Posted by Father Haskell on December 22, 2008, 1:17 am
> > nicksans...@ece.villanova.edu wrote:
> >>> 20 or so feet of 4" flexible aluminum dryer vent stuffed into a glazed
> >>> box,
> >>> maybe 2 x 3 feet by 6" deep.
> >> Why all the dryer vent, vs a glazed box that's colored dark on the
> >> inside?
> >> And why 2x3'? Anything less than 4'x8' seems like a toy, for space
> >> heating.
> >> Nick
> > Has anyone tried the common size vent tube but flattening the tube into an
> > elongated oval before installing? Seems that it would get the surface area
> > to volume ratio up while still utilizing readily available material.
> > Charlie
> We just used the 3" round as is but did try flattening one as a test. It is
> easier to construct with it round in terms of making the holes ino the
> collector boxes 9using hole saw), and keeping it evenly sized. Also looks
> more professional when done since it is hard to flatten them evenly without
> it denting and such.
Build a labyrinth-shaped "mold" from scrap ply and 2 x 4. Lay the
ducting into the labyrinth. Cover with another sheet of plywood
and stand on top to squash the pipes to a uniform, 1-1/2" thick,
already bent and ready to install into the box.
Posted by nicksanspam on December 21, 2008, 6:46 pm
>Has anyone tried the common size vent tube but flattening the tube into
>an elongated oval before installing?
Why use a tube at all?
Nick
Posted by schooner on December 21, 2008, 7:45 pm
>>Has anyone tried the common size vent tube but flattening the tube into
>>an elongated oval before installing?
> Why use a tube at all?
> Nick
Why not? It is just another form of collector. It acts as both the
collector plate and ducting in one basically. The dry duct also affers a
bigger surface area with the grooves and they also disturb the airflow to
improve heat transfer to the flowing air. The tube design is just one of
many collector designs, be it a flat plate, screen, felt, etc.
What do you feel is the best overall design? Be interested to hear various
options and opinions.
Posted by Morris Dovey on December 21, 2008, 8:53 pm
schooner wrote:
>>
>>> Has anyone tried the common size vent tube but flattening the tube into
>>> an elongated oval before installing?
>>
>> Why use a tube at all?
>
> Why not? It is just another form of collector. It acts as both the
> collector plate and ducting in one basically. The dry duct also affers
> a bigger surface area with the grooves and they also disturb the airflow
> to improve heat transfer to the flowing air. The tube design is just one
> of many collector designs, be it a flat plate, screen, felt, etc.
>
> What do you feel is the best overall design? Be interested to hear
> various options and opinions.
Would not the best overall design use all available plenum cross
sectional area to minimize friction (maximize airflow) and keep
everything in the absorber plenum at the lowest possible temperature to
minimize re-radiation and conductive losses - while presenting the least
amount of friction-producing wall surface area?
And would not the best absorber not have a geometry in which fully half
of the absorber was positioned to re-radiate toward either glazing or
box wall - and would it not also have the lowest possible thermal mass
and produce the least resistance to airflow?
Of course, carrying those factors to the extreme might not result in
either the cheapest nor easiest design - but "cheap and easy" may not be
fully compatible with "best". :)
--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto/
Posted by schooner on December 21, 2008, 9:47 pm
> schooner wrote:
>>>
>>>> Has anyone tried the common size vent tube but flattening the tube into
>>>> an elongated oval before installing?
>>>
>>> Why use a tube at all?
>>
>> Why not? It is just another form of collector. It acts as both the
>> collector plate and ducting in one basically. The dry duct also affers a
>> bigger surface area with the grooves and they also disturb the airflow to
>> improve heat transfer to the flowing air. The tube design is just one of
>> many collector designs, be it a flat plate, screen, felt, etc.
>>
>> What do you feel is the best overall design? Be interested to hear
>> various options and opinions.
> Would not the best overall design use all available plenum cross sectional
> area to minimize friction (maximize airflow) and keep everything in the
> absorber plenum at the lowest possible temperature to minimize
> re-radiation and conductive losses - while presenting the least amount of
> friction-producing wall surface area?
> And would not the best absorber not have a geometry in which fully half of
> the absorber was positioned to re-radiate toward either glazing or box
> wall - and would it not also have the lowest possible thermal mass and
> produce the least resistance to airflow?
> Of course, carrying those factors to the extreme might not result in
> either the cheapest nor easiest design - but "cheap and easy" may not be
> fully compatible with "best". :)
> --
> Morris Dovey
> DeSoto Solar
> DeSoto, Iowa USA
> http://www.iedu.com/DeSoto/
Well with little airflow resistence and the lowest possible tempurature youd
have little heat transfer so I don't see the value.
I prefer practical ideas to theoretical ones personally. If you cannot
easily build it for a reasonable cost and have it produce a useful amount of
heating then it is of no value, you may as well use tradtional heating
sources as in the end it will be simplier and cheaper.
> >>> 20 or so feet of 4" flexible aluminum dryer vent stuffed into a glazed
> >>> box,
> >>> maybe 2 x 3 feet by 6" deep.
> >> Why all the dryer vent, vs a glazed box that's colored dark on the
> >> inside?
> >> And why 2x3'? Anything less than 4'x8' seems like a toy, for space
> >> heating.
> >> Nick
> > Has anyone tried the common size vent tube but flattening the tube into an
> > elongated oval before installing? Seems that it would get the surface area
> > to volume ratio up while still utilizing readily available material.
> > Charlie
> We just used the 3" round as is but did try flattening one as a test. It is
> easier to construct with it round in terms of making the holes ino the
> collector boxes 9using hole saw), and keeping it evenly sized. Also looks
> more professional when done since it is hard to flatten them evenly without
> it denting and such.