Ceiling mountable luminaire with co2 sensor

Abstract

A ceiling-mountable luminaire (100) is provided. The ceiling-mountable luminaire comprises a carbon-dioxide, CO2, sensor (106) configured to measure a CO2 level at a ceiling (20) of a room (10). The luminaire further comprises a thermopile sensor (108) configured to determine a surface temperature of a surface (30a, 30b) below the ceiling. The luminaire further comprises a temperature sensor (110) configured to determine a ceiling temperature at the ceiling, and a processor (116). The processor is configured to determine a temperature difference (Tdiff) between the surface and the ceiling based on the surface temperature and the ceiling temperature, determine a validity factor (V) of CO2 measurements of the CO2 sensor based on the temperature difference. The validity factor of the CO2 measurements indicates a level of confidence that the CO2 measurements reflect a room CO2 level.

Description

[0001] CEILING MOUNTABLE LUMINAIRE WITH CO2 SENSOR

[0002] TECHNICAL FIELD

[0003] The present disclosure relates generally to the field of monitoring air quality. Specifically, it relates to ceiling-mountable luminaires comprising carbon-dioxide sensors.

[0004] BACKGROUND

[0005] Ventilation is a major factor in energy consumption of modern buildings. Quantifying a (dynamic) amount of ventilation that is actually needed, might thus have a large effect on overall energy use.

[0006] Carbon dioxide (CO2) is an important parameter for Indoor Air Quality (IAQ) monitoring and Demand Controlled Ventilation (DCV). Scientific studies have investigated the influence of CO2 on the human body. For example, some studies suggest that CO2 at low concentration may influence decision making. Further, CO2 can act as a proxy for other correlated parameters of air quality. For example, levels of CO2 in a room may be correlated with unpleasant smells and concentrations of airborne pathogens.

[0007] Different proposals have been made for how to best position CO2 sensors for accurately measuring the CO2 level in a room. Current consensus in the field, as prescribed by LEED and proposed ASHRAE standards, is that CO2 sensors should positioned at the wall at 0.9 - 1.8 m (3 - 6 ft) height.

[0008] The recent pandemic has further drawn attention to the importance of air quality monitoring and ventilation. With the general interest in reducing energy consumption in all fields of technology, development within the air monitoring and ventilation is ever ongoing, searching for more energy efficient and reliable solutions.

[0009] JP2012215403A discloses a plurality of sensor units that detect different physical quantities. US2018 / 372364A1 discloses a light fixture comprising a sensor device. US2020 / 352001A1 discloses a luminaire with a sensor system in its base housing.

[0010] SUMMARY

[0011] One general aim of the present disclosure is to provide improved indoor CO2 monitoring. Specifically, there is a desire to be able to arrange CO2 sensors at the ceiling. It is therefore an object of the present invention to meet at least some of the above-mentioned goals, and to provide an improved luminaire including CO2 sensing functionality.

[0012] This and other objects are achieved by means of a luminaire and a method as defined in the appended independent claims. Other embodiments are defined by the dependent claims.

[0013] According to a first aspect of the present disclosure, a ceiling-mountable luminaire, or light fixture, is provided. The ceiling-mountable luminaire comprises a carbondioxide sensor (CO2-sensor) configured to measure a CO2 level at a ceiling of a room. The luminaire further comprises a thermopile sensor and a temperature sensor. The thermopile sensor is configured to determine a surface temperature of a surface below the ceiling. The temperature sensor is configured to determine a ceiling temperature at the ceiling. The luminaire further comprises a processor. The processor is configured to determine a temperature difference between the surface and the ceiling based on the surface temperature and the ceiling temperature and determine a validity factor of CO2 measurements of the CO2 sensor based on the temperature difference. The validity factor of the CO2 measurements indicates a level of confidence that the CO2 measurements reflect a room CO2 level.

[0014] In exhaled air, carbon atoms (C) have been added to inhaled oxygen molecules (O2), forming CO2. The exhaled air has a higher temperature than the air that was inhaled and it further comprises added H2O vapor.

[0015] It is well known that warm air rises, and cool air sinks. This is due to air buoyancy resulting from differences in air density. The density is affected by the temperature of the air, as well as the weight of the gas molecules making up the air. In exhaled air, the added H2O vapor has a comparatively low molecular weight, while the added carbon atom increases the molecular weight of exhaled CO2 compared with inhaled O2. The inventor has realized that, in exhaled air, the positive buoyancy of H2O approximately compensates for the negative buoyancy of CO2, so that thermal buoyancy is the most dominant factor.

