I first became aware of the Stirling engine when reading about inventor Dean Kamen many years ago. He didn’t talk about the Stirling Engine in detail, but what I did find out was that it is an incredibly efficient non-combustion engine, that is powered by differences in temperature. (e.g. you can buy small a Stirling engine that is powered by the difference in the heat from your hand and the ambient temperature.

Sounds great right? In our home, maybe we could generate heat on the roof, and take cool from the ground and generate some free power, right? As is often the case, the first tip-off that there might be a problem with this logic is that nobody has done so already.

I did a little more research and it seems that unless you can get a heat differential of about 300 degrees Celsius, a Stirling engine practical for powering a typical home would itself need to be about the size of a typical home. Stirling engine size is proportional to the amount of power one needs, and inversely proportional to the heat differential between the cold and hot sides of the engine.

Another problem would seem to be the noise. The seemingly inappropriately named WhisperGen of New Zealand specializes in producing Stirling engine water-heater/power-generator combination units. According to their literature, these devices produce 63dBA of noise (and only a fraction of a house’s power requirements). While that’s quite quiet for a generator, it’s still the volume of a loud conversation, or air conditioner. That’s fine if one is encountering it from time to time, but to have it going in one’s home all the time would likely get a little grating.

It might very well be possible to overcome the heat differential limitation, but given the noise they generate it seems unlikely that Stirling Engines can be a part of any urban sustainable build.

Alex had mentioned that as a general guideline, energy prices are assumed to rise on average 5% per year, even though they’ve risen 7% per year in recent years. I actually find it hard to believe this would be the case over a 25 year period. This would mean energy costs would be over 3x more expensive than they are today (without factoring in inflation) by 2031.

As energy prices rise, the viability of various technologies to make energy generation more efficient rises. But if we do assume this number is correct that just removes the interest portion from our calculation and results in a monthly cost for solar panels of $83.39, which is still more expensive than simply buying the power from Bullfrog.

This advantage might disappear if there were financial incentives offered for providing solar power to the grid, but so far I’ve been unsuccessful at finding any. I had heard that the price paid for adding power to the grid was significant, but have also heard from someone else that those incentives are no longer available.

In addition, when those subsidies were offered, there was no commitment as to their term. An incentive that can be withdrawn at any moment is not much of an incentive at all. I’ll have to investigate further.

Our fifth design meeting continued to refine the garret and the access to it. It now includes an area which will be open to the ground floor and should act as a large chimney to allow hot air to rise and vent out, in the summer. We decided a curved, narrow but fixed staircase would be the best way to access the garret (instead of a pull-down staircase that would be less stable). The area will also include a narrow walkway through open ‘chimney’ to get to the attic space at the front of the house.

I took this opportunity to discuss my previous ideas about the economics of solar panels with Alex. He had read the article and suggested I’ve messed up the math in a couple of ways:

1. I didn’t include the usual 5% rise in energy costs (5% is used even though energy costs have actually averaged 7% in recent years).
2. There was no allowance given for the financial incentives offered by the utilities.

I’ll continue the discussion of these factors in the follow-up to the solar panel post.

There’s an interesting video on YouTube about a new(ish) style of wind turbine called an AeroTurbine. It was developed by Bill Becker from the University of Illinois and has some tremendous advantages over traditional wind power generation.

In particular, his turbine doesn’t require a constant wind source; It works just fine with gusts of wind, as are common in urban settings. Also, this type of turbine cannot be spun too fast, whereas horizontal-axis turbines need to be shut down in high winds. AeroTurbines apparently run much quieter than H-axis wind turbines (though I’ve personally stood right beside a wind turbine and couldn’t hear a thing).

They are hoping to promote AeroTecture amongst architects to better capture wind with these devices in newly constructed buildings.

Unfortunately, no projected cost information is available at this time.

As mentioned previously, we aren’t going to be able to afford solar panels for our house, initially. We are planning space and wiring for them, and are confident solar technology will become quite affordable within a decade. Unfortunately, even our smallish appetite for 350kWh/mo. can only currently be sated by a $25,000 photovotaic array (factoring in the amount of sun we’d receive in Toronto).

But considering 350kWh/mo. only costs $49.22¹ from Toronto Hydro, I decided to run the numbers on the approximate cost of ownership for solar panels and was very surprised at the result. The disruptive force in the calculations was Bullfrog Power.

Even though I’ve skewed the numbers in support of buying solar panels, that option is still 60% more expensive, for no real benefit to the environment (considering one can buy clean power from Bullfrog).

When I first thought about writing this entry, it was supposed to be about the revolution of distributed power generation that will come with low-cost, high-efficiency solar panels. But now that I’ve run the numbers I don’t see that happening.

A relatively small power generation company like Bullfrog can already sell green power at very reasonable prices. Given the overhead involved in managing one’s own power generation, Bullfrog are in a much better position to take advantage of changes in technology than individual consumers are. When prices drop for individuals, they’ll drop even more for Bullfrog, and other power generation companies.

In fact, companies are just the sorts of long-lived entities that thrive on long term capital investments such as solar panels… when there is actually any profit in it. The fact that no power-generation company is generating with solar (at least not around here) leads me to believe that buying solar panels for home power generation is terrible investment (financially and environmentally). For those living anywhere near an urbanized area, it seems likely there will always be a company able to generate green power with the latest technology far more efficiently than any individual could.

Using solar water heaters in the home still seems like a good idea. (Water can’t be heated ‘cleanly’ by someone else and then piped into your house.) But this also raises a question: If heating our home or water via non-solar means, is it better to do it with less efficient but green electricity, or more efficient but dirtier natural gas? I will have to do a few more of these types of studies on the cost of solar water heaters for tap-water and radiant floor heating vs. electrical heaters.

