Below is a description of a very simple solar collector from the company that produces them. I also have a pdf. file showing the detailed breakdown of the unit if interested...
- ADVANCED HOMEBUILT AIR-BASED SOLAR COLLECTOR -
BUILDING INSTRUCTIONS
OVERVIEW
The instructions below are for a homebuilt version of Sol-Air Company's
air-based SHVC (Solar Heating and Ventilation Cooling) system (description
at bottom). Our commercial version differs from the homebuilt in having an
internal air-handler (the AutoVent automatic mode-switching control), and a
proprietary absorber material that has somewhat higher surface area and
selective properties.
Homebuilt Solar Collector Output
Like its commercial cousin, this homebuilt unit produces more energy for the
money by far than other forms of solar utilization, including PV and solar
DHW systems. The output for a 20 square foot unit is approximately
5,000,000 Btu per year, equal to approx. 50 gallons of heating oil (or 50
Therms of natural gas). This output is produced primarily in the spring and
fall, with a decided dead spot in the middle of a cold winter.
Mounting
The collector is mounted vertically on the outside wall (the rule that tilt
= latitude is for another type - DHW collectors, which need year-round
input). The lower sun angle in winter reduces the performance penalty, and
the avoidance of summertime sun is an important factor in increasing system
life. Another advantage gained is ease of installation.
House connection
Air passes into and out of the collector through a manifold which connects
it to the inside of the house. Instead of using the collector to replace a
window, plan to install your homebuilt collector with the manifold passing
through a hole in the wall, (you can install it beneath a window, or with
the manifold passing across the window sill of a slider-type of window).
That way, you will have two solar devices, the collector and the window.
WINDOW COMPARISON
Gain from a solar collector, as with a window, is directly proportional to
glazed area; it occurs for 5-6 hours on sunny days. Both a window and a
solar collector "leak" some of the energy taken in, but there is a net gain
during collecting hours on a good day. The difference between a solar
collector and a window is that the window leaks energy 24 hours a day, while
the solar collector leaks energy only during those 5-6 hours. People with
"passive solar" homes must play an active role in reducing nighttime losses.
During non-collecting hours, an active solar collector loses virtually no
energy, without manual intervention. A solar collector is a large no-loss
window with a virtual window plug that self-installs, whether you're home or
not.
What's a Window Plug?
While windows have greater losses, these can be reduced if you manually
insulate them at night, with "window plugs" that you make from 1" blue
Styrofoam, edged with wood strips (3/4" x 1", ripped from a 1x4). Each
night, or right when you come home from work, you plug your windows. As you
put a window plug in, you feel immediately warmer - right now. You can put
them behind a couch or door during the day. Plug north windows all winter
if you like.
Build a Window Plug:
The monetary payback period for window plugs varies from instant (if you
have spare time and materials) to six months. In winter, they have an
immediate effect on room comfort.
To make one, tack together a rectangular frame of the 3/4" x 1" wood, to fit
the inside of your window frame. Use one nail at each corner, through the
end of one piece into the end grain of the next). Brace the frame with
diagonal pieces of wood while it's in the window; remove it, lay it on top
of the Styrofoam on the floor, and mark inside the wood with a pointy marker
pen. Leave 1/16" clearance all the way around (1/8" overall). Use a very
sharp, very thin knife to cut the foam.
Double 6" long fabric strips into loops to aid removal from the window.
Slip the foam into the frame, with a loop in the joint at each side near the
top. First use dots of hot glue, then sawdust-thickened wood glue. Cover
one or both sides with Contac shelf paper, muslin in glue, wallpaper, etc.
For all-winter window plugs, prevent condensation by installing 3M V-seal on
the edges: Make the plugs 1/8" undersize (insert corrugated cardboard
underneath and on one side of the frame as you build it in the window. Sand
and prime the wood edges with shellac before you apply the V-seal. Cut the
V-seal strips to meet nicely at the corners.
Now is also the time to caulk drafts around the window trim.
COLLECTOR FEATURES
The Absorber
The most important characteristic for an air-cooled absorber is super-high
surface area. For your home-built unit, the best solar absorber is 1" thick
furnace filter media, painted flat black and located in a reflective cavity.