[0016] Thus, exhaled air, being warmer than the surrounding air, e.g., 20-25°C in normal office settings, may rise to the ceiling while mixing with the surrounding room air. As the exhaled air is diluted with the surrounding air, the exhaled air buoyancy decreases. Nevertheless, the exhaled air tends to collect near the ceiling. At the ceiling, the mixed exhaled air can be further diluted by air flows from air supply inlets arranged near the ceiling, which air flow often has a large horizontal component. Sensors positioned near or in the ceiling, such as in a ceiling mounted (mountable) luminaire, may thus register CO2 faster, compared with wall sensors arranged at the standard height of 0.9 - 1.8 m. The buoyancy of exhaled air may lead to the exhaled air taking longer to reach the walls of a room while mixing with the room air. Thus, the CO2 levels at the ceiling may be slightly higher than what is measured at the walls. Ideally, CO2 sensor values should reflect the concentration of CO2 in the inhaled air. As the exhaled air rises, variability between ceiling mounted sensor values may be lower than that from wall mounted sensors, and sensor measurements made at the ceiling may better represent the CO2 concentration of inhaled air, such as an (average) room CO2 level or a CO2 level at breathing height.

[0017] Air flow is essential for dispersing and diluting warm exhaled air, comprising H2O and CO2, into the room air. However, differences in air density may in some cases prevent air in a room from flowing and mixing.

[0018] Usually, warmer air rising, and colder air sinking contributes to convective air circulation in a room. However, when warm air collects at the ceiling and cold air gathers at the floor, convective air circulation may decrease or stop. For example, if the environment outside the building is cold, downwards convection may occur at the outer walls. As ventilation inlets are often arranged at the ceiling or on walls close to the ceiling, warm air may both be inserted and extracted at the ceiling. Thus, vertical mixing of the air in the room may be reduced.

[0019] Air stratification describes a phenomenon in which an air layer of lower density, such as with a higher temperature, higher humidity or less CO2, is settled above a layer of higher density air, with little mixing between the layers. If the stratification is too severe, exhaled air may have difficulty penetrating the upper layer, and may fail to reach the ceiling. This may result in CO2 measurements made at the ceiling not being representative of the room CO2 level.

[0020] The present disclosure provides a ceiling-mountable luminaire comprising a CO2 sensor. Thus, CO2 measurements are made at the ceiling. The luminaire comprises a plurality of sensors, including the CO2 sensor, the thermopile, and the temperature sensor. These may be arranged or combined in a sensor bundle or a sensor unit of the luminaire. The sensors may thus benefit from the power supply of the luminaire, instead of, e.g., battery power. The sensors of the luminaire may draw power from a power supply of the luminaire.

[0021] According to the present disclosure, a temperature of a surface below the ceiling is measured using a thermopile sensor arranged in a luminaire at the ceiling. A thermopile is a sensor capable of measuring temperatures of objects or surfaces at a distance, based on thermal radiation received from the object or surface.

[0022] A temperature at the ceiling is measured using a temperature sensor. The processor determines a temperature difference between the surface and the ceiling, such as a vertical temperature difference, or a vertical temperature gradient.

[0023] As mentioned above, air stratification may result from differences in temperature at different heights of a room. A difference in temperature between a surface below the ceiling, such as a table or a floor, and the ceiling may indicate a level of stratification, or reduction in convective circulation, of the air in the room. Thus, based on the temperature difference a level of stratification may be estimated. Therefore, a validity factor of CO2 measurements made at the ceiling may be determined based on a temperature difference between a surface below the ceiling and the ceiling. The validity factor may represent a level of confidence with which the CO2 measurements may be trusted to reflect the CO2 levels in the room. For example, if it is determined that there is a low risk for air stratification, the CO2 measurements may be labeled with a validity factor indicating a high level of confidence or trust in the measurements, or that the CO2 measurements are valid. If the temperature difference indicates that there is a risk of reduced air convection, the CO2 measurements may be labeled with a validity factor indicating a lower level of confidence or trust in the measurements, or that the CO2 measurements are uncertain. If the temperature difference indicates that there is a large risk that the air is stratified, the CO2 measurements may be labeled with a validity factor indicating a low level of confidence or trust in the measurements, or that the CO2 measurements are (or may be) invalid.

[0024] According to some embodiments, the processor may further be configured to compare the temperature difference to a first threshold. If the temperature difference is below the first threshold, the processor may classify the CO2 measurements with a first validity factor. If the temperature difference is above the first threshold, the processor may classify the CO2 measurements with a second validity factor. The first validity factor may indicate a high level of confidence in the CO2 measurements. For example, the first validity factor may correspond to the CO2 measurements being labeled valid. The second validity factor may indicate a lower level of confidence in the CO2 measurements. For example, the second validity factor may label the CO2 measurements as uncertain.

[0025] For low temperature differences, the risk of air stratification is minimal. Thus, the first threshold may be determined or selected to correspond with a temperature below which it is very unlikely that air stratification will occur. Below such a temperature difference, it may be assumed that air circulates in the room, and that CO2 measurements made at the ceiling may accurately (validly) represent a CO2 level of the room.

[0026] For example, the first threshold may be in a range between 3 and 4 °C. At temperature differences above the first threshold, the possibility of the air in the room being stratified, or of reduced convection or air flow, may increase. Thus, air circulation / convection may slow down, and the accuracy / validity of CO2 measurements made at the ceiling may be uncertain.

[0027] According to some embodiments, the processor may further be configured to compare the temperature difference to a second threshold. If the temperature difference is above the second threshold, the processor may classify the CO2 measurements with a third validity factor. The third validity factor may indicate a low confidence in the CO2 measurements. For example, the third validity factor may label the CO2 measurements as invalid.

