HVAC & Environmental Systems Division
While attention to IAQ has intensified in office buildings and schools, hotels have been preoccupied with a construction and remodeling boom with little consideration for IAQ. This will be changing.
Several articles in the Wall Street Journal covering IAQ in hotels have focused on the subtler but insidious comfort and health threats: bacteria, mold and mildew, odors and VOCs. The angle is that hotel guests routinely are subjected to unhealthy indoor air, and the hotel industry is not addressing the problem. A major article printed last summer in the Wall Street Journal’s Travel section reported that the hotel industry spent more than $3 billion in 2009 on renovations, while paying little attention to modernizing or upgrading HVAC systems. The article points to a problem not unique to hotels: capital investment focused on finishes and fixtures; neglect for back-of-house infrastructure improvements.
Wall Street Journal Investigation
The Wall Street Journal reporters stayed in nine hotels, set out petri dishes in their rooms during each stay, and then sent the petri dishes to a lab to do bacteria and mold counts. The reported results showed that the counts varied widely between the hotels and pointed to potentially health-threatening levels in some of the hotels. Of course, the results are highly suspect from a scientific perspective due to the questionable sampling method, lack of identification of types of microorganisms counted, and failure to test the outdoor ambient microbial level for comparison.
One indisputable fact, the coverage of this issue in the Wall Street Journal is both an indication of and contributor to growing concern about IAQ on the part of hotel guests. And, if there is one problem that attracts attention from hotel ownership and management, it is guest dissatisfaction.
Determining the correct outdoor air ventilation rates for hotels has not been the most difficult task. Although debate and controversy continue around various other aspects of ASHRAE Standard 62, the recommendations for hotel ventilation have changed little over the last 30 years. For some occupancy areas, recommended outside air quantities have gone up slightly, while others have been reduced. Using guest bathrooms as an example: the 1973 standard recommended 30 to 50 cfm (14 to 24 L/s) of exhaust per room. In 1981, it became 50 cfm (29 L/s), and the 1989 through present standards have settled on 35 cfm (17 L/s).
While outdoor air quantity has not been a principal causative factor in hotel IAQ problems, outdoor air quality definitely has been. Finding a good location for outdoor air intakes can be difficult for any facility, but hotels pose unique challenges. There are many obstacles to avoid: restaurant exhausts, laundry exhausts, parking garage and loading dock fumes, and, of course, cooling towers. It is surprising how many IAQ problems can be traced to contaminants entering through poorly located intakes.
Sometimes the original design is sufficient until a major renovation (i.e., when a new restaurant exhaust is inadvertently located adjacent to the outdoor air intake). Filtration is often a solution for poor outdoor air quality. The degree and type of filtration can be selected based on the severity of the situation.
The introduction of unconditioned outdoor air is also a major problem, particularly in hot and humid climates. HVAC systems can introduce outdoor air into a building in two ways: intentionally and unintentionally. As far as the intentional introduction of outdoor air through the ventilation system, the designer can pre-condition the outdoor air to avoid the multitude of problems caused by moisture and condensation in hot and humid climates. There is little excuse for an HVAC system design that does not pre-condition outside air, given the availability of proven, economically attractive and energy efficient means of pre-conditioning, and the dire consequences of not doing so.
Designing to prevent the problems associated with unintentional introduction of outdoor air via infiltration is a more difficult assignment. A major study of problem buildings in Florida concluded that, "Given the present state of the practice, whether a building will avoid serious, even catastrophic problems due to uncontrolled airflow (which introduces outside moisture), is primarily a matter of luck."
It has been suggested that to build hotels in hot and humid climates without mold and mildew problems, mechanical design engineers must understand in great detail how building envelopes and interior wall finishes function, and architects must understand the role of HVAC systems in moisture control. This may be too much to expect. If we can at least focus the mechanical design on thoroughly addressing pressurization issues, there is a hope for success.
It is commonly recognized that buildings in general should be slightly pressurized versus the outdoors. Infiltration of unconditioned and unfiltered outdoor air is never desirable. In a hot and humid climate, it is even less desirable, due to the moisture content of the outdoor air, the propensity for high indoor humidity conditions, condensation on interior surfaces, and the resultant microbial growth.
Hotels in hot and humid climates exacerbate these factors with internally generated moisture from guestroom showers and housekeeping procedures. Add the complexity of various potential HVAC system operating modes with changing supply and exhaust airflows, and the task of maintaining positive pressurization can become quite daunting.
Using guestrooms as an example: the bathrooms must be negative to the bedroom areas, the bedrooms must be negative to the common hallway, and every area, including wall cavities, chases and ceiling spaces, must be positive to the outdoors. At various times, depending on system design and control, the bathroom exhausts could be on or off, and the guestroom HVAC units could be on or off. A hotel facilities management textbook concludes, after a brief discussion of guestroom pressurization issues like these, "Coping with these types of problems can be a real headache for management and staff."
The impact of improper pressurization is not limited to moisture-related problems in hot and humid climates. Pressurization determines the pollutant pathways inside the hotel as well. Proper pressurization is one of three methods for dealing with indoor pollutants, along with dilution and filtration. Sources of undesirable air are everywhere in hotels (kitchens, laundries, indoor pools, health spas, anywhere smoking is permitted, etc.). Again, proper pressurization must be maintained under varying conditions, whether building areas are occupied or unoccupied and individual HVAC systems are on or off.
Many of the IAQ problems hotels experience can be prevented during initial construction or major renovation with sound engineering design, quality construction, and thorough commissioning. However, a hotel's life cycle does not end at this point. To ensure good IAQ past the transition from startup to ongoing operation, effective maintenance is required. Every well-intentioned HVAC design element can be superseded, every ventilation system component can be defeated, every perfectly configured pressurization relationship can be destroyed, with a good dose of improper maintenance.
As HVAC professionals, we should not breathe easy just because we have created an elegant design, or even contributed to a successful commissioning process. We must communicate to hotel owners and operators that effective maintenance and well-trained building personnel are essential for sustaining healthy indoor environments.