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re: ceiling mass air heater options
3 dec 2003
david delaney   wrote:

>hi nick

hi david...

>>would an unstratified mass (eg a poly film duct containing 1" of water over
>>a shiny ceiling, with insulation above that) be warmer with david delaney's
>>flow separator 
>
>see "solar air heater with flow organizer baffle array for right-angle
>crossing of hot and cold air sheets",

>
>>or 70 f house return air filling a sunspace/air heater?
>>
>>consider 2 steady-state 8' r10 cubes with 64 ft^2 of r2 glazing with 80%
>>solar transmission, after a long string of 30 f average january days in
>>phila, with 1000 btu/ft^2 of sun on a south wall...
>>
>>1.  --------------
>>   |fs|    tc     |       cube 1 has a flow separator and a transpired
>>   | .|           | r10   mesh collector. we might assume the air hear the 
>>   | .|           |       glazing is about the same as the ceiling temp tc. 
>>s  | .|   70 f    | 30 f  this sunspace might be uncomfortably hot, but the
>>   | .|           |       amount of airflow is not limited by the cube temp.
>>   | .|           |       how does the ceiling keep the cube 70 f? 
>>   | .|           |        
>>    --------------   
> 
>i don't understand why cube 1 is worth analysing.

its one way to store overnight heat from a sunspace, with a solar closet
or shelfbox on the ground for cloudy-day heat. putting a little flat mass
above a ceiling seems a lot simpler than building the tall overhead
block/drum structure you have in mind.

>if i understand your text and drawing, the flow
>separator (i prefer "flow organiser", hmmm...
>perhaps "flow intersector" would be even better)
>can have no useful effect because there are not
>two moving sheets of air of different temperatures
>that need the flow organiser in order to cross
>through each other.

it seems to me your flow organizer would help here. without it, the air
near the glazing would be warmer, and it's likely there would be less flow.
i remember some pictures of how hot and cold fluids mixed in an hourglass-
shaped container with the hot fluid below. very slowly, as they fought
each other in the narrow part. adding a small dip tube through the neck
helped a lot...

nick




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