Method for determining a water content in an air flow in a temperature-control system

Abstract

The invention relates to a method (200) for determining a water content in an air flow (11) in a temperature-control system (100) having a refrigerant circuit (120) which contains a refrigerant (12) and comprises a compressor (124) for compressing the refrigerant (12) and a heat exchanger (130) for transferring heat between the refrigerant (12) and the air flow (11), in particular in a vehicle, the method (200) comprising determining (212) an air mass flow through the heat exchanger (130), determining (210) an enthalpy difference in the air flow (11) across the heat exchanger (130), determining (220) a heat output of the refrigerant (12) in the heat exchanger (130) and determining (218) the water content in the air flow (11) on the basis of the determined heat output of the refrigerant (12), the enthalpy difference and the air mass flow. The invention also proposes a computing unit (140) and a computer program for carrying out such a method.

Description

[0001] Description

[0002] title

[0003] Method for determining a water content in an air stream of a temperature control system

[0004] The present invention relates to a method for determining a water content in an air stream of a temperature control system as well as a computing unit and a computer program for carrying out the method.

[0005] Background of the invention

[0006] A temperature control system, particularly a vehicle air conditioning system, is designed to set a temperature, e.g., the cabin air inlet temperature, according to a requested target temperature. This temperature can be set, for example, by the speed of a refrigerant compressor, such as an air conditioning compressor. The required heat output can be subject to significant fluctuations depending on the humidity of the air to be tempered. Such fluctuations can be compensated, for example, by a controller of the temperature control system. As soon as the requirements of the cabin air conditioning system, e.g., the requested target temperature and / or air volume, change, a change in the compressor speed is typically necessary.To achieve acceptable response times given the typically long response times of the cabin air inlet temperature to the implemented speed change, pre-controlled speed changes are used. For example, if the requested temperature is reduced, the speed can initially be increased significantly to reach the target temperature as quickly as possible, while the speed can be reduced again at a later point if the temperature only needs to be maintained, meaning only compensation for heat input into the cabin air is required. If no humidity sensor is present, the air humidity is usually unknown.However, due to the different specific heat capacities of water compared to the other components of air and in particular due to the latent heat output of water, i.e. the heat output resulting from the phase change between liquid and gaseous, this has a massive influence on the required heat output. Especially during cooling, the released condensation heat (at least when the air to be cooled is locally saturated with water vapor) must also be dissipated in order to achieve the desired target temperature. Therefore, the pre-controlled value can only contain an assumption regarding the required heat output, and the controller may have to subsequently correct any incorrect assumptions. When parameterizing the controller, a compromise between temperature overshoot and response time typically has to be determined and accepted.

[0007] Disclosure of the invention

[0008] According to the invention, a method for determining the water content in an air stream of a temperature control system, as well as a computing unit and a computer program for implementing the method, are proposed, having the features of the independent patent claims. Advantageous embodiments are the subject of the dependent claims and the following description.

[0009] The invention makes use of the measure of determining the water content of an air flow in a temperature control system, e.g. in a vehicle air conditioning system, by comparing the heat output of a refrigerant in the temperature control system with a temperature difference of an air flow with a known air mass flow achieved by this heat output. The water content can be deduced from the temperature difference actually achieved, since water differs considerably from the other components of air in terms of its specific heat capacity and the latent heat output already explained at the beginning. For this reason, knowledge of the water content is also useful, among other things, for controlling the temperature control system, since with a high water content, a higher heat output is required to set a predetermined target temperature than is the case with a low water content.The invention makes it possible to determine the water content of the air even without dedicated sensors. In the following, the term "heat absorption capacity" is used when referring to a combination of heat capacity and latent heat output in the sense already explained.

[0010] Specifically, the invention proposes a method for determining a water content in an air stream of a temperature control system with a refrigerant circuit. The refrigerant circuit contains a refrigerant and comprises a compressor for compressing the refrigerant and a heat exchanger for transferring heat between the refrigerant and the air stream, and can be used in particular in a vehicle. The method comprises determining an air mass flow through the heat exchanger, determining an enthalpy difference of the air stream across the heat exchanger, determining a thermal output of the refrigerant in the heat exchanger, and determining the water content in the air stream based on the determined thermal output of the refrigerant, the enthalpy difference, and the air mass flow.

