Method and device for measuring the heat output of low-temperature radiators

Abstract

1. Method and device for measuring the heat output of low-temperature radiators. 2.1 The heat output of radiators is usually recorded using electronic heat cost allocators for the purpose of consumption-based heating cost billing. This typically involves measuring the surface temperature of the radiator and a temperature difference between this surface temperature and the room air temperature using temperature sensors. However, with so-called low-temperature radiators, where increased convective heat output is achieved through forced airflow via fans, recording the heat output with conventional heat cost allocators is not possible, as the heat output depends not only on temperature differences but also on the operating state of the fan. 2.2 Additional sensors in the convection shaft of the radiator allow for consideration of the increased flow through the radiator due to fan operation and the resulting increased heat output. 2.3 Recording the heat output of low-temperature radiators.

Description

[0001] The heat output of radiators is typically recorded using electronic heat cost allocators for consumption-based heating billing. This typically involves measuring the surface temperature of the radiator and another temperature between this surface temperature and the room air temperature using temperature sensors. Fig. Figure 1 shows a schematic cross-section of a typical panel radiator with a heat cost allocator mounted on the front. Conventional radiators typically have an actual heating surface made of metal profiles (1) through which water flows, and additional convection plates (2) connected to the metal profiles in a heat-conducting manner. The heat cost allocator (3) is mounted on the front of the radiator to measure the surface temperature of the radiator or a temperature difference between the radiator and the room.

[0002] The basic principle of heat cost allocators is based on the dependence of radiator heat output on the so-called radiator surface temperature, i.e., the difference between the radiator surface temperature and the room air temperature. The difference between the temperatures detected by the sensors is, to a first approximation, proportional to the radiator excess temperature. Conventional heat cost allocators calculate the consumption value based on these relationships, using the following basic calculation rule: ΔZ=Ktot⋅Δϑx with ΔZ display progress K ges Rating factor Δϑ Temperature difference between radiator and room temperature sensor x exponent

[0003] The evaluation factor K ges takes into account the standard heat output of the radiator and the so-called thermal coupling, which is determined by the ratio of the measured temperature difference to the total radiator excess temperature.

[0004] The radiators commonly used to date release heat primarily through natural convection and radiation. With such radiators, a sufficiently accurate relationship is assumed between the determined consumption values ​​and the actual heat output. However, for some time now, so-called low-temperature radiators have been increasingly used. These are particularly intended for heating systems with heat pumps, which have a higher heat output than conventional radiators of the same size at the same operating temperatures. This is achieved by significantly increasing the convective heat output through additional forced convection with the help of fans integrated into the radiator. The performance of the radiator is adjusted not only - as with conventional radiators - by varying the water flow using a valve, but also by varying the air flow, e.g.by controlling the speed of the fans.

[0005] With such radiators, the radiator output depends not only on the radiator overtemperature, but also on the operating status of the fans. The aforementioned relationship between the consumption values ​​determined with conventional heat cost allocators and the actual heat output is no longer sufficiently accurate with these low-temperature radiators.

[0006] To solve this problem, a method for recording the heat dissipation of radiators and a correspondingly enhanced heat cost allocator are proposed. In addition to the usual recording and evaluation of temperature measurements, additional measurements of other physical quantities are evaluated. These are, in particular, measurements that can be used to determine the increased convective heat dissipation during fan operation.

[0007] In one embodiment, the radiator can be equipped with two recording devices, with the first device operating like a conventional heat cost allocator and recording consumption corresponding to the heat dissipation of the radiator in the absence of fan support. The second recording device must accordingly record the additional heat dissipation during increased convection. The following describes the operation of the additional recording device. As with conventional radiators, the heat dissipation in the convection shaft, here with forced convection due to fan operation, depends on the temperature difference between the radiator surface and the air to be heated. Therefore, temperatures must be recorded, as with conventional heat cost allocators.However, the heat transfer coefficient, which describes the heat transfer from the heating surface to the air, is not determined solely by the temperature difference between the heating surface and the room air, as is the case with natural convection, but primarily by the imposed air velocity within the convection shaft. To accurately measure heat transfer in the convection shaft, additional parameters, such as the air velocity or the volume flow in the convection shaft, must be recorded. Various solutions are proposed for this purpose.

