Buying a house with passive solar hot water

[Grabcon]

Are you sure your schematic is correct? I suspect that the hot water may be meant to circulate freely between the tank and the panels through convection.

The schematic is correct. All of the valves are just above the DHW, see photo. Valve position is an assumption if the valves were operational. The way it is piped there is no return back to the collectors.

The hottest water is on the roof so I dont think convection works here. There is one valve that doesnt really need to be there but it is closed. Its the valve thats between the cold supply and hot. Reason? It would just bypass the heater.?

Why the bypass between cold and hot I have not a clue. I have not see a bypass on any before. If it is not required I will eliminate when I change the DHW heater since I will be replacing all valves.

 

[wpns]

Okay I am reviving this thread. I have finally gotten around to the hot water solar. Life kind of got in the way so this has waited until now.

I have never work with hot water solar so I need to understand how this is suppose to work. Please ignore previous diagram. Attached is the actual piping configuration. There are no thermostats or pumps attached to the system. It is a closed system with a relief valve on the outlet of each of the panels. I have not tested the relief valves at the panels. It is difficult for me to really test anything as the valves at the hot water tank are inoperable. I do need to replace the electric hot water heater as it is nearing end of life along with all of the valves.

So before I replace the DWH and the 5 valves I would like to understand how this system is suppose to work in theory. So please shed some light on this for me before I spend money on something that is useless.

Thanks


It has not froze year in 2 years. No glycol and no heat exchanger.

Honestly at that age it’s time to replace everything. Given a low cost of PV generation, if you concerned about power, I would just add more solar panels.
If you have a check valve, you absolutely need to have an expansion tank. My Florida condo has a 20 (?) Gallon electric heater, and my pressure spikes every time the heater cycles:

An expansion tank is definitely on the list, but my condo association is fighting it (long rat hole), and my wife doesn’t see the problem, so I’m off to fix other things that I can.

 

[RussNM]

The way it is piped there is no return back to the collectors.

Correct. This simply a batch heater not some highly sophisticated system that involves heat exchangers, pumps, etc. It takes the cold water that comes in at 55f and raises thru solar radiation SO that the dhw wont have that 55f water dumping into the tank when someone turns on the faucet. It now has 150f water on the cold side dumping into a dhw thats probably set for 120f. Its a simplisticly brilliant concept. no moving parts.. nothing to wear out. It sits there and does its job and quite well I might add. For example.. I had a propane dwh. With domestic use we were going thru 24gal of propane every 2 weeks. I build a solar preheater similar to the one above in concept and the propane usage goes from 2 weeks to 1 1/2 months. Do the math. Its quite a savings.

 

[Grabcon]

If you have a check valve, you absolutely need to have an expansion tank. My Florida condo has a 20 (?) Gallon electric heater, and my pressure spikes every time the heater cycles:

I currently have a check valve just after the cold supply valve to the solar collectors. See Picture. So the expansion tank would go on the cold supply to the collectors after the check valve. Correct? See schematic

 

[WindWizard]

I used one for over a decade and never once did the water in the batch tank even get close to boiling. Dead of summer it reaches 150f or so and thats in a high altitude clear sky desert environment. .. with 6in rigid foam insulation and double pane glazing. I could understand if it was painted black 3/4in copper tubing under glass but it looks like a 30 gal or so tank in each collector.

My system uses evacuated tubes which reach boiling temperatures as I found out when my circulator pump malfunctioned.

I looked outside and steam was shooting out of the pressure relief valve on top of the evacuated tubes. I immediately covered the tubes and then proceeded to repair the circulating pump. It turned out to be a bad relay controlling the pump.

If OP's system never gets hotter than 150f as you suggest, then he should be fine with it. But if the temperature drops below zero, he is toast.

 

[Grabcon]

But if the temperature drops below zero, he is toast.

I have never seen anything at my location below 25 degrees. The historic average low for January is 28 degrees. And that is early morning, 4 or 5 AM.

