Sustaining indoor air quality

Indoor air quality and design has historically been an important — and sometimes overlooked — design topic.

When designing ventilation systems, it is imperative that the designer understand the applicable code requirements, standards such as ASHRAE Standard 62.1: Ventilation for Acceptable Indoor Air Quality and programs like the U.S. Green Building Council’s LEED rating system.

Ventilation is the process of supplying or removing air from a space to control contaminant levels, humidity or temperature. In a typical process, outdoor air and return air are mixed, which effectively dilutes indoor particulates/contaminants and the resulting mixed air stream is subsequently filtered and conditioned before being supplied into the space.

Designers should always investigate outdoor air quality in their region and survey the immediate surroundings to determine the local air quality and its ability to maintain acceptable IAQ. The Environmental Protection Agency collects air quality data and has an interactive map that shows locations of air quality monitoring stations located across the United States. These air quality monitoring stations provide the required data to assist engineers with designing ventilation systems.

Deficient ventilation systems, such as those operating with inadequately sized outdoor air quantities or improper ventilation control, can impact occupant health and productivity. Sick building syndrome and building-related illness are some of the negative impacts on occupant health with symptoms ranging from headaches, nausea and chest pain to asthma, Legionnaires’ disease and sinusitis. On the other side of the spectrum is excessive ventilation, which increases energy use and increases indoor concentration of outdoor contaminants if ambient air quality is unsatisfactory.

There are studies relating sick building syndrome prevalence and the amount of outdoor air provided. These studies show that when the ventilation rate is increased, sick building syndrome prevalence is reduced. There are also studies that indicate a direct correlation between performance and amount of outdoor air introduced in office buildings. It is important to balance the outdoor airflow rate with the additional power and energy required to condition the air. This is where codes, standards and other rating systems can be a useful tool.

ASHRAE Standard 62.1 is frequently referenced or incorporated in codes for ensuring acceptable IAQ. ASHRAE Standard 62.1 defines acceptable IAQ as air in which there are no known contaminants at harmful concentrations as determined by applicable authorities and where 80% or more of people do not express dissatisfaction when exposed to the air.

IAQ for human occupants

ASHRAE Standard 62.1 specifies the minimum ventilation rates and related measures to ensure acceptable IAQ and minimize adverse health effects. The standard applies to spaces intended for human occupancy within buildings except for dwelling units in residential occupancies with nontransient occupants. The origin of Standard 62.1 dates back to 1973. It has been revised multiple times since; the latest version is 2019.

In addition to outlining the design requirements, the standard also provides requirements related to installation, commissioning and operations and maintenance of equipment. Ensuring compliance and acceptable IAQ therefore requires coordination and collaboration among stakeholders and continued diligent efforts on the O&M side.

Some frequently overlooked items in Standard 62.1 as it applies to commercial buildings are:

Design related:

