Ventilation
Air quality:measurement and control
Well-being and the ability to concentrate are dramatically influenced by air quality and room climate. Factors such as CO2 and VOCs (volatile organic compounds) in the air can affect performance and well-being, meaning that fresh air is an issue for environments beyond schools and office buildings. So what actually constitutes ‘good’ indoor air? And how can it be maintained? Elsner Elektronik explains.
T
he most important substance in indoor air for human well- being is oxygen. However, as this oxygen is converted into ‘used air’, the carbon dioxide levels rise. CO2 is unusable for
humans, and too much of it in the air leads to tiredness and lack of concentration, and can even cause headaches in sensitive people. Fatal CO2 concentrations are not to be feared in living rooms, but the situation is different in spaces fermentation cellars, where CO2 measurement is mandatory. The decreasing performance associated with increasing CO2 concentration makes the topic particularly relevant for companies and schools. In the workplace, everyone should have a clear head, therefore the CO2 value must be below the MAK (maximum workplace concentration according to DIN 1946) of 1500 ppm. This value is already very high, as the recommended level is just 500-1000 ppm. For comparison: fresh air has 350-500 ppm.
VOC - Out with the fug The second group of interesting indoor air substances are mixed gases (VOCs). Mixed gases include harmful substances originating from adhesives, paints, building materials and cleaning agents. These can occur in harmful concentrations especially in new buildings and conversions. Ideally, the problem is reduced from the outset by the choice of building materials. Mixed gases can also be known as ‘stale air’. Unpleasant odours such as
perfume, sweat, pets, food or tobacco are undesirable in a functioning room. In rural areas, additional odour pollution can come from agriculture; in the city, from exhaust fumes.
Measuring and controlling air quality In smart buildings, sensors measure the current concentration of CO2 or VOC. They should be installed in every room used for a longer period of time (living room, kitchen, bedroom or office). Ideally, they should measure at head height to obtain the relevant concentration. Also, the sensor should not be placed in a draught, because the values can be inaccurate and seem
Combined devices installed in the switch frame measure and control air quality and room climate, either with individual adjustment options via display and buttons or fully automatically.
artificially better. It makes sense to measure directly where inhabitants spend time, for example in the corner with the couch. An intelligent sensor, for example for the KNX system, will also control the
ventilation. This can be so-called natural ventilation via windows, which are opened and closed by motors, or via a ventilation system. From a technical point of view, PI control is used here, which constantly determines how much readjustment is required (fresh air supply) in order to achieve the target state (setpoint). Of course, opening the window only helps with carbon dioxide and
mixed gas sources in the interior. Ventilation should be prevented if there are odours from outside. In polluted areas, an outdoor VOC sensor may even be worthwhile.
The device for installation in the switch range is simultaneously a sensor, automatic control and a manual regulator.
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A positive influence Ventilation also plays an important role in the air conditioning of indoor spaces, as outdoor air is usually cooler and drier than the air in a room used by people. Ventilation is therefore also necessary if the temperature and humidity are too high. A ventilation block is effective for the few cases where this is not the case, especially when the supply air is too warm in summer and too cold in winter. Too cold a supply air can cause damage to house plants or lead to condensation on building parts. In the latter case, the dew point indicates when things become critical. In summer, night re-cooling is often used, in which the building is cooled down considerably by night alone via windows, skylights and supply air flaps. The cool walls then continue to act as passive components long into the day and reduce the energy required for air conditioning.
October 2020 electrical wholesaler | 25
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