Furnace filter media presents a surface area to the air flow that is about
50 times the filter's face area. This is a higher surface area, by an order
of magnitude, than that of conventional metal absorbers, whether finned,
rippled, dimpled, or screen type. The sun shines on the filter fibers which
get very hot; the heat is transferred to the air passing through the filter,
taking advantage of intimate contact and good turbulence.
The "inside out" outer-surface heat exchange of this type absorber means
that fibers transfer their heat to the air coolant directly at or
immediately adjacent to the directly sun-lit sites at which the heat is
generated. Dividing the material into small fibers produces an extremely
short internal path - through the fiber material - from a sunlit fiber site
to an adjacent shaded site.
Low Cost Absorber Material
A virtual doubling of the heat transfer surface area is presented via a
conduction path length of one fiber diameter. Because the "doubled-area
path length" is extremely short, non-metallic material may be used without
any performance penalty - a significant material-cost savings.
Material note: I have used both glass fiber and polyester fiber furnace
filter media as a solar collector absorber for 18 years without observing
significant material degradation. As a pro-active precaution, observe the
"Operation Caveat" stated below.
Low Cost Design
A liquid-cooled collector cannot take advantage of this type absorber
construction, which is very light. The low weight of the absorber produces
a cascade of weight and cost savings in the support structure of the
collector.
Absorber Efficiency
The absorber's high efficiency produces a low operating temperature. A
collector built to these specifications was tested at Western Michigan
University's Energy Learning Center - no longer operating, I understand -
using the ASHRAE 93-77 procedure, yielding a greater than 72% maximum
theoretical efficiency. This was the highest efficiency air collector they
ever tested; it bettered all liquid collectors but one, which it virtually
equaled. I know of no other non-concentrating air collector, Conserval's
SolarWall included, with better full-system efficiency.
You will want furnace filter media that comes in roll form so you can
customize the size and shape of the collector. See a Grainger industrial
supply catalog, item 4WZ72 (roll, 36" W. x 90 ft.; 1" thick); other widths
are available there. You could go to an HVAC contractor and ask them to cut
you the lengths you need. Use hi-temp stove paint, and spray it at a 45
degree angle (a "glancing" angle) from both sides, so little of the paint
passes through.
The Reflective Cavity Enhances The Absorber
The foil-faced inside surface of the collector is left reflective (not
painted black) so the black filter fibers do all the absorbing. Sunlight
that passes unabsorbed from the front direction is reflected back to the
absorber for another pass, doubling the effectiveness of the absorber.
--
MAKING THE SOLAR COLLECTOR
Build the collector case of 1" foil-faced isocyanurate (urethane)
foam-board. A good final case size is 46" x 64" (the case-back is 43-1/2" x
61-1/2"). The depth of the collector case is 6". With the back material
being 1" thick, this leaves 5" for air passages. The sides are 6" wide, and
they overlap the edges of the back.
Use urethane construction adhesive for all joints. On heat-exposed joints
like the case-side/case-back joint, protect the joint with a fillet of
silicone adhesive at the inside of the case. Apply the silicone adhesive
after the urethane adhesive has set (24 hours). Use spots of hot glue to
hold temporary right-angled pieces of foam-board at three places on each
side, to keep the sides straight and to hold them square to the back while
the urethane adhesive sets overnight,.
Both urethane adhesive and silicone adhesive use water (humidity) to
initiate curing; speed curing by spraying a tiny bit of plain water on the
edges of the seams after you put the pieces together.
To provide a surface that will hold the mounting bracket screws, glue 1/4"
plywood pieces, 6" wide and full length (short sides can overlap long sides,
or the reverse), on the sides only - no plywood is needed on the back. You
can also use luan underlayment plywood. It's slightly lighter, thinner and
cheaper, but it's a less "green" material. Glue the pieces on the four
sides of the case with a single 3"-wide wavy line of urethane adhesive.
There's no need to use 3/8" plywood - it just adds weight. Even though it
would give you a chance to screw-fasten the plastic glazing, using screws
doesn't produce an even line of pressure on the edge of the glazing, only a
point pressure at each screw. You're going to cover the case with an
aluminum sheathing, so use the even pressure of the corner bend of the
aluminum sheathing to pull the glazing against the edge of the case more
evenly.
