Building with Dirt (Part 2)

The first post about our house was literally about building with dirt. Here, I wanted to write about the home's energy efficiency systems. Although there are a few things that we would do differently if building all over again, which I'll mention below, the house in general performs very well---cool in the summer, warm in the winter. Our total energy bill was under $20 per month for the first few years we lived there. Adding a chest freezer and supplemental heat in the greenroom---plus a rise in energy prices---brought the bill to about $28/month, where it remains today.

Kitty contemplates the woodburning stove. Photo by Aaron.

Heating

Our house is heated with passive and active solar, supplemented with a wood-burning stove. The “passive solar” is simply the orientation of the home: we have large south-facing windows (despite the fact that our best views are to the east) with the right length eave (about 2 ft) to provide shade in the summer and sunlight in the winter, when the sun’s lower in the sky.

Although this is just the downstairs, the upstairs is passive
solar too. These windows face south.

When we were building, in the dead of summer, a friend remarked on how dark our unfinished house seemed, despite all the windows. Although natural light looks great, we were thrilled. The house was performing exactly as it should! It is dark and cool and shady in the summer, and glowing and sunny in the winter. Better living through trigonometry!

From the upstairs, looking down. The house stays dark in the summer.

Sunny outside, nice and cool inside.

On the other hand, plenty of sun gets through these windows in the winter.

Sun through the south windows in February.

(Side note: when I was a precalculus teacher, I had the students do a trigonometry assignment where they calculated the length of eave necessary for good passive solar design.)

Trigonometry assignment on
designing a passive solar house.

The “active solar” is 3 solar hot water panels, 4 x 10 ft, which provide plenty of hot water for our domestic needs 99.5% of the time.

Solar hot water panels on the roof.

When the 120 gallon water tank reaches a chosen temperature, excess hot water is routed through the concrete floors of the house for hydronic heat.

Aaron laying Wirsbo for the in-floor
solar hydronic heat.

What this means for us, practically speaking, is that in the winter we use hot water sparingly, because all the excess goes to heating the floors; in the summer, hot water is a waste product (we do not want it going through the floors), so we take hotter showers, run hot water in the laundry, etc. The panels are at an angle that maximizes solar gain in the winter, which helps avoid too much summer heat, and we also cover one panel with a tarp when necessary. The system is a very simple one (it lacks a “heat dump” which would avoid this summer heating problem) but it works very well.

Solar panels on a sunny winter's day.

The solar-heated hot water tank has an electric backup, in case it’s cloudy for a while. Because we get so much sun all year round here in New Mexico, we almost never need it. In fact, we keep the electric backup breaker flipped off at all times, and have only had to flip it on a handful of times when it was cloudy for too long or the solar system needed repairs.

Sometimes it is cloudy in New Mexico! But not often. Go solar.

The only downside to the solar hot water/hydronic heat system: it has needed far too many repairs since it was installed in 2008. The pump broke, a panel sprung a leak, and the contractor has been unable to solve a “knocking” problem (boiling inside the pipes – it literally sounds like someone knocking on the roof in the hottest hours of the afternoon; it’s also bad for the pump). We love having a solar hot water system and would recommend the overall setup to anyone, but get references before you choose a contractor.

Insulation

The 14-inch thick compressed earth block walls do a great job of providing thermal mass and moderating temperature swings. The summers are cool and crisp inside our walls (no AC needed). We have foam insulation on all sides but the south side of the house, and blown-in cellulose in the stick-frame upstairs and in the roof.

Yellow spray foam insulation.

We hired a contractor for the blown-
in cellulose in the upstairs walls.

However, it is easy to rent a blower and
do it yourself. We did the cellulose in the
ceiling/roof spaces ourselves.

It is messy, though.

Aaron working on the blown-in cellulose.

So the summertime cooling of the house is great; as far as the wintertime is concerned, I was slightly disappointed; I had read tales of passive solar homes that “bake” during the cold sunny winter months, so much so that doors and windows have to be thrown open. That sounds dreamy. Our house is not that. I think the high ceilings in the big room, leaks around the windows and doors, and the relatively low final total R-value of the walls and ceiling are the culprits. Between the passive and active solar, the home stays in the low to mid 60s almost all the time in the winter. That’s better than nothing---a stick-frame house with no solar hot water and indifferent orientation with respect to the sun would be much worse off.

To raise the heat to a more comfortable high 60s/low 70s temperature (Aaron and I disagree on “comfortable”), we supplement the passive and active solar with our Vermont Castings Encore wood stove. We also enjoy cooking on the wood stove.

Aaron tending the wood stove.

Cozy cat.

