Capturing Sun & Water in the High Rockies: Page 4 of 4

Intermediate

Inside this Article

Diana and Darin Anderson in front of their solar-powered home, at 9,200 feet of elevation in the Rocky Mountains.
The Anderson's Rocky Mountain view.
A snow-capped horizon is reflected in the south face of the home’s high-efficiency, triple-pane windows, which admit solar heat gain while protecting from low winter temperatures.
The main living spaces are all aligned across the south wall to receive solar gain into the high-mass stained-concrete floor. Abundant natural light and stunning views are a bonus.
The home’s long east-west orientation incorporates living, dining, kitchen, and gym space into one “room.”
An integrated greenhouse provides space for vegetable growing and aquaponics (fish farming).
The workout space contributes to the occupants’ sustainability by allowing healthy indoor activities during winter.
A solarium with spa tub provides a four-season experience.
Double-stud, advanced framing provides room for ample insulation. The outer cavity is foam-filled to help exceed Passivhaus standards.
The inner wall cavity is filled with high-density cellulose (center).
A blower-door test revealed 161 CFM air exchanges—exceeding Passivhaus standards.
The greenhouse dominates the southeast end of the home, providing good morning light. The solarium occupies the center space, with the living area on the southwest corner.
Having few windows on the west face reduces summer afternoon heat gain. Metal roll-down shutters and cement-board siding help reduce fire hazard.
Tight construction necessitates an ERV for efficient ventilation. Its ductwork connects to a 140-foot-long earth tube that tempers incoming air.
Twenty-eight 260 W PV modules on tilt-up racks provide enough energy annually to offset all household energy use and, in the future, charge an electric car.
Two SMA 3000TL-US inverters provide grid-tie. During a grid outage (and if the array is receiving sunshine) up to 1.5 kW of power per inverter is available at two dedicated outlets.
Three 4,000-gallon rainwater catchment tanks that provide a year’s worth of water storage and huge thermal mass sit between the garage area and greenhouse.
he north side of the house contains a cold-storage room and the bedrooms, which are thermally isolated from the living space.

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. 

Final Thoughts

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.

Comments (13)

Peter Gruendeman_2's picture

[Doug Kalmer wrote]
>To install enuf 15% efficient PV to heat water
> would cost considerably more,...
The metric I work with is dollars per Watt, or since this is 2016, cents per watt. Single-crystal made in USA PV panels cost at most 1.00 USD per Watt now though the little ones for RVs cost more.
My own PV for DHW system is 1,200 Watts, providing more hot water than this household of one can use even with showering twice a day, laundry, standby losses, etc.
My neighbor's system has 1,920 Watts of SolarWorld panels, purchased new in 2016 (with 2016 dollars) for $1,782, including shipping. Their system, on a sunny day, provides more hot water than the two adults and their two children, ages 4 & 7, can use. One day of solid overcast can be managed without the grid being needed at all. After that the grid is used to to heat the water that is at least partially heated by the PV array. They too have a standard resistance-type electric water heater, which came with their house when they bought it four years ago. Their 50 gallon water heater will soon be replaced with a 80 or 100. 50 gallons is smaller than is appropriate for 2kW as this array provides a LOT of energy in one day.
Pete Gruendeman

Doug Kalmer's picture

My self installed PV pumped closed loop solar water heater cost $1100 and has been working well for 26 years with only an expansion tank failure. To install enuf 15% efficient PV to heat water would cost considerably more, and be less efficient than solar thermal.
http://www.builditsolar.com/Project...

Peter Gruendeman_2's picture

[the author wrote:]
> the water heating is standard electric but in an ultra high efficiency Marathon water heater. When looking at the cost comparison (including the ongoing maintenance) between the electric option (offset by PV panels) and solar hot water heating it was the better all around solution in the build.<

It is difficult to make an economic case for solar thermal based DHW, especially on the modest scale of the single-family home. The author's concerns are all valid. In addition to that, the competing technology of PV is typically guaranteed for25 or more years, has better part-sun/ cloudy day performance and is immune to reduced output in cold weather. That the author was building a large PV array anyways made PV for DHW the obvious choice.

