## Downspout collector manifold puzzle/challenge

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• Hi, I ve been doing a little work on downspout collectors with the aim of doing a side by side comparison with the screen collector. Having a little trouble
Message 1 of 30 , May 4, 2011
Hi,
I've been doing a little work on downspout collectors with the aim of doing a side by side comparison with the screen collector.

Having a little trouble working out a good manifold that distributes the air evenly to all the downspouts. Here are the details on the problem:
http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColFlow.htm

Some pictures of the construction used on the prototype:
http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColProto.htm

Any suggestions on a better manifold design would be appreciated.

Gary
• Hey Gary, This is extremely interesting and will be a super test! Off the top of my head, my guess for the anomaly on blowing distribution where the ends get
Message 2 of 30 , May 4, 2011
Hey Gary,

This is extremely interesting and will be a super test!

Off the top of my head, my guess for the anomaly on blowing distribution where the ends get most of the airflow, that doesn't occur when sucking, is that air is forced into the entry manifold and its easiest course is to each end of the manifold.  It can't come back to the center because of the continued flow outward, to the end downspouts, whose pressure drop is low enough to allow the air to exit there rather than flow back to the center.  I wonder is this same phenomena occurs with hydronic collectors?

Here is Gary's content from his website:

# Downspout Test Collector Construction

This page details the construction of a solar air heating test collector that uses gutter downspouts as the absorber.   The downspouts are laid out side by side to form the collector absorber. The downspouts are all connected to air supply and return manifolds that run along the top and bottom of the collector. Air is forced through the collector and picks up heat from the sun heated gutters.

Here are some pictures of working downspout collectors from Scott's site...

The aim of building this test collector is to do a side by side performance comparison with other solar air heating collector designs.

The collector box uses exactly the same construction as the "Reference Collector", which is described in detail here...   The details below cover adding the downspout absorber and manifolds to the basic box described in the Reference Collector.  I'm not recommending this as a design to build for the long haul -- see the end of page for some things I would think about changing for a "production" design.

The depth of the collector box from the top surface of the insulation to the bottom surface of the corrugated glazing is 4.5 inches.
 Painting the downspouts Cutting the downspouts to length Splicing together the cutoffs to make additional lengths. Two of the cutoffs from the 10 ft long gutter sections were just long enough to make a full length section. One is just slipped inside the other and fastened with a couple short self taping screws. A bead of silicone caulk was applied before pushing the sections together.
The downspouts used are from Lowes and are standard 2 by 3 inch aluminum downspouts.

I spaced the downspouts about 3.5 inches apart -- this leaves only 0.5 inches between downspouts.   I discussed with Scott several alternative options for placing the downspouts, including 1) spacing the downspouts further apart with aluminum sheet installed under the downspouts to conduct solar heat into them for sun that hits between the spouts, 2) flattening the downspouts to make them wider but not quite so tall  -- this would reduce the number needed for a given width collector, and 3) spacing the unaltered downspouts quite close to each other (as I ended up doing).  I think that approaches 1 and 2 above deserve a look, and may be more cost effective, but I wanted to test the downspout collector design that looked like it would have the best chance at being as efficient as a downspout collector could be.  The close spacing of the downspouts gives the highest ratio of absorber area in contact the flowing air to area that the sun shines on, and makes full use of the ability of the downspouts to conduct solar heat around to the back side of the downspouts to provide more heat transfer area.  It is also the most expensive approach in that more downspouts are needed for a given width of collector, which is where the other two options may be better.

The collector takes 13 downspouts to cover the 47.25 inch inside width.  I bought nine of the 10 ft downspouts and was able to splice together the cutoffs from the 9 to make a total of 13.

### Manifolds

A 6 inch inlet duct goes into the bottom of the collector, and a 6 inch exit duct leaves the top of the collector.  A full width manifold distributes air from the 6 inch duct to all of the downspouts, and a 2nd manifold along the top picks up the air from all the downspouts.
Half inch plywood with cutouts for the 13 downspouts were used to seal the side of the manifold where the downspouts enter.
 Laying out the downspout cutouts. Cutting the openings for the downspouts. Installing the manifolds.
Note the two small blocks of plywood used on the ends of the manifold to attach the downspout board to and also to attach the cover plate for the manifold to.
 Its easier to pull the downspouts up into the slots in the downspout board than to put the board down onto the downspouts. downspout seal board in place. Clamp the downspout seal board down tight so that it pushes the downspouts against the insulation, then screw in place.
Some more views of

 inlet duct entry and downspouts. downspouts installed. Sealing of downspouts to the downspout seal board with silicone caulk.
 The aluminum manifold cover before painting it black.
The manifold top (glazing side) cover is a single sheet of 0.018 inch thick aluminum -- this allows the manifold areas to act at solar collectors.
In order to maximize the airflow area, the manifold covers are as close to the glazing as possible without contacting it.
 Finished collector without glazing. The bumpy appearance of the manifold covers is due to starting with grooved alum soffit material and hammering it flat.
The manifold covers are sheet aluminum held in place with a lot of short screws.  I made them easy to open because I wanted to be able to make changes inside the manifold, but they should be either sealed or  gasketed down to prevent air leaks.

The glazing is identical to the reference collector...

The construction shown here is for a test collector, and is probably not the best way to build one that you want to last for 30 years -- that said, it does seem to work out pretty well.  A couple changes that I would want to be made is to pick a better joint at the top of the collector box to exclude rain from entering, and pick a water resistant material for the board that the downspouts penetrate to get into the manifold so that if there is any condensation in the collector it will hold up better.

# How to Get Even Flow in Downspout Collectors?

I built a simple prototype of the gutter downspout collector as shown here..

The air inlet and outlet areas look like this:

### Target Flow Characteristics

The aim is to achieve about 3 cfm per sqft of collector area, or 90 cfm for the full collector.  The idea being that 3 cfm per sf should give good efficiency.
With this flow rate, the flow per downspout is 6.9 cfm, and the downspout velocity is about 170 fpm for the 3 inch by 2 inch downspouts.
At this flow rate, the calculated pressure drop in each downspout is only about 0.005 inches of water -- this is not counting pressure losses at the inlet and outlet of the downspout and is using a hydraulic radius of 2.4 inches.  So, quite a small pressure drop.

The Reynolds number for the flow in the downspout is about 5000 -- so, the downspout flow should be turbulent and well mixed.
This is mostly from this calculator: http://www.pipeflowcalculations.com

### Manifolds -- a Compromise

In thinking about how to design the inlet and outlet manifolds, the first thought was to design them as plenums with the inlet at the lower left and outlet at the upper right of the collector.  For a good plenum, you would want the plenum velocities to be relatively low and the pressure in the plenum to be high relative the pressure drop in the runners (downspouts in our case) -- this way the plenum operates close to the ideal of a constant pressure source for each of the downspouts.    But, the manifolds get pretty large if you do this -- the total area of all the downspouts is 13 * 6 = 78 sqinches.   If you made the plenum such that its inlet velocity was equal to a downspout velocity (170 fpm), then the plenum would end up being 4.5 inches deep (the depth of the collector) and 17.3 inches tall -- so you would end of with 34 inches of plenum covers in the 94 inch tall collector.  This seems excessive given that the area occupied by the plenum covers is not going to be as efficient a solar collector as the downspout area.
So, I ended up putting the inlet ducts into the middle of the collector manifolds (for flow in both directions), and cut the area back from 78 sqinches to about 30 sqinches.  This makes for a manifold that is 4.5 inches deep by about by 6.5 inches tall.  This gives a flow near the center of the manifold of about 90/2 = 45 cfm and a velocity of  (45 cfm)/(30/144 sf) = 216 fpm, or somewhat higher than the downspout velocity.  This is not based on any science -- just a guess.
The top (glazing side) cover on the manifolds is a sheet of black painted aluminum, so the plenum areas are still somewhat effective as solar collection area.

### Checking the Evenness of Airflow Distribution Across the Downspouts

To see how good a job the inlet manifold did of spreading the air flow evenly to each duct, I left the cover plate off the outlet manifold, hooked up a blower to the inlet manifold, and measured the flow velocities in each of the downspout tubes at the outlet manifold end.   I tried this with the blower hooked up to blow into the collector and with the fan turned around to suck air out of the collector.

