There are many, many tradeoffs to consider when you're designing an unconventional house. To help us evaluate different strategies for building a sustainable home we decided to start with a baseline model that would meet minimum IECC and Georgia requirements. This allows us to make changes to the model and see the effect. My primary focus has been on heating and passive solar design.
Aside from the size and orientation of the house itself, the major factors that go into the baseline model are Climate, Insulation, Air Infiltration and Windows.
Aside from the size and orientation of the house itself, the major factors that go into the baseline model are Climate, Insulation, Air Infiltration and Windows.
Climate
Climate, of course, plays a major factor in the design of an energy efficient home. An approach that's appropriate for a cold climate may not work for a hot climate.
North Georgia is in the southern edge of IECC 2009 Climate Zone 4.
Climate, of course, plays a major factor in the design of an energy efficient home. An approach that's appropriate for a cold climate may not work for a hot climate.
North Georgia is in the southern edge of IECC 2009 Climate Zone 4.
We are lucky to have a small weather station on a mountain just a few miles from our site and at the same elevation (about 2800 feet). http://www.canoodlenest.com/weather/
The station has established an average of 4147 Heating Degree Days (HDD) and an average of 857 Cooling Degree Days (CDD) over the past ten years.
For a passive solar design it's also important to have an estimate of the solar energy available at your site. The National Renewable Energy Lab (NREL) publishes detailed solar data for all 50 states here http://rredc.nrel.gov/solar/pubs/redbook/ and has a dynamic map visualization site here http://www.nrel.gov/gis/
The station has established an average of 4147 Heating Degree Days (HDD) and an average of 857 Cooling Degree Days (CDD) over the past ten years.
For a passive solar design it's also important to have an estimate of the solar energy available at your site. The National Renewable Energy Lab (NREL) publishes detailed solar data for all 50 states here http://rredc.nrel.gov/solar/pubs/redbook/ and has a dynamic map visualization site here http://www.nrel.gov/gis/
Insulation and Air Infiltration
The DOE recommended insulation levels for Zone 4 are:
- Attic or Ceiling R38
- Walls R21
- Floor over unheated space R25
- Slab R5
Georgia code requires a maximum ACH50 score of 7 air changes per hour (not very good).
The DOE recommended insulation levels for Zone 4 are:
- Attic or Ceiling R38
- Walls R21
- Floor over unheated space R25
- Slab R5
Georgia code requires a maximum ACH50 score of 7 air changes per hour (not very good).
Windows
There is some confusion on the allowable characteristics for windows. The prescriptive window requirements in the 2009 IECC specify U of 0.35 for Climate Zone 4 and place no restriction on SHGC for Climate Zone 4.
See the Efficient Windows Collaborative link here http://www.efficientwindows.org/code_overview.cfm
There is some confusion on the allowable characteristics for windows. The prescriptive window requirements in the 2009 IECC specify U of 0.35 for Climate Zone 4 and place no restriction on SHGC for Climate Zone 4.
See the Efficient Windows Collaborative link here http://www.efficientwindows.org/code_overview.cfm
Energy Star, however, has somewhat different zones and sets different standards than the IECC. The Energy Star North-Central Zone roughly corresponds to IECC Climate Zone 4.
The table lists the Energy Star maximum U-Factor and maximum SHGC allowed for each region.
The table lists the Energy Star maximum U-Factor and maximum SHGC allowed for each region.
In future posts I'lll compare the overall heating loads for a base design with no solar consideration and then compare the effects of high SHGC windows versus the low SHGC windows madated by Energy Star.
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