A Cold Study Brings A Gratifying Result

The situation

Chris and Maddy Ecker recently sent Monolithic a study they did of the internal temperatures their “dome-in-progress” maintained during the first two months of 2010. The Eckers live in Galax, Virginia, where, in July 2009, they broke ground for their Monolithic Dome home, a 50-foot diameter oblate ellipse on a 2-foot stemwall. Bad weather halted its completion.

So at this point their dome is unoccupied and has no electricity or heat source, except for a 50-pint dehumidifier powered by an extension cord running from the Eckers’ double-wide trailer.

The dome’s windows remain closed, and the doors are only opened when Chris or Maddy go in to check the inside temperature and empty the dehumidifier.

Chris tells their story that he calls: A Cold Study

So you’re nested in the mountains and up comes a cold spell. What to do? Maddy and I decided to turn our dome-in-progress into a controlled laboratory with the goal of putting the thermodynamics of thin shell concrete domes to the test.

What would our study show? Would the dome stay warm, or plummet to unbearable temperatures inside as some naysayers predicted? We felt challenged. We had a bitter north wind and then there was our physical location!

Elevation: 2900 feet in the Blue Ridge Mountains of Virginia
Approximate Longitude/Latitude: 36D 39’N by 80D 55’W

Exterior of Dome: Bare Airform, with stucco window and door surrounds
Interior Floor Area: 1963 square feet, minus exterior wall thickness
Interior Volume: 27,500 cubic feet

Dome Engineering: 2/3 oblate ellipse thin shell concrete dome with approximately 3 inches of closed-cell spray foam insulation sandwiched between the Airform and a 3-to-4 inch thick concrete wall

Thermal mass: 102 cubic yards of concrete in shell (4000 psi) and slab (2500 psi)

Entry Doors: insulated fiberglass, 63 square feet

Windows: double hung acrylic with coastal storm and insulation ratings, 102 square feet. Glass slider with southern exposure, 72 square feet.

With a New Year’s cold snap in place, our work schedule diminished to a couple of minimally intrusive small jobs. We recorded daily temperatures, humidity and weather conditions in text and graphic format to attempt to plot trends and log comments.

We took interior dome temperatures and humidity data in the northern, shaded half of the dome interior away from windows, 2 feet off the bare concrete floor. Data collection occurred near mid-afternoon, as our weather and schedules allowed.

A 50-quart dehumidifier ran continuously. One small, office-cubicle style electric heater was run for two consecutive days near the main entry, but did not appear to affect the interior temperature by more than 1/10 of a degree Fahrenheit per 24 hours and was discontinued. There were no other atmospheric controls (i.e. heaters, HVAC, air exchange unit, etc.) in place during the data collection period.

Another point of interest: four door knob holes were stuffed with plastic bags to keep rain and snow outside the main entry (northern exposure). Doors and windows remained closed except to enter or exit dome through the side entry, or to dump water from the dehumidifier that collected 1 to 1 1/2 gallons of water daily.

We noted that PM exterior temperatures were typically 15 to 20F less than the day temperatures recorded on our spreadsheet. Interior temps would fall 1/2 to 1F during the same time.

The information we charted says quite a lot for the dome’s thermodynamic stability. Needless to say, we were absolutely pleased with this raw data in these very chilly conditions. Here’s a summary of temperature data:

	..High..	…Low…	.Median.	..Range..
Interior January	50.70F	45.60F	48.08F	5.10F
Exterior January	54.00F	17.00F	33.81F	37.00F
Interior February	49.80F	44.90F	46.86F	4.90F
Exterior February	52.00F	23.00F	33.64F	29.00F

Some of Chris and Maddy’s conclusions:

Although the wind chill factor was not calculated every day, it’s very much worth noting where logged. Wind chill is a very apparent factor in the double-wide trailer we currently occupy. It drops interior temperatures more quickly when the wind howls across the mountains.

In contrast, the dome construction is so airtight that there’s no noticeable wind effect on interior temperatures. And Maddy says it was difficult to tell how hard the wind was blowing while she was inside the dome. The thin shell dome is nearly sound-tight too, despite some unfinished interior windowsill work. (Be sure to read David South’s article on the R-factor Fairy Tale!)

Exterior temperatures didn’t have as big an anticipated impact on interior temperatures. Instead, the biggest climbs or drops appear to follow the amount of time that full sunshine was able to penetrate the southern glass slider door. Since the sun appears lower during the winter months as it arcs across the southern sky, the angle of entry was less steep and more square feet of concrete were sunlit during these two coldest months.

The dry, dirt foundation that lies under the concrete slab along with the slab insulation set below the frost line are both paramount to interior temperature stability. That said, it’s been previously demonstrated that the shear amount of concrete in the dome shell and slab carry the majority of the thermodynamic workload.

Once again David South and MDI have made a claim about the efficiency of domes in general that proves true in the field. Domes are very thermodynamically stable. Then again, would anyone really doubt a renaissance man who’s been theorizing, building, insulating and constructing concrete domes for decades?

With this cold season data collected, we are very excited to finalize the construction and begin appreciating decreased utility bills while living full time in our new dome. For Maddy it’s been a 20-year dream come true. Dream big. Dome big.

Read Chris Ecker’s follow-up story: A Cold Study Followup

Read Chris Ecker’s third story: A Year of Energy Data for a Monolithic Dome