Page 30 - Zero Net Energy Case Study Homes-Volume 2

CASE STUDY NO. 6
PASSIVE HOUSE LOS ANGELES (PHLA+)
Energy Performance
Energy Modeling and Post-Occupancy Measurement
Energy Use—Modeling
Small house projects typically do not employ energy modeling as the design proceeds. Usually, the roof space is utilized to the maximum extent possible for the solar PV panels or space is left for the installation of additional panels once the use patterns of the house are established. With the advent of the battery storage component as an integral part of the solar PV system and the planned addition of an electric vehicle (EV), there is little need to estimate the energy demand in advance.
Passive House certification, however, requires the completion of a Passive House Planning Package (PHPP), which is a spreadsheet form of energy use calculation for the house by cat- egory of load. The PHPP therefore demonstrates that the high energy efficiency as prescribed by the Passive House standards are met. At the same time, it is a form of “energy modeling” for the house, providing expected amounts of monthly energy use over the course of a “typical” year for a specific climate zone. This can be used to size the solar PV system necessary to provide ZNE performance. The PHPP numbers can also be compared with the actual measured amount of energy use to identify any unusual effect of post-occupancy use patterns.
The results of the PHPP calculations for this case study house are shown in the chart on the opposite page.
Energy Use—Post-Occupancy Measurement
Southern California Edison (SCE) provides monthly net meter reports to the homeowner each month. A net meter report is the record of the total net electrical energy provided by SCE to the house every month. If the energy produced by the solar PV system exceeds the energy use for a reporting period, typically a month, the total net energy total provided by SCE will be negative for that month. (For a short term period such as an afternoon, the energy from the solar PV sys- tem can be sent to the battery or, if the battery is fully charged, the energy will be pushed out to the SCE electrical grid. In the latter case, the house electrical meter runs backward for a while.)
For solar PV systems without battery storage, if a meter is installed on the system to record the monthly energy generation, then the monthly energy use can be determined from this solar PV meter data and the SCE net meter report: a simple addition of the two numbers will provide the energy use of the house for that period.
For solar PV systems with certain batteries (for example, as in this case, a Tesla Powerwall), the historic data on energy generation and energy flows to and from the SCE electric grid can be recorded and accessed using a built-in metering app at the battery. The house energy use is calculated by the metering app using the same simple addition of energy generated and the net energy imported from the SCE electrical grid. In addition, the charting output of this data by this built-in app at the battery is useful visual information about energy performance trends that the owner can employ to adjust energy use behaviors.
The charts of this case study utilize the data recorded by the Tesla battery system for the record- ed period of operation from March through September of 2019. For the remaining five months of one full year (October 2019 through February 2020), both the energy use and on-site solar energy generated can be reasonably estimated in order to demonstrate the expected ZNE per- formance at the end of one full year.
The energy use for these final five months is estimated utilizing the PHPP calculation for those particular months multiplied by the factor that the actual energy use in the first seven months exceeded the PHPP model, namely 1.5. For the on-site solar energy generated during these final
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Zero Net Energy Case Study Homes: Volume 2