[0028] The second threshold may be determined or selected to correspond with a temperature above which air stratification is likely to occur. When the air in a room is stratified, CO2 levels made at the ceiling may differ significantly from CO2 levels in other height regions of the room. Thus, CO2 measurements made at the ceiling may provide an invalid representation of the CO2 levels in the room.

[0029] The inventor has realized that, in for example an office setting, stratification may be expected at an 8 °C temperature difference between, e.g., the floor and the ceiling. The second threshold may for example be set in a range between 6 and 8 °C.

[0030] According to some embodiments, the thermopile sensor may comprise a single-pixel thermopile.

[0031] Single-pixel thermopiles are cheap and may be easy to implement in a ceiling- mountable luminaire. A single-pixel comprises a single measurement unit (pixel) for measuring a temperature of an object within a field of view of the pixel. Thus, careful installation may be needed to ensure that the surface intended for measuring, and no other object, is in the field of view of a single-pixel thermopile.

[0032] A measurement signal from a thermopile may be processed, e.g., using signal processing, to compensate for other objects which may be in a field of view of the thermopile. For example, the measurement signal may be averaged over time to compensate for warm or cool objects, such as a person, temporarily being in the field of view of the sensor. According to some embodiments, the thermopile sensor may comprise a multipixel thermopile. The multi-pixel thermopile sensor may be configured to detect a temperature of a surface below the ceiling for each pixel of the multi-pixel thermopile and determine a determined surface temperature of the surface based on the temperatures detected at each pixel.

[0033] Multi-pixel thermopiles are more expensive than single-pixel thermopiles, but they provide more advanced functionality.

[0034] A multi-pixel thermopile comprises a plurality of measurement units, pixels, which each measure a temperature of an object based on thermal radiation received from the object. Each pixel may receive a slightly different thermal radiation, originating from different objects / surfaces, or from different parts of the same object or surface. Thus, in embodiments including a multi-pixel thermopile, the surface temperature may be determined based on a plurality of measurements from the plurality of pixels. For example, if a pixel temperature (i.e., temperature measured by a pixel) differs significantly from the others, the pixel temperature may be disregarded as an outlier or error. In order to determine the determined surface temperature, the measurements from each of the pixels may be averaged. While averaging or processing, different pixels may be weighted differently than other pixels. For example, the pixels are often arranged in a grid or a pattern covering a certain area. In such an arrangement, central pixels may provide a more reliable measurement than peripheral pixels. Thus, central pixels may be weighted higher than peripheral pixels.

[0035] According to some embodiments, the multi-pixel thermopile sensor may be configured to select, among the temperatures detected at each pixel, a lowest detected temperature as the determined surface temperature.

[0036] The lowest detected temperature may be selected to provide a cautious estimate of the temperature difference. A higher temperature difference may correspond to a higher risk of air stratification, and thus a lower validity of the CO2 measurements. It may therefore be better to overestimate the temperature difference by selecting a lower value than what may be accurate, than to underestimate the temperature difference and thus potentially overestimate the validity of the CO2 measurements.

[0037] According to some embodiments, the luminaire may further comprise a humidity (H2O) sensor. The H2O sensor may be configured to measure a humidity level at the ceiling. The processor may further be configured to determine the validity factor of the CO2 measurements based on humidity measurements from the H2O sensor. As previously mentioned, exhaled air comprises added H2O vapor, which has a relatively low molecular weight, and thus contributes to a positive buoyancy of the exhaled air. The level of humidity, i.e., concentration of H2O vapor, in the surrounding room also affects the buoyancy of the surrounding air.

[0038] In normal office temperatures, such as between 20 and 25°C, air temperature of the exhaled air is the dominant buoyancy factor of the exhaled air. The CO2 and H2O contributions to density change in exhaled air approximately compensate for each other. At higher ambient air temperatures, the temperature difference between exhaled air and the surrounding air may be smaller, and thus the temperature-based buoyancy effect of the exhaled air may be smaller. Instead, the relative buoyancy contribution of H2O may become more dominant.

[0039] As the level of humidity in a room affects the buoyancy of exhaled air, and thus how the exhaled air disperses in a room, H2O measurements made at the ceiling may further be considered in order to better determine the validity factor.

[0040] The H2O sensor may form part of a sensor bundle or a sensor unit of the ceiling mountable luminaire.

[0041] According to some embodiments, the luminaire may further comprise a sensor unit arranged at a distance from the thermopile sensor. The sensor unit may comprise a second thermopile sensor and a second temperature sensor. The second thermopile sensor may be configured to determine a second surface temperature of a surface below the ceiling. The second temperature sensor may be configured to determine a second ceiling temperature at the ceiling. The processor may further be configured to determine the temperature difference between the surface and the ceiling based further on the second surface temperature and the second ceiling temperature.

