Wednesday, August 4, 2010

Thermal Imaging and Insulation

Around two years ago, we had a thermal imaging study done of our exterior walls and ceiling of our house. In a thermal imaging study, the walls are photographed using an infrared camera. Areas that are colder show up dark blue to purple, areas that are warmer show up light red to white. The study also involves a blower door test, where the house is otherwise sealed and a blower is installed on one door to exhaust air out of the house. Infrared photos are then made of areas where there might be air leaks, for example around light fixtures, plugs, etc. The study showed that our house had average insulation compared to other houses, with several areas where the insulation had failed or was not properly installed resulting in thermal holes. There were also numerous places where the blower door test showed extensive air leaks. "Average" sounds fine, except the baseline is very low. Most houses built before 1970 in California have little to no insulation. After all, the climate here is mild compared to the Midwest and East Coast. Of course, we get subfreezing temperatures in winter at night and 100 degree temperatures in summer periodically, but back in the 50's and 60's, energy was cheap and people who moved from the East Coast were happy with running the furnace.

I subsequently built a spreadsheet model of our house and calculated that we could get about a 30% improvement by doubling the insulating power (R-value) of the insulation  using closed cell foam. That prompted us to move forward with the current plans to seal up the thermal envelope of the house in order to reduce natural gas usage for heating. With the exception of a couple areas, the drywall and insulation are now off the inside of the house. The temperature inside is about twice as warm during the day as beforehand (and maybe twice as low at night). Just as for the solar hot water tank I measured last fall (reported on here), insulation does seem to make a real difference in temperature control. This is good news, since our primary effort on this job is to substantially increase the insulation.

Here's some pictures of the inside of our house without drywall. Here you can see the pellet stove and the fireplace without insulation around it:

The fireplace area was one of the worst areas in the thermal imaging study. There was essentially no insulation around the fireplace. This thermal image shows the area above the fireplace:

The colored bar on the side shows colors corresponding to temperatures. Further toward purple is colder,  further toward red is warmer. The horizontal  light green to yellow lines are the studs you see in the picture above with the drywall off. They are warmer than the cavities, which are the turquoise areas between the lines. Typically, in a well insulated wall, the cavities are warmer than the studs because the insulation material filling the cavities transfers heat much less efficiently than the studs.

Here is what the west wall of the family room looks like with the drywall off:

This shows the wall between the sunroom (protected from construction dirt by the plastic curtain) and the side door.

In the thermal image below, you can see that the insulation in the stud bay next to the door was either omitted or was so poorly installed that it collapsed:

In the thermal image above, you can see that the insulation along the header at the top and the stud in the middle has sagged away from the stud.

The thermal images point out a major problem with the most common form of insulation used in the US: fiberglass batting. Batting is very difficult to install correctly and even when installed, has a tendency to sag with age. Any areas where the batting detaches from the studs results in thermal holes or air leaks. In California, the likelihood that batting will sag is relatively high because of the high amount of ground movement (i.e. earthquakes). Even small movements can result in tears to the paper surrounding the fiberglass, eventually causing the paper to fail and the insulation to sag. Tightly packing the stud bays with batting, blown fiberglass or, even better, cellulose is a superior way to get the same amount of insulating power (R-3 per inch). Closed cell foam is yet better because it seals air leaks tightly and has twice the insulation power (R-6 per inch) but is more expensive. Open cell foam provides the same tight air seal but has the same insulating power as blown fiberglass or cellulose.

Air leaks cause even more heat loss than simple conductive transfer through the walls. In the picture below, you can see some insulation peeking out from under the drywall that was not removed from the area in front of the upstairs bathroom:

 In the thermal image below done with the blower on, you can see the air being pulled in around the light on the ceiling right outside the bathroom where the insulation above is at:

Notice how the pink fiberglass is discolored by black dirt? That is from 30 years of air flow entering and leaving the  house in winter when the heat is on (and taking the heat energy with it). The fiberglass acts as a filter, removing all the dirt from the air. While it is nice to have fresh, filtered air inside the house, pulling it randomly through the ceiling and walls doesn't seem the right way to do it.

Our plans for the system remodel are to seal the thermal envelope and instead ventilate the house through the heat recovery ventilation system. This will pull fresh air into the house and exhaust stale air  out in a controlled manner, through a heat exchanger which transfers heat from the inside air to the outside, so the heat doesn't get lost. It also filters the air so that the black dirt you see above doesn't end up on random inside parts of the wall, but rather on a removable filter that can be washed periodically.


  1. I had a few comments not specific to this post, but since they relate to multiple posts, I figured I'd put them here on this most recent post:

    First off, I haven't had the chance to look through your EV posts, but I used to have a converted S-10, but sold it a few months ago before I moved, I hope to get another project going once I get into a house with a garage. I think you'll be pretty satisfied with a Leaf being the real deal and not a science fair project like I had! Though I was happy with my converted pickup.

    Second, on your hot water issues, I had a few comments.

