Demand-based and energy-efficient extraction of kitchen exhaust air

Abstract

1) Method and device for rapidly increasing the throughput of an extraction device, in particular for the energy-efficient and demand-based extraction of kitchen exhaust air, comprising at least the following components: - Extraction hood 110 - preferably a centrifugal grease pre-separation - a fan 140 which is provided with a speed control for a variable amount of extraction air and - which can therefore increase the extraction rate from a low partial load operation particularly quickly, i.e. preferably by a factor of at least two, particularly preferably by a factor of at least five and most preferably by a factor of at least eight characterized by the fact that To rapidly increase the extraction volume, at least one of the following methods and devices must be used. - Increasing the speed of the fan 140 by providing a flywheel 146, preferably designed as a flywheel or a technically equivalent design, which can ideally transfer the (mechanical) energy stored in the flywheel or the technically equivalent design quickly to the fan by means of a coupling 144. - Introduction of jet-pulse compressed air 120 - Switching on a separate peak load fan 162, which is advantageously integrated into the extraction system via at least one control damper 166. - Connection of a vacuum reservoir 168, which is preferably kept under negative pressure for a long term or permanently by means of an evacuation blower 170 and which can advantageously be integrated into the extraction system via at least one valve or flap 172.

Description

[0001] The invention primarily aims to increase energy efficiency, especially in the area of ​​kitchen exhaust air extraction, preferably in commercial kitchens.

[0002] In commercial kitchens with multiple cooking stations, exhaust air is often extracted at maximum volume throughout operation. The extracted air is then replaced by naturally flowing fresh air. This is particularly noticeable during the heating season when the incoming cold air must be heated separately. The demand-based extraction system proposed by the invention preferably captures only the cooking stations currently in use and optimizes the fan speed to capture the constantly changing total volume of kitchen exhaust air, while minimizing or ideally eliminating excess extraction. In addition to saving heating energy, this also reduces the electricity required to power the fan.A particular challenge in the demand-based extraction of kitchen exhaust air is capturing steam surges when pot and pan lids are opened. The invention focuses specifically on the rapid and time-limited increase in the extraction air volume to capture these surges.

[0003] The peripheral components, such as the grease separators that operate on the centrifugal principle, must be adapted to fluctuating suction volumes and flow velocities.

[0004] The invention further proposes a heat recovery system, preferably implemented via air-to-water (heat transfer fluid) finned heat exchangers. The advantage of air-to-water systems over air-to-air heat exchanger systems lies in their smaller dimensions, resulting from the significantly higher heat transfer coefficient on the water side. For further details, reference is made to the relevant sections of the VDI Heat Atlas. When the heat energy of the exhaust air has been transferred to water or another liquid medium, the recovered heat energy can be distributed via smaller pipe cross-sections compared to warm air distribution systems. This is particularly advantageous in existing buildings, for example, when the heat demand for fresh air preheating, domestic hot water heating, or a potential feed point into a heating system is located some distance from the exhaust air heat exchanger.Optionally, the heat recovered from the exhaust air can be raised in temperature using an electrically driven heat pump. A temperature increase of approximately 40 to 50 Kelvin is generally targeted to ensure a favorable ratio between electrical energy input and thermal energy output. The COP (coefficient of performance) or seasonal performance factor should be above 3, ideally above 4, and at most 5. For further information, please refer to the publications of heat pump manufacturers such as Vaillant, Viessmann, and Buderus.

[0005] In Fig. Figure 1 schematically illustrates the invention in a preferred embodiment, using as an example a cooktop 100, the fumes 102 of which are extracted by means of an extraction hood 110 and an exhaust fan 140. Preferably, a sensor 122, preferably an infrared sensor, is provided above the cooktop and monitors each cooktop from above. This sensor can preferably control a control flap 124, so that the cooktop can be vented through an open control flap when in operation. When the cooktop is not in operation, the sensor detects this based on the lower temperature, and the control flap can be closed so that the amount of air drawn in by the fan is directed to the cooktops in operation, which are shown in the diagram for clarity. Fig. 1. These are not shown separately in pictures, so that the focus can be concentrated.

[0006] Often, grease separators (here: 112, 114, 116) are integrated into the extraction hood. These separators remove a large portion of the grease load directly from the gas stream after extraction, thus significantly reducing contamination of the downstream exhaust system. These grease separators operate on the centrifugal principle, in which the extracted gas stream is guided through deflectors. At high gas velocities, the larger grease droplets, due to their inertia, can no longer follow the deflection of the gas stream and are carried by centrifugal force to the deflector walls, where they adhere and are thus separated from the gas stream.