[0042] The sensor unit may provide that surface and / or ceiling temperatures may be measured at a second position, separated from the (first) thermopile sensor. Thus, local differences in temperature between the different measured positions may be considered when determining the temperature difference between the surface and the ceiling. For example, in case a warm object is temporarily within the field of view of the first thermopile sensor, the measurement from the second thermopile sensor may be lower and may better represent the surface temperature.

[0043] The sensor unit may be external to the ceiling-mountable luminaire. The sensor unit may also be ceiling-mountable. The sensor unit may be in communication, such as wired or wireless communication, with the ceiling mountable luminaire. Specifically, the sensor unit may be in communication with the processor of the ceiling-mountable luminaire.

[0044] According to some embodiments, the thermopile sensor may be configured to measure a temperature of a floor of the room.

[0045] In other words, the surface may be the floor of the room. As cool air sinks, the floor of the room may be the coldest area. Thus, the temperature difference between the floor and the ceiling may provide a good indication of whether the air in the room is stratified.

[0046] According to some embodiments, the processor may further be configured to transmit a signal to an external recipient if the validity factor is below a predefined level.

[0047] For example, the processor may issue a warning signal to the external recipient in case it is determined that the validity of the measurements is too low, i.e., below the predefined level. Alternatively, the processor may issue a signal for the external recipient to take action, e.g., to increase ventilation or open a window.

[0048] According to some embodiments, a ceiling-mountable luminaire system is provided. The luminaire system may comprise a plurality of ceiling-mountable luminaires as described in the present disclosure. The luminaire system may further comprise a system processor in communicative contact with the plurality of ceiling-mountable luminaires. Each of the ceiling-mountable luminaires may be configured to measure a local CO2 level at the ceiling using its CO2 sensor, determine a local a surface temperature of a local surface below the ceiling using its thermopile sensor, and determine a local ceiling temperature at the ceiling using its temperature sensor. The system processor may be configured to determine, based on the local CO2 measurements, a CO2 level estimate for the room. The system processor may further be configured to determine a temperature difference estimate between the surface and the ceiling based on the local surface temperatures and the local ceiling temperatures of the plurality of ceiling mountable luminaires. The system processor may further be configured to determine a validity factor for the CO2 level estimate, based on the temperature difference estimate.

[0049] The system processor may be a processor of one of the plurality of ceiling- mountable luminaires. Alternatively, the system processor may be a separate processor.

[0050] The temperature at the ceiling or of the surface may differ across a room. For example, the temperature may be locally higher if near a heat generating or spreading object or person. Furthermore, the temperature may be lower or higher near a door, a window, or a ventilation inlet. By deriving the CO2 levels and validities from a plurality of ceiling and floor temperatures spread throughout a room, a more reliable estimate may be provided.

[0051] According to some embodiments, an air quality indication system may be provided. The air quality indication system may comprise a ceiling-mountable luminaire as described in the present disclosure. The air quality indication system may further comprise an indicating unit in communicative contact with the ceiling-mountable luminaire. The indicating unit may be configured to provide a visual output based on the CO2 measurements of the ceiling-mountable luminaire. The indicating unit may further be configured to indicate the validity factor of the CO2 measurements.

[0052] Since the Covid- 19 pandemic, air quality indicators, such as CO2 traffic lights, have become increasingly common in offices, meeting rooms and schools. In some countries, they are even required by law. Air quality indication systems often use CO2 as a measure for general air quality. As previously mentioned, CO2 levels may for example correlate with a concentration of airborne pathogens.

[0053] CO2 traffic lights communicate a measured level of CO2 in a room by a traffic light system, i.e., by using a color scheme in which green corresponds to good air quality, yellow to a less good air quality, and red indicates that the air quality is poor. When the CO2 traffic light, or other air quality system, indicates that the air quality has dropped below accepted levels, a person or system may be instructed to open a window or increase ventilation in order to improve air quality.

[0054] The air quality indication system may further indicate the validity factor of the CO2 measurements. When the vertical air flow in a room is reduced, CO2 levels may be higher at breathing height than at the ceiling. Thus, if the validity factor indicates that the confidence in the CO2 measurements is low, the users present in the room may take action to improve air circulation, and thus increase confidence in the measurements. The potential actions for removing or reducing air stratification overlap with the ones taken to improve air quality, e.g., open a window or door or increasing ventilation.

[0055] The indicating unit may for example comprise a light source. The light source may change color or intensity of the emitted light based on the CO2 measurements. The air quality indication system may have a separate indicator (e.g., LED, or similar) for indicating the validity factor. Alternatively, the same indicator may be used to indicate the validity factor, e.g., by blinking.

[0056] In an example, the air quality indication system may comprise a light source of the ceiling-mountable luminaire. A controller or processor of the ceiling-mountable luminaire may control the light source of the luminaire based on the measured CO2 measurements. For example, the controller may control an intensity or color of light emitted by the light source based on the CO2 measurements.

[0057] According to some embodiments, a controlled ventilation system may be provided. The controlled ventilation system may comprise a ceiling-mountable luminaire as described in the present disclosure. The controlled ventilation system may further comprise a ventilation system comprising a controller in communicative contact with the ceiling- mountable fixture. The controller may be configured to control the ventilation system based on the CO2 measurements of the ceiling-mountable fixture and on the validity factor of the CO2 measurements.

