Over the Christmas break I went on what I am now referring to as my “Zero Energy Design Binge.” I started thinking about the through wall air conditioner we are considering to handle the cooling demands for the home and thought it would be fantastic if there was a way to economically eliminate the cooling demand altogether via passive design. This thought quickly put me into research mode and when I couldn’t find anything in stock at my local Borders or B&N, I found an 800 page e-book on the subject from www.ZeroEnergyDesign.com.
While I normally don’t buy e-books if they are not immediately downloadable, I made an exception and the CD-ROM arrived just in time for Christmas break. The book consumed many hours over the break. While there is a ton of great info in the book, it became very evident very quickly why it was an e-book and not actually available in bookstores… Skipping over the 200 pages of political ranting helped cut down the time to read a bit.
The biggest thing in the book that caught my attention was the concept of a “Thermal Buffer Zone (TBZ)” or double shell envelope that could significantly reduce the cooling and heating demands if designed and built properly. Basically the idea is to build a double envelope on the North and South sides of the house as well as above and below the house. This would create TBZ around the interior shell of the house where air that is not conditioned but is milder than the outdoor air could freely circulate. See the image below for clarification.
The concept allows each envelope to be built economically without the need for extreme amounts of insulation and top of the line energy efficient windows. This is because having two smaller differences in atmosphere (outside – TBZ & TBZ – Interior shell) are more efficient than on large difference in atmosphere between the outside and inside of traditionally built houses.
The diagram above shows how the home would operate in the summer with cool air originating under the home, gaining heat and humidity as it rises and being exhausted out the top of the house. In the summer the TBZ could get up to 80 degrees or so when it is the hottest outside but it will still be cooler and less humid than the outside air.
In the winter the design functions differently. The South face of the house is actually encouraged to use as much single pane glass as possible in order to let in the most heat from the sun in the winter. The South side is on the right of the diagram above. The air on the South is warmed by the sun during the day, rises to the top and slowly falls to the North side of the building to warm the side of the house that is not getting direct sunlight. This air then cools and continues down under the house and flows naturally back to the South side where the process starts over again. Temperatures of 80 degrees or more in the TBZ have been recorded in houses of this design during the winter when snow is on the ground.
One of the things that got me excited about this concept was the possibility of incorporating a glass garage door on the South side of the house on the ground floor. This had been investigated early on by ISA but thrown out due to thermal losses that would occur. With the TBZ design we could possibly incorporate it again and have a large atrium type space in the back that could be opened wide to the back yard when weather permitted.
To cut my story down a bit, we ultimately agreed that the TBZ design is interesting but should be shelved for a future project due to cost constraints on this project. Besides simply materials costs, there will most likely be added labor costs for throwing too many new ideas at our builder and subs at once. The design we have now is still very unique and extremely energy efficient compared to the average home and probably even the average LEED home.
Here is a list of some of the things I took away from the ZED book that may be applicable to our project. None are really groundbreaking but it helps to have a review again close to the end of the design process on passive design:
- Minimize or eliminate all windows on the West side of the house. This is not an issue for the 100K house but it is for the corner house that has a 40′ exposed wall facing West.
- Minimize the amount of windows on the North side of the house. We have a lot of glass there now and may be able to reduce while still letting in a lot of light.
- Radiant barriers are extremely important, especially on the roof, for keeping the house cool in the summer. Traditional insulation is not enough.
- Designing windows that open on the bottom of the North side of the house and on the top side of the South side will aid in passive cooling via breezes in the summer (especially at night). The windows at the bottom should be half the size of the windows at the top.
- Exterior shading is extremely important for the South side of the house and low-cost, permeable shading material may be able to shade the entire back yard in the summer if designed correctly.
- Interior, thermal shades can be effective in both the summer and winter months for maintaining the atmosphere in the conditioned space.
In a future project with a larger budget I think the TBZ could be implemented without sacrificing the design of the house or impacting the budget too much. It would also be nice to explore low-cost home automation in more detail. If you were able to design the home to automatically control windows, vents, exterior shading and interior shading the cost of mechanical HVAC could be reduced dramatically if not altogether.
As it stands with our current design, we still feel that it will be energy efficient enough to add a reasonably sized PV solar array on the roof to supply most or all of the power to the home. If incentives return to PA in the near future this could be a $5K-$10K decision for the homeowner which is manageable. Then the homeowner can consider things like selling their car in exchange for a nice bike and a solar array that will get their home to zero energy for the rest of their life.
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The enertia house is this design taken to the nth degree. see it at enertia.com
The big concern is that of the fire marshall’s. The excellent airflow is also excellent for smoke and fire. Bummer.
Keep up the good work.
God is good
jpu
Thanks! I’ve been searching for this site for a week. I saw it months ago and couldn’t find it again.
Hey, i just read the article in Metrop! good schtuff. YOu r a pioneer. Congats! I just got a write up in Finland in a little news paper… know anyone who can translate?
http://www.turunsanomat.fi/kulttuuri/?ts=1,3:1005:0:0,4:5:0:1:2008-01-16,104:5:511412,1:0:0:0:0:0 :
Enertia.com violates zeroenergydesign.com principles
Enertia uses bad thermal elements like roof angled glass
See Wikipedia “passive solar building design”
and “sun path”
Meyer – I understand your issue with roof angled glass but if Enertia is achieving zero energy homes and able to allow more daylight in through their window design, does it really matter? Maybe the point is that they could achieve their zero energy goal easier or for less cost with a better design but they seem to have carved out a nice niche for themselves with their current designs.