[0008] In one embodiment, an analog or digital electrical signal can be derived directly from the fan unit. Depending on the fan's operating mode or control system, current, voltage, or frequency are suitable. Furthermore, a digital signal indicating the fan's current operating status can be determined in the fan unit and forwarded to the heat cost allocator's evaluation unit. A prerequisite for these solutions is therefore that the radiator or fan manufacturer provides a suitable interface.

[0009] This limitation is avoided with a further embodiment of the invention. The flow velocity in the convection shaft is measured using an anemometric method. Due to their small size, thermal anemotricity methods are particularly suitable for this purpose. The sensor can be designed in a robust semiconductor design. A disadvantage is the necessary heating of the sensor, which must be covered by the battery of the heat cost allocator. This problem can be reduced by only operating the sensor in pulsed mode, e.g. by heating it up for just a few seconds at regular intervals of a few minutes. To save battery capacity, the energy required for heating can in principle also be obtained from the environment, in particular using a thermoelectric method utilizing the temperature difference between the radiator and the room air.The thermogenerators used can in principle also be combined with temperature sensors that are required anyway or even replace them, since the thermoelectric voltage generated depends on the prevailing temperature difference.

[0010] The flow through the convection shaft generated by the fans leads to different temperature distributions depending on the flow velocity. Fig. Figure 2 schematically shows the temperature curves of both the radiator surface and the air in the convection shaft (e.g., in the center of the flow channel formed by the shaft). With a large water-side mass flow (valve open), the surface temperature of the radiator follows an almost linear temperature curve (curve (4)). The air temperature, in contrast, has a non-linear curve depending on the air velocity. The air flowing through the convection shaft heats up. At low flow rates, particularly when the fan is switched off or the fan speed is low, the air in the convection shaft heats up to near the heating surface temperature (curve (5)). At stronger air-side flow, however, the air heats up less, and the temperature curve remains significantly flatter (curve (6)).By measuring temperature differences between the surface and heated air at different points in the flow shaft, an approximate value for the heat transfer coefficient can be determined.

[0011] For heating energy recording with a heat cost allocator, the exact determination of heat transfer is not necessary. Rather, there must be a sufficiently accurate relationship between the display progress determined from the sensor measurements and the actual heat output for the relevant operating conditions. The measuring points for recording the temperature differences should be as far apart vertically as possible. Depending on the radiator design, however, the sensor positions should be a certain distance from the upper or lower edge of the convection shaft to avoid measurement distortions, e.g., due to radiation influences or similar. Suitable positions for the respective sensor pairs are in the upper and lower thirds of the convection shaft. It is crucial that the measuring points are always positioned according to uniform rules for the respective radiator design, e.g., always at 10% and 90% of the height of the convection shaft.

[0012] In a preferred embodiment, both of the measuring principles shown can be used to take the air flow in the radiator into account, i.e. measurements from several temperature sensors as well as additional measurements with at least one anemometer can be evaluated. With the help of the anemometric measurements, the measuring behavior of the temperature sensors can be checked, e.g. distortions due to contamination can be detected in order to adapt the evaluation of the temperature signals when determining the display progress. The comparative evaluation of the measured values ​​of the temperature sensors and the at least one flow sensor can then take place at longer intervals, e.g. once a day. At other times, the flow sensor can be switched off to save energy.