[0058] The ventilation system may for example include a room ventilation system, or a building management system. The ventilation system may include destratification fans. Such fans are often arranged in the ceiling to force air to circulate in the room.

[0059] The ventilation system may be configured to increase the air flow into the room if the CO2 levels are above accepted levels. The ventilation system may be configured to increase the air flow within the room or into the room if the validity of the CO2 measurements is too low.

[0060] According to a second aspect of the present disclosure, a method for monitoring carbon-dioxide, CO2, levels in a room is provided. The method comprises measuring a CO2 level at a ceiling using a CO2 sensor arranged in a ceiling-mounted luminaire. The method further comprises determining a surface temperature of a first surface below the ceiling using a thermopile sensor arranged in the ceiling-mounted luminaire. The method further comprises determining a ceiling temperature at the ceiling using a temperature sensor arranged in the ceiling-mounted luminaire. The method further comprises determining a temperature difference between the surface temperature and the ceiling temperature and determining a validity factor of the CO2 measurements of the CO2 sensor based on the temperature difference. The validity factor of the CO2 measurements indicates a level of confidence that the CO2 measurements reflect a room CO2 level.

[0061] The ceiling-mounted luminaire may be a ceiling-mounted luminaire in accordance with the first aspect of the present disclosure.

[0062] According to a third aspect of the present disclosure, a computer program product is provided. The computer program product comprises instructions which, when the computer program product is executed by a processor, cause the processor to carry out the method in accordance with the second aspect of the present disclosure. The instructions may for example be executed by a processor of a ceiling- mountable luminaire in accordance with the first aspect of the present disclosure.

[0063] It is noted that other embodiments using all possible combinations of features recited in the above-described embodiments may be envisaged. Thus, the present disclosure also relates to all possible combinations of features mentioned herein.

[0064] BRIEF DESCRIPTION OF DRAWINGS

[0065] Exemplifying embodiments will now be described in more detail, with reference to the following appended drawings:

[0066] Fig. 1 is an illustration of a room in which a ceiling-mountable luminaire, a ceiling-mountable luminaire system, an air quality indication system, and a controlled ventilation system, in accordance with some embodiments, are installed;

[0067] Fig. 2 is a schematic illustration of a ceiling-mountable luminaire, in accordance with some embodiments; and

[0068] Fig. 3 is a flow-chart illustrating a method for monitoring carbon-dioxide levels in a room, in accordance with some embodiments.

[0069] As illustrated in the figures, the sizes of the elements and regions may be exaggerated for illustrative purposes and, thus, are provided to illustrate the general structures of the embodiments. Like reference numerals refer to like elements throughout.

[0070] DETAILED DESCRIPTION

[0071] Exemplifying embodiments will now be described more fully hereinafter with reference to the accompanying drawings in which currently preferred embodiments are shown. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled person.

[0072] Figure 1 is an illustration of a room 10 having a ceiling 20 and a floor 30a. In the room 10 a first person 50a is standing, and a second person 50b is sitting at a table, having a table surface 30b.

[0073] In Figure 1, the room is divided in three height regions, a ceiling region Z1 closest to the ceiling 20, a breathing height region Z2 including the breathing height / head height of the standing person 50a and the sitting person 50b, and a floor region Z3 closest to the floor 30a. If air in the room 10 is stratified, vertical exchange of air between the ceiling region Zl, the breathing height region Z2, and the floor region Z3 may be reduced or stop completely. Thus, air exhaled at breathing height Z2 may stay in the breathing height region Z2, and not disperse into the ceiling region Zl and the floor region Z3.

[0074] At the ceiling 30, in the ceiling height region Z3, two luminaires 100a, 100b are mounted, a first luminaire 100a, e.g., a ceiling dome luminaire, and a second luminaire 100b, which is a pendant light. With further reference to Figure 2, a ceiling-mountable luminaire 100, such as the first luminaire 100a and the second luminaire 100b, will be further described.

[0075] The luminaire 100 comprises a sensor unit or bundle 114 including a CO2 sensor 106, configured to measure a CO2 level at ceiling height, i.e., in the ceiling height region Zl. The sensor bundle further comprises a thermopile sensor 108, a temperature sensor 110 and a humidity sensor (H2O sensor) 112.

[0076] A thermopile sensor measures temperature of a surface or an object at a distance, based on thermal radiation from the object or surface reaching the thermopile sensor. The thermopile sensor 108 is configured to measure a temperature of a surface below the ceiling 20, from its position at the ceiling 20.

[0077] In Figure 1, the first luminaire 100a is arranged above the floor 20a. Thus, the thermopile sensor 108 of the first luminaire 100a is arranged to receive thermal radiation Ri from the floor 20a. Based on the thermal radiation Ri, the thermopile sensor 108 of the first luminaire 100a may determine a temperature of the floor surface 20a.

[0078] The second luminaire 100b, on the other hand, is arranged above the table. The thermopile sensor 108 of the second luminaire 100b is arranged to receive thermal radiation R2 from the table surface 30b, and to determine a temperature of the table surface 20b.

