ASHRAE 90.1 reduces energy consumption
ASHRAE recently published the 2010 version of its energy standard, which is expected to provide guidance for reducing energy consumption by more than 20% over savings realized in the 2004 version. The purpose of the standard is to establish minimum energy efficiency requirements of buildings—other than low-rise residential—for design, construction, a plan for operation and maintenance, and use of on-site renewable energy resources. The standard addresses the building’s envelope, HVAC, service water heating, power, lighting, and other equipment. A designer can affect a building’s energy use well into its lifecycle through an astute understanding of the applicable energy codes and standards and proper implementation in the design.
Many revisions to ANSI/ASHRAE/IES Standard 90.1 – 2010, Energy Standard for Buildings Except Low-Rise Residential Buildings, are anticipated to contribute to the significant energy reduction provided by following the requirements of the standard. This article will focus on the changes in Sections 6, 8, 9, and 10; Section 7, Service Water Heating, is unchanged from the 2007 version.
Section 6: HVAC
In general, Section 6 has many additions in the simplified and prescriptive approaches, as well as in the mandatory provisions of the standard, related to higher efficiency. Additional energy reduction is anticipated in ASHRAE Standard 90.1 – 2010 by modifying its purpose and scope to expand the coverage of the standard for economizers to recognize and detail provisions for computer rooms (see Figure 1).
For example, data center cooling systems will now be required to include an air or water economizer. For the economizing provision of the simplified approach and mandatory provisions, all computer room cooling applications above the tabled geographic capacities, apart from the listed exceptions, will require air or waterside economizing. Water economizing systems are called to use indirect evaporative means for 100% of the expected system cooling load.
Two exceptions have been added specifically for computer rooms allowing for evaporative water economizers or dry cooler water economizers at lower ambient wet bulb and dry bulb conditions. Of note is the large number of exceptions listed for computer rooms below 50 tons of design room load or 250 tons of total building computer room load. These exceptions also seem to apply for mission critical facilities and Tier IV designs. For comfort cooling applications, economizers may be eliminated only if the minimum climate zone efficiency improvements can be met.
Additionally, HVAC equipment for computer rooms will now be required to have minimum performance requirements. The minimum equipment efficiencies section of the mandatory provisions now list the requirements for computer room air conditioners based on the method of heat rejection and net sensible capacity of the zone where they are utilized.
In addition to these computer room focused provisions, the simplified compliance path approach now details requirements with variable airflow, air and water economization changes, exhaust air energy recovery, intake and exhaust systems, demand control ventilation, shut-off damper controls, and parking garage ventilation, to name a few. Perhaps most significant is the call for variable air-volume (VAV) control on single-zone systems. Chilled water air handlers with fans of 5 hp or greater will need to control fan speed via variable frequency drives (VFDs) or two-speed motors when cooling demand is below 50%. Starting Jan. 1, 2012, this requirement will also apply to direct expansion air handlers greater than 110 MBH. Where this standard is adopted by local jurisdiction, it will require the consulting engineers to seriously investigate how the new standard will impact their design approach. Clients’ geographic zone will heavily impact the winter or summer efficiency approach (Figure 2).
The mandatory provisions have been expanded to better detail requirements of damper control and leakage levels, ventilation control, and temperature reset. Also included is information for the requirements of shut-off dampers, including ventilation outdoor air, and exhaust/relief dampers.
There are also prescriptive additions for multizone VAV systems with direct digital control (DDC) of boxes reporting to a central controller, to automatically reduce outside air intake in response to changes in system ventilation requirements. Supply air temperature reset control has been added for multizone systems to automatically reset supply air temperature in response to building loads or to outdoor air temperature. The controls shall reset the supply air temperature a minimum of 25% of the difference between the design supply air temperature and the design space temperature. Controls that adjust the temperature reset based on zone humidity are also acceptable. Zones that are expected to experience relatively constant loads (i.e., electronic equipment rooms) are to be designed for the fully reset supply temperature.
The standard has addressed hydronic water loop efficiency, new to ASHRAE Standard 90.1 – 2010. All water source heat pumps and water-cooled air conditioners shall have a two-way valve that shall shut when the compressor is off. All units with pumps over 5 hp shall use variable speed control to limit pump motor demand to 30% of design wattage at 50% flow requirement. All chilled water and condenser water piping shall now meet the tabled pipe size requirement based on flow rate and hours of operation for the system. Variable flow/variable speed controlled systems are listed separately from systems without variable flow control and generally will allow greater maximum design flow. A new provision has been added for centrifugal fan open-circuit cooling towers mandating that fan efficiency meets the tabled values for axial fan open-circuit cooling towers.