Measuring the flow for each downspout outlet.

The plot below shows the results.

Downspouts 1 and 13 are the left right end downspouts, and downspout 7 is in the middle right where the inlet air comes in.
So, in the blow case, the center downspouts get very little flow and the outer downspouts get quite a bit of flow.  This was a bit of a surprise given that the center downspouts are right next to the inlet duct.

In the suck case, the opposite happens -- the center downspouts get more flow than the outside downspouts.  Also puzzling?
Thinking that maybe having the outlet manifold cover off was effecting the flow distribution, I put the outlet cover on, and measured the flow in three of the downspouts by cutting holes in them about half way up and inserting the Kestrel wind meter in the holes.  The holes were taped over when not taking velocity measurements.
The plot below is the result.
This plot shows the same runs as are on the other plot PLUS three new runs -- for the new runs, the velocity measurements were taken by cutting holes in three of the downspouts (numbers 12, 10 and 7) half way up the downspout, and using the Kestrel wind meter inserted in the holes.  The holes are closed off with tape when not taking reading.
Green triangle -- sucking, inlet manifold cover on, exit manifold cover off -- ie same as red square except measured at mid downspout.
Purple circle -- sucking, inlet and exit manifold covers on -- ie same as Green Triangle, but exit cover on.
Aqua square -- blowing, inlet and exit manifold covers on -- ie same as Blue Diamond, but with exit cover on.

So, for the sucking case, putting the exit manifold cover on makes the downspout velocity quite even all the way across -- just what is wanted.

For the blowing case, putting the exit manifold cover on helps to even out the downspout velocities somewhat, but they are still much lower near the center.  Even though its better, there is still more than a 3 to 1 difference between lowest and highest.
The green triangle is the same as the red square (exit cover off) except that the velocities are measured mid duct rather than at the end.  This was done as a sort of control, and they track very well.

I'll probably go ahead and test the collector in its current configuration, but I'd be very interested in hearing if anyone has any good explanations for what's going on with the flow distribution, or ideas on how do design a manifold system with some assurance that it will distribute flows to each downspout evenly.  Gary...
For people with finished downspout collectors who want to check on flow distribution, taking the glazing off and measuring the outside temperature of the downspouts with an IR temperature gun would probably give a good indication.  Please let me know what the result is if you do this.

Gary May 3, 2011

-----Original Message-----
From: yreysa <gary@...>
To: SimplySolar@yahoogroups.com
Sent: Wed, May 4, 2011 10:01 am
Subject: [SimplySolar] Downspout collector manifold puzzle/challenge

Hi,
I've been doing a little work on downspout collectors with the aim of doing a side by side comparison with the screen collector.

Having a little trouble working out a good manifold that distributes the air evenly to all the downspouts. Here are the details on the problem:
http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColFlow.htm

Some pictures of the construction used on the prototype:
http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColProto.htm

Any suggestions on a better manifold design would be appreciated.

Gary

• Looks great Gary! Off the top of my head ; what about a baffle plate that has slots cut in it that are narrower near the input and get wider as they go
Message 3 of 30 , May 4, 2011
Looks great Gary!  Off the top of my head ; what about a baffle plate that has slots cut in it that are narrower near  the input and get wider as they go outward?  The idea is to make the flow even by restricting the air where the velocity is higher.  This would of course need trial and error to tune, but the slots could be formed with tape until optimum flow is established and then used as a template to cut a final piece of sheetmetal.

On Wed, May 4, 2011 at 10:01 AM, yreysa <gary@...> wrote:

Hi,
I've been doing a little work on downspout collectors with the aim of doing a side by side comparison with the screen collector.

Having a little trouble working out a good manifold that distributes the air evenly to all the downspouts. Here are the details on the problem:
http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColFlow.htm

Some pictures of the construction used on the prototype:
http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColProto.htm

Any suggestions on a better manifold design would be appreciated.

Gary

--
So It Is, Here in the Eternal Now.
Fritz Schantz

• Hi Gary, What a great project you got going. I think Fritz s idea of using a baffle will solve the air distribution problem. Is it possible for you to install
Message 4 of 30 , May 4, 2011
Hi Gary,
What a great project you got going. I think Fritz's idea of using a baffle will solve the air distribution problem. Is it possible for you to install the fan so it sucks air, then use smoke from incense or some other source. The smoke will help you see what the air is doing. Something similar to the aerodynamic drag tests they do in a wind tunnel.
Good luck and I look forward to your results.
Jeff

--- In SimplySolar@yahoogroups.com, "yreysa" <gary@...> wrote:
>
> Hi,
> I've been doing a little work on downspout collectors with the aim of doing a side by side comparison with the screen collector.
>
> Having a little trouble working out a good manifold that distributes the air evenly to all the downspouts. Here are the details on the problem:
> http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColFlow.htm
>
> Some pictures of the construction used on the prototype:
> http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColProto.htm
>
> Any suggestions on a better manifold design would be appreciated.
>
> Gary
>
• Looks neat Gary. Nice job. The header is large and that should help. My suggestions for uniform flow is to place the input pipe on the left side of the bottom
Message 5 of 30 , May 4, 2011
Looks neat Gary. Nice job. The header is large and that should help.
My suggestions for uniform flow is to place the input pipe on the left side of the bottom header and place the exit pipe on the right side of the top manifold.
This should help distribute the flow of air uniformly in the same way as your parallel flow hot water collectors. Hot air collectors. As you know I have done very little work with hot air collectors. I understand the value has to do with the simplicity of the system and also concerns about leaks, but if I did get involved with hot air systems I believe I would favor the screen or the polyester absorber plate since the materials used for heat collection are more cost effective. Still it will be interesting to see a comparison of the downspout collector with the screen collector. Where do you get all your energy, Gary?
John

On Wed, May 4, 2011 at 10:01 AM, yreysa wrote:

Hi,
I've been doing a little work on downspout collectors with the aim of doing a side by side comparison with the screen collector.

Having a little trouble working out a good manifold that distributes the air evenly to all the downspouts.  Here are the details on the problem:

Some pictures of the construction used on the prototype:

Any suggestions on a better manifold design would be appreciated.

Gary

• scroll down to page 12 on this link from Gary s website and you can see an example of air disruptors built into a plenum on this soda can design, which is
Message 6 of 30 , May 4, 2011
scroll down to page 12 on this link from Gary's website and you can see an example of air disruptors built into a plenum on this soda can design, which is basically the same as the downspout design.  This is what came to mind when i started looking at garys work and when i was initially building my air collector, but i didnt incorporate it into the project.  I wonder how efficient we could make these things. hmmmm?

Jeremy, WV

On Wed, May 4, 2011 at 11:50 AM, John Canivan wrote:

Looks neat Gary. Nice job. The header is large and that should help.
My suggestions for uniform flow is to place the input pipe on the left side of the bottom header and place the exit pipe on the right side of the top manifold.
This should help distribute the flow of air uniformly in the same way as your parallel flow hot water collectors. Hot air collectors. As you know I have done very little work with hot air collectors. I understand the value has to do with the simplicity of the system and also concerns about leaks, but if I did get involved with hot air systems I believe I would favor the screen or the polyester absorber plate since the materials used for heat collection are more cost effective. Still it will be interesting to see a comparison of the downspout collector with the screen collector. Where do you get all your energy, Gary?
John

On Wed, May 4, 2011 at 10:01 AM, yreysa wrote:

Hi,
I've been doing a little work on downspout collectors with the aim of doing a side by side comparison with the screen collector.

Having a little trouble working out a good manifold that distributes the air evenly to all the downspouts.  Here are the details on the problem:

Some pictures of the construction used on the prototype:

Any suggestions on a better manifold design would be appreciated.

Gary

• ... From the sun soon I suspect, no? ;)
Message 7 of 30 , May 4, 2011
--- On Wed, 5/4/11, John Canivan <canivan@...> wrote:
> Where do you get all your energy, Gary?

