Indoor air quality becoming more important in modern buildings

By Dave DeWitte

Air quality and humidity control have become front-burner issues as today’s buildings are tightened down to reduce heat loss.

A lack of air turnover and moisture control in a building can lead to serious problems including mold growth, oxygen starvation, and buildup of volatile organic compounds in the air, according to architect Bradd Brown of OPN Architects, Cedar Rapids.

The basic answers to those concerns — better ventilation and dehumidification — have long been known. But tighter, more energy efficient buildings have made them more important.

Addressing air quality “is part of sustainable design,” Brown said. When designing a project, Brown says OPN typically specifies materials that have low emissions of volatile organic compounds.

Project plans also specify steps contractors must take to protect air quality. They include “flushing” the building’s air supply before it is occupied, and ensuring ductwork and air handling equipment are sealed against construction dust until it is time to turn on the systems.

Designing a building’s mechanical systems to provide proper air quality and humidity control requires some knowledge of not only the building, but how it will be used, according to engineer Dwight Schumm of Design Engineering, Cedar Rapids.

The intended use and number of people in each area of the building has a “very big impact on ventilation needs,” Schumm said.

A new University of Iowa Hygienic Lab that OPN designed at the University of Iowa’s Oakdale campus required ventilation systems that could turn over the entire air content of laboratories six to 10 times every hour in order to prevent gases from building up.

Fresh air flow is often combined with in-building filtration systems to protect air quality, Schumm said. His usual point of reference is an industry standard, ASHRAE 62.1. The industry standard was published in May 2007. It brought requirements for separation of areas with environmental tobacco smoke from the remainder of the building and clarified how designers must analyze mechanical cooling systems to limit the relative humidity in the space.

Schumm says it’s necessary to analyze the amount of air turnover needed based on the amount of space in the building and per occupant. A conference room capable of holding many people, for instance, would require more ventilation than an office space that would hold a fairly constant number of people.

The total air flow needed in a building was traditionally based largely on the cooling need of the building, Schumm said.

“One thing that’s changed is that engineers are paying more attention to taking moisture out of the atmosphere, even when there’s no cooling demand,” he said.

Energy and heat recovery ventilators are often part of the solution. They bring in fresh outdoor air, preheating it with heat captured from the exhaust air, and transfer humidity between the two air streams. Additional dehumidification is often needed in addition to the ventilator, however, so that a comfortable and healthy humidity level can be maintained when it’s cool and moist outside.

Building design must also address moisture accumulations that occurs due to condensation, primarily caused when warm indoor air comes into contact with structural components or wall materials that conduct cold from outside the building. The typical solution is to insulate the surfaces to block any “thermal bridge” bringing cold into the building. Proper wall design also contains impermeable barriers that prevent indoor air from penetrating into outside walls, and allows any moisture from outside the walls to be wicked or vented away.

“There’s a debate about moisture barrier placement, but there’s never a debate about moisture control,” said Jim Koch, a project manager for OPN.

Koch said moisture problems can surface when the envelope of an existing building is tightened with caulking and additional moisture barriers, usually in an effort to improve energy efficiency. That can raise the humidity level indoors and require the addition of dehumidification or ventilation capacity.

Problems can also surface when the use of a building is changed from one that adds relatively little moisture to the air to one that generates considerable humidity.

A portion of a strip shopping center might be well ventilated for an insurance office, but need additional ventilation if it is converted into a restaurant or coffee shop.

The level of sophistication in some buildings can be very high, OPN’s Brown said. Some hospitals, for instance, use ultraviolet light “scrubbers” to kill microbial life in air being vented into the building.

Many steps to protect air quality don’t have to cost much, Brown said. Low-VOC adhesives used to install floorings and wallcoverings, for instance, don’t have to cost more.

Kevin Monson of Neumann Monson Architects in Iowa City considers good indoor air quality to be one of the best investments an owner can make in a building.

“Obviously, the biggest cost of the building is not the building itself, but the salaries of the people working there,” Monson said. “You want to make sure you keep those people as healthy and productive as possible.”

Monson said well-designed buildings often have carbon dioxide monitors to increase air flow when carbon dioxide levels rise too high.

Not all air quality problems are caused by tight building envelopes, Monson said. Buildings that are not tightly sealed can also cause problems such as mold by allowing large amounts of humid air to enter. But Monson said tightening the building envelope often increases the risk of air quality problems if the ventilation and humidity issues are not controlled.

One wild card in the building ventilation wars is the growing trend back to windows that can be opened and closed. Even though many building managers would prefer to have buildings remain closed, Brown says a growing number of building owners are asking for windows that can be opened in their new buildings. That can improve the occupants’ comfort and enjoyment of nature when done responsibly, but can also waste energy and cause impure unfiltered air to enter the building, among other things.