Achieving sustainability in today's increasingly complex and cost-constrained working environment requires a greater appreciation and knowledge of related environmental impacts (e.g., greenhouse gases), and their associated societal costs, related uncertainties1, and achievable benchmarks for demonstrating improved performance across the whole range of building types and occupancies that our HVACR industry impacts.

To better understand the term "sustainability," I recall reading a quote that I liked from Ray Anderson, chairman of Interface, Inc. He said: "Sustainability implies allowing a generation to meet its needs without depriving future generations of a way to meet theirs." What, then, is building sustainability?

ASHRAE's recently adopted policy statement supporting building sustainability defines it as a means to provide a safe, healthy, comfortable indoor environment while simultaneously limiting the impact on the Earth's natural resources.

ASHRAE plans to do this by integrating building sustainability principles, effective practices, and emerging concepts into all of its appropriate standards, guidelines, handbook chapters, and society publications. Additional methods include actively participating with internationally recognized building sustainability groups where deemed appropriate, and promoting and providing educational materials on building sustainability to its members and society at large through the ASHRAE Learning Institute as well as through grassroots college student chapter activities.

Furthermore, the goal of newly formed ASHRAE Technical Committee (T.C.) 2.8, Building Environmental Impacts and Sustainability, is to give added emphasis to finding ways to reduce the impact of buildings on the environment. These impacts include:

  • Biological and mineral resource depletion;
  • Environmental impacts of energy production, conversion, delivery, and use;
  • Availability of future energy resources;
  • Pollution of air, water, and soil; and
  • Encroachment on sensitive habitats and ecosystems.

The committee also intends to continue working on its planned ASHRAE Green Guide, which will provide practical information for owners, consulting engineers, and others on the design and operation of environmentally friendly buildings.

Perhaps our most important strength in dealing effectively with the essential "spirit" of building sustainability is our industry's ability to innovate, and, in the process, to create new methods and processes leading to improved sustainable buildings that can serve as next year's benchmarks to beat. Taking another look at how we model energy use in our buildings is what is now needed if we are to surpass last year's "status quo" energy budget goals.

Defining the Challenge

The demand for innovation in our current fast-paced and globalized HVACR industry remains ever constant in both HVACR product and design process.

Building MEP consultants, constructors, and operators must be more actively engaged with building owners if building sustainability is to be achieved. This involves active engagement extending beyond initial project conceptualization, design development, and contract document preparation as part of a professionally managed construction process - including commissioning, and hands-on training of building operators in whose hands a building's actual vs. planned sustainable performance will depend.

Greenhouse Gas Emissions Reductions

The Voluntary Reporting of Greenhouse Gases Program, required by Section 1605(b) of the U.S. Energy Policy Act of 1992, is part of the U.S. government's effort to develop innovative, low-cost, and non-regulatory approaches to limit emissions of greenhouse gases2 (Greenhouse gases, which include carbon dioxide, methane, nitrous oxide, hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6), absorb infrared energy and prevent it from leaving the atmosphere2).

A total of 228 U.S. companies and other entities reported to the Energy Information Administration's (EIA) Voluntary Reporting of Greenhouse Gases Program that they had undertaken 1,705 projects to reduce or sequester greenhouse gases in 2001.

The electric power sector, with 103 companies reporting, has continued to provide the largest number of participants to the program. Reporters included nearly all of the largest electricity generating utilities. The companies reported projects such as improved plant efficiencies, cogeneration, use of non-fossil fuels such as nuclear and renewable fuels, and demand-side management programs that reduce power use by their customers. Other projects cover many different approaches to reducing or offsetting emissions, including activities such as methane recovery projects at landfills, urban forestry, and worldwide tree planting projects.

The number of participants from outside the electric power sector (125 reporters) was ten times the number reported for 1994, the first year of the program. These companies now comprise more than half (55%) of the reporters to the program and include firms engaged in automobile manufacturing, petroleum production and refining, coal mining, food processing, and the chemical industry. Also reporting on projects were alternative energy providers, agriculture and forestry organizations, and organizations in other sectors (government, commercial, and residential).

Reported emission reductions included 222 million metric tons of carbon dioxide equivalent (MMTCO2e) in direct emissions reductions, 71 MMTCO2e in indirect emission reductions, and 8 million metric tons of reductions from carbon sequestration. In addition, 15 million metric tons of reductions were reported. Relative to 2000 levels, direct emission reductions increased by 5.2%, indirect reductions grew by 14.4% and unspecified reductions expanded by 20.9%, while carbon sequestration fell by 11.7%.

Figure 1 illustrates the growth in reported reductions since the program's inception in 1994. Implementation of new clean burning combustion technology called ultra-clean low-swirl combustion - developed by Lawrence Berkeley Laboratory, and which research confirms emits 10 to 100 times less nitrogen oxide than conventional burners - should in time have a significantly more pronounced effect upon such voluntary reductions.

