ASHRAE Journal - January 2009 - (Page 20) overestimation of energy savings and lack of consideration of the latest retrofit technologies.4 Opportunities Although large office buildings present a broad set of challenges, they also bring unusual opportunities. The size of the buildings allows for economies of scale in energy audits and implementation, and energy savings can be large. A single owner, frequently a private entity or individual, can allow for easier decision-making. Repeating space types, from area-toarea and floor-to-floor and building-to-building, can simplify the energy audit: offices, corridors, stairwells, kitchenettes, toilets, first floor/lobby, and conference rooms. A few large loads can offer large energy savings opportunities: ventilation, HVAC plant, HVAC distribution components such as large motors for air handlers and pumps, and adjustments to incorrectly operating HVAC systems. Repeating (often identical) loads also make things easier: computers and peripherals, kitchenette appliances, lighting, and windows. Lighting, in particular, has long hours of use, unlike in many other building types for which occupancy is more sporadic, and so offers greater opportunity for energy savings. A Comprehensive Approach A comprehensive approach can be used to leverage the opportunities offered in large commercial office buildings and to minimize the risks presented by their challenges. This approach, looking at all loads and all equipment, offers the most savings and the biggest selection of improvements from which the owner can choose. Methodical data collection further maximizes savings, makes analysis easier, and documents recommendations in a way that greatly simplifies implementation. Solid energy modeling and billing analysis can further help and can identify unusual energy losses and opportunities. Calculation procedures should place an emphasis on calibrating the building’s energy use with weather-corrected billing data before beginning evaluation of potential improvements. The interaction among improvements should be accounted for to avoid double-accounting for savings between two improvements that affect each other, for example, HVAC plant replacement and space temperature control improvements. In addition to the routine analysis of repeating loads and equipment, the energy auditor should treat each building as unique, not as a commodity, and should look for anomalies in use, wearing the hat of a building scientist or diagnostician to identify buildingspecific energy efficiency opportunities. Gathering actual HVAC operational data, such as temperature trends, equipment use, and flow rates, can augment the understanding of building-specific problems and energy savings opportunities. Lighting offers an example of the methods that can be used. Tables 1 and 2 show an example of a data sheet from an actual commercial office energy audit.5 Lighting measurements are taken in every room. Note the dramatic variations in light levels in the small sample of offices, ranging from 55 to 115 20 ASHRAE Journal footcandles (592 to 1238 lux). Some offices are highly overlit and so offer opportunities for reducing lamps or fixtures. As data is taken while still in the building and before leaving each room, the energy auditor formulates a variety of recommendations. The end result is a customized energy audit with specific recommendations and multiple improvements possible for each room and with a report that provides sufficient detail for the owner to proceed with implementation. An example of a specific office further illustrates the potential approaches and savings. A 120 ft2 (11 m2) executive office was found with two light fixtures, each with four lamps. A simpler walkthrough energy audit might have noted that the existing lamps are T8, and the ballasts are electronic, and so would not have made any recommendations. A comprehensive energy audit measured light levels at 150 footcandles (1615 lux), far above the IES-recommended range of 30 to 70 footcandles (323 to 753 lux) for offices. The audit recommended removing four of the eight lamps and replacing the single toggle switch with a dual switch (one switch for each of the two fixtures) and an occupancy sensor and photocell integrated into the switch. A tenant education program helped the office occupants learn how to use the new double switch and switch-integrated photocell and occupancy sensor effectively. The results are savings of more than 70%, since only two lamps are used most of the time (instead of the original eight); savings accrue when the occupancy sensor or photocell turns off the lights. Note the multiple improvements (delamping, controls, tenant education) made possible by a comprehensive and room-specific approach. What is meant by “comprehensive energy audit”? A comprehensive energy audit includes evaluating all energy loads and equipment in a building: the HVAC plant (in a commercial office building, typically chillers and boilers); the HVAC distribution systems; envelope improvements (walls, windows, roof, foundations, insulation); lighting; plug loads such as appliances and computers; operation and maintenance improvements; tenant education; and more. The energy audit should capture roomspecific opportunities and document recommendations in the audit report to allow for clear implementation of improvements. Improvements should focus not only on equipment efficiency, but also ensuring that the equipment meets the required load. For example, do not just replace T12 lamps with T8; also measure light levels to make sure that each space is not overlit. Another example: Do not merely change the boilers to high-efficiency; also make sure that the new boilers are not oversized. The trend towards comprehensiveness in energy audits likely started in residential buildings more than 10 years ago. On-site measurement of HVAC plant efficiency, such as combustion testing for furnaces and boilers and even advanced testing of air conditioners and heat pumps, are becoming increasingly common. Analysis of distribution systems, for example through duct leakage testing, has arrived. Evaluating the replacement of plug loads, such as appliances, has become commonplace. Diagnostic tools, such as blower doors and infrared thermography, have allowed advanced analysis of the building envelope. Advanced techniques for retrofit insulation, such as spray foam ashrae.org January 2009 http://www.ashrae.org
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