Congratulations to author Ed Dean and the team at Southern California Edison for their new publication, Zero Net Energy Case Study Homes, Volume 1 — and to all the project teams whose work it describes!

My favorite thing about the book is that, with just five case studies, it demonstrates that ZNE performance is achievable across a wide spectrum of housing types: new single-family homes (the easiest), a single-family renovation, a modestly-sized modular home, single-family production-built homes, and new multifamily housing.

Here’s an excerpt from my foreword:

Members of the ZNE community outside California – in places that have “real” weather – sometimes scoff at the lack of challenge of accomplishing ZNE here. Admittedly, our populous coastal areas benefit from benign climates, but we also have both very cold climates, such as Redding (similar in heating degree days to Chicago), and very hot ones, such as Palm Springs. Other factors also make this a challenging environment for housing innovation, among them high costs, a highly mobile workforce, and a notoriously litigious culture. Thus creating successful, marketable, ZNE projects is a non-trivial feat.

All the projects represented here have met the pinnacle of ZNE achievement: verified site ZNE. That is, not only was each project designed to be capable of achieving ZNE, but utility bills provide objective evidence of occupants’ energy use yielding ZNE in actual operation over the course of a full year. Further, site ZNE (explained in the introduction) is the most difficult definition to meet. These projects therefore demonstrate, importantly, that operational site ZNE (to which source ZNE is equal, for all-electric projects) is an achievable benchmark. These proofs of viability are absolutely critical to supporting the State’s likely push towards residential electrification in years to come. The project developers whose work is showcased here are thus to be both congratulated and thanked for their significant contributions to the future of housing in California, and beyond. Read on, and benefit from their experience.

AIA ZNE Primer cover image

The American Institute of Architects California Council recently published the Zero Net Energy Primer. I had the privilege of developing the Primer for them under a contract with PG&E. The Primer (if I do say so myself) is a handsome, concise, and accessible guide — a mere 24 pages, including lots of pictures of ZNE homes of all flavors (small, large, single- and multifamily, luxury and affordable). The AIACC’s goal in publishing the document is to ease the task facing California architects with the roll-out of the State’s 2019 energy code (“Title 24”). The new code will go into effect January 1, 2020 and — while it doesn’t quite get us to ZNE — represents a significant advance in residential energy performance, and the first time that homes will be required to install renewable energy systems. (Of course, there will be byes for projects where it’s simply not feasible to install them.) The Primer will, I hope, help architects get a handle on the ZNE requirements ahead of the looming 2020 deadline.

Kudos and many thanks to designer Debra Turner for the engaging design, and to architect Steven Lee for his terrific illustrations.

From Predictability of Energy Use in Homes, Lachut, D., et al. (http://www.cs.usfca.edu/~srollins/pubs/igcc14.pdf)

Lots of people complain about energy models — specifically, how they don’t accurately predict how much energy the occupants of a home (or building) will actually use. This complaint misses the point.

The REAL problem with energy models is that there is widespread confusion about what they can/should be expected to do. Predicting actual energy use for one specific household is not on the list of realistic expectations. Approximating the amount of energy a reasonably large aggregation of households might use? Yes, perhaps, in skillful hands.

The main thing that energy models can and should be used for is to compare the relative effects of different variables on a building’s energy performance, holding constant certain assumptions about the occupants’ usage patterns — which, even in the best circumstances, are fundamentally unknown and must be generalized.

It’s important to remember that a home (except in extraordinarily rare instances) outlives any particular set of occupants and behaviors many times over; those are subject to frequent change. Even one set of occupants will change energy-using behaviors after a time — for example, as toddlers outgrow bathtubs and graduate to shower usage … and then avoid bathing at all … and then evolve to multiple changes of clothing and multiple showers a day (think: soccer and muddy shorts and shoes).

Thus it’s a pointless exercise to attempt a precise fit of behavioral assumptions to a specific set of occupants, or think that we can predict their energy use for any but the most fleeting time period. What we should be doing is designing homes to efficiently serve any household that might reasonably be expected to live there over the life span of those homes.

\With that understanding, and the use of standard occupancy assumptions*, we can certainly use models effectively to compare the relative effects of different features on energy use.

Gas & Electric will be hosting our 4-part class series on retrofitting existing homes to achieve deep energy reductions while targeting zero net energy. Here’s the schedule:

• May 9: Overview – yours truly (Ann Edminster)
• May 23: Mechanical Systems – Rick Chitwood
• May 30: Enclosure – Rick Chitwood + Gavin Healy
• June 6: People & Plug Loads – Chris Calwell + Chris Hunt

Register here.