Solar Thermal Project

August 2018

This month, I re-plumbed the solar thermal system to by-pass components of the system that reduced the fluid flow to see if that would improve thermal efficiency. I disconnected the small-diameter manifolds that distributed heat to the radiant heating system, and plumbed the solar loop direclty to the pre-heat water tank for the domestic hot water. The tank is a new 80-gallon stainless steel tank with internal stainless steel heat exchanger that I ordered to accompany our new geothermal heating and cooling system. The geothermal system dumps waste heat into the 80-gallon tank, raising the temperature to about 75 degrees.

I found that adding the solar loop increased the temperature another 20 degrees on a partly sunny day in August. This represents quite an improvement over the old system with the flow-constricting manifold and the pex-wrapped water tank. By comparison, I was never able to raise the temperature of the 40-gallon tank more than 11 degrees on a sunny day.

I have yet to see how the system performs on a fully sunny day.

July 2018

As of June 2018, I have disconnected the solar thermal heater from the water preaheating tank and from the hydronic heaters. We had a geothermal system installed that month, which required disconnecting the water preheat tank so that a new, larger preheat tank could be installed to recover waste heat from the geothermal unit. I plan to plumb the solar loop back into this new preheat tank to augment the waste heat recovery form the geothermal unit. Given the poor performance of my home-made solar heater, it will only be able to augment the solar heater, but not the basement heat.

July 2017

The solar hot water collector has not met expectations owing to a couple of poor design choice that I made.

The first design flaw had to do with the manifolds in the collector. For a collector of this size, I learned that I should have installed some valves within the manifold to adjust the fluid flow through the system. As it stands too much fluid flows in the out sections of the panel, and almost none through the center sections of the panel, result in major heat loss.

The second flaw had to do with mounting the collector under an overhang that partially shaded the collector in the summer. I initially though this would be a good design feature to prevent the system from over-heating, but it reduced collection, when combined with the flaw discussed above to the point of providing a small fraction of the heat I initially estimated that it would.

I plan to disassemble this collector, and rebuild it in a more suitable location in the yard to improve the results.

One of the hazards of being a do-it-yourselfer and doing this kind of experiment, is that sometimes, ya just mess up and have to start over again...

December 2015

I installed two high-efficiency baseboard heaters intended specifically for low-temperature heating applications. THese went into the hard-to-heat basement, and were connected to the storage tank by PEX. The baseboard heaters were produced by Smith's Environmental (http://smithsenvironmental.com/products/he2-heating-edge-baseboard/). They are attractive and easy to install. They are not yet providing as much heat as I would like, because I need to install a more efficient heat exchanger to pull more heat from the solar panels. I found that the 250 feet of PEX I used in the storage tank since July was still insufficient for effective heat transfer from the solar panels. So, i'm going to use use a standard brazed plate heat exchanger like those typically used in hydronics systems. This should provide 2-3 times the efficiency of the PEX loop, but I'll also have to plumb in a circulation pump. That's my next step.

One of the installed hydronic baseboard heaters.

Update: July 2015

Status: Way Behind--owing to having too many projects and hobbies.

I filled the tank by June, after lining it with plastic. I insulated it with a combination of 4" of closed-cell styrofoam board above and below, and with fiberglass bat around its perimeter. After running the pump intermittently to ensure that I didn't have an overheating problem, I ramped up the amount of run time. I soon figured out that I probably have the opposite problem-In the summer the overhang shades the array enough that I may not be getting enough heat to the tank. In addition, the 100' PEX that I used as a heat exchanger inside the tank probably is not enough to do the job. I probably will need to double it or swap it out for copper.

I found out also that we had a problem with the water getting stagnant in the tank and smelling faintly of rotten eggs. Apparently it had something growing in it. I used a handful of sanitizer used for brewing beer to control the problem.

I still have a little cosmetic work to do on the collector itself. The trim is unfinished, and I would like to do a little painting.

The goal remains to have this plumbed into the domestic hot water system and to add heating loop for the basement by fall or winter.