[0007] Different deflection radii are required for different gas velocities, enabling optimal separation. This means that a single flow force separator cannot always operate in its optimal range with highly fluctuating gas flows. Fig. Figure 1 shows an example of a grease separator divided into three segments. At low extraction rates, only the fixed separator 112 is active. At medium extraction rates, the second grease separator 114 is also activated (see Figure 1). Fig. 4) And at high extraction rates, the third grease separator 116 is also activated. With increasing extraction rates, more separator surface area is exposed to the airflow, so that the flow velocity fluctuates in significantly smaller intervals and the centrifugal separation effect is improved. A different configuration of the grease separator than the three-part one described here as an example is also possible and, even without explicit mention, is part of the invention.

[0008] Preferably, the switching on and off of the flexibly deployable grease separators 2 and 3 is based on the pressure difference, particularly preferably on the pressure difference between the inlet and outlet sides of the grease separators, which results from the different flow velocities. Fig. 4. This is achieved, for example, by means of springs. The grease separation serves to pre-clean the exhaust air.

[0009] The optional exhaust air purification system 130 shown can consist, for example, of filters, potassium permanganate packings, electrostatic precipitators, or UV / ozone and plasma units, as well as combinations of the aforementioned and other individual components. This system performs a fine purification of grease and odor particles.

[0010] Furthermore, the individual air currents are in Fig. 1 shown separately, namely the warm exhaust air before exhaust air purification 132, the cold supply air before heat exchanger 2 134, the heated supply air after heat exchanger 2 136, which may optionally contain recirculated air (partially), and the cooled exhaust air after heat exchanger 1138.

[0011] The following components are provided for heat recovery from the extracted air: 150 Heat exchanger 1, preferably in finned design for heat exchange from air to water or less preferably with other heat transfer fluids, 152 Heat exchanger 2, preferably in finned design for heat exchange from water to air, (less preferably: other heat transfer fluids), advantageously with circulation pump 154 ​​for water / heat fluid circuit, 156 optional heat pump, 158 optional recirculation of air, preferably partial, the volume flow control of the recirculation portion is shown here without detailed illustration, furthermore an optional separate fan 160 can be provided for supplying the supply air.

[0012] When the lid of a cooktop is opened, a phenomenon known as steam surge occurs, in which a large amount of steam rises in a very short time. The amount of extraction air required to capture this brief surge is many times greater than that required for continuous operation of the cooktop, especially with the lid closed. The maximum extraction rate required in this case can be eight to ten times the normal extraction rate with the lid closed. In a kitchen with, for example, 10 cooktops requiring separate extraction, the extraction air rate can therefore theoretically fluctuate by a factor of approximately 8-10 x 10 = 80-100 when considering the two extreme cases: "one cooktop operating with the lid closed" and "all cooktops operating with the lid open." However, these extreme cases rarely, if ever, occur in quick succession.

[0013] The invention addresses the practical application of reliably capturing the steam surge from typically one lid opening, or at most two to three parallel lid openings, when used with 10 cooking zones. For a single cooking zone, this means that the extraction rate for that zone must be increased by a factor of approximately eight to ten within preferably less than one second. However, this factor decreases when multiple cooking zones are operating simultaneously and the baseline extraction airflow is higher.

[0014] Nevertheless, the amount of air extracted to capture the surge must be increased more quickly than a fan under load can normally increase its speed. The invention provides the following solutions for this: a) Preferred solution: rapid speed increase via a flywheel 146, which can be engaged by means of a clutch 144 and, due to its stored rotational energy, can quickly overcome the comparatively low moment of inertia of the fan 140 and its motor 142, preferably speed-controlled by a frequency converter, for normal operation without surge, thus significantly increasing the extraction volume almost instantaneously. During normal operation without surge, the flywheel 146 is maintained at its operating speed by a separate motor 148.

[0015] To ensure that the increased extraction volume resulting from the higher fan speed can be directed as quickly as possible, essentially back towards the exhaust hood, mounting the fan near the hood is beneficial. Smaller duct cross-sections can also promote the rapid propagation of the increased extraction volume due to the higher flow velocities, although this approach is limited by the general limits of typical flow velocities in kitchen exhaust systems, which are typically up to about 5 m / s.

[0016] Optionally, the flywheel can be equipped with a 145 gearbox, allowing its rotational speed to be significantly higher or lower than the maximum speed or the target speed for surge capture of the fan. Many exhaust fans are operated in practice at maximum speeds between 2,000 and 3,000 revolutions per minute. If the gearbox has a 1:5 ratio, for example, the rotational speed of the flywheel can be selected five times higher or lower.

