California - Energy/HVAC Design

The real idea was to have no HVAC system at all.  It a mild climate with many sunny days, and the site has excellent solar access, so our primary heat would be the sun.  There are also usually cooling breezes from 4pm on most of the summer, and it gets quite cool at night except when the Santa Anna winds blow (usually late Sept), so we will use passive cooling as well. If we get a prolonged period of Santa Anna's, the house will undoubtedly get hot, but since they usually only last 3-5 days and we're usually not here anyhow, it shouldn't be a problem.  We will need to have movable shades for the windows, since the September sun position is about the same as the March position, meaning that we will have to block all solar gain on those hot days.  When we're not there, all windows will be covered with fire shutters, so there will be no solar gain

We decided on an R30 walls/R40 ceiling more for convenience and budget reasons than based on modeling that said this was enough insulation.  I did throw together a simple model and based on that, this seemed like a good insulation amount..but then I don't really know how many degree days we actually have, so its just a guess (likewise, our solar insolation numbers are a guess also, since we're in an area that just moving a few miles can make a big difference in how often your site is in the fog/clouds).

For backup heat we have a woodstove as our primary source.  Since heat from the woodstove may not be easily moved to the north side of the house, we are installing an electric toe kick heater for the occasion when the bathroom has stayed cold.  We've designed in a path for a duct to run from near the woodstove back toward the bathroom and bedroom, but won't build it until we know its a problem.   The biggest issue is that unless we can tie into the blower kit that is available for the woodstove we won't be sucking in warm enough air to make it worth using the fan energy to move air from south to north.

There is no central ventilation system, but there are spot fans in the bathroom, kitchen and laundry.  The idea is to run them regularly in the cold season, and open windows when it is warm enough out to do so.

Because we want to be zero carbon, we will use no propane.  This means that we will have an electric hot water heater, and have to deal with its slow recovery time. We originally were going to put in a solar hot water collector, but since we're usually not there in the summer, we have to worry about overheating.  A simple solution would be cover, but since the only logical location was up on the dormer, and tile roofs are subject to breakage when you walk on them, this wasn't practical.  The other option is a heat dump, but then you're using energy all summer to get rid of heat you didn't want to collect in the first place: it just seemed like a bad idea.  Someday maybe we'll figure out a way, in the meantime we're going to try a heat pump water heater (which alas has an even longer recovery time yet), and see how that goes.