Note that the vactubes are lined
up north south to catch all of the east west sun from dawn to dusk. Because
they are round they receive light from 360 degrees. Keep shading from the
frame to a minimum.
6000 watt vactube heater design.
Build a 6000 watt solar evacuated tube space heater that heats a
2500 sq. ft. room by circulating air in the room through 25 evacuated tubes
on the roof using one 65 watt fan even on a cloudy day.
Evacuated tubes are like long thermos bottles
with a clear outside glass and coated inside glass that changes light to
heat. The vacuum between the two locks the heat in.
This one generates 250 watts
We should manufacture them here in the USA.
Always wear gloves when
working with sheetmetal and glass.
Cut a 3 inch hole in each end
of the outside manifold for the inside manifold to slide in to. Cut a notch
for the tabs that will stick up once you are finished building the inside
makifold. Refer to the pictures below.
Building the inside duct
To make the inside duct slide the 3" x
8' galvanized duct into the outside manifold and mark it for drilling.
Use a jig to center the marks. Drill 5/16 holes in a perfectly straight
line for start holes and cut an 8 slice pie our from each hole for shoulders
and tabs that hold the copper air riser tubes in place. Straighten the
seam, align the holes perfectly straight again and then solder the seam
so the hole manifold can't twist or come apart.
The fan forces filtered air from
the room into this end and the only way the air can get out is through the
holes and up the riser tubes. Then it blows the heat down out of the evacuated
tubes into the ourside manifold and back into the room.
Seal off the end opposite the
input with an oval of sheetmetal installed with screws and silicone diagonally
from just past the last riser hole angleing in so the air is angled up into
Cut the pie slices on the sides and ends into
shoulders for the riser tubes to sit on. Use a small piece of tubing to
form the fit around and make sure the sheetmetal is formed so the seal
will be good between the copper tube and the inside manifold.
the slices on the diagonal into tabs that stick up to hold the risers in place
the diagonal points long to hold the riser tubes in.
The copper riser tubes fit on top of the 3 inch input
manifold. Make sure nothing protrudes down inside the manifold or the air
turbulance from it will reduce performance.
The vactubes sit on the rubber shoulders at the base
of these holes.
Install the inside manifold and
cut the input end flush and the other end inside a couple of inches so it
can be insulated with foam and covered with sheetmetal.
Cut a 4" hole in the outside
manifold for the output duct before you mount the inside duct.
Mount the outside manifold pointing
north south where it receives the most sun and where you can easily run
the ducts into the attic and to the ceiling vents.
Always wear gloves when handeling
the glass tubes.
The risers are made from 60 inches of thinwall
copper tubing from Home Depot. Cut 10 foot pieces in half and be sure
to remove all burs and clean off all stickers or they will burn and stink.
Keep the inside of the manifold
smooth. Anything inside will create turbulence and reduce performance.
Seal the inside and outside ducts
air tight with high temp silicone and install with 1/2 inch sheetmetal screws.
Make the input and output ducts out of 8 inch
and 4 inch galvanized duct with foam in between. Seal them and paint with
galvanized metal primer. Install them with silicone and 1/2 " sheetmetal
Make a jig to hold the tubes in place while you install
Drill a hole for the photocell
to go through to the outside.
Seal everything in with foam.
8 inch centrifugal fan Grainger
Use a yard light photocell to switch a 120 volt
single pole double throw relay to turn the fan on at dawn and off at dusk.
Note that everything plugs in to a standard outlet to avoid an electrical
inch flexible duct from Home Depot.
all the joints with silicone.
Run a section of flexible duct
to the input vent. Use 25 feet to deaden the fan noise. Use 14 x 21 vent
cabinets with filter in the input vent and 8 inch reducers for the flex
duct. Insulate the fan, intake and output vent cabinets.
The output duct can be shorter
because it is not noisy.
25 tubes heats a 2500 square foot room even
on cloudy days here in the Northwest.
The output vent has a remote
temprature sensor so I can monitor the temprature rise
The input duct is 14 x 21 inches with drop down
door and filter.
The thermostat is below on the wall and a thermometer
with a remote sensor so I can monitor input and temperature rise.
Cut a 4" hole in the outside
manifold for the output duct before you install the inside duct.
Make your frame on the ground
first from the supplied stainless. Make sure the plastic holders fit and
the top does not touch the tips of the vactubes. I installed the feet on
the back legs with bolts through the roof and used washers and nuts.