Maintaining good indoor air quality through ventilation

This article originally appeared in the May'22 magazine issue of Electronic Specifier Design – see ES's Magazine Archives for more featured publications.

Extractor fans provide an effective solution to preventing condensation and the onset of mould through extracting moist air and steam that is released during washing, cooking, bathing, cleaning, and drying clothes.

Continuous ventilation works by extracting stale and moist air from the home at a low rate all of the time. Continuous ventilation uses less energy than traditional intermittent ventilation and is therefore much more cost effective and a low carbon option.

Providing an ‘exit point’ in the form of a continuous extract fan stops moist air in your home from seeping through the fabric of the building and therefore reduces the chances of mould forming.

Optimal ventilaiton conditions

Fans are designed to work with the natural air infiltration and control the air path from the building thus preventing migration of damaging humidity and pollutants. This is achieved by using continuous low speed running extract fans in the wet rooms (bathrooms, kitchen and utility rooms) with a boost via the light switch, an integral pull cord or sensor when higher ventilation rates are required.

Also known as a decentralised Mechanical Extract Ventilation (dMEV) fan, these fans are designed to be extremely economical to be extremely quiet and costs less than a lightbulb to run for a year.

Fan installations can strongly vary in respect to the geometry of the flow channel as well as the flow rate required for optimal ventilation conditions. A thermal flow sensor with a wide dynamic range is well suited for this control task. IST AG`s anemometric flow sensor FS7 is a compact sensor that can be integrated in various flow channels in the proximity of the fan and calibrated for highest accuracy around the required setpoint. The ceramic based FS7 flow sensor is an ideal solution for HVAC and industrial automation tasks primarily due to its long-term stability and easy system integration. The simple measurement principle of contant temperature anemomentry, as explained in the following figure, contributes greatly to the functionability of the FS7 sensor.

Heat dissipation

The greater the mass flow in the ventilation channel is, the faster heat dissipates from the heated tip of the FS7 sensor and the more power is required to maintain a constant overtemperature against a reference temperature sensitive structure, which is on integrated on the same sensor chip.

The thermal gas flow sensor FS7 with positioning housing, as shown in Figure 2, has variable assembly options available. These include bare die and applications requiring high sensitivity to 400°C.

The FS7 has a flow range from 0 to 100 l/s, temperature range -20°C to +150°C.