Large drainback solar hot water project

[ESharp]

Over the past year I’ve been picking away at a large ground mounted solar hot water system for my house. I got a lot of inspiration to do it from a few members of this forum and Gary’s Build-It-Solar $2k drain-back design. I’ll make a few separate posts to get my count up so I can upload some pictures.

[ESharp]

It all started when I was browsing Kijiji (like Craigslist) last September and noticed some used panels for sale. There was a picture of five of them and I thought great, five should be able to do most, if not all, of my domestic hot water. I called the fellow up and it turned out he had 16 8’x3’ panels! They were older ones removed from an apartment building while the roof was being redone and I guess they thought it was not worth it to put them back. I bought the whole lot for $1000 and the possibilities for my project got a bit larger.

[ESharp]

I had to start thinking where I could fit 16 panels. 16 was too many for the roof and with that many panels, contributing to winter heating was my goal. The roof is at ~25deg pitch, whereas 65-70deg would be preferred. I decided on a ground mount structure off to the side of my house. Fortunately my neighbours are through the trees and it is not in my windows view plane.

[ESharp]

After a bit of layout work I decided I only really had space for 12 panels, even on the ground. The structure is 40’ long, with 10 post holes (4 sections, each 10’ long). The design is similar to Daox’s. Post holes are dug below the frost line and concrete poured into tubes with galvanized 4x4 post supports set into the tops. I tried to make it very forgiving on construction tolerances (post locations, lumber straightness, etc). Once the posts were set, I used lines to achieve one flat plane with fully adjustable 2x4’s along the sides of the posts. I built this over the fall of last year.

[ESharp]

I really liked the simplicity of Gary’s drainback system and the large low cost storage tank. I went with a 6’ long x 3.5’ wide x 4’ tall tank as that was the biggest I could reasonably fit in my mechanical room. It holds ~350 gallons. To maximize water space (and save a bit of money) I only used 1” of poly-iso to line the interior of the tank, regular fiberglass batt is between the 2x4 reinforcements on the exterior. Unfortunately I didn’t take any pictures during construction.

[Daox]

Awesome stuff Eric! Cant wait to see more.

I'm still widdling away at my project one baby step at a time.

[ESharp]

Thanks Daox, I'll be posting in bits as I have time. It has been certainly the same for me, slow progress, step by step. These systems are more work then they first appear. I'm still not quite finished.



Although the panels were in reasonable shape, the demo crew had unfortunately cut the header pipes flush with the side of the panel frame. In order to make any connections I had to install couplings to all 4 corners. This involved drilling the rivets off the back side, and flipping the insulation up to allow access to clean up each header end. I soldering the new couplings on and re-riveted the cover back on. It was an annoying and tedious job.

Mounting the panels was the fun part since I could finally see some tangible progress. I riveted pieces of aluminum angle to the sides and screwed those down into the cross-members of the structure. I made 2 banks of 6 panels each. They both have slight slopes back to the supply line. The banks are plumbed with a parallel-reverse-return configuration to help with balanced flow. I used 1” PEX for the main supply and return, but 1” copper to connect the 2 banks since PEX has quite a bit different larger thermal expansion coefficient.

After I got one bank on and soldered up, I sent a bit of water through with the hose. Since the panels had been sitting in the sun for a while, steam was the result!

[Daox]

Great stuff. 384 sq/ft of panels is wonderful! I was quite happy when I got my ~200 sq/ft of panels.

I also had/have to do the same thing with my panels. Each had to be disassembled, cleaned and pressure tested, fittings soldered on every corner to I can set them up to connect to each other. The un-installer did the same thing, zipped them with the sawzall.

[randen]

Esharp

Nice to see another Canuck toiling away saving money collecting solar. If I may ask what are you going to do with all that heat. Heated floors, indoor pool, hot water fan center,??

Randen

[ESharp]

I currently have an older oil forced air furnace which I’d love to stop buying oil for I’ve installed a water-to-air heat exchanger (Finned Coil Water to Air Heat Exchangers) in the return plenum and the heating loop pump circulates water directly from the storage tank through it. I realize that relatively low-temp solar isn’t an ideal supply for this, but installing hydronic in-floor heat is a project for another day. The exchangers are typically used for those with back-yard wood boilers and are pretty decently priced. We typically turn the heat down quite low at night and it’s also off during the day while away. This gives a bit larger of a delta-t to work with.

As for the summer, I think I’m going to need a pool

Here are some pictures of the plumbing. I followed Gary’s design fairly closely here. I am using a TACO-011 for the solar circulating pump. The smaller pump is a TACO-005 for the heating loop. The domestic supply to the hot water tank is a 300’ coil of 1” PEX. I plan to add a few spacers to spread the coil out a bit in the tank.