Controlling Mold Growth in Exterior Walls of Buildings by
Continuously Maintaining Positive Pressure Flow through
Dynamic Ventilation Strategies

By David Dougan and Len Damiano
EBTRON, Inc.

ABSTRACT
Building pressure control is essential to assure acceptable indoor air quality in today’s buildings, especially in humid climates. Mold growth inside exterior walls can result in significant IAQ and health problems. Moisture is a prerequisite for microbial growth. Minimizing the infiltration of humid air into a building, where it could condense within the exterior walls, can reduce microbial activity.

Positive and continuous internal building pressure will minimize (or prevent) infiltration. Positive pressurization requires that a "pressurization flow" is created. This occurs when the total quantity of outside air supplied exceeds the sum of local exhaust and exhaust at the air handler. Traditional HVAC control methodology employing indirect measurement of control variables (e.g. fixed outside air damper, VFD proportional drive slaving and space static pressure control of the return fan), are insufficient for control and verification in dynamic systems. To insure that the HVAC system is performing as required under variable internal or external conditions, a positive pressurization flow must be developed as a result of directly measuring and controlling critical volumetric flow rates.

INTRODUCTION -
Since the middle1980s tighter building construction has dramatically reduced infiltration through the building envelope. Also during this period the increased use of variable air volume (VAV) ventilation system design s has unintentionally reduced the outside air distributed through the supply duct.^{1, 2, 3, et.al.} Both of these factors have reduced the dilution rate for contaminants emitted from people and the building and have been a major factor in degrading indoor air quality (IAQ) to levels that are 100-1000 times more polluted than outside air.⁴ Since people typically spend 90% of their time indoors, and of that 50% at their place of work,^{5, 6} IAQ has become a worldwide concern.

In 1998 the United Nations attributed 2.2 million deaths / year from indoor air pollution, more than 4 times the mortality rate for outdoor air pollution ⁷ . A 1997 joint study between the U.S. Department of Energy and Lawrence Berkley National Laboratory estimated total costs to the U.S. economy range as high as $168 billion/yr. ⁸ The report attributed $6-19 billion from increased respiratory disease, $1-4 billion from increased allergies and asthma, $5-10 billion from sick building syndrome, and a potentially huge amount, $12-125 billion, from reduced productivity.

In 1998 the EPA reported 50% of U.S. schools have IAQ problems ⁹ and a report commissioned by the National Contractors Association found that 15-35% of U.S. office buildings have significant IAQ problems.¹⁰ U.S. asthma rates have escalated since IAQ problems have become prevalent.¹¹ Several studies link IAQ and respiratory symptoms in homes, schools, and office workers.^{12, 13, 14, 15} Children and hospital or health care patients are especially susceptible due to their underdeveloped or compromised immune systems. In 1999 the New York Times reported an asthma rate of 38% for children in New York City shelters (with notoriously poor IAQ)—more than six times the national rate for children.¹⁶

IAQ liability has also become a major consideration for the construction industry. In 1996 Owen McGowan of the law firm Mitchell, Heilein, and DeSimions commented, "virtually unheard of until the mid-1980s, problems with indoor air quality are growing in frequency and severity.¹⁷ "More recently, in 1998 the New York Law Journal reported a "deluge" of sick building syndrome claims.¹⁸ IAQ claims and awards can easily run into millions of dollars.^{17, 18}

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