Page 88 - Zero Net Energy Case Study Buildings-Volume 3

CASE STUDY NO. 14
CALIFORNIA DMV FIELD OFFICE
Energy Design Analysis and Energy Performance
Modeling versus Post-Occupancy Measurement
Energy Modeling
The energy modeling done as part of the PV system sizing included a comprehensive analysis of energy use by type of load for the building as designed. eQuest v3.65 was used for this purpose and automatically provides the energy use estimates by category of use. The modeling results yielded a total annual energy use of 311,200 kWh, or an EUI of 53.5 kBtu/sf per year. Since the purpose of the modeling was not “predictive” in any way or done as an assist to the building de- sign effort, the result was somewhat conservative to ensure that the PV system was right-sized to produce ZNE performance.
Energy Use—Actual Measurement and Comparison to Modeling Results
Because of the late introduction of the ZNE performance goal to the project, no plan was made to meter the various types of energy use in the building. The energy production by the PV system is monitored, however, so it is possible to obtain totals of energy use for the project by combining the energy production totals with the utility’s net metered electric energy and the metered use of natural gas.
Calculating this, the total energy use for the project in the year July 2015 through June 2016 was 224,250 kWh, or an EUI equal to 38.6 kBtu/sf per year. As expected, this was a good deal less (30%) than the amount conservatively estimated in the energy modeling.
The result is the total energy use by type of energy only, electricity and gas, not by category of use. Since gas is used only for heating and domestic hot water, a rough comparison can be made of this categories with gas use. Again, the intention of the modeling was not to inform the design, so there is limited value in drawing comparisons between modeled and measured totals.
Energy Production versus Energy Use: Zero Net Energy Performance
The solar PV system produced 232,000 kWh in that year from mid-2015 to mid-2016, equal to 43.4 kBtu/sf per year, therefore more than adequate to provide a cushion for ZNE performance, the immediate goal of the state agencies.
The Cumulative Net Energy Performance curve exhibits a near ideal representation of a well- balanced ZNE production versus use over the course of a year.
Post Occupancy: Observations and Conclusions
This concluding section of the case study typically identifies those important aspects of the building where the ZNE design goals were not completely met, where an innovative system or building feature design failed to some extent to achieve the performance objective, or where unanticipated user behavior affected the energy use in a significant way. Because of the history of this particular project—a sufficiently large solar PV system was added to the project during construction to make it ZNE—this same type of cataloging of “lessons learned” cannot be done.
It is possible to observe generally that such “ZNE retrofits” can be done with sufficiently energy- efficient buildings and ample site area for the PV system. As the California DMV constructs simi- lar new-building facilities with ZNE performance goals in the many types of climate zones across the state, it will be interesting to compare design features and performance results for the entire set of buildings in this programmatically prescribed typology.
Moreover, in contrast to this case study, these new facilities will be designed to achieve ZNE performance beginning at project inception and will employ integrated design strategies, fea- tures and technologies to minimize the energy use of the building to a higher standard. Such an integrated approach to the energy use and energy production building systems will necessarily result in the most cost-effective design choices.
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Zero Net Energy Case Study Buildings: Volume 3