Blair
New Member
Posts:8
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| 13 Apr 2011 07:32 PM |
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Solar Water Heater Evacuated Tubes – When our electricity goes out the system blows out the PEX pipe at the head manifold. This is not a problem for people in Southern Ontario because their power rarely fails.
The system runs using a WILNO circulating pump that draws 0.9 amps using regular AC power (~115 V). When there is temperature differential of 6 degrees Celsius between the manifold (outside) and the indoor storage tank, the pump turns on intermittently and circulates the glycol. My problem arises when the power fails (during the day and it’s sunny), as it does quite a few times in Parry Sound, Ontario, then the glycol becomes super heated (above the 82 degrees Celsius rated PEX pipe) and blows the pex pipe approximately eight inches below the manifold. I have an expansion tank inside the house, but it is approximately 25 feet from the manifold. so it does not help out (or so I think).
I could use all copper then the system could not blow; however, I have been told that the propylene glycol starts to break down under extreme heat. When the glycol breaks down it becomes acidic and could start eating out the copper heat exchanger – costly.
I would like to use a UPS, perhaps a NOMA 1800 Watt system which has an automatic switch when the power fails. I do not know how to calculate how long this UPS system will keep the pump running intermittently. Plus, I have read several bad reviews regarding this NOMA unit.
Perhaps I could use 2 deep cycle batteries with an inverter connected to the unit (somehow) which would run the pump when the power fails.
Any suggestions would be greatly appreciated. I do not want to buy a generator. I would like to come up with an economical solution to the problem. |
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jonr
Senior Member
Posts:5341
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| 13 Apr 2011 08:22 PM |
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I believe that PEX is only rated for solar if pressure is kept at atmospheric - so vent the system. Or at least add a pressure relief valve.
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tandemsforus
New Member
Posts:24
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| 13 Apr 2011 08:37 PM |
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How bout this
1. relay that normaly closes when power is lost or is in a normaly relaxed state. put it between a solar powered pump and its solar powered source. (takes ac power to open relay and circuit).
2. set up with solar powered pump so that when relay closes it complete the circuit to run pump that is parallel to normal pump using check valves in system to isolate when not running
3. Have simple temp snap switch that closes at 70 degree C or so also in series to the system.
Thus the solar powered pump will run system if the sun is out, power is lost, and temp is above 70c. All three conditions must be met for the pump to run. And thats when you need it to run.
Would that work? |
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Blair
New Member
Posts:8
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| 14 Apr 2011 09:24 PM |
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I believe the pressure is atmospheric. If I vent the system will I lose any of the glycol? What make of vent or pressure relief valve would you recommend? I'm not a plumber, but I can usually put things together - with good advice.  |
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Blair
New Member
Posts:8
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| 14 Apr 2011 09:27 PM |
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Posted By tandemsforus on 13 Apr 2011 08:37 PM
How bout this
1. relay that normaly closes when power is lost or is in a normaly relaxed state. put it between a solar powered pump and its solar powered source. (takes ac power to open relay and circuit).
2. set up with solar powered pump so that when relay closes it complete the circuit to run pump that is parallel to normal pump using check valves in system to isolate when not running
3. Have simple temp snap switch that closes at 70 degree C or so also in series to the system.
Thus the solar powered pump will run system if the sun is out, power is lost, and temp is above 70c. All three conditions must be met for the pump to run. And thats when you need it to run.
Would that work? |
| Subject: |
Posted By tandemsforus on 13 Apr 2011 08:37 PM
How bout this
1. relay that normaly closes when power is lost or is in a normaly relaxed state. put it between a solar powered pump and its solar powered source. (takes ac power to open relay and circuit).
2. set up with solar powered pump so that when relay closes it complete the circuit to run pump that is parallel to normal pump using check valves in system to isolate when not running
3. Have simple temp snap switch that closes at 70 degree C or so also in series to the system.
Thus the solar powered pump will run system if the sun is out, power is lost, and temp is above 70c. All three conditions must be met for the pump to run. And thats when you need it to run.
Would that work? |
| Subject: | That sounds good, but I'd prefer not to buy another pump. I've seen them around $ 300 ... Thanks for the ideas |
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jonr
Senior Member
Posts:5341
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| 14 Apr 2011 10:08 PM |
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You can try something like this:
http://www.watts.com/pages/_products_details.asp?pid=788
so the pressure cannot build up.
Or get a 12V battery plus an inverter/charger (perhaps 300 watt or more to account for startup load) to run the pump.