Cut an 11-1/2" square hole, centered side-to-side, in the back wall of the
case; the upper edge of the hole is 3" from the outside top surface.
Bend the Aluminum Sheathing
To make the box weather resistant, you need an aluminum outside skin, or
sheathing. The dimensions are shown in the illustration. Make up the
pieces before you install the glazing, so you can install them immediately
after, thus holding the glazing in place.
You can do the case sheathing two ways. You could use pre-painted aluminum
coil-stock (house trim material). But, the material is too thick to bend by
hand, so you should have the bends made by a siding company on their trim
brake. Plain aluminum flashing is satisfactory, just be sure to apply a car
wax to the aluminum. Aluminum flashing can be bent by hand over the edge of
a piece of plywood Press and slide your hand along the length of the bend,
"milking" it a few degrees at a time. Protect your working hand with a
leather glove, and hold an old towel to press onto the work. Back up the
aluminum with a backup block - a length of 1" x 3-1/2" pine ripped from a
straight 2x4. Set the backup block on edge on top of the aluminum, right at
the edge of the plywood, and apply a clamp at each end. Use the same backup
block to make the 1/2" x 1" x 1-1/2" aluminum flashing angles to cap the
edges of the inner "C" baffle. For the slight amount of over-bend
specified, bend the aluminum as far as you can clamped, then unclamp it and
work in some more bend by hand.
Also the flow of air through the case is guided by a "C"-shaped baffle, for
which you will need two 4-foot-long pieces of aluminum cap-angle to cover
the raw edges of the baffle. The dimensions are shown in the illustration.
Last, make ten aluminum flashing mounting-rail pieces, 1"x1" x 4 feet long,
legs a 90 degree angle.
Install the "C"-shaped baffle
The center leg of the "C" baffle runs across the 11-1/2" square hole in the
upper back wall of the case. The "C"-shaped baffle is glued with urethane
adhesive to the inside of the case, oriented with its center horizontal, at
the top, and with the two legs descending, parallel to each other. The
upper passage of the manifold is above the center leg of the "C", and the
lower passage is below. There is 6" vertical dimension of the hole below
the center leg of the "C", and 4-1/2" above. The distance between the
descending legs is 12".
Fillet all of the inside collector joints, including all around the "C"
baffle, with silicone adhesive. Cap the baffle with the aluminum cap-angle
you bent up earlier using a 3/8" bead of silicone inside the angle.
Install the Absorber Mounting-Rails
The filter absorber sits on mounting-rails aligned on a diagonal to the air
flow. Air enters the collector between the absorber and the glazing. As it
moves through the collector toward the outlet, the diagonal absorber
placement forces air to pass through the absorber to the back side, away
from the glazing. The diagonal progression starts with the absorber near to
the back wall at the inlet, and moves near to the glazing at the outlet; the
progression continues all along the air flow path. This keeps the hottest
air away from the glazing, reduces conductive heat loss, and increases
efficiency.
Use the 1"x1" angles of aluminum flashing that you bent up earlier as
mounting-rails. Install each mounting-rail so the leg touching the
collector is oriented toward the back wall. Use dots of hot glue a foot
apart to hold the mounting-rails in place temporarily; then run a continuous
fillet of silicone adhesive along the joint between the angle and the
collector wall.
Install the Mounting-Rails
Install horizontal mounting-rails at the top and bottom inside surfaces of
the collector. Use two or your pre-bent angles pieces, overlapped by an
inch, to make up the needed length. Stop the rails 3/8" short of the
adjoining surfaces. The top mounting-rail has its absorber-mounting-surface
spaced 1-1/2" from the glazing plane. The bottom mounting-rail has its
absorber-mounting-surface spaced 2" from the back wall (3" from the glazing
plane).
Install diagonal rails beginning at the inside of each "C" leg starting
below the fan; at this end, the absorber-mounting-surface is spaced 1/2"
from the back wall of the collector. The rails run in a straight line to
overlap the rail at the bottom of the collector; that is, they run at a
slight angle away from the back wall down each "C" leg, continuing past the
bottoms of the "C" legs to overlap the bottom rail. Snip a small piece from
the back leg of the angles so they can overlap the bottom rail.
