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Indoor Air Quality (IAQ)

Animation Series Visual Reference Modules for the Indoor Air Quality Building Education and Assessment Model

Animation Series 1 - Controlling Ventilation Air Flows

  1. Desired Ventilation Flows
  2. Overcrowded Offices
  3. Air Handling Unit Contaminated
  4. Outdoor Air Damper Opening Reduced
  5. Exhaust Not Operating Properly
  6. Supply Air to Office Shut Off or Pinched Down
  7. Economizer Operating
  8. Contaminated Outdoor Air

Pressure relationships between rooms is designated at the bottom of each room (with a plus for positive and minus for negative pressure).

1. Desired Ventilation Flows

Diagram of an office showing desired ventilation flows
  1. [Supply Air] Ventilation air is constantly being supplied to all occupied spaces through the supply air stream. Notice that the supply air is made up of some clean outdoor air and some recirculated air. Recirculated air often makes up the major portion of the supply air stream.
  2. [Return Air] Air inside the offices is accumulating pollutants from occupants and their activities and from the building fabric or other indoor sources. Contaminated office air is leaving the offices through the return air vent. Some portion of this contaminated return air exits the building through the “relief air vent”. The remainder is being “recirculated” and “diluted by the outdoor air” entering the air handler from outside.
  3. [Outdoor Air] Outdoor air is being drawn into the supply air stream to “dilute indoor pollutants”. The pollution from indoor sources to which occupants are exposed is directly proportional to the strength of the indoor sources, and inversely proportional to the amount outdoor air in the supply air stream. Since occupants and their activities are often the major source of pollution, ventilation standards for indoor air quality provide for a minimum quantity of outdoor air “per person”. This is designed to insure that as pollution sources from occupants increase, outdoor air increases proportionally to insure adequate dilution.
  4. [Relief Vent] Building atmospheric pressure relative to the atmospheric pressure outside is the force that is always equalizing the flow into the building with the flow out of the building. The relief vent provides a convenient way for flows to equalize.
  5. [Exhaust Ventilation] The laboratory contaminants are exhausted directly to the outside. Since the laboratory is a significant potential source of toxic pollutants, none of the laboratory air is recirculated. Ideally, an exhaust hood directly above and close to the laboratory chemicals should be used to trap the pollutants into the exhaust stream and prevent any pollutants from contaminating the breathing zone of the laboratory staff.
  6. [Indoor Relative Pressure] Pressure relationships between rooms is designated at the bottom of each room. The pressure relationships indoors are being controlled mechanically through supply, return, and exhaust air flows. Since the office is being maintained at a higher pressure relative to the laboratory, air that may sometimes flow through wall cavities or doorways flows “FROM” the offices “TO” the laboratory but not vice versa.
  7. [Building Pressurization Exfiltration] Air always flows from areas of high atmospheric pressure to areas of low atmospheric pressure. If more air is entering than is leaving the building, the atmospheric pressure inside increases relative to the outside, and thus increases the flow of air exiting the building until the incoming and outgoing flows are equal. The converse is also true. Notice how, except for the laboratory, this building is slightly pressurized to insure that the direction of air flow is from the inside to the outside to prevent outdoor pollutants from infiltrating into the building. Where outdoor humidity is a problem, this might not be a good strategy.
  8. [Laboratory Depressurization Infiltration] The exhaust in the laboratory is depressurizing the laboratory relative to the outside and relative to the office areas. That is why air is flowing into the laboratory. Depressurization is insuring that pollutants from the laboratory do not migrate into the office environments.

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2. Overcrowded Offices

Diagram of an office showing overcrowded offices
  1. [Occupancy] As more people are crowded into offices, indoor pollution increases unless outdoor air ventilation is also increased. Notice how pollution levels inside the crowded offices have increased because of overcrowding without adequate ventilation. The risk of disease transmission among occupants also increases because they are close together. Overcrowded office space is not good for occupant health.
  2. [Outdoor Air] In order to maintain good indoor air quality, the outdoor air volume must be increased when occupancies increase in order to provide adequate dilution of indoor contaminants. But increasing the outdoor air in hot weather could strain the cooling capacity of the HVAC system, and in cold weather, may call forth additional demand for preheating incoming air to avoid coil freezing. Overcrowded office space is not good for energy efficient building operations.
  3. [Air Handling Unit Capacity] More people means additional outdoor air and higher internal heat gains. This could strain the cooling capacity of the HVAC system. Further, more outdoor air in cold weather could result in coil freezing. Building managers should keep a close eye on the actual occupancy of the building relative to the existing outdoor air settings and the HVAC system’s cooling capacity and preheat needs. Overcrowding is not a good idea for HVAC equipment.

