Control Moisture to Reduce Mold and Fungi

Mold/moisture relationships are now recognized as significant sources of indoor air problems. Pressure driven water transport is one of the greatest paths of water intrusion into a building. Moisture is wicked into building materials when humidity levels are high. The building materials act as a substrate to catalyze mold growth. Saturated conditions are not required for mold growth. Although most toxic molds thrive in saturated conditions, only a relative humidity of 70% or more is required for growth.

Pressurization is Critical!

Use your HVAC system to create a pressurization flow and control that flow using airflow measurement devices. Your goal is to provide a net positive (cooling) or net neutral (heating) pressurization flow. You cannot overcome wind driven infiltration. The best you can do is net control. You should control the pressurization flow directly and not try to control building static pressure.

Mold growth may occur in negatively pressurized buildings during periods of dehumidification

An outside dew point of 65° F or greater will result in conditions favoring mold growth in a negatively pressurized building with an indoor air temperature of 74° F. The condition where the outside air dew point exceeds 65° F is quite common in most areas of the country.

Mold Growth Potential during periods of dehumidification (cooling)

The map is based on real hourly dry-bulb and dew point temperatures over a five year period at over 100 weather stations. The map shows the amount of time that the dew point exceeds 65° F, the temperature where the envelope humidity can exceed 70%. Florida has this condition 60-70% of the time. Even in Boston (5%-10% of the year) there are at least 36 days where DP is 65% or above – this is important because mold can develop within hours.

Annual Gallons of Water Transported across the building envelope…

This chart demonstrates how much water can be carried across the building envelope in a year per 1,000 cfm of negative pressure. It was based on water transported when the dew point temperature of the outside air exceeded 65° F.

In Miami, for example, for every 1,000 CFM of negative airflow, almost 1000 gallons of water can be brought through the walls of a building (not being filtered by the outside air intake system). In New York almost 200 gallons.

Water can also condense in the exterior walls of a building which is demonstrated by the ‘saturation’ part of the graph (when the dew point was greater than 75° F). In Miami a little over 200 gallons could actually condense in the envelope from improper building pressure.

Net Positive pressure will result in a Net Drying Effect

Proper pressurization will have a tendency to dry out the building envelope during periods of dehumidification (cooling).

Mold growth may also occur in positively pressurized buildings during periods of humidification (heating)

Your goal is to keep the building net neutral during humidification. If you keep the building positive, you can get condensation in the winter that could lead to mold growth and damage to the envelope structure. If you keep your building negative in the winter you will have problems with temperature control. You will also be using your walls as an outside air filter (not a good idea).

Net Neutral pressurization reduces moisture development during periods of humidification (heating)

Net neutral control requires precise instrumentation and is a perfect application for EBTRON products.

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