Vapor Intrusion: How a building works and breaths

The “Breathing Building” The top five floors of this seven-story structure are covered in 734 gold, copper and bronze-colored steel plates that can be raised or lowered via 82 computerized motors. The plates function as a second skin for the building, increasing its ability to permit natural ventilation and lowering energy consumption by cutting down on the use of air conditioning. The plates are peppered with micro-holes to allow visibility from within. Geox occupies the ground and first two floors, while the remaining four floors house non-retail tenants.

Goals for Today Understand how buildings are working What can effect movement of vapor through a building Understand how subtle the air movement can be through a building What are the different forces that affect the air movement.

At what pressures do our buildings function? Blower door tests and COE testing 75 Pa. Ductwork and ventilation system 1”-2” water column

What are the pressure equivalents? 1 atmosphere 2.96077 e-5 atmosphere 14.69 psi .000435 psi .06 psf 2116 psf .012 inches of water column 406.79 inches of water column 3 Pa 101325 Pa

What happens in a building Convection Stack Effect Mechanical ventilation Static Pressure Natural Wind pressure Adjacent spaces Fresh air intakes (leakage and powered) Recent building control innovations Buoyancy

What do we do for Ventilation? Building codes require: Living areas - 0.35 air changes /hr or > 15 cfm/person Garages-100 cfm/car Enclosed parking .05 cfm/sf AND capable of 1.5 cfm/sf Commercial Buildings – 4-10 air changes /hr ASHRAE-ventilation design is anticipated to be thru infiltration. Energy issues have changed that. For tight houses .5-.41 ACH For loose insulated homes 1.1-1.47 ACH Westminster Palace venting

Building Occupancy Differs with how the building is used: Health care Higher air volumes Required to be full ducted return Office space Could be return plenum ceiling Apartments and hotels Usually parking below and furnace inside Does not have make up air system except in corridor Make up air is via opening a window Often referred to as Magic Pak or Ptac

Convection Warm air rises, cold air falls

Stack Effect Areas like stairwells, atriums and elevator shafts show the volume of air that is moving vertically through the building. E.g. IDS Building, 52nd floor. Difficult to open the door to the mechanical room on the 52nd floor

Mechanical ventilation Air moves by the difference in pressure Fan forced “push” or “pull Plenum spaces versus full ducting Think about the Metrodome. Air pressure is only about 0.04-.4 psi Air balancing is a vital requirement. The in and the out need to be about equal Try blowing or sucking air out of a pop bottle

Static pressure differential Air in ducts is measured in inches of water column Different zones require

Natural wind pressure Wind air pressure can be in the 20#+ psf (.13 psi)

Building Air Leakage Case Study Buildings: Two – 3 story barracks buildings Steel frame construction Composite concrete decks Metal studs/exterior sheathing air barrier/rigid insulation/brick PTO roof membrane over rigid Insulation Test Requirements: USACE Protocol for TESTING Air Leakage in Occupied Buildings ASTM E779 – Standard Test Method for Measuring Air Leakage Rate by Fan Pressurization Pressure boundary: total area of floor slab, exterior walls & roof Allowable CFM: 25% of pressure boundary area Passing grade: 0.25cfm/sq ft @75 Pa (0.3 inches H2O) Ft Leonard Wood Barracks Building Air Leakage Testing

Building Air Leakage Building Air Leakage Air Pressure inside a building on a calm day Depressurization Test Cycle -75Pa to -25Pa with Bias pressure readings pre & post test

Air pressure inside the same building on a windy day Building Air Leakage Air pressure inside the same building on a windy day Depressurization Test Cycle -75Pa to -25Pa with Bias pressure readings pre & post test

Adjacent spaces Balancing Issues Air transfer in Roof Deck flutes between building tenants Air transfer at material joints Air barrier installation (not “weather barrier” or “vapor retarder”)

Fresh air intake Normal fan powered units pass a 6-10% fresh air or # cfm per occupant. Fin tube radiation has no fresh air unless a separate system is provided. PTAC and Magic Pak units have a small amount of fresh air, but unit must be running and balanced with the exhaust fan Pressurization Supply air-air loss=>return air + fresh air. Normally building is slightly positive in pressure. Apartments and condos Corridor has make up air, but stopped from getting to the units due to fire gasketing Opening locations

Building Control system innovations LEED monitoring Low level conditioning Occupied versus unoccupied modes CO2 Sensors Mixed return air or air exchange systems and heat wheels Breathable Buildings

Buoyancy Warm air makes a difference Chemicals also make a difference.

Vapor prevention Consider particle/molecular size- “Coffee Filter” Water proofing versus vapor retarding Think of Gore-Tex Vapor passes through Water beads up Issue is really molecule size Water liquid 90 molecules in size Water vapor 2 molecules in size If vapor is larger than water it will not go through normally

Slab on grade and foundations Negative pressure zone under floor Membrane selection and sealing Materials Concrete block is porous and will allow air/smoke/vapor through it Concrete block can also transport air vertically and up into the second floor Vapor retarder- Quality material, not lumber yard poly Virgin polyethylene. Stego, Raven etc. Exterior wall waterproofing

EPA moisture control

PNC Breathable Building in Pittsburgh. Worlds Greenest Building Incorporates Convection, stack effect, and natural conditions This allows the building to operate with no mechanical system 45% of the time. https://youtu.be/z8ScZsOBB7k

Underground garages Make up air and exhaust

Radon and passive systems

Conclusions There are many effects taking place in the building and they vary by season. Not all buildings are the same. The ventilation systems, design and operation all impact the vapor potential. Nature affects the way buildings operate. The mitigation system needs to work with the mechanical system, if possible. The engineer needs to deal with all of these different issues in the design of the building and systems. Remember there is a potential for the buildings to operate outside of the norm. Mainly due to human interference.

What can get in the way? Weather Other building systems or openings for fresh air Insulation systems that want to add a porous material to the perimeter of the building. Making a connection between all the membranes through structure. Future occupants Trying to save on the costs of energy, modifying the building by disabling or shutting off systems. Tenant changes (pizza ovens; high volume exhaust etc)

Q&A