A modern ventilation system works completely autonomously. The most important parameters are continuously monitored in a discreet manner. Additional fresh air is supplied if one of the parameters deviates. No interaction from the residents is required for the proper functioning of the ventilation system. The system only provides an indication when maintenance is required.
However, not every room in a building is used for the same purpose. Depending on the way a room is used, ventilation will have to be controlled differently. In this article we would like to discuss some typical situations for optimally controlling a ventilation system. The choice of sensor type is usually determined by the circumstances.
However, not every room in a building is used for the same purpose. Depending on the way a room is used, ventilation will have to be controlled differently. In this article we would like to discuss some typical situations for optimally controlling a ventilation system. The choice of sensor type is usually determined by the circumstances.
CO2 sensors for spaces with variable occupancy
Indoor carbon dioxide concentrations are the result of a combination of outdoor CO2, indoor breathing and the ventilation rate of the building. When people breathe, they release CO2 into the air. If there's too much CO2, extra fresh air must be supplied to reduce the CO2 level. As buildings and homes become more energy-efficient and thus airtight, this means we have less fresh air coming naturally into the building. Many of today’s ventilation systems recycle air to conserve energy, thus pushing contaminated air back into the building rather than cycling in new fresh air. This results in high CO2 concentrations and poor indoor air quality. Air flow should be monitored to ensure fresh air is supplied in due time.
Indoor carbon dioxide concentrations are the result of a combination of outdoor CO2, indoor breathing and the ventilation rate of the building. When people breathe, they release CO2 into the air. If there's too much CO2, extra fresh air must be supplied to reduce the CO2 level. As buildings and homes become more energy-efficient and thus airtight, this means we have less fresh air coming naturally into the building. Many of today’s ventilation systems recycle air to conserve energy, thus pushing contaminated air back into the building rather than cycling in new fresh air. This results in high CO2 concentrations and poor indoor air quality. Air flow should be monitored to ensure fresh air is supplied in due time.
Moderate to high levels of carbon dioxide can cause headaches, reduced concentration and fatigue while higher concentrations can even produce nausea, dizziness and vomiting. Indoor CO2 levels constantly change, depending on the ventilation, the amount of people and the length of time they are present in an enclosed space. Indoor CO2 levels between 450 - 1.000 ppm are acceptable. When the values exceed this range, additional ventilation is required. Sentera CO2 sensors accurately measure the CO2 levels in the ambient air. They are available in different enclosure types, depending on the application.
In areas with variable occupancy such as meeting rooms, auditoriums or other rooms where many people periodically come together, there will be strong fluctuations in CO2
concentration. Also in a living room or bedroom CO2 sensors are the best choice to control a ventilation system and optimize the supply of fresh air. The CO2 concentration must be measured in the extracted air. In residential environment, room or duct CO2 sensors usually used for this application. In general we can assume that the CO2 level of the supplied air is quite constant and in all cases is lower than the CO2 level of the indoor air. Other parameters such as relative humidity and VOC concentrations usually remain more stable in these spaces.
concentration. Also in a living room or bedroom CO2 sensors are the best choice to control a ventilation system and optimize the supply of fresh air. The CO2 concentration must be measured in the extracted air. In residential environment, room or duct CO2 sensors usually used for this application. In general we can assume that the CO2 level of the supplied air is quite constant and in all cases is lower than the CO2 level of the indoor air. Other parameters such as relative humidity and VOC concentrations usually remain more stable in these spaces. If the rooms in the building are equipped with control valves to regulate the amount of supplied air and the amount of extracted air, the exhaust valve should be controlled by a CO2 controller in the room. The supply valve should follow the position of the exhaust valve to avoid over pressure or under pressure in the room (balanced ventilation). If there is only one central exhaust fan or one heat recovery unit, it can be directly controlled by the CO2 controller. Another option is to install multiple sensors and to control ventilation based on the highest CO2 measurement in the building. For this purpose, Sentera developed the solution FS-D-000064.
