The cool pantry has maintained an average temperature of 55°F—even during the summer months—using just the external fan and differential thermostat.
Greenhouse growing. The greenhouse area in the garage space was one of the project’s biggest design gambles. The main goal was to grow food year-round without having to actively heat and cool that space. The cisterns, with their large concrete and water thermal mass, were employed, with the sun providing the heat source. Both raised beds and an aquaponics system were built into this space to see which would work the best, both efficiently and productively, year-round.
In an attempt to decrease the garage-building expenses, I chose 2-by-6 wall construction with a layer of external EPS as a thermal break. However, the labor to install the EPS, add angle iron to support the heavy fiber cement board cladding, and the use of extended-length fasteners negated my planned savings. Besides less insulation in the walls, it also introduced a moisture issue given the exposed and thinner part of the stem wall (versus the double wall used in the remainder of the house). This lower-temperature stem-wall section exposed in a warmer, higher-humidity space causes water condensation, introducing mold concerns if left unchecked.
The greenhouse area has performed very well (validating the passive heating and cooling approach with the cisterns), but has also introduced some other issues. The aquaponics system showed a growth rate of about 30% greater than the raised beds at growing the same vegetables, and I was extremely excited about expanding that system. However, when the temperature dropped into the high 50s and low 60s in the greenhouse, the Rocky Mountain white tilapia went dormant or died off, which then also slowed the symbiotic growth of the plants. This can be remedied by using slower-growing, colder-temperature fish varieties like blue gill, catfish, and carp, but tilapia have easier maintenance characteristics that make the other species less desirable.
The aquaponics system has also considerably increased the humidity levels in the garage. In the summer, the humidity is exhausted outside through the automatic vents. However, in the winter when the windows need to stay closed to preserve heat, the humidity levels rose from 30% to roughly 60%, causing some mold and moisture issues across that entire garage space. I installed an ERV there to conserve energy and heat while exchanging the internal moisture-laden air with less-humid outside air.
The winter temperature in the garage-greenhouse dipped to 58°F at its very lowest; it was usually in the low 60s. This is an almost 2,000-square-foot space that is not actively heated, but uses passive solar gain and the thermal mass in the concrete slab, along with the cisterns and the water within them. I expect that performance to increase next year, since the cistern water is estimated to gain 7°F to 10°F over the summer, becoming a significant thermal battery for the greenhouse to draw from in the winter.
I must admit, we were holding our collective breath the first year as we tracked how all the systems operated. When the initial results started coming back, I became cautiously optimistic. As the year progressed, those results continued to be very positive and some of the systems demonstrated performances above their predicted capabilities. By the end of the year, we knew we had made good choices and now we can’t imagine living any other way. There are some things I would have done differently in hindsight, and some that I didn’t predict well, but overall, we are thrilled with the results.
Our friends and neighbors walk through our house and are amazed at how it operates so well with so few energy inputs. Many of them expect to find us huddled, wearing blankets for warmth, and trying to figure out which few appliances we can run from the PV modules. Instead, what they see is a “normal” house—but one that operates with few external inputs besides the sun and rain.