CHICAGO - For a subject so problematic for hvac engineers and contractors as mold, they sure do like to talk about it.

Some of the most popular sessions during the winter meeting of the American Society of Heating, Refrigerating and Air-Conditioning Engineers were on the subject. The Jan. 28 free public session, "Residential and Small Building Humidity and Mold Control," was perhaps the best attended. It filled a large meeting room at McCormick Place convention center.

Hundreds of people turned out to hear experts explain how to deal with the growing public perception of mold-related problems.

Philip Morey, Ph.D., of Air Quality Sciences Inc. in Gettysburg, Pa., reminded attendees that molds are from the kingdom of fungi. "They are not plants or animals. They produce microscopic cells, spores, which are seeds that are born to fly," he said.

Common types of molds found in buildings include alternaria, penicillium, stachybotrys, and chaetomium.

Mold problems are increasing because "more biodegradable construction materials are used in modern buildings than ever before," Morey said. "Buildings leak and moisture can be trapped."

When moisture is present, speed is key. "Within 24 to 48 hours, ceiling tiles and gypsum can develop 'baby mold' and then 'teen mold.' First fix the water problem, then remove the mold," Morey said.

Dr. Joseph Jarvis, of the University of Nevada in Reno, cautioned that "mold is not another asbestos. It causes discomfort, not impairment."

"All mold is a potential allergen. The illnesses that can be associated with indoor mold exposure are allergic respiratory conditions, such as allergic rhinitis, asthma, and hypersensitivity pneumonitis. Contractors working on air-handling systems with mold contamination may protect themselves from exposure by using properly fitted, maintained, powered air-purifying respirators with HEPA filters," according to Jarvis.

Ray Patenaude, P.E., of The Holmes Agency Inc. of St. Petersburg, Fla., cautioned that condensation in hvac systems could cause unseen moisture problems. "The maintenance of refrigerant lines and ductwork is extremely important," he said.

An audience member asks a question.

Legal protections

Whether or not hvac contractors are directly involved in mold remediation or mitigation, their involvement in the indoor air quality of a building makes them liable if any mold problems develop.

Attorney Maralynne Flehner explained that the legal liability for contractors is significant but manageable. Damages sought by plaintiffs could include those for personal injuries and property damage, and these could be compounded by judgements that include punitive damages and attorney fees.

She definitely recommended that contractors set up corporate entities for their businesses in order to protect their personal assets. Those who already have corporations should consider establishing a second corporate entity to assume any mold-related risks.

"Evaluate any job carefully before you take it," Flehner said. "Inspect the premises carefully and look for potential water intrusion before you accept the job. If the risk is too great, or you don't like what you see, walk away. The value of the lost business will be much less than the potential judgements against you."

According to Flehner, contractors should take a base-line reading at the beginning of a job, so they know the mold level before they start, and then conduct periodic testing to evaluate the level at every stage of the project, including its completion.

Some of the mold session's panelists.

Contracts for contractors

  • A blanket disavowal of all liability for mold-related damages

  • A prompt notification clause so that if moisture or mold problems are not reported within a stated short period of time, the contractor cannot be held liable

  • A limitation of liability clause that places a ceiling on the amount for which the contractor can be held liable

  • A prohibition against the recovery of consequential damages, such as lost business

  • A clause that prohibits the recovery of plaintiffs' attorney fees from the contractor so that prospective plaintiff attorneys will see that they stand a good chance of not getting paid

  • A clause that obligates the parties to place disputes before arbitration instead of the courts, and that allows contractors to help choose the arbitrators. According to Flehner, this option carries some risk because, by submitting to arbitration, contractors give up their rights to appeal a ruling against them. But arbitrators may be less likely than a court to award huge sums, especially for ancillary damages.

    "Create good documentation at every step in the process," Flehner said. "Get insurance, even though your coverage may be limited. And retain a good lawyer before you run into trouble."

    Speaker Joseph Lstiburek.

    Role of stupidity

    Joseph Lstiburek, Ph.D., P.E., of Building Science Corp. in Westford, Mass., was blunt in his assessment of why mold has taken hold in the public consciousness as a significant problem.

    "We're stupid," he said. "Buildings should be suited to their environment, but we build the same kind of structure in both the North and the South. We use plywood for building, and plywood is mold candy. And we don't focus on how to dry the inevitable wetness in a building."

    According to Lstiburek, venting attics in southern climates "was dreamed up by some disgruntled Yankee wanting to get even."

