What every TAB technician needs to know about indoor air quality
Poor indoor air quality (IAQ) contributes to a substantial number of health problems. ASHRAE Standard 55-1992 addresses the most common factors related to the comfort of occupants within the space. This article outlines the guidelines.
The U.S. Environmental Protection Agency (EPA) defines indoor air quality (IAQ) as:
“The temperature, humidity, ventilation and chemical or biological contaminants of the air inside a building.”
This represents any condition inside the building that effects the health and comfort of the building occupants; including temperature, humidity, and the concentration of pollutants. ASHRAE defines Acceptable Indoor Air Quality as:
“Air in which there are not known contaminants at harmful concentrations by cognizant authorities and with which a substantial majority (80% or more) of the people exposed do not express dissatisfaction.”
Effects of poor indoor air quality
Poor indoor air quality contributes to a substantial number of health problems. Studies have linked it to poor performance in both the school and work environments. Effects can be immediate and the result of a single exposure or delayed, not showing up for years. Short term and immediate problems may manifest as allergic reactions, headaches, fatigue or asthma. At the other extreme, years of exposure to Radon may result in lung cancer. A single exposure to asbestos may cause mesothelioma, a fatal lung disease.
Different segments of the population may react differently to exposure. The very young, the elderly and those with suppressed immune systems may be much more likely to succumb to disease as a result of exposure. This increases the significance of these issues in schools, nursing homes and hospitals.
Causes of indoor air problems
Pollution sources inside the building that release or off gas pollutants can include, but are not limited to: air fresheners, smoking, perfume, cleaning products, cooking or process by-products, propane forklifts, boiler combustion by-products and off-gassing of chemicals by furniture, carpets and building materials.
Examples of outside sources of pollutants being taken in to the building through outside air intakes or infiltration into the building can include: radon, pesticides, atmospheric pollution, carbon monoxide and other combustion by-products from vehicle traffic.
ASHRAE Standard 55-1992, Thermal Environmental Conditions for Human Occupancy, addresses the most common factors related to the comfort of occupants within the space and addresses temperature, radiation, humidity, air movement, temperature stratification and drift as well as factoring in the clothing and activity level of the occupants.The scope of indoor air quality extends to temperature, humidity and lighting within a facility.
The conditions outlined in the table are guidelines from the standard that satisfy the thermal comforts required by the standard.
In addition to comfort issues, extremes in temperature and humidity can also exacerbate other potential sources for IAQ problems. Higher temperatures increase the reactivity of chemicals and accelerate off-gassing of compounds from building materials and interior furnishings. Increased humidity raises the risk of microbial growth and proliferation.
Beyond the physical values of temperature and humidity, many other factors can contribute to the perception of comfort. Air movement also plays a large role in thermal comfort. The lack of air movement can create a sensation of hot/stuffy air. Increased air velocity on the skin accelerates evaporation of perspiration which increases cooling. The same higher level of air movement can induce a chill in others. The goal is to find the balance of these variables that will provide the client with the highest level of satisfaction.
Increased humidity is a major cause of mold growth within the building environment. In high humidity parts of the country, it can be a considerable detriment to indoor air quality. The conditions for mold to grow require three components: mold spores, a media to feed on and moisture. Mold spores are essentially everywhere and mold is capable of using most media as food sources, including drywall, ceiling tiles, carpet and wallpaper. That leaves the control of moisture as the only practical method to control the growth and proliferation of mold.
Control of indoor air quality issues
Control of indoor air quality is typically addressed at three levels. The first step is administrative controls. Some examples of administrative controls are:
- Making decisions which would prevent the source of the pollutant in the first place
- Having a no smoking policy or using a different process for an in-house procedure
- Choosing low emitting products for maintenance and cleaning
- Isolating some processes in a remote location
Whenever practical, administrative controls are the best solution.
There are times when because of financial cost or sheer practicality, an administrative control cannot be used; in such cases engineering controls provide the next best solution. Engineering controls utilize a line of defense to separate the sources of pollution from the occupants in the conditioned spaces. These controls may:
- Utilize pressure barriers such as those seen in fume hoods or in isolation rooms operating under a negative pressure.
- Employ physical barriers such as a glove box in a laboratory or special filtration procedures.
There are times when the contaminant in the space does not come from one point source. This can include the off gassing of chemicals from building materials, cleaners used to clean and wax floors and body odors from building occupants. To address issues such as these, the best solution implements the third level of control, dilution ventilation.
One such solution is to introduce large amounts of fresh air to dilute the concentration of the pollutant to a level where it does not pose a problem.
TAB related issues
It is not the test-and-balance (TAB) technician’s job to design the project, but there are many aspects of the job that can ensure the design intent is fulfilled and the building occupants are provided a healthy facility for their use.
