Technical Updates

Posts Tagged ‘ASHRAE’

Best Practices for Design, Construction, and Commissioning

We are extremely excited to announce the release of ASHRAE’s new publication, Indoor Air Quality Guide – Best Practices for Design, Construction, and Commissioning. Our own Vice-President, George DuBose, was one of the contributing authors for this comprehensive guide, which you will definitely want for your reference library.

George DuBose – Contributor 

George DuBose’s experience in green building design, indoor air quality, and construction added a significant contribution along with many other experts whose combined efforts and combination of skills, knowledge, and talents are now available to you in this informative guide. 

Indoor Air Quality Guide

Written by experts in the field of indoor air quality (IAQ), the Indoor Air Quality Guide is the most comprehensive and practical resource ever developed on design and construction for enhanced IAQ.

For architects, engineers and building owners who want commercial and instructional buildings with high-quality indoor environments, this guide provides the strategies needed to achieve good IAQ using proven technologies and without significantly increasing costs.

Most building designs provide minimally acceptable indoor environments through compliance with requirements in building codes and standards. Enhancing IAQ can improve occupant health, comfort, and productivity while increasing building value and reducing risk for owners. As the industry moves toward high-performance green buildings, building professionals must become more knowledgeable about principles and methods for achieving enhanced IAQ.

This guide bridges the gap by focusing on the major IAQ issues: moisture management, ventilation, filtration and air cleaning, and source control. Equally important, it highlights how design and construction teams can work together to ensure that good IAQ strategies are incorporated from initial design through project completion.

The Indoor Air Quality Guide – Best Practices for Design, Construction, and Commissioning is a valuable resource which experts will be using as reference for years to come.  Make sure you have this guide available for your information and implementation as soon as possible.

Click here to order your copy of The Indoor Air Quality Guide.

Download summary here. Get more information about the guide here.

Problems from excess moisture can be controlled if proper humidity levels are maintained in a building. (ASHRAE recommends a range between 40 and 60 percent RH.) Architects usually do not calculate or estimate quantities of moisture expected from the above sources as they design buildings. Fortunately, however, the amount of moisture from the four possible sources combined is usually insufficient to cause problems.

Microbial growth is the number one indoor air contaminant, according to a 700-building, 10-year survey (Business Council on Indoor Air 1991). In the hotel industry alone, fungi (mold and mildew) cause several hundreds of millions of dollars in repair costs annually (American Hotel and Lodging Association 1990). Unlike other types of indoor air contaminants, microbial growth (mold and mildew) is composed of living microorganisms. (For the purposes of this blog, the term mold will hereafter refer to mildew, mold, fungi, and other similar forms of microbial growth.)

ASHRAE’s moisture threshold for space conditions of 60 percent RH is commonly accepted design practice, but using RH alone as the index for microbial growth overlooks the critical interrelationships between mold growth rates, elevated RH, and ambient temperature. According to Brundrett (1990), once the threshold moisture conditions for germination of mold spores has occurred, even a slight increase in moisture will cause the growth rate to rise exponentially. Furthermore, the moisture level at which germination begins is species-specific. For example, Stachybotrys chartarum (formerly called Stachybotrys atra) requires significantly higher amounts of moisture for initial germination than many other mold species (that is, more than 90 percent RH, compared to 70 to 80 percent RH for many other species).

Understanding this difference in moisture germination requirements is especially useful in pinpointing the source of moisture in a building. For example, the high level of moisture required for Stachybotrys chartarum is usually the result of plumbing leaks or rainwater leaks through the building envelope, not just high RH.

Because of its growth characteristics, simply removing mold from affected materials and equipment will not resolve a mold problem. Mold will grow back, and the problems associated with it will reoccur. The real key is to modify the environmental conditions within the building to eliminate one or more of the five conditions required for microbial growth. The condition most easily controlled is excess moisture.

To be continued…

According to ASHRAE, a humid climate can be defined as one in which one or both of the following conditions occur:

1) A 67 degrees Fahrenheit [20 degrees Celsius] or higher wet bulb temperature for 3,000 hours or more during the warmest six consecutive months of the year.

2) A 73 degrees Fahrenheit [23 degrees Celsius] or higher wet bulb temperature for 1,500 hours or more during the warmest six consecutive months of the year.

This definition is somewhat problematic. First, it is difficult to interpret and apply to problem solving. Second, high dew-point conditions can also indicate areas where moisture problems occur. Atlanta, Georgia, for example, does not qualify as a humid climate under the ASHRAE definition, but high dew points are experienced in this area and problem buildings are often found there.

Industry experience with building failures suggests the need for a new definition of humid climates that more clearly identifies the geography where problem buildings are more likely to be found, and better explains why these problems occur at all. This new definition is based on observations about latent and sensible load: A humid climate is defined as one where the average monthly latent load of outside air meets or exceeds the average monthly sensible load for any month during the cooling season. (Latent load is the moisture in outside air that is brought into the building and requires removal via dehumidification. Sensible load is the air temperature that is sensed and addressed by the HVAC system, either by heating or cooling the air, to reach the established set point.)

