refrigeration circuit. A temperature sensor located near the compressor inlet can be particularly advantageous for this purpose.
[0021] The air inside the housing is "overheated," meaning that when measuring the temperature inside the housing, it is particularly advantageous to also measure the relative humidity. Otherwise, the overheating within the housing would lead to excessively high overheating. To give a numerical example: assuming an ambient temperature of 21°C and 60% relative humidity, the air in the heat pump can be heated to, say, 50°C. This would lower the relative humidity to, for example, 30%. If 100% relative humidity were then assumed, for instance, because the humidity is not measured by a sensor, this would result in very high overheating.
[0022] Preferably, the throttling device is controlled to the maximum determined value for refrigerant superheat, at least in certain operating modes of the compression refrigeration system. For example, certain temperature thresholds can be set to activate condensation protection. Conversely, condensation protection can also be deactivated, for example, during defrosting or start-up. However, providing condensation protection is generally advantageous in the majority of operating modes.
[0023] Preferably, the temperature that is representative of the surface temperature of a component of the refrigeration circuit is measured at at least one component of a refrigerant pipe, the internal heat exchanger, or a refrigerant separator.
[0024] Preferably, the minimum temperature to ensure that the dew point is not exceeded is calculated based on a room temperature sensor and a room humidity sensor to detect the environmental parameter.
[0025] Preferably, the compression refrigeration system is a compression refrigeration system installed inside a building.
[0026] Preferably, the superheat value used to control the throttling device is maintained within a superheat range permissible for the compressor. According to the invention, it is possible to achieve an efficiency of the refrigeration circuit close to or at its optimal range while simultaneously ensuring the protection of the components, since the superheat is controlled in such a way that it remains within the permissible range for the compressor.
[0027] In another aspect, a compression refrigeration system is proposed with - a refrigerant, - an evaporator, - a compressor, - a liquefier, - a thoracic organ, - an internal heat exchanger for transferring heat energy from the refrigerant before it enters the throttling device to the refrigerant before it enters the compressor, and - a control unit a) for detecting superheating of the refrigerant upon entry into the compressor, wherein superheating is defined as a difference between a dew point temperature and a temperature of the refrigerant, and b) for regulating the throttle device based on overheating, the control unit is set up to control the compression refrigeration system according to the following steps: - Measurement of a temperature that is representative of a surface temperature of a component of the refrigeration circuit, which during operation of the refrigeration circuit can fall below a dew point temperature of the air surrounding the refrigeration circuit containing water vapor, - Calculation of a minimum temperature to ensure that the surface temperature of the component does not exceed the dew point, based on a recorded environmental parameter, - Calculation of a minimum refrigerant superheat value from a) the minimum temperature to ensure that the dew point is not exceeded and b) a corresponding evaporation temperature of the refrigerant underlying the superheat calculation, which would result in the dew point being exceeded on the surfaces of low-pressure-side components of the refrigeration circuit, - Determining the maximum from a) a provided setpoint for the superheat of the refrigerant for regular operation of the compression refrigeration system and b) the calculated minimum value of the refrigerant superheat, and - Control of the throttling device to the maximum determined value for the superheating of the refrigerant.
[0028] The compression refrigeration system according to the invention enables the achievement of the same advantages as the method according to the invention. Likewise, a combination with all preferred embodiments of the method is advantageously possible.
[0029] Preferably, the refrigerant has a temperature glide, and in particular, the refrigerant comprises or consists of R454C. Furthermore, the method is also applicable to refrigerants without a temperature glide.
[0030] According to another aspect, a heat pump, in particular a heat pump installed inside a building, is proposed with a compression refrigeration system according to the invention.
[0031] According to further preferred embodiments, which can be combined with all aspects of the invention, details of the control strategy are implemented as follows. During the commissioning phase of the compression refrigeration system, a control value is influenced by a deviation in the evaporator outlet superheat, thereby controlling the throttling device. After the commissioning phase, during a stable operating state of the compression refrigeration system, the control value is further determined based on the compressor inlet superheat, and the throttling device is preferably controlled after the commissioning phase based on the determined evaporator outlet superheat and the compressor inlet superheat.
[0032] A control variable for the evaporator outlet superheat is preferably calculated. Using a target value for the evaporator outlet superheat, a control deviation for the evaporator outlet superheat is preferably calculated. Furthermore, a control variable for the compressor inlet superheat is preferably calculated. Using a target value for the compressor inlet superheat, a control deviation for the compressor inlet superheat is preferably calculated. The control value R is then preferably calculated from a weighted influence of the control deviation for the evaporator outlet superheat and a weighted influence of the control deviation for the compressor inlet superheat. The expansion valve is preferably controlled using this control value.
[0033] Another advantageous method is to perform the subtraction "inversely," whereby the actual value is subtracted from the target value to calculate the control deviations. The control deviation is advantageously calculated by determining the difference between an "actual value" and a "target value."
[0034] According to an advantageous process step, the evaporator outlet superheat is weighted against the compressor inlet superheat using a parameter to determine the control value. Particularly advantageously, the control deviations of an evaporator outlet superheat or the compressor inlet superheat from a setpoint are weighted.
[0035] In another advantageous process step, the evaporator outlet superheat is weighted against the compressor inlet superheat to determine the controlled variable using a parameter. Particularly advantageously, the control deviations of an evaporator outlet superheat or a compressor inlet superheat are weighted with a setpoint.
[0036] In a further advantageous embodiment of the method, the evaporator outlet superheat is determined from an evaporator outlet temperature measurement value, which is measured with an evaporator outlet temperature sensor, and from a low pressure, which is measured with a low pressure sensor.
[0037] In a further preferred process step, the compressor inlet superheat is determined from a compressor inlet temperature, measured with a compressor inlet temperature sensor, and a low pressure, measured with a low pressure sensor.
[0038] In an advantageous process step, a first control deviation of the compressor inlet superheat is calculated in the controller together with a second control deviation of the evaporator outlet superheat to form a total control deviation, and the total control deviation is used to adjust the throttling device.
[0039] The figures show an example of implementation: Fig. 1 heat pump 100 with a vapor compression circuit 200 Fig. 2 log p / h - Diagram of the vapor compression process with recuperator 250 Fig. Figure 3 shows a schematic and exemplary flowchart of a process.
