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Modern BMS (Building Management Systems) are expected to do more for HVAC than merely heating, cooling and air-conditioning and more attention is being paid to indoor pollutants which are monitored by air quality sensors.

Tenants in office buildings and retail space demand higher levels of comfort than ever before. This goes beyond keeping temperature, humidity and CO2 levels within acceptable limits and correlates directly to air quality. 

Measuring CO2 levels

Currently, CO2 levels are monitored for Demand Controlled Ventilation (DCV) applications to improve building health and reduce energy costs. The benefits of healthy and “green” buildings have been recognised and great progress has been made in the control of ventilation rates to achieve this and more progress is being made. 

One area of indoor air-quality that is receiving a lot of attention is the measurement and control of indoor pollutants with the help of air quality sensors.

What are indoor pollutants?

When we think of pollution, we think of vehicle exhaust, the haze over a city or emissions from industrial chimneys. However, many substances present in buildings are pollutants. 

These are known as Volatile Organic Compounds (VOC) and are generated by the activities in the building. These indoor VOCs are hydrocarbons that originate mainly from bio-effluents, such as human respiration and perspiration and vapours generated from building materials, furnishings and office equipment. 

There are thousands of these unique VOCs that may be present in the air and affect air quality. 

The table below lists some of the more common VOCs and their source.

Air quality sensors

Greystone Energy systems

Generally, in addition to high levels of CO2, the root cause of indoor air quality problems lies with VOCs. Up to now, it has been difficult to measure these levels because of a lack of effective sensing equipment.

Measuring Volatile Organic Compounds With Air Quality Sensors

Air quality sensors

The first VOC sensors suffered from long-term stability issues and an output signal that was difficult to define and apply to control systems in a reliable way. As a result, CO2 sensors were used as a useful air quality indicator with easily utilised output signals which served as an adequate air quality indicator.

For DCV applications, this has worked because of its straightforward design, predictable results and energy savings. It is however not optimal because it ignores other contaminants. On demand ventilation needs versatile air quality sensors, and needs to react to all air contaminants, not only CO2.

The Indoor Air Quality Sensors from Greystone

Air quality sensors

The Indoor Air Quality Sensor from Greystone Energy Systems uses an advanced MEMS metal oxide semiconductor sensor to detect poor air quality. It reacts rapidly to airborne contaminants such as smoke, cooking odours, bio-effluence, outdoor pollutants and from human activities. 

The sensor captures all VOC emissions that are completely invisible to CO2 sensors.

Extensive studies have shown that CO2 and VOC levels are directly correlated. The IAQ has been developed over several years to give  total CO2 and VOC levels and has been calibrated  so that the Air Quality Sensor provides a “CO2-equivalent” ppm measurement value, which is compatible with HVAC CO2 ventilation standards. 

The air quality sensor from Greystone  also includes control algorithms to correct sensor drift and ageing and so  provides  long-term consistent DCV solutions while overcoming the deficiencies of CO2 measurement by detecting the true root-cause of ventilation demand, VOCs. 

The IAQ sensor emulates the human perception of air quality much more than a CO2 sensor and even detects odourless, potentially hazardous substances such as carbon monoxide.

To find out more about VOC and air quality sensors, give us a call.