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3. Air Handling Unit Contaminated

Diagram of an office showing a contaminated Air Handling Unit

[An Air Handling Unit (AHU)] The AHU can release dirt, mold, or chemical contaminants into the supply air stream. Dirty filters, filter changes when the fan is operating, dirty coils or drip pans, excess moisture anywhere leading to mold, deteriorating duct insulation, trash or housekeeping/maintenance products in the mechanical room/mixing chamber—these are common examples of pollution sources in the AHU. Does this describe your buildings? Good maintenance and cleanliness not only keep the system running well, they also insure that the AHU does not become a source of indoor air pollution. Who suffers from contamination in the AHU?

  1. Occupied Spaces: Notice how the contamination in the AHU spreads to every occupied space serviced by the AHU through the supply air stream. If you have health complaints that are widespread – consider whether the AHU or air ducts are contaminated by improper building maintenance or from other causes.

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4. Outdoor Air Damper Opening Reduced

Diagram of an office showing the reduced Outdoor Air Damper Opening
  1. [Outdoor Air] The outdoor air flow was reduced, ostensibly to save energy. As a result, pollutants have built up in the offices. Do you think that this is the only effect? What do you think has happened to the exhaust system?
  2. [Exhaust] Because total air flow out of the building can not exceed air flowing into the building, the air that the exhaust fans are now capable of drawing out of the laboratory is also reduced because the outdoor air dampers are closed. What will happen to the laboratory chemicals?
  3. [Pressure] Since the pressure differential between the offices and the laboratory are reduced, laboratory chemicals may now migrate throughout the building.
  4. [Occupied Spaces] The reduction in outdoor air had multiple effects: It reduced the dilution of contaminants in the offices; reduced exhaust and thereby increased pollution in areas of high pollution loads such as laboratories, toilets, and copy rooms; and reduced pressure differentials between the offices and laboratory, thereby allowing laboratory pollutants to migrate into the office areas. Reducing outdoor air BELOW APPLICABLE STANDARDS is a BAD IDEA.
  5. [Infiltration] Because outdoor air flow is reduced, the building is no longer slightly pressurized as intended, and is now depressurized. This causes air to infiltrate from the outside into the office area.

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5. Exhaust Not Operating Properly

Diagram of an office showing the Exhaust Not Operating Properly and flowing through the office
  1. [Exhaust] Exhaust air flow needs to be checked periodically. Many factors can account for inadequate exhaust flow. Exhaust fans may not be operating properly or the building may become depressurized because of inadequate outdoor air or for other reasons. Notice how contaminants have accumulated in the laboratory when the exhaust does not operate properly.What happens to laboratory pressure?
  2. [Pressure] When the exhaust air flow was eliminated, the laboratory became positively pressurized from the supply air. Now chemical contaminants are more likely to spill out into the offices.
  3. [Outdoor Air] Because less air is being drawn out of the building through the exhaust, the building has a higher atmospheric pressure so that less air enters the building. What does this do to the office contaminants?
  4. [Office Space] Reducing exhaust air flow has had multiple effects in the office area. Laboratory contaminants spill into the office environment from the laboratory through unintended pathways, and outdoor air which once diluted office contaminants is now reduced. Office pollutants in the office area increase and are joined by laboratory chemicals. Exhaust fans and air flow should be checked periodically to make sure they are functioning properly.

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6. Supply Air to Office Shut Off or Pinched Down

Diagram of an office showing the Supply Air to Office Shut Off or Pinched Down
  1. [Supply Air] Supply air to a given space may shut down for different reasons--a mechanical failure, an ill conceived renovation (e.g. a renovation splits an existing room but does not provide for supply and return to each room), or because of VAV pinch down. In a VAV system, the supply air may be reduced because of thermal neutrality (i.e. the room does not require conditioning), but the VAV box should be set with a MINIMUM STOP high enough to provide adequate outdoor air even when demand for conditioning is low. Notice that contaminants in the space with diminished supply are not diluted but rather build up. Occupants with inadequate supply air may suffer both excess pollution exposure and thermal discomfort.