Ventilation is probably the single item over which we have the greatest influence. Most buildings are designed with criteria based on ASHRAE Standard 62, Ventilation for Acceptable Indoor Air Quality, which has become the generally accepted standard for commercial buildings in the United States. This standard combines many parameters to designate the appropriate amount of fresh air for a given space, such as the number of occupants, square footage of the space, the intended use of the space, building schedules, etc. This replaces older references to a fixed cfm per occupant.
Many systems use carbon dioxide (CO2) levels as criteria to control outside air levels. CO2 occurs naturally in the atmosphere typically at levels around 400 parts per million (ppm). Many control systems are designed to increase the outside air when the CO2 level reaches a set value, typically 1000 ppm. CO2 itself is not a problem at these levels: OSHA sets their permissible exposure limit at 5000 ppm. CO2 is used instead as an indicator of the ventilation effectiveness. If CO2 levels are rising to the 1000 ppm level due to generation from the human occupants then it follows that other pollutant levels will rise to potentially unsafe levels.
Outside air flows should be set up so that they satisfy the requirement outlined in the project documents under all conditions. If outside air flow is set on a VAV system at 100% flow then the same system may not provide the design requirement in a minimum flow condition when all terminal unit boxes are satisfied or in a heating mode. While some control systems accommodate such conditions many do not. A failure to meet the design in all modes should be reported and corrective action should be implemented by the project team.
Rooms hosting large groups such as classrooms, conference rooms or training spaces often have intermittent occupancies. ASHRAE allows the outdoor air requirement to be based on average occupancy as long as the peak occupancy is for a period of three hours or less. There should never be less than 50% of the maximum.
Many systems are wired such that the fan shuts off when the system is satisfied. Under such conditions the system is not meeting the requirements of the project documents and corrective action is required.
Sometimes the outside air itself can cause problems. In warm, humid environments a constant volume unit when satisfied may shut down the coil at the thermostat while the fan continues to bring humid unconditioned air into the space. When the air hits cool surfaces in the space the moisture in the air condenses and provides an avenue for mold propagation. Outside air can also be the source for pollutants. Outside air intakes situated over loading docks may capture truck exhaust and bring it into the space. Exhaust fans discharging polluted air, if located near outside air intakes, may result in kitchen or sewer gas odors being carried into the occupied space. In the worst case you may be exhausting air from an isolation room or chemical fume hood which can then be carried back into the space, resulting in dangerous conditions for the occupants.
Building pressure for most facilities is designed to be neutral to slightly positive. There are exceptions to this such as laboratories, restrooms, etc. which maintain negative pressures by design. In most conditions the amount of outside air will exceed the amount of exhaust air for a given space; this ensures that slight positive pressure and minimizes the chance for infiltration.
An excess of air can lead to over-pressurization of the building and result in problems with doors closing and bubbles in roofing membranes.
Building changes can result in creating IAQ problems where there weren’t any previously. Often walls are moved around, creating areas with no return or poor air mixing. Problems such as these are frequently seen in tenant modifications in office buildings.
LEED IEQ requirements
LEED is a set of rating systems for the design, construction, operation, and maintenance of buildings. It was developed by the U.S. Green Building Council to help designers, builders and owners create and use their facilities efficiently while promoting the concepts of sustainability.
Part of the LEED scoring process involves indoor environmental quality. It has two prerequisites required to certify the facility and numerous other credits which are optional opportunities to gain points and improve the overall score of the facility. Below are listed those that pertain most to the TAB industry.
- Minimum IAQ performance meet requirements of ASHRAE 62.1-2007
- Control of smoking in and around the building
Credit 1 (Outdoor air delivery monitoring)
- Provide monitoring of outdoor airflow or
- Install controls based on CO2 levels in space
Credit 2 (Increased ventilation)
- Increase outside air ventilation rate by 30% over ASHRAE 62.1-2007
Credit 3.1 (IAQ management plan during construction
1. Integrate IAQ requirements into specification
2. GC creates comprehensive IAQ plan
- Avoid use of HVAC equipment during construction
- If HVAC equipment used install MERV 8 filters
- Cap and cover ductwork, grilles, etc.
- Use low VOC materials
- Install temporary barriers to separate construction from occupied areas.
- Maintain housekeeping with regular sweeping and damp mopping of space.
- Plan schedules to limit occupant exposure to construction area.
- Document with photos
- Replace air filters used during construction
Credit 3.2 (Construction IAQ prior to occupancy)
1. Option 1 – Flush out building with fresh air. Do either of the following:
- Prior to occupancy flush out building at a rate of 14000 cfm per square foot of occupied space. Maintain at least 60 F and do not exceed 60% relative humidity.
