Normally, I don't spend much time factoring in the amount of carbon generated by manufacturing something that I'm going to use for carbon mitigation when figuring out how much carbon it will reduce. My reason is that we have to use the carbon-based technology we have to build the carbon-free society we want. Most calculations I've seen for, say, the amount of carbon generated by manufacturing solar panels v.s. the carbon they save over their 30 year lifetime indicate that the scales are heavily weighted towards massive savings in carbon emissions for solar cells. Even renewable energy sources with marginal carbon saving, such as corn-based ethanol, have become more efficient over the past 5 years. If you don't take indirect carbon into account - the amount of carbon generated by land that is put into production to make up for the land devoted to corn for ethanol - there is a savings, though not much. Indirect carbon accounting is controversial, however. If the same accounting method were used for other technologies, for example, the carbon generated by nickel mining to make up for the nickel that goes into a Prius battery, almost any technology would come out losing in the end. The people who came up with indirect carbon accounting were just looking for an argument against corn ethanol because they don't like the idea of trading off food for fuel with the population still headed upwards, and I agree totally. There are plenty of other ways to achieve a carbon free transportation network which don't involve that tradeoff, and we would be pursuing them more forcefully if it weren't for politics.
But a couple of nights ago, I came up hard against this issue of global warming gas emissions from technologies that are good at reducing energy use and thereby carbon emissions. I'm not talking about carbon here, but rather HFCs. HFCs are gases containing fluorine, carbon, and hydrogen that are used most commonly in refrigerators and air conditioners. They replaced CFCs after the Montreal Convention was passed, because CFCs were causing reductions in the ozone layer, an even more serious - but now thankfully receeding - environmental problem than global warming. HFCs have no impact on ozone but they are a global warming gas. Their impact on global warming can be many thousands of times as powerful as carbon dioxide. On the positive side, they do not remain in the atmosphere very long, around 7-10 years, unlike carbon dioxide which has a atmospheric lifetime of around 450 years.
I was interested in what impact our spray foam insulation might have so I sent email to Paul asking what product Ponzini used for their closed cell spray foam. As usual, he didn't reply so I checked Ponzini's web site and found a link to the product, Johns Manvill Corbond III SPF. I had done some research before on spray foam, and there are some green products out there, advertised as made from recycled plastic and soy oil, like Demlec. I had used Demlec in a previous open cell foam job to seal the wall between the attic/garage and the house. JM's Corbond doesn't appear to use soy oil, it's petroleum based, but, as mentioned above, using food crops for nonfood applications has some powerful arguments against it. JM's Corbond claims around 16% recycled content, that is about what Demlec claims too, even though JM doesn't make a big deal about being a green manufacturer. Quite to the contrary, their page on sustainability is filled with a lot of high minded rhetoric, but when you look at the pages on their products the information on ecological effects, such as about recycled content, is buried deep in the data sheets (for example, this data sheet on the B component of Corbond). Demlec, on the other hand, calls out this information in a completely separate page. Both Demlec and JM Corbond use HFC 245fa, a powerful global warming gas, as the blowing agent to blow small bubbles into the foam. So if you drill down on it, the only real difference between a "green" product such as Demlec and JM Corbond is the fact that the green product uses soy oil instead of a petroleum derivative.
I should say something about spray foam insulation here (unfortunately, there's no good Wikipedia page on this). Spray foam insulation comes in two basic types: open cell and closed cell. Open cell foam has a R-value about the same as fiberglass batt, R-3/R-4 per inch, while closed cell foam has a much higher R-value, R-6 per inch. Closed cell foam is the "gold standard" in insulation. Only aerogel does better, at R-10 per inch, it is the platinum standard. "Platinum" and "gold" here refer not just to their insulation potential but also to their cost. Spray foam, even open cell spray foam, is about 2-3x as expensive as fiberglass batt, while aerogel is completely unaffordable except for very limited applications such as my planned thermal bridging treatment. Both closed cell and open cell foam reduce air penetration, unlike fiberglass batt, but open cell foam is permeable to moisture while closed cell foam tightly seals against it, thereby acting as a vapor barrier.