I built a PV array just for DHW because the economics of modest-scale solar thermal really is that far off the pace of PV for DHW. When using it for DHW only, one does NOT need an inverter or grid-tie-- just wire it direct. This is especially true for those of us in a heating dominated climate who get little benefit from the expense of inverter + grid-tie just to run a heat pump water heater. Readers in cooling dominated climates would be well-advised to take this latter approach, unless your state or country does not offer net metering. DC direct from the panels to an electric resistance water heater is a cost-effective option everywhere, especially at cold sites and or under frequently overcast skies.

Electric resistance water heaters have been 100% efficient since the heating element was designed into the interior of the tank some time around the Second World War. [Prior to that, some makers put them on the outside of the tank, under an insulated cover.] The Marathon mentioned by the author is no doubt a much better insulated unit but still uses the same 100% efficient element everybody else uses.
Pete Gruendeman

mp5a2@kyfho.net's picture

Would you be interested in selling your plans and related information / contractor cost breakdowns?

drandersoninc's picture

I had not considered that up to this point, but yes I believe I would. Alternatively, or in addition, there could be (for the lack of a better term) 'consulting time' to address any specific questions / clarifications from the plans. Just bear in mind that I'm not going to be a certified professional, it will simply be my personal building experiences both positive and negative that can be applied in concept to other projects.

mp5a2@kyfho.net's picture

Thanks. If you could provide a way for me to contact you?

drandersoninc's picture

Message sent, please reply via that email if you received it. If you don't see it check your 'Spam' folder as it may initially go in there.

Peter Gruendeman_2's picture

[The author wrote]
> I installed an ERV there to conserve energy and heat
> while exchanging the internal moisture-laden air with
> less-humid outside air.
Based on your description, this would be spelled HRV as you are recovering the heat but discarding the moisture. See:
https://en.wikipedia.org/wiki/Energ...
People love the term "energy recovery" so they apply it to all heat exchangers, whether they recover the latent energy or not. In the author's case it was installed specifically to discard the moisture so installing an ERV to recover that moisture would have been pointless.
Pete Gruendeman
La Crosse, WI

drandersoninc's picture

For the intent of the ventilation unit (moisture removal as the primary purpose) that is a fair statement. However the unit is a "Panasonic FV-04VE1 WhisperComfortTM Spot ERV Ceiling Ventilator" so it is referred to in the article as what the manufacturer markets the unit as (ERV vs HRV). In full disclosure Panasonic tech support attempted to dissuade me from using the unit for moisture removal as that is not it's intended application. However for the specific characteristics of my implementation it has functioned very well in that role.

Anonymous _6033's picture

The "Power Points" email mentions solar water heating as part of the design but I see no mention in the article. How is domestic hot water heated?

drandersoninc's picture

That statement in the "Power Points" was incorrect, it was a portion of the article that was not sent for my proof reading unfortunately. To answer your question the water heating is standard electric but in an ultra high efficiency Marathon water heater. When looking at the cost comparison (including the ongoing maintenance) between the electric option (offset by PV panels) and solar hot water heating it was the better all around solution in the build.

drandersoninc's picture

There is a cost breakdown but at a subcontractor / construction area level. There is also areas that I constructed on my own (the general contracting, building the greenhouse area, painting, wall trim, etc) that make the breakdown more difficult. An estimation of the cost per square foot with assumptions on hourly rate or % for my effort would be more readily possible.

The cistern construction, plumbing, and layout as a part of the larger rain harvesting system I do have all the diagrams, spreadsheets, and details. This has the potential to be another sub-article in a future HP issue provided enough interest from the community.

ben_marko's picture

It would be great to see a materials cost for the project. I would like to see how the cisterns were constructed, as well as how they are plumbed.

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