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Dome Home Heating and Cooling
This page is dome home heating and cooling for all the domes in the earthbag village (Pod 1). Once we’ve finished this tutorial and open sourced all the details for a 3-dome cluster as part of our crowdfunding campaign, we’ll do the same for the complete Earthbag Village (Pod 1) and Duplicable City Center®, and then the other 6 villages.
This page is divided into the following sections:
This page will continue to evolve until building the earthbag village is complete and we can definitively say what approaches are determined to be most effective. We will then further evolve this page with the experience of others also choosing to build earthbag teacher/demonstration communities, villages, and cities using our blueprints.
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HEATING A DOME HOME
Designing comfortable homes without extensive energy use or associated cost for people in freezing temperatures is essential to the earthbag village. The issue with earthbags is that they provide fantastic thermal mass (see “Thermal Lag” below) but truly aren’t a great insulator. The R-value of compacted earth is roughly R-1 per foot, so a standard earthbag wall might yield no better than R-2 (about the equivalent of a dual-pane glass window). Their insulating properties can be improved by adding materials that create air pockets inside them like volcanic rock, rice hulls, perlite, or vermiculite. This, however, has positive and negative elements.
| Comparison of Material R-Values | ||
| Material | R-value/inch | R-value/15″ |
| Rice hulls | R-3 | R-45 |
| Perlite | R-2.7 | R-40 |
| Vermiculite | R-2.13 | R-32 to 36 |
| Extruded polystyrene | R-3.6 to R-4.7 | R-54 to R-70 |
| Molded low-density polystyrene | R-3.85 | R-58 |
Simple thermal dynamics state that heat travels from warm spaces to cooler spaces and air pockets inhibit this heat transfer. If the goal is keeping heat in, inhibiting the transfer of heat through walls can be very good. The more you add air pockets or insulate the walls, the less heat will move through those walls. The downside of this is in the summer when heat being absorbed by the walls would have a cooling affect that would be lessened by this reduction of heat transfer. Here are the calculations used for a dome-shaped structures:
Earthdome Heating and Cooling Equations – Click to Enlarge
Suggestions and options on what is the best approach vary and can be affected dramatically based on the building environment. For areas that are consistently cold, with a quality internal heating system, a person would do well with a solid earth-filled earthbag wall that has an external insulating layer. This would provide thermal mass on the inside and a barrier to that thermal mass losing its heat to the outside. In areas that are consistently hot, however, this external insulation approach could create environments that warm up and are difficult to cool again, so building deeper in the ground and eliminating insulation is a better approach.
Our living model has the additional relevant factor that the homes we are creating are not purposed for a sedentary living experience. People are not expected to spend all day sitting in their homes, entertaining in their homes, and/or relaxing in their homes. Visitors and residents alike will use them more like hotel rooms. The fulfilled living model, culture of personal growth and interaction, and the enviroartistic design of One Community provide better reasons and additional spaces (ex: Duplicable City Center) that are specifically purposed for the activities people would normally use for their home for.
This creates a need for heating One Community homes primarily in the evening when people are returning to these living spaces, and wanting them cool in the middle of the day when we might want to relax out of the sun. With this desire for maximum individual comfort specifically during the coldest nights and the hottest days (versus all-day temperature control), we explored our options for heating and insulation with respect to energy needs, cost to implement, and labor hours to implement.
The result was this chart showing our calculations for heating with passive solar (zero cost), electric blankets (heat only the person with very low energy), space heaters with energy rationing (immediate heat but uses a lot of electricity), and rocket mass heaters (slow to heat a room but producing super efficient and long-lasting heat):
Earthdome Heating Option Comparisons – Click to Enlarge
We also calculated the different insulation options including tapestries (cheap and removable), insulating the outside of the structure (insulates thermal mass), and insulating the inside of the structure (insulates structure and isolates thermal mass):
Earthbag Home Insulation Comparisons: Click to Enlarge
CONCLUSION
Because our building environment will be hot in the summer and sunny but cold in the winter, with use focusing primarily on mid-day and evening rest and relaxation, we want to maximize the benefits of in-ground building and passive solar. We also want to provide the ability to be warm in a cool environment as quickly as possible. Passive solar for free heat and electric blankets for low-energy and immediate heating of the individual (versus the room) make the most economic sense for specific heating. Parabolic dish heaters (also heat just the person) or small space heaters with limits on individual energy use are a secondary option. Rocketmass heaters are not an option due to their cost and constant (non-sustainable) fuel needs for a group as large as ours.