Exhaust air energy recovery has been modified for the simplified approach to account for the geographic zone and the percentage of outside air required at design conditions. The 5,000 cfm threshold has been lifted for a requirement of energy recovery on systems with smaller supply air cfm and higher percentages of outside air. Demand control ventilation is also now required for high-occupancy areas and may apply under the simplified approach. The kitchen and fume hoods sections have been expanded to include kitchen exhaust systems and laboratory exhaust systems and have been thoroughly detailed. Maximum limitations have been set for outside air on compensating hoods and conditioned air supplied to any space with a kitchen hood. Where the exhaust airflow rate exceeds 5,000 cfm, requirements are tabled for the maximum exhaust airflow rate per linear foot of hood, based on hood type and duty. Finally, for kitchen exhaust systems there is the requirement for field performance testing to evaluate design airflow rates and demonstrate proper capture and containment.
Additionally, tabled efficiencies for positive displacement air- and water-cooled chillers have been added along with a mandatory provision for the determination of required pump head and pressure drop throughout a system at design conditions.
Section 8: Power
Low-voltage dry-type distribution transformers are now required to comply with the provisions of EPAct 2005 where applicable. Minimum nominal efficiency levels for these transformers are outlined in a table, and the standard requires all equipment installed in new buildings and additions to existing buildings to comply with the requirements outlined in the section.
Section 9: Lighting
Changes to the lighting section include:
- Automatic control of a minimum of 50% of all 125 V, 15- and 20-amp receptacles including those installed in modular partitions in private offices, open offices, and computer classrooms. Options for this control include time-of-day scheduling, occupancy sensors, or signal from another control or alarm system indicating an area is unoccupied.
- ASHRAE Standard 90.1 – 2007 required automatic lighting control for buildings larger than 5,000 sq ft to shut off interior building lighting in all spaces (less required emergency lighting) based on time-of-day scheduling, occupancy sensors, or a signal from another control or alarm system indicating an area is unoccupied. ASHRAE Standard 90.1 – 2010 removes the minimum square footage.
- Spaces enclosed by ceiling height partitions must have multilevel control capability, and the list of space types requiring occupant sensors was expanded. A new requirement mandates that lighting controls be functionally tested to ensure they are located, calibrated, adjusted, programmed, and in proper working condition so that energy savings are realized.
- Parking garage lighting control details and the definition for automatic daylighting control for both primary side-lighted and top-lighted areas have been added.
- Control requirements for display/accent, case, guest room, task, stairwell and other unique lighting applications are defined. Exterior lighting control requirements have been expanded in the current version. For example, all building façade and landscape lighting shall be automatically shut off between midnight or business closing (whichever is later) and 6 a.m. or business opening (whichever is earlier) or between times established the authority having jurisdiction.
Section 10: Other equipment
Detail was added in the 2010 version of this standard to define minimum manufacturing requirements for electric motors, pressure control for service water booster systems, and lighting and ventilation power requirements for elevators.
Compliance with these changes can be accomplished in most if not all cases by implementing a comprehensive building automation solution. As many of the ASHRAE Standard 90.1 – 2010 requirements incorporate multiple sensing technologies and comparative control strategies for compliance, a properly designed building automation system can serve a critical role not only in initial compliance with the standard but also in continued operation and monitoring and verification of system performance over time. With advances in DDC, the requirements of ASHRAE Standard 90.1 – 2010 become more readily achievable. Current options in energy monitoring technology for all forms of energy and the interface and interoperability capabilities with building automation systems can provide significant opportunity for ongoing system efficiency and continued performance improvements.
An engineer’s direct involvement in a project typically ends when final inspection is completed. These design professionals, however, can affect change well into the life cycle of a building through an astute understanding of the energy standard. Combined with experience and product technologies that can translate to more effective energy management over the long term, this aggregated knowledge could place engineers and their firms in the position of being able to recommend options for compliance with energy codes and standards.
McClain is BAS construction manager, buildings business. He is a provisional member of ASHRAE TC7.6 Building Energy Performance. Sifferlen is mechanical systems manager, data center solutions, IT business. He has been a member of ASHRAE since 1987 and served as the refrigeration chair of the Granite State Chapter. Stoppelmoor is industry standards manager energy efficiency, power business. He is a member of IEEE, IAEI, NFPA, and ASHRAE, where he is a member of the Standard 90.1 Standing Standard Project Committee and Lighting subcommittee, Standard 189.1 Standing Standard Project Committee, and Standard 100 Standard Project Committee.