In the United States, the two most common energy-efficiency standards are ANSI/ASHRAE/IESNA Standard 90.1, Energy Standard for Buildings Except Low-Rise Residential Buildings, and the International Energy Conservation Code (IECC). These standards play a key role in curbing the energy consumption and greenhouse-gas emissions of new and renovated buildings. Several states have adopted variations of these standards or developed their own standards to address unique energy-efficiency issues. In general, each of these standards includes:

• Requirements concerning building-control capabilities, equipment efficiencies, and installation.
  
  
• Compliance paths specifying minimum requirements for building components, allowing limited trade-offs between building components, and demonstrating a proposed design performs at least as efficiently as the baseline design.

According to the U.S. Department of Energy, more than half of the states in the country have adopted energy codes at least as stringent as Standard 90.1-2004/IECC 2006, while more than two-thirds have adopted energy codes at least as stringent as Standard 90.1-1999/IECC 2001.

Appendix G of Standard 90.1-2004 provides a method of rating the energy performance of a project. This method requires the development of energy simulations for a baseline building and a proposed design and provides explicit guidance concerning building-control systems.

Building Energy Codes and Standard Practice

Energy audits of older buildings reveal many instances of inefficient control implementation, such as constant-speed fan control in multizone systems, inadequate outdoor-air-shaft sizes, simultaneous humidification and dehumidification, limited simultaneous heating and cooling, and substantial operation of HVAC and lighting systems during unoccupied periods. This has led to innovation and the deployment of new approaches to building control. In jurisdictions requiring compliance with Standard 90.1 or a similarly stringent energy standard, newer buildings incorporate numerous controls to promote energy-efficient operation:

• On larger air-handling units (AHUs), optimum start/stop controls, which allow minimal operation during unoccupied periods while ensuring comfort conditions are met during occupied periods.
  
  
• For HVAC and lighting systems, zone-isolation controls, which allow automated shutoff in specific areas.
  
  
• Controls limiting simultaneous humidification and dehumidification to spaces with narrow environmental-control requirements, such as computer rooms.
  
  
• Ventilation controls in areas with high occupancy limits for times of partial occupancy.
  
  
• For buildings in dry climates, air- or water-economizer controls for free cooling throughout much of the year.
  
  
• Hydronic distribution loops designed for variable-flow operation.
  
  
• Variable-speed fan controls on air-handling systems serving multiple zones.
  
  
• Chilled-water and hot-water-reset controls for lowering building energy consumption during part-load operation.
  
  
• On AHUs providing large quantities of outside air, exhaust energy-recovery systems, which transfer heat from the exhaust stream to ventilation supply air.

Building-Energy-Performance Rating Systems

Energy-efficiency codes and standards have helped to transform the building-controls market. This transformation has been aided by energy-efficiency incentive programs and energy and environmental rating systems. For instance:

• The Energy Policy Act of 2005 (EPAct) provides federal tax credits for commercial buildings exceeding Standard 90.1-2001 Appendix G requirements by 50 percent or more. Partial incentives are available for lighting-, envelope-, and/or HVAC- and service-water-heating-system-performance improvements.
  
  
• The Leadership in Energy and Environmental Design (LEED) Green Building Rating System uses Standard 90.1 Appendix G performance-rating methodology to rate the energy efficiency of new-construction and major renovation projects under Energy & Atmosphere Credit 1 (EAc1).
  
  
• Many utilities provide incentives for projects that exceed minimum local energy-code requirements.

The influence of energy-performance rating methods on the implementation of building controls is limited to controls that must be reflected in baseline-building models and controls that receive credit in proposed-building models.

In accordance with the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) performance-rating method, controls modeled in a baseline building include supply-air-temperature reset for multizone systems, variable-speed pumps, and condenser-water wet-bulb reset, while building-control efficiency measures that receive credit within a proposed building include automated fenestration shades, daylight-harvesting controls, occupant-sensor lighting controls, demand-control ventilation (DCV), variable-speed chillers, variable-speed compressors for direct-expansion (DX) equipment, electronically commutated motors, and chilled-water and hot-water reset based on building demand. Controls that generally cannot be modeled for credit in the ASHRAE performance-rating method are those that involve schedule changes, such as night ventilation controls or programmable communicating thermostats, and control-system functions associated with monitoring and verification or fault detection. Appendix G places significant restrictions on the modeling of controls used to facilitate natural ventilation in a natural/mechanical (hybrid) ventilation system.