A systems future for commercial buildings
The need for efficiency improvement has traditionally been converted into incremental goals that could be ratcheted up through the revision of standards.
- Recognize the industry's transition to a new, systems-based approach toward measuring and achieving energy efficiency in commercial buildings.
- Understand engineering opportunities and challenges when viewing a commercial building through a systems lens.
- Learn what efforts are underway internationally, and what affect they could have on the rest of the world.
The energy efficiency challenge in a new light
In 1979, the U.S. had 50 billion sq ft of commercial building floor space, according to the U.S. Energy Information Administration. By 2012, we had 90 billion sq ft. Simultaneously, there has been an increase in the number of buildings with less than 25,000 sq ft and even less than 5,000 sq ft, the latter accounting now for more than half of the nation's commercial built environment. Such developments reflect the new face of the American economy as it emerged in the second half of the 20th century. The resulting commercial building stock now consumes 18% of the nation's primary energy and is responsible for the corresponding carbon emissions.
That vast experiment in commercial building growth is the context within which many are beginning to rethink our entire approach to buildings. Recent moves in the U.S. and globally to reduce carbon emissions—from the Administration's Clean Power Plan to the UN-based agreement reached in Paris in December 2015—are setting goals that likely cannot be achieved without dramatic improvement in commercial building energy efficiency. So we need to ask whether the practices of the past 35 to 70 years can generate those dramatic improvements.
The need for efficiency improvement has traditionally been converted into incremental goals that could be ratcheted up through the revision of standards. The focus was on component efficiencies. Standards were set at full load and at a national design ambient. Progress moved forward on the assumption that incremental innovation could meet the ever-rising targets.
It is now increasingly doubtful that the old approach can meet the new targets, and it is increasingly certain that the traditional approach to efficiency is too simplistic for the new era of buildings. First, the cost of incremental improvements has risen sharply, as equipment has improved steadily over the decades. This translates to a higher cost to buyers, hence a longer payback period. In the end, the economic case for replacing equipment will get harder to make, and less equipment will likely be replaced.
There are other considerations, as well. The search for better building energy efficiency has typically focused on HVAC. But, as is widely recognized, HVAC systems in practice rarely (i.e., virtually never) run at full load and design ambients, and standardizing at full load does not reflect the building operating loads and local ambient conditions that influence operational energy efficiency. Moreover, the focus on equipment design has meant little or no attention to systems, subsystems, and the need for continued high performance. Hard-fought equipment improvements have distracted researchers from what can be achieved through a more comprehensive systems-based approach and from the requisites of performance over time. Indeed, current metrics do not cover all dimensions of the relevant systems nor reward for innovative improvements at the system level.
In addition, HVAC technologies are approaching "max tech"—when the constraints of the laws of physics limit the new efficiencies that can be achieved. And short of max tech, improvements are proving harder to get and more difficult to sustain over time in practice. We will need a redefinition of the terms of commercial building energy efficiency to ensure its achievement at levels thought consistent with overall sustainability. And that redefinition may need to reach not only to the building system level, but also to operational maintenance, monitoring, diagnostics, and linking the whole of these together through a smart grid to ensure performance over the life of the product.
A new approach to building energy efficiency
The key to past thinking about building energy efficiency was the maxim that HVAC is an appliance with a single overall metric. The key to new thinking about energy use is recognition that energy use is influenced by a complex matrix of factors—including ambient temperature, building load, occupancy, ventilation, and building controls. In addition, it should be noted that the refrigerants that are decisive for HVAC function are changing, and the new low Global Warming Potential(GWP) refrigerants may be less efficient than their past counterparts.
A range of new optional approaches has emerged, focusing variously on part-load and annualized metrics, hybrid systems, subsystems (e.g., entire HVAC systems), whole building systems, and commissioning and monitoring requirements to ensure continuous performance. Broadly, each of these approaches reflects the insight that building energy performance is a more comprehensive engineering problem than reflected in a component-based approach. Commercial buildings, in particular, are complex multisystems performing a variety of energy-relevant functions simultaneously. Cooling and heating may both be provided to a building at any moment—as but one example of an opportunity to explore innovative heat transfer, energy storage, and other steps to reduce overall energy use and sidestep peak-power issues. Controls and communications can provide a new kind of central nervous system to the complex organism that is the modern commercial building.
Taken together, such insight points in one way or another to a systems-based approach to efficiency. Systems—entire HVAC systems, more complex interdependent building subsystems, or whole building systems—are likely to be the cornerstone of the next-generation commercial building energy efficiency.
But that will have consequences for the engineering community—the engineering challenge presented by a building when viewed through a systems lens is markedly more complex.
A building must be modeled to an industry-defined benchmark to determine the load profile. Modeling results need to be integrated with a standardized climate-zones benchmark to define the ambient temperature profile. The proposed system would then need to be contrasted with a common industry-defined benchmark system to establish whether the annual energy consumed is an improvement over the industry standard.
There are other approaches to a systems-based efficiency evaluation, and the systems that are focused on can be more or less comprehensive when taken together. But the overarching fact is that the "plug-and-play" approach, in which a component product rating was deemed sufficient to establish an efficiency improvement, would be history.
