280 feet 300 feet

24 feet

Loops are 6 inches from outer walls and roughly 12 inches apart.

I felt that 2 inches would be too thin, and the concrete contractor refused to pour less than 3 inches due to the risk of damaging or exposing the tubing. The 3 inches still allows me to use a single household thermostat to control the heating, though it is less responsive. I'm still testing, but I believe that the system can raise the building temperature by about 3°F (1.6°C) per hour.

Building a Solar Roof

I needed a structure on the south side of the barn to put the solar collectors on, so I built a small shed with a steeply sloped roof. At this latitude, a 45 degree slope is recommended and is easy to build.

My neighbor John Rogers, who is a building contractor, helped me design the shed and gave me a hand for an hour or so to get the collectors mounted on the roof. I was lucky that the weather was still warm enough to sweat the exposed 3/4 inch copper pipe fittings in early October! Maine can be quite chilly at that time of year!

The collectors came with small L-brackets that did not seem to be big enough to raise the collectors more than 1/2 inch (13 mm) off the asphalt roof. Ken Olson suggested that an inch or so would be better, so I made up my own brackets from extruded, 3 inch (7.6 cm) angle aluminum with a 1/8 inch (3 mm) wall.

Thermostat Relay Box

I built a relay box that allows my standard, centralized heating, digital thermostats to control the AC circulation pumps. To power the relays, I used a 12 VDC, "wall wart" plug (wall cube, or AC-to-DC converter), and wired it to solid state relays in a nice plastic box with two LEDs to indicate when each pump was running. I used solid state relays rather than mechanical ones, since they consume a fraction of the energy when activated.

The relay box is quite simple. All it contains is a 12 VDC power supply, pillaged from an old phone answering machine. I actually broke open the plastic housing of the wall wart, and extracted the transformer and electronic parts so I could silicone them into the box nicely. The dissected and reassembled wall wart sends power to the thermostat, which switches the solid state relays and turns an LED indicator on. The digital thermostat that I used runs on its own two AA batteries.

The control box LED requires a 1 K-ohm resistor in series with it for current limiting. I used relays that are rated at 10 amps at 240 volts. These can be found surplus for around US$7. When switching a motor with a relay, it is best to rate the relay at double the current and voltage of the load to allow for protection from the inductive surges that occur during switching.

A homebuilt, solid-state relay box allows standard thermostats to control the system's AC circulation pumps.

Expansion Tank

Expansion Tank

Pressure Relief Valve

I used three, stainless steel, sheetmetal screws to attach each 3 inch long bracket to the collectors, and used a 5/16 inch by 2 inch (8 x 50 mm) stainless lag screw with galvanized washers per bracket to secure them to the roof. I also put a bit of silicone around the lag screw heads to prevent ice from working down into the roof.

Lots of Plumbing

One thing that is rarely mentioned in articles about homebrew solar installations is the emotional ride. For me, it has ranged from excitement to total freak out at the daunting complexity and overwhelming amount of detail. Fortunately, I already had considerable experience in all the skills needed to accomplish my installation, so I was able to trust in my knowledge that I could complete the project almost single-handedly.

I am an experienced home and light industrial plumber from a previous life in photo processing. Nonetheless, it took many visits to the hardware store over a period of a couple of weeks to locate all the copper fittings for the system components. The plumbing assembly took more than a week to build. I sweated together each section of the various assemblies of valves, gauges, and pumps, which I then assembled into a complete system.

It was very helpful and timely that HP85 came out as I began the plumbing phase. That issue contains Ken Olson's excellent article on closed loop antifreeze systems. I downloaded a copy and used it as a working reference on the job.

Some Plumbing Tricks

One neat plumbing solution that I found was a good way to mount thermometers into 3/4 inch copper pipe. The thermometers that I used come standard with a 1/2 inch pipe thread, and if you sweat a 1/2 inch thread adapter onto a 3/4 inch tee with a short length of 3/4 inch pipe, the thermometer sensor stays out of the fluid flow. This can give inaccurate readings, especially if the tee is mounted so that air stays trapped in the stub tube.

A brass seat tee with reducer (right) keeps the thermometer sensor in the fluid's flow. Copper fittings (left) don't work as well.