From the sun soon I suspect, no? ;)
• As always it s great to see the detailed descriptions and photos of your experiments. Manifold issues aside, I d be interested in your costs compared to a
Message 8 of 30 , May 4, 2011
As always it's great to see the detailed descriptions and photos of your experiments. Manifold issues aside, I'd be interested in your costs compared to a screen collector. Even assuming the better heat transfer results in each piece of downspout being equivalent to a flat width of 10" (3+2+3+2) the cost of downspouts would seem to be much more than a multilayer screen absorber.

• Gary do you feel there is any compromise to the downspout design by doing the airflow in one direction at the width of your design? Steve in PA
Message 9 of 30 , May 4, 2011
Gary do you feel there is any compromise to the downspout design by doing the airflow in one direction at the width of your design?

Steve in PA

--- In SimplySolar@yahoogroups.com, "yreysa" <gary@...> wrote:
>
> Hi,
> I've been doing a little work on downspout collectors with the aim of doing a side by side comparison with the screen collector.
>
> Having a little trouble working out a good manifold that distributes the air evenly to all the downspouts. Here are the details on the problem:
> http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColFlow.htm
>
> Some pictures of the construction used on the prototype:
> http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColProto.htm
>
> Any suggestions on a better manifold design would be appreciated.
>
> Gary
>
• Thanks Fritz, Are you thinking baffles at the inlet to each downspout, or baffles across the inlet manifild and perpendicular to its long axis? Gary
Message 10 of 30 , May 4, 2011
Thanks Fritz,
Are you thinking baffles at the inlet to each downspout, or baffles across the inlet manifild and perpendicular to its long axis?

Gary

--- In SimplySolar@yahoogroups.com, fritz schantz <fritz.schantz@...> wrote:
>
> Looks great Gary! Off the top of my head ; what about a baffle plate that
> has slots cut in it that are narrower near the input and get wider as they
> go outward? The idea is to make the flow even by restricting the air where
> the velocity is higher. This would of course need trial and error to tune,
> but the slots could be formed with tape until optimum flow is established
> and then used as a template to cut a final piece of sheetmetal.
>
> On Wed, May 4, 2011 at 10:01 AM, yreysa <gary@...> wrote:
>
> >
> >
> > Hi,
> > I've been doing a little work on downspout collectors with the aim of doing
> > a side by side comparison with the screen collector.
> >
> > Having a little trouble working out a good manifold that distributes the
> > air evenly to all the downspouts. Here are the details on the problem:
> >
> > http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColFlow.htm
> >
> > Some pictures of the construction used on the prototype:
> >
> > http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColProto.htm
> >
> > Any suggestions on a better manifold design would be appreciated.
> >
> > Gary
> >
> >
> >
>
>
>
> --
> So It Is, Here in the Eternal Now.
> Fritz Schantz
>
> www.fritzdesigns.com
>
• Hi John, I thought about the opposite corner feed, but it seems like you either end up with very high velocities or a very large manifold. I went to the center
Message 11 of 30 , May 4, 2011
Hi John,
I thought about the opposite corner feed, but it seems like you either end up with very high velocities or a very large manifold.
I went to the center feed when the height of the corner feed manifold went up to 17 inches just to keep the manifold velocity down to the same as the downspout velocities.

Gary

--- In SimplySolar@yahoogroups.com, John Canivan <canivan@...> wrote:
>
>
> Looks neat Gary. Nice job. The header is large and that should help.
> My suggestions for uniform flow is to place the input pipe on the left
> side of the bottom header and place the exit pipe on the right side of
> the top manifold.
> This should help distribute the flow of air uniformly in the same way as
> your parallel flow hot water collectors. Hot air collectors. As you know
> I have done very little work with hot air collectors. I understand the
> value has to do with the simplicity of the system and also concerns
> about leaks, but if I did get involved with hot air systems I believe I
> would favor the screen or the polyester absorber plate since the
> materials used for heat collection are more cost effective. Still it
> will be interesting to see a comparison of the downspout collector with
> the screen collector. Where do you get all your energy, Gary?
> John
>
> On Wed, May 4, 2011 at 10:01 AM, yreysa wrote:
>
> Hi,
> I've been doing a little work on downspout collectors with the aim of
> doing a side by side comparison with the screen collector.
>
> Having a little trouble working out a good manifold that distributes the
> air evenly to all the downspouts. Here are the details on the problem:
>
> http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColFlow.htm
> <http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColFlow.htm>
>
> Some pictures of the construction used on the prototype:
>
> http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColProto.htm
> <http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColProto.htm>
>
> Any suggestions on a better manifold design would be appreciated.
>
> Gary
>
>
> <http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColProto.htm>
> <http://docs.yahoo.com/info/terms/>
>
• Hi Jeremy, Thanks for reminding me of those -- I knew I had seen them somewhere but could not rememeber where. After looking at them, its not really clear to
Message 12 of 30 , May 4, 2011
Hi Jeremy,
Thanks for reminding me of those -- I knew I had seen them somewhere but could not rememeber where.

After looking at them, its not really clear to me how they work?

Gary

--- In SimplySolar@yahoogroups.com, Jeremy Styles <jeremysstyles@...> wrote:
>
> scroll down to page 12 on this link from Gary's website and you can see an
> example of air disruptors built into a plenum on this soda can design, which
> is basically the same as the downspout design. This is what came to mind
> when i started looking at garys work and when i was initially building my
> air collector, but i didnt incorporate it into the project. I wonder how
> efficient we could make these things. hmmmm?
>
> Jeremy, WV
>
>
> http://www.builditsolar.com/Projects/SpaceHeating/GregCanCol/Can%20Colllector.pdf
>
>
>
> On Wed, May 4, 2011 at 11:50 AM, John Canivan <canivan@...> wrote:
>
> >
> >
> > Looks neat Gary. Nice job. The header is large and that should help.
> > My suggestions for uniform flow is to place the input pipe on the left side
> > of the bottom header and place the exit pipe on the right side of the top
> > manifold.
> > This should help distribute the flow of air uniformly in the same way as
> > your parallel flow hot water collectors. Hot air collectors. As you know I
> > have done very little work with hot air collectors. I understand the value
> > has to do with the simplicity of the system and also concerns about leaks,
> > but if I did get involved with hot air systems I believe I would favor the
> > screen or the polyester absorber plate since the materials used for heat
> > collection are more cost effective. Still it will be interesting to see a
> > comparison of the downspout collector with the screen collector. Where do
> > you get all your energy, Gary?
> > John
> >
> >
> > On Wed, May 4, 2011 at 10:01 AM, yreysa wrote:
> >
> > Hi,
> > I've been doing a little work on downspout collectors with the aim of doing
> > a side by side comparison with the screen collector.
> >
> > Having a little trouble working out a good manifold that distributes the
> > air evenly to all the downspouts. Here are the details on the problem:
> > *
> > http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColFlow.htm
> > *<http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColFlow.htm>
> >
> > Some pictures of the construction used on the prototype:
> > *
> > http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColProto.htm
> > *<http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColProto.htm>
> >
> > Any suggestions on a better manifold design would be appreciated.
> >
> > Gary
> >
> > <http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColProto.htm>
> > <http://docs.yahoo.com/info/terms/>
> >
> >
> >
>
• Yes!! :)
Message 13 of 30 , May 4, 2011
Yes!! :)

--- In SimplySolar@yahoogroups.com, Martin Fick <mogulguy@...> wrote:
>
> --- On Wed, 5/4/11, John Canivan <canivan@...> wrote:
> > Where do you get all your energy, Gary?
>
> From the sun soon I suspect, no? ;)
>
• Hi Steve, All things being equal, it seems like the short, one direction pass should make it more efficient because the temperature rise would be less, so the
Message 14 of 30 , May 4, 2011
Hi Steve,
All things being equal, it seems like the short, one direction pass should make it more efficient because the temperature rise would be less, so the absorber should be cooler and losses lower?

But, the main reason I did that was that the screen collector just uses a single bottom to top, 8 ft flow path, and I wanted to the two collector to be similar for a good performance comparision.