For insulating our structures, the ideal scenarios would be external insulation in the summer and internal insulation in the winter. Our maximally cost effective solution is building 4 feet into the ground to benefit from the 55 degree thermal mass and lag (see below) of the earth and using tapestries in conjunction with the heating methods above. This will allow us to apply these when the tendency of the material to resist temperature changes is desired and advantageous. It will also add character and beauty to each of the homes.
Installing lofts in the domes will also allow us to insulate and separate the top half of the domes to create smaller and easier spaces to heat in the winter and larger and easier spaces to vent and cool in the summer.
Using the above approaches will guarantee maximally affordable, minimal-energy-usage, and individual comfort options for all residents. As we build the first few structures and further weigh all the factors (convenience, energy-needs, etc.) of each of our heating and insulation measures specifically during days (or weeks) that could reach zero degrees F (-18° C), we’ll then decide what other heating and insulation options we may desire to explore and compare with this initial strategy. Everything we try and learn we will also open source share.
THERMAL MASS AND THERMAL LAG
Thermal lag is a time unit assigned to a material that indicates the amount of time it takes to heat up or cool down. Thermal mass is the material heated or cooled. Heating a material (and its effectiveness as thermal mass) depends on how much heat it can absorb (Specific Heat: Cp), the rate at which the heat can penetrate (thermal conductivity: k), the density of the material in question (density: ρ), and the thickness of the material. The time that passes from heating one side to the other side heating up too is the “thermal lag” expressed by:
This means that when our domes experience cyclical temperatures (day and night, seasonal) the temperature inside the domes lags behind. For our domes, we have calculated a 44-day lag in temperature meaning that the exterior temperature would not reflect the un-heated interior temperature of the dome. You can see this depicted in the image below where the blue line represents the average daily temperature of Page, AZ, and the red line is the resultant 44-day lag temperature inside the dome. The green line is what a lag of over a year would look like, which happens to be the same principle that creates the 55°F below-ground temperature people reference as the benefit of building in-ground versus above ground.
Temperature Analysis for Page, AZ (not our location)
The good news is that extremely hot days in the summer would benefit from these cooler interiors. The bad news is that after 44 days or more of cold temperatures, the inside of the domes are going to reflect that average cooler temperature. At that point, trying to heat the structure becomes hard to predict because you not only have to heat the air in the dome, but the material of the dome itself, and the overall trend of the elements cooling the dome over 44 days is hard to offset.
To put it another way, the thermal mass of the domes resists temperature change much like a heavy object resists changes in velocity (inertia). Once the temperature outside is pushing that mass colder, it takes a lot of energy to push back and keep it warm in the space. The equations that represent the system of thermal properties move into the realm of advanced calculus and show traditional heating and insulating of these spaces would be cost prohibitive for our affordability goals for these initial structures.
Thermal Lag Calculations
Here are these calculations applied to our specific domes:
Earthdome Heat Fluctuations During Freezing Temperatures – click to enlarge
Castles Used Wall Tapestries
This is what led us to consider more creative options for heating. For instance, what if we could change when the tendency of the material to resist temperature changes is desired verses when it is advantageous? One possible solution comes from the middle ages. Castles are not known to be the homiest of places, especially in the winter. To combat the chill coming off the walls in the winter people put up floor to ceiling drapes and tapestries. These cloths added insulation to the inside of the space and kept heat in the room while reducing the amount of heat that was absorbed by the thermal mass of the castle walls. Nowadays we have space blankets (or products like radiant barrier) and other wall-hanging material options that could be substituted or combined to make this approach even more effective.
Other options under consideration (as described above) are space heaters with energy rationing, parabolic dish heaters or electric blankets (heat the person, not the room), and other creative insulation approaches. As we continue to explore all options, the key criteria are affordability, sustainability, labor needs for implementation, maintenance, and our limited energy supplies when using solar.
COOLING A DOME HOME
Due to the effects of thermal lag, and the temperature below the frost line, a semi-underground dome house is the perfect place to be in arid hot environments. The cool temperature underground chills the air inside the dome and helps keep the temperatures cooler. While the lag of the dome can’t keep the heat out forever, with enough lag the high temperatures during the day and the cold temps at night even out and the average temperature of the day gets transmitted through the dome walls. For instance, a day with a high of 100 and a night that hits 50 would have an average temperature of 75 (a fairly normal work/house temperature). The dome is ideally designed to even out these temperatures and make life in desert climates more bearable, and it uses no generated power.