- Prior to occupancy flush out the building at a rate of 3500 cfm per sq ft of occupied space. Ventilate once occupied at a rate of .30 cfm per sq ft or the design outside air flow rate whichever is greater. Begin three hours prior to occupancy and continue during occupancy. Maintain the flush out until 14000 cfm per sq ft of occupied space has been delivered to the space.
2. Option 2 – Conduct baseline IAQ testing prior to occupancy. Use EPA protocols test for the following: Formaldehyde, Particulates, Total volatile organic compounds, Carbon monoxide and 4-Phenylcyclohexane.
- 1 test per 25,000 sq ft
- 1 test per floor
- 1 test per ventilation system
- Collect during the occupied mode for a minimum of four hours.
- Take samples between 3 and 6 ft
- Include areas with the lowest ventilation and highest source strength.
Credit 5 (Indoor and chemical pollutant source control)
1. Permanent entry way walk-off system at least 10 ft long
2. MERV 13 filtration on return and outside air intakes
3. For hazardous gas and chemical use areas
- Exhaust with rate of .5 cfm per sq ft
- Use self-closing doors
- Use deck to deck partitions or hard lid ceilings
There are additional IEQ credits related to low emitting materials, acoustics, daylighting and ergonomics that have little involvement with the TAB process.
A certified TAB technician should be aware of conditions which can contribute to IAQ problems. Below is a list of items which should be verified to minimize the chance of IAQ problems related to the HVAC system and its balance.
- Are coils clean?
- Are face velocities low enough to prevent water from being carried off of the coil?
- Are there any leaks in the valving assembly?
2. Drain pans
- Are there any leaks?
- Is the pan installed so that it slopes to allow all water to drain from the pan?
- Is there any sign of standing water in the pan?
- Is there any evidence of biological growth in the pan?
- Is the drain properly sized and installed?
- Is the drain clogged?
- Are filters clean?
- Are filters properly sized?
- Are filters tight fitting?
- Does filter efficiency meet design requirements?
4. Air distribution & louvers
- Do supply grills show signs of smudging or dirt patterns?
- Are return air grills dirty?
- Is the location of supply and return grills such that the air is not short cycling?
- Does the throw of the air create drafts or interfere with the collection of air by hoods such as those used in laboratories or kitchens?
- Does the location and throw of the grills in the room allow good air mixing in the space and minimize stratification of temperatures?
- Are outside air louvers located in close proximity to exhaust discharge louvers?
- Is the outside air intake in a location away from environmental pollution sources such as traffic, loading docks, dryer vents, downwind from stacks, etc.?
- Is the outside air intake located near stagnate water sources?
- Does the outside air intake have a fine mesh insect screen that can become easily clogged?
During construction is duct work protected from dust and debris?
- Is duct wet inside?
- Is duct work properly sealed this is especially critical for return ducts which can draw in contaminants from the attic, basements, etc.?
- Are duct linings dry?
6. Exhaust Systems
- Is discharge louver location far enough away from outdoor air intakes?
- If this is local exhaust does it capture the source pollutant?
- Is a source for makeup air provided such as undercut doors, transfer grills, etc.?
- Does the space pressure meet the design requirements?
- Are the controls operating properly?
- Can the system handle the latent load while in economizer mode?
- Economizers are not typically used in hot & humid environments?
8. Cooling Towers
- Is drift being minimized?
- Is a water treatment program in place?
- Is the proximity of the cooling tower to the outside air intake to close?
9. Humidifiers and de-humidifiers
- Is there any indication of microbial growth?
- Does the duct or liner near the equipment get wet?
- Are drains functioning as designed?
- Is potable water used in the humidifier?
10. Return air plenums
- Are there any chemicals being stored in the mechanical room?
- Is the plenum clean?
- Are there exhaust ducts in the plenum which could be leaking contaminated air into the air stream?
- Are there any water sources in the plenum that could contribute to microbial growth such as condensation on ducts and pipes, or leaky valves?
- Verify boiler room is under a positive pressure adequate enough to prevent siphoning of combustion gases from the flue.
- Gaskets should be in good condition
- No water leaks or drips
- Verify location and height of exhaust stack will prevent the flue gases from being drawn into the outside air intakes.
While this outline is not all-inclusive, it provides a basis for understanding indoor air quality and the technician’s role in the success of maintaining a healthy work space for customers.
William Carson Judge, TBE, CxA, Bay to Bay Balancing Inc. has many years of experience in AABC & NEBB testing and balancing and ACG, ASHRAE, LEED PR1 & enhanced commissioning. This article originally appeared on the Associated Air Balance Council (AABC) TAB Journal. AABC is a CFE Media content partner. Edited by Joy Chang, digital project manager, CFE Media, firstname.lastname@example.org