I have been talking the talk for a long time, but walking it is a different story.
Building a passive solar home and designing one are two different things, measuring it's performance is another. While over the years I have built several homes that were designed for passive solar all to some varying degree. In 2008 I had the chance to design and build a passive solar home for Linda Johnson and her two children, Rachel and Max. After over twenty years of construction, the last ten having been dedicated to building better buildings, I finally had my chance to use my years of knowledge as a Design/Builder to create the most energy efficient home I have ever built. It was great to work with a home owner to design the home of her dreams, while I focused on ways to reduce the energy demands and cost of the homes construction. Below is a list of the house specifications, along with the total energy usage to date.
Location: Middleboro MA
Size: 1,976 sq/ft = 183.5/sqm
style: Modified single level ranch style
3 bedroom, 2 bath, kitchen/dining/living, laundry, utility, and entertainment/wetbar
Oriented to capture as much passive solar as possible 180 degrees south along long side 68'
Roof slope maximized for active solar to be added in the future, conduit in place
Cost of construction $269,000 plus extras and appliances total cost of $290,000
$135 sq/ft base costs $145 sq/ft final cost
10% ratio of floor to south facing glazing,196 sq/ft, 46 sq/ft conventional,
150 sq/ft of specialized thermal mass windows: More info on these windows
Completely insulated slab-on-grade foundation w/integrated radiant heating/cooling R-15
6-1/2" Structural Insulated Panels for all exterior walls R-24
10-1/4" Structural insulated panels for the ceiling 1,300 sq/ft R-40, conventional frame above
7" of closed cell spray foam in cathedral roof section between conventional rafters,940sq/ft R-40
Additional insulation at sill points to address thermal bridging
Air sealing,using negative pressure during construction to find and seal all air leaks
Heat Recovery Ventilation system w/programmable control
Ground source heat pump to provide heating and cooling to the radiant slab
Energy efficient appliances
Whole house De-humidification system
All energy supplied to the house as Electricity
Date loggers to record efficiency of systems and monitor comfort levels for Temp/Humidity
The standard for total annual energy use under the Passive house Institute standards is < 120 KWh/Sqm. To meet the standard this house would have to use less than 22,000 Kwh's annually: 183.5X120=22,020.
While the house is about to undergo it's first New England winter while occupied, the performance to date has been consistent with the energy model. The house has been occupied for 6-1/2 months now and the total energy used to date is 6,020 Kwh's. If it continues through the winter meeting the expectations the total annual energy consumption will be around 12-14,000 Kwhrs surpassing the standards set by the passive institute by 33% or more. While I didn't do a blower door test to measure the air leakage rate or have a way to separate heating energy from total energy, the final Kwh's of energy consumed will be the measure. No complicated measure devises and costs, just the electric meter the electric company provides. We have been logging the energy use by simply reading the meter at different intervals and recording the actual energy consumed. On April 20th 2010 the house will have gone through one full year of occupation, on that date I will be able to confirm if it has met or exceeded the standard.
It's going to be a long winter's wait !
Tom Pittsley
ecobuilder@aol.com
www.eebt.org