The upstairs of the house is entirely unheated, except for big south-facing passive solar windows and the chimney of the woodburning stove, which runs through the bedroom. The chimney is double-wall and insulated at that point, for safety and to code, but it still gives off just enough warmth to make the upstairs temperatures pleasant without cooking (as upstairs rooms often are).

Woodburning stove pipe running through the
bedroom. The built-in fan in the wall to the right
of the pipe draws hot air from above the stove
downstairs into the bedroom.

Greenroom

The greenroom was a later addition, although it would have been really, really smart to design it into the house in the first place. It supplements the heat in the house by pumping hot air into the living room. (For example: the greenroom encloses two large non-operable south-facing windows. It would have been really smart to have those windows operable, for easy air transport between the house and greenroom.) It’s my new favorite room in the house---when I get home on a cold winter day, and the house temperature is in the 60s, it’s great to go lounge in the greenroom in the 80s until the woodburning stove kicks in.

Kitty on the greenroom roof.

Rainwater Harvesting

Aaron installing rainwater gutters.

We collect water from all of the roof area on our property, including two small sheds. We have four rainwater cisterns:

2500 gallons

1600 gallons
300 gallons
300 gallons

For a total of 4700 gallons of water storage. Every year, we’ve tried to water a fairly large vegetable garden using only rainwater. Every year, we’ve failed to succeed completely, but at least two years were very, very close and would have worked if there hadn’t been unfortunate cistern-draining accidents. The other years have been stymied by exceptional drought (three years in a row).

The basic idea is that the cisterns are full of snowmelt at the end of the winter and just need to last through the planting season (May) and the dry month of June before the monsoon rains refill the tanks in early July.

300 gallon cistern by the shed/chicken coop.

The setup is simple and gravity-fed, although we’ve become too greedy with plantings in our upper garden and now we think a pump will be necessary to supply water to the upper garden from the 2500 gallon cistern behind the house. The 1600 gallon cistern has plenty of elevation drop above the lower garden.

The 1600 gallon cistern. We did all the plumbing of the rainwater system. The 2500 gallon cistern is hidden behind the house.

This cistern drains by gravity to a spigot at the lower garden. From here there is an automated drip system.

We’ve had to learn a bit of plumbing to handle our rainwater systems, and we do have problems with freezing and bursting in the winter if we’re not careful about preventative measures.

The drip irrigation is hooked directly to the tank with the auto-watering controllers shown here. When we first went to Home Depot and Lowe’s, we were told that auto-watering systems rely on high water pressure to open the valve and that they wouldn’t work on gravity fed, low-pressure systems. Indeed, we tried a few controllers just to make sure and <link>this is the only brand we found<link> that works on a gravity-fed system. The upper garden is divided into three drip zones to minimize the pressure required to water it all. The lower garden is on two zones. We use the 300 gallon tanks on the chicken coop and on the back shed to water various fruit trees.

The drip irrigation controller in a patch of mint. This is the
only brand of drip controller that we've found will work with
low-pressure, gravity-fed systems. This is an old picture;
we now have multiple zones and a single controller that
alternates watering between the zones.

Dripper dripping in the spinach.

Gray/Black Water

All of our household’s water goes to a septic tank first and long rows of shallow plastic infiltrators for the leachfield second. The system is designed to shunt water effectively to a small orchard of 11 fruit trees which are planted on the leachfield.

Septic leachfield infiltrators.

The roots of the trees are tapped in to the gray and black water coming from the infiltrators; we provide supplemental water when it’s hot, but much of the time the trees get enough from the “liquid gold” coming from our toilets and sinks. We do nothing to stop shrubby weeds from growing under the trees and above the infiltrators, as their roots will also help with aerobic decomposition in the soil; shallow leachfield systems like this need to have relatively oxic conditions to effectively deal with breaking down waste.

Happy fruit trees.

Conventional wisdom is that you don’t want to grow any ground crops on black water (er, that’s poopy water, in case you were wondering) because of risk of disease transmission, but fruit trees are allegedly very effective at filtering out the nasty stuff. I say “allegedly” because concrete, peer-reviewed evidence in the literature is hard to find. I’ve heard this given as the reason it’s usually safe to eat tree fruit when travelling in the third world, but not uncooked vegetables, like lettuce. At any rate, we grow our fruit trees right on top of our leachfield infiltrators without worrying about root damage. The system is performing perfectly in terms of smell, and we do occasionally peek into the infiltrators through the observations ports (ew) and everything looks fine, as far as we can tell.

We make sure to use household products (dish soap, laundry detergent, shampoo, etc) that seem the most biodegradable and benign (although this is somewhat of a guessing game). We never let paints or solvents or other harsh chemicals go down the drain (although this should be true for anyone with a septic tank; it’s bad for the microbial flora that help make any septic system work).

Part 1: Building with Dirt