[0040] Fig. Figure 1 shows a schematic and exemplary heat pump. 100 The heat pump 100 It essentially consists of a vapor compression system forming a compression refrigeration system. 200 , which contains the following components: • A compressor 210 for compressing the superheated refrigerant, • a liquefier 220 , with a refrigerant-side condenser inlet 221 and a condenser outlet 222 for the transfer of heat energy Q H from the steam compression system 200 to a heating medium of a heating system 400 , with a heating medium inlet 401 , a heating medium leak 402 and a heating medium pump 410 , to a building heating system or a hot water heating system, • advantageously a refrigerant collector 260, which is used as a refrigerant reservoir to compensate for varying refrigerant quantity requirements depending on operating conditions, • a throttling device designed as an expansion valve 230 to expand the refrigerant, • an evaporator 240 , with an evaporator inlet 241 , for the transmission of source energy Q Q from a heat source system 300 , with a heat source inlet 320 and a heat source outlet 310 , where the heat source system 300 in particular a brine system which can store thermal energy Q Q absorbs heat from the ground or an air system that captures thermal energy Q Q absorbs from the ambient air and transfers it to the vapor compression system 200 emits or any other heat source • a recuperator as an example of an internal heat exchanger 250 , which is designed to dissipate internal heat energyQ i between the liquefier 220 to the expansion valve 230 flowing refrigerant onto the surface from the evaporator 240 to the compressor 210 to transfer flowing refrigerants and • a refrigerant, in particular a refrigerant mixture of at least two substances or two refrigerants which flows in one direction S HD and S ND through the vapor compression circuit 200 flows, whereby in the vapor compression cycle 200 Refrigerant vapor through the compressor 210 on a high pressure HD is brought to a liquefier 220 is guided, whereby a high-pressure path with the high-pressure flow direction S HD from the compressor 210 up to the expansion valve 230 is formed. After the expansion valve 230 up to the compressor 210 is a low-pressure path with a low-pressure flow direction S ND of the refrigerant in which the evaporator 240 lies.
[0041] The actuators listed below are advantageously at least partially connected to the controller via a data connection. 510 , which can be connected via cable, radio or other technologies: compressor 210 , heating medium pump 410 , brine pump 330 , expansion valve 230 Compressor inlet temperature sensor 501 , low pressure sensor 502 , high-pressure sensor 503 , hot gas temperature sensor 504 , Recuperator inlet temperature sensor 505 , Recuperator outlet temperature sensor 506 and / or evaporator outlet temperature sensor 508 Additionally or alternatively, a [something] can be [something] in the Fig. 1. Evaporator inlet temperature sensor (not shown) measures the temperature at the evaporator inlet. 241 determine.
[0042] In the Fig. The first example shown is the heat pump. 100The example shown is a brine-to-water heat pump. Of course, similar considerations and advantages can be achieved with air-to-water heat pumps. In particular, with air-source heat pumps, a brine pump can be used instead of a brine circuit. 330 A fan / ventilator is positioned as a heat source.
[0043] The compressor 210 It is used to compress the superheated refrigerant from an inlet port. 211 on a compressor outlet pressure P Va at a compressor outlet temperature corresponding to the hot gas temperature at the compressor outlet 212 The compressor 210 It typically contains a drive unit with an electric motor, a compression unit, and advantageously the electric motor can be operated at variable speeds. The compression unit can be designed as a rotary piston unit, scroll unit, or otherwise. At the compressor outlet 212 is the compressed superheated refrigerant at the compressor outlet pressure P Va at a higher pressure level, especially a high pressure HD , as at the entrance 211 with a compressor inlet pressure P Ve , especially a low pressure ND , at a compressor inlet temperature T VE , which determines the state of the refrigerant temperature at the inlet connection 211 describes the process of entering a compression chamber.
[0044] In the liquefier 220 The transfer of heat energy takes place Q H from the refrigerant of the vapor compression system 200 to a heating medium of the heat sink system 400 . First, the liquefied 220 The refrigerant is deheated, whereby superheated refrigerant vapor transfers some of its heat energy to the heating medium of the heat sink system through a temperature reduction. 400 transfers.
[0045] After the refrigerant vapor has been deheated, this advantageously takes place in the condenser. 220further heat transfer Q H This occurs through condensation of the refrigerant during the phase transition from the gaseous to the liquid phase. This process releases further heat. Q H from the refrigerant in the vapor compression system 200 to the heating medium of the heat sink system 400 transmitted.
[0046] The one in the liquefier 220 adjusting high pressure HD the refrigerant corresponds to the operation of the compressor. 210 approximately with a condensation pressure of the refrigerant at a heating medium temperature Tws in the heat sink system.
[0047] The heating medium, especially water, is circulated by means of a heating medium pump. 410 through the heat sink system 400 in a SW direction through the condenser 220 promoted, thereby the heat energy Q H transferred from the refrigerant to the heating medium.
[0048] In the following collector260 is produced from the liquefier 220 escaping refrigerant is stored, the amount of which depends on the operating point of the vapor compression circuit. 200 It should not be fed into the circulating refrigerant. It is taken from the condenser. 220 More refrigerant was injected than through the expansion valve. 230 As the collector is forwarded, it fills up. 260 , otherwise it will become emptier or emptied.
[0049] In the following recuperator 250 , which can also be referred to as an internal heat exchanger, internal heat energy Q i from under high pressure HD standing refrigerant, which is from the condenser 220 to the expansion valve 230 in a high-pressure flow direction S HD flows, onto which the low pressure ND The flowing refrigerant transfers heat from the evaporator to the compressor in a low-pressure flow direction. SND The fluid flows and is transferred. This process involves transferring the fluid from the condenser to the expansion valve. 230 The flowing refrigerant is advantageously subcooled.
[0050] First, the refrigerant flows through an expansion valve inlet. 231 into the expansion valve. In the expansion valve 230 The refrigerant pressure is reduced from high pressure. HD on low pressure ND , by the refrigerant advantageously passing through a nozzle arrangement or throttle with an advantageously variable opening cross-section, wherein the low pressure is advantageously approximately at the suction pressure of the compressor 210 This corresponds to a replacement for an expansion valve. 230 Any other pressure-reducing device can also be used. Pressure-reducing pipes, turbines, or other pressure-relieving devices are advantageous.
[0051] An opening degree of the expansion valve 230is adjusted by an electric motor, usually designed as a stepper motor, which is controlled by the control unit or regulator. 500 is controlled. The low pressure is controlled in this process. ND at the expansion valve outlet 232 of the refrigerant from the expansion valve 230 controlled in such a way that the resulting low pressure ND of the refrigerant during compressor operation 210 approximately with the evaporation pressure of the refrigerant and the heat source medium temperature T WQ This corresponds to the evaporation temperature of the refrigerant, which is advantageously a few Kelvin below the temperature of the heat source medium T. WQ They lie so that the temperature difference drives heat transfer.
