Preventing Mold

1
Preventing Mold MildewIn GSA Buildings

• A Multi-disciplinary
• (Project Managers) Opportunity
• Lew Harriman
• Mason-Grant Consulting

2
Building Mold - A Classic Example
3
Everybody Participated

• Architect - Lousy exterior details. The wall
  leaked
• Interior designer - Fragile design. Interior
  vinyl trapped water and promoted condensation
• General Contractor - Lousy craftsmanship. AC Unit
  penetrations leaked air water
• HVAC designer - Unsealed exhaust ducts. Created
  suction that pulled humid air into cool wall
  cavities

4
How mold grows
5
Growth Rates Vary By Species, Food Source Water
Activity
6
How Does Water Get Into Walls?

• 1. Water leaks in the exterior walls let in rain
  sprinkler water
• 2. High internal dew point cool surfaces cause
  internal condensation
• 3. High internal dew point allows sorption from
  humid air (over 60 dew point)

7
How much humid air does leaking ductwork REALLY
pull in?
About 50 of total flow, in this measured test
by Florida Solar Energy Center
8
But then how much does the whole building leak?
9
RH can seem OK but moisture can still condense
and drip

• Monitor control the dew point, and the rh will
  take care of itself

10
Lots of water comes in with ventilation air 96
gph!
11
Lots of hours of high dew points in the 8760
hours of a year!
12
...Which is why Project Managers in humid
climates should insist on

• Continuous D/H of ventilation air to a 55F dew
  point (24hrs/365days - no resets)
• Continuously positive air pressure more dry air
  supplied than exhausted... all the time
• Duct work and connections ALL sealed

13
Dry the ventilation air deeply enough to remove
internal loads
14
Drying ventilation air with a dedicated outdoor
air unit
15
For large buildings two ventilation systems

• Saves energy operating cost (bigtime!)
• Provides constant pressure dehumidification

16
Sealing duct workand connections
17
Because without sealed return air connections
18
How much positive air pressure?

• Easy to test... Just use smoke or tissue paper at
  the door jamb.
• Hardly any is needed! Just make sure that air
  moves OUT through the doors rather than INward.

19
Summary of suggestions

• Architects general contractor make sure the
  exterior wall doesnt leak water
• Interior designer dont put vinyl on exterior
  walls
• HVAC designer contractor
• Dry all ventilation air to 55F dew point, all
  year long
• Seal all ducts and all duct connections
• Supply 10 excess dry ventilation air
• Operators
• Change ventilation air filters once a month (at
  least)
• Make sure ventilation air is dried to 55F
  dewpoint, all the time
• Think positive! Keep the building air pressure
  positive

20
Some Resources Experts

• General ASHRAE Humidity Control Design Guide
  ISBN 1-883413-98-2 [phone]
• Mold in buildings ASHRAE Humidity Design Guide
• Duct leakage Florida Solar Energy Center - Jim
  Cummings [phone]
• Building pressurization
• CH2M/Hill (Orlando) - J. David Odom (407)
  423-0030
• AirExpert Systems - David Bearg [phone]
• Building Science Corp - Joe Lstiburek (978)
  852-9220