[0011] In at least one embodiment, the water content is determined as the relative humidity and / or the mass fraction and / or volume fraction and / or molar fraction of water in the air flow. Additional useful information can be derived from the relative humidity, such as the probability of condensation or the perceived temperature. The other parameters mentioned can be used directly to control the compressor, as they provide a concrete indication of the heat absorption capacity of the air to be tempered.

[0012] In at least one embodiment, the method further comprises determining a thermal output of the air flow in the heat exchanger based on the thermal output of the refrigerant. The heat balance with respect to the air flow can be determined relatively easily from the thermal output provided by the refrigerant, in particular if heat loss to the environment and / or components of the temperature control system is known or can at least be well estimated. In this case, the method can in particular comprise determining a theoretical thermal output of a dry air flow based on the thermal output of the refrigerant, the enthalpy difference, and the determined air mass flow, and determining the water content based on a difference between the theoretical thermal output of the dry air flow and the determined thermal output of the air flow.As already explained, the water content has a decisive influence on the specific heat capacity of the air, or rather, the heat output required to cool the water-containing air (including the latent heat output of the condensing water). Conversely, the water content can be determined if the heat output is known. In other words, the water content can be determined from the theoretical heat absorption capacity and the actual heat absorption capacity of the air, since the difference is essentially due to the water contained in the air.

[0013] In at least one embodiment, the thermal output of the refrigerant and / or, if determined, the theoretical thermal output of the dry air can be determined from a respective inlet temperature upstream and / or at an inlet of the heat exchanger and a respective outlet temperature downstream and / or at an outlet of the heat exchanger and a respective mass flow through the heat exchanger. These variables can be determined relatively easily using sensors and / or models. Mass flows can be determined, for example, from the conveying or compression capacity of the compressors, fans, or pumps used and the respective associated physical properties (e.g., density, pressure, temperature, etc.) of the fluids being moved (refrigerant and / or air).

[0014] In at least one embodiment, the method comprises adjusting a compression power of the compressor and / or a delivery power of a fan conveying the air flow based on the determined water content. As already mentioned, the water content particularly influences the heat absorption capacity of the air, so that this parameter can be used as an input variable for precise and targeted control of the compressor. When adjusting the compression power and / or the delivery power, a target temperature of the air flow downstream of the heat exchanger can be taken into account, with the target temperature optionally being determined based on a user specification. Typically, a predetermined target temperature is to be controlled by means of a temperature control system, which can often be specified by a user, so that this target temperature is expediently also used as an input variable in the control of the compressor.

[0015] A computing unit according to the invention, e.g. a control unit of a temperature control system, in particular of a motor vehicle, is configured, in particular in terms of programming, to carry out a method according to the invention.

[0016] The implementation of a method according to the invention in the form of a computer program or computer program product with program code for carrying out all method steps is also advantageous, since this entails particularly low costs, in particular if an executing control unit is also used for other tasks and is therefore already present. Finally, a machine-readable storage medium is provided with a computer program stored thereon, as described above. Suitable storage media or data carriers for providing the computer program are, in particular, magnetic, optical, and electrical memories, such as hard disks, flash memories, EEPROMs, DVDs, and others. Downloading a program via computer networks (Internet, intranet, etc.) is also possible. Such a download can be wired or cable-based or wireless (e.g., via a WLAN network, a 3G, 4G, 5G, or 6G connection, etc.).

[0017] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

[0018] The invention is illustrated schematically in the drawing using an exemplary embodiment and is described below with reference to the drawing. Brief description of the drawings

[0019] Figure 1 shows a temperature control system as it can be used in embodiments of the invention, in a schematic representation.

[0020] Figure 2 shows schematically an embodiment of the invention in the form of a simplified flow chart.

[0021] Embodiment(s) of the invention

[0022] Figure 1 schematically shows a temperature control system, as can be used in embodiments of the invention, designated overall by 100. The temperature control system 100 comprises a refrigerant circuit 120 with a compressor 124 (also referred to as a refrigerant compressor) and an air system 110, which are in thermal exchange with one another by means of a heat exchanger 130, so that heat can be transferred between a refrigerant 12 contained in the refrigerant circuit 120 and an air flow 11 guided in the air system 110 via the heat exchanger 130.

