Critique my DIY solar hot water plans

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SolarGuy

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Hi all. I'm new to this forum and glad I found you guys. I have drawn up some plans for a drainback solar hot water system and hoping for some feedback. Looking for any "gottchas" before I build it. My town plumbing inspector has already given his approval, but he's just concerned with code, not with it actually working correctly. I live in NJ, so freeze protection is mandatory. 2 adults and 2 kids live in my house. We burn corn for heat and use propane for everything else and as backup.

Here is a link to the PDF drawing

Details:
  • Rheem 80 Gal. Solaraide tank with internal heat exchanger. Located in basement.
  • Solar loop (closed) will contain RO water. No glycol. Pumped using a Taco 008 bronze pump wired to a differential controller. Head is only 10 FT because the drainback tank will be located on the 2nd floor just below the attic.
  • Backup heater is a Takagi propane fired instant water heater.
  • Solar collector will be an Apricus AP-30 mounted flush on the roof at 40 degrees facing SE with an approx 5 degree rotation toward South for header drainback purposes.
I am comfortable that I can complete this project. All plumbing will be hard and soft copper with sweat connections. Worst case, I end up with an 80 gallon cold water storage tank that does nothing. :eek:

Assuming I'm able to succesfully drainback the 3/4" pipes within the unconditioned space, is there anything else I need to watch out for?

Jason
 

Jimbo

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First, you cannot put RO water in copper!!!! The ph attacks the copper and produces bad taste, and eventually pinholes.

I am not an engineer, but I think you need some check valves in the system. I envision reverse flow at night transferring heat OUT of the storage tank and up to the roof!

I have no expertise in solar, so this is just an off the cuff observation. Stay tuned, because you will get a lot more feedback as soon as some of the more experienced experts wake up!
 

Dunbar Plumbing

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Yep, and if you use PEX or CPVC, the UV rays will destroy the piping in no time flat.


A water heater (electric or gas) heaviliy insulated will provide the best efficiency without spending thousands on a system that will have to be maintained for health reasons. Too many failure points in that design and if not properly maintained, it will either cause health conditions or it will be abandoned if someone other than the designer cannot maintain it. i.e. wife and kids.
 
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Rancher

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jimbo said:
I am not an engineer, but I think you need some check valves in the system. I envision reverse flow at night transferring heat OUT of the storage tank and up to the roof!
This is a Drain back system, when the pump is not running the water empties out of the collectors and back into the 5 gallon tank.

One comment is, make sure that 5 gallons in enough to handle all the piping in unheated spaces and collector.

You need an air vent and vacuum valve at the top of the collector.

See: http://store.altenergystore.com/Solar-Pool-Heaters-and-Solar-Spa-Heaters/Spa-Hot-Tub-Kits/Heliodyne-QTY-2-Gobi-408-Collector-Kit/p652/


A Taco 008 will do about 8 GPM at 10', Thats according to Taco... I used a 009 (30' cutoff) and was disappointed with no flow, and ended up putting two 009's in series, I had about a 20' head.

What are the filling vents and filling caps?

Rancher
 
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SolarGuy

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Rancher said:
You need an air vent and vacuum valve at the top of the collector.

What are the filling vents and filling caps?

According to Homepower Issues 86 & 88, an open-loop drainback would use the air vent and vacuum release. But in a closed system, these are not recommended.

The filling valves are both opened to allow filling. The water level (with pump off) would be to the top of the drainback tank. One for water in, the other for air out.

jimbo, thanks for letting me know about the RO problem with copper.

Jason
 
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Rancher

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SolarGuy said:
According to Homepower Issues 86 & 88, an open-loop drainback would use the air vent and vacuum release. But in a closed system, these are not recommended.
I can only get to Homepower issue 107 and it doesn't specify.

Here's a couple of links:

http://www.freepatentsonline.com/4397294.html
http://cedarmountainsolar.com/solar_h20.htm

Think of your pipes back to the water tank heat exchanger as if they were a straw, and you had your finger over the top of the straw, how is the water going to drain back? On my closed system the hot water side of the collector doesn't go under the water in the tank, so my system kind of burps it way back to empty, but if it was under water there would be no way for the collectors to drain.


Rancher
 

Master Plumber Mark

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this sounds like a nightmare from my past

been there and done 200 of these panels back in 82-84
it was back breaking work.....

the system could fail in time...... or the ph will get all out
of wack in that untreated water....and the panels will eventually
lime up or fail to drain down due to a sensor failure and freeze up.


or the auto Air vents on the top of the panels might get froze shut and
would not allow the water do drain back down quickly.


we also had a problem with those Auto Air vents pissing water all over the
shake shingled roofs when the panels filled up....

air bubbles in the system was a problem too...

it looks to me that you should put that 6 gallon tank at the bottom
of the system in the mechanical room....not at the top
and keep everything simple pipeing
on the second floor or up in the attic..

