Page 66 - Zero Net Energy Case Study Buildings-Volume 1

CASE STUDY NO. 3
IDeAs OFFICE BUILDING
Energy Design Analysis and Energy Performance
Modeling versus Initial Post-Occupancy Measurements
Energy Use - Modeling
The whole building energy modeling for the IDeAs Building was done in 2002 using the eQUEST interface version 3.61 of the DOE-2 analysis engine using modeling assumptions based on the well-known schedule patterns for the owner/occupant. The modeling analysis early in the design process showed a building EUI (site energy) tabulated at 24.8 kBtu/gsf-year, about 25% above the energy use target of 20 kBtu/gsf-year. A bar chart showing the results of the modeling analy- sis by month is shown on the facing page.
Energy Use – Actual Measurement and Comparison to Modeling Results
Metered data for energy use and energy production has been collected for this building since it was occupied in 2007. For energy use, there is an overall energy use meter and sub-metering for each circuit at the panel board. The solar photovoltaic system is monitored both in the aggregate (the entire system) and by the individual panel.
One of the initial post-occupancy issues was the observation that the metered data for energy use did not match the metered data for the solar photovoltaic system production combined with the PG&E meter for power drawn from the grid. Change-out of some defective meters did not correct the problem and it was determined that the meters were sized for too high a load and can be inaccurate for lower energy demand. Replacing the type of meter resolved the issue and recording of good data started shortly afterward.
As noted above, the measurement of the building’s annual energy use was substantially better than the modeling results over the course of the past four years. For the year from July 2011 to June 2012, the total energy used was 36,000 kWhr with an EUI = 18.7 Btu/sf-year compared to the modeling result of 47,700 kWhr and EUI = 24.8 Btu/sf-year.
The average EUI of office buildings in the western region of the U.S. between 5,000 sq. ft. and 10,000 sq. ft. as recorded in the 2003 CBECS (Commercial Buildings Energy Consumption Survey1), is 72.1 kBtu/sf-year. The EUI for the IDeAs Building is less than 30% of this average amount. (See the bar chart below.)
1 U.S. Energy Information Administration, EIA Commercial Buildings Energy Consumption Survey, Table C5
80
70
60
50
40
30
20
10
0
CBECS
Average 2003 Energy Use for Small Western U.S. Office Bldgs
Modeled Annual Use
Energy Measured Annual Energy Use (2011)
IDeAs Office Building Total Annual Energy Use
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Zero Net Energy Case Study Buildings: Volume 1
Site EUI kBtu/sq.ft. per year
Axis Title