[0052] In the evaporator, heat energy Qv is transferred from the heat source fluid of the heat source system. 300 , which is a brine system, a geothermal system for the use of heat energy Q Q from the ground, an air system for energy utilization Q Q from the ambient air or another heat source that provides the source energy Q Q to the vapor compression system 200 hands over.
[0053] The one in the evaporator 240 The incoming refrigerant is reduced as it flows through the evaporator. 240 through heat absorption Q Q its wet steam content and leaves the evaporator 240 Advantageously with a low wet steam content or also advantageously as a superheated gaseous refrigerant. The heat source medium is supplied by means of a brine pump. 330 In the case of brine-to-water heat pumps or an outdoor air fan in the case of air-to-water heat pumps, through the heat source medium path of the evaporator. 240 promoted, whereby the heat energy is transferred to the heat source medium as it flows through the evaporator. Q Q is withdrawn.
[0054] In the recuperator 250 heat energy is Q i between the liquefier 220 to the expansion valve 230 flowing refrigerant onto the surface from the evaporator 240 to the compressor 210 flowing refrigerants are transferred, with the one from the evaporator 240 to the compressor 210 The flowing refrigerants, in particular, are further overheated.
[0055] This superheated refrigerant, which has a superheating temperature T Ke from the recuperator 250 The outlet becomes the refrigerant inlet connection. 211 of the compressor 210 guided.
[0056] The recuperator 250 is in the vapor compression circuit 200 used to determine the overall efficiency as the quotient of heat output and output. Q H and absorbed electrical power P e to increase the drive of the compressor motor.
[0057] For this purpose, the refrigerant which is in the condenser is 220 thermal energy Q H releases at a temperature level on the heat sink side to the heating medium, in the high-pressure path of the recuperator 250 Further heat energy is generated through subcooling Q i withdrawn.
[0058] The internal energy state of the refrigerant upon entering the evaporator 240 is caused by this heat extraction Q i reduced, so that the refrigerant releases more heat energy at the same evaporation temperature level Q Q from the heat source 300 can record.
[0059] Subsequently, the refrigerant is released after exiting the evaporator. 242 from the evaporator 240 , in the low-pressure path at low pressure ND and at a low-pressure temperature corresponding to an evaporator outlet temperature T Va in the recuperator 250 the heat energy extracted in the high-pressure path Q i The energy is then supplied again. The supply of energy advantageously reduces the wet steam content to a state without wet steam, and then further energy supply leads to superheating.
[0060] Furthermore, the following are required to record the operating status of the steam compression system. 200 Advantageously the following sensors are arranged, which are particularly useful for safeguarding and optimizing the operating conditions of the steam compression system. 200 In particular, model-based feedforward control is implemented when operating conditions change.
[0061] On the one hand, the process values recorded by sensors advantageously provide safeguards regarding permissible operating ranges of the components, such as the compressor in particular. 210 On the other hand, model-based feedforwards are made based on the sensor data, in particular for the speed of the compressor. 210and / or a valve opening degree of the expansion valve, so that the controller only has to make smaller corrections to compensate for a control deviation that is nevertheless smaller due to the feedforward control: • A high-pressure sensor 503 advantageous for detecting high pressure HD of the refrigerant at the compressor outlet 212 or between the compressor outlet 212 and the expansion valve inlet 231 , • a hot gas temperature sensor 504 advantageous for measuring a hot gas temperature T HG of the refrigerant at the compressor outlet 212 , or in the refrigeration circuit section between the compressor outlet 212 and the liquefier inlet 221 , • an indoor temperature sensor 506 advantageous for measuring the indoor temperature T le of the refrigerant between the high-pressure side internal recuperator outlet 252of the refrigerant from the recuperator 250 and the expansion valve inlet 231 The internal temperature is also advantageously referred to as the "recuperator outlet temperature high-pressure path" and • A recuperator internal temperature sensor is advantageous 505 The recuperator internal temperature sensor 505 advantageously captures condenser outlet temperature T FA of the refrigerant in the flow direction at the condenser outlet or the high-pressure side recuperator inlet, and therefore the condenser outlet temperature is advantageously T FA from the recuperator internal temperature sensor 505 measured.
[0062] The following sensors are particularly advantageous for carrying out the method according to the invention: • A low-pressure sensor 502 for measuring low pressure ND of the refrigerant at the compressor inlet 211 , or between the expansion valve 230and the compressor inlet 211 , • an evaporator outlet temperature sensor 508 for measuring the evaporator outlet temperature T Va of the refrigerant at the evaporator outlet 242 or between the evaporator outlet 242 and the low-pressure side entry of the refrigerant into the recuperator inlet 251 of the recuperator 250 and • a low-pressure temperature sensor 501 Advantageously measures a compressor inlet temperature or is advantageously used to measure the refrigerant low-pressure temperature T ND or advantageously a compressor inlet temperature T KE at the compressor inlet 211 , or between the low-pressure side recuperator outlet 252 of the refrigerant from the recuperator 250 and the compressor inlet 211 .
[0063] The process parameter that has a significant influence on the overall efficiency of the steam compression circuit 200 as the quotient between that of the vapor compression circuit 200 transferred heating power Q H to one from the compressor 210 absorbed electrical power P e The problem is the overheating of the refrigerant at the compressor inlet. 211 To maintain permissible compressor operating conditions, it is advantageous to adhere to restrictions regarding the allowed superheat range of the refrigerant at the compressor inlet. Excessively low superheats particularly compromise the lubricating properties of the machine oil, while excessive superheats result in excessively high hot gas temperatures.
[0064] Superheating describes the temperature difference between the measured compressor inlet temperature and the temperature of the compressor inlet. T KE of the refrigerant and the evaporation temperature of the refrigerant at saturated vapor.
