#12.007.02: EUI, ARC vs. NRELPosted: 11 June 2012 | Author: bcooper | Filed under: Uncategorized | Leave a comment »
Author: Chad Edwards
In the previous post, we took a look at the Energy Use Intensity (EUI) rating as a standard metric for a building’s energy economy and its relationship with the Commercial Building Energy Consumption Survey (CBECS). We made a connection between these metrics and a Net Zero Energy Capable (ZEC) or NZE Ready building. Let’s take a look at how this can be applied to a built facility.
The Greater Cincinnati-Dayton Region American Red Cross (ARC) needed to leave their outdated space on 720 Broadway downtown. They were interested in a highly flexible building that would remain emergency-response ready during the worst weather Cincinnati can muster. Their new headquarters needed to be a statement building, as sustainable as their budget allowed with LEED Silver as a minimum target, close to 50,000 square feet, squeezed between a park and a freeway. They needed all of these attributes while making sure to have the best value for their non-profit mission and being good stewards of their financial resources. The American Red Cross board had a great attitude regarding high performance issues, if the suggestion came with a 10 year pay back or less, then it was worthy of consideration. With this threshold, the design team developed project specific design solutions, instead of focusing on rule-of-thumb scenarios.
Energy modeling is a tool that was incorporated early. Instead of simply using the tool to document what had been designed to document the energy efficiency per the LEED Rating System, the design team used several models to help make design decisions. Duke Energy assisted with several comparisons of competing systems. This helped the design team get specific data to make better decisions. Alternate 1 included water source heat pumps with air distribution systems, dedicated outside air units using geoexchange closed loop wells, and an electronic building automation system (BAS). Alternate 2 employed water source heat pumps with air distribution systems, dedicated outside air units using roof mounted cooling towers and a BAS. Alternate 3 included two 75 or80 ton air cooled chillers, central air handling equipment on each floor with full economizer capability, VAV air distribution system and a BAS.
It is important to understand the difference between geothermal and geoexchange mentioned in Alternate 1. The design and construction industry and user culture have wrongfully merged the two terms leading to some confusion and unintended consequences. Geothermal taps into the heat of the earth 2 to 3 miles deep. This heat is most often used by a utility operator or central plant for a community or campus and is considered a renewable energy technology. As architects and engineers design systems for clients with renewable energy criteria or mandates, this is a critical point.
Geoexchange uses the earth as a heat sink, exchanging the building’s heat in the summertime into the earth or pond while utilizing the lower temperatures to cool the building. Geoexchange wells are usually between 250-400 feet deep. Geoexchange is an energy efficient measure, not an energy source. Tempering from 55 degrees is less energy intensive than tempering from 10 degrees in the winter time. In the summer, utilizing the 55 degrees found in the earth is an energy bonus when removing heat from the interior spaces.
The energy models proved useful in understanding the best system for the Red Cross and their 10 year payback approach. It was widely accepted and predicted that the geoexchange system would prevail. A test well was drilled to study the conductivity of the soil. As geoexchange pipes are installed in the well, conductive grout is used to maintain continual contact and transfer of energy with the surrounding soil. This conductive grout is designed to match the surrounding conductivity of the soil. If it is not as conductive, then the grout will not transfer the maximum energy into the soil. If the conductivity is greater than the soil, then money is wasted. The tipping point for the Red Cross project was the price of the conductivity grout and its installation. In the end, the water source heat pumps of Alternate 2 were installed, which was counter to the team’s original assumption. The commissioning agent even ran through a second analysis to verify the findings, and a university ran through the scenario a third time for confirmation due to the counter-intuitive results.
With our upfront study, how does the Red Cross building compare with the national average as well as the top efficient structures in the country? Through systems analysis, lighting selection and controls, a strong thermal envelope, and other approaches, the building is able to achieve a greatly reduced EUI. The first year’s energy data calculates an Energy Use Intensity (EUI) of 35.4. We expect year two to be even better due to the facility team making adjustments and the mild winter this past year. To put that into perspective, per the U.S. Department of Energy, the 2003 national average for this building type is 90. This national average is the 2030 metric that several architects measure against as base line. Further, the National Renewable Energy Lab (NREL) in Colorado, the U.S. Department of Energy’s flagship Net Zero Energy facility, has an EUI of 35.0. It is important to keep in mind, that the NREL design team worked very closely with the user to design policies built around plug loads, for instance using laptops in lieu of PC workstations. In the 35 EUI range, plug loads can account for a quarter or more of the energy consumption of a building. While this is a significant contributor to the energy usage of a faculty, in the case of the Red Cross, plug loads were not within the scope of the design team. Looking at the costs, the NREL was built to a tune of $288 per square foot, while the American Red Cross building came in at $117 per square foot. That’s $8.23 per EUI for NREL compared to just $3.30 per EUI for the Red Cross. The end result is a very high performing building while staying within, even under, the given budget. Having a high performing building does not have to drive the costs out of control. It is important to think holistically and look for tradeoffs to maximize the budgeted dollars.
The building is not just a high performing building, the design, while award winning, has also served the Red Cross as a billboard to the community. The building also serves the community by hosting life-saving training sessions and seminars, as well as key sustainable events, such as the Green Umbrella Community Forums. This is a great way for the general public to learn about more advanced sustainability strategies, not just energy efficiency, such as the Metropolitan Sewer District of Greater Cincinnati funded vegetated roof and bioswale.
“(The) bottom line is that the building is doing what it was designed to do…be a green building, save on energy costs, be a training/community center and when the tornadoes hit with a flick of the switch a fully functioning Disaster Operations Center. We are very pleased with how the building is performing and serving the community.”
Steve Drefahl, Chief Operating Officer, Greater Cincinnati-Dayton Region American Red Cross
Chad Edwards is a principal of emersion DESIGN LLC which has assisted in Melink Corporation’s Net Zero Energy retrofit, created sustainability guidelines for MSD’s nation leading Lick Run Watershed Master Plan and is guiding Village Life Outreach through a Master Plan for the Roche Health Clinic Campus in Tanzania.