    Hot, humid outside air is brought into an attic where it can diffuse through the vapor barrier-less attic insulation and get to the cold, air-conditioned ceiling. It hits the cold, virtually uninsulated duct and fittings and drips water.

    Avoid oversizing

    Glenn Hourahan, P.E., vice president of research and technology for the Air Conditioning Contractors of America, focused on the role of proper hvac system design in preventing mold growth. He identified oversized air conditioning units for causing multiple problems.

    "An oversized unit is subject to frequent cycling. This causes degraded humidity control, which increases the potential for mold growth," Hourahan said.

    Other drawbacks to oversizing include large temperature swings between rooms, drafts and noise, higher installed and operating costs, and occupant discomfort, leading to nuisance service calls.

    Hourahan said the too-common problem of equipment oversizing has a basic cause: the absence of a load calculation.

    "The contractor guessed on the load and then an 'on hand' unit was installed," Hourahan said. "Maybe a simple replacement was done, using the same size unit as the one being replaced. This assumes that the original installation was correct, and ignores whether building functions have changed or any building upgrades in lighting or insulation."

    Instead of doing load calculations according to the ACCA's Manual J, some contractors use inadequate rules of thumb, such as sizing one ton of cooling for every 500 to 600 sq. ft. of space, he said.

    Hourahan showed how this rule of thumb compared with the latest Manual J calculations for a 2,800 sq. ft., three-bedroom home in three U.S. locations.

    In Augusta, Maine, the 600 sq. ft./ton rule dictated 4.7 tons of cooling, where Manual J showed only 2.1 tons were required. In Tallahassee, Fla., the 4.7-ton estimate greatly exceeded the real need for only 2.5 tons. And even in Tempe, Ariz., just 2.8 tons of cooling was needed.

    Hourahan set out five steps for sizing and selecting equipment correctly:

    1. Establish building design and criteria requirements. Match the hvac system to the building application. Pay attention to ventilation requirements, occupant needs and expectations, zoning needs, and special uses.

    2. Determine the design loads by performing a load calculation. Factor in building construction parameters, such as envelope tightness, solar orientation, the type and amount of insulation, the location and tightness of ductwork, the type of glass used, and the presence of overhangs and shading. Consider the outdoor design temperature for the region, and the interior design conditions. Ascertain sensible and latent loads.

    3. Do not arbitrarily increase the load with a so-called "safety factor." Avoid overly conservative assumptions on building construction details, and do not round up loads to the next equipment size. Select the equipment to match the calculated loads.

    4. Ascertain system capabilities. Use manufacturers' application data and be guided by recognized industry practices. Remember that, for moisture control, part-load performance is more important than full-load performance.

    5. Evaluate latent loads. If "standard equipment" cannot satisfy full-load or part-load latent requirements, then consider using different equipment types, additional control strategies, dual- or variable-speed equipment, and independent control of temperature and humidity.

    According to Hourahan, "Controlling humidity, as opposed to merely moderating it as a byproduct of the air tempering process, generally requires a dedicated set of equipment and controls."

    ASHRAE book

    At the seminar, ASHRAE promoted its publication, Humidity Control Design Guide for Commercial and Institutional Buildings.

    "Problems related to excess moisture can be reduced or avoided entirely through better understanding of humidity control issues, techniques and equipment. The potential benefits are large because more than 50,000 commercial buildings are built every year in America alone," co-author Lewis Harriman told attendees.

    A study by the American Hotel & Lodging Association showed that more than $68 million is spent annually by its members to mitigate problems caused by mold and mildew.

    Specific advice in the book includes:

  • Installing a separate ventilation system to dry or humidify the incoming ventilation air

  • Calculating the moisture load separately from the sensible heat load

  • Sealing all ductwork, air handlers and duct connections tightly

  • Never oversizing the cooling equipment

  • Calibrating humidity sensors in-place, after installation and before commissioning.

    The book includes sections on humidity effects, system design, equipment and controls, applications and design references. Guidance is provided for schools, office buildings, retail buildings, hotels, restaurants, museums, libraries and archives, hospitals, eldercare buildings, dormitories, swimming pools, ice rinks, dry air storage and laboratories.

    The information was developed as part of the ASHRAE Research Project 1047, funded by ASHRAE, the U.S. Department of Energy, and the Gas Technology Institute.

    The books available for $120 from ASHRAE. Call (800) 527-4723 or see on the Internet.