Easy Ways to Improve IAQ
Indoor Air Quality Seems Easy to Understand, But (without an automation system like BOB) It’s Really More Complicated than You Think
Indoor Air Quality (IAQ) serves occupants with both physical and emotional comfort. Humans are constant temperature creatures with a normal internal body temperature of 98.6 F [37 C] and are continuously producing heat during all activities. If the external environment causes the human body to gain or lose heat, then the body reacts immediately to bring the body back to the correct temperature by either increasing blood flow to the skin or boosting perspiration.
Physiological interpretation of comfort is as how quickly the body’s external surface area (skin) reaches thermal equilibrium with internal core body temperature (98.6 F) and minimum temperature regulation activities are required to be initiated within the human body. Therefore, the perception of comfort relates to an individual’s physical condition, bodily heat exchange rate with their surroundings, and other physiological characteristics.
While ideal thermal conditions for comfort are not easy to define for any one individual due to personal preferences, ASHRAE Standard 55 specifies conditions that are likely to be thermally acceptable to at least 80% of the adult occupants in a space.
Temperature vs Thermal Comfort
The difference between the temperature on the skin and the internal core temperature determines whether a person is comfortable or uncomfortable in their environment. Buildings and HVAC systems need to account for the type of activities being conducted in the space, as well as the frequency of their occurrence, in order to provide the right temperature and humidity of supplied air to keep occupants comfortable. Occupants using a fitness center or indoor swimming pool will have different temperature and relative humidity requirements from occupants using an administrative office or classroom.
Space Temperature and Humidity
The design space temperature and humidity for both heating and cooling seasons should be based on ASHRAE Standard 55 for most applications. The standard establishes a comfort zone for people in both the summer and winter seasons, taking into account the clothing they are likely to be wearing as well as their metabolic activities. ASHRAE Standard 55 recommends a temperature of 74°F [23°C] with a relative humidity below 60% for summer, and a temperature of 71°F [22°C] with a relative humidity above 35% for winter.
Relative humidity (RH) does not have a significant impact on thermal comfort in most situations as long as the space Dry Bulb Temperature is within the comfort range. While humans don’t always experience thermal comfort issues as a result of relative humidity, the human body is sensitive to humidity because it uses evaporative cooling, enabled by perspiration, as the primary mechanism to remove excess heat. Perspiration evaporates from skin more slowly under high indoor humidity and the human body experiences a lower rate of heat loss as the space temperature is increased.
For example:
Maintaining humidity within ASHRAE Standard 55 can cause additional energy use when supply air is precooled to condense the moist air and then reheated to the desired temperature. The process of cooling and heating can also strip the air of its moisture requiring additional humidification to be added back into the air before it can be supplied to occupants.
Relative humidity also affects the quality of the indoor air and should be maintained between 35%–60% to control volatile organic compound (VOC) emissions, viruses, bacteria, molds, and fungi. This relative humidity level may also prevent odor from organic compounds and human activity.
Indoor Air Distribution
ASHRAE Standard 55 prescribes a maximum rate of air movement of 50 feet per minute (fpm) for summer and 30 fpm for winter. Low air velocity affects the ability of the HVAC system to maintain uniformity of temperature throughout the occupied space. To dilute contaminants generated within a zone, a minimum rate of air movement of 0.6 to 0.8 cubic feet per minute (cfm) per square foot (ft2) is adapted in typical applications.
Ventilation System Design
ASHRAE Standard 62.1 is for nonresidential building ventilation and filtration, and addresses controlling air contamination levels for the purpose of supplying outdoor air and removing return air from a space. The total amount of air supplied to a particular space is determined by the cooling load requirements of that space, while also complying with applicable code specifications and standards for minimum ventilation airflow.
Buildings are usually ventilated by supplying filtered outdoor air through the HVAC system. Exhaust systems complement a ventilation system by containing and removing selected contaminants at the source. It is common practice to supply sufficient outdoor air through an air conditioning system to make up for the air that is exhausted plus an additional amount of air to provide the building with slight positive pressurization.
