Re: SB: Passive solar SB designs

[Rene Dalmeijer <rened@cistron.nl>]

Keith,

No tar and feathers just a few observations. There are no stupid questions 
and I am sure that many others have wondered about the same

At 08:12 PM 9/28/02, you wrote:
>My question is this: Is there ever really a net energy
>GAIN, over the course of a year, by using the concept of windows to heat our
>homes?

Snipped

>1)Windows are a huge sucker of energy, or at least they are at my latitude....
>... I built the frames myself. But do the math. On a SUNNY December the 21st I
>get about 2 1/2 hours of energy coming in of any beneficial amount from the
>sun, but for 24 hours of that day I have energy being sucked out of a big,
>R-6 surface in an otherwise R-40 house.(don't start arguing with me about
>the ins and outs of R values and how inaccurate they are, I'm just making a
>point) I'd be floored if that equation came out in my favor.

Like I said to John Glassford a few days ago Whoa not so fast. Direct and 
even indirect sunshine transfers heat by means of radiation. I won't bother 
you with all the details but here in the Netherlands at 53 North lat the 
amount of heat coming in through a vertical window on a clear mid winter 
day is about 200W for 4 hours average with a midday peak of 350W this is 
for every m^2 of glass. At the same time the loss due to radiation through 
the glazing would be about 10W for -10C.  Therefore in a 24h cycle the gain 
is 2880 kJ and loss 864 kJ per m^2 of glass. (the previous is based on a 
simple multiplication and is therefore a  gross simplification but good 
enough to illustrate what is happening) The big difference is caused by the 
very high radiation temperature of the sun and the relatively low interior 
radiation temperature of the house, making the losses much lower then the 
gains.

>P.S. I think I've figured out a truly efficient design, but I don't think
>it's exactly passive...
>
>1) Make a house with a big central pillar, on which it rotates, and tilts
>with the sun as it tracks across the sky, so the light is coming in the one
>wall of windows the whole day.
>2) Screw, nail, or glue down all objects in the home so they don't slide
>when the floor tilts. Practice balancing on this ever changing plane

The gain by doing all the above is not so great in the higher latitudes 
because the sun stays relatively low at 52 lat it is only about 15 deg. midday.

>3) Paint the inside of your house black to absorb ALL the heat from the sun.

This can make an appreciable difference. There are even specific spectral 
selective coatings maximizing sun radiation absorption albeit the 
difference with plain black is not that big.

>4) Build huge blocks of solid styrofoam and as soon as your 'spidey senses'
>tell you there is no longer an energy gain, run around the house and place
>them carefully in the window cavities to seal them up.

This is an excellent idea. It also means you can get away with a little 
less super duper triple glazing and settle for double instead and avoid the 
losses. It really works I know it from experience that you can feel when it 
is the right time. It is like closing a window when it has become too 
chilly for it to be open.

>5) Get up before dawn,which will be a different time each day, and run
>around taking out the styrofoam blocks. Find an appropriate place for them
>so all your guests that come to visit you in your black, tilting, rotating
>straw bale house won't trip over them.
>6) Wind the big huge spring that moves the house around.
>7) Have a nice life.

I again fully support this last suggestion.


Rene Dalmeijer


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