[0079] The temperature sensor 110 and the H2O sensor 112 are configured to respectively measure a temperature and a humidity at the ceiling 20.

[0080] In the second luminaire 100b, the sensor bundle 114 may be arranged in a ceiling unit 102 of the luminaire 100b. The ceiling unit 102 is arranged or mounted at the ceiling, at ceiling height Zl, while a light source 122 of the second luminaire 100b is arranged in a pendant unit. As an example, ceiling unit 102 is illustrated as including a hook 130 for mounting the luminaire 100 to the ceiling 20.

[0081] The luminaire 100 may further be in contact with a sensor unit 104, comprising a second thermopile 108-1 and a second temperature sensor 110-1. As is illustrated in Figure 1, the sensor unit 104 may be arranged at a distance from the luminaire 100b. The second thermopile sensor 108-1 may thus be arranged to measure a second surface temperature at a second surface or at a second position at the same surface as the first thermopile sensor 108. Specifically, in Figure 1, the sensor unit 104 is arranged above the floor 30b, such that thermal radiation R3 from the floor may reach the second thermopile sensor 110-1 of the sensor unit 104. Thus, the luminaire 100b may measure a temperature of the floor 30a, despite the luminaire 100b being arranged above the table.

[0082] The luminaire 100 further comprises a processor 116. The processor 116 is in communication with the sensors 106, 108, 110, 112 of the sensor bundle 114. The processor 116 is also in communication with the sensor unit 104. The sensor unit 104 may be connected by a wire to the luminaire 100, and the processor. Alternatively, the sensor unit 104 may be in wireless communication with the luminaire 100. For example, the luminaire 100 may comprise a communication module 126 for wired or wireless communication with, e.g., the sensor unit 104. Further, the communication module 126 may also be configured to send signals to an external recipient 60. External recipients 60 may be external to the luminaire 100.

[0083] The luminaire 100 further comprises a light source 122 for illuminating the room 10. The light source 122 may be detachable from the luminaire 100.

[0084] A power source 124 of the luminaire 100 may provide power to the different units of the luminaire 100. Specifically, the power source 124 (illustrated as an electrical plug 124 for plugging into an electrical socket) may power the sensors 106-112, the light source 122, the processor 116 and the communication unit 126.

[0085] The processor 116 is further in communication with a memory 118. The memory 118 comprises a computer program product 120 comprising instructions executable by the processor 116. For example, the instructions may cause the processor 116 to execute a method, such as the method 1000 for monitoring carbon-dioxide, CO2, levels in a room, illustrated in Figure 3.

[0086] The processor 116 and method 1000 will be described below with reference to Figures 1-3.

[0087] The processor 116 is configured to measure, at method step 1010, a CO2 level at the ceiling 20, i.e., at ceiling height Zl, using the CO2 sensor 106. In other words, the processor 116 may receive a CO2 level measurement from the CO2 sensor 106.

[0088] At step 1020, the processor is configured to determine a surface temperature of a first surface 30a, 30b below the ceiling 20 using the thermopile sensor 108. The thermopile sensor 108 itself may have processing functionality, such that the processor 116 receives the surface temperature from the thermopile sensor 108. Alternatively, the processor 116 may determine the surface temperature based on measurements from the thermopile sensor 108.

[0089] The processor 116 is configured to determine a ceiling temperature, at step 1030, at the ceiling 20, using the temperature sensor 110. The temperature sensor 110 may have processing functionality, such that the processor 116 receives the surface temperature from the temperature sensor 110, or the temperature may be determined by the processor 116 based on measurements from the temperature sensor 110.

[0090] At step 1040, the processor 116 is configured to determine a (vertical) temperature difference between the surface temperature and the ceiling temperature. The temperature difference may be related to a level of air stratification in the room 10, between the surface 30a, 30b and the ceiling 20.

[0091] Thus, at step 1050, the processor 116 is configured to determine a validity factor of the CO2 measurements based on the determined temperature difference.

[0092] For example, as is illustrated in Figure 3, the processor 116 may compare the determined temperature difference Tdiir with a first threshold tl. The first threshold may differentiate between there being no (or at least a very low) risk for stratification, and there being a risk for air stratification. If the temperature Tdiir difference is below the first threshold tl, it may be determined that the risk of air stratification is small. Thus, the processor 116 may be configured to classify the CO2 measurements with a first validity factor VI, corresponding to a high confidence level, or “valid” measurements.

[0093] If the temperature Tdiir difference is above the first threshold tl, the temperature difference Tdiir may be in an uncertain zone or a risk zone. In this zone, above tl, the air convection in the room may slow down. The CO2 measurements in the ceiling zone Z1 may correspond to the CO2 levels in the breathing zone Z2. However, the air flow between the zones Z1-Z3 may take longer time. Thus, the processor 116 may be configured to classify the CO2 measurements with a second validity factor V2, corresponding to a lower confidence level, or “uncertain” measurements.

