Tuesday, October 5, 2010

Strategies to Reduce DOD Building Energy Use by 50%

DOD manages over two billion square feet of building space. According to DOE, “Residential and commercial buildings account for almost 39 percent of total U.S. energy consumption and 38 percent of U.S. carbon dioxide (CO2) emissions.” With the very aggressive goals established for energy reduction in DOD over the next several years, this sector must be considered carefully. Vince Marshall of Cherokee Energy Management & Construction took a look at a couple recent reports, one from Amory Lovin’s Rocky Mountain Institute and the other from the National Renewable Energy Laboratory. It’s a good day for Colorado! Highly recommend reading for Energy Managers and Commanders responsible for making energy goals. Read on…….

Building energy consumption is a significant portion of the total energy consumed by DOD. Within the past few weeks, studies by the Rocky Mountain Institute (RMI) and National Renewable Energy Lab (NREL) have focused on whole building approaches to reducing building energy use.

Rocky Mountain Institute’s- Whole Building Retrofits: A Gateway to Climate Stabilization. Is a high level approach to create significant energy savings by looking at a building as an entity and not as individual systems. Many times designers, engineers and even building owners see building systems such as space cooling, heating and domestic hot water heating as having independent functions and not how they can all work together.

It is extremely cost effective to upgrade major HVAC systems by “piggybacking” on planned capital improvements. That is to identify ageing systems and upgrade to a more efficient system when that unit reaches the end of its useful life. Often we see a “Replace in Kind” approach with whatever was there before instead of spending a small amount of capital to significantly increase efficiency. Paybacks on these marginal expenses are superb.

NREL’s Technical Support Document: Strategies for 50% Energy Savings in Large Office Buildings is a 163 page, in-depth road map to attain a 50% reduction in energy use for large commercial buildings. This is as compared to ASHRAE 90.1 2004/ 2007 editions. The report is lengthy, but easy to read and makes good sense.

The following are summaries from this document:
  • Achieving 50% energy savings cost effectively requires an integrated building design—an approach that analyzes buildings as holistic systems rather than as disconnected collections of individually engineered subsystems. We analyze the complex interactions between building systems and ensure the building will operate as efficiently as possible. 
  • Careful attention is paid to simulated comfort indices to ensure indoor environmental quality is not sacrificed in the interest of energy savings or costs 
  • We recommend off-the-shelf technologies that are available from multiple sources, as opposed to technologies or techniques that are available only in limited quantities or from one manufacturer. 
The following energy efficiency measures played important roles in reaching the 50% energy savings target:
  • The baseline hydronic VAV system was replaced with radiant heated and cooled slab ceilings with DOAS for ventilation. ( Dedicated Outside Air System) 
  • The DOAS design was tailored to address climate-specific requirements as follows: sensible and latent energy recovery equipment was used in humid climates, sensible energy recovery equipment was used in marine and very cold climates, and indirect evaporative cooling (IDEC) was included in dry climates. 
  • Waterside economizing was incorporated in dry climates. 
  • Lighting power density was reduced to 0.63 W/ft2 in offices spaces and occupancy sensors were assumed in infrequently occupied zones. 
  • Day lighting controls tuned to maintain a 27.9 fc (300 lux) set point. 
  • Entrance vestibules and envelope air barriers were included to reduce infiltration. These features were important to avoid condensation on radiant cooling surfaces in humid climates. 
  • High efficiency boilers (condensing, nominally 98% efficient), chillers (COP of 7), air distribution units (69% total fan efficiency), and service water heating (SWH) equipment (90% thermal efficiency) was installed. 
  • Façade WWR (Window to Wall Ratio) was reduced to 20% and window properties were modified to reduce solar gain, improve overall envelope insulation, and reduce construction costs. In low-rise buildings, double pane windows with low-emissivity film and argon fill (U-0.235, SHGC-0.416, VLT-0.750) were installed; in high-rise buildings, double pane windows with low-emissivity film and tinted glass constructions (U-0.288, SHGC-0.282, VLT- 0.55) were used.
  • Exterior wall insulation was added in cold climates (up to R-19.5 continuous insulation (c.i.) for the low-rise case and R-22.5 c.i. for the high-rise case). 
  • Total plug loads were reduced by 23% to 0.68 W/ft2 (7.3 W/m2) by purchasing high efficiency electronic equipment and employing control strategies to eliminate plug loads when equipment was not being used. 
As we all strive to meet annual energy reduction goals, these are two really good articles filled with solid ideas and it is worth your time to read them.

[i] U.S. Department of Energy (DOE), 2008 Buildings Energy Data Book. Prepared for the DOE Office of Energy Efficiency and Renewable Energy by D&R International, 2008.

1 comment:

Anonymous said...

I would also add that they integrate variable speed drives to regulate power output, along with some high-tech solar panels.