The Secret of Controlling IAQ is Measuring
Published by Lisa Hickey
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On average, we spend approximately 90% of our lives indoors and take about 20,000 breaths a day. We assume the air is "clean" in the buildings and will not affect our health. It is surprising how little we know about the importance of indoor air quality.
The parameters that affect indoor air quality are carbon dioxide (CO2), humidity, temperature, and volatile organic compounds (VOCs). The most significant source of carbon dioxide is the combustion of organic matter and human respiration. An increase in carbon dioxide causes dizziness, confusion, difficulty breathing, sweating, vision problems, and loss of consciousness after prolonged exposure. Primary indoor humidity sources are outside air, which brings in water vapors, leaking pipelines, or open water sources. Elevated humidity levels promote mold, bacteria growth, and dust mites that aggravate allergies and asthma. Indoor temperatures are altered by computer systems, HVAC systems, server rooms, and humans. Temperature can impact job performance and affect morale. The prime sources of volatile organic compounds are office furnishings, construction materials, carpet, maintenance, and external contaminants. Occupants can experience headaches, loss of concentration, and breathing problems.
Essential parameters such as C02, humidity, temperature, and VOC concentrations are sometimes not measured, controlled, or displayed. Measuring and monitoring indoor air quality is the first step when maintaining healthy and comfortable building environments. Measurement leads to control and improvement. If you can't measure something, you can't understand it. Furthermore, if you can't understand it, you can't control it.
Sensors verify the operation and system accuracy to improve performance and ensure occupant safety, comfort, and productivity. Musty odors or condensation provides clues that there are IAQ issues, but they do not illustrate the problem. With seamless, integrated sensors, the HVAC system can pick up signals of health-threatening pollutants like VOCs.
A central ventilation system with air handling units provides several zones in the building with controlled, continuous, low-level air movement in and out of the building. It consists of filters, a pre-cool coil, cooling coil, reheat coil, fan, and air mixing box with dampers and actuators controlling the amount of return and fresh outdoor air going into the AHU to service the building. Air handling units are equipped with filters to prevent dust from entering the supply air ducts. If the exhaust air is mixed back into the supply air, air contamination occurs. HEPA filter H13, according to EN1822:2009, prevents infectious microbes in the air. Replacing or cleaning clogged air filters is a critical maintenance task. It is essential to use pressure sensors and dynamic airflow measurements to monitor and maintain the filters. When contamination of the filter increases, the pressure drop across the filter also increases. Simultaneous measurement of the flow can determine filter replacement.
For healthy indoor air, air enters a room, flows through the room, and then leaves. Ideally, fresh air flows from the bottom up and extracts directly from the room. Indoor air should not "swirl" through the room several times or become lodged. Correct design placement and alignment of air outlets can avoid serious air distribution. Individual zones supplied with variable volume flow (VAV) in the supply and return with differential pressure sensors between zones help maintain well-balanced and controlled air. For example, if the room sensor detects excessively high C02 content, the VAV boxes open, and additional fresh air flows through the room. Either way, facility operators and building owners can evaluate their building systems to ensure the indoor air meets the ASHRAE guidelines. ASHRAE Standard 170 is a guideline for proper pressurization in positive and negative pressurized spaces. Every HVAC system needs to be analyzed to ensure the appropriate measures are being taken to improve and maintain adequate ventilation and reduce virus transmission in the building.
Download Tips for Complying with ASHRAE Guidelines for Indoor Air Quality during COVID-19