Moving to the side bays, install diagonal mounting rails at the sides of
each bay, so the rails make a continuous straight line from the bottom rail
to the top rail. Again, snip a small piece from the back leg of the angles
so they can overlap the bottom and top rails.
Where the four central rails of the collector cross open space, snip the
back leg of each rail near the "C" baffle and fold the rail flat. This
allows air to travel unimpeded between the center bay and the side bays.
Install the Absorbers
With the exception of the fan/intake shroud area, the entire face of the
collector is covered with filter-media absorber sitting on mounting-rails.
In preparation for installing the absorber, cut the pieces you will need to
size, and paint them from both sides with hi-temp stove paint from a spray
can, holding it at a 45 degree angle to the face of the. Work quickly,
covering first the back, then the front; favor the front with the most
paint. Use nearly the entire spray can, leaving enough to paint the fan
shroud. At the very end, just before you put on the glazing, use the last
of the paint to touch up where needed.
Working one foot at a time, glue the absorber to the mounting-rails in a
continuous bead of silicone adhesive, again using occasional dots of hot
glue as a temporary aid.
Install the Fan
Install your collector fan (Grainger, 4WT48 70 cfm, or 4WT47 105 cfm) and a
pre-set snap-disc cooling thermostat (Grainger 2E245, close at 110 degF,
open at 90 degF) in a shroud of aluminum flashing or house trim. Make a
one-piece fan-and-solar-thermostat inlet shroud, or you can use a two-piece
shroud. One piece, to mount the fan, is an 11-7/8" x 6" pan with 1" flanges
on top and bottom (make from 11-7/8" x 8" material); it has a 4-3/4" hole at
its center and a 3/8" hole at one side to pass the thermostat leads out from
the collector. Mount the fan over the hole with 1/8" x 1/4" pop rivets and
a fillet of silicone adhesive, and bond the assembly in place with silicone
adhesive vertically in the intake, at the back wall of the collector. Make
sure the fan's air-direction arrow points into the collector.
The other shroud piece is also mounted with silicone adhesive. It has a 1"
horizontal leg, a 4" 45 degree surface to mount the thermostat facing the
sun and to redirect the incoming air downward, and a descending 3" leg.
Mount the thermostat through a hole the size of a quarter, and fasten it
with pop rivets. Bond the thermostat shroud in place so the vertical leg is
spaced 1/2" away from the plane of the glazing. Pass the thermostat leads
through the 3/8" hole in the fan mounting plate. Wire the fan and the
thermostat in series - tie one lead from the fan to one lead from the
thermostat with a #14 wiring nut, and finish with an 8" length of electrical
tape. Seal the thermostat wire hole with silicone adhesive. The remaining
unattached leads, one from the fan and one from the thermostat, will be
wired to the power cord leads at final installation.
Touch-up
Use the rest of your spray paint to paint the inlet shroud (paint the nose
of the thermostat) and touch up the absorber.
Install the Glazing
The glazing can be Plexiglas (acrylic), which does well in this application
because of the vertical angle and the efficient (low) temperature at which
this collector runs, or another material of your choice (Kalwall).
Polycarbonate (TwinWall, etc.) is strong, but may yellow. Cut the glazing
to size to match the inside line of the plywood. Install the glazing with
1/8" pop rivets (1/4" grip range), spaced every 8" along the baffles.
Install pop rivets through the glazing every 8" along the "C" baffle. Put
four rivets across the center of the "C" baffle.
Lift the glazing edge slightly and put a 5/16" bead of silicone adhesive
around the collector sides where the glazing will sit. Place the silicone
adhesive bead near the inside edge of the surface, so that as you allow the
glazing to rest on it, the adhesive squeeze-out just reaches the inside of
the collector.
Install the Aluminum Sheathing
Press the aluminum sheathing in place using an aid made from two 2-foot-long
- x 1-1/2's glued together to make a 90 degree angle. As you do, install
- /8" pop rivets through the sheathing into the plywood, all around the sides
of the collector, located 1" from the front edge, and every 8".
Install the sheathing angle all around the rear of the collector with 1/8"
pop rivets into the plywood spaced, located 1" from the rear edge, every 8".