[0094] However, in the embodiment in Figure 3, a second threshold t2 is also used. This second threshold t2 differentiates between there being a risk of air stratification (below the threshold) and there being a high likelihood of air stratification (above the threshold).

[0095] In the method 1000, if the temperature Tdiir difference is above the first threshold tl, the temperature difference Tdiiris compared with the second threshold t2. If the temperature difference Tdiir is below the second threshold t2, the processor 116 is configured to classify the CO2 measurements with the second validity factor V2, i.e., to label the CO2 measurements as uncertain, or with a lower confidence level.

[0096] If the temperature difference Tdiiris above the second threshold t2, the processor 116 may be configured to classify the CO2 measurements with a third validity factor V3. At this level, there may be a high likelihood that the air is stratified. Thus, there may be a low confidence level in the CO2 measurements corresponding to a CO2 level of the room, e.g., in the breathing zone Zl. The third validity factor V3 may thus correspond to a low confidence level, or “invalid” measurements.

[0097] At step 1060, the processor 116 may be configured to transmit a signal to an external recipient 60 if the validity factor V is below a certain level. In the example illustrated in Figure 3, the processor 116 may be configured to transmit a signal to an external recipient 60 if the CO2 measurements are classified with the second or the third validity factors V2, V3, corresponding to uncertain or invalid measurements.

[0098] The external recipient 60 may for example be a building management system or a ventilation system. The signal may for example be a warning signal or a signal to take action, e.g., to increase ventilation.

[0099] According to embodiments of the present disclosure, ceiling mountable luminaires 100a, 100b may form part of different systems.

[0100] For example, the first and second luminaire 100a, 100b, may form part of a ceiling-mountable luminaire system. The ceiling-mountable luminaire system may further comprise a system processor 240, illustrated in Figure 1. The system processor 240 may be configured to determine a CO2 level estimate from the room 10, based on local CO2 measurements from the CO2 sensors 106 of each of the luminaires 100a, 100b. The system processor 240 may further be configured to determine a temperature difference estimate between the surface, e.g. the floor 30a, based on local (floor) surface measurements measured by the thermopile sensors 108, 108-1 of each of the luminaires 100a, 100b, and local ceiling temperatures measured by the temperature sensors 110 of each of the luminaires 100a, 100b. Based on the temperature difference estimate, the system processor 240 may be configured to determine a validity factor V for the CO2 level estimate.

[0101] In Figure 1, an air quality indicator, or an indicating unit 350, is illustrated on the table. The indicating unit 350 may, together with at least one luminaire 100a, 100b, form part of an air quality indication system. The indicating unit 350 may be in communicative contact with the luminaire 100a, 100b. The indicating unit 350, or indicator 350, may be configured to provide a visual output based on the CO2 measurements of the ceiling- mountable luminaire. For example, the indicator 350 may comprise a display on which the CO2 measurements are displayed. The indicator 350 may comprise at least one light source which may provide a light based on the CO2 measurements, such as a traffic-light system. The indicating unit 350 may further be configured to indicate the validity factor of the CO2 measurements. For example, a display of the indicator 350 may display the validity factor. Alternatively, or additionally, a light output of the indicator 350 may change depending on the validity factor.

[0102] Furthermore, a luminaire 100a, 100b may form part of a controlled ventilation system. The controlled ventilation system may further comprise a ventilation system 460, including a controller 462. The controller 462 may be in communicative contact with the luminaire 100a, 100b. In Figure 1, the ventilation system 460 is illustrated as a fan 460, such as a destratification fan. The controller 462 may be configured to control the ventilation system 460 based on the CO2 measurements of the luminaire 100a, 100b. For example, if the CO2 levels are too high, the controller 462 may increase ventilation or circulation. Further, the controller 462 may be configured to control the ventilation system 460 based on the validity factor of the CO2 measurements. For example, if the validity factor indicates uncertain or invalid measurements, the controller 462 may control the ventilation system 460 to increase ventilation. Thus, air flow in the room 10 may increase, which may reduce the risk of air stratification, and increase the validity of the CO2 measurements. Increasing the air flow / ventilation may also result in fresh air entering the room 10, and thereby reduce CO2 levels.

[0103] The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims.

[0104] For example, the air quality indication system and / or the controlled ventilation system described in the present disclosure may comprise a ceiling-mountable luminaire system as described in the present disclosure. The air quality indication system may be advantageously combinable with the controlled ventilation system.

[0105] Although features and elements are described above in particular combinations, each feature or element can be used alone without the other features and elements or in various combinations with or without other features and elements.

[0106] Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain features are recited in mutually different dependent claims does not indicate that a combination of these features cannot be used to advantage.

Claims

CLAIMS:

1. A ceiling-mountable luminaire (100) comprising: a carbon-dioxide, CO2, sensor (106) configured to measure a CO2 level at a ceiling (20) of a room (10); a thermopile sensor (108) configured to determine a surface temperature of a surface (30) below the ceiling; a temperature sensor (110) configured to determine a ceiling temperature at the ceiling; and a processor (116) configured to: determine a temperature difference (Tain) between the surface and the ceiling based on the surface temperature and the ceiling temperature; and determine a validity factor (V) of CO2 measurements of the CO2 sensor based on the temperature difference; wherein the validity factor of the CO2 measurements indicates a level of confidence that the CO2 measurements reflect a room CO2 level.

