Page 56 - Zero Net Energy Case Study Buildings-Volume 2

CASE STUDY NO. 8
IBEW-NECA JATC TRAINING FACILITY
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Zero Net Energy Case Study Buildings: Volume 2
Energy Design Analysis and Energy Performance:
Modeling versus Post-Occupancy Measurements
Energy Use — Modeling
Energy modeling was used extensively during the design phase to evaluate whole building en- ergy performance and to do parametric studies of the cost effectiveness of low-energy design alternatives. Whole building modeling was carried out using the eQuest program, which showed for the final design a total energy use of 237,500 kWh per year, or an EUI of 18.0 kBtu/sq. ft. per year.
Since natural ventilation is a principal strategy to reduce energy use and needed to be included in the energy use estimate, the design team used CFD analysis in and around the 3-D model of the building, combined with the temperature data contained in the weather file, to evaluate when natural ventilation and night flushing could replace normally mechanical cooling. Through these meticulous calculations, the modelers determined that the annual reduction in cooling load seen by the mechanical system would be 16%. This factor was then used directly to reduce the cooling load results from the eQuest energy model in order to simulate the effect of natural ventilation. The accompanying charts on the energy modeling results incorporate this reduction factor.
Energy Use — Actual Measurement and Comparison to Modeling Results
The master system integrator reports the measured performance results for the second year of the building’s operation (July 2014 — June 2015) as shown in the accompanying charts. The second year is reported since commissioning was completed at this point and the operational characteristics had been established. The total energy used by the building in this year was 215,300 kWh, or an EUI = 16.3 kBtu/sq. ft. per year. This total is approximately 10% less than that indicated by the energy modeling.
Metering on the building does not correspond exactly to the energy categories of the modeling results. The charts showing measured results therefore combine heating, cooling, pump energy and ventilation energy (fans) into the single category of “mechanical”. Another difference is that the energy modeling input assumed that the building would be closed in June and July, since there would be no classes during this period, thus showing little consumption in those months. Not surprisingly, the building is now open for other uses in that time period. In spite of this added functional use of the building, the actual energy consumption is still less than the modeled total. The measured data shows a much lower fraction of energy use going to the plug loads, which likely explains the lower overall measured annual energy consumption despite year-round activi- ties at the facility.
As a further note, the solar thermal system was not metered as part of the overall energy use monitoring system to determine the non-renewable energy offset by this system. Electric energy used for its pumps and backup heating is included in the “mechanical” energy total, however.