[0023] For example, the temperature control system 100 can be provided in a vehicle, in particular to control the temperature of the air in a cabin 112 of the vehicle. For this purpose, the air flow 11 can be taken entirely or partially from the cabin 112, for example, using a fan 114, and fed to the heat exchanger 130. Alternatively or additionally, the air flow 11 can be taken partially or completely from the vehicle's surroundings and temperature-controlled in the heat exchanger 130 before being introduced into the cabin 112.

[0024] In the example shown, sensors 116, 126, 118, 128 are provided both in the refrigerant circuit 120 and in the air system 110, upstream and downstream, or at a respective inlet and outlet of the heat exchanger 130, by means of which state variables of the refrigerant 12 or the air flow 11 can be detected. In particular, these state variables can comprise one or more of a temperature, a pressure, and a mass flow. State variables not detected by sensors can also be determined model-based in embodiments, for example, using a calculation rule or on an empirical basis.

[0025] A computing unit 140 is connected to sensors 116, 118, 126, 128 to receive data and controls compressor 124 and / or blower 114, in particular to set a target temperature in the cabin 112.

[0026] It goes without saying that a functioning temperature control system may require additional components, such as valves, additional heat exchangers, and the like. However, these are not explicitly shown here for the sake of clarity.

[0027] Figure 2 illustrates an embodiment of the invention, in particular a method according to the invention, using a simplified flowchart and designated overall by 200. In the following, the method 200 is also explained in connection with the temperature control system 100 shown in Figure 1. However, it should be expressly emphasized that the method can also be carried out with other temperature control systems, so that references to components of the system 100 are to be understood merely as examples for illustration and not as a definition of the invention for the specifically described system 100.

[0028] In the example shown, an air mass flow is determined in step 212, which can be done using a corresponding sensor (e.g., hot-wire air mass meter or the like) or model-based, e.g., using a speed of the fan 114.

[0029] A model-based determination of the air mass flow can be implemented, for example, based on a physical model of the fan 114 as follows: The current air mass flow can be calculated, for example, from an air volume flow and the air density. The air volume flow is, in turn, determined from the voltage and current of an electrical power supply to the fan 114 (alternatively or additionally, other signals, such as speed and air damper position in the HVAC or supply voltage, duty cycle, and air damper position in the HVAC, can also be used to calculate the air volume flow). The air density upstream of the heat exchanger 130 is calculated from the air humidity, the temperature upstream of the heat exchanger 130, and the pressure upstream of the heat exchanger 130 (each on the air system 110 side).

[0030] In a step 210 of the method 200, an enthalpy difference in the air stream 11 via the heat exchanger 130 is further determined. For example, a difference between an inlet temperature detected by the sensor 116 and an outlet temperature of the air stream detected by the sensor 118 can first be determined. From this temperature difference, the desired enthalpy difference can be determined using the air mass flow determined in step 212 and other influencing variables, which can be entered, for example, as empirically determined constants or as numerically determined parameters. In particular, the enthalpy before and after the heat exchanger 130 can be determined using air properties and the air pressure, the temperature, and the water content.

[0031] From mass flow and enthalpy difference, a heat output of the air flow 11 in the heat exchanger 130 can be determined:

[0032] QAIV Air (HU s Hds^

[0033] Where Q Air the heat output of the air flow, m Air the air mass flow and (H us - H ds ) the enthalpy difference across the heat exchanger 130.

[0034] In a step 220, a thermal output of the refrigerant 12 in the heat exchanger 130 is also determined. For this purpose, a temperature difference or enthalpy difference on the refrigerant side across the heat exchanger 130 can be evaluated. The thermal output of the refrigerant can be determined, for example, based on the following equation:

[0035] Where Q Ref the heat output of the refrigerant, m Ref the mass flow of the refrigerant and (H us - H ds ) the enthalpy difference of the refrigerant across the heat exchanger 130.

[0036] For example, the current refrigerant mass flow m Refbe determined by means of a compressor model which is based, for example, on the speed of the compressor 124, the compression ratio and the refrigerant density upstream of the compressor 124.

