With Zero Net Energy requirements for new residential construction in California looming on the horizon, it can be tempting to seek out the next high-tech solutions to get a project over the ZNE hurdle. From solar shingles to heat pumps to LEDs, the options are numerous…and sometimes unnecessary.
On California’s Central Coast we are fortunate to live in a climate zone where sunshine is plentiful and cold weather limited. Because of this, the fundamentals of passive solar design – such as thermal mass, sun angle calculations, and appropriate shading – are still very effective measures for ZNE construction.
Recently, we worked on a residential project where part of the building was south-facing and had a proposed 7.5-foot porch overhang for shading.
We created an energy model for the entire building and noticed some dramatic results when we played with the overhang depth. While maximum shading was effective in keeping cooling costs down (aka zero), it had a marked (and detrimental) effect on heating loads. As the overhang depth was reduced, space cooling increased slightly, but only by a fraction of the decrease in heating energy.
Note: We is modeled with an electric heat pump (for heating and cooling).
After working with several options, we suggested to the project team an optimal depth for the shading, which would balance more direct sun (free heat) with some additional cooling load in the summer. The result was almost 30% savings on electricity use over the proposed design, getting the project that much closer to ZNE.
Interestingly, no overhang could have reduced the total energy use even further in our southern California climate zone, but we know from experience that comfort is negatively impacted when a space receives too much direct summer or autumn sun.
So, on your next ZNE project, consider starting with the basics. Then, when it’s time to optimize daylight or energy efficiency, contact us for some of the more technical calculations.