Gary

--- In SimplySolar@yahoogroups.com, "newsteve001" <newsteve001@...> wrote:
>
> Gary do you feel there is any compromise to the downspout design by doing the airflow in one direction at the width of your design?
>
> Steve in PA
>
> --- In SimplySolar@yahoogroups.com, "yreysa" <gary@> wrote:
> >
> > Hi,
> > I've been doing a little work on downspout collectors with the aim of doing a side by side comparison with the screen collector.
> >
> > Having a little trouble working out a good manifold that distributes the air evenly to all the downspouts. Here are the details on the problem:
> > http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColFlow.htm
> >
> > Some pictures of the construction used on the prototype:
> > http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColProto.htm
> >
> > Any suggestions on a better manifold design would be appreciated.
> >
> > Gary
> >
>
• Hi Gary, Would a piece of vented soffit placed 3/4 below the ends of the downspout (or angled) slow the higher velocity air without restricting the total air
Message 15 of 30 , May 4, 2011
Hi Gary,
Would a piece of vented soffit placed 3/4" below the ends of the downspout (or angled) slow the higher velocity air without restricting the total air flow?
Just a thought,
Kenneth W

--- In SimplySolar@yahoogroups.com, "yreysa" <gary@...> wrote:
>
> Hi,
> I've been doing a little work on downspout collectors with the aim of doing a side by side comparison with the screen collector.
>
> Having a little trouble working out a good manifold that distributes the air evenly to all the downspouts. Here are the details on the problem:
> http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColFlow.htm
>
> Some pictures of the construction used on the prototype:
> http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColProto.htm
>
> Any suggestions on a better manifold design would be appreciated.
>
> Gary
>
• Posted by: yreysa gary@BuildItSolar.com ... Hi Gary; That is because you are not tapering the manifolds. Make the manifolds wider at the duct end, tapering
Message 16 of 30 , May 4, 2011
Posted by: "yreysa" gary@...

> I thought about the opposite corner feed, but it seems like you
> either end up with very high velocities or a very large manifold.

Hi Gary;

That is because you are not tapering the manifolds.
Make the manifolds wider at the duct end, tapering to
the opposite ends.

-Laren Corie-
Natural Solar Building Design and
Solar Heating/Natural Cooling/Energy
Efficiency Consultation Since 1975
www.ThermalAttic.com

www.EarthWeekPlus.com

Read my Solar house design articles in:
www.essnmag.com

Home base-LittleHouses YahooGroup
http://groups.yahoo.com/group/LittleHouses/

Founder-WoodGas - Power from wood
http://groups.yahoo.com/group/WoodGas

Founder-RefrigeratorAlternatives YahooGroup
http://groups.yahoo.com/group/RefrigeratorAlternatives

My Music - www.MoonlightRed.com
• Something like the attached. ... -- So It Is, Here in the Eternal Now. Fritz Schantz www.fritzdesigns.com
Message 17 of 30 , May 5, 2011
Something like the attached.

On Wed, May 4, 2011 at 9:42 PM, yreysa <gary@...> wrote:

Thanks Fritz,
Are you thinking baffles at the inlet to each downspout, or baffles across the inlet manifild and perpendicular to its long axis?

Gary

--- In SimplySolar@yahoogroups.com, fritz schantz <fritz.schantz@...> wrote:
>
> Looks great Gary! Off the top of my head ; what about a baffle plate that
> has slots cut in it that are narrower near the input and get wider as they
> go outward? The idea is to make the flow even by restricting the air where
> the velocity is higher. This would of course need trial and error to tune,
> but the slots could be formed with tape until optimum flow is established
> and then used as a template to cut a final piece of sheetmetal.
>
> On Wed, May 4, 2011 at 10:01 AM, yreysa <gary@...> wrote:
>
> >
> >
> > Hi,
> > I've been doing a little work on downspout collectors with the aim of doing
> > a side by side comparison with the screen collector.
> >
> > Having a little trouble working out a good manifold that distributes the
> > air evenly to all the downspouts. Here are the details on the problem:
> >
> > http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColFlow.htm
> >
> > Some pictures of the construction used on the prototype:
> >
> > http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColProto.htm
> >
> > Any suggestions on a better manifold design would be appreciated.
> >
> > Gary
> >
> >
> >
>
>
>
> --
> So It Is, Here in the Eternal Now.
> Fritz Schantz
>
> www.fritzdesigns.com
>

--
So It Is, Here in the Eternal Now.
Fritz Schantz

• A couple more ideas Gary- 1) Plenum extension is a second layer of polyiso 3 off of the back of the collector, boxed in with the intake mounted on top of
Message 18 of 30 , May 5, 2011
A couple more ideas Gary-
1) Plenum extension is a second layer of polyiso 3" off of the back of the collector, boxed in with the intake mounted on top of that.  The air would travel down the back side and normalize flow the time it hits bottom, passes through a slot in the back of the collector into the internal intake plenum.

2) Intake extension is based on of Laren's idea of passing the incoming air over the outsides of the downspouts in the collector interior, and then passing through a slot in your bottom manifold into the intake plenum.

Both of these "should" in my untrained mind produce even airflow to each downspout.

On Thu, May 5, 2011 at 7:03 AM, fritz schantz wrote:

[Attachment(s) from fritz schantz included below]

Something like the attached.

On Wed, May 4, 2011 at 9:42 PM, yreysa <gary@...> wrote:

Thanks Fritz,
Are you thinking baffles at the inlet to each downspout, or baffles across the inlet manifild and perpendicular to its long axis?

Gary

--- In SimplySolar@yahoogroups.com, fritz schantz <fritz.schantz@...> wrote:
>
> Looks great Gary! Off the top of my head ; what about a baffle plate that
> has slots cut in it that are narrower near the input and get wider as they
> go outward? The idea is to make the flow even by restricting the air where
> the velocity is higher. This would of course need trial and error to tune,
> but the slots could be formed with tape until optimum flow is established
> and then used as a template to cut a final piece of sheetmetal.
>
> On Wed, May 4, 2011 at 10:01 AM, yreysa <gary@...> wrote:
>
> >
> >
> > Hi,
> > I've been doing a little work on downspout collectors with the aim of doing
> > a side by side comparison with the screen collector.
> >
> > Having a little trouble working out a good manifold that distributes the
> > air evenly to all the downspouts. Here are the details on the problem:
> >
> > http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColFlow.htm
> >
> > Some pictures of the construction used on the prototype:
> >
> > http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColProto.htm
> >
> > Any suggestions on a better manifold design would be appreciated.
> >
> > Gary
> >
> >
> >
>
>
>
> --
> So It Is, Here in the Eternal Now.
> Fritz Schantz
>
> www.fritzdesigns.com
>

--
So It Is, Here in the Eternal Now.
Fritz Schantz

--
So It Is, Here in the Eternal Now.
Fritz Schantz

• Sorry - I just realized that the ilustrations I provided might be confusing on a white background. The attached have the bounding box of the collector. ... --
Message 19 of 30 , May 5, 2011
Sorry - I just realized that the ilustrations I provided might be confusing on a white background.  The attached have the bounding box of the collector.

On Thu, May 5, 2011 at 12:12 PM, fritz schantz wrote:
A couple more ideas Gary-
1) Plenum extension is a second layer of polyiso 3" off of the back of the collector, boxed in with the intake mounted on top of that.  The air would travel down the back side and normalize flow the time it hits bottom, passes through a slot in the back of the collector into the internal intake plenum.

2) Intake extension is based on of Laren's idea of passing the incoming air over the outsides of the downspouts in the collector interior, and then passing through a slot in your bottom manifold into the intake plenum.

Both of these "should" in my untrained mind produce even airflow to each downspout.

On Thu, May 5, 2011 at 7:03 AM, fritz schantz wrote:

[Attachment(s) from fritz schantz included below]

Something like the attached.

On Wed, May 4, 2011 at 9:42 PM, yreysa <gary@...> wrote:

Thanks Fritz,
Are you thinking baffles at the inlet to each downspout, or baffles across the inlet manifild and perpendicular to its long axis?

