Green building associations around the world are now offering credits if carbon dioxide (CO2) detectors are installed inside a building. But is it really worthwhile to monitor CO2 levels in your home? Even to improve your green star rating?
Monitoring CO2 levels in large or commercial buildings
To know whether it is worthwhile to install CO2 detectors in your home, we need to understand why CO2 detectors are being installed in commercial buildings.
There can be a number of reasons why you should monitor CO2 levels in buildings ( http://www.edaphic.com.au/why-you-need-to-measure-co2-inside-buildings/ ). But there are three main reasons why CO2 should be monitored and controlled in large, commercial buildings: 1) health; 2) productivity; and 3) energy efficiency.
Monitoring CO2 levels for your health
Inhaling large amounts of CO2 can displace oxygen in your blood and lead to asphyxiation. CO2, in large amounts, is also a toxin. The Canadian Centre for Occupational Health and Safety has provided examples of how CO2 can be harmful to human health (see: https://www.ccohs.ca/oshanswers/chemicals/chem_profiles/carbon_dioxide.html ).
Therefore, where there is exposure to potentially high levels of CO2 it is definitely recommended to monitor and control for safe levels. For example, in breweries or where CO2 gas cylinders are stored in confined spaces, there is a potential for CO2 gas leakage and CO2 should be monitored.
It may also be possible, in some circumstance, that CO2 can be used as a surrogate for other, potentially harmful gases. If ever you are concerned that there may be a harmful gas in your environment, you should always seek advice and action from a local expert. But CO2 detectors have been used to monitor for general air quality in buildings. If CO2 levels are high, it is possible that the air in your building is not of generally poor quality. By monitoring CO2, action can be taken to alleviate potentially poor quality air.
Monitoring CO2 levels for productivity
In clean air, CO2 levels are approximately 400 parts per million (ppm). Inside a generally clean building, CO2 levels can range from 400 to 600 ppm. Once CO2 levels reach 1,000 ppm, scientific studies have shown that productivity can decrease. CO2 levels above 2,500 ppm can lead to significant declines in decision making performance. Therefore, green building councils generally recommend that indoor CO2 levels should not exceed approximately 800 ppm.
Monitoring CO2 levels for energy efficiency
In large or commercial buildings, ventilation systems can run constantly at a set temperature or air flow level. However, this is a very energy inefficient management strategy as most rooms in a large building are empty or have low occupancy. Therefore, a more efficient strategy is to control and set air flow where it is needed – that is, where there is the demand or where there are actually people. The best method to determine if, and how many, people there are in a room is to monitor CO2 levels.
Each human breath exhales approximately 30,000 ppm of CO2. A CO2 detector can sense whether a person is in a room if CO2 levels start to increase. If the CO2 levels increase very rapidly, then a large number of people are occupying that room. Air flow can therefore be set automatically – if CO2 reaches 800 ppm, turn on air. If CO2 reaches 400ppm, turn off air. The on/off switch will be slower or faster depending on how many occupants are in a room. This approach saves energy as air conditioning will only be on when it is needed. It also improves health/productivity as CO2 levels are kept below 800 ppm.
This approach is called Demand Controlled Ventilation (DCV) and is one of the principle reasons why CO2 levels are monitored in buildings for green star accreditation.
Will this system work in your average home?
In theory, DCV will certainly work in your average home. But a cost/benefit analysis should be performed to see whether installing CO2 detectors throughout the household, as well as a building management system and duct ventilation, will lead to the required energy savings. CO2 detectors are an order of magnitude cheaper today than 10 or 20 years ago, but they can still costs in the hundreds of pounds. Saving costs on energy in a green home may be better, and more easily, achieved in other ways.
But monitoring CO2 for general health in the home is certainly an option. A range of portable meters, wall mounted meters with alarms, or even desktop meters with temperature and humidity readings, are available (for example, see http://www.airqualitysensors.com.au/co2-carbon-dioxide/). Once CO2 reaches an uncomfortable level, it may be as simple as opening a window for some fresh air to resolve the problem. But if CO2 levels remain persistently high, it is definitely recommended to seek local expert advice.