> This installation was completed in 2007 - and has been adequate to maintain the indoor temperature above 65°F/18°C since that time – even though outdoor temperatures in winter dropped below -20°F/-29°C and even though the nine-foot by nine-foot overhead door has been opened every morning and every evening.
> Before the end of 2009 the panels had saved more than their purchase price in fuel costs and the owner expects that the future savings will exceed the original cost of the entire structure. He told me he really likes starting every day (checking his livestock) in a nice warm truck.
Inserting something like this into the duct work of a normal heating or cooling system is fairly simple. The real issue is they increase construction costs and most buildings are built by people that don't use them. Further, they don't look like something out of a Norman Rockwell painting.
> most buildings are built by people that don't use them
Having rented for the past 6 years in 4 different houses, I've become convinced that this is one of the most significant factors for why so many house aren't enjoyable to live in.
Even if the overall design and layout of the house is good (I'm talking about the Christopher Alexander sense of good design), there are always small and not-so-small features that would never have been built that way had the person designing or building the house been intending to occupy it. Or had they moved in, said problems would be remedied in short order.
A problem of insertion into ductwork of a passive-design system component, is that when the heating system runs at night, it will cause air to pass through the panels, and thus cool the building at night in winter.
Since the solar panel-system is passive in design, insertion into ductwork would be a new design issue.
No, windows fail, as can be seen by reviewing the linked pages.
Windows are not the same:
- Windows do not passively aid circulation of warmed air, which the panels are particularly designed to do.
- Windows also do not passively reduce or eliminate overnight-losses of energy (heat) on a cold night (consider negative-centigrade temperature or less), which the linked-to design does do, by passively preventing circulation of air that would cool the building overnight
The design linked-to is specifically designed to passively deal with the prevention of the transfer of heat outside on a cold night, among other things, including limited cost, simple construction, and rapid payback over the life of the building in a cold winter environment. Windows fail as a passive solar source.
Very interesting. I live in a place where we have significant issues with ice build up on roof surfaces, gutters, etc. One way to deal with this is to electrically heat the roof and gutters. This of course is expensive (very!). So I had the ideal that one could use the available solar energy (it is reasonably sunny in winter here) to melt the ice. My idea is not to use PV panels and restive electrical heating but to directly transfer the solar energy as heat to the ice. This would be done with some sort of heating panel, coupled to the metalic gutters with a heat pipe. Sometime I need to do some analysis to see if it is a viable idea. How to ensure snow does not cover the panel/solar heat collector is also a potential problem.
I actually built a similar system as an experiment, basically a 1 x 2 x ¼ meters (multi-layered) cardboard box painted all black inside and covered with a sheet of transparent plastic on one of the larger sides. It was really cheap, around $10-15 in materials. Then I added two holes (in and out), and put some cheap flexible air duct hoses with some old CPU fan, which was another $8. On a sunny day it heats up the air incredibly well, where it actually could be beneficial during the winter season.
Unfortunately there are big problems that I encountered that I couldn't solve cheaply.
1) Mounted on the roof, it has to be sturdy enough to resist heavy rains and strong winds. We get winter windstorms, and one winter it got up to 55 knots with 70 knot gusts. I have no idea how to cheaply mount this box on the roof so it doesn't fly off and kill someone.
2) Intake and exhaust hoses would have to go either through the walls or through the windows. And since I don't own the house, my only real option would be to cut circular holes in the windows, and then replace the glass when we move out. Again, not cheap.
3) For the winter months I would have to also insulate these hoses, or they would lose most of the heat on the way to the house.
EDIT:
I also think if you don't care about what your house looks like, you can either paint it black or wrap it in black plastic.
Some people build these with painted beer can columns on the inside serving as air ducts, see this video for an example: https://youtu.be/nuxanLdtwZQ
They also tend to install it on the side wall; it doesn't get that much sunshine in the summer, but it becomes more efficient in the winter when the Sun stays at lower angles. External circulation of air is still required and is usually done by using an electric fan.
Yeah, I'm fully aware of that design. I've seen tests of it against a much simple design with the sheet of fabric in the middle, and there's basically no difference. Cutting so many cans' tops and bottoms is actually not an easy task, I had tried.
A couple of pieces of plywood, for each window, and some foam strips for air-flow sealing would do. This is not a big effort, just more than your (exceedingly short-lived) cardboard design contemplates.
The gain in creature-comfort in the apartment, might be more than the money saved in avoided heating, as a renter of the apartment.
> I also think if you don't care about what your house looks like, you can either paint it black or wrap it in black plastic.
Such heating will work during the day but transporting the energy from the heated plastic into the house is another matter. The hot surface also would radiate a lot of heat immediately away. And when the night comes you heat the sky with what you have stored up.
