Home Economics 101 - Envelopes

When food was a greater proportion of household income, and much of it's preparation performed in the home, we were taught to conserve and efficiently use it. Today, energy is the new food, and a modern home economics should address our use of that commodity. The major energy expenditure for most of us is in heating and cooling, and a major determinant of that is how tightly sealed the barrier surrounding the conditioned space we live in is: the so-called building envelope.

There is a simple but little known or appreciated way to measure this precisely: the blower door test. It operates on a very elementary principle: just as we inflate a punctured tire and submerge it in soapy water to find the leaks, the blower door test pressurizes - actually more often de-pressurizes - our homes so we can discover the sources and extent of infiltration. Some air exchange is essential of course, or we would suffocate. Often expressed in ACH - 'air changes per hour', a healthy house should have a natural rate of about 0.35 - i.e. all new outdoor air in a little under every three hours.

It's called a blower door because it is an air-tight, adjustable frame that fits inside a doorway, open only where a powerful fan is mounted to suck air in, or blow air out of the house. Older, more primitive (uncalibrated) systems only allowed you to locate leaks (usually by following puffs from a smoke pencil or just by feeling the air rush on your skin), whereas modern calibrated systems can also quantify the results in a particularly vivid way: as the cumulative area open to the outdoors. The test on my recently purchased, 2200 square foot house yielded 370 square inches, or the equivalent of leaving a 30" sash window open more than 12 inches year-round (this resulted in a 0.62 ACH rate).

Blower door tests are administered by energy auditors: usually local, small-time operators who own the equipment and are skilled in their use. The service is doubtless still too expensive, and as it becomes more pervasive, prices will fall. But even today, it remains one of the single best ways to gather information with which to formulate an energy-efficiency improvement plan for your home.

Indigestion - The HydroMaid Experience

All experiments teach us, the negative outcomes often more than most. A few years ago, my garbage disposal failed. We are told that replacement gives us a unique opportunity for green living - for at these times we don't need to engage in murky calculations over whether it would be better to replace aging but functional stuff (with all it's embodied energy of production, transportation, etc) with newer, more efficient stuff. When it's broke, we get a free pass. Well, nearly free, since we then shoulder the responsibility thoroughly to research the field to ensure we have selected the most efficient and eco-friendly alternative available.

So I was quite pleased when I came across the HydroMaid. Besides the retro name, and the fact that it looked like a low-budget sci-fi spaceship or a cartoon stomach from a 1950's Pepto Bismol commercial, it promised an ingenious technology I could not resist: using only regular water pressure as it's power source. Internally, it reminded me of an orrery, with gears turning counter-gears and the like. Whatever doubts I had about new, unproven technology were assuaged by the reassuring press releases: they had raised venture capital, had a manufacturing plant in Hong Kong; Bob Vila demoed it on TV!

While you have already guessed that the HydroMaid was a stinking pile of crap - I'm afraid it took me a fair while to make the discovery. After paying a large premium to buy it ($325 if I recall, vs $80-$100 for a good conventional one), the plumber charged another $100 to install it. Which is nearly what he charged again to replace the 'O-rings' when it failed in a few months (wasn't that the space shuttle problem?), and again when he removed it after the second failure (in July, I think, when the undigested garbage had begun to ripen).

But you would be completely wrong in supposing the take-away is the importance of being conservative in such decisions. On the contrary, I believe that we as consumers must accelerate the pace of adoption of energy-saving devices, which includes unproven technology. The real story is about how we can socially pool and therefore mitigate the risk inherent in these experiments. Had a site like this been published, I and others could have saved ourselves a lot of aggravation and expense. We still don't appreciate how simple and pervasive communication technology like the web can make our group experiments fail-fast.

I think there is a bright future indeed for products that harvest their energy in the form they need it - here mechanical energy for pushing a piston - rather than relying on the extremely dirty and lossy trip from coal seam to electrical outlet. But this is the subject of a future post.

Why I Write

Whether you care about global warming or worry about the family budget, you ignore the importance of energy use at your peril. The recent run-up in the price of gasoline is just a shot across the bow: almost all conventional sources of energy are both limited and in greater demand. Much of the energy use that contributes to our lifestyles we cannot directly control, like that embodied in the products we buy. But in a few areas, like personal transportation, we enjoy fairly direct control. We may buy a more fuel efficient car, use public transit, ride our bikes, telecommute etc. These decisions are often not easy, involving wrenching value conflicts (that additional 1/2 hour on the bus you used to spend reading to your child), but at least the energy calculation is clear (45 mpg Prius vs 28 mpg Focus x 30 miles per day x $4.?? per gallon).

When it comes to energy in the home (which with transportation, amounts to almost 1/2 the energy Americans use), it's another story entirely, and on the face of it that's puzzling. After all, almost all energy we consume at home is metered and regularly billed, and we mostly can (within our budgets and physical tolerances) decide exactly how much heat, A/C, lighting, etc we will consume. What complicates the picture is how many variables are at work:

• Prices change over time, so even constant use appears as increase
• Weather variability skews otherwise predictable energy demand
• Shifting life patterns (vacations, house guests, etc) add spikes and dips

and countless others. The more difficult it becomes to isolate or quantify the effects of any single energy conservation measure, the less able we are to justify or undertake it. We are operating 100 million energy management labs in America (viz. our homes), but cannot get any good - that is general - results.

I'm writing from the belief that by sharing our individual experiments, we can begin to build a body of knowledge that can guide practical decisions, almost like the approach taken in evidence-based medicine, where clinical scientific results are interpreted in light of individual goals, circumstances, and previous outcomes. I have found very little information of this sort in the blogosphere or the web - mostly corporate blogs with a product to sell or their sockpuppets - so even one set of particular, local, results can be of value. The more so if it provokes others to open the doors to their labs as well.