To control the ventilation system not only on the basis of the CO2 measurement, but on the basis of both CO2 and relative humidity (and possibly also temperature), a CO2 controller must be used. This device has a built-in control algorithm that can control a valve or fan speed. All (or some) of the measured values will be taken into account by the algorithm.
A CO2 sensor converts the measured CO2 value as well as the relative humidity (and temperature) into three separate analog signals. A valve position or fan speed can be controlled with one of these signals. Not with all three at the same time.
Prevent condensation in wet rooms
Spaces such as toilets, bathrooms or kitchens have greater variations in relative humidity. Relative humidity indicates the actual water content of air as a percentage of the maximum amount it could possibly hold at its current temperature. Warm air can possess more water moisture than cold air, so with the same amount of absolute/specific humidity, the relative humidity of cold air would be far higher than of warm air. Other parameters such as CO2 or VOC generally remain more constant here. It therefore makes more sense to ventilate these areas in such a way that the risk of condensation is minimized. Condensation or excessive humidity can lead to mold and mildew, which isn't good for anyone's health.
Controlling the ventilation system based on the relative humidity in the room itself is not effective. The relative humidity of the supplied air will also not be constant. When controlling the ventilation system based on CO2, it can be assumed that the CO2 concentration of fresh outside air is fairly constant. That is not the case with relative humidity. The relative humidity outside on a warm summer day or a wet autumn day will be completely different. Regulating a ventilation system only on the relative humidity measurement inside, doesn’t work.
Based on the temperature and relative humidity measurements, the dew point temperature can be calculated. Sentera relative humidity sensors measure both temperature and relative humidity and automatically calculate the dew point temperature. When the air comes into contact with an object that has a temperature lower than the dew point temperature, condensation occurs. So, the dew point temperature of the supplied air must always be lower than the temperature inside the wet room. When we obtain this, we can avoid condensation.
So when the relative humidity in a wet room is too high, this can be solved by ventilation if the dew point temperature of the supplied air is sufficiently low. This requires a relative humidity sensor in the interior space as well as a dew point temperature calculation of the supplied air.
VOC sensors in rooms with specific destinations
Then there are also the spaces where VOC sensors are best to assess the indoor air used and control the ventilation system. VOCs or Volatile Organic Compounds are a large group of chemicals that are found in plenty of products we use to build and maintain our homes and buildings. Common examples of VOCs that are present in our daily lives are: benzene, xylene, ethylene glycol, formaldehyde and methylene chloride. Typical sources are paints or varnishes, new carpets, adhesives, cleaning products, dry cleaning, photocopiers and building materials like foam. Also cigarettes and burning of wood emits VOCs. The risk of health issues from inhaling any chemical depends on the exact chemical compound, the concentration and the duration of the exposure.
Breathing in low levels of VOCs for a longer period in time may increase some people’s risk of health problems, especially persons with asthma or particularly sensitive to chemicals. Since VOCs refer to a group of chemicals, each of them has its own toxicity and potential for causing different health effects. In general, breathing in high levels of VOCs is known to cause eye, nose and throat irritations, headaches, drowsiness, nausea, reduced concentration and fatigue. In the long run it can lead to cancer and damage to the liver, kidney and the central nervous system.
Controlling a ventilation system based on a VOC measurement of the extracted air is recommended in areas such as: storage rooms, room where the copy machine is located, printing companies, warehouses for building materials, etc. VOC sensors are usually used where controlling ventilation based on CO2 measurement or humidity is not an option.
If the rooms in the building are equipped with control valves to regulate the amount of supplied air and the amount of extracted air, the exhaust valve should be controlled by a VOC controller in the room. The supply valve should follow the position of the exhaust valve to avoid over pressure or under pressure in the room (balanced ventilation). If there is only one central exhaust fan or one heat recovery unit, it can be directly controlled by the VOC controller.