Design-team communication as important to successful building performance as efficient mechanical systems
With the advent of the 2030 Challenge; proposed ASHRAE/IESNA/USGBC Standard 189, Standard for the Design of High-Performance Green Buildings Except Low-Rise Residential Buildings; the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) and Energy Star building-energy-labeling programs; and green-building rating systems, such as the U.S. Green Building Council's (USGBC's) Leadership in Energy and Environmental Design (LEED) Green Building Rating System, energy and carbon use are becoming priorities for building owners and design teams. High-performance buildings are becoming increasingly popular.
Creating buildings that respond to increased demands for energy efficiency and carbon accounting while balancing efficiency goals with economic constraints is no easy task. To compound this problem, no concrete definition readily exists for high-performance buildings because, to date, they have consisted of a mix of certified green projects and structures that have one or more notable environmental features.
This article will discuss the meaning of the term "high performance" and the changes in thinking and systems approach that can lead to high-performance buildings. It also will explore underutilized mechanical-system technologies and several effective mechanical systems that have helped create high-performance buildings.
The term "high performance"--when applied to energy-consuming objects, such as cars or boats--conjures thoughts of speed, power, energy consumption, and expense. However, the opposite generally is true when the term is applied to buildings. "High performance" can refer to any building that performs better than average for a particular metric, such as utility consumption (kilowatt-hours or British thermal units per square foot) and environmental quality (air temperature, acoustic loudness, or lighting foot-candles).
First, an agreeable baseline or benchmark to measure performance against should be established. Next, a common measurement and reporting system should be used to evaluate actual performance against the baseline. Common building-energy baselines include the Energy Information Administration's "Commercial Buildings Energy Consumption Survey" (www.eia.doe.gov/emeu/cbecs) and ANSI/ASHRAE/IESNA Standard 90.1-2004, Energy Standard for Buildings Except Low-Rise Residential Buildings, which is the foundation of modern energy codes.
A common measurement and reporting system has been proposed under the U.S. Department of Energy's (DOE's) Performance Metrics Research Project (www.eere.energy.gov/buildings/highperformance/performance_metrics). A commercial-buildings research activity, the project was created to standardize the measurement and characterization of building energy performance.
However, to be sustainable, high-performance buildings also must be economical, considering first cost while basing decisions on life-cycle cost and return on investment. Economy is achieved first on a system level and then on a component level. For example, a building shell can be tuned to reduce heating and cooling loads, offering a reduction in mechanical-system cost on a system level. Variable-frequency drives are then used at pumps and air-handling units to further tune a system to respond to load requirements.
High-performance buildings do more than just conserve energy. Economical high-performance buildings use less material more effectively. The systems within a high-performance building are durable and typically require less maintenance. A high-performance building conserves water and all of the precious resources from which it is made. It operates as one system in which individual components operate synergistically for mutual benefit.
Hallmarks of High-Performance Design
Many of the most successful high-performance buildings utilize several key approaches, such as:
- The entire design team is part of the design process from the start. The team includes the building owner, architecture/engineering team, commissioning authority, installing contractors, and occupants.
- The team collectively sets goals and holds themselves accountable to deliver a building that meets the owner's requirements.
- Any value-engineering efforts and changes are tracked back to the basis of design and the owner's requirements to ensure efficiency items are not eliminated.
- The whole building is approached as one system.
- Modeling software is used to evaluate items, such as heat flow through building components, mechanical-system energy use, and daylighting profiles.
- Economic decisions consider life-cycle costs.
- Energy, resources, and materials are used efficiently.
- Materials and systems used are durable, require less maintenance, and are recyclable.
- The quality-assurance process of commissioning is incorporated into the building design and delivery process to ensure that the building system is performing as expected and that information needed to maintain performance is provided to the owner.
- The building is intentionally created to have a positive effect on its occupants and the environment.
Fundamentals of Resource-Efficient HVAC Design
No single mechanical system fits all of the needs of a building in a particular climate zone, let alone a high-performance building. However, high-performance buildings have mechanical systems that consider the fundamentals of energy- and resource-efficient HVAC design, such as:
- Heat flow through building elements is examined via computer economic analyses, and building loads are reduced as much as possible. This ensures that mechanical-system size is reduced.