[0065] According to the invention, the compressor inlet superheat is preferably controlled in such a way that no condensate forms on components of the refrigeration circuit, particularly in the section between the refrigerant outlet of the recuperator, due to a drop in the dew point of the water vapor content contained in the ambient air. 252 and compressor inlet 211 fails. The refrigeration circuit section between the evaporator outlet 242 and recuperator entry 251 Although it is usually colder because it is typically only a short pipe section, it offers better insulation compared to the section between the refrigerant outlet of the recuperator. 252 and compressor inlet 211 possible. For example, it is located at the compressor inlet. 211The refrigerant separator, which needs protection, is located at the compressor. It's difficult to enclose it completely, so the temperature needs to be kept high enough to prevent condensation. Condensation problems don't typically occur on the high-pressure side. This also applies to the passage between the high-pressure side recuperator outlet. 252 and entry into the expansion valve 231 Cools regularly depending on the operating point under ideal heat transfer conditions in the recuperator 250 to the temperature level of the refrigerant at the evaporator outlet 242 However, since this passage is also typically short and very easy to insulate, this section is generally not problematic either. It should be noted, however, that the method according to the invention can fundamentally prevent condensate from dropping throughout the entire heat pump circuit.
[0066] If - for the purpose of a numerical example - an evaporation temperature level of approximately -10°C is assumed and the temperature at the brine inlet 330 at approximately -10°C, at the brine outlet 310 The temperature is approximately -13°C and 5°C at the compressor inlet, which affects overheating. 15K .
[0067] Many systems benefit from room temperature and humidity sensors, which allow for precise determination of the condensation conditions in the air. For example, at 21°C and 60% relative humidity, the condensation temperature is around 13°C. Under these conditions, no condensation occurs as long as the pipe temperature is above 13°C, plus a possible buffer of, for example, 1K.
[0068] Sticking with this non-exhaustive numerical example, we now assume that a superheat of 15K is achieved at a compressor inlet temperature of 5°C. This temperature is below the 13°C that is determined to be the condensation temperature of the water vapor present in the ambient air under the current ambient conditions. Therefore, condensation occurs. If the compressor inlet temperature is to be at least 14°C, i.e., the condensation temperature plus a buffer, the superheat must be increased by 9K, i.e., a superheat of 24K must be maintained.
[0069] Limit values, especially for overheating, define the permissible overheating range of the components at the compressor inlet, depending on the operating point. 211 fixed. However, dependencies also exist between the compressor inlet superheat dT. U ̈ E and the overall efficiency of the vapor compression circuit 200or also between compressor inlet superheat dT U ̈ E and a stability S of a control value R is advantageous in the control of compressor inlet superheating.
[0070] To take all these requirements into account, the following are advantageous depending on the operating point of the steam compression circuit. 200 , the heat source medium temperature, the heating medium temperature, the compressor power P e and target values Z or the target value Z for a calculation of the compressor inlet superheat dT ÜE used. Alternatively or additionally, the refrigeration circuit parameters dependent on the operating point, such as heat source medium temperature, heating medium temperature, compressor power P, can be used. e and parameterizable coefficients, i.e. adapted to the behavior of the respective refrigeration circuit components, a calculation of the target value Z as a setpoint for the compressor inlet superheat dT U ̈ Eto be carried out. In the simplest case, the target value for the compressor inlet superheat dT is U ̈ E It is constant regardless of all operating conditions, e.g., 10 Kelvin. With a more complex adjustment, it is determined as a function of an operating point parameter, e.g., the compressor power P. e It varies, or with even more complex adjustments, it varies as a function of several operating point parameters.
[0071] A deviation in the compressor inlet superheat dT is detected. U ̈ E and a deviation in the evaporator outlet superheat dT̈ U ̈ A combined and weighted together, resulting in the controller 500 A total control deviation is calculated, which is used to control the steam compression circuit. 200 is fed in. The control deviations from the compressor inlet superheat dT become advantageously more precise. ÜE and evaporator outlet superheat dT ÜAformed by calculating the differences between the respective measured values and target values. • Control deviation of the compressor inlet superheat dT U ̈ E = Measured value compressor inlet superheat - Target value compressor inlet superheat Z TÜE • Control deviation of the evaporator outlet superheat dT ÜA = Measured value evaporator outlet superheat - Target value evaporator outlet superheat Z TÜA
[0072] Then, the weighted influence of the compressor inlet superheat deviation dT is advantageously applied. U ̈ E and the weighted influence of the control deviation of the evaporator outlet superheat dT̈ U ̈ A in the controller 500 the total control deviation is calculated, which is used to control the steam compression circuit 200 is fed in.
[0073] In the vapor compression circuit 200After expansion, the refrigerant passes through the expansion valve. 230 two sequentially arranged heat exchangers, the evaporator 240 and the recuperator 250 in which the refrigerant heat energy Q Q and Q i is supplied.
[0074] In the evaporator 250 Source heat energy is applied to the refrigerant Q Q from the heat source system 300 supplied. The temperature level of the supplied source heat. Q Q is at a temperature level of the heat source, in particular such as the ground or the outside air.
[0075] In the high-pressure flow direction of the refrigerant S HD subsequent recuperator 250 Heat energy is transferred to the refrigerant Q i after leaving the condenser 220 extracted. The temperature level of the refrigerant at the condenser outlet is approximately equal to the return temperature of the heating medium.
[0076] This evaporator circuit 240 with the recuperator 250 The series connection has a decisive influence on the transfer function of the control loop for the control of compressor inlet superheat dT. ÜE .
[0077] The control value R is advantageously the weighted relationship of the control deviation of the compressor inlet superheat dT. U ̈ E with the control deviation of the evaporator outlet superheat.
[0078] Actuator operating condition variables with an influence on the control value R, in particular the compressor inlet superheat dT U ̈ E , are in the relevant steam compression circuit 200 the compressor speed and / or the opening degree of the expansion valve 230 , which also makes the low pressure advantageous ND and the evaporation temperature level is determined.
[0079] Actuators have a particularly advantageous influence on the control value R, especially on the weighted relationship between the control deviation of the compressor inlet superheat and the control deviation of the evaporator outlet superheat. In the relevant vapor compression circuit 200 are in particular the compressor 210 by varying the compressor speed and the expansion valve 230 These actuators influence the degree of opening. These two actuators affect the low pressure. ND and the evaporation temperature level.
[0080] Not all influences are desirable. For example, changing the compressor speed to regulate the desired heating output without further compensatory changes to the opening degree of the expansion valve alters the control value R into undesirable ranges, so that a model-based supported change in the opening degree of the expansion valve, accompanying the change in compressor speed, is advantageous, and may even be necessary, to regulate R.