Gary

--- In SimplySolar@yahoogroups.com, fritz schantz <fritz.schantz@...> wrote:
>
> Looks great Gary! Off the top of my head ; what about a baffle plate that
> has slots cut in it that are narrower near the input and get wider as they
> go outward? The idea is to make the flow even by restricting the air where
> the velocity is higher. This would of course need trial and error to tune,
> but the slots could be formed with tape until optimum flow is established
> and then used as a template to cut a final piece of sheetmetal.
>
> On Wed, May 4, 2011 at 10:01 AM, yreysa <gary@...> wrote:
>
> >
> >
> > Hi,
> > I've been doing a little work on downspout collectors with the aim of doing
> > a side by side comparison with the screen collector.
> >
> > Having a little trouble working out a good manifold that distributes the
> > air evenly to all the downspouts. Here are the details on the problem:
> >
> > http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColFlow.htm
> >
> > Some pictures of the construction used on the prototype:
> >
> > http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColProto.htm
> >
> > Any suggestions on a better manifold design would be appreciated.
> >
> > Gary
> >
> >
> >
>
>
>
> --
> So It Is, Here in the Eternal Now.
> Fritz Schantz
>
> www.fritzdesigns.com
>

--
So It Is, Here in the Eternal Now.
Fritz Schantz

--
So It Is, Here in the Eternal Now.
Fritz Schantz

--
So It Is, Here in the Eternal Now.
Fritz Schantz

• Or, possibly just keep the rectangular dimensions of the plenum, but make the plenum smaller. This would make it harder for the air to reach the far
Message 20 of 30 , May 5, 2011
Or, possibly just keep the rectangular dimensions of the plenum, but make the plenum smaller.  This would make it harder for the air to reach the far downspouts and hopefully equalize flow.  It would also have the advantage of increasing the downspout area, maximizing their heat transfer ability.

Scott

-----Original Message-----
From: fritz schantz <fritz.schantz@...>
To: SimplySolar@yahoogroups.com
Sent: Thu, May 5, 2011 12:43 pm
Subject: Re: [SimplySolar] Re: Downspout collector manifold puzzle/challenge [2 Attachments]

[Attachment(s) from fritz schantz included below]
Sorry - I just realized that the ilustrations I provided might be confusing on a white background.  The attached have the bounding box of the collector.

On Thu, May 5, 2011 at 12:12 PM, fritz schantz wrote:
A couple more ideas Gary-
1) Plenum extension is a second layer of polyiso 3" off of the back of the collector, boxed in with the intake mounted on top of that.  The air would travel down the back side and normalize flow the time it hits bottom, passes through a slot in the back of the collector into the internal intake plenum.

2) Intake extension is based on of Laren's idea of passing the incoming air over the outsides of the downspouts in the collector interior, and then passing through a slot in your bottom manifold into the intake plenum.

Both of these "should" in my untrained mind produce even airflow to each downspout.

On Thu, May 5, 2011 at 7:03 AM, fritz schantz wrote:

[Attachment(s) from fritz schantz included below]
Something like the attached.

On Wed, May 4, 2011 at 9:42 PM, yreysa <gary@...> wrote:

Thanks Fritz,
Are you thinking baffles at the inlet to each downspout, or baffles across the inlet manifild and perpendicular to its long axis?

Gary

--- In SimplySolar@yahoogroups.com, fritz schantz <fritz.schantz@...> wrote:
>
> Looks great Gary! Off the top of my head ; what about a baffle plate that
> has slots cut in it that are narrower near the input and get wider as they
> go outward? The idea is to make the flow even by restricting the air where
> the velocity is higher. This would of course need trial and error to tune,
> but the slots could be formed with tape until optimum flow is established
> and then used as a template to cut a final piece of sheetmetal.
>
> On Wed, May 4, 2011 at 10:01 AM, yreysa <gary@...> wrote:
>
> >
> >
> > Hi,
> > I've been doing a little work on downspout collectors with the aim of doing
> > a side by side comparison with the screen collector.
> >
> > Having a little trouble working out a good manifold that distributes the
> > air evenly to all the downspouts. Here are the details on the problem:
> >
> > http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColFlow.htm
> >
> > Some pictures of the construction used on the prototype:
> >
> > http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColProto.htm
> >
> > Any suggestions on a better manifold design would be appreciated.
> >
> > Gary
> >
> >
> >
>
>
>
> --
> So It Is, Here in the Eternal Now.
> Fritz Schantz
>
> www.fritzdesigns.com
>

--
So It Is, Here in the Eternal Now.
Fritz Schantz

--
So It Is, Here in the Eternal Now.
Fritz Schantz

--
So It Is, Here in the Eternal Now.
Fritz Schantz

• Hi Gary, A couple of other ideas: 1)-a much larger plenum...tapered like Laren suggested. or 2)-feed your plenum with multiple pipes (like headers on a car
Message 21 of 30 , May 5, 2011
Hi Gary,

A couple of other ideas:

1)-a much larger plenum...tapered like Laren suggested.
or
2)-feed your plenum with multiple pipes (like headers on a car exhaust)...maybe t the intake duct into 2 ducts, then t them again to make 4 evenly distributed into the plenum
or
3)After looking at your graphs, I wonder what the distribution would look like if you used 2 fans in series...one on the outlet pulling and one on the inlet pushing.

Scott S.

--- In SimplySolar@yahoogroups.com, "yreysa" <gary@...> wrote:
>
> Hi,
> I've been doing a little work on downspout collectors with the aim of doing a side by side comparison with the screen collector.
>
> Having a little trouble working out a good manifold that distributes the air evenly to all the downspouts. Here are the details on the problem:
> http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColFlow.htm
>
> Some pictures of the construction used on the prototype:
> http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColProto.htm
>
> Any suggestions on a better manifold design would be appreciated.
>
> Gary
>
• Hi, Two layers of alum screen runs about \$0.7 per sqft. The alum downspout the way I did it runs about \$3.40 a sqft. So, there is a significant difference.
Message 22 of 30 , May 5, 2011
Hi,
Two layers of alum screen runs about \$0.7 per sqft.
The alum downspout the way I did it runs about \$3.40 a sqft.
So, there is a significant difference.
But, when some of the commercial air heating collectors are going for \$40 a sqft, they both offer very large saving, and maybe a \$2 per sqft difference is not that important -- especailly if there is a performance gain.

Also think that the way I stacked the downspouts in nearly right next to each other can be improved, and that would cut the cost some.

Gary

--- In SimplySolar@yahoogroups.com, "solarinterested" <solarinterested@...> wrote:
>
> As always it's great to see the detailed descriptions and photos of your
> experiments. Manifold issues aside, I'd be interested in your costs
> compared to a screen collector. Even assuming the better heat transfer
> results in each piece of downspout being equivalent to a flat width of
> 10" (3+2+3+2) the cost of downspouts would seem to be much more than a
> multilayer screen absorber.
>
• thanks very much Ken, Fritz, Laren, Scott^2, Steve, Jeff All good stuff and down in the notebook. I did a little more work this morning with our part day of
Message 23 of 30 , May 5, 2011
thanks very much Ken, Fritz, Laren, Scott^2, Steve, Jeff
All good stuff and down in the notebook.

I did a little more work this morning with our part day of sun (a rarity this spring).

One interesting thing is that the pressure drop across the collector when its flowing 92 cfm (3 cfm/sf) is 0.33 inches of water -- more than I would like. The calculated pressure drop for the downspouts is only 0.005 inches of water, so I gather most of this drop is from the manifolds and the turns. One thing I like about laren's tapered manifold is that it would probably reduce the collector pressure drop.

The IR pictures of the operating collector with the glazing off tend to verify the differences in flow rates with the low flow downspouts running hotter than the full flow ones.

Still waiting for a really clear day to run the screen and downspout collectors side by side.

Gary

--- In SimplySolar@yahoogroups.com, "yreysa" <gary@...> wrote:
>
> Hi,
> I've been doing a little work on downspout collectors with the aim of doing a side by side comparison with the screen collector.
>
> Having a little trouble working out a good manifold that distributes the air evenly to all the downspouts. Here are the details on the problem:
> http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColFlow.htm
>
> Some pictures of the construction used on the prototype:
> http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColProto.htm
>
> Any suggestions on a better manifold design would be appreciated.
>
> Gary
>
• Hi Gary humm! I thought the downspout parallel flow hot air coillector would work like the parallel flow hot water collector. I wonder why it would be
Message 24 of 30 , May 5, 2011
Hi Gary humm!
I thought the downspout parallel flow hot air coillector  would work like the parallel flow hot water collector. I wonder why it would be different?
John

On Wed, May 4, 2011 at 9:45 PM, yreysa wrote:

Hi John,
I thought about the opposite corner feed, but it seems like you either end up with very high velocities or a very large manifold.
I went to the center feed when the height of the corner feed manifold went up to 17 inches just to keep the manifold velocity down to the same as the downspout velocities.