It would be optimistic to suggest that we are on the threshold of a systems approach to commercial building efficiency. Building modeling is decisive for a systems approach, but today only about 20% of buildings are modeled. Modeling is complex and costly. There are no simplified, easy-to-use modeling tools for the smaller and midsized buildings that today make up the bulk of the building stock. So modeling is limited to larger, high-end buildings. A prescriptive approach to efficiency compliance predominates in the marketplace, and much that is necessary to make a systems approach a mainstream reality remains to be designed, commercialized, and brought into standard practice.
Still, the industry is moving. The Air-Conditioning, Heating & Refrigeration Institute (AHRI) is making progress toward certification of the complete operating map for the HVAC&R product. ASHRAE is developing standards for representation of product performance and the electronic transfer of data to simulation tools. ASHRAE Standard 90.1 has very recently included a compliance performance path that allows designers to be far more imaginative and to compare their results to a base efficiency level of 2004. Work also is underway to develop better models for equipment and components that will allow for improved modeling of systems, as well as modeling new systems and subsystems concepts that cannot be accurately modeled today. AHRI and others are developing the tools required to facilitate compliance strategies at a subsystem and system level. And new part-load and annualized metrics are being developed that allow focus on the annual energy use, and not only on full-load design.
These and similar steps being taken in industry organizations, and companies acting on their own, are lighting a path to a new operational definition of building energy efficiency and the dramatic efficiency improvements required by emerging emissions targets. The work to be done, however, exceeds by far what has been accomplished. The systems revolution in the United States remains on the horizon. But if carbon goals are to be met, there is no going back.
Other benefits also can be obtained by looking at the equipment as a system and setting targets at a system level—that is, defining the whole building's energy-performance goals, or subsystem performance goals, but not the means whereby the goal is achieved. Such a step would imply an elemental break with existing energy-standard strategies, which aim to define the solution (i.e., equipment with a certain performance rating) and not the ultimate building performance goal. Today's focus on components means that new concepts that improve the overall operating on an annualized basis are often not, and cannot be, factored into metrics. Setting future targets for efficiency improvements at a subsystem and system level will allow for new creative solutions to be developed as well as allow the use of innovative solutions at the overall building system level. The result will be simpler standards that create ample room for innovation.
Progress in Europe, global implications
Developments in Europe may encourage American efforts on systems building efficiency. Factors reaching back to the oil shocks of the 1970s encouraged Europeans to focus on building efficiency, and it is commonplace to site European advances. The "separate tracks" approach that often characterized the relationship between U.S. and European markets, however, is cited just as frequently to underscore the irrelevance of the product-related practices of each to the other. To grasp the relevance of Europe to the American building marketplace today it is helpful to explore both European thinking on building efficiency and what is emerging as the new global significance of European standards.
The European Committee for Standardization (CEN) is the principal European Union standard-setting institution. Within the CEN framework, energy-efficient buildings are assessed holistically. CEN aims to reduce the need for energy by meeting minimal thermal building-envelope requirements; minimize the use of energy by a systems approach to HVAC, Domestic Hot Water (DHW), and lighting systems; and, finally, address the remaining energy requirement with sustainable-energy sources. Simultaneously, the building is to meet relevant indoor-environmental requirements for thermal comfort, indoor air quality, noise levels, task-efficient adaptive-lighting levels, and such issues as human health, well-being, and productivity. In the end, building energy performance is to be evaluated with a threshold number—such as kWh/square meter or Btu/square foot per year—and a second number indicating the role of renewables in the building energy supply, all of which are to be reported.
Writing a standard does not make it so, and the member states of the European Union determine codes. But the direction and force of the CEN regime are unmistakable.
In addition to action being taken by CEN, however, another factor is in play with vast implications for the future of buildings around the world. In 1991, CEN and the International Organization for Standardization (ISO) signed the "Vienna Agreement," which came into force in the mid-2000s. The agreement sought to avoid duplications and conflicts between European and the international standards on which ISO is focused. Under the agreement, CEN adopted many pre-existing ISO standards; but in principle, the migration of standards can move in either direction. A working group between CEN and ISO has been established with the goal of jointly developing building standards.
The result would be an international standard of great force within the relevant industries around the world, articulating in operational detail a systems-based concept of building efficiency. A CEN official leading the joint working group described the situation: "CEN and ISO are on a fast track to develop the procedures and standards for buildings, systems, and products toward low-energy building that could meet the nearly zero energy building targets. The developed standards and procedures will offer the flexibility to apply them throughout Europe and globally." Products, to underscore the point, are to be evaluated not as products, but as parts of a system, and the holistic approach is to be based on tested product characteristics. Presently, however, there is very limited information on the performance of products from manufacturers that will meet those requirements.
-Drake H. Erbe has been with Airxchange for 16 years. In his position as vice president of market development, he is responsible for continued development of the company's strategic focus on Original Equipment Manufacturer OEM relationships and market transformation in rotary energy-recovery components and technology.
-Richard Lord is a senior fellow with 43 years of experience in the design and application of commercial air conditioning equipment and controls. He has expertise in systems, fluids, refrigerants, heat transfer, heat-exchanger design, software, controls, diagnostics and commercial efficiency, and building standards and controls.
-Lisa Tryson is director of corporate communications and public relations for Danfoss North America, a manufacturer of high-efficiency controls, compressors, and variable frequency drives for HVAC and allied industries.