2. The ceiling-mountable luminaire of claim 1, wherein the processor is configured to: compare the temperature difference to a first threshold (tl); classify the CO2 measurements with a first validity factor (VI) if the temperature difference is below the first threshold; and classify the CO2 measurements with a second validity factor (V2) if the temperature difference is above the first threshold; wherein the first validity factor is indicative of a high level of confidence in the CO2 measurements; and the second validity factor is indicative of a lower level of confidence in the CO2 measurements.

3. The ceiling-mountable luminaire of any of the preceding claims, wherein the processor is configured to:compare the temperature difference to a second threshold (t2); and classify the CO2 measurements with a third validity factor (V3) if the temperature difference is above the second threshold; wherein the third validity factor is indicative of a low confidence in the CO2 measurements.

4. The ceiling-mountable luminaire of any of the preceding claims, wherein the thermopile sensor comprises a single-pixel thermopile.

5. The ceiling-mountable luminaire of any of claims 1-4, wherein the thermopile sensor comprises a multi-pixel thermopile, and wherein the multi-pixel thermopile sensor is configured to: for each pixel of the multi-pixel thermopile, detect a temperature of a surface below the ceiling; and determine, based on the temperatures detected at each pixel, a determined surface temperature of the surface.

6. The ceiling-mountable luminaire of claim 5, wherein the multi-pixel thermopile sensor is configured to select, among the temperatures detected at each pixel, a lowest detected temperature as the determined surface temperature.

7. The ceiling-mountable luminaire of any of the preceding claims, further comprising a humidity, H2O, sensor (112) configured to measure a humidity level at the ceiling; wherein the processor is further configured to determine the validity factor of the CO2 measurements based on humidity measurements from the H2O sensor.

8. The ceiling-mountable luminaire of any of the preceding claims, further comprising a sensor unit (104) arranged at a distance from the thermopile sensor; wherein the sensor unit comprises: a second thermopile sensor (108-1) configured to determine a second surface temperature of a surface below the ceiling, and a second temperature sensor (110-1) configured to determine a second ceiling temperature at the ceiling; andwherein the processor is further configured to: determine the temperature difference between the surface and the ceiling based further on the second surface temperature and the second ceiling temperature.

9. The ceiling-mountable luminaire of any of the preceding claims, wherein thermopile sensor is configured to measure a temperature of a floor (30a) of the room.

10. The ceiling-mountable fixture of any of the preceding claims, wherein the processor is further configured to transmit (1060) a signal to an external recipient (60) if the validity factor is below a predefined level.

11. A ceiling-mountable luminaire system comprising: a plurality of ceiling-mountable luminaires (100a, 100b) according to any of the preceding claims; and a system processor (240) in communicative contact with the plurality of ceiling-mountable luminaires; wherein each of the ceiling-mountable luminaires is configured to: measure a local CO2 level at the ceiling using its CO2 sensor; determine a local a surface temperature of a local surface below the ceiling using its thermopile sensor; and determine a local ceiling temperature at the ceiling using its temperature sensor; and wherein the system processor is configured to: determine, based on the local CO2 measurements, a CO2 level estimate for the room; determine, based on the local surface temperatures and the local ceiling temperatures of the plurality of ceiling mountable luminaires, a temperature difference estimate between the surface and the ceiling; and determine, based on the temperature difference estimate, a validity factor for the CO2 level estimate.

12. An air quality indication system comprising: a ceiling-mountable luminaire (100) in accordance with any of the claims 1-10;an indicating unit (350) in communicative contact with the ceiling-mountable luminaire, the indicating unit being configured to provide a visual output based on the CO2 measurements of the ceiling-mountable luminaire; wherein the indicating unit is further configured to indicate the validity factor of the CO2 measurements.

13. A controlled ventilation system comprising: a ceiling-mountable luminaire (100) in accordance with any of the claims 1- 10; and a ventilation system (460) comprising a controller (462) in communicative contact with the ceiling-mountable luminaire; wherein the controller is configured to control the ventilation system based on the CO2 measurements of the ceiling-mountable luminaire and on the validity factor of the CO2 measurements.

14. A method (1000) for monitoring carbon-dioxide, CO2, levels in a room, the method comprising: measuring (1010) a CO2 level at a ceiling using a CO2 sensor arranged in a ceiling-mounted luminaire; determining (1020) a surface temperature of a first surface below the ceiling using a thermopile sensor arranged in the ceiling-mounted luminaire; determining (1030) a ceiling temperature at the ceiling using a temperature sensor arranged in the ceiling-mounted luminaire; determining (1040) a temperature difference between the surface temperature and the ceiling temperature; and determining (1050) a validity factor of the CO2 measurements of the CO2 sensor based on the temperature difference; wherein the validity factor of the CO2 measurements indicates a level of confidence that the CO2 measurements reflect a room CO2 level.

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