- Natural-energy flows, such as passive solar heating, daylighting, natural ventilation, and occupant-generated heat, are exploited.
- Internal loads are reduced through daylighting integration and the use of Energy Star-labeled equipment.
- The building is divided into thermal zones that are served by mechanical systems. This results in higher system controllability, resulting in greater occupant satisfaction.
- Mechanical systems are decentralized, or multiple-zone control is used within larger units.
- System losses, such as those in ducts and piping, are reduced.
- Air systems use low-pressure ductwork.
- Premium-efficiency motors are employed.
- Variable-load fan systems are used, and part-load performance is considered in equipment selection to maximize operating efficiency.
- Occupancy-based controls, including time-of-use and demand-based control, are used in areas that have varying and high-occupancy loads.
- Energy recovery is used for ventilation air.
- Electric loads are shifted or curtailed during peak demand periods.
- High-efficiency mechanical systems are used.
- Testing, adjusting, and balancing are specified and performed completely.
- Noise and vibration control is provided for mechanical systems and commissioned.
- An operations-and-maintenance program is established and documented.
- Provisions are made for proper performance monitoring and verification.
Three real-world examples of high-performance buildings exemplify whole-building high performance.
Mapleleaf Orthopedics. The Mapleleaf Orthopedics building in Pueblo, Colo., is southern Colorado's first LEED-certified building and has made a statement in the local building and design community. The 8,000-sq-ft building is oriented along an east-west axis to better harness the sun's heat energy. Renewable-energy and energy-efficiency features dramatically decrease the building's carbon footprint.
A 30.6-kw photovoltaic (PV) system meets nearly 90 percent of the all-electric building's energy needs. The owner requested that the PV panels be a highly visible and dramatic part of the building's architecture. The PV system is connected directly to the utility power grid, and any excess generated energy is fed back into the grid. Essentially, the utility grid operates as a battery, storing excess energy. This building is an example of how renewable energy can be incorporated easily into a building's design.
Windows are located throughout the building to provide daylight and views for more than 90 percent of all of the occupied spaces. Shading techniques are used to block direct sunlight during summer. Daylight harvesting and occupancy-based lighting controls are used to further reduce expended lighting energy to roughly 0.8 w per square foot.
Heating and cooling are provided via ground-source heat pumps with field-verified heating efficiency of 350 percent (a coefficient of performance of 3.5) and an energy-efficiency ratio of 19. An energy-recovery ventilation air-handling unit tempers outdoor air and reduces ventilation load by 75 percent. Twenty air exchanges per hour improve indoor-air quality. Low- and no-volatile-organic-compound (VOC) paints, glues, stains, and flooring add to the quality of the indoor environment. Other notable high-performance features include low-flow water fixtures and landscaping, pervious paving, sustainable lumber, recycled-content product, and wheat-board casework.
All of this results in a building that performs at 19 kBtu per square foot per year, nearly 80-percent lower than a typical building. Builders can learn how incorporating renewable, sustainable concepts in their own designs can be easy and cost-effective for the owner and healthy for occupants.
Namaste Solar Electric. Namaste Solar Electric remodeled a 15,000-sq-ft warehouse for its new offices in Boulder, Colo. The company, which manufactures and installs PV systems, has submitted the project for LEED for Commercial Interiors Gold certification. The building benefits from daylighting, recycled building materials, increased insulation, evaporative cooling, and environmentally friendly finishes.
The building's electricity is provided by a 10-kw solar system. The PV panels are located on the rooftop, as well as a solar awning. The project's insulation consists of a combination of fiberglass batt, spray foam, and wet-blown cellulose.
The building's HVAC system provides heat via a central high-efficiency, gas-fired hot-water boiler serving baseboard convectors with individual zone control. Cooling is provided via zoned direct-evaporative-cooling systems for all areas except the conference room, which is served by an Energy Star-rated packaged rooftop heating and cooling system. A dedicated outdoor-air system provides tempered ventilation air during the heating season.