Working on each side on turn, tip the collector up on the side on a flat
work table, to help ensure the sheathing edge is straight and cannot slip
toward the side. Install 1/8" pop rivets, through the bend line where the
sheathing touches the glazing (drill these holes through both sheathing and
glazing). Rivet around the collector face on the contact line using a 12"
spacing.
Dress and Fill the Glazing Joint
Use a gentle leather-glove touch to adjust the gap where the edge of the
aluminum sheathing "returns" away from the glazing. The gap should be at
least 1/4". Completely fill the gap with silicone, and finish it the joint
with a spoon. Allow the fillet to extend 1/4" out onto the face of the
glazing. Don't try to clean up until the silicone cures.
This seal design is tough and won't be broken by shock or expansion from
temperature change.
The Manifold
The collector connects to the house via a manifold box made using the same
construction materials and gluing method you used for the case - a urethane
foam-board box with an outer layer of plywood around the sides. It also has
a sheathing of aluminum flashing, made from a 9" x 1-1/2" angle, 60" long
(this allows an overlap). The 14" square, 9" long, two-way, over-and-under
manifold connects to the house through the wall or across the window sill.
You can use plywood on just the top and bottom, or on all four sides of the
manifold. The manifold is divided by a foam-board "center divider" into a
lower intake and an upper exhaust passage (back to the house). The lower
passage is 6" high, the top is 4-1/2" high.
On the upper surface inside the upper passage, 1" away from the front face,
install an 11" length of 1" x 1" flashing angle. Use hot glue dots and
silicone adhesive. Face the angle legs away from the front face. This will
act as a stop and support the edge of the inlet/outlet filter. Do the same
at the lower surface inside the lower passage. Cut an 11-1/2" square piece
of furnace filter to use for an inlet/outlet filter. The filter will span
the center divider of the manifold, and rest against the 1" x 1" stops.
Install a Grainger 2W050 three-wire power cord up through a 3/8" hole in the
bottom front edge of the manifold; make an overhand knot for a strain
relief. Put a ring terminal on the green ground wire. When you make the
final installation, fasten the ring terminal to the fan shroud with a 3/16"
aluminum pop rivet. Note: You could install an additional room temperature
thermostat (open on temperature rise) in the inlet to disable the fan on
rising room temperature; this would partially limit warm weather output.
But the unit will still thermosyphon slowly. To fully prevent the unit from
heating in summer, without damaging it, you will have cover it with a cloth
or plywood cover. Do not close or stop up the manifold openings without
also covering the collector, as this would cause very high collector
temperatures and consequent material damage.
The grilles for the manifold should be split, to eliminate heat cross-over.
Don't choose moveable-louver grilles. You could use perforated metal. The
best and cheapest pre-made grilles are white painted steel, available from
Hart and Cooley through your local HVAC supplier. Order one
#672-steel-white, 12 x 4 for the upper air passage, and one
#672-steel-white, 12 x 6 for the lower passage. These are approximately
13-3/4" long, and 5-3/4" high for the 12 x 4, 7-3/4" high for the 12 x 6.
There are two mounting holes in the grilles (one at each side). Use
urethane adhesive to glue a block of wood into the foam-board to accept a
screw at each mounting hole location. Install the grilles with the bottom
grille's louvers angled down, and the top grille's louvers angled up, to
help prevent air from crossing over from outlet to inlet (short-circuiting).
The hot outlet air tends to segregate itself by rising away.
INSTALLATION
Plan the Installation
My preferred installation method is to cut a 14-3/8" square hole through the
wall between studs (assuming a 14" square manifold). Or, if you choose, a
sliding window installation is an option. Just pre-mount the manifold to
the collector the day before with urethane adhesive. Give the adhesive a
full 24 hours to cure. Prop the collector in place with the manifold coming
across the window sill. If you have a storm sash, seal that one first.
Shut the sash on the manifold and block off the gaps with 1" urethane
foam-board - the same foam-board used to make the collector. Trim the
foam-board edges with aluminum foil tape. Next do the same to the inside
sash. Caulk only the joints at the bottom and sides of the foam-board. Use
peel-and-stick foam strips on the underside of the sliding sashes so you can
open them when needed. Install a security catch on the inside sash if
desired.