[0013] The determination of the display progress corresponding to the additional power compared to a conventional radiator without fan support can be carried out similarly to a conventional heat cost allocator according to the following basic relationship: ΔZ2=K2⋅Δϑ2

[0014] This means: Δ Z2 display progress K2 dynamic rating factor to take into account radiator size and operating condition of the fan Δϑ temperature difference

[0015] No exponent needs to be applied to the temperature difference Δϑ2, since the load-dependent heat transfer coefficient is taken into account when determining the evaluation factor K2.

[0016] The evaluation factor K2 is calculated depending on the design type based on the available measured values ​​or signals: K2=f1(s1) or K2=f2(s2) or K2=f3(Δϑo, Δϑu)

[0017] This means: s1 analogue or digital signal from the control unit (8) of the fan (7) to the evaluation unit (13) s2 measured value of the flow sensor (11) Δϑ o Temperature difference measured at the upper position with the sensor pair (9) and (10) Δϑ u temperature difference measured at the lower position

[0018] The functions f1, f2, f3 must be determined based on laboratory measurements or evaluations by the radiator manufacturer.

[0019] The temperature difference Δϑ2 should correspond to the average temperature difference between the radiator surface and the air in the convection shaft. This average value can be calculated by averaging the temperature differences measured at the upper and lower positions, for example, using the following equation: Δϑ2=Δϑu−Δϑoln(ΔϑuΔϑo)

[0020] Fig. Figure 3 shows a preferred embodiment of the device according to the invention mounted on a low-temperature radiator. Reference numerals (1), (7), and (8) indicate the actual radiator. The convection plates (2) are not shown here for clarity.

[0021] In detail they mean: 1 Water flowing through metal profiles of the radiator 7 Fan with drive motor 8 Control unit for the fan 9a Surface temperature sensor in upper position 10a Air temperature sensor in upper position 9b Surface temperature sensor in lower position 10b Air temperature sensor in lower position 11 Flow sensor 12 measuring or signal lines 13 Evaluation unit

[0022] The individual measurement or signal lines (12) can be combined, for example, as ribbon cables or similar. In principle, these lines (12) can also be replaced by suitable wireless transmission paths. Furthermore, the evaluation unit (13) can also be integrated into a single device with the conventional heating element distributor (3).

[0023] When determining the evaluation factor K2 using temperatures measured by sensors (9a) and (10a) as well as (9b) and (10b), precise positioning of the sensors and good thermal contact between the sensors (9a) and (9b) are important. For this purpose, it is proposed to arrange the sensors in an elastic sensor carrier (14), which is clamped between the water-carrying metal profiles during installation.

[0024] Fig. 4 shows in detail: 1 Water-carrying metal elements 2 convection plates 9a,b Surface temperature sensors 10a,b Air temperature sensors 14 elastic sensor carrier

[0025] For this purpose, the sensor carrier (14) is inserted, for example, from below into the convection shaft of the radiator and positioned precisely using a suitable gauge. Once the sensor carrier has been positioned, it can be permanently fixed in place using a force-locking or form-locking mechanism, for example using a suitable clamping device or a metal claw that hooks into the radiator elements (1) or (2). The clamping device or metal claw can be actuated, for example, using a screw element during assembly. It is also proposed to secure the position of the sensors (9a), (9b), (10a), (10b) or the sensor carriers using a suitable seal in order to prevent unauthorized removal or displacement of the sensors and to be able to detect such unauthorized intervention.

[0026] For accurate temperature and air flow measurements, it is advantageous to minimize disturbances to the flow field. It is proposed to position the sensors at the bottom of the sensor carrier (14), on the air inlet side, in order to achieve the most undisturbed flow to the sensors. Furthermore, the sensor carrier (14) should restrict the flow cross-section for vertical flow as little as possible. It is also advantageous to position the sensor carriers (14) for the upper and lower measuring positions, and if necessary, the sensor carrier (14) for the flow sensor (11), offset horizontally, i.e., to mount them in different vertical flow channels formed by the convection plates, so that unavoidable disturbances to the flow field do not affect the other sensors.

