How Green Is Green?

Feb. 1, 2009
The movement is taking the construction field by storm. Some are looking to reduce their impact on the environment, while others are motivated to control

The “green” movement is taking the construction field by storm. Some are looking to reduce their impact on the environment, while others are motivated to control costs in an era of rapidly rising energy prices. The government- and institutional-building sectors have jumped onboard in a big way, as have numerous businesses. This is a good thing. But buyers of “sustainable” building technologies should beware. Sustainable design is in its infancy. There is much we do not know and much more we do not know how to do. Much of what is sold as “green” are merely old solutions repackaged and renamed.

Too many firms lack the knowledge and skills to provide environmentally sustainable designs. Those that have yet to receive their first sustainable-building award often find themselves at a disadvantage when competing for projects. Thus, they may be tempted to represent their projects as “green,” whether or not their projects actually are.

This kind of behavior not only is highly unethical, it is sanctionable in most jurisdictions, with the professional licenses of individuals and firms subject to forfeiture. In most jurisdictions, a complaint must be filed for action to be taken. Many professionals, however, find such “tattling” distasteful. Thus, most activity goes unreported.

I have been a practicing professional engineer for 30 years. During that time, I have seen multiple buildings that clearly failed to meet prerequisite requirements receive Leadership in Energy and Environmental Design (LEED) certification.

The most serious flaw in the LEED certification process is the lack of a credible review process. I have been advised by members of the U.S. Green Building Council (USGBC) staff that a review of construction documents is not required and that the issuance of an occupancy permit routinely is accepted as proof of compliance with ANSI/ASHRAE Standard 62.1, Ventilation for Acceptable Indoor Air Quality, and ANSI/ASHRAE/IESNA Standard 90.1, Energy Standard for Buildings Except Low-Rise Residential Buildings. Based on an honor system, the process essentially permits self-certification by designers.

The LEED certification process minimally should require submission of construction documents, as well as checklists and computations, for third-party verification of prerequisite compliance.

There is, however, a simple, low-tech way to measure overall building efficiency: “effectiveness.” Developed by Willis Carrier for rating the performance of evaporative coolers and later extended for rating the performance of cooling coils, it is as valid today as it was when introduced in 1937. One of the key principles is that once the effectiveness of a process is established, performance can be predicted under all other conditions of operation. It is computed simply by dividing actual performance by potential. A similar approach independent of climatic effects could be employed in comparing building energy efficiency.

Standard 90.1 provides minimum-performance requirements for building-envelope, HVAC, and lighting systems. Artificial lighting is governed similarly with watt-density limits. As such, both design and permissible-limit values can be computed easily and compared. However, building-envelope losses are an element of and incorporated into HVAC-system loads. In an evaluation of the effectiveness of an HVAC system, energy falls into one of three general categories: envelope loads, internal gains, and ventilation. In the design of HVAC systems, internal gains typically are disregarded for heating purposes and applied for cooling purposes.

The term “ventilation” historically has been used to define the amount of outdoor air provided to a space; the term “ventilation effectiveness” is used in Standard 62.1 to describe the portion of outdoor air introduced into the occupied region of a space. However, HVAC systems also must account for outdoor-air ventilation loads, systemic inefficiencies, and distribution losses. To provide a truly meaningful evaluation of HVAC-system performance, the definition of HVAC-system design capacity must include all energy requirements necessary to process and deliver heating and cooling to spaces at design conditions, including fan and pump energy and combustion inefficiencies. “Ventilation energy,” then, can be computed simply by subtracting the energy that must be added to envelope losses to define heating design capacity. Cooling-capacity requirements would be computed similarly.

The effectiveness of building-envelope, lighting, and HVAC design values is determined by dividing the design value by the Standard 90.1 permissible value.

Design values for ventilation systems should include capacity-reduction credits taken for air-to-air energy recovery and thermal storage. Similar equations would apply to cooling. Design values for lighting systems similarly should take credit for daylighting and uninterruptible-power-supply storage systems designed for demand-management purposes. Envelope designs should take credit for passive-solar design features.

Finally, the relative amounts of energy required for envelope, lighting, and ventilation systems will be different. To evaluate the overall energy efficiency of a structure, a weighted value is needed. This can be computed simply by multiplying the effectiveness of each function by the permissible load, summing the results, and dividing by the sum of the loads.

This would produce a non-dimensional number. For compliant designs, the value of the decimal fraction would be less than 1.00. For super-efficient structures, it would be less than 0.5. For “net zero” structures, it would be zero.

The sustainable-building movement is important and needs to not only survive, but continue to grow. On the other hand, its adherents need to recognize that, as a movement and, more importantly, as a technology, it is in its infancy. Sustainability standards require continued development, but even more importantly, they need to adhere to their own rules so that their certifications actually mean something. This means instituting credible review processes and both meaningful and increasingly rigorous measures of performance.

Individuals wishing to build sustainable buildings should be encouraged to do so. However, given the difficulty of meeting prerequisites and the very real potential for fraud, they would do well to protect their interests by engaging reputable, independent experts to review their building designs. The cost of this type of review is insignificant relative to the life-cycle cost of failure.

The basic computations for Standard 62.1 and Standard 90.1 compliance already are required of designers under those standards and, thus, do not represent any added effort. Individual parameters and equations can be entered quickly and computed on a simple one-page spreadsheet. This information can be a useful tool for design teams by indicating whether or not project goals are being met and, if they are not, where improvements are needed.

Historically, introducing new ideas and practices in the construction industry has been difficult at best. That task is made more difficult with every fraudulent green-building certification issued. How the USGBC, Green Globes, the Collaborative for High Performance Schools, and other sustainable-building standard-writing organizations choose to deal with this situation undoubtedly will have a tremendous effect on the future of the sustainable-building movement. I sincerely wish them the best, but they have some serious problems and much work to do.
Mark S. Lentz, PE
Lentz Engineering Associates Inc.
Sheboygan Falls, Wis

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