DE102021211258A1 - Evaluation device and sensor system for spatially resolved room air monitoring - Google Patents

Abstract

Battery-operated CO2 sensors, which are connected wirelessly, are distributed in the room and their measured values are recorded wirelessly by a central device for spatially resolved room air detection, in particular carbon dioxide measurement to determine an aerosol concentration. Processing is carried out there and a result signal is output. The result signal is output to subscribing devices such as smartphones directly or via a cloud service.

Description

In the case of infectious diseases that can be spread by aerosols, the probability of infection between people is significantly favored by physical proximity and the duration of this proximity. This is particularly the case where there are large numbers of people, for example in meeting rooms, classrooms and catering establishments. A possible reduction in the probability of infection results from consistent ventilation, which demonstrably reduces the aerosol concentration in the room.

In the simplest case, the room is manually ventilated at fixed intervals by opening the windows. In the case of professional building technology with central room ventilation, this can be set to a suitable value with a high air exchange volume. However, such is not available in most buildings, especially in schools. Another variant is the use of portable room air filters. These offer good protection against aerosols, but are comparatively expensive and therefore unaffordable for many institutions. Therefore, ventilation often relies on the rules of "common sense". If the weather conditions permit, all windows will be permanently open. If the outside temperature is too low, you rely on shock ventilation about every 20 minutes. In addition, the number of people allowed in the room at the same time can be limited. However, it is not clear to the people present whether these measures are sufficient in individual cases or whether ventilation is even unnecessary.

The aerosols emitted during breathing and their concentration in the room air correlate directly with the carbon dioxide concentration in the room, which is also caused by breathing. It is known that an indication of the aerosol concentration can be derived from the carbon dioxide concentration. A carbon dioxide sensor arranged in the room to be monitored can therefore be used to emit a signal that triggers ventilation of the room, where the signal can cause an automated response, for example by a ventilation system or a manual response if the signal is a visual one, for example or acoustic signal.

The disadvantage is that such a classic carbon dioxide sensor is arranged on a wall or in a corner of the room and therefore cannot detect locally different concentrations of carbon dioxide. As a result, a carbon dioxide concentration that is actually already critical and therefore also a critical aerosol concentration can remain hidden from the carbon dioxide sensor for a short or even long term. This can be countered by providing limit values, which cause a signal for room ventilation, with appropriate safety margins from the actually critical values. However, this in turn has the disadvantage that the resulting ventilation specifications become unfulfillable, especially in the cold season or when other reasons speak against prolonged ventilation.

It is the object of the present invention to specify an evaluation device with which the disadvantages mentioned at the outset can be overcome.

This object is achieved by an evaluation device having the features of claim 1.

The evaluation device according to the invention for a distributed sensor system in a room in a building comprises a microcontroller and an interface for wireless or wired communication. It is also designed to receive measured values from a plurality of gas sensors via the interface and to determine from the measured values whether and when fresh air needs to be supplied to the room or increased, and to generate a first signal in this case. Furthermore, the evaluation device is designed to determine from the measured values whether and when a supply of fresh air to the room can be prevented or reduced, and to generate a second signal for this case. Finally, the evaluation device is designed to send the signals directly by means of a second interface for wireless communication or indirectly via an interposed data network to one or more mobile data processing devices registered for receiving the signals.

By the distributed sensor system is meant a system comprising a plurality of individual gas sensors arranged at different locations. In this case, these gas sensors are distributed in the space for which the measurement is to be made. The evaluation device includes a microcontroller as the data-processing central unit. Microcontrollers are typically used in technical devices in which the computing capacity and peripherals of a microprocessor, such as those used in PCs, are unnecessary or cannot be installed. The interface for communication can be a WiFi interface, for example. The measurement data from the gas sensors are received via this interface and subsequently evaluated. It goes without saying that the gas sensors expediently have the same interface for this purpose. The mobile data processing devices are, for example, smartphones, smartwatches or tablet PCs. In order to receive the signals, they are registered, for example as a subscription registered with a cloud service. The signals can then be, for example, SMS messages or notifications about an installed app. The app can be an app specific to this process or an app that is already installed elsewhere, such as a messenger service.

The evaluation device can form a sensor system together with the gas sensors. The sensor system includes at least two gas sensors, which are arranged in a spatially distributed manner in a room of a building and include, for example, a wireless communication device for wirelessly transmitting measured values to the evaluation device.

• Die Auswerteeinrichtung kann ausgestaltet sein, Schwellwerte für die Messwerte der Gas-Sensoren, insbesondere für die Kohlendioxid-Konzentration von einer öffentlich verfügbaren Quelle zu beziehen. Das Beziehen solcher Schwellwerte kann beispielsweise über das Internet erfolgen.