[0081] Advantageous in the vapor compression circuit 200 the compressor speed is set so that the steam compression circuit 200 heating power transferred to the heating medium QH The required target value Z corresponds to this. To comply with this requirement, the compressor speed must be adjusted to control the compressor inlet superheat dT. U ̈ E advantageously subordinate or not appropriate.
[0082] The degree of opening of the expansion valve is advantageous. 230 as a control parameter for the regulation of the compressor inlet superheat dT ÜE used. The influence of the opening degree of the expansion valve 230 on the compressor inlet superheat dT ÜE It takes place as follows: The expansion valve 230 acts as a nozzle with an electrically adjustable nozzle cross-section, in which a needle-shaped nozzle needle is usually moved into a nozzle seat via a thread using a stepper motor.
[0083] The refrigerant flow rate through the expansion valve is at the expansion valve inlet when operating with liquid refrigerant. 231 approximately proportional to the square root of the pressure difference between the expansion valve inlet 231and outlet 232 multiplied by a current relative value of the nozzle cross-section or opening degree and advantageously one of the refrigerant and a geometry of the expansion valve 230 dependent constant.
[0084] Since, at an operating point with a compressor speed assumed to be constant and a heating medium temperature Tws assumed to be constant, the corresponding high pressure is also HD of the refrigerant upon entering the expansion valve 230 The degree of opening of the expansion valve, which can be assumed to be constant, is influenced by this. 230 primarily only the low pressure ND , i.e., the outlet pressure from the expansion valve 230 .
[0085] Will the opening degree of the expansion valve be adjusted? 230 This reduces the amount of refrigerant that passes through at constant high pressure. HD and initially constant low pressure ND the expansion valve 230Since the compressor 210 but continues to initially convey the same refrigerant mass flow, in the high-pressure flow direction S HD through the expansion valve 230 Less refrigerant was supplied than by the compressor. 210 is sucked away.
[0086] Since refrigerant vapor is a compressible medium, the low pressure then decreases. ND on the low-pressure side of the steam compression circuit 200 . As low pressure decreases ND The mass flow rate of refrigerant through the compressor decreases approximately proportionally. 210 , since its delivery rate can be approximately described as volume / time, due in particular to the piston strokes, and a correspondingly reduced low-pressure value results. ND one in which the expansion valve 230 The supplied refrigerant mass flow is equal to that from the compressor. 210 discharged refrigerant mass flow is.
[0087] Will the opening degree of the expansion valve be adjusted? 230 By increasing the volume, more refrigerant passes through at a constant high pressure. HD and initially constant low pressure ND the expansion valve 230 Since the compressor 210 but continues to initially promote the same refrigerant mass flow, the low-pressure side ND of the refrigeration circuit through the expansion valve 230 More refrigerant was supplied than by the compressor. 210 is extracted. Since the refrigerant vapor is a compressible medium, the low pressure increases. ND on the low-pressure side of the steam compression circuit 200 With increasing low pressure ND The mass flow rate of the compressor increases. 210 approximately proportional, since its pumping capacity can be roughly described as volume / time, and a correspondingly increased low pressure results. ND one in which the expansion valve 230 The supplied refrigerant mass flow is equal to that from the compressor. 210 Discharged refrigerant mass flow is.
[0088] The low pressure ND This in turn significantly influences the heat transfer between the heat source medium and the refrigerant in the evaporator. 240 The heat flow Q Q from the heat source system 300 is transferred between the heat source medium and the refrigerant at different temperatures, whereby the heat flow Q Q depending on the temperature difference between the heat source medium and the refrigerant and the heat transfer resistance of a heat transfer layer of the evaporator. 240 is.
[0089] The heat transfer resistance between the heat source media path of the evaporator and the refrigerant path of the evaporator is in a respective vapor compression circuit. 200It can be assumed to be approximately constant. Therefore, the magnitude of the heat transfer power in the evaporator is 240 significantly dependent on the integral of the temperature differences of all surface elements of the heat transfer layer.
[0090] To ensure a sufficient level of heat energy Q Q from the heat source system 300 In order to transfer the heat to the refrigerant, it must be ensured that the temperature of the heat source medium is maintained in as many surface elements as possible of the heat exchanger's transfer layer, in this case the evaporator. 240 , is greater than the temperature of the refrigerant at the respective surface element.
[0091] Is the state of matter of the refrigerant when it flows through the evaporator 240 In saturated vapor, a refrigerant temperature is established which, according to the saturation vapor characteristic curve as a material property of the refrigerant, is a function of the low pressure. ND of the refrigerant. Thus, by controlling the low pressure, it is possible to ND or indirectly, an evaporation pressure controls the evaporation temperature of the refrigerant as it flows through the recuperator. 250 steer.
[0092] The heat energy Q Q , which from the heat source system to the evaporator 240 The transfer of the refrigerant flowing through the system causes a change in the state of matter of the refrigerant.
[0093] The wet vapor fraction in saturated refrigerant vapor decreases at constant low pressure during heat transfer to the refrigerant. With incomplete evaporation, the wet vapor fraction, and thus also the internal energy state of the refrigerant upon exiting the heat exchanger, is a function of: • Wet steam content at the entrance to the evaporator 240 , • Refrigerant mass flow, • Transferred heat output Q Q , and from a • Enthalpy difference in the wet steam region at the respective low pressure ND , which exhibits the refrigerant as a material constant as a function of pressure.
[0094] For complete evaporation, an additional energy supply is provided in the recuperator. 250 , in order to superheat the refrigerant beyond the state of saturated vapor.
[0095] The method is used under given operating conditions of the steam compression circuit. 200 Depending on the control variable “opening degree of expansion valve 230”, a corresponding refrigerant state is achieved upon exit from the evaporator. 240 set.
[0096] In steady state, the gradient of the "isolated" control loop "evaporator" is determined with regard to the control loop gradient. 240“A control loop behavior with moderate steepness. The control loop behavior is characterized in particular by a control loop output value (evaporator outlet superheat) as a function of a control loop input value (expansion valve opening degree).”
[0097] Advantageously, a refrigerant, in particular a refrigerant mixture, is used which exhibits a "temperature glide," especially R454C. With a refrigerant mixture exhibiting a temperature glide, a relative change in the opening degree of the expansion valve actuator of 1% rel. typically results in a superheat change of less than approximately 1 K at the refrigerant outlet from the evaporator.
