[Greenbuilding] Solar pre-heat system

[Speireag Alden]

On 2008, Jan 08, at 00:05, someone wrote:

>   I understand the temperature at the source can be above boiling,  
> particularly in the summer.  I like the idea of a system that is as  
> simple as possible too.

     This depends on a number of variables.  One is how fast you pump  
the fluid through, and how much heat you extract from it.  If you're  
heating a mass which never gets above, say, 35°C, and you're ramming  
the stuff through fast, then you can get away with a lot more than if  
you're trying to thermosiphon very hot fluid into a store which goes  
up to 60°C.

     Of course, the design has to withstand the peak temps and  
pressures, not the usual ones.

Then Sacie wrote:

> Any idea out there about the ratio of sun to heat?  How many hours  
> of sun result in how much heat---(Gt Plains summer and winter)?    
> I'm told to forget sun before 9 and after 3, but how about in the  
> winter?   To what degree does the angle of the sun affect the  
> heat?   There must be a book about this.  SL

     There are solar insolation tables on the net which give you  
heating degree days per month, and angle of inclination, and so on.   
I'm pretty sure that the insolation is usually assumed for surface  
flat on the ground.  I'm off-line, so I can't get at them now, but  
Google on "HDD" and "annual" and "insolation" and "table" and you  
should get plenty.

     The angle of the sun affects the insolation as a sine function.   
So you have a multiplier of 1 with the sun's rays at 90° to the  
collector surface, and for any other angle, multiply by the sine of  
the angle.

     This is complicated by the fact that the sun arcs through the  
sky during a given day, and the angle changes with the season, and so  
on.  That's why, for a high degree of accuracy, you have to break it  
down by month and add things up.  However, you can get sufficient  
accuracy to make design decisions by deciding what your minimum needs  
are in the winter, because that's your least productive season, and  
then designing so that the system does not self-destruct in other  
seasons.  For instance, with a large system with only household  
storage, you might warm a pool, or a hot tub, or a sauna, with  
overproduced energy.

-Speireag.