Advantageous configurations of the evaluation device according to the invention emerge from the dependent claims. The embodiment according to claim 1 can be combined with the features of one of the dependent claims or preferably also with those of several dependent claims. Accordingly, the following features can also be provided for the evaluation device:

• The evaluation device can be designed to obtain threshold values for the measured values of the gas sensors, in particular for the carbon dioxide concentration, from a publicly available source. Such threshold values can be obtained, for example, via the Internet.

Advantageously, this ensures that current specifications regarding the indoor air quality are always complied with, without manual intervention or other maintenance of the system being necessary for this purpose. One source for current and officially valid guidelines in Germany is the German Federal Health Office. However, it makes sense to adapt the source used to local conditions, e.g. to use the official values of a respective country. If official threshold values are generally not available or are not currently available, a secondary source, such as stored threshold values, can be used as a fallback position. These saved values can be the last available official threshold values or basic values saved as factory settings.

The evaluation device can have three or more communication interfaces of different types. For example, the evaluation device can have a Bluetooth interface, a WiFi interface and a LAN connection. While there is a wireless communication interface for connecting to the gas sensors, the other communication interfaces do not all have to be wireless.

The communication interfaces enable the evaluation device to establish a connection to all necessary devices in a particularly flexible and unproblematic manner. For example, a connection to the gas sensors can be established via Bluetooth, a connection to smartphones or tablets via WiFi and a connection to the Internet via a LAN connection. The evaluation device thus represents an ideal hub between the gas sensors and the recipients of the information on indoor air quality.

The evaluation device can include a device for determining the position of the gas sensors. For example, it can be designed to determine the three-dimensional position of the gas sensors relative to the evaluation device. The gas sensors can be configured in hardware and/or software to support position determination.

If the position of the gas sensors is known, it can be used to advantage for an improved evaluation of the measurement results. For example, a weighting can be assigned to the individual measured values of the gas sensors. This weighting can, for example, turn out to be lower for gas sensors that are arranged spatially close to one another than for those gas sensors that are arranged far away from other gas sensors. Also, gas sensors located near the ceiling may be scored differently from those located near the floor to account for the fact that carbon dioxide is heavier than oxygen and nitrogen and therefore tends to accumulate near the floor.

The position can be determined, for example, by means of a radar system or by means of acoustic signals. Triangulation can be used.

The gas sensors are preferably designed in such a way that the measured value is a measure of the carbon dioxide concentration. Carbon dioxide is a good indicator of indoor air quality because humans emit this gas in quantities that are large compared to other substances such as aromatic hydrocarbons. Aromatic hydrocarbons also have a high diversity of substances, which makes detection more difficult and less reliable. Carbon dioxide, on the other hand, is emitted by people in a reliable manner and the concentration is certainly directly related to the number of people in a room and the presence or absence of fresh air supply men. On the other hand, other sources of carbon dioxide are rare in normal building spaces, while substances such as aromatic hydrocarbons are also emitted, for example, by cleaning agents.

The sensor system can include an internet-based cloud service, in which the evaluation device is designed to forward the measured values or values determined from the measured values to the cloud service. The measured values or the values determined from them are thereby available in a simple manner and can be called up by subscribing devices. Such subscribing devices can be smartphones, tablets or a building management system, for example.

Further advantages and features can be found in the following description of exemplary embodiments with reference to the figures. In the figures, the same reference symbols designate the same components and functions.

• 1 einen Besprechungsraum mit einem Netzwerk drahtlos gekoppelter Kohlendioxid-Sensoren,
• 2 den Aufbau des Kohlendioxid-Sensors,
• 3 den Aufbau einer Auswerteeinrichtung für die Kohlendioxid-Sensoren,
• 4 ein von den Kohlendioxid-Sensoren, der Auswerteeinrichtung, einem Cloud-Service und mobilen Kommunikationsgeräten gebildetes Netzwerk.

Show it:

• 1 a meeting room with a network of wirelessly coupled carbon dioxide sensors,
• 2 the construction of the carbon dioxide sensor,
• 3 the construction of an evaluation device for the carbon dioxide sensors,
• 4 a network formed by the carbon dioxide sensors, the evaluation device, a cloud service and mobile communication devices.

1 shows a schematic of a meeting room 10. The meeting room 10 has an area of about 80 m^2. Several tables 11 are assembled in the meeting room 10 to form a U-shaped arrangement. Chairs are in for a better overview 1 not shown. A cabinet 12 is placed on one side of the meeting room 10 .

