Sagebrush

Happy Pi Day!

Enjoy  some Pi-ku.

[This is the fourth in a series of articles describing installation of a solar hot water system.]

System Start

The plumbing is all connected and leak-free. Now let’s put coolant in the system and see if we get heat! Ordinarily we might use equal parts propylene glycol (not the more poisonous ethylene glycol) and water, about 4 gallons in all. However, we turned this system on in early autumn with no freezing nights possible, so we use tap water in the coolant loop. Once we gain confidence in the system we can refill with glycol/water mixture after a few days.

First we connect a hose from a nearby faucet to the upper boiler drain valve, and another hose from the lower boiler drain valve to a drainage area out in the yard. We run the water for several minutes to flush out any flux and solder and other junk from the coolant loop.

Now we connect two short hoses, actually “washing machine hoses”, to a drill-powered pump and large bucket like so:

Following the directions in The article in Home Power magazine “DWHW Installation Basics Part 2” from June 2003 we run the pump with both valves open, and keep running until no air bubbles appear in the bucket. Then slowly close the lower valve and keep pumping until the pressure in the coolant loop reads about 20 PSI, then close the upper valve.

We keep the bucket and hoses and pump together as a dedicated kit for possible future maintenance.

One final task is to connect the pump to the PV panel on the roof. (We angle this panel a bit West of direct South, so in winter the solar water panel has a chance to warm up before sun hits the PV panel and starts the pump starts circulating. Otherwise cold coolant from the panel might cool the water in the storage tank enough to cause the auxiliary electric water heater to turn on each winter morning.)

With the pump running, take a trip to the roof to purge any air from the coin vent. Be careful: hot coolant might spray out and scald if you turn the vent valve too far too fast.

With the pump running, we feel the pipes in the heat-exchange loop get warm, and then hot. I expected  the storage tank to take several days to heat, but hot showers were available after only one-half day of system operation.

Later we insulate the pipes exposed on the roof, secured with wire-ties. These pipes might get too hot for the insulation used to insulate regular home hot water plumbing; we used insulation rated for this temperature sold by our solar heating supply vendor.

Go back onto the roof in a day or so and purge any air from the coin vent that might have collected.

Lessons Learned

1. We would change the placement of the mounting board with pump and expansion tank to be more accessible for later repairs: lower and not as far in the corner. This is in an area where people pass by frequently and I thought the equipment would get in the way, but there was enough room.
2. We would change the routing of the pipes going to and from the storage tank heat exchanger to first turn towards the wall and then make a right angle bend up to the mounting board. Once reaching the wall the pipes could be fastened with clamps for better support.
3. We would attach components to the mounting board prior to attaching the board to the wall. We would follow more closely the example shown in “DWHW Installation Basics Part 2”, Home Power Magazine.
4. Too many trips to the big-box home store for extra pipe fittings was caused by not carefully sketching in detail the plumbing for the entire coolant loop system, indicating every single fitting required– and then buying a few extra for last-minute changes.
5. We added temperature gauges at both the inlet and outlet of the heat exchanger. In practice the difference in temperature is very small almost all the time. The heat exchanger relies on many trips around the coolant loop to get enough heat transfer to the storage tank.
6. We learned this project is indeed possible for someone with a technical bent and little experience. If you have ever dabbled in car repair or significant home repair project then this is well within your grasp– at least if you have a flat roof.
7. Our solar storage tank includes an auxiliary electric heater. If we had hooked up this electrical connection just after connecting the hot and cold water pipes, we would not need to be in a hurry to complete the coolant loop connections.

Regular Operation

Here is a graph from our gas bill in winter.

See how much less gas we burn than last year? We are now paying much more for “access fee”, taxes, and fees than per/therm gas usage. If we could stop using natural gas for the stove and clothes dryer, we could unhook from the utility. We really like a gas range, but propane might do. We have ideas about the clothes dryer that might appear in a later post.

After running for several months, we are encountering no problems. It just works!

During winter months we do encounter winter storms with several consecutive days of no sun, and then the auxiliary electric heating element in the storage tank does turn on. During non-winter months we can turn off electricity to the tank altogether.

Our March magnetic drive DC circulating pump might tend to be noisier than other type pumps, according to Home Power November 2007 article “Pick the Right Pump“. We live in a quiet neighborhood, and my office is located not far from the pump, and my personal preferences tolerate very little ambient noise. Our noise- meter measured 53dB at a distance of one meter during regular operation, not much louder than our refrigerator when the compressor is running. Somewhat more noticeable is the variation in pitch of the pump during semi-cloudy days, but nothing too objectionable.

Future

What will it take for solar hot water system panels and other system components to be sold in big-box home-improvement stores? Should light-weight solar thermal panels be used, or heavier but very durable panels such as ours? Should flexible copper tubing be used to ease the process of installation, or some sort of temperature-resistant plastic pipe? What diameter tubing still gives reasonable coolant flow and heat transfer? What components can sold in pre-assembled form for faster and easier installation? We welcome your thoughts.

Related Posts: Solar 1, Solar 2, Solar 3

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• The Sagebrush Variety Show, audio theater with political satire and commentary
• The Nevada Sagebrush, student voice of University of Nevada, Reno
• Parsley & Sagebrush Band, bluegrass combo
• Sagebrush & Serendipity, personal blog of artemisia
• Sagebrush Wisdom, “common sense thoughts from the country”
• Sagebrush Valentine, 6 artists with 1 title create 6 songs in 1 hour
• Sagebrush Strokes, Nevada landscape prints online store
• The Sage Brush from Montana, a memoir of a youngster studying art with western muralist Bernard Preston Thomas.
• Sagebrush Spinoni, puppy pictures from a dog breeder.
• Sagebrush Bob, political diary on dKos.

Related Post: Hello, World!