I wonder if you did not make it a closed system and literaly sucked water
up from the bottom of that 10 gallon bucket then let it pass down back through the
water heater coil then back into the top of that bucket....into open the air at the top ???..

that would eliminate the need for a prv valve...and it would certainly drain down better

you would have to monitor the amountof water in the system like a boiler,
and perhaps put some bleach in it to keep it from getting too nasty...
..
..

either way you will literallly BOIL the water if the pump fails and it stands still in those panels
on a sunny winter day...

as long as the coil never leaks the
stagnant water from the solar panels into your potable water system.....

thats sort of iffey



but if your inspector says its ok....go for it...



my only advice if you are in an region that needs winter heat....

for what you are doing would it not be better and more cost effective
to take another line off that large heater and run a forced air heat
exchanger to your furance????

your pay back would be much faster....



now please tell me about your CORN burning furnace....how do you like it????
 
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SolarGuy

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master plumber mark said:
now please tell me about your CORN burning furnace....how do you like it????

A little off topic, but I hope the mods don't mind....

Its a lot of work. Expect to spend about the same amount of time as you would with a wood stove. I have easy access to dried/cleaned corn and thats a big help. My stove is the Baby Magnum Countryside and it was a first year production unit and they were just getting their manufacturing kinks out. It had to be completely replaced under warranty. My local dealer was awesome and the 2nd stove works 100% better. The heat distributes itself really well throughout my house, and the stove is capable of heating the entire house when its above 32 degrees outside. Below that I supplement with propane. My home is a well insulated center-hall colonial 2350 sqft. Burned about 3 tons of corn last winter and less than a 1/4 of my usual propane bill.

Thanks for everyone's advice with the solar hot water project.

Jason
 

varmint

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In the 90's, we lived in an old Victorian farmhouse in the Hudson Valley of NY- it came with a working drain-down solar water heating system, and it must have worked fine the 8 years we lived there, since I don't recall fussing with that system much at all. You've gotten some good advice, but I would be concerned with the boiling water issue if your pump isn't working, for whatever reason (you could max out storage temp, or have a power failure, etc.) so you want it to drain under that condition. There's a great resource guy out in Colo. who operates a company called Conifer Engineering, or Conifer something... who rebuilds controllers, sells them and provides advice as requested. I could send a link, if needed. I am putting together a closed loop (oil fluid) solar heating system for my workshop, and he rebuilt the used controllers I had gotten when I bought the used system. (it had 5 big collectors, so a friend is using most of the gear for heat in his house- my system will be pretty simple, with a oil cooler and fan to heat, only when the panels get hot... Good luck, this is a worthwhile project to be doing.
 

NHmaster

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Why over complicate the whole thing? Drainback is a pain in the ass. Go with closed loop anti-freezed system.

Veissman, Buderus, Caleffi and a bunch of others put together packaged units with tank, valves, controls and pumps, panels and piping, even the brackets. Takes all the guess work out of it and costs less.

Here's a link to Caleffi. download and read Idronics 3

www.caleffi.us/
 

protech

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see replies in red
First, you cannot put RO water in copper!!!! The ph attacks the copper and produces bad taste, and eventually pinholes. No it won't, because there is no new RO water being introduced into the system. It's the same water being circulated in the solar loop over and over.

I am not an engineer, but I think you need some check valves in the system. I envision reverse flow at night transferring heat OUT of the storage tank and up to the roof! Check valves are not needed in a drainback setup because it's brained into a tank at night. No water is in the collector at night and it won't reverse thermo siphon like an open loop or glycol system would.

I have no expertise in solar, so this is just an off the cuff observation. Stay tuned, because you will get a lot more feedback as soon as some of the more experienced experts wake up!
 

protech

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see quote. responses in red

Yep, and if you use PEX or CPVC, the UV rays will destroy the piping in no time flat. correct

A water heater (electric or gas) heaviliy insulated will provide the best efficiency without spending thousands on a system that will have to be maintained for health reasons. Too many failure points in that design and if not properly maintained, it will either cause health conditions or it will be abandoned if someone other than the designer cannot maintain it. i.e. wife and kids. If there ever was an uninformed statement that was it. I routinely work on systems that have been in operation for 20+ years without problems. Statements like this usually come from plumbers that are afraid to work on solar systems so they just tell the home owner that they don't work or aren't worth the money. No tanked water heater is a match for a well designed solar heater in terms of cost of ownership in the southern part of the country. .
 

hj

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drain back

Without reading the vouminous replies, I may be repeating something. A closed drainback system has a finite amount of air and water in it. When teh system is pumping air in the collector is forced into the drain down tank. When pumping stops, the water drains down from the collector forcing the water out of the storage tank and up into the collector. Thus it does not need an air vent or a vacuum relief valve. IF IT HAD either, the water volume would/could be diminished and then the system would stop functioning until the system was refilled. There is no need for R/O water and its use could be detrimental to the system.
 
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