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tandemsforus
New Member
Posts:24
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| 15 Apr 2011 08:33 AM |
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clementsb
After reading you problem I posted a question on the radiant floor board about pex and fluid temps as I have pex in a solar heated radiant floor. Read it its quite an eye opener. Kinda looks to me as if there is no easy fix to make your system safe. As for me I am going to take out the pex on the incomming run to the floor and replace it with copper. They convinced me there is just not enough safety factor in pex, it fails at to low a temp to be safe anywhere near a solar collector.
Just a question you say you are having pex fail at the head manifold, you mean the pex is attached to the manifold, not is the manifold. And is this an open or closed loop system, I am assuming its closed loop. If your worried about corrosion solar flex would work as was suggested to me by a member on that post, it stainless steel flex pipe.
I think I read about "buffers" you can put in gycol to make it less acidic. Any body know about these? |
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Eric Anderson
Basic Member
Posts:441
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| 15 Apr 2011 02:48 PM |
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You have a system that has no redundancy. The simplest way to deal with this is to repipe with copper, or use one of the stainless steel insulated linesets expensive made for this purpose. Sure you could add a PV pannel with a dc pump to the system and that may avoild stagnation, but why bother. Just repipe it
Also make sure the insulation you are using is high temp pipe insulation. Alot of the stuff sold will not handle elevated temperature either.
http://www.altestore.com/store/Solar-Water-Heaters/Solar-Thermal-Piping/SunMaxx-FlowMaxx-58-Pre-Insulated-Line-Set-w-mounting-clips-30/p8858/
would be one possibility.
I like PEX, I have my DHW set up as a home run system with pex and (seperately) all the baseboard in my house. The solar is all type K copper.
Good Luck
Eric |
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| Think Energy CT, LLC Comprehensive Home Performance Energy Auditing |
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Blair
New Member
Posts:8
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| 15 Apr 2011 09:48 PM |
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I'm not sure if a pressure relief valve would work. I do not want to lose any glycol, perhaps ann expansion tank might work. Regarding the battery anbd inverter, do you know how to calculate how long a pump could run at 0.9 amps, size of battery AmpH. The calculations confuse my brain. |
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Blair
New Member
Posts:8
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| 15 Apr 2011 09:54 PM |
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I'll read your post. Thanks. The system is closed. The PEX pipe is attached (with a sharkbite) to half-inch copper tubing which then enters the header/manifold. If I could post pictures you might be surprised as to how the pex pipe looks after it blows. Wild. If you hear anything about buffers, please let me know. Re the acidic issue - I worried that the acid created by superheating the glycol would eat out the copper in my heat exchanger - a coil of copper within a 40 gallon tank - an expensive part of the system. |
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Blair
New Member
Posts:8
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| 15 Apr 2011 10:01 PM |
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I was thinking of repiping it, then it couldn't blow. I'm concerned that with no back up circulation pump, the gylcol will become acidic and eat out hthe copper in my heat exchanger. The supplier warned me about this acidic issue.
Yes, I am getting the proper insulation. Thanks |
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jonr
Senior Member
Posts:5341
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| 15 Apr 2011 11:16 PM |
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My understanding is that inhibitors should always be added to glycol to stop that.
Figure around 6 hours for a car battery. |
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Blair
New Member
Posts:8
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| 16 Apr 2011 06:25 AM |
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Can you recommend an inhibitor that I should add to the glycol? Can you clarify "Figure six hours for a car battery." Is that how long you would expect a car battery to run my pump (0.9 amps) continuously? Thanks
I have learned to go all copper, or at least copper within 6 ' of the panel. |
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jonr
Senior Member
Posts:5341
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| 16 Apr 2011 10:45 AM |
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Yes, a typical car battery should run that pump for ~6 hours continuously. I don't know specifics on inhibitors.
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Blair
New Member
Posts:8
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| 16 Apr 2011 12:07 PM |
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Thanks. A few questions.
How did you figure out that the battery would last ~6 hours?
Do you know if I hooked up two deep cycle batteries in parallel would that allow the pump to run for ~12 hours? I have to remember that the pump runs intermittently, so that would allow the battery to last longer, correct.?.
Thanks for the feedback. |
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jonr
Senior Member
Posts:5341
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| 16 Apr 2011 12:34 PM |
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Say roughly the AmpHour (AH) rating of the battery(s) divided by 11. Yes, intermittent operation or batteries in parallel would increase it.
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tandemsforus
New Member
Posts:24
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| 17 Apr 2011 12:13 AM |
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As to bufferrs
This might sound crazy
Try calling Serria brand antifreeze company. Look them up on the net.They make polypropylene auto antifreeze. Its made with buffers for dissimular (sp) metals and higher temps. I was told they might have a buffer you can add for even more protection, but never checked into it myself. Yet...
Good luck |
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