 

[RussNM]

So the solar collectors should be fine because they should have plenty of "heat" in them but the pex should be insulated because they are small and more subject to the freezing temps.
And yes you are correct...the expansion tank goes on the downhill side of the checkvalve.

 

[Grabcon]

Well here is an update. I can't push water either direction thru the tanks. I have removed the relief valve and the lower drain plug at each tank pushed 60 psi water both directions and no water flow thru either tank. We do have very high calcium in the water here so maybe they are just plugged. I did replace one hot water heater when we moved in and that had an 8 to 10" plug of build up in the bottom of the tank.

So I guess my hopes are dashed for the moment. Any thoughts on this would be helpful.

 

[RussNM]

What is the batch tank made of? Stainless? Are there any galvanized iron fittings anywhere in the loop? Are you able to get access to the batch tanks?

 

[Grabcon]

What is the batch tank made of? Stainless? Are there any galvanized iron fittings anywhere in the loop? Are you able to get access to the batch tanks?

I am think they are steel. But don't really know for sure unless I open up the box again. Which is a real pain. 3/16" Tempered glass which is sealed in place with silicone. Then 2 thin sheets of opaque fiber glass sheets which are also sealed in place with silicone. Nothing that is difficult but just a pain to do.

All visible fitting on the outside of the box are copper and brass. How they are connected to the tank I don't know. I would guess that there is no dielectric fitting where the copper meets the tank.

I was planning in just pushing something thru the pipes where the relief and drains (they are a straight shot into the tank) are but I need something flexible like a fish tape/plumbers snake. Which I don't have need to run to HD. If you look at post 15 you will see pictures. The boxes are placed in a way that I need something flexible to push in the pipes.

The drain plugs are iron in brass fittings and there was build up of some corrosion on the plugs, that looked like little black wafers.

 

[WindWizard]

I would try to use compressed air to see if you can get air to flow through the piping.

 

[RussNM]

From what I can see it looks like there are t&p valves at the end of the tank feeds. You might pull one off and see if its plugged there.
And I wonder just why there is a "diffuser " over the glass? Id want as much straight up- hard core sunlight as i could get in on the tank!

 

[RussNM]

These...

 

[Grabcon]

From what I can see it looks like there are t&p valves at the end of the tank feeds. You might pull one off and see if its plugged there.
And I wonder just why there is a "diffuser " over the glass? Id want as much straight up- hard core sunlight as i could get in on the tank!

I have pulled both top and bottom T&P and plugs on b both tanks. The tank that I opened up did have some build up in the hot out pipe. Cleared that up and was able to push a drain snake 4 plus feet in both top and bottom. So those pipes are clear. But I am still not able to get flow on that tank. It will build some pressure but does not fill.

The tank nearest to the wall had very clogged pipes. The bottom took a little work with the drain snake but the top had about 12" of build up/plug. I was able to push and hammer a 1/2" copper pipe in about an inch at a time then I would have to pull it and empty the end that was full of calcium. It took some time to get that cleaned up. It does flow now and is under pressure and leak test. Fingers crossed.

I will work in tank one tomorrow. Not sure what to do but I will do something.

 

[wpns]

I currently have a check valve just after the cold supply valve to the solar collectors. See Picture. So the expansion tank would go on the cold supply to the collectors after the check valve. Correct? See schematic

That’s correct

 

[Rednecktek]

Get some CLR from the hardware store, pump as much as you can in there and let it sit. Rinse, repeat.

IF you can get them cleared enough to get some flow, even a little bit, you'll want to rig up a flushing system. Fortunately that's as easy as some hose fittings, a 5gal bucket, a cheap submersable pump, and a cheap garden hose you can cut up. Connect the sump pump to one side of the heater, connect the heater outlet to the other heater inlet, connect a hose from the second outlet and clip/tape/tie it so it dumps into the bucket. Put the pump in the bucket and grab a few gallons of either CLR (expensive but WOW does it work) or white vinegar (cheap but takes longer) and fill the bucket. Let that circulate for a few days until the outlet pipe is flowing at full volume. Then re-flush with clean water a few times and plumb it back in.

