Page 33 - Zero Net Energy Case Study Homes-Volume 2

PASSIVE HOUSE LOS ANGELES (PHLA+)
CASE STUDY NO. 6
five months, the estimated monthly amounts can be directly estimated by using the PVWatts® Calculator16. The correlation is almost exact for the actual recorded solar generation data and so the numbers for the final five months will be a reasonably close estimate.
The chart on p.17 shows the monthly energy use as metered between March and October of 2019 and estimated for the remaining period through February 2020. It can be observed that the actual energy use is 45% higher than that estimated by the PHPP. However, the actual EUI = 10.2 represents a low energy use intensity for three people in the 2,000 sq. ft. house. With the solar energy generated on-site, it will be performing at 25% better than ZNE at the end of the year.
Energy Production versus Energy Use: Zero Net Energy Performance
The charts on the opposite page show the solar PV system performance over the course of one year (March, 2019, through February, 2020), with the first seven months’ performance based on actual data and a reasonable estimate for the balance of the year. The chart of solar energy pro- duction versus energy use shows that the house system will generate about 25% more energy than will be used by the end of the 12-month period.
The cumulative net energy production is a chart that essentially shows the progression of the energy performance toward ZNE by adding each month’s net energy performance to the previ- ous month’s total—if, at the end of the 12-month period, the curve remains on the positive side of the “Net Zero” axis, then the building in indeed performing better than ZNE, i.e., Net Positive. (This chart can also be constructed from the monthly SCE net meter reports.)
Post-Occupancy: Observations and Conclusions
Although the house did not achieve the level of energy performance indicated by the PHPP calculation, it is still Net Positive by a large margin. The solar PV array appears to be right-sized to comfortably meet the building loads. As a demonstration of applied Passive House principles and a ZNE home, the project has proven to be a great success.
Since there are always “lessons learned” in any building project, there are issues to note for consideration in future projects. This is particularly true in these case study homes, which are on the leading edge of design and construction innovation and therefore unfamiliar to most building trades and designers.
For this project, as a case in point, the windows selected proved to be difficult to handle due to their weight. While the triple glazing provided desirable noise control characteristics, it proved to be unnecessary for ZNE performance in this relatively mild climate. The house remains a very quiet environment, but the tradeoff was significant added cost and on-site labor.
The air-sealing of the structure proved to be a challenge, especially with the Passive House standards. The building trades simply are not familiar with the “dos and don’ts” of the particu- lars of their trade with regard to the effect on airtightness. A specialized sub-contractor may be necessary unless the contractor has experience with air-sealing products and techniques. A certain amount of ongoing training in the methodologies of air-sealing wood-frame construction is recommended.
After almost one year’s experience with the kitchen recirculation hood, the owner now thinks that a low-power direct exhaust fan is a better choice because of the lingering air pollutants from cooking by-products as well as odors.
16 See https://pvwatts.nrel.gov/pvwatts.php. The PVWatts Calculator gives the monthly energy generated (kWh) by a particular solar PV system of a specified power level (kW), panel tilt, panel azimuth and geographical location.
Zero Net Energy Case Study Homes: Volume 2
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