HONOLULU, HI — As the nation continues to grapple with increasing mold problems indoors, it is clear that ventilation and moisture play key roles in feeding mold and then spreading it. The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) has been questioning whether its own standards, specifically 90.1 on energy-efficient buildings and 62 on indoor air quality (IAQ), have contributed in a significant way.

The seminar, “The Impact of Standards 62 and 90 on Moisture-Related Problems in Facilities,” gave the impression of a defendant preparing for trial. The room was packed — testimony in itself to the importance of the topic, because the 2002 Annual Meeting was held in Hawaii.

Everyone present was asked to keep the discussion civil.

The first speaker was Rodney H. Lewis, P.E. “These two standards have made an existing problem a lot worse, in my opinion,” he stated in his presentation, titled “ASHRAE Has Created This Mess.”


The standards themselves have worthy goals, continued Lewis. Standard 90 was written to save energy and extend fossil fuels, while 62 and its revisions/addenda were meant to improve IAQ.

The mission of any HVAC system designer is to provide a comfortable indoor environment. “Old systems controlled mainly temperature,” Lewis pointed out. “Humidity control was a byproduct.” Today’s clients expect more than temperature control, he added, but they don’t expect to pay more for it.

In HVAC litigation, he said, the current mission is health. “If you’ve got mold in your building, you’ve got an unhealthy building.”

Still, how does this make ASHRAE culpable? By not loudly proclaiming the goals of its standards, so that they cannot be misinterpreted. “Less than 10% of the employees of contractors and engineers participate in ASHRAE in any meaningful way,” Lewis pointed out. This makes it more difficult for them to counter the unreasonable demands of building owners. “Less than 1% of building owners and operators know what we’re trying to do,” Lewis said. “First cost governs everything.”

Additionally, these contractors and engineers may not fully understand the ramifications of the systems they recommend, from a health-comfort point of view. “Our systems have become extremely complex,” he said.

Finally, “Installers and operators are not adequately trained.”

One of the main flaws with 90.1, he pointed out, is its limited use of reheat to reduce humidity during the cooling season. In hot, humid climates, “You can’t meet both standards without reheat at full load to maintain space humidity.”

In summation, he implied that since ASHRAE is the body that wrote these seemingly conflicting standards, the society could find itself at the business end of a litigation rifle. “If I can’t reheat the air, who do I sue over mold and mildew?”


Steven Taylor, P.E., mounted an able defense in his presentation, “Standard 90.1 Is Not the Culprit” (to which title he added, “Lousy Engineers Are”).

Today’s mold problems are a result of moisture problems, he pointed out. Resolving them requires control of moisture entry through ventilation, infiltration, and rainwater through the building envelope.

“Ventilation is by far the largest of these sources,” he said. However, “90.1 doesn’t cover ventilation rates,” he continued. It does address ventilation control (using CO2 sensors). The rest of the standard should have no impact. For instance, “There’s nothing in 90.1 that says you have to design a lousy envelope,” he said. In fact, the standard offers several areas of improvement, such as insulating ducts and plenums.

As for system oversizing, 90.1 can help with this, Taylor said wryly: “It says you have to run load calculations.”

And what about active moisture-removal reheat? Standard 90.1 has little to no impact, Taylor said. “Many exceptions [within the standard] do allow reheat.”

On the residential/light commercial side, “We conclude that the latent moisture removal of small unitary equipment has no impact,” he said. The moisture-removal capacity of new, higher efficiency equipment is the same as older units. Research presented by the fourth speaker bore this out.

In most cases, he said, 90.1 has no impact on building IAQ. “With proper design, it has no impact at all.” And while design solutions may cost more, they do exist.

An engineer who works with public schools asked if there is some way to reconcile first-cost constraints with these design solutions. “Do I have to settle?”

There’s always a balance, Taylor conceded. “Budgets aren’t large enough. We need to tell people that this affects our children’s health and learning.”

How can HVAC designers create the best system for moisture removal when first cost is still their clients' prime motivator, asked an attendee at the ASHRAE session pitting the interests of Standard 62 against 90.


“The problem,” began Dennis Stanke of Trane “ — you pretty much know what it is. Is 90.1 affecting it?

“You can’t just point to any one standard,” he stated, sensibly. Standard 90.1 seems to lower the sensible heat ratio (SHR).

Are Standard 62’s outdoor air rates to blame? “Again, nothing is that simple,” Stanke said. “True, more outdoor air means higher load. But it’s the condition of air leaving the coil that counts, not the air entering the coil.”

The greatest problem, he pointed out, is the misapplication of equipment. For instance:

  • “If you have to use a package unit due to budget, and do nothing else, and increase from 5 to 15 cfm, you will have RH problems.”

  • Don’t use a constant-volume system with total energy recovery. It reduces tons, raises cfm/ton, and maintains IAQ — at full load. It has little impact on space RH at part load.

  • Don’t blindly use mixed-air bypass.

    Here is what Stanke said HVAC designers can do:

  • They can design an enhanced, constant-volume system with true return air bypass. It offers lower supply air dewpoint, and while there is little or no reheat, it indirectly lowers dewpoint RH.

  • They can apply supply air reheat as stated in 90.1.

  • They can separate outdoor air from indoor air by having two coils.

  • They can have a dedicated outdoor air system.

  • For variable air volume (VAV) systems, consider multiple constant-volume units, Stanke said. “Staged units provide lower supply airflow and dewpoint at part load.”

  • They could also design a multiple-speed, constant-volume system.

    Designing for Standard 62 causes problems “sometimes,” Stanke said. “Pick the right system, ventilate properly, control properly. Stop whining and start designing.”


    Karim Amrane, Ph.D., from the Air-Conditioning and Refrigeration Institute (ARI), presented a wealth of data on unitary equipment showing that while efficiencies have changed over the years, the equipment’s latent moisture-removal capacity has been relatively unchanged.

    Improper moisture removal, he said, has many causes, but primarily it’s the mismatch of building latent load and equipment latent capacity.

    “Proper sizing and selection are critical to control RH at full and part load,” he said. Part-load analyses are necessary for humidity control with today’s systems.

    Essentially, his presentation (“Latent Performance of Unitary Equipment”) analyzed the SHR of large and small unitary products (from ARI data), and from 1996, 98, and 2001 tests from industry labs. The products were single-package and split-system air conditioners and heat pumps.

    “SHR doesn’t seem affected by efficiency in either commercial or residential units,” he stated. It likewise is unaffected by brand, and has remained constant for about 30 years.

    It is most affected by ambient air dewpoint conditions.

    “Latent capacity is not a function of efficiency,” Amrane said. “Efficiency has increased but SHR has remained the same.”


    This would seem to let the equipment manufacturers off the litigational hook. And ASHRAE’s conclusion is that misinterpretation or ignorance of ASHRAE materials is not ASHRAE’s fault.

    Design contractors must apply the information and equipment correctly for their own protection, as well as for the sake of their clients.

    Publication date: 07/15/2002