Page 138 - Zero Net Energy Case Study Homes-Volume 2

ZERO NET ENERGY CASE STUDY HOMES OBSERVATIONS
Observations
It has been only one year since the publication of Volume 1 of Zero Net Energy Case Study Homes, yet the context of the design and construction of these types of buildings has shifted sig- nificantly. Interestingly, the case study projects in this Volume 2 incorporate the new features that are now being recognized as currently important even though they were completed well before this awareness was widespread.
One issue, discussed in the Introduction, is the need for load shifting in the California power grid to prevent the exacerbation of the Duck Curve and the effect on carbon emissions. (This issue was discussed also at the end of Volume 1 as an emerging “new design issue”.) But perhaps the most significant new issue, at least to the California consumer, is the phenomenon of grid power outages, both planned (to inhibit the chance of wildfires) and unplanned. Both issues have given rise again to the discussion of battery storage connected to the solar PV systems. Where this was always a system feature for off-the-grid housing, it is now a design strategy to be considered for all grid-connected ZNE homes.
Remarkably, of the six case study projects presented in this Volume 2, three utilize this design strategy and a fourth is slated to add a battery storage system in the near future. The remaining two case studies, as affordable housing projects, understandably could not adopt such a design feature from the primary cost perspective. These six case studies therefore prove to be quite timely in providing attention to the practical issues and experiences with these particular systems and how they have an impact on the project design decisions.
In addition to the new battery storage feature, the six case studies continue to show the com- mon ZNE design strategies employed to create a very low energy use, as measured by the EUI, so that the on-site solar PV systems can provide the annual balance of this amount of energy. Yet there are within these strategies differences in approach that are informative for future ZNE residential projects, as can be seen in the detailed descriptions of the individual case studies.
Observations from the Case Studies in Volume 2
As in the case studies of Volume 1, the principal advanced design strategies used for the proj- ects of Volume 2, beyond the basic ZNE design measures of insulation values higher than code for the entire building envelope and energy-efficient lighting and equipment, were the following:
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Airtight construction to a standard of very low air leakage, which was tested and mea- sured in five of the six case study projects by a Blower Door test.
Since two of these projects are certified Passive Houses, the airtightness achieved was required to be even lower than usual. The concept of airtight construction, and verifying the level achieved via testing and measurement, is now standard practice for almost all ZNE homes. (In the case of projects like the Silver Star Apartments, airtightness is an important design strategy, but inspection by the HERS rater is required in lieu of the testing and measurement.)
Use of heat pump heating and cooling systems for maintaining comfortable indoor space conditions, either ducted or ductless systems.
Heat pump water heater.
All the case study projects utilize this type of water heating equipment, which is now the cost effective non-carbon choice for ZNE homes.
Use of a heat recovery ventilator (HRV) or energy recovery ventilator (ERV).
Zero Net Energy Case Study Homes: Volume 2