The article is fascinating as it shows what can be achieved on a system engineering level. As an engineer however I would also like to see some performance measurements like air flow and temperature deltas going beyond the anecdotal story keeping the build warm in the northern US. Did not see anything on his homepage.
There have been related posts on HN that showed advances on material science level where the absorption and radiation wavelengths of surfaces have been optimized.
> Unfortunately there are big problems that I encountered that I couldn't solve cheaply.
PV system cost these days is dominated by other costs than the solar cells. Engineering something that can withstand weather for a sustained period is both non-trival and not cheap. There may be some overlap in what PV systems require and what a passive heating system requires. Maybe the massive investments in the PV space make passive heating systems these days more practical?
If he just made large windows out of the same double walled polycarbonate panels, wouldn't they collect just as much heat from the sun during the day? The problem with windows however is they don't insulate as well. Perhaps just doubling up or tripling their thickness would achieve the same result in the end, and be much simpler. What am I failing to understand?
You might be missing that maximizing heat collection while the sun is shining is not the goal, that too hot in the day can be just as bad as too cold at night, that each layer of "clear" polycarbonate (ie, 2 for twinwall) blocks about 10% of the light, and that gaping curtainless windows are not always a desirable architectural feature.
How many buildings have you been in that have expansive south facing windows? How many of them have been comfortable day-and-night year-round in a harsh climate without mechanical heating and cooling? Very few buildings achieve this, and I'd guess that none of them have large windows.
The Introduction to to the article is a good "introduction" to the issues. The rest of the article explains the introduction. If you are interested in the issues, it's a good article, worth reading in depth. But as the author says in the preface, "I’d suggest reading this when you’re in a “learn” mode – because if you’re in “skim” mode, you’ll just be wasting your time."
It depends on your goals. One saying is that "a good window is still a poor wall". A quality double glazed window still has about 10x the heatloss of a well built wall. Here's a summary with a link to more: http://www.energyvanguard.com/blog-building-science-HERS-BPI...
Shades can help with privacy, but what if you want the privacy at the same time you want to be capturing heat? And if requires active control --- well, that's by definition not passive. Interestingly, the new movement in high efficiency houses is frequently for low solar gain windows: well insulated windows with special coatings to admit less heat while still admitting light.
From another standpoint, gigantic expanses of windows are rarely the best way to build a pleasant room. As well as being a rare crossover between Computer Science and Building Architecture, Christopher Alexander's "A Pattern Language" has lots to say on this. Some excerpts here: http://kk.org/cooltools/a-pattern-language/
Which is to say that opaque heat-gathering walls serve a purpose that is separate than that served by windows. Both have their place, and they don't tend to replace each other directly.
The black box surface and vanes maximize the conversion of light into heat. The construction with the airflow traps and chimney effect maximize the transfer of the heat into the building while minimizing the heat transfer out of the building when the sun isn't shining.
Windows are not nearly as efficient because the material behind the windows is not optimized to convert light into heat (see his section on the design of the black vanes) and the airflow spreading the heat throughout the building will be poor compared to the design in the article.
You're right about the airflow traps preventing the heat transfer out at night. However, I think windows will trap the heat from incoming sunlight as well as the black vanes since a window allows the light to reach farther into the building and get absorbed by the floor (or opposite wall). Ultimately he wants the heat in the floor anyway, so it's best to get it there via radiation. Not much of it will be radiated back out the same window. In fact the black vanes and the rest of the collector should radiate more of the energy back out to the world because they're hotter than the interior space.
The key difference between windows and the solar panels, as designed, is the passive design of the solar panels. No need to close curtains on these panels, as windows would require, for reduction of heat loss on winter nights.
The black vanes are cooled, during the day, by induced air flow, such heated airflow going into the building (passively), and results in heating the building, without further action. The panels are designed to prevent winter-night cooling via the panels. Thus you're missing the passive intent heating intent of the design: windows fail as a passive heat source, because of the need to actively insulate them in some fashion in the winter night.
I knew about vacuum tube, but they are expensive, require a pump and something to convert the heat back from liquid to air. This on the other hand has zero moving part and requires no maintenance. Amazing!
> This installation was completed in 2007 - and has been adequate to maintain the indoor temperature above 65°F/18°C since that time – even though outdoor temperatures in winter dropped below -20°F/-29°C and even though the nine-foot by nine-foot overhead door has been opened every morning and every evening.
> Before the end of 2009 the panels had saved more than their purchase price in fuel costs and the owner expects that the future savings will exceed the original cost of the entire structure. He told me he really likes starting every day (checking his livestock) in a nice warm truck.