A projector 13 is attached to the ceiling of the meeting room 10 and is used to display digital content on one of the walls of the meeting room 10 . Furthermore, an outlet 14 of a ventilation system is arranged on the ceiling of the meeting room 10 . The ventilation system also includes air conditioning.

There is a separate WLAN router 15 in the meeting room 10 for the wireless connection of PCs, smartphones and tablets. This is arranged on a wall of the meeting room 10 near the ceiling.

Meeting room 10 also includes an in 1 only indicated entrance door as well as several windows, which in 1 are not shown.

Although ventilation is possible via the ventilation system and also by opening the windows, these opportunities to improve air quality are often either overused or underused. On days when the weather is nice and the outside temperature is pleasant, the windows may be open all the time, which is not a problem for protection against infection and air quality.

In most cases, however, the windows will be closed and the ventilation will not be used. The reasons for this are, for example, noise pollution from outside, which makes opening the windows unattractive, heat or cold or other weather conditions in which opening the windows is uncomfortable and also a lack of will on the part of the people present. Furthermore, even with a gradual deterioration in air quality, the people present may not notice the air quality and therefore take no countermeasures.

If the people present do not pay attention to the air quality, the carbon dioxide concentration and the concentration of aerosols in the room air will increase over time. Apart from subjective influences such as lack of concentration, the aerosols in the air represent a risk of infection that should be countered.

A sensor system is arranged in the meeting room 10 for this purpose. The sensor system includes a number of carbon dioxide sensors 21 which are distributed in the meeting room 10 . The sensors 21 are distributed both in the plane over the meeting room 10 and mounted at different heights. Advantageously, the room air is not monitored at a fixed point. A fixed location of a single sensor is inevitably problematic. If it is too close to a window, it judges the air in the room to be better than it actually is. If he is far away from all windows, possibly also in a place where air circulation is prevented, he judges the room air to be worse than it really is. Distributed sensors, on the other hand, record the air quality at different points in the meeting room 10, so that individual disadvantageous positions of sensors 21 are compensated for by better positions of other sensors 21.

Part of the gas sensors 21 are attached to the underside of the tables 11 with a layer of adhesive. Advantageously, this means that even when the tables 11 are changed, the Senso ren 21 always remain distributed over the room. In addition to gluing, the sensors 21 can also be attached to the tables 11 in some other way, for example screwed or with a magnetic holder. Magnet holders are particularly flexible and allow easy and non-destructive maintenance or replacement of the sensors 21.

In addition to the sensors 21 arranged on the tables 11, further sensors 21 are arranged on the projector 13, ie near the ceiling of the meeting room 10, on the cupboard 12 and on two opposite walls of the room. In the present example, the sensor system thus includes twelve sensors 21. However, this number is an example and depends on the desired accuracy of the measurement and the size of the room. In smaller rooms, the sensor system can also include only four sensors 21, while even more sensors 21, for example 30 or 40 such sensors 21, can be used in even larger rooms.

The structure of a sensor 21 is shown schematically in 2 shown. A sensor 21 includes a sensor unit 211. This can be based on an infrared measurement, for example. In this case, an air path is illuminated by infrared light, for example from an infrared laser or a light-emitting diode. A light sensor, for example a photodiode, is arranged opposite the light source and picks up the light after it has passed through the air gap. The concentration of carbon dioxide can be determined from the absorption of certain wavelengths that are characteristic of carbon dioxide. Another variant of sensors uses photoacoustic spectroscopy.

The output signal from the sensor unit 211, ie the signal from the photodiode, for example, is digitized and output to a simple microcontroller 212. The microcontroller 212 controls a wireless communication device 213 in order to send the signal wirelessly.

The sensor unit 211, the microcontroller 212 and the communication device 213 are supplied with power by a battery 214. Since a measurement of the carbon dioxide concentration is usually not required frequently, for example only once every minute or even only once every five minutes, the operating time of the sensor 21 is not too limited by the finite battery capacity. In other configurations of the sensor 21, however, it can also be operated by means of energy harvesting. A solar cell can be used for this purpose, for example. Alternatively or additionally, the energy of an interrogation signal that is picked up by the communication device 213 can be stored and used for the measurement. This makes the sensor 21 independent of a finite charge battery.

The signals from the sensors 21 are evaluated centrally in an evaluation device 20, which is also part of the sensor system. In this exemplary embodiment, the evaluation device 20 is arranged in the vicinity of the router 15 near the ceiling. As a result, on the one hand a good connection to the router 15 and thus to the Internet via WLAN or a short cable connection to the router 15 is possible and on the other hand the wireless connection to the sensors 21 is made more difficult by as few obstacles as possible.

