Page 79 - Zero Net Energy Case Study Buildings-Volume 2

Commissioning
Commissioning was managed and carried out by the general contractor and design-build team, as well as by the master system integrator with the extensive work on the omni-control system and the continuing supervision of operations during the early occupancy period.
Renewable On-Site Energy Supply
The building uses a standard flat-panel solar photovoltaic system as its on-site renewable en- ergy supply. Roof area is more than adequate for the size of the system (113 kW) needed to offset the annual energy consumption by the building energy systems, even with the requirement to avoid shading the south-facing skylight glazing.
Energy Design Analysis and Energy Performance:
Modeling versus Post-Occupancy Measurements
Energy Use — Modeling
Energy modeling was carried out during the design phases using EnergyPlus v7.2. The model- ing provided whole building energy use, allowing the team to size the solar photovoltaic system needed for ZNE performance. It was also used for parametric studies to evaluate energy savings resulting from different designs, in particular for the passive systems. The final design model yielded a total annual energy use of 197,000 kWh, or an EUI of 21.2 kBtu/sf per year.
Temperature sensors placed at the concrete floor slab have indicated that the energy model un- derestimates heat absorption by the mass and over-estimates the release of heat from the mass. In future projects, energy modelers will note this difference in the output reporting.
Energy Use — Actual Measurement and Comparison to Modeling Results
Energy use data was separately recorded with the cloud-based monitoring system that also communicated this information to the energy dashboard. The accompanying charts show the energy-use performance over the one-year period from October 2014 through the same month in 2015. The total energy used by the building in this year was 125,500 kWh, or an EUI = 13.5 kBtu/sf per year. This total is approximately 35% less than that indicated by the energy modeling, which uses a “standard” weather file for the location.
This lower-than-expected energy use is likely due to the sunnier winter in a California drought year as well as the tenant’s attention to energy-efficient use of the building, particularly the free- cooling available in the relatively mild climate. (The building was fully occupied in the year that the energy use data was collected.) Another factor may have been the better overall performance of the concrete floor for passive cooling compared to the calculations of the energy model.
The charts on the following pages summarize the modeled performance and the actual perfor- mance of the building in its first year of occupancy. This first year included about three months of non-occupancy by the tenant that now occupies the entire building.
SPECULATIVE OFFICE BUILDING AT 435 INDIO WAY
CASE STUDY NO. 9
Zero Net Energy Case Study Buildings, Volume 2
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