Evacuated Tube Racking System For Flat Commercial Rooves

Introduction:
SHEM recently installed two SunTask 30 tube evacuated tube sets on an 80DB at a local elementary school. The main challenge was designing a racking system that is durable and strong, while allowing for the 1/4" per foot minimum tilt needed for drainback systems. Using all off the shelf parts and standard tools the following design is what we came up with. The following plans are a rough outline of our design. Dimensions, materials, and overall design are for reference only. Make sure you follow your local codes regarding solar collectors and roof penetrations. Over the course of this installation many future design changes were discovered, and they will be discussed towards the end of this post.

Supplies:

• 4x 10' Unistrut sections
  
• 6x Roof boots
  
• 6x 1/2" UNC 5' all-thread sections
  
• 6x Threaded beam clamps
  
• Black roofing sealant
  
• Box of roofing screws
  
• Box of self drilling screws
  
• 1/2" Nuts
  
• Channel nuts
  
• 2x 4 Hole Unistrut straps
  
• Washers
  

Walkthrough:


We started by locating the beams under the roof, and drilling holes for 1/2" all-thread to be fed through.


Using threaded beam clamps, we clamped the all thread to the main metal beams. A 1/2" nut was used to lock the all thread in the clamp.


A black tar roofing sealant was applied directly around the hole, and in about a 3" square surrounding the hole. Sealant was applied to the threads to ensure the nuts were secure.


Flashing was placed around the all thread. Two washers and a nut were then fed onto the all-thread, and the nut was tightened down.


After the nut was tightened, a piece of unistrut was cut and placed around the all-thread. A third washer was put on top of the uni-strut. General purpose adhesive was applied to prevent walking and settling of the parts.


More sealant was applied to the edge of the roof boot. After the boot was fed over the all-thread it was fastened down to the roof with long roofing screws. A washer and nut were then used on top of the boot to secure everything to the roof.


Section view of assembled mount.


This process was repeated six times for our six roof mounts. The next step was achieving the tilt required for the drainback process.


After the six mounts were finished, short pieces of unistrut were used as spacers for the different heights. On the lower end, no spacers were used, and on the highest end two pieces of unistrut were stacked. Since we didn't have a 20' piece of unistrut, we had to join two shorter pieces in the middle of the racking. This was achieved using channel nuts, bolts, and a piece of 4 hole unistrut strapping. The strapping was fed over the piece of all-thread (the second hole from the right) then secured through both pieces of unistrut with the channel nuts and bolts. A short piece of all thread was used on the left to secure both pieces of all thread together.


On the highest end, two pieces were stacked. Since two pieces of unistrut didn't need to be joined, like in the middle, shorter pieces were used. On the left, a square washer and nut were used in conjunction with the main piece of all-thread clamped to the beams to secure the rack to the roof. On the right, a short piece of all-thread and two square washers were used to provide extra security.


After everything was assembled and securely tightened, the racks for the tubes were ready to be attached to the unistrut sub-rack. Using the supplied feet, the racks were attached to the sub-racks using self drilling screws. The SunTask tubes don't come with feet for the middle legs, so 90 degree L brackets were used in conjunction with the self drilling screws.

After the racks were secured to the sub-rack, the manifolds were adjusted so they would meet up in the middle of the rack. Then the tubes were installed and the racking installation was complete!

Discussion:
After this installation, many future design changes and ideas were discovered.

Instead of using a short piece of unistrut in between the roof and the boot, 1-1/2" diameter galvanized cast iron nipples might be a better choice. The width of the unistrut caused the corners of the unistrut to contact the rubber roof boot on the smallest diameter step. If sufficient vibrations, or agitations are applied to the boot or unistrut (wind, hail, animals), wearing of the boot may occur and cause leaking. If this option is chosen, care must be taken to ensure the cast iron pipe remains centered around the all-thread. A thick washer with an outside diameter just smaller than the inside diameter of the pipe could be used to center the pipe.

A more symmetrical and attractive looking spacer arrangement could be utilized.

Instead of using self drilling screws to attach the collectors to the sub-rack, a U-Bolt could be used to attach the feet to the sub-rack. This method might supply a little more insurance against the self-drilling screws coming loose or stripping in high wind locations.