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re: usages of heat from solar collectors?
4 feb 1997
wally bently   wrote:
 
>this posting is to seek out market ideas for heliostat and line 
>focused solar collectors thermal heat usages other than electrical 
>production.

dr. roland winston (one of the inventors of non-imaging optics) gave a talk
and demonstration last may in philadelphia about evacuated tube collectors
used as the movable line focus for fixed solar trough reflectors on flat roofs
of large buildings. he spent a few minutes describing the uses for such heat.
one of the main uses was for absorption cycle air conditioning, which is
apparently widely used now with heat sources like natural gas. another was
"industrial process heat." he would be reachable through u chicago.

>solar collector thermal heat usages (potential markets) from my
>current perspective...   
 
>baking (cooking)   in third world countries to eliminate
>                   deforestation problems such as in haiti. 
>                   heating a well insulated oven to 350+ degrees
>                   the day before.  

this seems useful on a small scale. thermal storage works better for
bigger ovens. how about designing and building a village-sized solar
oven, something like an 8' cube with a 2 month rc time constant, with
a common scrap metal 400 f heat store (engine blocks, etc) and individual
cooking compartments which can be separately temperature regulated?
how will you move the heat around? oil?

>pasturization      1.  compost to destroy weed seeds and other 
>                       pathogens.  apparently heating the material
>                       to 200 degrees f and holding in a well 
>                       insulated container for 2 hours is adequate.

commercial greenhouses use a lot of energy doing this...

>                   2.  sewage sludge before dumping onto farm land
>                       or back into water ways.  control of disease
>                       spreading. 

this could be an alternative to chlorination as the final stage of an
individual on-site system.

>home heating       storage of heat up to 350 degrees f. in rock,
>                   (or metal) in a well insulated 1,000 cubic
>                   foot (15 feet x 15 feet x 5 feet) buried vault.

i think this is more practical and economical to do with water, eg water in
sealed containers in an insulated room above ground at a lower temperature,
eg 130 f. water stores about 3x more heat by volume than rock, with lower
effective thermal resistance. iron and steel have about the same heat
capacity by volume as water, and they can store heat at higher temperatures,
but they are more expensive and heat transfer is more interesting.

>                   forced air fan to remove heat as required
>                   (temperature controlled) on cloudy days and
>                   at night. mostly applicable to rural areas. 

a fan can work in a roomfull of water containers, but rocks more likely need
a blower consuming a lot more electrical energy, eg a 400 watt blower vs a 
40 watt fan, because piles of rocks have larger airflow resistance, and the
rock pile volume has to be 3 times larger than a volume of water storing the
same amount of heat, if the max temperature is the same. it seems to me that
people may come to value sunspaces more than solar concentrators, even in
less rural areas, since they can add beauty and floorspace to a house,
vs making it look like the martians have landed. 

>ranching           as a means of melting ice in stock tanks 
>(stock tank water) for ranch animals or for wild life access
>                   during winter months. 

32 f...

>air conditioning    the collector would provide the heat for
>                    an evaporative cooler from which ice can
>                    history shows that one person did so in 
>                    california in the 1930's. 

it seems to me that a lot of these things have been done once.

>water distillation:  to be effective,  extensive insulation 
>                     is required for the unit.  a very efficient
>                     heat exchanger(s) (or heat pump?) would have
>                     to recover the steam heat of condensation 
>                     (for heating the incoming water to steam).  

how about some sort of large ew trough with two concentric tubes running
along the focus as a counterflow heat exchanger, with multiple effect
distillation, ie boil some water at 300 f, and use the condensing steam
to make steam in the next section at 280 f, etc? how can this be done
in a continuous vs stagewise process?

nick



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