 

[SolarRich]

For a system like this to work the hot water tank must be higher than the solar hot water collectors. Without a pump this system will only circulate water thru the collectors when you turn the hot water faucet on. If it were me I would not waste any time on this and just remove it all. You might as well just run a black hose across the roof as a solar collector.

 

[Grabcon]

There are no collectors. There is only a tank in each box. And yes water only flows when the domestic water is being used.

Removing for me is not an option. If anything I would just disconnect and leave it.

 

[RussNM]

There are no collectors. There is only a tank in each box. And yes water only flows when the domestic water is being used.

Removing for me is not an option. If anything I would just disconnect and leave it.

So thats kind of a bummer. About running CLR thru the system.. is that safe? This is potable water and even rinsing a couple times might not get it all out. Sorry but if its me, I aint drinkin any CLR! Might try something a bit less toxic like extra strength vinegar.
After reading some of the replies youre getting its obvious they havent a clue about batch heaters and just how simple they are. No pumps, no convection, no electronics, nuthin'. Water goes into the batch heater and sits there heating up in the sun till you turn on the hot water in your home. It then runs in to the cold side of the dwh.

 

[Grabcon]

Good news today. The batch tank nearest the wall see post 15 passed its leak, pressure and heating test last night. Started test at sundown with a full tank at 60 PSI. Overnight the PSI drop to 45, which I expected. Ambient temp when I checked and read the gauge this morning was 62. At 3PM today the PSI was up to 65, which is good and the water temp I am going to guess as a hair over 100. A good shower temp. But that was only 6 hours of heating. Ambient 85 with full sun.

I also found a local plumbing company that gives away old hot water heaters I will see them on Wednesday and see what they have in throw away stock. The Tank 1 is too clogged to deal this so I will try one of the old tank. I know it is a risk but hey it keeps out of the pub. And costs less.

 

[Grabcon]

I ended up pulling tank 1 and getting it off the roof. The box is still in place. I was able to do a leak and pressure test all that is good. But the inside is really full of scale, mostly calcium. Small pieces and sediment to larger pieces that barely to fit thru the 3/4" fitting. I turned almost upside down and flushed as much as I could. At least now I get water flow thru the tank. I drained it completely and looked inside with an endoscope and there still is a fair amount of crud in the tank.

Currently it is soaking upright in the driveway with a gallon of vinegar. You can put your ear to a fitting and hear it bubbling inside. We will see what happens after a day. We have a test piece of crud in a dish with vinegar on the kitchen counter and the vinegar seems to be doing the job. Fingers crossed.

My lead on another tank was kind of a bust. The had 3 gas heaters but no electric. They were also too tall to fit in the box. They took my name and will call when they get something suitable in for me to look at.

 

[RussNM]

Saw this at Home depot and thought of you bro.

 

[Grabcon]

Weekend progress report.

Tank 1 has been cleaned on the inside and outside. Outside painted and reinstalled in box. Box is all back together and waiting further work on the outside plumbing. I need to solder a couple of fittings but we have had some high winds the last couple of days so that must wait.

I can now move to the inside and install all new valves, an expansion tank and maybe a mixing valve. I would like thoughts on the mixing valve. The solar heated water goes directly to the cold water input.

I should replace the DHW tank at the same time I do the valves but will need to wait until I get a few bucks.

 

[wpns]

I would like thoughts on the mixing valve.

My experience with mixing valves has been that at low flows they let the hottest water through, so you are better off with lower temperatures overall, or an expectation of "I better check this hot water, it might be really hot!", rather than "I don't have a scalding hazard, I have a valve!" Old and young folks can be badly scalded, which is why most plumbing codes restrict hot water temperature.