[0098] This state can advantageously also be achieved by influencing at least one or more of the following various time constants through control engineering; these ultimately determine the process variable refrigerant superheat at the evaporator outlet. 242 influence: • A first time constant advantageously delays the mechanical change in the opening degree of the expansion valve. 230 by limiting the travel speed through the controller 500 The control value R is reduced in this first time constant Z at the travel speed by a braking value. The braking value can, for example, be the controller cycle time in which a process step of the expansion valve takes place. 230 is controlled, include. • A second time constant acts through the controller 500Advantageously specified for a delayed adjustment of a corresponding low pressure when the opening degree of the expansion valve changes. 230 due to the compressibility of the refrigerant vapor at low pressure ND in the low-pressure path. • A third time constant is advantageously a thermal time constant of the heat transfer layer of the evaporator. 240 , whereby a change in the evaporation pressure and thus the evaporation temperature results in a delayed temperature change of the heat transfer layer of the evaporator, which often contains several kilograms of metal, and of the heat source medium. • A fourth time constant is advantageously obtained from delayed changes in the state of matter of the refrigerant during changes in evaporation temperature. • A fifth time constant is advantageously obtained from the transport of the refrigerant through the evaporator. 240 with a finite flow velocity.
[0099] Therefore, after changing the control variable "opening degree of the expansion valve 230", it is advantageous to delay the corresponding change in the refrigerant state at the exit from the evaporator outlet. 242 The total time constant Zges is advantageously in the range of 30 seconds to about 5 minutes, depending on the operating point.
[0100] After flowing through the evaporator 240 The refrigerant is released at low pressure ND into the low-pressure path of the recuperator 250 a.
[0101] The state of matter of the refrigerant when flowing into the recuperator 250 In a typical operating scenario, either saturated vapor with a low vapor content between 0 and 20% or, in particular, already superheated refrigerant is advantageous.
[0102] With advantageously saturated vapor, a refrigerant temperature is established which, according to the refrigerant's saturation vapor characteristic, is a function of the refrigerant pressure. Upon the entry of superheated refrigerant, the refrigerant temperature will at most reach a value corresponding to the inlet temperature of the heat source medium. In this case, this value preferably corresponds to the inlet temperature of the refrigerant entering the high-pressure path of the recuperator. 250 , that is, the temperature of the refrigerant after it exits the condenser 220 .
[0103] To transfer a sufficient amount of heat energy from the refrigerant of the high-pressure side refrigerant path to the refrigerant of the low-pressure side refrigerant path in the recuperator 250 In order to be able to transfer, it must be ensured that the temperature of the refrigerant in the high-pressure side refrigerant path is at high pressure. HD in as many surface elements as possible of the transmission layer of the recuperator 250 greater than the temperature of the refrigerant in the low-pressure side refrigerant path at low pressure ND at the respective surface element.
[0104] The corresponding temperatures of the heating system 400 of the steam compression system 200 are higher in a heating scenario than the corresponding temperatures of the heat source, such as the ground or the outside air.
[0105] The heat energy Q i , which are produced by the refrigerant at high pressure HD of the high-pressure side refrigerant path to the refrigerant at low pressure in the low-pressure side refrigerant path of the recuperator 250 The transfer of this process causes a change in the state of matter of the refrigerant on the low-pressure side. The wet vapor component of the recuperator 250 low-pressure side at low pressure ND The temperature of the refrigerant flowing through decreases during heat transfer to the refrigerant, and after complete evaporation, superheating of the refrigerant advantageously occurs.
[0106] The internal energy state of the refrigerant upon exiting the low-pressure side path of the recuperator is advantageously influenced by one or more of the following factors. It should be noted that the change in energy state is based solely on physical dependencies, with the controller influencing the control of the actuators, which in turn naturally affects physical quantities such as the refrigerant mass flow rate. • Wet steam content upon entry into the recuperator 250 , • Refrigerant mass flow, • transferred heat output Q i , which is advantageously dependent on the temperature difference between the temperature of the refrigerant at high pressure HD in the high-pressure side refrigerant path and the temperature of the refrigerant in the low-pressure side refrigerant path at low pressure ND is regulated, and / or • an enthalpy difference in the wet steam region at the respective low pressure ND .
[0107] This advantageously results in the following: depending on the given operating conditions of the steam compression circuit 200 as well as, depending on the control variable "opening degree of expansion valve 230", a corresponding refrigerant state at the outlet. 252 from the recuperator 250 at low pressure ND adjusts.
[0108] In steady state, the gradient of the "isolated" controlled system at low pressure is determined with regard to the control loop gradient. ND of the refrigerant in the low-pressure side path of the recuperator 250a control loop behavior with a high steepness, with an approximately constant internal energy state of the refrigerant at the inlet 251 in the low-pressure side ND recuperator path 250 A change in the relative opening degree of the expansion valve of 1% results in a change in superheat at the refrigerant outlet from the evaporator. 230 Advantageous is approximately 10 K or even more than 10 K.
[0109] opposite the recuperator 250 This results in a significantly higher heat transfer in the evaporator. 240 between the source medium and the refrigerant in the evaporator 240 .
[0110] This is how it happens in the evaporator. 240 a significantly higher heat transfer than in the recuperator 250 adjusted, as the environment is controlled by means of an evaporator 240 a significantly greater amount of energy is to be extracted than is stored in the recuperator alone. 250to transfer heat within the refrigeration cycle. The driving temperature difference in the recuperator, for example, is between 20 K and 60 K, while in the evaporator it is only between 3 K and 10 K. In order to transfer the desired energy despite the different driving temperature differences, the heat exchanger surface area of the evaporator is designed to be approximately 5 to 20 times larger than that of the recuperator. 250 .
[0111] This state is advantageously set using at least one of the following time constants Z: • With an eleventh time constant Z 11 A delay in the mechanical opening degree change of the expansion valve is advantageous. 230 by limiting the travel speed. • A twelfth time constant Z 12 This has a beneficial effect on the delayed adjustment of a corresponding low pressure. ND during changes in the opening degree of the expansion valve 230 due to the compressibility of the refrigerant vapor in the low-pressure path ND . • One 13 Time constant Z 13 is a thermal time constant of the evaporator's heat transfer layer. Therefore, a change in the evaporation pressure, and thus the evaporation temperature, causes a delayed temperature change in the heat transfer layer, which often contains several kilograms of metal, and in the refrigerant in the evaporator's low-pressure path. 240 . • One 14 Time constant Z 14 is advantageously determined or specified from delayed changes in the state of matter of the refrigerant during changes in evaporation temperature. • One 15 Time constant Z 15 This results advantageously from the transport of the refrigerant through the evaporator. 240 with a finite flow velocity and is taken into account.