[This is the third in a series of articles describing installation of a solar hot water system.]

With the panel now securely mounted on the roof, we can turn our attention to plumbing. With an electronics background, I have done plenty of soldering– but only wires, not copper pipe. YouTube has several videos demonstrating the procedure, so it is time to get some pipe and practice “sweating”…

Time to “tool up” for the job:

From the top and counter-clockwise: propane torch, teflon tape and pipe dope (more on that below), lead-free solder, 4-in-1 cleaning brush (for removing oxide from 1/2″ and 3/4″ copper tube and fittings), flux with brush, and pipe cutter. Not shown but also recommended are leather work gloves and a bench vise.

We want to avoid as much down-time for hot water availability as possible: teenagers getting ready for school in the morning are not particularly open minded about the advantages of solar energy when they are taking a cold shower. Without disconnecting the current system I could start on the roof and connect the solar panel with pipe near to where the pipe will pass through the roof to turn down towards the storage tank.

Our panel has four connecting ports, two on top and two on bottom. One top port is used for coolant output, and the other can be connected to another panel– not necessary in this installation.

We used the extra top port to connect a pressure relief valve and a coin vent used to purge air bubbles from the coolant loop, which should be installed at the highest point in the system.

Since the solar panel might someday have to be temporarily removed when our tar and gravel flat roof is redone, we installed unions at the top and bottom ports.

After roof work, I soldered several sub-assemblies of parts together, to make final assembly go faster. Several parts, such as boiler drain valves, pump, and gauges, had pipe threads and required solder-to-pipe adapter fittings.

I tested sub-assemblies when possible, using a collection of threaded end-caps and a Schrader valve adapter. I built the adapter using a Schrader valve stem (from an auto parts store), a brass 1/4″ female to 1/2″ male threaded adapter, and a small quantity of JB Weld metal epoxy. The brass adapter is not sized to thread with the valve stem, and relies on epoxy to seal and hold the parts together.

Here is the gadget in action, testing a sub-assembly.

Pressure testing showed no leaks on solder joints, but revealed several leaking threaded joints. Searching the web, we ended up using three layers of yellow (not the thinner white) teflon tape on a male pipe thread, and on top of that brushing on a modest coating of RectorSeal TPlus2 pipe joint compound. Problem solved.

The plan is to remove the old water heater and replace with the solar storage tank on Friday, after the dread teenagers have left for school. My goal is to get cold water back by the end of Friday, finish connecting the coolant loop by end of Saturday, and fill coolant Sunday morning to begin heating water. A professional could work much faster, but I wanted to be methodical, and expected to take breaks to ponder any problems.

Behold our old gas water heater.

In addition to the hot and cold water connections, you will observe the required pressure relief valve and pipe, as well as some other  devices particular to our installation: a pressure limit switch on the cold water line for our water pump, and a valve connecting to 1/4″ copper tubing supplying water to an evaporative cooler. Our new installation will try to “neaten up” this extra hardware.

After turning off the gas supply to the water heater, I turn off the water supply, drain any extra water in the lines, unscrew the hot and cold supply to the tank, cut the soldered pressure relief line, and remove the exhaust vent. The hole in the roof for the exhaust vent will make a handy pipe run (passageway) for the coolant loop going to and from the solar panel. After connecting a hose to the tank drain valve, I let the tank empty and moved it out of the way.

Before putting in the new tank, I attached a plywood mounting panel to studs in the wall with lag bolts. (With hind-sight, I would have mounted the pump-gauges-and-expansion-tank assembly to the panel beforehand, and would mount the panel lower for improved accessibiilty. More on woulda-shouldas in Part 4 of this series.)

I rolled in the new tank and made connections for hot, cold, pressure relief, and the extra bits mentioned above. All threaded connections used the tape and pipe dope combination mentioned previously. I added a anti-scald mixing valve sub-assembly to prevent scalding in case water in the storage tank got hotter than a normal water heater.

Notice I added thermometers at both the input and output to the mixing valve, which is overkill. The mixing valve requires an extra connection between hot and cold lines, making the connections look more complicated.

See the aluminum foil? I placed that on tank and sometimes walls to shield parts from solder drops and heat.

After turning on water, I was delighted to find no leaks! After a well-deserved break it is time to complete the coolant loop.

I fastened the expansion tank and coolant circulation pump to the mounting board with metal plumber strap, after cushioning between the board and parts with foam rubber to reduce vibration. Unions were used for the pipe runs up to the roof, to make it easier to disconnect for servicing. I thought about adding unions to make it easy to remove the pump– the most likely part to fail after decades of service.  Too many unions have aesthetic and reliability issues, so I plan to cut and solder for pump replacement.

With everything connected in the coolant loop, it is time to pressure test.

I used a bog-standard bicycle pump with integrated gauge, and pressured up to 10PSI. Sadly, the pressure did not hold, so soap solution was applied to solder joints and threaded joints until a leak was identified:

This was one of the last solder connections made, so perhaps I was in too much of a hurry or too complacent. After using wire brush and flux on the pipe and fitting, I did have to let this joint wait for several minutes before sweating. Perhaps this time delay was also a factor. Re-heating and applying more solder did fix the leak.

I pumped the pressure up to 20PSI and discovered another leak that did not leak at 10PSI. This leak would not close with more heat and solder, so I actually had to cut out the leaky fitting and try again with fresh clean parts. Rather than be discouraged, by this time I was getting quite comfortable with cutting pipe and soldering, and glad to be able to take time to do the job right.

After fixing the two leaks, the coolant loop held air at 20PSI for hours with no noticeable loss, so the system is ready to add coolant. I wanted to do that in the morning before the sun is up to begin heating the panel. More on that in Part 4 of this series.

Related Posts: Solar 1, Solar 2

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