Accurate monitoring and control of indoor environments has a significant impact on energy efficiency and is also important to ensure the comfort and well-being of people occupying the building. However, a wide range of parameters can impact IAQ (indoor air quality) from gases such as carbon monoxide, carbon dioxide, volatile organic compounds, humidity, particulates and bacteria such as legionella.
One of the major variables that affect indoor environmental quality is carbon dioxide, as this gas is produced by building occupants. The production of carbon dioxide is a function of the size, number and activity levels of the people living in the building. Therefore, local levels of concentrations can differ significantly, for instance when staff are on coffee or lunch breaks or when a meeting room is occupied.
High levels of carbon dioxide can lead to tiredness and affect the concentration level. It can even lead to symptoms of Sick Building Syndrome such as itchy skin, eye, nose and throat irritation, nausea and headaches. Therefore, measurement of carbon dioxide levels is an important part of indoor environmental quality plans such as demand control ventilation.
IAQ Control Methods
The aim behind cost effective IAQ strategies is to control building ventilation so that indoor air quality is maintained as a virtue of fluctuating ambient conditions, and energy consumption is ultimately reduced. Demand control ventilation is a popular technique based on carbon dioxide measurements. Instead of utilizing pre- determined ventilation rates based on maximum occupancy, this method can regulate ventilation rates in line with the actual levels of carbon dioxide present. Other solutions are also available which change ventilation rates depending upon the measurement of other ambient parameters and carbon dioxide.
It is possible to sample air either by pumped or a combination of convection and diffusion sampling methods. An integral pump is used by pumped systems to draw air via the detector for constant sampling. These pumped systems also prove handy when the sensor is difficult to mount at the preferred sampling point. Convection or diffusion sampling techniques use convection to circulate gas between a diffusion cell and the sensor head with gas exchange occurring at the diffusion membrane’s surface, rendering a fast response time. Given that the gas in the cell circulates inside a closed system, optics is protected from dust.
Self-Contained Monitoring Systems
In demand ventilation control applications, self-contained monitoring solutions can prove suitable. Edinburgh Sensors offers the Plug & Play Guardian NG series of NDIR gas monitors (Figure 1) that are designed to detect gases from sampling points up to 30m away, by means of the integral pump. These pumped aspirated wall-mounted monitors are versatile and provide near-analyser quality measurement, sampling and display of target gas concentrations.
Figure 1. Guardian NG gas monitor
Concentration ranges of carbon dioxide (0 - 3000ppm) cover standard target levels of carbon dioxide for IAQ; however, models covering wider ranges are also provided. Standard pressure and temperature compensation is provided to reduce drift. The monitors are accommodated in a rugged IP54-rated enclosure with a liquid crystal display, and offer user-selectable alarm set-point controls.
OEM Carbon Dioxide Sensors
Manufacturers of multi- parameter ventilation control systems and demand ventilation control systems based on carbon dioxide need to integrate carbon dioxide sensors into their products. The Gascard® NG pumped aspiration dual wavelength NDIR carbon dioxide sensors from Edinburgh Sensors include automatic pressure and temperature corrections for real-time and consistent measurements of actual levels of concentration in the 1000, 2000, 3000 and 5000ppm ranges. Both the electronics and sensor head are positioned on a Eurocard PCB with several bit-switches, which allow users to control different aspects of the sensor's behaviour such as filter type selection and analogue output.
Features such as true RS232 communications for data logging and control, coupled with the option of TCP/iP communications protocol, make it possible to integrate the Gascard® NG into a broad range of proprietary gas detection instruments and various sensor architectures. In addition, built-in features are available for multi-sensor and multigas operation along with the flexibility to integrate supplementary gas detection technologies.
Edinburgh Sensors’ Gascard® NG sensors have been integrated into IAQ systems, which are deployed in many prominent buildings across the globe. The company supplies the latest sensor instruments that provide fast, precise, reliable and continuous measurements day after day. The company’s engineers provide technical support and one-to-one customer service throughout the entire assessment and system integration process.
This information has been sourced, reviewed and adapted from materials provided by Edinburgh Sensors.
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