People vary in their sensitivity to contaminants in the air, with low concentrations of certain impurities causing serious discomfort and impairment while most of the other occupants remain unaffected. Standards for vapors specify the quantity of acceptable pollutants per unit volume of air is in parts per million (ppm).
Potential Contaminants in the Supply Air can include:
• Respirable particulates
• Pollen, fungi, mold spores
• Bacteria and viruses
• Gasses/vapors
• Carbon dioxide (CO2)
• Carbon monoxide (CO)
• Radon (decay products)
• Other VOCs
Ventilation Rate
ASHRAE Standard 62.1 provides the design engineer with the means of determining ventilation rates needed to achieve acceptable indoor air quality.
Two procedures for determining the required ventilation rate:
1. Air Change per Hour (ACH) derives the ventilation rate from a calculation that includes the number of occupants and the floor space.
2. Demand Ventilation Reset provides requirements for minimum ventilation changes based on measuring indoor CO2 concentrations and other VOCs.
Filtration and Air Cleaning
Extensive research on the health benefits of cleaning air to reduce particle concentrations in the breathing spaces of commercial buildings revealed cleaner air, reduced symptoms from seasonal allergies and asthma attacks, as well as decreased transmission rates of communicable diseases. The most studied air cleaning technologies include mechanical air filtration and ultraviolet disinfection.
· Mechanical air filtration utilizes fibrous filter media to remove contaminants from the air stream. The Minimum Efficiency Reporting Value (MERV) is determined by the density of the physical filter media and how effective it is at removing particles. The higher the MERV rating, the more efficient the filter and the smaller the particles it can remove. The highest efficiency mechanical filter is the High-Efficiency Particulate Air (HEPA) filter with 99.97% efficiency.
· Ultraviolet disinfection, also known as ultraviolet germicidal energy, utilizes high intensity ultraviolet light waves (between 220-300 nm) to rapidly degrade organic material and micro-organisms. While this is not a physical filtration method, its benefits have been tested and proven in many clinical environments and is widely accepted as an air cleaning technology.
Why is Indoor Air Quality so Important?
Indoor air quality is important to maintain the health, comfort, and productivity of the occupants within a space. It can be maintained and improved with proper space temperature control, ventilation, and air filtration methods. Thermal comfort has an impact on occupant performance with warm temperatures reducing alertness and cold temperatures reducing dexterity. Frequent and widely fluctuating temperatures can hinder an occupant’s ability to focus, affecting their productivity. Failing to properly manage ventilation can increase the concentrations of CO2 levels and can also lead to occupant sickness and poor performance. Indoor air pollutants like chemicals from cleaning agents, VOCs, mold, and other particulate matter need to be managed and removed, where possible, through both air filtration and air purification.
Beyond the obvious health benefits, there are also several other reasons organizations should invest in IAQ improvements:
1. Improved student academic test performance in K-12 schools.
2. Reduced employee sick days and increased productivity in office environments.
3. Enhanced customer experience.
4. Improved online reviews.
5. Enhanced public image.
How to Ensure IAQ?
Where IAQ is compromised, building occupants start to complain of temperature discomfort, and can also experience headaches and irritation in eyes and throat. To ensure all occupants are comfortable and to prevent buildings from becoming sick from poor IAQ, it is best to look at and correct the following within your system:
• Select the proper Plant Capacity to provide adequate cooling and heating for local peak ambient temperatures.
• Use the correct controls algorithms for connecting the temperature, humidity, and ventilation control loops.
• Frequently monitor indoor air quality with equipment and system trends.
• Use BOB when you want advanced, proactive building analytics.
What’s the next step?
When you are ready to improve the indoor air quality in your building(s), you to meet BOB, the world’s first building optimization broker. BOB can provide you with insight into your building automation system to proactively identify and diagnose problems with your indoor air quality (along with other equipment and systems across multiple sites) leading to more comfortable and healthier occupants. To learn more about BOB, visit www.k2a.com/BOB