Claims

[1] Method for measuring the heat consumption of a radiator equipped with one or more fans, characterized by that in addition to the components of a conventional heat cost allocator, further sensors are installed whose measured values ​​are related to the increased convection during fan operation and these measured values ​​are evaluated to determine the increased convective heat emission. [2] Method according to claim 1, characterized by that measured values ​​of at least one additional sensor are essentially related to the air flow in the inner convection space of the radiator and that these measured values ​​are evaluated to determine the increased heat emission of the radiator. [3] Method according to claim 2, characterized by that the measured values ​​of the additional sensor depend directly on the operating state of the fan and are derived in particular as an electrical signal from the fan control unit. [4] Method according to claim 2, characterized by that the at least one additional sensor is designed as a flow sensor (11), the measured values ​​of which are influenced by the speed of the air flow in the inner convection space of the radiator. [5] Method according to claim 1, characterized by that at least two additional sensors (9) and (10) are arranged in the inner convection space of the radiator, with which temperatures or differences are recorded, which are evaluated to determine the increased convective heat emission. [6] Method according to claim 5, characterized bythat at least four additional sensors (9a) and (10a), as well as (9b) and (10b) are arranged in the inner convection space of the radiator, wherein the sensor pairs (9a) and (10a) as well as (9b) and (10b) are arranged to detect temperature differences at different heights of the convection shaft, in particular the sensor pair (9a) and (10a) in the upper third of the convection shaft, the sensor pair (9b) and (10b) are arranged in the lower third of the convection shaft. [7] Method according to claims 4 and 6, characterized by that the flow condition or correction factor K2 determined with the aid of the temperature measured values ​​from the sensors (9a), (10a), (9b) and (10b) is compared with the measured values ​​of the flow sensor (11), whereby the flow sensor (11) is only operated at long intervals (e.g. once a day for a few seconds) to save energy. [8] Device, in particular for carrying out the method according to claims 1 to 7, characterized by that in addition to the components of a conventional heat cost allocator, further sensors are installed whose measured values ​​are related to the increased convection during fan operation, and these measured values ​​are evaluated to determine the increased convective heat emission. [9] Device according to claim 8, characterized by that the additional sensors are combined with a separate evaluation unit to form a second heat cost allocator, whereby the sum of the consumption values ​​determined by this heat cost allocator and the consumption values ​​determined by the conventional heat cost allocator together represent the total heat output of the equipped radiator. [10] Device according to claim 8, characterized bythat the components of a conventional heat cost allocator and the other sensors are combined to form an integrated heat cost allocator, whereby the measured values ​​of all sensors are evaluated in a common evaluation unit and a uniform consumption value is determined for the entire heat output of the equipped radiator. [11] Device according to claims 8 to 10, characterized by that the control unit (8) of the fan (7) has an electrical interface via which electrical measured variables or digital signals are transmitted to the evaluation unit (13) and these measured variables or digital signals represent the air flow in the inner convection space of the radiator. [12] Device according to claims 8 to 10, characterized bythat at least one sensor is designed as a flow sensor (11), e.g. as a thermal anemometer, whose measured values ​​are influenced by the speed of the air flow in the inner convection space of the radiator. [13] Device according to claim 12, characterized by that the heating current of the flow sensor (11) designed as a thermal anemometer is generated by means of thermogenerators. [14] Device according to claims 8 to 10, characterized by that sensors are arranged in the inner convection chamber of the radiator to record temperatures or differences in temperature. [15] Device according to claim 14, characterized by that sensors (9a) or (9b) measure the surface temperature of the radiator and, with further sensors (10a) or (10b), the air temperature of the air flowing through the convection chamber. [16] Device according to claims 12 to 15, characterized bythat the sensors are positioned in the convection chamber of the radiator using elastic sensor supports (14). [17] Device according to claim 16, characterized by that the sensor carriers (14) are fixed in the convection chamber of the radiator in a force-locking or form-locking manner and that unauthorized dismantling is prevented by a seal.

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