The kind of foam insulation that we are having installed is polyurethane, a commonly available product used not only in home insulation but also for insulating refrigerators, hot tubs, coolers, etc. Prior to installation, polyurethane spray foam comes as two separate liquids, an A component and a B component. The A component contains a mixture of isocyanates while the B component is primarily a polyol with some other chemicals. When the two components combine, the two chemicals react to form polyurethane plastic. A blowing agent pushes the two chemicals together and expands to form tiny bubbles in the plastic. The tiny bubbles give the plastic its insulation value. Depending on the blowing agent, the result is either soft open cell foam or rigid closed cell foam. If the blowing agent is water, the result is open cell foam because the water reacts with the chemicals to form carbon dioxide, which expands rapidly resulting in a less dense foam with less insulation value. If, however, closed cell foam is desired, the blowing agent is HFC245fa. HFC245fa expands more slowly than carbon dioxide so the bubbles are smaller. But both types of spray foam insulation generate green house gases, however closed cell foam generates a gas, HFC245fa, with 1000 times the greenhouse gas potential of carbon dioxide.
The fact that the insulation would result in greenhouse gas emissions was, of course, somewhat depressing since the whole point of this work is to eliminate greenhouse gas emissions. However, as pointed out in this article, the net impact depends on how much global warming gas emission is eliminated by the treatment over the lifetime of the product. So I went about calculating what the rough impact was of the global warming gas emissions v.s. the amount of gas eliminated. I took the crude architectural model of the house I created a few years ago and measured the depth of the studs in all areas so I could calculate the volume of the foam that would be blown into the stud bays. For the floor, I estimated the area as 2500 square feet. Then I calculated out the volume of foam, correcting for the volume of the walls, floor and ceiling that are structural members, as described in the thermal bridging post. I came up with a volume of 1435 cubic feet, or around 1500 cubic feet. This is probably a bit high but should be a good enough estimate.
Closed cell foam has a density of 2 lb/cubic foot. This gave me the weight of the foam, around 3000 lbs. Of that, half is the B resin which contains HFC 245fa, or around 1500 lbs. HFC 245fa makes up between 7-12% of the B resin fraction. Taking the higher number, the amount of HFC 245fa released should be around 180 lbs. Since HFC 245fa has a global warming potential around 1000x carbon dioxide, this would amount to around 180,000 lbs, or 90 English tons, of carbon dioxide. Then comes the question: how much carbon dioxide will be eliminated? That is harder to calculate, but I've estimated that R-6 per inch foam insulation in our walls should reduce gas usage by around 30%. Using that as the figure, the insulation should eliminate 106 therms/year of gas. At 11.7 pounds of carbon per therm, that's 2907 lbs of carbon per year, or around 3000 lbs rounding up. So it will take 60 years for the house to break even from the HFC245fa released during the insulation.This was truly distressing. Here I am trying to do the right thing and reduce the carbon footprint by making my house energy efficient and the technology I've used will take 60 years before there is breakeven in the carbon emitted by the insulation!
So what were the alternatives? We had originally planned to install a geothermal heat pump with blown cellulose insulation in the walls and spray foam only in the ceilings and the floor. Geothermal heat pumps use HFCs too, and can leak them slowly out in the atmosphere, but not as much as spray foam. But the geothermal heat pump turned out to be too expensive and too complex. We could have continued with blown cellulose, but it does not achieve an air barrier and is therefore much less effective than spray foam. It is possible to make a house air tight with blown cellulose, but it requires going over the entire house and sealing up all the cracks in the siding. In addition, most newer houses have complicated vapor barriers on the exterior between the siding and plywood sheathing. Our house has no plywood sheathing, there is just the exterior plywood siding and the interior drywall, with a thin layer of tar paper under the siding. This is a rather poor vapor barrier, even in California's Mediterranean climate. So the spray foam should give us a much better vapor barrier. Blown cellulose also has a tendency to sag over time, and completely loses its insulation value if it becomes wet. Finally, spray foam increases the structure integrity of the building envelope, an important factor when considering earthquake.
So having foam insulation has some really desirable properties which we don't want to give up. In a situation like this, my feeling is the best solution is to pay for carbon offsets. It's like flying, in some cases there are alternatives to flying (taking a train or driving for example) but they are often impractical. We offset our our familial carbon emissions for housing and transportation every year anyway. We use carbonfund.org, a nonprofit, which means our carbon offsets are tax deductible. As it turns out, the carbon emissions from our insulation job should be about what a family of 4 in the US emits in one year, which in and of itself is kind of sobering. The cost at $0.004/lb is around $810. So next year, after the insulation job is finished, I plan to send a check to carbonfund.org for the carbon offsets. Carbonfund.org lets you select the type of offset, so I'll select forestry to establish a long lasting sink for carbon that will span the 60 years that I hope our house will still be around (though of course I'll be long gone).
I've asked Paul to get the amount of the B resin used by Ponzini so I can refine the estimate, and I will report on the exact amount when I have it.