Page 128 - Zero Net Energy Case Study Homes-Volume 2

CASE STUDY NO. 11
SOL LUX ALPHA
The developer provided a practical solution for the owner: set the default operation of the system so that the EV is charged at night directly from the utility grid, not the house batteries. This is best for the utility’s demand profile and the cost to the owner, since utility rates are typically lowest at night. Another advantage of this operational design is that a 240V charging station can be used with the utility power connection, whereas charging from the Tesla Powerwall is limited to 120V power, which provides a much slower rate of charge.
Therefore, as designed and installed, under normal operating conditions the house batteries are only used in conjunction with the house energy demands and can be scheduled accordingly. However, if the power from the grid is interrupted for an extended period of time, the EV can be charged from the house batteries, though only at “level 1” rate of charge to prevent excessive battery drain.
Battery storage for common areas and the elevator is an entirely different system. The elevator requires battery equipment that produces 208V and 3-phase power. The system selected was a lithium ferrous phosphate (LiFePO4) Blue Ion6 battery to provide the necessary voltage capabil- ity, combined with three Schneider inverters7 to produce the 3-phase power.
Energy Performance
Energy Modeling and Post-Occupancy Measurement
Energy Use—Modeling
In order to receive the Passive House Institute US (PHIUS) certification, the developer was required to submit the completed Passive House Planning Package (PHPP) to document that all required standards for certification were met. The resulting energy use “model” represents an ideal performance for the conditioned space of the building (the four identical condominium units). The chart on the opposite page shows the monthly energy use per square foot as calcu- lated by the PHPP.
Energy Use—Post Occupancy Measurement
Data on the energy use and production for each unit and its assigned solar PV system is routine- ly recorded on the Tesla Powerwall and can be accessed using the system’s software (its app). This was done for the three units that were purchased in 2016 and 2018, for which there is more than 12 months of recorded data. (The third unit, Condominium Unit C, is recently purchased and does not yet have one full year of recorded data.)
The charts on pp. 111-112 show the actual measured monthly energy use for Units A, B and D, the identical units located on the second, third and fifth floors. During this period of time, only the occupants of Unit A owned an EV. As described above, the EV charging occurs directly from the utility grid; it is not included in the data monitoring of the Tesla Powerwall, so the chart of measured monthly energy use for Unit A does not include the monthly energy use data for the EV. It is useful to compare these to the “modeled” energy use for the “ideal” unit, which shows the variation caused by the different behavior patterns of the occupants.
6 See Blue Planet Energy, https://blueplanetenergy.com/products/blue-ion2. 7 See https://solar.schneider-electric.com/product/conext-cl/
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Zero Net Energy Case Study Homes: Volume 2