If a connection via a router is not possible, the evaluation device 20 can also be designed to establish a connection to the Internet 30 using LTE, for which a corresponding communication device must be available.

The structure of the evaluation device 20 is shown schematically in 3 shown. The evaluation device 20 accordingly includes a microcontroller 201. The microcontroller 201 is connected to a WiFi interface 203, a Bluetooth interface 204 and a LAN interface 205. In contrast to the sensors 21, the evaluation device 20 includes a connection 202 for an external power supply . For the microcontroller 201, peripheral devices such as memory are available, but in 3 are not explicitly shown.

The evaluation device 20 is designed to record the measured values sent wirelessly by the sensors 21 . Depending on the number of sensors 21, this can be done, for example, by means of the Bluetooth interface or with another form of wireless communication.

The evaluation device 20 can receive information about how many sensors 21 are present in the meeting room 10 . However, it is more flexible if the evaluation device 20 creates this information itself from the signals recorded by the sensors 21 or if a connection is made, for example, by means of a pairing, as is known from routers for WLAN coupling. For this purpose, the measured values sent by the sensors 21 preferably include a unique identifier for the respective sensor 21. The evaluation device 20 can thus create a table with the sensors 21 currently present at any time from the signals received. The evaluation device 20 can also emit a warning signal if a sensor 21 is no longer sending any signals.

Once the measured values have been recorded, they are processed by the evaluation device 20 . The Depending on the configuration of the sensors 21, processing can include a conversion of the signals into a concentration. Alternatively, this step can also have already been carried out by the sensors 21 .

A subsequent step is the creation of a final value for the carbon dioxide concentration, which is used as a total value for the meeting room 10 . This value can be calculated, for example, as a weighted average of the sensors. The weighting can include various factors. For example, values that deviate greatly from values that precede them in time or that differ greatly from the values of other sensors 21 can be given a low weighting or be ignored entirely. It is also possible to include previous measured values.

It is particularly advantageous if the position of the sensors 21 can be included in the determination of the final value for the carbon dioxide concentration. The position of the sensors can be specified for the evaluation device 20 from the outside. For example, an installer can use a smartphone app to mark the position automatically using a camera or manually using a graphic editor. However, it is more flexible if the evaluation device 20 itself determines the position together with the sensors 21 . For this purpose, for example, a triangulation based on signal strengths of the wireless communication can be carried out. Alternatively or additionally, other signals such as sound or radar can also be used to determine the position of the sensors 21 relative to the evaluation device 20 . At least this advantageously determines the direction and distance, but ideally the three-dimensional position of each of the sensors 21 .

If the position of the sensors 21 is known, the measured values can be weighted better. For example, the height of the sensor above the ground can be included in the weighting. Because carbon dioxide is heavier than air (heavier than molecular oxygen and nitrogen), it tends to collect on the ground. The signals from sensors 21 arranged near the ceiling can then, for example, be weighted less than the signals from sensors 21 near the floor.

A further possibility of weighting consists in weighting sensors 21 which are arranged close to one another less than those which are arranged far away from other sensors 21 . As a result, the influence of systematically correlated measured values can be reduced.

A three-dimensional distribution of the concentration of carbon dioxide can also be determined. With this three-dimensional distribution, it is possible to detect when the limit values are exceeded in parts of the room, even if the average concentration in the room remains below the threshold value.

Once a final value for the concentration of carbon dioxide has been determined, this can be compared with one or more threshold values to determine whether a change in the ventilation of the meeting room is appropriate. Threshold values for this can be stored in the evaluation device 20, for example as a factory setting. This is also useful as a fallback position if current threshold values are obtained from another source, in order to still be able to act if this source fails.

One way of obtaining the threshold values from another source is to access a cloud service 40 via the Internet 30. The integration of the evaluation device 20 and the other components in a communication network is shown schematically in FIG 4 shown.

As already described above, the sensors 21 are wirelessly connected to the evaluation device 20 . The evaluation device 20 receives measured values from the sensors 21 via this connection. The evaluation device 20 is also connected to the router 15, and this connection can be wired, ie a LAN connection, or wireless as a WiFi connection. The evaluation device 20 is connected to the Internet 30 via the router and in turn to a cloud service 40 via the router. The cloud service can be part of the sensor system. In this case, the evaluation device 20 has all the data that is necessary for establishing a connection and bidirectional communication with the cloud service, ie at least the IP address, but also cryptographic data.