[0112] The low-pressure side refrigerant path of the recuperator 250 is extracted from the evaporator outlet 242 of the evaporator 240 supplied. The internal energy state of the refrigerant is also determined here by at least two time constants Z, Z. 11 , Z 12 , Z 13 , Z 14 , Z 15 , Total time is delayed after changing the control variable “opening degree of expansion valve”.
[0113] After changing the control variable "opening degree of expansion valve 230", a further delay in the corresponding refrigerant state change occurs due to the time behavior of the recuperator. 250 at the exit from the low-pressure side refrigerant path of the recuperator 250 a.
[0114] The time response of the recuperator 250The total recuperator time constant Zges can be advantageously considered depending on the respective operating point of the steam compression circuit in the range of approximately 1 minute to 30 minutes.
[0115] A weighted combination of compressor inlet superheat dT is advantageously used. U ̈ E and the evaporator outlet superheat dT U ̈ A , in particular by means of a weighted combination of the control deviation of the compressor superheat and the control deviation of the evaporator outlet superheat dT ÜA The total control deviation is calculated, which is in the controller 500 for regulating the steam compression circuit 200 is fed in.
[0116] The compressor inlet superheat dT U ̈ Eis advantageously used as the main controlled variable and the corresponding signal flows and signal processing take place in particular in the following process steps: Step 1
[0117] First, the process variables compressor inlet superheat dT are determined. ÜE advantageous as the main control variable and the evaporator outlet superheat dT̈ U ̈ A Advantageously, it can be measured as an auxiliary variable in a first process step.
[0118] For this purpose, the evaporation temperature of the refrigerant at the respective measurement point is either • directly measured using a temperature sensor positioned to detect a temperature corresponding to the refrigerant temperature in the wet vapor region or • indirectly determined using a pressure sensor which detects the refrigerant pressure of the refrigerant evaporating in the wet steam region and then calculates the evaporation temperature from the refrigerant-specific dependence between pressure and temperature in the wet steam region.
[0119] Furthermore, the respective overheating measurement point, in particular the evaporator outlet, is used. 242 and / or at the compressor inlet 211 assigned temperatures of the refrigerant temperature using temperature sensors 501 , 508 The temperature difference between the refrigerant at the respective measuring point and the evaporation temperature is then calculated, and this temperature difference value corresponds to the respective superheat of the refrigerant at the measuring point.
[0120] Input variables of the calculation in step 1 are then the compressor inlet superheat dT U ̈ Eand the evaporator outlet superheat dT ÜA . Step 2
[0121] The process variables compressor inlet superheat dT ÜE and evaporator outlet superheat dT̈ U ̈ A In a second step, the associated deviations from the standard are advantageously offset against their respective target values to form the corresponding deviations from the standard: The target value for the compressor inlet superheat dT U ̈ E The temperature is advantageously varied in the range between approximately 5 K and 20 K to ensure the permissible compressor operating range and the highest possible efficiency of the refrigeration circuit.
[0122] The target value for the evaporator outlet superheat dT̈ U ̈ A at the evaporator outlet 242Depending on the refrigeration circuit operating mode and the refrigeration circuit operating point, the evaporator superheat is then varied so that, in the steady-state normal case, it is approximately equal to the established process value of the evaporator outlet superheat dT. ÜA This corresponds to the target value for the evaporator outlet superheat dT. ÜA can be model-based depending on an operating mode or operating point, the evaporation temperature, the condensation temperature, the compressor power, and a setpoint for the compressor inlet superheat dT. U ̈ E and / or component properties are pre-calculated and adaptively corrected.
[0123] The deviation of the compressor inlet superheat dT will then be determined. ÜE calculated by taking the process value of the compressor inlet superheat dT U ̈ E the target value of the compressor inlet superheat dT U ̈ E is subtracted.
[0124] The deviation from the control parameters of the evaporator outlet superheat dT will then be determined. ÜA calculated by taking from the process value of the evaporator outlet superheat dT̈ U ̈ A the target value of the evaporator outlet superheat dT̈ U ̈ A is subtracted. Step 3
[0125] In a third process step, the deviation of the compressor inlet superheat dT is measured. ÜE and the control deviation of the evaporator outlet superheat dT̈ U ̈ A advantageously combined to prevent overall control deviation and overheating.
[0126] The combination is achieved in particular by means of a weighted addition of the individual rule deviations.
[0127] The weighting influence is a measure of the proportional combination of the individual rule deviations and, in extreme cases, can result in the exclusive inclusion of only one individual rule deviation, but usually it results in the weighted inclusion of both individual rule deviations.
[0128] Advantageously, the weighting influence is estimated as a value between 0 and 1, i.e., 0 to 100%, and this value is applied to the degree of inclusion of the control deviation of the compressor inlet superheat dT. U ̈ E included in the total control deviation, resulting in the following dependency for calculating the total control deviation: Total − control deviation U ¨ overheating = ( weighting influence * control deviation compressor inlet u ¨ overheating ) + ( ( 1 − weighting influence ) * control deviation evaporator outlet u ¨ overheating ) Tva
[0129] The value of the weighting influence can be advantageously determined by the operating mode and / or the operating point of the heat pump. 100 The following variations may occur depending on the circumstances: • During the changeover between operating modes = operation with the compressor switched off 210 and operating mode = operation with compressor switched on 210 During heating operation, due to the dynamic process value changes when starting up the steam compression system, 200 Advantageously, only the control deviation evaporator outlet superheat dT̈ is initially addressed. U ̈ A included in the overall rule deviation, in particular the value of a weighting influence is initially = 0 or a value advantageously below 20%. • After a stabilization phase of the vapor compression system 200It is advantageous not to switch spontaneously to the weighting influence value designed for normal operation, but rather to design the transition as a ramp. In this case, it is advantageous for the weighting influence value to be increased from the initial value of 0, or a value particularly below 20%, to the intended target value in a ramp-like manner. This avoids, in particular, value discontinuities during a spontaneous switch and thus prevents control oscillations. • The target value of the weighting influence is advantageously adapted to the respective operating mode and operating point. Operating points characterized by increased oscillation tendency advantageously require a lower weighting of the control deviation of the compressor inlet superheat dT. U ̈ E , in particular, this addresses a control-technically critical signal behavior of the compressor inlet superheat dT U ̈ Edue to the evaporator outlet superheat dT ÜA Larger signal delays and steeper track gradients prevented oscillations. Step 4:
[0130] In a fourth process step, the calculated total control deviation of the overheating is then entered into the controller. 500 processed, which includes the corresponding actuators of the refrigeration circuit, in particular the expansion valve 230 with the adjustable opening degree and / or the compressor 210 with adjustable compressor speed, so that in the regulated case the control deviation of the superheat is set to approximately 0 Kelvin.