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7. Economizer Operating

Diagram of an office showing the Economizer Operating with outdoor air entering the building
  1. [Outdoor Air] The weather is cool outside. So the economizer is bringing in large quantities of outdoor air to provide “free cooling”. Humidity is also being carefully controlled. How does increased outdoor air effect pollution levels in the building?
  2. [Occupied Space] The increased outdoor air flow from the economizer provides greater dilution of indoor generated contaminants in occupied spaces. However, indoor concentrations of outdoor contaminants has slightly increased. As suggested in the picture, except in cases where the outdoor air is highly contaminated, the net effect of increasing outdoor air flow is usually to lower indoor air pollution.

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8. Contaminated Outdoor Air

  • <a class="colorbox-gallery" data-cke-saved-href="/sites/production/files/styles/large/public/2015-01/1-8.gif" href="/sites/production/files/styles/large/public/2015-01/1-8.gif" role="dialog" title="Contaminated" outdoor="" air"="">[Occupied Spaces] Outdoor pollution enters the building through the outdoor air supply and is carried through the supply air ducts to the occupied spaces. It is not diluting indoor sources but is adding to them. Overall pollution levels inside the building are elevated from both the indoor and the outdoor pollution sources.

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Animation Series 2 - Pressure Relationships

  1. Balanced Flows are Precarious
  2. Unbalanced Flows Pollutes Office

Mouse over the animated pictures below to see messages which are referenced in more detail below.
Pressure relationships between rooms is designated at the bottom of each room (with a plus for positive and minus for negative pressure).
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1. Balanced Flows are Precarious

Diagram of an office showing precarious balanced flows
  1. [Kitchen Exhaust] Exhaust fans in the kitchen are on manual switch. In the early morning and late afternoon hours, a small set of exhaust fans are operating to accommodate light cooking for lunch. This places the kitchen and cafeteria area under slight negative pressure that draws some transfer air from the office area.? What happens at noon?
  2. [Copy Room] The exhaust is maintaining a slight negative pressure which draws some transfer air from the office space during the early morning and late afternoon. What happens during the lunch?
  3. [Office Supply] The office supply air flow is sufficient in the morning and late afternoon to keep the office under slight positive pressure relative to the copy room and kitchen. Neither copy room pollutants nor kitchen pollutants are entering the office area. All is well in the morning. What happens during the lunch?

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2. Unbalanced Flows Pollutes Office

Diagram showing an unbalanced flow polluting an office building
  1. [Kitchen Exhaust] It's lunch time. When preparing lunch, the main exhaust fans in the kitchen are turned on. These are drawing a large volume of air out the exhaust so that the kitchen and cafeteria area under greater negative pressure that draws more transfer air from the office area. What happens in the office area?
  2. [Office Area] Since the kitchen exhaust fans are running full, the kitchen is drawing enough transfer air from the office area to place the office under negative pressure relative to the copy room. This draws copy room exhaust into the office environment. Complaints occur only around lunch and only if the copy room is being heavily used. By the time the building engineer arrives to investigate in the late afternoon, the kitchen exhaust fans are turned down, and the problem has gone away. Other offices in the building think that the IAQ was actually better than other times of the day. The problem recurs only periodically. The engineer thinks these particular occupants are just periodic complainers. Sound familiar?
  3. [Copy Room] Copy room exhaust and supply are operating normally. But since the kitchen exhaust fans are running at full load, the draw from the kitchen is sufficient to draw copy room contaminants into the office area and generate complaints.
  4. [Outdoor Air] The flow of outdoor air into the building automatically increases when the kitchen exhaust fans are turned on full. The extra outdoor air replaces the air removed by the added exhaust from the kitchen area. However, although the building itself has added dilution ventilation, giving rise to improved IAQ elsewhere in the building, air the office next to the copy room becomes more polluted when the copy machines are heavily used during the lunch period.

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Animation Series 3 - Containing Construction Containments

  1. Construction Area Contained
  2. Poor Containment Strategy
  3. Temporary Exhaust is OK
  4. Incorrect Ventilation Concept
Pressure relationships between rooms is designated at the bottom of each room (with a plus for positive and minus for negative pressure).

