HVAC Strategies to Improve IAQ
Published by Lisa Hickey
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Even in a pandemic-free world, there are important reasons to maintain healthy indoor air quality (IAQ). Indoor air quality is a concentration of thermal conditions and airborne contaminants in commercial buildings. The indoor air quality parameters are carbon dioxide (CO2), humidity, temperature, and volatile organic compounds (VOCs). IAQ is essential for our well-being; poor indoor air pollution is a leading risk factor for premature death. The IHME estimates it's responsible for 1.6 million deaths each year. The WHO puts this figure at 4.3 million.
- 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.
- Humidity sources are outside air, which brings in water vapors, leaking pipelines, or open water sources. Elevated humidity levels will promote mold, bacteria growth, and dust mites that aggravate allergies and asthma.
- Temperature levels indoor are altered by computer systems, HVAC systems, server rooms, and humans. Temperature can impact job performance and affect morale.
- Volatile organic compounds are from office furnishings, construction materials, carpet, maintenance, and external contaminants within a building. Occupants can experience headaches, loss of concentration, and breathing problems.
What are acceptable indoor air quality levels, and how do we achieve and maintain them? ANSI/ASHRAE Standards 62.1 and 62.2 are the recognized standards for ventilation system design and acceptable indoor air quality (IAQ). Expanded and revised for 2019, both standards specify minimum ventilation rates and other measures to minimize occupants' adverse health effects. ANSI/ASHRAE 62.1-2016 recommends outdoor air supply rates to take into account people-related sources as well as building-related sources. The recommendation for office spaces, conference rooms, and reception areas is five cubic feet per minute (cfm) of outdoor air per person. Advice for people-related sources an additional 0.06 cfm for every square foot (cfm/ft2) of occupied space to account for building-related sources, elementary and high school classrooms, ten cfm/person plus 0.12 cfm/ft2 of outdoor air. To find rates for other indoor spaces, refer to Table 6.2.2.1 in ANSI/ASHRAE 62.1-2016 standard.
Measuring and monitoring indoor air quality is the first step to maintaining healthy and comfortable building environments. Sensors that are faulty or out of calibration affect the ability to control temperature, humidity, air quality, and building pressure. Sensors must be verified for operation and accuracy to improve system performance and ensure occupant safety, comfort, and productivity.
Facility operators and building owners need to evaluate their building systems to ensure they meet ASHRAE guidelines. Strategies such as increased ventilation, improved filtration, and air cleaning aim to enhance occupant safety, comfort, and productivity. Every HVAC system needs to be analyzed to ensure appropriate measures are taken to improve the ventilation and reduce virus transmission in the building.
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, a cooling coil, a reheat coil, a fan, and an air mixing box with dampers and actuators controlling the return and fresh outdoor air going into the AHU to service building. Air handling units are equipped with sensors and filters to prevent dust from entering the supply air ducts. 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 to monitor and maintain the filters. When contamination of the filter increases, the pressure drops.
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, the VAV boxes open if the room sensor detects excessively high C02 content, 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.
Every HVAC system needs to be analyzed to ensure appropriate measures to improve and maintain adequate ventilation and reduce virus transmission in the building.