At the moment, I’m thinking the answer might just be Bullfrog.

FOLLOW-UPS TO THIS POST ARE NOW AVAILABLE (Follow-up 1, Follow-up 2).

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Follow-up to: Book: The Natural House

Alex was just showing me an article called Smart and Cool ($) that appeared in a 2005 issue of Home Energy magazine.

In summary: Over-sized air conditioners aren’t just inefficient, they can make your house uncomfortable to live in. As I hypothesized about furnaces in the previous post: AC units cool and dehumidify more efficiently, the longer they run.

A heavy-duty AC unit will run in short bursts; not long enough to dehumidify at all because the water won’t have time to run off the cooling unit in the ventilation system. When the AC turns off, but the blower keeps going, the air picks up the small amount of water that had started to collect, and sends it back into the house making it uncomfortably humid.

In contrast, an AC unit that runs all the time eventually adds so much condensation to the cooling coils, that the water drips off and is drained away out of the ventilation system and therefore, out of the air.

When planning your mechanical systems it seems to me that it is actually worse to wind up with a heating or cooling system that is too strong than one that isn’t strong enough.

We aren’t planning to install AC at this point. We think we can keep the house cool by opening windows in the evening to collect cool air, and relying on good insulation and air circulation to keep the house cool through the day. In Toronto’s climate, we find there is only about 1 week every year where our current home (even as badly insulated as it is) is uncomfortably warm. In our new house, we’re hoping we find that to never be the case.

I think people would be amazed at how comfortable they could make their homes if they stopped relying on AC and simply opened their windows in the cool evenings, and sealed their house during the day. In our climate, residential AC really seems like an enormous waste for its limited benefit.

The Natural House, Daniel D. Chiras
ISBN: 1-890132-57-8

The first half of this book, while interesting, was dedicated to alternate forms of home construction (cob, rammed earth, straw bale, etc.) that aren’t of much use for our particular project; The city isn’t quite ready to have folks try out these methods in locales where their house can actually fall on another house.

But the second half is chock full of very practical suggestions to keep in mind when designing a house. One suggestion in particular came to mind yesterday, after our furnace received its winter maintenance visit.

“Don’t pay extra to give your heating contractor peace of mind.”

The technician indicated that our 26 year old furnace was putting out 90,000 BTU, whereas our small house probably needed 45,000 BTU “at the very most.”

According to the book (and as was apparently the case when our furnace was bought) most heating contractors will over estimate the amount of heating you need for your home. This happens, if not for the unscrupulous reason that they get to sell you a bigger furnace, because they don’t want your furnace to be unable to adequately heat your house.

But consider this: when have you ever encountered a house who’s furnace couldn’t heat the house? Indeed, it probably stayed off most of the time and came on from time to time to blast the temperature up a couple of degrees and then shut down again.

This can’t be more efficient than a system that runs steadily. To my thinking, a furnace which is the ‘right size’ for your house is one that has to run constantly on the coldest day of the year to keep your house at a comfortable temperature.

And what happens if you have an unusually cold run of weather for your region? It’s not as if the furnace, unable to maintain 22°C will drop to 0°C. If it can’t keep up, it might become 19°C and you’ll have to put on a sweater, or run an electric space heater when and where you need it.

Obviously electric heat is expensive, but just think how much is wasted by running an over-sized furnace every winter, compared with running an electric heater for a few hours on a couple record-breaking cold days in a rare extra-cold year?

But I think I’ve digressed…

The Natural House also covers topics on insulation, window technologies, flooring, non-toxic paints, solar electricity, solar water heating, and much more. It’s a great read for anyone trying to get to the crux of what they need to know about the materials that go into their home.

Follow-up: Properly sizing mechanical systems

While solar panels are not something we’re considering in the immediate future, we’re still keeping an eye on it as an emerging technology.

An article in the July, 2007 edition of Wired magazine had me performing the obligatory ‘of course’ slap to my forehead as I read about The Sunflower: an array of mirrors that collect light over a few dozen square feet, and concentrate it up to a single, highly efficient solar panel. (So, instead of having to invest in many solar panels to collect light over that much area, you only have to buy mirrors and motors to control them.)

This setup is actually being designed for residences and apparently cuts the cost of going solar by 30%. That’s still outside our budget at the outset of this project, but great to see innovations driving their price further down.

Technology Review also published this article a few months later, along the same lines.

An interesting press release about a shower head insert developed by CSIRO in Australia that claims it can cut water usage by 30%:

http://www.csiro.au/csiro/content/standard/ps2g2,,.html

The result is, apparently, a shower which feels just as wet and strong as an unmodified shower head.

Today I was out measuring the position of existing electrical, water and gas services, in addition to gathering more information about the trees that will shadow our house.Positioning your house and windows to best take advantage of the sun (to capture it in the winter and avoid it in the summer) is one of the easiest ways to improve the efficiency of a home.

All buildings and most trees were already on our survey, but it didn’t include unusual details such as how tall and wide the trees are. This can have a big impact on the amount of light we’ll need to avoid in the summer and somewhat reduce the sun we’ll receive in the winter.

I don’t have any tools to precisely measure tall heights so for the time being I just put a standing tape measure, extended 6′, at the base of various trees and took a photograph. I then counted the number of pixels in the photo that made up the 6′ tape measure, and compared it to the object in question.

The obvious problem with this method is that the tops of the trees are farther away than the bottoms of the trees, so the taller the tree is, the more inaccurate my measurement will be. But it should give us a good estimate.

The attached images illustrate why deciduous trees are useful to have around your property. With leaves, the trees block the sun in the summer. Without, they allow us to gather more heat through our windows.