Infiltration of air with a high latent load will cause moisture to accumulate in building materials such as gypsum wallboard, with subsequent material degradation and mold growth. This infiltration may also exceed the ability of the HVAC system to remove moisture from the supply air. On any given day in many temperate areas, the latent load may be greater than the sensible load without causing problems; however, when these conditions persist for a longer period (a month, for example), the resulting moisture accumulation is sufficient to cause building failure.

The occurrence of a high latent load during the cooling season is a critical factor in building failure. Thus, defining hot, humid climates in terms of the relationship of sensible to latent load in ambient air expands the ASHRAE humid climate zone to include other parts of the  United States that are highly susceptible to moisture-related building failures.

To be continued…

In the summer of 1988, construction of a large luxury resort was coming to a close. Because the vinyl wall covering on the interior side of the exterior walls had an impermeable finish, it functioned as a vapor retarder (also referred to as a vapor barrier). The HVAC system consisted of a continuous toilet exhaust and packaged terminal air-conditioner (PTAC) units. The outside air exchange rate in each guest room averaged six times an hour, all from infiltration. In this case, problems developed inside the building and inside the wall.

The combined effect of excessive outside air infiltration and an improperly located vapor retarder caused $5.5 million in moisture and mold damage, even before the facility was opened. If these same design combinations had occurred in a more temperate climate, the problems would have been limited to increased energy consumption and possibly to complaints about guest comfort.

This is one example of how hot, humid climates present unique challenges that are often overlooked by the design and construction community. However, challenges also occur for buildings located in other climates. Meeting these challenges depends on understanding a building’s local climate conditions and how those contribute to IAQ problems.

Cold climates offer challenges for moisture flow through the building envelope that are similar to those in hot, humid climes. Cold climates are defined by the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) as those that experience at last 4,000 heating degree days (HDD at 65 degrees Fahrenheit [18 degrees Celsius] base) per year. Most problems occur during the winter, when the warm and relatively moist interior air is forced (due to high differential vapor pressures between indoors and outdoors) to the dryer and colder outdoor conditions. Moisture flow can be trapped and condensed on an improperly located vapor retarder. In addition, if the building is air-conditioned during the summer, the wall systems designed to address the heating condition can experience moisture damage inside the walls during the air-conditioned months. Therefore, few locations in the United States are completely free of potential moisture problems.

To be continued…

The inevitable is about to happen and most people don’t even know it is coming — green buildings are going to become, by codification, the law of the land. For some firms, this will just mean business as usual. For other firms, this change will be cataclysmic.

ASHRAE produces standards that are adopted by most model building codes, and the ASHRAE Draft Standard 189.1P is the new “Standard for the Design of High Performance Green Buildings Except Low-Rise Residential Buildings.”

This new ASHRAE Standard (currently in its final draft) is written in code language and will have the impact of mandating that all new buildings will be green buildings, thus eliminating the option of constructing anything less robust. Even if this standard is not adopted by all model codes, it will become the de facto standard of care. On the surface this sounds like a very good thing — mandating better-performing, more energy-efficient buildings – and it certainly has many redeeming aspects.

Here’s the downside:

• Lack of Experience Will Increase Design and Construction Deficiencies – Many of the optional aspects of the current USGBC LEED® guidelines will now be mandatory for designers and contractors. This means that, even if your designer or contractor doesn’t fully understand the key technical issues (e.g., envelope air barriers), they will still be required to use them. This practice of forcing designers and contractors to implement building features that they don’t fully understand creates a dilemma in the industry: either represent yourself as technically savvy, or face certain extinction. Given these as choices, building failures becomes more likely as firms design and construct buildings with components that they do not understand in an effort to keep the work coming in.

• Standard of Care Will Be Elevated – These new code requirements will automatically raise the required standard of care for the design and construction industry. This will increase the risk profile of their projects and may (at least initially) trigger some exclusion clauses in their current insurance policies. What are now considered “best practices” will soon be considered the minimum standard of care.  

• Regional Issues Not Addressed – The new standard mandates national green building requirements throughout the country with very little regard of the unique regions of the country where certain concepts may not be appropriate. This is almost always a problem when national standards are uniformly imposed on climates with unique requirements (e.g., hot and humid, very cold, or very rainy climates).

The inevitable result is that everyone will quickly morph into a green practitioner and the true marketplace differentiators (those with experience and unique technical expertise) will become difficult to discern. While codes can dictate that the industry follows certain standards, it cannot mandate that they get correctly implemented — with an increase in design and construction deficiencies and lawsuits being the inevitable result.   

Recognizing that this new standard (due to be issued in final form in 2010) could be a game-changer in the building marketplace, what’s the path forward?

• Review a copy of the current draft version of ASHRAE 189.1P and begin to understand the impact of the new requirements on your firm’s business, insurance, risk management, and technical expertise. (Note: This is available on line from www.ASHRAE.org)
•  Identify what requisite skills and knowledge your firm will need once this new standard is implemented.
• As this draft standard is finalized, expect more updates from Liberty Building Forensics Group with our analysis on its impact.