[0037] The enthalpy upstream of the heat exchanger 130 can be determined, for example, via refrigerant properties and pressure and temperature information at the point upstream of an expansion valve (not explicitly shown) in the refrigerant circuit 120, since subcooling of the refrigerant 12 usually occurs there (isenthalpic change of state via expansion valve).

[0038] The enthalpy after the heat exchanger 130 can be calculated, for example, using refrigerant properties and pressure and temperature information after the heat exchanger 130, since superheating of the refrigerant usually occurs there.

[0039] If subcooling or superheating is not present, the enthalpies of the dew line or boiling line can be used. As the deviation of the refrigerant quality from the values ​​underlying the model increases, the error or inaccuracy with which the heat output is determined increases, and thus also the error in the determined humidity.

[0040] Alternatively or additionally, the heat output of the refrigerant 12 in the heat exchanger 130 can be calculated from a current electrical power and / or a speed of the compressor 124, in particular taking into account an operating point-dependent efficiency.

[0041] From the influencing variables determined in steps 210, 212 and 220, a water content in the air stream 11 is determined in a step 218, for example in the form of a mass fraction of water in the air stream 11 or in the form of a relative humidity of the air stream 11. Since the water content is included in several of the partial calculations already explained here, an analytical calculation of the same is difficult to implement. The determination of the water content can therefore be carried out in particular by numerical means, e.g. as numerical optimization. Such a numerical determination of the water content is possible both in a calculation step with several iterations (e.g. bisection method) or within the framework of an optimization that approximates the solution by means of a large number of calculation steps (e.g. integrator that calculates a difference between the two heat outputs Q Ref and Q Air minimized).

[0042] Based on the determined water content, the performance of the compressor 114 is adjusted in a step 224, in particular by adjusting the speed, in order to achieve a desired target temperature in the cabin 112 as quickly and accurately as possible. The water content can also be used to control the delivery rate of the fan 114, which is indicated in Figure 2 by a step 214.

Claims

Claims 1. A method (200) for determining a water content in an air flow (11) of a temperature control system (100) with a refrigerant circuit (120) containing a refrigerant (12) and comprising a compressor (124) for compressing the refrigerant (12) and a heat exchanger (130) for transferring heat between the refrigerant (12) and the air flow (11), in particular in a vehicle, the method (200) comprising: Determining (212) an air mass flow through the heat exchanger (130), Determining (210) an enthalpy difference of the air flow (11) across the heat exchanger (130), Determining (220) a heat output of the refrigerant (12) in the heat exchanger (130) and Determining (218) the water content in the air flow (11) based on the determined heat output of the refrigerant (12), the enthalpy difference and the air mass flow.

2. Method (200) according to claim 1, wherein the water content is determined as relative air humidity and / or as mass fraction and / or volume fraction and / or molar fraction of water in the air stream (11).

3. The method (200) according to claim 1 or 2, comprising determining a thermal output of the air flow (11) in the heat exchanger (130) based on the thermal output of the refrigerant (12).

4. The method (200) according to claim 3, comprising determining a theoretical heat output of a dry air flow based on the heat output of the refrigerant (12) and the determined air mass flow, and determining the water content based on a difference between the theoretical heat output of the dry air flow and the determined heat output of the air flow (11).

5. Method (200) according to one of the preceding claims, wherein the heat output of the refrigerant (12), and / or, if dependent on claim 4, the theoretical heat output of the dry air, are determined from a respective inlet temperature upstream (116, 126) and / or at an inlet of the heat exchanger (130) and a respective outlet temperature downstream (118, 128) and / or at an outlet of the heat exchanger (130) and a respective mass flow through the heat exchanger (130).

6. Method (200) according to one of the preceding claims, comprising adjusting a compression power (224) of the compressor (124) and / or a delivery power (214) of a fan (114) conveying the air flow on the basis of the determined water content.

7. The method (200) according to claim 6, wherein a target temperature of the air flow (11) downstream of the heat exchanger (130) is taken into account when setting the compression power (224) and / or the conveying power (214), in particular wherein the target temperature is determined on the basis of a user specification.

8. A computing unit (140) configured to carry out all method steps of a method (200) according to any one of the preceding claims.

9. A computer program which causes a computing unit to carry out all method steps of a method according to one of claims 1 to 7 when executed on the computing unit.

10. A machine-readable storage medium having a computer program according to claim 9 stored thereon.

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