The project also reused existing materials. Salvaged-wood framing was used to frame interior and exterior walls and create exposed flat-stacked low partitions.
Eco-finishes and fixtures, such as zero-VOC paints and carpet, a polished concrete slab, recycled-content ceramic tile, carpet and toilet partitions, eco-friendly furniture systems, and waterless urinals, dual-flush toilets, and low-flow faucets, were chosen to reduce toxicity and conserve resources. The project garnered $29,086 in efficiency rebates from the flexible-rebate division of the city's business-incentive program.
Hyland Village Community Center. Designed to be the first zero-energy community center in Colorado,
Hyland Village Community Center is under construction and will include meeting rooms, a small kitchenette, restrooms, and an associated outdoor seasonal pool. Zero-energy buildings use the equivalent of the energy provided by on-site renewable sources.
The project will harness passive solar energy through south-facing windows and a Trombe wall. The Trombe wall will collect and store solar energy in a concrete-mass wall during the day and release energy to help heat the building at night. All of the facility's electric needs are fulfilled via 14.5 kw of PV panels. Solar-thermal panels are employed to handle domestic water and space and pool heating.
The center's insulated building shell will require little cooling, which will be provided by a fan that will flush the building with cool air at night. Other notable features include a greywater system for shower-water reuse in toilets, air-to-air heat recovery on ventilation air, low-flow plumbing fixtures, and a live green roof. The project has been submitted for LEED Platinum certification.
Promising HVAC technologies
Data from Arthur D. Little, an international management-consulting firm, estimates that roughly 59 billion sq ft of commercial floor space in the United States consumed 14.7 quads of energy in 1995. HVAC systems consumed 4.5 quads of this total, representing the largest percentage of energy end-use. In July 2002, the DOE published a report, "Energy Consumption Characteristics of Commercial Building HVAC Systems, Volume III: Energy Savings Potential," in which 55 technology options were analyzed for energy-savings potential. The 15 most attractive options were given a more refined analysis (Table 1).
Figure 1 presents the simple payback of 11 of these options. Radiant-cooling and dedicated outdoor-air systems have an instantaneous payback requiring no additional capital outlays.
Several areas absent from the DOE's list of 15 promising technology options include cogeneration/waste-heat utilization opportunities, building-envelope technologies that reduce building heating/cooling loads, renewable energy, and natural-cooling/ventilation technologies. As previously mentioned, these technologies often are present in high-performance buildings.
There is no single path to a high-performance building, although enhanced collaboration and team commitment to goal success is paramount. Delivering a high-performance building on time and within budget is a top priority. Experience is a valuable commodity in teams designing a high-performance project. Measurable goals should be established early and accomplished throughout the duration of a project. Modeling should be used to inform the design, commission the project, and monitor post-occupancy. These steps will ensure a high-performance project has the greatest chance for success.
Peter C. D'Antonio, PE, CEM, LEED AP, is the director of business development at PCD Engineering Services Inc., an award-winning provider of mechanical/electrical engineering, commissioning, and energy analyses for buildings. His work has been recognized with design and service awards from various organizations, including the U.S. Green Building Council, Colorado Governor's Energy Office, and American Solar Energy Society. He can be reached at firstname.lastname@example.org.
Sidebar: Resources for More Information
Resources for additional information on high-performance-building mechanical-system design include:
• "Advanced Energy Design Guides," which can be found at www.ashrae.org/technology/page/938.
• "Los Alamos Sustainable Design Guide," which can be found at www.eere.energy.gov/buildings/highperformance/lanl_sustainable_guide.html.
• "High Performance HVAC," which can be found at www.wbdg.org/resources/hvac.php?r=dd_hvaceng.
• "Energy Design Guidelines for High Performance Schools," which can be found at www.eere.energy.gov/buildings/highperformance/design_guidelines.html.
• "High Performance HVAC," which can be found at www.highperformancehvac.com.
• "IAQ Design Tools for Schools," which can be found at www.epa.gov/iaq/schooldesign/hvac.html.
• "Building Energy Software Tools Directory," which can be found at apps1.eere.energy.gov/buildings/tools_directory/subjects_sub.cfm.