Preparation
In preparation for installation, make (4) brackets of 1/8" x 3/4" flat
aluminum bar, 9" long , bent to give a 6" and a 3" leg. Use a 3/16" drill
for #10 stainless pan head screws. Drill (3) holes in the 6" leg, (2) holes
in the 3" leg. Put (3) #10 x 3/4" stainless screws through the 6" leg into
the collector, and (2) #10 x 1-1/2" stainless screws through the 3" leg into
the building. Use one bracket near each corner of the collector.
Begin the Installation
Wall installation:
Cut a 14-3/8" square hole through the wall between studs (assuming a 14"
square manifold). Make a small hole in the center of where you think you'd
like the hole to be. Probe with a coat hanger to find the studs. Measure
the manifold and mark lines for a hole 3/8" bigger than the manifold
dimensions. Cut the inside wall board with a utility knife. Stuff the
insulation from the hole into the wall cavity. Square from the inside hole
over to the outside wall, and drill holes at the corners to the outside.
From the outside mark the lines, check the dimensions, and make them plumb
and square. Use a saw to cut the hole.
Sliding Window installation:
Pre-mount the manifold to the collector the day before with urethane
adhesive. Give the adhesive a full 24 hours to cure. Prop the collector in
place with the manifold coming across the window sill. If you have a storm
sash, seal that one first. Shut the sash on the manifold and block off the
gaps with 1" urethane foam-board - the same foam-board used to make the
collector. Trim the foam-board edges with aluminum foil tape. Next do the
same to the inside sash. Caulk only the joints at the bottom and sides of
the foam-board. Use peel-and-stick foam strips on the underside of the
sliding sashes so you can open them when needed. Install a security catch
on the inside sash if desired.
Flash the Hole
Next, line the hole with a piece of aluminum flashing. This will be flush
with the inside wall surface, with 3" wide ears bent to sit against the
outside wall. To make this, cut a piece of flashing 60" long, and 3" wider
than the wall thickness. Make a 90 degree, 3" wide bend down the length of
the piece. Make cuts through the 3" leg, to allow you to wrap it around the
outside of your 14" square manifold, making 90 degree bends at the four
manifold corners. Set the manifold aside to attach to the collector later,
from inside the house. Staple the pre-bent flashing into place in the hole,
putting some staples inside the hole and at least four in each outside ear.
Caulk under the ears (don't neglect the corners) with silicone adhesive.
Pre-Mount the upper Brackets
Mount the upper two mounting brackets to the collector (use (3) #10 x 3/4"
stainless screws). Take care to locate the brackets so the collector will
be spaced about 9/16" away from the wall (or from the clapboard bottom
edges, if you have clapboards; and locate the brackets so they fall just
under a clapboard edge).
Before you place the collector against the wall, press sticky-back foam seal
strips (3/16" thick x 1-1/2" wide, the type used to mount camper caps onto
pickup trucks) to the back of the collector around the 11-1/2" square
manifold hole. Space the foam strips 1-3/4" away from the hole edge. Build
up three layers of the strips, so the seal is 9/16" thick.
Prop the collector in position
Now use short pieces of 2x6, on edge, as braces under the collector to raise
it to the right height on the wall (so the foam seal rests on the flashing
ears). Use a long 2x4 as a brace to keep the top brackets of the collector
against the house. Use a level to get the collector plumb. Now take the
manifold inside the house. To check whether the collector is aligned with
the hole, insert the manifold into the hole and check that the center
divider lines up with the "C" baffle in the collector case. Readjust
everything until it's plumb and aligned.
Outside, fasten the upper collector brackets first, then install the lower
ones (keep the collector vertical, viewed from both ways. From the inside,
with the manifold removed, use silicone adhesive to caulk around the
perimeter of the hole against the foam seal. Completely fill the space
between the collector and the flashing.
Install the Manifold
To install the manifold, lay a generous 1/2" bead of urethane adhesive
around the manifold rear edges and across the center divider. Place it in
the hole, and press it onto the collector. It should stay there by itself,
or you can wedge it in position to cure overnight. You can immediately
caulk the gap around the manifold at the inside wall with siliconized latex
caulk. For a finished look, trim with quarter-round or picture frame
molding.