There are, of course, more extreme climates where insulation or other methods to keep a dome cool are still recommended. Here is a chart (reference PDF) showing GWT (ground water temp) averages for different locations around the world. Because as the soil gets thicker between it and the sun/weather the lag becomes greater until you have the average of a whole year. Depending on the soil content and moisture, this happens at about 4 feet down, more specifically it’s called the “frost line.” The chart below is hugely relevant (thermally) for any endeavors in extreme locations. In places like Austin, TX a home built mostly below the frost line would be a comfortable 71 degrees all year round. In Fairbanks, AK however, this is below the permafrost line and it will always be below freezing.
Average Ground Temperatures Around the World – click to enlarge in a new window
Additional elements to aid in keeping the domes cool in our not-so-extreme location will include 16-foot high ceilings with a heat vent and the ability to completely cover all windows when passive solar is not desired. Light colored walls to reflect the light and deciduous trees to provide shade in the summer and that lose their leaves and allow sun through in the winter can also help. For additional passive cooling options, we suggest researching windcatcher construction coupled with evaporative or subterranean-piping cooling.
Below is a video of someone talking about some of these approaches and a few others that are only appropriate for the hottest climates.
POSSIBLE MODIFICATIONS
This is the area where we will add possible modifications we explore after we build our first 10-20 domes. If you have suggestions for this area, please use our Suggestions Form. As we implement and compare the different modifications, we will add all the open source data and details for duplication here as well.
SUMMARY
One Community desires to demonstrate the earthbag village (Pod 1) as a maximally affordable, adaptable, and functional option for our self-propagating self-sufficient teacher/demonstration communities, villages, and cities model. How these homes will be used, variable weather, energy limitations, and a lack of consensus on the best insulation methods have led us to begin with a strategy that is focused on guaranteeing comfortable people while we explore ways to maximize the comfort of the environment itself. This strategy combines the ability to change the size of our environment by 30% (open or closed loft), passive solar, 4 feet of in-ground building, tapestries, electric blankets, and parabolic and/or space heaters. This strategy is the result of our research and calculations to this point and will evolve with more details as we build the earthbag village and identify through our experience what additional modifications (if needed) provide the best and most effective balance of investing more time, labor, and resources. We will open source share any additional modifications here as we build and evaluate them.
RESOURCES
- The Myth of Earthbag Insulation
- How to Build an Insulated Earthbag House
- Heating the person versus the room on Permies.com
- Earthbags for Insulation discussion on Permies.com
- Climate Batteries – storing heat in the ground
- An example of using earthtubes as a cooling option
- Article: 23 Low-tech Energy-saving Ways to Stay Warm
- Permies.com details about rocket mass heaters – RMH Plans
FREQUENTLY ANSWERED QUESTIONS
Q: What is the purpose of the earthbag village?
Please see the complete earthbag village open source hub: Click Here
Q: I think I have a better approach (or an approach you’d like to see us include in our modifications), how do I share that with you?
Please use our Suggestions Page to share these ideas with us. Our goal is to build as sustainably as possible and we are interested in any and all ideas people have for how to do this. Even if your idea doesn’t meet our immediate engineering, materials availability, or other needs, we’d still like to know about it because we’ll work indefinitely as an organization to explore, test, and open source share as many alternative and sustainable methodologies as possible. Doing this is an essential part of our global-change methodology and desire to provide the necessary data and demonstrations of safety and effectiveness needed so more counties (and The International Building Code) recognize and accept these sustainable options.
Q: How do you intend to help bring prices down to facilitate duplication of your models as teacher/demonstration villages?
We have a Win-Win-Win-Win partnering philosophy combined with a significant marketing and promotional engine that we feel brings value to any partnership. We are using these tools and resources to seek partners with the global distribution capability who see the free marketing and new and expanding customer base we will provide as beneficial enough to reduce their consumer prices and individual profit in favor of volume sales and supporting global change.
Q: How would you suggest keeping a dome cool in a place like the Sahara?
We’d suggest burying it in the ground as much as possible and closing all the windows and vents to keep heat and sunlight out. This would essentially create a “cave” environment. Further insulating the outside of the dome and adding a passive cooling system with underground pipes would help too. Here’s an example of the earthtube cooling option.
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