The amount of construction material and thermal mass is significant. The swimming pool in the TBZ house also adds to it.
I wonder if the same thing could not be equally achieved as a direct gain configuration with equal mass.
Conversely, if there was no pool and with that amount of solarium glazing, I’d wonder if the area would just overheat?
I’ve just found this project, and I was wondering why you had not chosen to go with a basement – whether it was purely for financial reasons (and if so, how much a basement changed the costs) or design reasons. This entry points toward design. Was that your primary reason for that choice?
Our primary reason for not including a basement was budget. This would most likely cost us another $20K which we would never be able to afford on our budget. The slab on grade also allows us to very affordably include a radiant heating system for the home which will be very comfortable and efficient.
I have just purchased an Ekose’a home built in 1981 in cincinnati ohio. I have been in it for 2 months, during about 5 or 6 days in that period, the humidity levels were in the 75% range, we have put shades on all the skylites and the upper windows. We have also installed a small room air conditioner with a dehumidifier switch, in the solarium, and this has greatly helped the comfort level. the house is 3100 sq ft and my electric bill runs me so far$135 per month, this is a Lee Porter Butler design. From the 70’s so this is all fairly old design work
FYI to all,
For several years now we have owned and lived in an “envelope” or “double shell” home that was built in 1981 in the Northeastern part of the USA.
It does not work in this climate and I would not recommend it!!!
Great in theory but absolutely not practical. It has numerous negatives and problems. Several more than listed above.
If we would have known the “issues” with this house I do not think we would have bought it.
My research indicates that there are now many home building technologies that are far better for our type of climate than this old, not clearly thought-out idea.
JJG
jjg – Can you give us a bit more detail into the issues you have experienced? It would be very helpful as we have a double envelope design sketched for a future project.
Thanks,
Chad
Read this:
http://en.wikipedia.org/wiki/Double_envelope_house
fyi, ALL of the above Wikipedia articles are extracted from our inexpensive $25 825-page ZED CD-ROM eBook with extensive full-color illustrations, plus over 1600 U.S. Department of Energy presentation slides. It now includes 2 hours of narrated videos and other supplemental materials like Barak Obama’s alternative energy plans. We donated many articles to Wikipedia for the benefit of all, but the specific design and construction details are only available on our comprehensive ZED CD-ROM (hundreds of megabytes long – too large to download online).
DOE recognized us as the foremost 30-year authority on the subject, and featured our all-day “Three Decades Of Lessons Learned” tutorial at their last International Buildings Conference.
Do NOT imitate the many mistakes from the 1981 passive solar design era, which erroneously persist to this day. Do not waste time and money trying to reinvent a square wheel that has already been proven to not work. Do not imitate the obsolete flawed designs from Lee Porter Butler and enertia. Do not use a design that is optimized for one climatic zone in another.
Larry Hartweg is a second-generation energy research scientist with three decades of recognized TBZ experience and a superior track record.
All ZED buildings are VERY location specific, with extensive computer thermal-and-climatic modeling using the free DOE EnergyPLUS software, plus our propietary ZED front-end TBZ data generator.
Our largest TBZ is a new 5-story $250 million Zero Energy Design residential ski lodge for construction at Lake Tahoe CA. It will be earth sheltered on the South side of a mountain facing the North slopes of Sugar Bowl Ski Resort, across the street from the gondola. To the North is Donner Ski Ranch.
R Meyer – A bit heavy on plugging your book here, but thanks for the info nonetheless. We may be contacting you guys in the future as we still are interested in the double envelope strategy. For now, we are implementing the Passive House standard to see how that effects our budget compared to the first 100K Homes.
$20K for the basement is REALLY tempting. Although it may only net $20K in resale value, it provides the ability to DOUBLE the living space. This will be worth about $80K to Chad and Courtney when they find out their second child is twins.
Realtors in Denver have this rule of thumb: If the house is in a good neighborhood, no basement, built before 1950, and isn’t brick, then it’s a prime candidate for scraping off.
As sustainable as the 100K is, making sure it lasts 100 years instead of 50 years is the most sustainable quality you can endow it with.
The surplus of vacant lots in Philadelphia makes basements less imperative, though.
I just ordered the ZED CD-rom e-book and will look forward to studying. But I’ve been very interested in the Enertia homes – which seem to combine double shell with increased thermal mass (the “gluelam” beams made of laminated yellow pine). I would be very interested to hear more about the disadvantages. I only have one shot at choosing what to build, so I need to choose wisely. I’ve heard about the fire hazard. What else is a disadvantage, especially for the mid-Atlantic region (PA, DE)?
JER – The Enertia is a great system. I’m sure it’s not cheap, but it is much more proven and clearly explained than what you will find in the ZED documentation.
I would highly recommend using ICF foundation with SIPs walls and roof. You will be 50% better than anything else out there if you start there alone…
This contains another opinion on double envelope houses from a passive solar designer.
http://www.greenhomebuilding.com/QandA/sustainable/misc.htm
FYI – The zero enegry design CD has virtually NOTHING that’s not on the web site. Very disappointing! It’s a (very poor) glorified sales pitch for their design services. Just a scam IMO.