• Quality of ambient air and its ability to maintain acceptable IAQ should be investigated during design. The EPA has established the National Ambient Air Quality Standards as authorized by the Clean Air Act and quality standards for six primary pollutants have been established: carbon monoxide, lead, nitrogen dioxide, ozone, particle pollution or particulate matter and sulphur dioxide.
  • Refer to Table 1 for the EPA established air pollutant standards.
  • For buildings located within areas where PM10 (particulate matter with a 10-micrometer diameter or smaller) threshold is exceeded, filters or air cleaning devices with minimum efficiency reporting value 8 should be provided to treat outdoor air before introduction into buildings.
  • For buildings located within areas where PM2.5 (particulate matter with a 2.5-micrometer diameter or smaller) threshold is exceeded, filters or air cleaning devices with minimum rating of MERV 11 should be provided to treat outdoor air before introduction into buildings. Refer to Table 2 for filter ratings and common applications.
  • For buildings located within areas where the most recent three-year average annual fourth-highest daily maximum eight-hour average ozone concentration exceeds 0.100 parts per million, ozone cleaning devices with a volumetric removal efficiency of minimum 40% should be provided. The devices need to be operated when ambient ozone levels are expected to exceed 0.100 ppm.
• Following are the exceptions to the ozone cleaning requirement:
  • Design outdoor airflow is 1.5 air changes per hour or less.
  • The system is equipped with controls that can sense ambient ozone level and reduce outdoor air to 1.5 air changes per hour or less while still complying with the other requirements.
  • Direct fired makeup air units are used to heat outdoor air introduced into the building.
• An observational survey of the building site and immediate surroundings is required to be conducted during expected hours of occupancy. The intent is to identify local contaminants that could impact IAQ if introduced into the building.
• Exhaust ducts conveying Class 4 air should be negatively pressurized relative to ducts, plenums or occupiable spaces through which they pass to eliminate the possibility of contaminant leakage. Positively pressurized exhaust ducts conveying Class 2 or Class 3 air should not extend through plenums or occupiable spaces other than the space from which the exhaust air is drawn. However, positively pressurized ducts conveying Class 2 air and sealed in accordance with SMACNA Seal Class A are an exception to the requirement. SMACNA Seal Class A requires all transverse duct joints, longitudinal seams and duct penetrations be sealed to minimize air leakage. Refer to Table 3 for air classification based on subjective contaminant concentration.
• Filters with minimum rating of MERV 8 are required upstream of cooling coils handling latent loads and other components with wet surfaces such as evaporative humidifiers.
• For buildings using mechanical cooling equipment, dehumidification provisions are needed to ensure indoor humidity levels do not exceed 60°F dewpoint at any time (occupied and unoccupied hours) when the ambient dewpoint is in excess of 60°F. Among other exceptions, the requirement does not apply to overnight unoccupied periods not exceeding 12 hours, provided the indoor relative humidity does not exceed 65% during that timeframe.
• Drain pans beneath wet components such as cooling coils and direct evaporative humidifiers should begin at the leading face or edge of the device and extend downstream a distance of half the vertical dimension of the device or as necessary to limit water carry-over beyond the drain pan to 0.0044 ounce/square foot of face area per hour under peak sensible and peak dewpoint conditions.
• Access doors or panels are required in infrastructure such as equipment, ductwork, plenums to allow for inspection, cleaning and maintenance of the following components:
  • Air cleaners.
  • Drain pans and seals.
  • Fans.
  • Humidifers.
  • Mixed air plenums.
  • Outside air plenums.
  • Upstream and downstream of each heating, cooling and heat-recovery coil comprised of more than four rows and direct evaporative coolers, air washers, heat wheels and other heat exchangers.
  • Upstream of heating, cooling and heat-recovery coil comprised of four rows or fewer.

Construction and startup related:

• Filters should be installed at equipment before startup to prevent fouling.
• Contaminants generated due to construction should be confined to the construction area and migration to occupied areas should be minimized by employing suitable measures.
• Drain pans should be field tested under conditions most restrictive to condensate flow to ensure they drain properly and water stagnation is eliminated.

O&M related:

• The standard has detailed requirement regarding maintenance activities and frequencies for system components that impact IAQ of the facility such as cooling towers, cooling and heating coils, louvers, bird screens, mist eliminators and the like. Continued compliance with these maintenance requirements is imperative to maintaining IAQ over the life of a facility. While the designer is not responsible for the maintenance of a mechanical system, the designer is responsible for ensuring the systems are provided with the proper features to allow for regular maintenance.

IAQ for data centers

Mechanical systems for data centers are unique in that their purpose is to maintain an operating temperature range and acceptable IAQ for information technology equipment. In the United States, the Toxic Substances Control Act influences materials of construction for ITE. The TSCA does restrict the use of certain materials similar to the European Union’s Directive 2002/95/EC – Restriction of Hazardous Substances.

Table 3: Common examples of the four classes of air per ASHRAE Standard 62.1 are outlined. Courtesy: ESD[/caption]

The following are the best practices for ensuring satisfactory IAQ within the data center critical environment, based on ASHRAE resources such as ASHRAE TC9.9 white papers:

• Recirculated air within the data center should be filtered using a minimum of MERV 8 filters.
• Air introduced into the data centers by systems such as makeup air units, direct airside economization, direct evaporative cooling, etc. should be filtered using MERV 11 or MERV 13 filters.
• Gas phase filtration should be incorporated where gaseous contamination is a concern. The corrosion rates, as measured by copper and silver foil coupons within the data centers, should be within the following thresholds:
  • Copper reactivity rate of less than 300 Angstrom/month.
  • Silver reactivity rate of less than 200 Angstrom/month.

Occupants rarely think about the air they breathe — and they shouldn’t have to. Maintaining good indoor air quality is imperative for occupant health and comfort as well as the longevity of ITE. If you have questions about indoor air quality, always refer to ASHRAE for the latest research and resources. That way, your space will always be the picture of health.

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