[0017] Other variants that can be used instead of the flywheel described and preferred here, with a technically comparable effect, i.e., a comparably rapid increase in the speed of the fan 140, are also part of the invention even without explicit textual and pictorial description, since they are to be regarded as "quasi-equivalent technical embodiments" and are therefore also considered and named as flywheels within the meaning of the invention. Such alternative variants could be, for example, spring (force) accumulators, compressed air and hydraulic motors, or storage devices for potential energy, such as weights on ropes on pulleys, as used, among other things, in old cuckoo clocks driven by wind-up weights.

[0018] A less preferred option (b) is the introduction of jet-pulse compressed air (120 m³ / h), where, based on Bernoulli's principle, a negative pressure is created in the vicinity of the rapidly flowing compressed air. This negative pressure can then be used to increase the extraction air volume. This principle of negative pressure generation is used in water jet and steam jet pumps, as well as in the cleaning of industrial bag filter systems with compressed air pulses. For detailed information, please refer to the relevant technical literature on industrial filters, such as those by Löffler or Vauck / Müller. For noise reduction reasons, the application of jet-pulse technology in kitchen areas is also considered a less preferred option.

[0019] Another less preferred variant c) of the invention is in Fig. The diagram shows that, in parallel to the speed-controlled fan 140, which is responsible for the base and medium load of the extraction, there is another peak load fan 162 with its associated motor 164, which preferably runs continuously at high speed against a closed control damper 166, which is preferably installed on the intake side. When a surge occurs, this damper can be opened quickly, so that an additional volume of air is extracted abruptly.

[0020] If this additional extraction volume is to be directed specifically to one of several cooking zones, an additional duct system with a preferably small flow cross-section is advantageous for rapid propagation. This is achieved by means of a [unclear - possibly referring to a specific duct system or system]. Fig. In addition to the main duct shown in Figure 1, which handles the medium and base load of the extraction system, a parallel duct system with its own control valves allows peak loads to be directed precisely to the extraction point. However, the complexity of this parallel system is so high that its practical application appears questionable due to structural and, above all, economic considerations.

[0021] A fourth, less preferred option d) is in Fig. Figure 3 schematically depicts a cooking station. A vacuum storage container 168 is provided, which can be maintained at negative pressure during normal extraction via an evacuation blower 170. Preferably, this container can quickly and for a short period of time bring the negative pressure to the extraction point for use in the event of a detected surge via a low-cross-section extraction duct network parallel to the normal extraction system. Preferably, each individual extraction point can be supplied with a peak extraction load via separate valves or flaps 172. However, due to the large dimensions of the vacuum storage container, which can be approximately in the cubic meter range, and the high strength requirements for vacuum containers, this variant is considered less desirable.

[0022] The in Fig. The four centrifugal grease separators shown horizontally are normally installed vertically in extractor hoods above cooking surfaces. The flow forces resulting from the deflection of the gas flow primarily separate larger grease droplets on the walls, from where they run down as a liquid film. These centrifugal grease separators serve as a pre-separation device and, in their simple form, correspond to the prior art. The novel aspect of the invention is that the separation is achieved by dividing the grease into different segments, several of which are activated at higher flow velocities and close again at lower flow velocities, so that the flow velocity over the respective active segments remains approximately the same or at least within a similar range.

[0023] In the left part of Fig. Figure 4 shows a single segment of the centrifugal grease separator. This segment 180 consists of the parts 182 centrifugal grease separator according to the state of the art, shown here by way of example with three parallel channels and deflector plates with separator troughs at the end, as well as the flow control unit 184.

[0024] The incoming highly fatty exhaust air 186 flows into the centrifugal grease separator 182 on the left side and, after the coarse separation of the grease load, exits again on the right side as slightly fatty exhaust air 188.

[0025] The centrifugal grease separator includes at least one deflector plate 190, which is advantageously equipped with at least one separator channel 192 or a differently designed separation geometry for grease droplets.

[0026] The trajectory of a larger grease droplet in the gas stream 196, which is separated after the second deflection at the deflector plate or the separator channel, is shown as an example, as is the trajectory of a smaller grease droplet 198, which passes through the grease separator without separation and exits on the right side with the slightly grease-containing exhaust air.

[0027] A control flap 200 is provided which, in the closed position, blocks the gas flow through the grease separator and, in the open position, releases it. Advantageously, the control flap is provided with an opening and closing mechanism, which can preferably be simply a spring (force) 202 with a mounting 204 and is driven by a higher or lower dynamic pressure of a higher or lower volume of air flowing through the separator.