Update: 28 March 2015

Project Status: About 80%?

I finished the plumbing for the solar loop in March, and conducted several pressure tests. The first few tests were with air only, It took a great deal of effort to solve the leak problems--it turns out that my sweat soldering skills were not what I thought they were. After a refresher in sweat solder from my cousin's husband, I rebuilt the pumping station from scratch, and replaced some fault joints in side the garage. After the array satisfactorily held pressurized air for 24 hours, I filled the solar loop plumbing with a mixture of about 50% propylene glycol and water. I added a quart of boiler sealer to ensure that any pinhole leaks I did not find were sealed.

Finally - Success! The loop held the solar fluid under pressure, and there were no leaks. I ran the charging pump for several hours to flush air from the system. As I did so, the temperature of the fluid was rising satisfactorily (it was a partly sunny day, and I had uncovered the collected to check for leaks and heat collection).

Next steps:

- Fill the tank with water

- Insulate the tank

- Insulate the plumbing

- Add a PEX heat exchanger to the tank that will provide hot water to the home plumbing.

I figure that will take several weekends.

Update: 9 February 2015

Project Status: About 75%?

We accomplished quite a bit of work in December before the weather got too nasty and cold. By Mid December, we had installed all of the solar absorbers, sweat-soldered them together, and installed glazing and some of the trim. By late December, I added plumbing connections inside the garage leading toward the basement, where the pumping station and tank would be. I made little progress after that until late January and early February, when I began assembling the pumping station.

By the time I assembled the pumping station I realized that I made a couple of errors in sizing my piping; I selected PEX over copper, which meant that the resistance to fluid flow was higher. This, in turn, meant that i needed a more powerful and expensive pump to push the fluid through the tubing. Not what I had in mind. Nevertheless, rather than redo the piping, I selected a variable-speed pump with built in differential speed controller from Taco.

I also purchased a 300-gallon galvanized stockyard tank, and painted the inside with a latex pint meant for roofs. i hoped this would provide another level of protection for the galvanized steel; time will tell. I plan to use PEX heat exchangers in the tank for the solar loop and for the domestic water heating loop. For hydronic heating, I may simply use the water in the tank rather than adding another heat exchanger loop.

Overall, the project is taking twice as much work as I expected. Isn't that always the case with plumbing?

Here are a few pics of the many we took:

The absorbers installed; a roll of fiberglass greenhouse

Glazing in the foreground is what I used for the solar

panel glazing

The Panels are now glazed, and trimming with aluminum

is under way.

A view of the plumbing on the rear of the solar panels

on the inside of the garage.

Update: 8 November 2014

Project Status: Construction has finally begun!

Over the past couple of weeks, I have been assembling the collector frame from 2 x 4 lumber. The design uses six solar absorber panels within an integrated framework that mounts as a single unit on the wall of the garage. The absorbers were manufactured by Sun Ray Solar, in California, and measure 8' long x 35" each, with 1" copper headers (basically manifolds at the top and bottom ends). The "risers" between the headers are 1/2" copper tubing, with aluminium absorption fins.

At this point, I have the frame mounted on the garage wall, and have insulated it with polyisocyanurate sheets. I then sealed the gaps in the insulation. Tomorrow, I'll start soldering the absorbers together.

The status last weekend with the frame for the six absorbers mounted on the garage wall

This is how the collector frame looked after the addition of the polyisocyanurate sheet insulation.

For this photo, I temporarily installed one of the black Sun Ray Solar absorbers to check for fit.

I am revising my estimate for the amount of energy savings owing to some early mis-measurements.

• With the six south-facing, vertically mounted 3' x 8' absorbers, I'll have about 144 square feet of collector area.
• I derated the ideal production to about 60% of maximum, owing to thermal losses, and transmission losses with the cover glazing I will use. Maybe I'll be pleasantly surprised with better performance.
• Based on historical averages, a conservative estimate suggests these should produce enough heat to meet about 40-45% of our winter heating and water heating needs.
• We could save about $840/year in propane costs, while reducing our carbon emissions by 3380 punds per year.