Gary

--- In SimplySolar@yahoogroups.com, John Canivan <canivan@...> wrote:
>
>
> Looks neat Gary. Nice job. The header is large and that should help.
> My suggestions for uniform flow is to place the input pipe on the left
> side of the bottom header and place the exit pipe on the right side of
> the top manifold.
> This should help distribute the flow of air uniformly in the same way as
> your parallel flow hot water collectors. Hot air collectors. As you know
> I have done very little work with hot air collectors. I understand the
> value has to do with the simplicity of the system and also concerns
> about leaks, but if I did get involved with hot air systems I believe I
> would favor the screen or the polyester absorber plate since the
> materials used for heat collection are more cost effective. Still it
> will be interesting to see a comparison of the downspout collector with
> the screen collector. Where do you get all your energy, Gary?
> John
>
> On Wed, May 4, 2011 at 10:01 AM, yreysa wrote:
>
>     Hi,
> I've been doing a little work on downspout collectors with the aim of
> doing a side by side comparison with the screen collector.
>
> Having a little trouble working out a good manifold that distributes the
> air evenly to all the downspouts.  Here are the details on the problem:
>
>
> Some pictures of the construction used on the prototype:
>
>
> Any suggestions on a better manifold design would be appreciated.
>
> Gary
>
>
>

• I was thinking the exact same thing as #3. Just do not think it works in his test setup, but in implementation it looks based on the graphs to probably be a
Message 25 of 30 , May 5, 2011
I was thinking the exact same thing as #3.  Just do not think it works in his test setup, but in implementation it looks based on the graphs to probably be a winner in flow values.

Makes sense in my mind as pressure at any one area would not have to be that great.  or so I would imagine as you would have both negative and positive pressures working together.

Matthew

On Thu, May 5, 2011 at 12:20 PM, wrote:

Hi Gary,

A couple of other ideas:

1)-a much larger plenum...tapered like Laren suggested.
or
2)-feed your plenum with multiple pipes (like headers on a car exhaust)...maybe t the intake duct into 2 ducts, then t them again to make 4 evenly distributed into the plenum
or
3)After looking at your graphs, I wonder what the distribution would look like if you used 2 fans in series...one on the outlet pulling and one on the inlet pushing.

Scott S.

--- In SimplySolar@yahoogroups.com, "yreysa" <gary@...> wrote:
>
> Hi,
> I've been doing a little work on downspout collectors with the aim of doing a side by side comparison with the screen collector.
>
> Having a little trouble working out a good manifold that distributes the air evenly to all the downspouts. Here are the details on the problem:
> http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColFlow.htm
>
> Some pictures of the construction used on the prototype:
> http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColProto.htm
>
> Any suggestions on a better manifold design would be appreciated.
>
> Gary
>

• Hi Gary, Are you saying that the air velocity was so high that you weren t taking enough the heat off the absorber or that it was too high because you were
Message 26 of 30 , May 6, 2011
Hi Gary,
Are you saying that the air velocity was so high that you
weren't taking enough the heat off the absorber or that it
was too high because you were trying to match the
air velocity of the reference collector?
-Steve
http://rimstar.org/renewnrg

-----Original Message-----
From: John Canivan canivan@...
Sent 5/5/2011 6:55:22 PM
To: simplysolar@yahoogroups.com
Subject: RE: [SimplySolar] Re: Downspout collector manifold puzzle/challenge

Hi Gary humm!
I thought the downspout parallel flow hot air coillector would work like the parallel flow hot water collector. I wonder why it would be different?
John

On Wed, May 4, 2011 at 9:45 PM, yreysa wrote:
Hi John,

I thought about the opposite corner feed, but it seems like you either end up with very high velocities or a very large manifold.

I went to the center feed when the height of the corner feed manifold went up to 17 inches just to keep the manifold velocity down to the same as the downspout velocities.

Gary

--- In SimplySolar@yahoogroups.com, John Canivan canivan@... wrote:

Looks neat Gary. Nice job. The header is large and that should help.

My suggestions for uniform flow is to place the input pipe on the left

side of the bottom header and place the exit pipe on the right side of

the top manifold.

This should help distribute the flow of air uniformly in the same way as

your parallel flow hot water collectors. Hot air collectors. As you know

I have done very little work with hot air collectors. I understand the

value has to do with the simplicity of the system and also concerns

about leaks, but if I did get involved with hot air systems I believe I

would favor the screen or the polyester absorber plate since the

materials used for heat collection are more cost effective. Still it

will be interesting to see a comparison of the downspout collector with

the screen collector. Where do you get all your energy, Gary?

John

On Wed, May 4, 2011 at 10:01 AM, yreysa wrote:

Hi,

I've been doing a little work on downspout collectors with the aim of

doing a side by side comparison with the screen collector.

Having a little trouble working out a good manifold that distributes the

air evenly to all the downspouts. Here are the details on the problem:

http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColFlow.htm

http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColFlow.htm

Some pictures of the construction used on the prototype:

http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColProto.htm

http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColProto.htm

Any suggestions on a better manifold design would be appreciated.

Gary

http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColProto.htm

http://docs.yahoo.com/info/terms/
• Hi Steve, I was trying for a collector flow of about 3 cfm per sf of collector, or about 90 cfm for the full collector. This works out to a fairly modest 170
Message 27 of 30 , May 6, 2011
Hi Steve,
I was trying for a collector flow of about 3 cfm per sf of collector, or about 90 cfm for the full collector. This works out to a fairly modest 170 fpm velocity in the actual downspouts. To me, this seems about right -- its enough airflow to pick up the heat, and the Reynolds number is high enough to get turbulent (well mixed) flow.

But, when you try to size the inlet and outlet manifolds using the opposite corner feed, the velocities in the manifold get pretty high unless you make the manifold quite tall.
The collector (and manifold) are 4.5 inches deep. So, if you try (as a start) to match the manifold velocity at the air inlet to the downspout velocity of 170 fpm, then the manifold area needs to be (90 cfm/170 fpm) = 0.53 sf -- at 4.5 inches deep, this makes the manifold (0.53)(144)/4.5 = 17 inches tall. This seems like a lot to me -- 34+ inches of the 94 inch collector height would be manifold. While the manifold with the black metal cover plate does count as collector area, its not going to be as efficient as the downspout part?

If you say that I'm just going to go with a square manifold at 4.5 inches square, then the velocity at the inlet and out let is (90 cfm)/((4.5)(4.5)/(144))= 640 fpm, which seems kind of high.
I think that the relatively high manifold velocities I have are contributing to the fairly high pressure drop across the collector of 0.33 inches of water. This high pressure drop makes for a more expensive and noisier fan.

Laren's tapered manifold seems like it might be a step in the right direction.

------
Just as a side note.
For water collectors, it seems like about 0.04 gpm/sf is about the right flow -- it gives a temperature rise across the collector of abot 7.5 F, which keeps the absorber heat losses down and makes for pretty efficient operation:
http://www.builditsolar.com/References/ColFlowRate.htm

For air collectors, doing the temperature rise calculation the same way as the link just above with 3 cfm per sqft of collector airflow gives a temperature rise of

Qout = Trise * FlowRate * SpecificHeat

Trise = Qout/FlowRate*Specificheat =
(150 BTU/hr-sf)/(3cf/min-sf)(60min/hr)(0.07lb/cf)(0.24 BTU/lb-F)= 50F

This is good in the sense that you need a temperature rise of about 50F just to produce air that feels warm when it comes out, but not so good for collector losses and efficiency -- the hotter absorber makes for more heat loss out the glazing.

