Sunday, September 12, 2010

Solar Sundays Part VI- building the behemoth

The large solar hot water system to provide space heating for the barn will consist of (9) 4x8 collectors vertically-mounted to the south wall of our steel cargo container. The solar-heated water will be pumped to the barn's in-floor hydronic system via underground insulated PEX tubing. The nearly 300 square feet of collector area will theoretically provide enough hot water for about 75% of our annual heat requirements, as well as domestic hot water needs during the spring, summer and fall months. But so far, it has all been 'on paper', and I've been hesitant to start building until all the design issues were cleared up in my head. After much deliberation, I finally strapped on the tool belt and got to work today. I started by bolting 4x4 beams across the bottom of the cargo container, then attaching short sections of 2x2s every 4 feet to act as ledger boards for the solar collectors.
I am building the array in smaller 8'X8' sections- a manageable size to lift into position without difficulty. I made the first framework today using 2X6 cedar material.

I rabbeted the backside of each 2X6 so that the plywood backing would be flush with the framing members.

Then screwed in place the two 4x8 sheets of plywood.

Because rainwater/runoff is a concern, I decided to protect the back side of the collectors by attaching a weather barrier layer. For this I used synthetic roofing underlayment that was leftover from the barn project. I stapled it to the plywood and taped the seams.
With Lisa's help, we set the finished framework on the ledger boards and screwed it in place. Mounting the solar collector array to the cargo container eliminates the labor and expense associated with building a separate support structure. But since the cargo container is only temporary (we hope to build a garage/workshop in a few years, then sell the container to someone else), the collector array must be built with ease-of-disassembly in mind. The modular design I came up with should allow the whole system to be disassembled, moved and reinstalled on our future garage with little difficulty.
On the top end, the framework is held in place by 1 foot lengths of 2x4's, which are bolted to the roof of the container via the 1/2" lugs that I had welded on previously. The 2x4 brackets are raised off the roof about an inch using pieces of PVC pipe as spacers. I also placed 1/2" shims between the collector frame and the container side wall. The spacers on the top and sides are to allow the rain water to run unobstructed around the collector and down the side wall of the container. Eventually, I'll also put a cap plate and a short metal roof over the brackets to protect the top frame members of the collectors. With the first section in place and looking successful, I built another on the ground and tilted it into place.The common frame member between each two sections can't be accessed from behind to attach the plywood, so I used pocket hole screws instead, from the front side. After another day of construction, the framing is done.