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home>Sustainable Living>Thermal Survey
A Thermal survey of my buildings
I became interested in improving the thermal performance of our
buildings (home - built in 2000, and workshop - built ca 1989) when I designed the
solar heating system for the
workshop back in 2001. Reducing heat loss from the building
envelope is critical to living sustainably in order to reduce fossil
fuel consumption and overall carbon footprint.
As I write this in early December 2008 we have seen outside temperatures dip below 0F already and they have remained below 20F for several days. Both buildings are heated with a combination of propane and wood and augmented by solar, so we are doing our best to use clean burning and sustainable fuels.
In a recent home energy audit we learned that the house has an equivalent leakage area of 120.2 square inches (.83 square feet), yielding a calculated .35 natural air exchanges per hour. This means that the building envelope is quite tight by contemporary standards and falls within the exchange rate recommended by ASHRAE.
So to better understand the heat loss from the building envelope I borrowed a thermal imaging camera. This camera sees in infrared and produces colors that are scaled from warm to cool to indicate relative temperatures. In each image there is a temperature reading that was taken from the center crosshair. The color range scale across the bottom indicates temperature colors in degrees Fahrenheit.
I took the thermal images below after dark when the air temperature was about 20F, I returned in the morning and shot the daylight reference images for comparison.
One thing that I wanted to see was how well the various window
treatments we have added are performing. For the master bedroom we
pleated window shades with side tracks that
claim an R value of 4.6. So I left the right hand window shade
open at night for reference and heated the room to about 70F a few hours
prior to photography. The windows themselves are double
pane, low-E, argon filled wood framed with vinyl sliders, so they
already have good thermal properties.
These images do show a measurable difference in temperature between the 2 windows. However IR images of reflective surfaces are misleading and can be inaccurate. (You can learn more about the solar collectors here)
|On the ground floor we installed double pane clear window insulation panels inside that add approximately R2 to the insulation of the already good windows, they also seal any potential air leaks. Again these images do seem to indicate that heat loss is being conserved by the added panels. I removed the panel from the window on the right.|
|Another project I completed earlier this year was to insulate the exterior of a section the exposed concrete foundation with 4" of rigid foam board. In theory this adds an R value of over 20. The thermal image clearly implies that heat loss is being reduced compared to the untreated concrete above and behind the insulated area. It is interesting to see the heat leaking out from under the insulation, next year I plan to bury 2" rigid foam extending out horizontally 2 feet from the wall to trap the ground heat around the foundation. Also look at how much the rock wall is absorbing the heat from the house - it looks like a lava flow! The basement was unheated and at 50F inside at the time. I am sure that the temperature differences would be much more dramatic if the space were heated to 70F or more.|
|One of the recommendations from the energy audit was that I continue to insulate all the exterior concrete foundation walls in the same way. Shown below is the north wall under the porch which has roughly 200 square feet of exposed area.|
|I went back in the following year and insulated the exposed concrete with 4" of rigid foam click the images to see details.|
|Looking closer at the wall to the right of the image above we see the wood wall at near ambient while the concrete is significantly warmer indicating the heat loss from the heated part of the house above.|
|In this rear (western) view of the house you can see the home made versions of the window insulation panels in the basement windows. The 2 large windows were so big that I made 2 panels that meet in the middle. These panels are really making a difference in that lower right corner of the basement where my wife has her office and studio space. Even though we had not had a fire in the stove for days the chimney is quite warm, showing that the heat from the interior of the house is warming it and causing convective losses. Thermally speaking the entire house is a chimney that convects heat up and out.|
|A closer look at the west wall of the basement shows the "rim of fire" from the concrete slab. The interior concrete floor is covered with 1" of rigid foam and 3/4" of plywood with carpet or vinyl flooring over that, so the floor is comfortably insulated. It also shows the construction detail of the basement door which was hand made from 2 layers of 3/4" pine boards with 1" of rigid foam in between - an effective R value of about 7 which is pretty good for a door. Our other 2 doors were constructed the same way, and of course they are thoroughly weather stripped. The bright dot on the wall is the vent for the closed combustion propane monitor heater for the ground floor.|
Back to the southern exposure you can see the studs in the walls
are a bit warmer than the spaces between them. The builders used a
fairly typical 6" stud wall, but added 1/2" of foil backed foam board
inside between the studs and the drywall. This acts as a thermal
break and reduces heat loss through the studs that have and R value of
about 5, compared to the R-24 fiberglass between them. There is no
foam installed in the attic and you can see that the studs are most
Note that the solar collectors in the middle of the wall (used for our domestic hot water) get very cold at night which is why they are filled with antifreeze. The blue solar panel to the left powers the fluid circulation pumps.
All things considered I am fairly pleased with the results of this
survey. The remaining work to improve the envelope will be adding
insulation to the exposed concrete basement walls. According to the energy audit
we could save as much as $888 per year in heating costs by doing that
My workshop is a super insulated building with R30 walls and R40 roof, the
insulation that I had sprayed in
has completely sealed the interior space so I am confident that the
walls are as well insulated as I can get them considering
cost-performance trade-offs. I also added
window insulation panels to compensate for the cheap single pane
windows that were originally installed. I guess the windows now
rate about R3.
The solar heating system (backed up by propane) that warms the radiant slab significantly reduces the heat load with free energy, and I also supplement the building heat with a wood stove. So costs to heat this building are relatively low already, but there is always room for improvement!
The remaining heat losses are from the exposed frost wall, and last year I managed to insulate the north and east sides of the building by adding 2" of rigid foam covered with T111 concrete board. In the images below you can see the heat leaking from the un-insulated frost wall along the west side.
|Below a section of the south wall that also remains un-insulated shows that it is over 10 degrees above the ambient of 20F.|
|Here is a section of the east wall showing the point where I stopped adding insulation. The interior surface temperature of the insulated section is 11F warmer than the un-insulated section as measured with an infrared thermometer. Clearly there is value in continuing this project next year.|
|I always wanted to see how the radiant floor tubing would show up on a thermal camera, and here's a great pair of views of the floor. There are 2 loops in the floor, both about 320 feet long, they both begin at the bottom right in the diagram and begin by following the outside edge of the building. In the center image below you can see the first pass against the wall at the top left - this is the section at the center right of the diagram.|
|In the center of the room you can see the hottest temperatures in the foreground and the gradual reduction in heat as the radiant tubing gives up its heat to the room.|
|The wood stove is pretty neat to look at too. Note the heat recovery unit in the flue that is blowing heat out into the room, that is a very effective efficiency add-on for the stove at a cost of about $130.00.|
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