Page 136 - Zero Net Energy Case Study Buildings-Volume 2

CASE STUDY NO. 11
THE EXPLORATORIUM
124
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 carried out during the design phases using eQuest v3.65. The modeling analysis showed a total energy use of 2,668 MWh per year, or an EUI of 47.2 kBtu/sq.ft per year. The much larger building (approximately 200,000 sq. ft.) with its limited access to daylighting and the added energy loads for a building of this type are the reasons for the larger EUI compared to the other case study buildings in this Volume 24. As a reference point, the ASHRAE 90.1 2007 baseline EUI was calculated to be 81.3, so the Exploratorium’s modeled energy performance is more than 40% lower than the recommended ASHRAE benchmark.
Energy Use — Actual Measurement and Comparison to Modeling Results
Since there was no master system integrator included on the project team, there is currently no integration of energy use data monitoring for the different energy subsystems and there is no design of the metering system to ensure that data recording is in place appropriate to type of energy use. As noted above in the section, Master System Integration and Control Systems, data from power meters installed at each panel is sent to the BMS via a PEMS. Data extraction from the BMS is difficult and time-consuming and there is no design for real-time reporting to a user interface. Trending information is therefore simply not available. Furthermore, these power meters at the panels may have some inaccuracies since power meters frequently drift and need regular checking.
The building’s energy use as measured by the power meter system has proven to be off by some margin—30% over the first two years of building occupancy—when compared with the utility’s main building meter at the power grid boundary. The latter is reliably accurate, recording the total net metered electric energy flows. The shortfall of the energy use recorded at the building’s elec- tric panels is likely due to a number of contributing factors, including errors in extracting the data from the BMS, some meters not programmed into the system, missed electric panels upstream of the meters, as well as meter inaccuracies that have yet to be determined.
The engineering team believes that the data recorded at the building’s electric panels accurately reflect the percentage of total energy use attributable to each category, namely the lighting, plug load and “mechanical” (that is, heating, cooling, pump and fan energy use) on a monthly basis and for the entire year. As with earlier case study buildings, separate metering for heating and cooling operation was not specified with the heat pump system. Thus the measurement data shows only the combined “mechanical” category.
The methodology used to produce the accompanying charts showing measured energy use by category is therefore to apply these percentages to the total building energy use as measured by the utility meter.
The general trend over the first two years (2014-2015) is that the energy use by the building is constant every month, which is due simply to the small variation in exterior conditions over the course of the year and the fairly constant exhibit lighting loads and plug loads. As can be seen from the annual pie charts and monthly bar charts, there is close correlation of the actual mea- sured energy use with the whole building energy modeling results for 2015. 2014 had similar per- formance results, though the building was still in its tune-up period. The measured annual energy use in 2015 was 2,461 MWh, or an EUI equal to 43.5 kBtu/sq.ft. per year. (Domestic hot water use was not measured separately and is included in the “Mechanical” category of energy use.)
4 Note: the floor area of the tenant space is not included in the EUI calculation except as noted in the chart on the opposite page.