It is possible that currently suitable threshold values for the carbon dioxide concentration are provided by the cloud service 40 and are retrieved and used by the evaluation device 20 . This data can be provided to the cloud service 40 manually or received there automatically.

In another embodiment, the evaluation device 20 takes current threshold values from an official source on the Internet, for example from the website of the Federal Environment Agency. As a result, locally valid threshold values that are always adapted to current knowledge are advantageously used.

A comparison of the final concentration of carbon dioxide with a first threshold value is carried out at fixed time intervals, which expediently correspond to the timing at which the sensors 21 send their measured values. If the threshold value, which is also referred to as the warning value, is exceeded, the evaluation device 20 generates a signal which is transmitted to the people present in the room and requests them to supply fresh air to the room.

In addition to simple signal tones or a light signal, the signal can also be transmitted by transmitting the signal to registered data processing devices such as smartphones 42 , 43 , smart watches or tablet PCs 41 . For this purpose, the signal is transmitted to the cloud service 40 as digital information. The cloud service 40 in turn transmits the information to data processing devices that have subscribed to the information, ie are registered with the cloud service 40 . Such a registration can take place, for example, via a QR code, which is printed, for example, on the evaluation device 20 or is provided on signs in the meeting room 10 . Finally, such a signal can also be sent directly to the data processing devices via WiFi or Bluetooth.

The signal prompts recipients to increase ventilation of the meeting room 10 to reduce carbon dioxide levels. This can be done, for example, by opening windows or increasing ventilation using an existing technical ventilation system.

A second signal is generated when the carbon dioxide concentration in the room air falls below a second, lower, threshold value (referred to as the all-clear value). This is made available to the persons present and subscribing (subscribers) in the same way as the first signal. The second signal states that the fresh air supply in the meeting room 10 can be reduced or switched off again, since the quality of the room air is good/harmless again. This advantageously signals not only the start of ventilation, but also the end of it, which is particularly important in winter or in the case of other disturbing circumstances, so that the windows are not closed too early, but also not unnecessarily late.

The ongoing measurements of the indoor air quality via the carbon dioxide content also make it possible to analyze the dynamics of the changing air quality and to make a prediction as to when the carbon dioxide concentration will cross one of the two threshold values. Depending on this dynamic, the all-clear value for the carbon dioxide concentration, i.e. the second threshold value, can then be adjusted so that ventilation does not have to be carried out too frequently.

Reference List

10

meeting room

11

Table

12

Wardrobe

13

projector

14

Inlet for air supply

15

routers

20

evaluation device

201

microcontroller

202

Connection for power supply

203...205

communication interfaces

21

carbon dioxide sensor

211

sensor unit

212

microcontroller

213

communication interface

214

battery

30

Internet

40

cloud service

41

tablet

42, 43

smartphone

Claims (10)

Evaluation device (20) for a distributed sensor system in a room (10) of a building, which comprises a microcontroller (201) and an interface (203...205) for wireless or wired communication and is designed, - to receive measured values of a plurality of gas sensors (21) by means of the interface (203...205), - to determine from the measured values whether and when a fresh air supply to the room (10) must be carried out or increased, and to generate a first signal for this case, - to determine from the measured values whether and when a supply of fresh air to the room (10) can be prevented or reduced, and to generate a second signal for this case, - the signals are sent directly by means of a second interface (203...205) for wireless communication or indirectly via an interposed data network (30, 40) to one or more mobile data processing devices (41...43) registered for receiving the signals. Evaluation device (20) after claim 1 , designed, threshold values for the measured values of the Gas sensors (21), in particular for the carbon dioxide concentration, can be obtained from a publicly available source. Evaluation device (20) after claim 1 or 2 , having at least three communication interfaces (203...205) of different types. Evaluation device (20) according to one of the preceding claims with a device for determining the position of the gas sensors. Evaluation device (20) after claim 4 , in which the device for determining the position is designed to determine the position of the gas sensors (21) by means of radar. sensor system with - a plurality of gas sensors (21) spatially distributed in a room (10) of a building, the gas sensors (21) comprising a wireless communication device (213) for the wireless transmission of measured values, - An evaluation device (20) according to any one of the preceding claims. sensor system claim 6 , in which the gas sensors (21) are designed in such a way that the measured value is a measure of the carbon dioxide concentration. sensor system claim 7 , designed to determine the position of the gas sensors (21) by means of a triangulation using acoustic signals. sensor system claim 7 or 8th with an Internet-based cloud service (40), in which the evaluation device (20) is designed to forward the measured values to the cloud service (4ß). sensor system claim 9 , in which the cloud service (40) is designed to pass on measurement results to subscribing mobile data processing devices (41...43).

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