ASHRAE Journal - January 2009 - (Page 24) Recommended Change Location Lighting Changes Replace EXIT Occupancy Sensor Plus Timer Occupancy Sensor Plus Timer Light Sensor Light Sensor Light Sensor Replace EXIT Light Sensor Light Sensor Light Sensor Light Sensor Remove Fixtures De-Lamping Control Savings Analysis Annual Energy Annual Cost Savings, Savings, $/yr kWh/Yr 166 1,754 $28 $167 Cost of Retrofit $115 $1,166 Simple SIR Payback, Years 4.1 7.0 5.6 1.7 106 Hallway 133 Boiler Room 134 Transformer Room 204 Office 205 Office 206 Office 207 Hallway 211 Office 213 Main Lobby 213 Main Lobby 213 Main Lobby 213 Main Lobby Replace Bulbs, Ballasts 1,635 376 376 564 166 282 279 658 877 431 $178 $36 $36 $54 $28 $27 $17 $62 $83 $36 $1,225 $194 $194 $194 $115 $194 $194 $194 $194 $91 6.9 5.4 5.4 3.6 4.1 7.2 11.3 3.1 2.3 2.3 1.7 2.2 2.2 3.3 5.6 1.6 3.2 3.8 5.1 9.2 Table 2: Lighting results (from an actual commercial ofá¼€ce energy audit). The Improvement Mix What improvements are best suited to commercial office buildings? The occupancy-driven nature of office spaces make occupancy-based controls attractive, such as demand-controlled ventilation, programmable temperature controls, and variable capacity distribution systems (VAV air handlers, variable speed pump drives, etc.). Large office spaces often result in interior/ core spaces with an associated high cooling demand, so economizers make sense in many climate zones, as do systems that recover core heat for use on the perimeter, such as water loop heat pumps. High-efficiency replacement HVAC is also always an option. Significant savings often can be achieved through operational adjustments to HVAC controls. Reducing overlighting is a frequently missed improvement, so a light meter in the toolkit is essential. While energy codes typically require a maximum of 1.0 to 1.1 W/ft2 (0.09 to 0.10 W/m2) for office lighting power density,7 and existing buildings often consume much higher than even these levels, 0.75 W/ft2 (0.07 W/m2) or lower are easily obtainable and should be used as a goal; these levels can be further reduced on a time-average basis through task lighting, daylighting, and occupancy-based lighting. These lighting savings are amplified by a reduction in air conditioning use in such typically core-dominated buildings. Installing pendant lighting fixtures in spaces with tall ceilings will also reduce lighting power densities. Energy savings are often accompanied by improvements in visual quality as well. In corridors and stairwells, 5 to 10 footcandles (54 to 108 lux) are adequate, and typical existing 24-hour use merits both reducing lighting to this level, in addition to occupancy sensors to turn off lights when the corridors and stairwells are not occupied, 24 ASHRAE Journal and photo controls for lights near windows. Low-level lighting can be maintained for safety and security. Plug loads, such as computers and kitchenette refrigerators, contribute substantially to electricity use and can be replaced with high-efficiency substitutes through purchasing policies, or used more efficiently, such as by setting display screens to turn off, or implementing policies regarding turning off screens and computers. Plug loads require engaging tenants in energy efficiency, which is a good thing. For engineers, who often feel most at home in the boiler room or looking at the chiller and air handler, envelope improvements often seem foreign. What can we do with the envelope in a high-rise office building? Stack effect and associated infiltration losses can be reduced through weather stripping of windows and caulking window frames, and by compartmentalization of the building interior (such as weather stripping of stairwell doors) and other air-sealing (plumbing chases, roof penetrations, and more). Such improvements will also dramatically reduce discomfort caused by airflow induced at the entrance to the building and on lower levels. Window replacements and storm windows can reduce heat loss in winter by half or more and similarly reduce heat gain in summer. Creative improvements, such as interior or exterior shades, can further reduce loads and reduce glare in offices. Even wall and roof insulation should not be ruled out. Two Examples Comparing two actual energy audits, a walkthrough audit and a comprehensive energy audit, provides insight into the difference between these approaches. Table 3 summarizes these two audits. ashrae.org January 2009 http://www.ashrae.org
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