Sustainability Benefits from Research

ASHRAE continues to publish the results of useful field studies that affect its practitioner members in meaningful ways. For example, take the results of two such research projects; namely RP-822 and RP-10553, both undertaken at the Institute of Environmental Research at Kansas State University. Their goal was to seek field data guidance in identifying actual patterns of equipment heat gains for common applications in office buildings, laboratories, and hospitals. What they found was quite interesting. Whereas the field data test results in laboratories and hospitals were too diverse for generalization, the very opposite was true for office building occupancies. What they found was:

  • Office equipment energy intensity had been decreasing through 2002;
  • Office equipment energy intensity would be increasing slowly from 2002 through 2010;
  • There was a disparity between heat gains taken from equipment nameplates provided by manufacturers and measured heat gains both with and without diversity considerations;
  • Assuming no diversity, approximately 50% of listed nameplate heat gain values were confirmed by field measurements taken over time; and
  • Actual heat gains (with diversity accounted for) amounted to approximately 21% of manufactured listed nameplate heat gain values.

Accordingly, we now realize that we need to better communicate this information to manufacturers who appear to be overstating equipment heat gains. Such misinformation results in significant oversizing of HVACR system equipment, distribution ductwork, and piping with the resulting waste of both material and energy cost further impacting building owner profitability and resulting in excessive generation of greenhouse gases.

Building Sustainability Benchmarks

With buildings now responsible for a third of the world's energy use, the HVACR industry needs to establish comparable energy use and greenhouse emissions equivalents to that illustrated in Figure 1. This may be possible by incorporating, for example, representative benchmark energy budgets for various occupancy types. This information could be determined from a statistical weighting of climatically normalized average building type values developed from monitored building data employing inverse modeling methods.

Collateral benefits of improved HVACR design methods can include lower emission rates of harmful pollutants entering our atmosphere, thereby improving air quality while reducing the potential for climate change. Similar concerns parallel to these above become the "driver" for improved worldwide automotive standards for increasing company average fleet efficiency (or CAFE) standards achieved by the design of more efficient and hybrid gas/electric engines, lower vehicle weight through material substitution, as well as lower cost recycling potential that such lighter weight material substitutions also afford.

The construction industry may also someday find itself embracing the benefits of construction material substitution4 should the cost of energy rise to the point where the energy cost to fabricate and assemble on-site various exterior and interior building materials, along with the cost of construction equipment operation, result in fundamental changes to the building design, and construction process. This would encourage recycling and more efficient on-site assembly and/or construction methods, including a greater reliance on prefabrication.

Being more actively and personally involved in HVACR work to achieve building sustainability is no longer optional; it is a mandate for continued innovation and a constant challenge for the HVACR industry in the years ahead.

Use of Advanced Inverse Models

Improvements to the performance of, along with significant reductions in the first cost of, commercially available HVAC sensors, controllers, and networking hardware have contributed to the development of smart building features (e.g., optimal supervising control, continuous performance control, real-time utility pricing, and automated diagnostics).

As an example of advancing the best use of available building materials, HVACR designers need to take advantage of a building's inherent thermal massing effect. To do this, one must first accurately predict transient cooling and heating building requirements and/or total building energy consumption using inverse models that are "trained" through better use of on-site data.

The 2001 ASHRAE Handbook, for example, separates modeling into two basic categories; namely, forward modeling and inverse modeling. Forward system modeling (Figure 2) commences with a physical description of a building, e.g., construction materials, geometry, physical location, microclimatic data, type of HVAC system proposed, and so forth, as typically employed by HVAC system designers.

Inverse system models (Figure 3), on the other hand, are derived from empirical behavior and are generally expressed in terms of one or more driving forces and a set of empirical parameters5. Hybrid or gray box models proposed by Braun, et al. employ transfer functions where parameters are constrained to satisfy a simple physical representation of energy flows in a building, including a methodology for training parameters of the constrained model by which initial values of, and limits on, physical parameters are estimated from a rough building description (Figure 4).

Better estimates6 are then obtained using search and non-linear regression algorithms while incorporating site-specific control strategies as illustrated in Figure 5. Algorithms used to identify optimal parameters by means of Braun's proposed system tool are illustrated in Figure 6.

Finally, Braun reported finding that only two weeks of accumulated on-site data were sufficient to train an inverse model to accurately predict transient heating or cooling requirements. He had extensively tested his above-described inverse modeling and parameter training methods for different buildings and locations using data generated from use of a detailed (forward model) simulation program along with data obtained from a field test site located near Chicago.

Subsequently, Braun reported assessing load shifting and peak shaving potentials through the control of building thermal mass for a 1.4-million-sq-ft building employing four nominal 900-ton chillers using similar robust inverse models resulting in less than a 5% difference in utility cost prediction5 (Figure 7).

Conclusions

Braun's conclusions of the latter major office building field test follow in Figure 8 and demonstrate the need to better calibrate our models. Using inverse modeling of our buildings for reasons summarized in Figure 9, as opposed to the widespread use of our more conventional forward modeling approaches, would suggest that if we are to achieve lower building energy usage, we must first improve the selection of building materials, reduce harmful emissions, and predict annual energy consumption with greater accuracy.

Through continued HVACR research, including field studies in actual buildings, more accurate predictions of the probable cost of operating our buildings is achievable. This should result in greater client profitability, HVACR innovation, and other related societal benefits in the coming years. Figure 10 describes, in general, the benefits to be achieved - including more predictable, sustainable buildings - by employing whole-building design, which is made possible through greater use of Braun's5 proposed inverse modeling methods. ES

EDITOR'S NOTE: Due to space constraints, some images associated with this article do not appear on this website. To view them please refer to the print version of ES.