Gary

--- In SimplySolar@yahoogroups.com, "Steven Dufresne" <stevend@...> wrote:
>
> Hi Gary,
> Are you saying that the air velocity was so high that you
> weren't taking enough the heat off the absorber or that it
> was too high because you were trying to match the
> air velocity of the reference collector?
> -Steve
> http://rimstar.org/renewnrg
>
> -----Original Message-----
> From: John Canivan canivan@...
> Sent 5/5/2011 6:55:22 PM
> To: simplysolar@yahoogroups.com
> Subject: RE: [SimplySolar] Re: Downspout collector manifold puzzle/challenge
>
> Hi Gary humm!
> I thought the downspout parallel flow hot air coillector would work like the parallel flow hot water collector. I wonder why it would be different?
> John
>
> On Wed, May 4, 2011 at 9:45 PM, yreysa wrote:
> Hi John,
>
> I thought about the opposite corner feed, but it seems like you either end up with very high velocities or a very large manifold.
>
> I went to the center feed when the height of the corner feed manifold went up to 17 inches just to keep the manifold velocity down to the same as the downspout velocities.
>
>
> Gary
>
> --- In SimplySolar@yahoogroups.com, John Canivan canivan@ wrote:
>
> Looks neat Gary. Nice job. The header is large and that should help.
>
> My suggestions for uniform flow is to place the input pipe on the left
>
> side of the bottom header and place the exit pipe on the right side of
>
> the top manifold.
>
> This should help distribute the flow of air uniformly in the same way as
>
> your parallel flow hot water collectors. Hot air collectors. As you know
>
> I have done very little work with hot air collectors. I understand the
>
> value has to do with the simplicity of the system and also concerns
>
> about leaks, but if I did get involved with hot air systems I believe I
>
> would favor the screen or the polyester absorber plate since the
>
> materials used for heat collection are more cost effective. Still it
>
> will be interesting to see a comparison of the downspout collector with
>
> the screen collector. Where do you get all your energy, Gary?
>
> John
>
>
>
> On Wed, May 4, 2011 at 10:01 AM, yreysa wrote:
>
>
>
> Hi,
>
> I've been doing a little work on downspout collectors with the aim of
>
> doing a side by side comparison with the screen collector.
>
>
>
> Having a little trouble working out a good manifold that distributes the
>
> air evenly to all the downspouts. Here are the details on the problem:
>
>
>
> http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColFlow.htm
>
> http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColFlow.htm
>
>
>
> Some pictures of the construction used on the prototype:
>
>
>
> http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColProto.htm
>
> http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColProto.htm
>
>
>
> Any suggestions on a better manifold design would be appreciated.
>
>
>
> Gary
>
>
>
>
>
> http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColProto.htm
>
> http://docs.yahoo.com/info/terms/
>
• Hi Gary, Thanks for the detailed response. However, I could be wrong but if you think about the corner to corner approach then the 0.53sf cross sectional area
Message 28 of 30 , May 6, 2011
Hi Gary,
Thanks for the detailed response.

However, I could be wrong but if you think about the corner to corner approach
then the 0.53sf cross sectional area is actually split between one
downspout and the manifold since the air flow splits after immediately
entering the manifold from outside. Some air flows down the first
downspout while the remainder flows down the manifold. At the next
downspout it splits again. So the manifold needs to be
[(0.53sf x 144sinch/sf) - (2" x 3")] / 4.5" = 15.6" long. No big difference
though.

I'm having trouble vizualizing how the flow changes as it progresses down
the manifold. I think it doesn't matter because the traversal length for
each downspout is always the same. It'll be interesting to see the
pressure drop with Laren's tapered approach.
-Steve
http://rimstar.org/renewnrg
PS. It took about 30 minutes of visualization before I understood that
0.53sf was the cross sectional area of the "hole" the air travelled through
given 90cfm at 170fpm and that 4.5" x 17" was simply a forced configuration
of that hole based on one dimension having to be 4.5". I learned a lot from
figuring that out so thanks for the starting point.

-----Original Message-----
From: yreysa gary@...
Sent 5/6/2011 10:47:16 AM
To: SimplySolar@yahoogroups.com
Subject: [SimplySolar] Re: Downspout collector manifold puzzle/challenge

Hi Steve,
I was trying for a collector flow of about 3 cfm per sf of collector, or about 90 cfm for the full collector. This works out to a fairly modest 170 fpm velocity in the actual downspouts. To me, this seems about right -- its enough airflow to pick up the heat, and the Reynolds number is high enough to get turbulent (well mixed) flow.

But, when you try to size the inlet and outlet manifolds using the opposite corner feed, the velocities in the manifold get pretty high unless you make the manifold quite tall.
The collector (and manifold) are 4.5 inches deep. So, if you try (as a start) to match the manifold velocity at the air inlet to the downspout velocity of 170 fpm, then the manifold area needs to be (90 cfm/170 fpm) = 0.53 sf -- at 4.5 inches deep, this makes the manifold (0.53)(144)/4.5 = 17 inches tall. This seems like a lot to me -- 34+ inches of the 94 inch collector height would be manifold. While the manifold with the black metal cover plate does count as collector area, its not going to be as efficient as the downspout part?

If you say that I'm just going to go with a square manifold at 4.5 inches square, then the velocity at the inlet and out let is (90 cfm)/((4.5)(4.5)/(144))= 640 fpm, which seems kind of high.
I think that the relatively high manifold velocities I have are contributing to the fairly high pressure drop across the collector of 0.33 inches of water. This high pressure drop makes for a more expensive and noisier fan.

Laren's tapered manifold seems like it might be a step in the right direction.

------
Just as a side note.
For water collectors, it seems like about 0.04 gpm/sf is about the right flow -- it gives a temperature rise across the collector of abot 7.5 F, which keeps the absorber heat losses down and makes for pretty efficient operation:
http://www.builditsolar.com/References/ColFlowRate.htm

For air collectors, doing the temperature rise calculation the same way as the link just above with 3 cfm per sqft of collector airflow gives a temperature rise of

Qout = Trise * FlowRate * SpecificHeat

Trise = Qout/FlowRate*Specificheat =
(150 BTU/hr-sf)/(3cf/min-sf)(60min/hr)(0.07lb/cf)(0.24 BTU/lb-F)= 50F

This is good in the sense that you need a temperature rise of about 50F just to produce air that feels warm when it comes out, but not so good for collector losses and efficiency -- the hotter absorber makes for more heat loss out the glazing.

Gary

--- In SimplySolar@yahoogroups.com, "Steven Dufresne" stevend@... wrote:

Hi Gary,
Are you saying that the air velocity was so high that you
weren't taking enough the heat off the absorber or that it
was too high because you were trying to match the
air velocity of the reference collector?
-Steve
http://rimstar.org/renewnrg

-----Original Message-----
From: John Canivan canivan@...
Sent 5/5/2011 6:55:22 PM
To: simplysolar@yahoogroups.com
Subject: RE: [SimplySolar] Re: Downspout collector manifold puzzle/challenge

Hi Gary humm!
I thought the downspout parallel flow hot air coillector would work like the parallel flow hot water collector. I wonder why it would be different?
John

On Wed, May 4, 2011 at 9:45 PM, yreysa wrote:
Hi John,

I thought about the opposite corner feed, but it seems like you either end up with very high velocities or a very large manifold.

I went to the center feed when the height of the corner feed manifold went up to 17 inches just to keep the manifold velocity down to the same as the downspout velocities.

Gary

--- In SimplySolar@yahoogroups.com, John Canivan canivan@ wrote:

Looks neat Gary. Nice job. The header is large and that should help.

My suggestions for uniform flow is to place the input pipe on the left

side of the bottom header and place the exit pipe on the right side of

the top manifold.

This should help distribute the flow of air uniformly in the same way as

your parallel flow hot water collectors. Hot air collectors. As you know

I have done very little work with hot air collectors. I understand the

value has to do with the simplicity of the system and also concerns

about leaks, but if I did get involved with hot air systems I believe I

would favor the screen or the polyester absorber plate since the

materials used for heat collection are more cost effective. Still it

will be interesting to see a comparison of the downspout collector with

the screen collector. Where do you get all your energy, Gary?

John

On Wed, May 4, 2011 at 10:01 AM, yreysa wrote:

Hi,

I've been doing a little work on downspout collectors with the aim of

doing a side by side comparison with the screen collector.