The solar loop portion of the system's plumbing, showing the Amtrol 2 gallon expansion tank, Secespol heat exchanger, and 2 El Sid circulating pumps.

A brass seat tee with reducer (right) keeps the thermometer sensor in the fluid's flow. Copper fittings (left) don't work as well.

The solar loop portion of the system's plumbing, showing the Amtrol 2 gallon expansion tank, Secespol heat exchanger, and 2 El Sid circulating pumps.

Guy Marsden's Solar Heating System

Photovoltaic Modules: Backup Heater:

Two, 10 watt and one, 20 watt AquaStar AQ125-B2P-S,

Solarex PV modules, propane fueled, power 12 VDC El Sid pumps on-demand

Photovoltaic Modules: Backup Heater:

Two, 10 watt and one, 20 watt AquaStar AQ125-B2P-S,

Solarex PV modules, propane fueled, power 12 VDC El Sid pumps on-demand

Valve: Drain

Valve: Fill

Valve: Drain

Valve: Fill

I used a brass sweat tee with 1 inch female threads instead. Then by putting in a 1/2 inch reducer bushing, I found that the thermometer's 1/2 inch thread would fit in snugly, allowing the thermometer sensor to protrude fully into the water flowing through the tee. I believe that this setup will guarantee accurate readings.

When plumbing the indoor section of the collector loop, I placed unions around the heat exchanger and pump sections. The sections can be removed easily for service or replacement, or to tighten the couplings. It turned out that I needed to make use of this feature, so it definitely paid off.

Another trick that I devised involves weatherizing the foam insulation on the exterior plumbing. I took some 2 inch PVC pipe and ripped it in half on my table saw and clamped it back around the insulated pipe using nylon cable ties.

The air vent needs to be located at the highest point in the system, which means at the top corner of the collectors for me. I ended up with a vent that is about 6 inches (15 cm) above the collectors. To insulate and protect it from the elements, I wrapped the pipe in foam, and put a length of PVC pipe with an end cap over it.

Solar Space Heating

That's not Gatorade! Filling and pressurizing the solar collector loop with the propylene glycol solution.

propylene glycol to turn acidic, which can be harmful to the copper collectors. Even with the high temperature (325°F; 163°C) Dow Frost HD propylene glycol I used, stagnation should be avoided in closed loop systems.

The Break-In Period

After a late night of filling and checking the system, I was up with the sun the next morning to watch the solar powered El Sid circulating pump kick in and begin warming my system. I was disappointed at how long it seemed to take with the sun shining brightly, until I realized that I had installed the pump in the wrong direction. The pump was trying to suck against the check valve to no avail. Being quite dyslexic, this is something I have grown used to— getting things backwards!

Filling the System

My workshop has no running water, so I had to pull a garden hose over 70 feet (21 m) from the house to fill the system. I came up with a neat way to monitor the fluid and air bubbles entering and exiting the system. I made up two, 3 foot (0.9 m) lengths of 5/s inch (16 mm) ID clear plastic hose and added garden hose fittings. One hose was connected to the fill pump outfeed, and the other to the system drain. This made it possible to monitor the fill process, and to clearly see when the air was purged from the system.

I let the fill pump continue to recirculate until the returning fluid stopped showing air bubbles. Air bubbles in a closed system can impede flow and limit the efficiency of the system, and should be carefully and thoroughly eliminated. When filling the water tank, I attached the clear plastic infeed hose directly to a garden hose, and let the overflow drain out the window!

My solar collector loop holds approximately 3 gallons (11 l), so it was relatively easy to prepare a 50:50 glycol solution by mixing it in a 5 gallon (19 l) bucket. Use propylene, not ethylene, glycol. Ethylene glycol, as used in automobile radiators, is highly toxic. The propylene glycol that I used is formulated for the high temperatures that the collectors can generate.

Without fluid flowing during summer for space heating, the collectors could reach stagnant temperatures of over 300°F (149°C) in certain extreme conditions, although maybe not in Maine. Very high temperatures (over about 250°F; 121°C) will eventually cause normal

The supply and return manifolds of the two hydronic floor loops. Notice the extra Taco 006 pump for a future heating loop in the barn's second floor.

Renewable Energy Eco Friendly

Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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