1. Construction Area Contained

Diagram of an office showing contained construction area
  1. [Contaminant Area] The room with an exhaust is being used as the containment area. A large exhaust machine (negative air machine) keeps the containment area under significant negative pressure. Blocking the supply air is helping to maintain negative pressure. The area is sealed reasonably well from all surrounding spaces (other than the construction area). This is also helping to maintain negative pressure. Construction pollutants are flowing FROM the construction room INTO the containment area and OUT the exhaust.
  2. [Construction Area] The return air in this room is blocked to insure that there is no recirculation of contaminated construction air. The construction area is under negative pressure relative to all surrounding areas except the containment area which draws construction contaminants into the exhaust air stream. Replacement air comes from infiltration, and from adjacent rooms above and below the construction area. An opened window in the construction room is sometimes used to improve the flow of air into the containment area.
  3. [Office Area] The office area is protected against the construction contaminants because it is kept at positive pressure relative to the containment room, which itself is well sealed. Additional supply air flow to this area during the construction activities can help assure positive pressure and good indoor air quality to the office occupants.

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2. Poor Containment Strategy

Diagram of an office showing poor contaminant strategy
  1. [Contaminant Area] Inadequate negative pressure in the containment area resulted because the containment area was not adequately sealed, and/or the exhaust fan horsepower was insufficient. There is thus insufficient flow of construction contaminants into the containment area and out the exhaust.
  2. [Construction Area] The return in this area was not blocked. Combined with the weak negative pressure in the containment area, some exhaust pollutants escape into the return air stream. Some contaminants also flow through wall cavities and other unplanned pathways to other parts of the building.
  3. [Office Area] Construction contaminants flow through the return air path and through unplanned pathways into the office. Occupants will soon complain.

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3. Temporary Exhaust is OK

Diagram of an office showing temporary exhaust
  1. [Construction Area] Access to a permanent exhaust port is not available, so a temporary exhaust was provided through a window or other opening in the outside wall. The exhaust is sufficient to insure that the construction area is under significant negative pressure relative to the surrounding spaces, including those above and below the construction area. The return air is blocked. The construction room is sealed sufficiently to insure adequate negative pressure is maintained at all times. If necessary, the supply air may also be blocked so that the construction area is served by transfer air from surrounding spaces in the building.
  2. [Office Area] The office area is well protected from the construction area. Air flows FROM the office area TO the construction area but not vice versa. And no construction contaminants enter through the return air stream.

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4. Incorrect Ventilation Concept

Diagram of an office showing incorrect ventilation
  1. [Construction Room] Someone doesn’t understand pressurization concepts. Construction workers thought they were providing good ventilation by putting a large fan in the window blowing resh air into the construction area. What is this doing? It is pressurizing the construction area, forcing the construction contaminants into surrounding spaces and through the return air stream to other parts of the building. Everyone in the building will be complaining.
  2. [Office] Since the construction room is under positive pressure relative to the surrounding spaces, contaminants flow into the office area. Construction pollutants are also contaminating the return air and are being recirculated to all spaces served by this air handling unit.

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Animation Series 4 - Pollution Flows in Underground Garage

  1. Normal Flows with Exhaust Fan
  2. Inadequate Pressure Control
Pressure relationships between rooms is designated at the bottom of each room (with a plus for positive and minus for negative pressure).

1. Normal Flows with Exhaust Fan

Diagram of an office showing  Normal Flows with Exhaust Fan
  1. [Garage] Exhaust fans in the garage are fully operational during significant use periods to insure that all garage contaminants are fully exhausted to the outside. Exhaust fans may be in partial use during slack periods. Sometimes carbon monoxide sensors are used to control fan operations. In any case, the garage should be maintained under negative pressure relative to the building at all times.
  2. [Vestibule] The vestibule is acting as a buffer between the garage and the occupied spaces in the building. It may be subject to slight depressurization because of a stack effect up the elevator shaft and stairwell which draws some air, and because of the exhaust fans in the garage. However, some ventilation air is supplied through a supply air duct to neutralize this effect. Some air flows up the elevator and stairwell, and some flows from the vestibule into the garage. But garage pollutants do not enter the vestibule.

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2. Inadequate Pressure Control

Diagram of an office showing inadequate pressure control

  1. [Garage]Exhaust fans are not operating, and a strong wind at the garage entrance pressurizes the garage. This allows garage contaminants to enter the vestibule.
  2. [Vestibule]Garage contaminants are entering the vestibule. At the same time, the stack effect is drawing a column of air up the elevator shaft and the stairwell and into the building. Building occupants are subject to carbon monoxide and other garage contaminants. garage fans should be operating during heavy use periods. Pressure relationships between the garage and the vestibule should be checked under different operating conditions.

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