Operation Caveat
As stated earlier, to fully stop the unit from thermosyphoning in summer
without damaging the unit (due to high stagnation temperatures), you must
cover it, not simply close or stop up the manifold openings. Do not close
or stop up the manifold openings without covering the collector, as this
will cause very high temperature and material damage.
The worst of the "new collector" smell is gone in a few hours (silicone
curing smells like vinegar) and will disappear in a day or two.
To Make Larger Arrays
In scaling up, keep these points in mind:
1. The geometry shown in the accompanying illustration permits daytime
thermosyphoning, and discourages nighttime thermosyphoning (the descending
and rising legs of the flow circuit are both at outside temperature at
night, and are of nearly equal height). If you change to a different flow
layout, you may need an anti-backdraft damper.
A manifolded array would use collectors 4 feet wide by any height, and
divided into left and right (rising and descending) halves by a vertical
baffle, with the halves interconnected at top or bottom by a gap in the
baffle, with the filter element mounted on "rails" in each half, on one long
diagonal from inlet to outlet.
2. With more than 25 square feet (one good-size collector per room), room
overheating becomes a concern in warm/hot weather. You will want large
size, automatic or manual collector vents (without these you will need to
cover the collectors in summer). In addition to collector vents (top and
bottom), you may still have to cover the outlets manually in the hottest
weather, and make sure the collector temperatures do not climb too high.
(This is why I invented the AutoVent control. This is what makes an SHVC
(Solar Heating and Ventilation Cooling) system. It integrates two three-way
valves (one at the inlet, one at the outlet), and four ports (an
inlet/outlet pair at both the interior and the exterior) into a drop-in
control module.)
3. A large array manifolded with a single fan should be segmented into areas
(separate collectors) with a parallel-flow circuit. You might need to
restrict the higher-flow collectors to get the array balanced.
You could use "in-at-the-bottom, out-at-the-bottom" collectors manifolded in
parallel. These could be served by a split over-and-under manifold duct
located at floor level on the inside wall, that might not be too intrusive.
It might be three to four inches thick out from the wall, by two feet in
height. The bottom 12 inches would be the intake manifold, with an intake
grille located at one side of the room; the lower part would be divided from
the top 12 inches, the outlet manifold, with a grille at the other side of
the room. Or, there could be small outlet grilles located all along the top
of the outlet duct and small intake grilles located all along the intake
duct.
In this scheme, the entry and exit connections to the collector are all
located low in the collector. This arrangement tends to thermosyphon at
night, in either direction unpredictably; it will need a positive manual
damper, or a timed electro-mechanical damper, that prevents nighttime flow
in either direction.
An alternative scheme that needs no damper is to place the over-and-under
manifold duct near the ceiling, serving "in-at-the-top, out-at-the-top"
collectors manifolded in parallel. There would be an auxiliary inlet duct
connecting to the inlet half of the split over-and-under manifold. It would
descend to the floor at one side of the room. there would be an auxiliary
outlet duct connecting to the outlet half of the manifold, descending to the
floor at the other side of the room (i.e. one descending duct at the left
side and one descending duct at the right side of the room, at the corners
against the outside wall). The reason for the descending ducts inside the
room is to receive the coolest inlet air and distribute heated air low in
the room.
In this scheme, the entry and exit connections to the collector are located
high in the collector. So, the descending and rising outside legs of the
flow circuit are both at outside temperature at night, the inside descending
and rising legs are at inside temperature, and all are of nearly equal
height, so you don't need any damper.
HAPPY BUILDING!
--
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comfort system. In a single wall-mounted module, it provides space-heating
in cold weather, ventilation cooling in warm weather, and both cool-air
conservation and system safety in hot weather - all done automatically. The
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As the room temperature rises in warm weather, Sol-Air's AutoVent(tm)
adaptive air handling control initiates room ventilation. In hot weather,
the system acts conservatively by sealing the house, power-venting the
collector with outside air to prevent collector damage. It thus conserves
cool inside air, and even allows conventional A/C to operate normally. You
don't cover the system manually to prevent overheating, or uncover it to
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gives the system a maximum efficiency greater than 72% - the SHVC solar
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Contact us!
Bill Kreamer
President,
Sol-Air Company
129 Miller St.
Belfast, ME 04915
tel 207-338-9513
fax 603-853-9339
mailto:kreamer@mint.net
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