[0028] Other designs of the grease separator are possible, for example, a variant with motorized adjustment of the control flap, which, via a control system using pressure or flow sensors, ensures a largely homogeneous flow velocity through the grease separator. These and other variants are also within the scope of the invention, provided they ensure that the flow velocity through the separator remains approximately constant even with strongly fluctuating air volumes.

[0029] In the right part of Fig. Figure 4 shows an example of a grease separator consisting of three segments, where the uppermost segment is permanently open, the middle segment is open with the spring engaged, and the lower segment is closed. This example represents operation with a medium suction rate. At maximum suction rate, the lower segment would also be opened by the spring due to the higher back pressure.

[0030] With regard to sound insulation and low power consumption, the preferred variant a) with flywheel mass appears to be the most advantageous.

[0031] Combinations of the individual variants or their components are also part of the invention, even if they are not explicitly mentioned in this combination. Reference sign 100 cooking stations 102 vapors 110 Extraction hood 112 Grease separators 1 114 Grease separators 2 116 grease separators 3 120 Introduction of jet-pulse compressed air 122 Sensor for determining the activity of the cooking area, preferably designed as an infrared sensor per cooking area, particularly preferably directed from above onto the cooking area 124 Control valve 130 Exhaust air purification, e.g., filters, potassium permanganate, electrostatic filters, UV / ozone / plasma 132 warm exhaust air before exhaust air purification 134 cold supply air before heat exchanger 2 136 heated supply air after heat exchanger 2, optionally with recirculated air (partially) 138 Cooled exhaust air after heat exchanger 1 140 exhaust fan 142 Motor of exhaust fan, preferably frequency converter speed controlled 144 Clutch 145 gearbox 146 Flywheel mass, preferably flywheel 148 Motor of flywheel 150 Heat exchangers 1, preferably finned design for heat exchange from air to water, less preferred: other heat transfer fluids 152 Heat exchanger 2, preferably finned design for heat exchange from water to air, less preferred: other heat transfer fluids 154 Circulating pump for preferred water circuit, less preferred: other heat transfer fluids 156 optional heat pump 158 Optional recirculation, preferably partial, volume flow control of the recirculation portion without detailed illustration here. 160 optional fan for supply air 162 separate fan for peak load extraction 164 Motor for peak load fan 166 Control damper for peak load fan 168 vacuum storage containers 170 evacuation blowers 172 valves or flaps for targeted delivery of the negative pressure to individual suction points 180 a part of the centrifugal grease separator according to the invention for fluctuating volume flows, shown here is the subcomponent with open pressure control 182 Centrifugal grease separators according to the state of the art, shown here by way of example with three parallel channels and deflection plates with separator troughs at the end 184 Passage regulation 186 Incoming highly greasy exhaust air 188 Outflowing slightly greasy exhaust air 190 Deflection plate 192 Separator channel at the end of the deflector plate 194 Example of the trajectory of a larger fat droplet in a gas stream 196 Example of separation of the larger fat droplet in the gas stream 198 Example of the trajectory of a small droplet of grease through the grease separator 200 Control valve shown here in the open position with a solid thick line, the closed position is shown in a dashed thin line. 202 Spring for loading the control flap 200, from a certain dynamic pressure of the flow the spring opens 204 Fastening for spring 202

Claims

[1] Method and apparatus for rapidly increasing the throughput of an extraction device, in particular for the energy-efficient and demand-based extraction of kitchen exhaust air, comprising at least the following components: - Extraction hood 110 - preferably a centrifugal grease pre-separation - a fan 140 which is provided with a speed control for a variable amount of extraction air and - which can therefore increase the extraction rate from a low partial load operation particularly quickly, i.e. preferably by a factor of at least two, particularly preferably by a factor of at least five and most preferably by a factor of at least eight characterized by , that To rapidly increase the extraction volume, at least one of the following methods and devices must be used. - Increasing the speed of the fan 140 by providing a flywheel 146, preferably designed as a flywheel or a technically equivalent design, which can ideally transfer the (mechanical) energy stored in the flywheel or the technically equivalent design quickly to the fan by means of a coupling 144. - Introduction of jet-pulse compressed air 120 - Switching on a separate peak load fan 162, which is advantageously integrated into the extraction system via at least one control damper 166. - Connection of a vacuum reservoir 168, which is preferably kept under negative pressure for a long term or permanently by means of an evacuation blower 170 and which can advantageously be integrated into the extraction system via at least one valve or flap 172. [2] Method and apparatus for centrifugal grease pre-separation, which can preferably be operated by switching individual segments on and off via flow control over a wide volume flow range of the extraction with optimal flow velocity or throughput.

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