    I question the logic, from a carbon standpoint, of replacing your gas water heater backup with electric. While it's nice to say that you're powering the backup heater with electrons you produced with your PV earlier in the year, the reality is much different. You're only going to need the backup when the sun isn't shining and your PV isn't producing near enough to offset a 4000 or so watts of demand while the heating element is on. This means you'll be getting the (marginal addition of) power from, most likely in California, a natural gas peaker plant (the nuke and hydro power is already being used elsewhere). That plant realistically will deliver 30%-40% of the therms to you in the form of electricity, which you'll covert to heat at near 100% efficiency. Compare that to your newer gas heater running at probably 80-90% efficiency and you'll see that a therm of gas used at your home produces 2-3 times the hot water as a the same therm of gas used at the power plant. On top of that, if you throw away a gas heater that has 10 good years left and replace it with a new product that emits carbon while being produced, it's hard to see how this will be a good decision environmentally. While I understand you're producing excess KWh's with your PV, the monetary savings seem like they'll be quite minimal, and not enough to justify the cost.

    That brings me to another point: the issue with tepid water after an extended period sitting in your gas water heater tank. I think there's a much cheaper solution than replacing the existing tank. Since you're not using this tank in the summer, simply bypassing it would probably solve this problem (assuming you don't need the 80 + 40 gallons of storage during peak use, and can live with just 80 in the summer). You could do this by installing a T just before the shut off valve between the solar tank and the gas tank, then run the new line through a new shut off valve and into a new T which would replace the elbow before the mixing valve (on the hot side). In the winter, you leave the new valve in the off position and the system runs as it does now. In the summer, when you shut off the pilot light, you can open this new valve and close the valve between the solar tank and the gas tank, thus bypassing the gas tank completely. The water in the tank will act as a pressure back-stop, but shouldn't mix with the water coming from the solar tank, allowing for direct use. In the winter you can just reverse the valves again when you light the pilot. You should also drain your gas heater's tank at this time (which you should really do anyway on ANY water heater once a year to minimize sediment buildup and maximize the tank life and heat transfer ability). You don't want use the water in the tank which has been at room temperature for months allowing bacterial growth. In the summer, the hot water that passes should sterilize any little bit that gets mixed at the new T on the hot side of the mixing valve. This should be healthier than what you're doing now, which is allowing the water in the gas tank to get down to temperatures where bacteria thrive. Though, being on city water, the residual chlorine should be taking care of this.

  2. Hi Brendan,

    Thanx for the comments.

    Your point about an electric on-demand heater not using solar photons directly is certainly true, but this is true of any grid tie system. Grid tie systems basically do carbon offset, not complete replacement of energy used at the time of use. The way I look at it, I'm providing carbon-free electrons to the folks in the Central Valley in summer when they need air conditioning. For that, I have to use carbon-based electricity for my hot water in winter when it's cloudy. Even when I expand the system, I'll be drawing from the grid in winter, since I don't get enough sunlight on my roof. And, of course, I am always drawing on the grid at night. The only way around this is to store the energy in batteries, but that would approximately double the cost of the system and I've got no room on the property for a shed full of batteries (though our lot is good sized, we live in the middle of a city).

    It is also true that the carbon efficiency of electric hot water heat is lower than gas, but that is now. The amount of renewable content in electricity is only going to rise over the years, and with geothermal, advanced utility storage, and grid management, that will be true during cloudy times as well. The amount of renewable content in "natural" (I prefer "fossil") gas will remain exactly the same: zero. It could go up, the US could put in place a comprehensive policy for supporting biogas deployment, like the Germans have, instead of the current policy which is to turn energy producing biomass into ethanol for motor fuel. But the reality is that US has huge fossil gas deposits, many just now being exploited due to new drilling technology, and we get a large percentage of our motor fuel (which is what ethanol is exclusively used for) from countries that, by and large, hate us. The Germans, on the other hand, don't particularly trust the Russians, from whom they get most of their gas, for good reasons, so they have policies in place to encourage biogas development. Nobody in the US seems to have considered that methane is a perfectly fine motor fuel and that it is a lot less energy intensive and chemically complicated to make biogas methane than ethanol, but that is politics for you.

    At any rate, an electric on demand heater allows the maximum utilization of solar, unlike an electric coil in the tank, while enabling offset of the electricity from solar PV. The gas tank that is being replaced is already around 8 years old, which I think is the average lifetime for such appliances, and we plan to donate it so that the embedded carbon in its manufacture doesn't go to waste.

    Regarding your point about the mixing valve, that thought occurred to me too. If we were keeping the gas tank, I would definitely put one in. I was also concerned about bacteria, I've heard that Legionnares' disease bacteria grow in water under 140F. We do have a whole house filter which takes some of the chlorine out of the water, but I don't think our gas fired tank heater was ever up at 140F since we kept it low, and the solar tank regularly gets up to 180F in the summer. In winter, it sits at around 80-100F depending on the weather.

    Thanx again for your comments. I always wonder if people are actually reading this thing, I can't seem to find any other blogs by people who are actually trying out green technologies in their daily life (as opposed to writing about futuristic stuff, etc.) so I keep writing but sometimes it is difficult when no comments come for a long time. Now and then, an insightful comment such as yours or Country Mouse's comes through, making the work a lot more worthwhile.