Why measure CO2 in HVAC applications?
The next time you step into a brand-new building, take a look at the wall. The "thermostat" you see may have another box with a CO2 sensor inside. That CO2 sensor is the end result of years of research into balancing indoor air quality (IAQ) and energy efficiency into building designs and HVAC applications.
Heating, Ventilation, and Air Conditioning (HVAC) environments or industries most commonly use carbon dioxide (CO2) and oxygen (O2) sensing technologies to monitor and control spaces.
While typical ambient air is comprised of approximately 21% Oxygen and 0.03% Carbon Dioxide, a lack of proper indoor air circulation can dramatically deter the gas concentrations from being unbalanced and unhealthy.
It is important to note that every home, classroom, or office building requires a constant flow of fresh, conditioned air to make it comfortable for the people who work, learn, and live inside these environments. In the past, finding fresh air was not a problem because most buildings were porous, i.e. outdoor air “leaked” into the building around windows and under doors. Everyone has experienced a cold draft in an old house or building.
While “leaky” buildings ensure fresh air, they are also expensive to heat and cool. As energy prices have risen dramatically over the last few decades architects started designing new buildings that minimized energy loss - they call it "closing the envelope". For example, throughout the 1970's many schools and office buildings were designed with permanently sealed windows. While this saved energy, it had the unexpected consequence of sealing in mold, bacteria, and potentially harmful gases like radon, VOCs (volatile organic compounds), and carbon dioxide (CO2). It had the additional unintended impact of creating egress issues during dangerous school events.
Studies showed that high concentrations of the gas and contaminants created health problems for occupants, and the term “sick building syndrome” was created to describe these new, sealed, air trapping structures.
To combat “sick building syndrome” HVAC (heating, ventilation, and air conditioning) designers and installers have developed HVAC systems that regulate a constant flow of fresh, outdoor air into buildings. The idea was that wasting energy to condition outdoor air was the price you had to pay to provide fresh air indoors. In some cases, these HVAC systems either provided non-stop fresh air, or in other cases they were set on timers that would open fresh air dampers when the building was occupied.
In other words, the solution to providing fresh air was to open a window for proper ventilation!
In countries where energy is more expensive, an alternative method of providing fresh air was used. Instead of constantly providing fresh air, buildings used carbon dioxide sensors to “sense” when the buildings were occupied. When enough people enter a room, the CO2 level rises because of the CO2 from their exhaled breath, and the HVAC system begins to bring in the fresh air. When the people leave, the CO2 level drops because they are no longer breathing in the room, and the fresh air dampers close.
Because most common uses for carbon dioxide in HVAC applications were due to saving energy, this also often correlated to leading to higher productivity rates and healthier overall environments for individuals. In addition, compliance also served as a second benefactor as many architects and building owners needed to rely on CO2 measurements in pursuing certifications that required the use of Demand Control Ventilations (DCV).
In addition, while emitting less carbon dioxide and using less water, sustainable designed buildings and DCV, cost less to operate. According to a report by the US Department of Energy's Pacific Northwest National Laboratory government facilities with sustainable HVAC practices cost 19 percent less to maintain. The results are included in a white paper released by the Government Services Administration, or GSA.
Another example in regards to CO2 monitoring and energy efficiency in HVAC is the Empire State Building. The Empire State Building had an energy-savings retrofit in 2011 including VAV systems controlled by CO2 transmitters. In 2014, the building management reported that they had surpassed the energy savings originally guaranteed for the third consecutive year. The property beat its energy-efficiency guarantee by 15.9 percent, saving $2.8 million. Over the past few years, the program has generated approximately $7.5 million in savings.
This system of using CO2 monitoring devices to trigger/control HVAC systems is starting to catch on in the U.S. Many new commercial buildings are now designed to meet LEED (Leadership in Energy and Environmental Design) specifications. LEED was designed and is administrated by the USGBC (United States Green Building Council) and the testing and certification of the program is conducted by the Green Business Certification Inc. (GBCI). The LEED program provides a rating system for energy-efficient building design. Included in LEED are specifications for utilizing CO2 sensors to control fresh air circulation.
Do note, that outdoor CO2 measurement is not required for LEED credit, and may only be useful under certain scenarios. Companies seeking LEED certification for new buildings should consult a LEED-certified engineer for the most recent rules.
Also note, that the American Society of Heating and Refrigeration Engineers (ASHRAE) recommendation for not exceeding 1,000 ppm of CO2 in office buildings still applies, as well as current ASHRAE workplace safety limits.
One of the sensor technologies that make buildings like the examples above possible, is the next generation of low power CO2 sensors like the LP8. These low-power sensors are already being designed into OEM Devices with long-life batteries and WiFi so they can easily be installed in every room. They can report back to the HVAC system to modify the environment or confined space in real-time.
At CO2Meter.com, we provide a variety of wall mount Indoor Air Quality Fixed and Portable Devices, used worldwide to control HVAC and DCV systems.
For more information on selecting the proper indoor air quality solution or technology, speak to an expert at Sales@CO2Meter.com.