[0131] A P, I, PI, PID controller can be used, whereby the control components are advantageously dynamically adapted to the respective operating mode and the operating point.
[0132] Fig. Figure 3 shows a schematic and exemplary flowchart of a process.1000 for controlling a compression refrigeration system 200 .
[0133] In one step 1010 A temperature is recorded that is representative of the surface temperature of a component of the refrigeration circuit, which during operation of the refrigeration circuit can fall below a dew point temperature of the air surrounding the refrigeration circuit containing water vapor.
[0134] In one step 1020 A minimum temperature is calculated to ensure that the surface temperature of the component does not exceed the dew point, based on a recorded environmental parameter.
[0135] In one step 1030 A minimum value for the overheating dT will be set. U ̈ Eof the refrigerant from a) the minimum temperature to ensure that the dew point is not exceeded and b) a corresponding evaporation temperature of the refrigerant used for the superheat calculation, which would result in the dew point being exceeded on the surfaces of low-pressure-side components of the refrigeration circuit.
[0136] In one step 1040 The maximum is determined from a) a provided setpoint value of the overheating dT. U ̈ E of the refrigerant for regular operation of the compression refrigeration system 200 and b) the calculated minimum value of the overheating dT U ̈ E of the refrigerant.
[0137] In one step 1050 The thoracic organ 230 then on the as in step 1040 The maximum value of the refrigerant superheat is regulated. QUOTES INCLUDED IN THE DESCRIPTION
[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature
[0000] DE 10159892 A1
[0005] DE 102005061480 B3
[0006]
Claims
[1] Method for controlling a compression refrigeration system (200) with - a refrigerant, - an evaporator (240), - a compressor (210), - a liquefier (220), - a thoracic organ (230), - an internal heat exchanger (250) for transferring heat energy from the refrigerant before it enters the throttling device (230) to the refrigerant before it enters the compressor (210), and - a control unit (500) a) to detect overheating (dT U ̈ E ) of the refrigerant upon entering the compressor, whereby the superheat (dT U ̈ E ) is defined as the difference between a dew point temperature and a temperature of the refrigerant, and b) for regulating the throttle device (230)) based on the superheat (dT U ̈ E ), the procedure comprising the following steps: - Measurement of a temperature that is representative of a surface temperature of a component of the refrigeration circuit, which during operation of the refrigeration circuit can fall below a dew point temperature of the air surrounding the refrigeration circuit containing water vapor, - Calculation of a minimum temperature to ensure that the surface temperature of the component does not exceed the dew point, based on a recorded environmental parameter, - Calculation of a minimum value of superheat (dT) U ̈ E ) of the refrigerant from a) the minimum temperature to ensure that the dew point is not exceeded and b) a corresponding evaporation temperature of the refrigerant underlying the superheat calculation, which would result in the dew point being exceeded on the surfaces of low-pressure-side components of the refrigeration circuit, - Determining the maximum from a) a provided setpoint for overheating (dT U ̈ E ) of the refrigerant for regular operation of the compression refrigeration system (200) and b) of the calculated minimum value of the overheating (dT) U ̈ E ) of the refrigerant, and - Control of the throttling device (230) to the maximum determined value of the refrigerant superheat. [2] Method according to claim 1, wherein the control of the throttling device (230) is set to the maximum determined value of the superheat (dT). U ̈ E ) of the refrigerant at least in assigned operating modes of the compression refrigeration system (200). [3] Method according to one of the preceding claims, wherein the temperature which is representative of the surface temperature of a component of the refrigeration circuit is detected at at least one of a refrigerant tube, the internal heat exchanger (250), or a refrigerant separator (260). [4] Method according to one of the preceding claims, wherein the minimum temperature to ensure that the dew point is not exceeded is calculated on the basis of a room temperature sensor and a room humidity sensor to detect the environmental parameter. [5] Method according to any of the preceding claims, wherein the compression refrigeration system (200) is a compression refrigeration system installed inside a building. [6] Method according to one of the preceding claims, wherein the superheat value (dT) used to control the throttling device (230) U ̈ E ) is kept within a permissible overheating range for the compressor (210). [7] Compression refrigeration system (200) with - a refrigerant, - an evaporator (240), - a compressor (210), - a liquefier (220), - a thoracic organ (230), - an internal heat exchanger (250) for transferring heat energy from the refrigerant before it enters the throttling device (230) to the refrigerant before it enters the compressor (210), and - a control unit (500) a) to detect overheating (dT U ̈ E ) of the refrigerant upon entry into the compressor (210), wherein the superheat (dT U ̈ E ) is defined as the difference between a dew point temperature and a temperature of the refrigerant, and b) for regulating the throttle device (230) based on the superheat (dT) U ̈ E ), wherein the control unit (500) is configured to control the compression refrigeration system (200) according to the following steps: - Measurement of a temperature that is representative of a surface temperature of a component of the refrigeration circuit, which during operation of the refrigeration circuit can fall below a dew point temperature of the air surrounding the refrigeration circuit containing water vapor, - Calculation of a minimum temperature to ensure that the surface temperature of the component does not exceed the dew point, based on a recorded environmental parameter, - Calculation of a minimum value of superheat (dT) U ̈ E ) of the refrigerant from a) the minimum temperature to ensure that the dew point is not exceeded and b) a corresponding evaporation temperature of the refrigerant underlying the superheat calculation, which would result in the dew point being exceeded on the surfaces of low-pressure-side components of the refrigeration circuit, - Determining the maximum from a) a provided setpoint for overheating (dT U ̈ E ) of the refrigerant for regular operation of the compression refrigeration system (200) and b) of the calculated minimum value of the overheating (dT) U ̈ E ) of the refrigerant, and - Regulation of the throttling device (230) to the maximum determined value of superheat (dT) U ̈ E ) of the refrigerant. [8] Compression refrigeration system according to claim 7, wherein the refrigerant has a temperature glide, wherein the refrigerant in particular comprises or consists of R454C. [9] Heat pump (100), in particular an indoor heat pump (100), with a compression refrigeration system (200) according to claim 7 or 8.