Posted by: "Snkdavis" SNKDavis@...

> Gary has a great, step by step template for the reference
> collector that we are both using for our comparative testing.
> It is a solid, backpass absorber design:

>But, how should I install the screen and vented soffit absorbers?

Hi Scott;

For the vented aluminum soffit collector, ask its originator........me

> I was planning to start them affixed against the back
> collector wall, at the bottom, just above the inlet hole.

That is fine......

> At the top, I would attach them maybe 2" high (just guessing)

What does "high" mean?

> against the top wall of the box, approximately an inch from the glazing

It should meet the top of the collector 1/2" -3/4" from the glazing.
(1/2" is better) This is important when the collector is so thin.
A large space in front of the absorber, reduces the size of the
space behind, restricting the air flow around the outlet vent.

> (the conduit takes about a half inch, so I have about
> 3 inches to work with).

> That way, when air comes into the collector through the hole at
> the bottom, it is forced to be above the absorber and it has to pass
> through the absorber to reach the outlet hole at the top.

Is the inlet in the back or actually in the bottom of the panel?

How big is the inlet?

The air should enter the collector through the back, blowing against
a baffle, which should be about 3/4" from the glazing (the baffle can
be made from solid soffit, or vented soffit with aluminum tape over
the back of the holes. The vent holes could also be hammered flat
with a rubber or wooden mallet or hammer and wood block, etc.

> Here is what I'm trying to describe. The red grid represents
> the vented soffit or screen heat absorber:

Can you email me the image, or post a link?
(I live out in the woods, with only dialup available)

Use I channel (made for mounting soffits) to mount the absorber.
Run the soffit across the collector (shorter span). Do not caulk
the edges, or connections between pieces. Just fit it together,
the same way that soffit fits together, in normal installation.

> I like the idea of bringing the air up through the soffit / screen
> without it being all the way against the back wall.

That is the way I do it. It works well. Run the vented soffit
to the back of the box, at the very bottom. Cut out for the
inlet duct. If it is rigid duct, cut tabs and fold them open, and
tape the edges. If using flex duct, bring it through and tape it.
If you bring the inlet through the absorber, you will also need
to seal between the duct and the back of the box, either out-
-side, or inside the panel, to stop air leaks. Then, install
the baffle, across the width of the panel.

> I may just raise it up 1 1/2" all the way around for the entire
> collector,

That will produce an inferior collector. It will create too high
velocity, at the both ends. The absorber needs even air flow
(with the front air-flow-path area reducing as the air that is left
in front of the absorber is reduced, and increasing behind the
absorber, as the amount of air behind the absorber increases)
therefore we angle the absorber across the air flow path, so
that the air flow path is 3" deep (at least 2½") , not just
1½" deep, and the flow is not restricted at the ends.

> The air will be forced to pass through,

The air should not be forced more in one area than any other.
The air flow path should taper, as the air it transports decreases.
Placing the absorber unnecessarily close to the inlet and outlet
creates restricted air flow at both ends, causing uneven passage
of the air through the absorber. That produces hot and cold
spots. The way to assure more even air flow, through the
absorber, is for the air flow restriction of the absorber, to be
the biggest resistance that the air encounters in the collector.

> Yes, I'll probably put a baffle on the bottom, through since
> I'm pulling instead of pushing, I think it's not as critical.

Air is not pulled or pushed (or it is both). What a fan
does, is to create higher and lower pressure areas, regardless
of which end of the flow-path it is located. When you create
a lower pressure (what you call "pull") what actually happens
is that the higher pressure is still pushing (while the low pressure
pulls) the air through, the same way that it does when the fan
is located before the collector. The purpose of the baffle is
to spread out the air flow, more evenly over the absorber,
to eliminate hot spots. Can you "pull" water, too, just by
moving the pump?

> By pulling, the air is drawn through the collector instead of
> first being forced up against the glazing.

That is incorrect The air, rushing in, through the collector inlet,
will do the very same thing, regardless of a fan location before
or after the panel. Air is not a string. It can't be just "pulled"
Placing the fan downstream is more like the fall of a river bed.
The flow will still be faster where the flow is restricted, and
anything in its path (the glass) will still have the air flow driven
up against it, by the momentum of the mass of the fluid. The
baffle keeps that concentration of air, as it flows out the inlet,
away from the glazing, and in the process, spreads it, more
evenly, to the full absorber area. A barrier can be made, to
more fully spread the air flow, by simply making two cuts into
the top edge of the baffle (aligned with the inlet), and bending
the metal between them, back toward the absorber. However,
care should be taken, for it not to rattle against the absorber,
when the air is flowing.

> Gary has a great, step by step template for the reference
> collector that we are both using for our comparative testing.

And I, as the originator of the vented aluminum soffit collector,
can tell you, step by step, how to build one of them.

Posted by: "kenneth wersinger" kennethwers@...

> I would have the bottom out from the back of the collector

Hi Kenneth;

Bingo....

>1/2 inch with a board (or insulation ) filling the crack. As you
> know you will need a baffle on the bottom to keep the incoming
> air from hitting the glazing.

And also to spread the air over the width of the panel.

> The baffle will work like a backpass collector.

Exactly.

> Or you could have the soffit (screen) run to the bottom of the collector
> spaced 1/2 inch from the back with a hole and pipe (metal tape)
> through it for the inlet with a small baffle next to the glazing. (more
> matrix area)

Generally, running the baffle all the way across the collector
will do a better job of spreading out the air flow, without the large
amount of scrubbing against the glazing. That is the most tightly
restricted area, therefore the air will be moving much faster, so it
not only contacts the glass, but does it at a greater wind speed,
which reduces the Rvalue. Make the baffle, all the way across,
and one 12" soffit section high. By the time the air is coming out
from behind it, the air will be spread out enough that it speed
will have been slowed, so the Rvalue of the glass (interior air
film) will be very close to that of still air.

>The top I would warp so that the outlet side(right side on the
> picture) is 1/2 inch from the glazing (easier air flow out the
> collector?)

I don't know about "warp" The absorber should angle
evenly across the air flow path, from the back wall, at
the bottom, to near the glazing at the top. This matches
the size of the air flow path to the volume of air that it
has to carry, with the front area decreasing as it loses
air, and the back pass increasing in depth, as it gains air.

> Just guessing!!

No. You seem to understand it, pretty well ;O)

> if the soffit slides in your hand it will cut like a knife!

You should try this metal roofing, that I have been working
with, thirty feet off the ground. The back of my right hand
looks like a blind guy was trying to carve his name into it :O(

-Laren Corie-
Natural Solar Building Design and
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