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.

High-Performance Design

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.

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