Having a little trouble working out a good manifold that distributes the

air evenly to all the downspouts. Here are the details on the problem:

http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColFlow.htm

http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColFlow.htm

Some pictures of the construction used on the prototype:

http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColProto.htm

http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColProto.htm

Any suggestions on a better manifold design would be appreciated.

Gary

http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColProto.htm

http://docs.yahoo.com/info/terms/
• Posted by: yreysa gary@BuildItSolar.com ... Hi Gary; That is not necessary, since the plenum is not a duct, therefore does not need to move all the air for
Message 29 of 30 , May 7, 2011
Posted by: "yreysa" gary@...

>The collector (and manifold) are 4.5 inches deep. So, if you try
> (as a start) to match the manifold velocity at the air inlet to the
> downspout velocity of 170 fpm, then the manifold area needs
> to be (90 cfm/170 fpm) = 0.53 sf -- at 4.5 inches deep, this
> makes the manifold (0.53)(144)/4.5 = 17 inches tall.

Hi Gary;

That is not necessary, since the plenum is not a duct, therefore
does not need to move all the air for any particular distance. Instead
the important factor is that the circumference of the inlet/outlet ducts
is greater than 17" and that there is clearance for the air that escapes
(or enters) through the wall sides of the inlet/outlet can get around the
sides of the duct opening. Since you are probably using a 6" round
duct, then the first two downspouts will have all of their airflow across
the plenum, rather than down it, The next few will also have their flow
running diagonally. Do as I suggested, and set the ends of the down-
spouts at a diagonal, and basically the air flow will "radiate" from the
duct, to the various downspout ends. The reverse will happen at the
outlet end.

> This seems like a lot to me -- 34+ inches of the 94 inch collector
> height would be manifold.

My suggestion (tapering the plenums with the downspouts like
the pipes of a pan flute) will reduce the plenum area by about 50%

> While the manifold with the black metal cover plate does count as
> collector area, its not going to be as efficient as the downspout part?

They are both backpass, so it won't make that much difference.

> If you say that I'm just going to go with a square manifold at
> 4.5 inches square, then the velocity at the inlet and out let is
> (90 cfm)/((4.5)(4.5)/(144))= 640 fpm, which seems kind of high.

So make it 4½" x 6¼", so that it is equal to a 6" round.
However, that does not solve the issue with the restricted
transition from the duct to the plenum, or the 90° turns,
from the plenum into the downspouts. Both will be
ameliorated by the tapered plenums.

> Laren's tapered manifold seems like it might be a step in the right
> direction.

It will only require a fairly small taper. The ends of the downspouts can
also be cut at that angle, with the far end downspout having its long side
almost touching the end of the collector box. The downspouts at the
close end will draw air almost directly from the inlet duct, so their flow
will not effect the plenum dimension (collector bottom, to downspouts).
Nor will the ones that are fairly close. So, close downspouts will not
need to be very far from the inlet, with the downspout ends tapering
to the opposite corner of the collector. All of the downspouts will be
the same length, because the pattern will be mirrored, at the outlet
end. So, it is real easy to build. However, as long as this is a back
pass collector, without a selective surface, it is not going to perform
as well as the matrix absorber panels. And, it costs three times as

> For water collectors, it seems like about 0.04 gpm/sf is about
> the right flow -- it gives a temperature rise across the collector
> of abot 7.5 F, which keeps the absorber heat losses down and
> makes for pretty efficient operation:

That is equivalent to 18.5CFM in terms of thermal mass.
However, air panel design has to be very different, in order
to make up for that. So, instead of an ideal of nearly five time
the glazing area (for air panels), in heat exchanger surface area,
hydronic panels only need about ¼ft²/ft² of glazing.

> 50F (temperature rise)

> This is good in the sense that you need a temperature rise of about
> 50F just to produce air that feels warm when it comes out, but not
> so good for collector losses and efficiency -- the hotter absorber
> makes for more heat loss out the glazing.

Let's say we have a net Solar gain of: (I'll use twinwall glazing)

Gain: 300BTU/ft²hr x cos45° x 0.82 x 0.95 = 165TU/ft²hr

Let's assume an average collector temperature of 100°F,
and an ambient temperature of 30°F, so our glazing heat
loss will be around 70/1.73 = 40BTU/ft²hr, and the net

So if we go for 50% efficiency with a flow rate of 3CFM/ft²
That will mean a temperature rise of

(125/(2x60)/0.018 = 58°, which reflects an inlet temperature
of about 71°F and an outlet of 129°F

However, With a matrix airflow path, the 70°F air is slowly
washing the glazing, to reduce the glazing heat loss, so the
average temperature will be significantly lower than 100°F,
and collector efficiencies will be higher. But, a calculation
would need to express the higher radiant temperature of
the absorber, as well as the cooler interior air temper-
-ature, and the slow air movement over the interior
surface of the glazing.

Posted by: "Steven Dufresne" stevend@...

>if you think about the corner to corner approach then the 0.53sf
> cross sectional area is actually split between one downspout and
> the manifold

The taper can be thought of as pivoting on the end that is by the inlet.

The full 17" width is only needed at the beginning, where there is the
full 90CFM of air flow. Each downspout reduces that volume of air
that the plenum must carry, beyond that point. And, since a portion
of the air will immediately leave the plenum, through the first two
downspout, the plenum does not need to carry it, at all. This situation
repeats itself, all the way to the end, which carries no air flow, past
the side of the last downspout. Since the inlet duct is about as wide
as the first two downspouts, and the next few will also receive airflow
that is running across the plenum, the average plenum width will not
need to be even half of the 17" that Gary calculated. So, as long as
it clears the inlet duct, it will be wide enough.

However, another factor to consider is the discharge area of the
outlet duct (into the plenum). A 6" round duct only has a perimeter
length of 18.85". Assuming that at least a quarter of that will
effectively
be useless, because of the corner walls, that only leaves us with 14.14",
which is less than Gary's 17" required plenum width. So, it is necessary
to either make the plenum deeper than 4½", or to move the plenum, at
least a little, out of the corner, so the air which escapes it, along its
corner sides, can freely get around it, and into the plenum.

>I'm having trouble vizualizing how the flow changes as it progresses
> down the manifold. I think it doesn't matter because the traversal
> length for each downspout is always the same.

It is reduced by the percentage of the total air flow, that is removed
by each progressive downspout. By the time you get to the end, there
is no more air flow. Therefore, there is no need for a plenum, beyond
the last downspout, just as there is no need for half the plenum size,
beyond the first half of the downspouts.

-Laren Corie-
Natural Solar Building Design and
Solar Heating/Natural Cooling/Energy
Efficiency Consultation Since 1975
www.ThermalAttic.com

www.EarthWeekPlus.com

Read my Solar house design articles in:
www.essnmag.com

Home base-LittleHouses YahooGroup
http://groups.yahoo.com/group/LittleHouses/

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• I feel that your graphs shows that in the air is moving to the area on the manifolds away from the inlet. The air that comes in at the side of the inlet away
Message 30 of 30 , May 8, 2011
I feel that your graphs shows that in the air is moving to the area on the manifolds away from the inlet. The air that comes in at the side of the inlet away from the downspouts has only the ends of the manifolds to go to. It has more air and time to slow down and make the bend into the downspouts with less tubulance.
I would try 1 to 4 layers of screening, adding one layer at a time to give some resistance to the air movement before doing some of the modifications that have been talked about. The first layer would be across the output ends of the downspouts so all of them act like little accumulators to possibly equal out the air flowing through them. Since you have the IR camera you should be able to test the difference each layer has on the collector. Second layer across the inputs of the downspout. Third on the output end and the fourth on the input end. I would give the second layers on the ends about 1/8 to 1/4 inch of a gap. you want to have more resistance than you would on the screen type collectors.

--- In SimplySolar@yahoogroups.com, "yreysa" <gary@...> wrote:
>
> Hi,
> I've been doing a little work on downspout collectors with the aim of doing a side by side comparison with the screen collector.
>
> Having a little trouble working out a good manifold that distributes the air evenly to all the downspouts. Here are the details on the problem:
> http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColFlow.htm
>
> Some pictures of the construction used on the prototype:
> http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColProto.htm
>
> Any suggestions on a better manifold design would be appreciated.
>
> Gary
>
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