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stmbtwle

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Reply with quote  #11 
Here are my thoughts on it, others will differ.

Drainback tank:

The tank needs to be lower than the collector and IMO should be in an area that does not freeze.  The crawl space would probably be a good location. You'll want to plumb it so that not only the collector but also the lines drain back, or THEY will freeze.  Generally the tank only needs to be a few gallons, so the 30 gal tank should be more than enough, UNLESS you are contemplating heat storage, then I'd use the 80 gallon tank. Which of those tanks will fit in the crawl space?

Crawl space:

Probably the easiest (though not necessarily the best) way to heat the crawl space would be a hydronic fan coil, either store bought or home made from a car radiator and a fan.  Hot water flowing through the heat exchanger (or radiator) will heat the air, which will rise against the floor above.  A better way would probably be to secure tubing directly to the floor between the joists, but this would be expensive and a lot of work.  I'd try the fan coil first.

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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay

Braebyrn

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Reply with quote  #12 
Thanks Willie. Both of the tanks will fit in the crawl space, but the short 30 gallon will fit on the other side of the wall closest to the system and closest to the house furnace, and DHW tank making it ideal for a shorter run.  The 80 gallon tank would have to be installed another 25' further away and still below the lowest drainback line height.  In other words, the slope from the evacuated tubes down to the ground level while still maintaining a slope to the top of the tank.

The 30 gallon tank is just a how water tank.  The 80 gallon tank has the heat exchanger coil built in.  If that info makes a difference.  

I am currently worried that the angle of the manifolds are not steep enough to get ALL the water out.  I tested it on a bench top which was 1 tablespoon of water left over in a 7' section at 9:12 pitch or 4.4* angle, slope is 7.7% according to the slope calculator. With 3-7' sections, is that a problem for freezing?

I watched videos by Dr. Ben (Gravely) on Youtube (https://www.youtube.com/watch?v=VlAfTYTA0Z0) on drainback systems which I think is brilliant.  He recommends 1" in 20' or 1/4* slope, however I think that is for a unobstructed manifold. The Thermomax manifolds have the (dry) heat pipe tubes going down the center of the manifold possibly creating some issues with the water or heating fluid draining completely out. Is there an acceptable remaining amount?  

According to the pitch app, I have a .6/12 pitch on the finished system as it sits today.




stmbtwle

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Reply with quote  #13 
I did not realize you were looking at a DHW system, my thought was space heating. If you want to use a drainback system for DHW, bear in mind you're combining a pressurized system with a non-pressurized system, so a heat exchanger is pretty much required.  That would indicate your 80 gallon tank. If your tank is still usable as a water heater you might consider hooking it up in lieu of your existing water heater.  It's my understanding this is the way most professionally installed systems are set up (including mine).  However you'll now need another tank for drainback.  You should be able to use the small water heater for that.

If the 80 gallon tank is old and NOT suitable for pressure, you might still be able to use it.  Connect the collector (non-pressurized) to the tank itself, and the heat exchanger coil to the other water tank (reverse of normal). You could use it as a "preheater" or add a pump to circulate water from the coil to the existing water heater.  

Also, not all solar water heater tanks have a heat exchanger.  Mine, for instance is an "open" system and the pressurized domestic water also circulates through the solar collector.  This is common in Florida but would NOT be suitable in areas where freezing is common.  It would behoove you to make sure which type your tank is before installation.

You're getting into an area where I don't have much experience.  Hopefully someone else will come in.

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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
Braebyrn

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Reply with quote  #14 
Willie,
   You are right that I was just going to use it for space heating for right now.  I don't seem to be able to finish things unless I have help, or if it is a quick and relatively easy task.  Disabilities are getting in the way, but I carry on the best I can.  

Recently the local electric company offered a rebate for a heat pump water heater, so that is already installed.  It was free after the rebates and an incentive program where they monitor the usage and pay you for it.  It was a $999. + tax for the A.O. Smith hpwh.  The power company sent us a rebate check for $800 and then they paid us $350 for a year and a winter of monitoring our usage.  

I also have one of the 66 gallon stainless steel Airtap heat pump water heaters that I have for sale.  It could be used as the preheater at some point of the A.O. Smith DHW I suppose?

Thank you for the info regarding the different types of tanks.  I didn't know that.  This is a Rheem Solaraide Model number 81V-80E-1.   Rheem solaraide.gif 


Product Applications:
 For closed-loop solar water 
  heating systems

Product Features:
 Double wall heat exchanger includes copper tubing wrapped around the tank and secured within the jacket for positive leak protection
 High efficiency 4500 Watt backup electric
water heater
 Electric backup model provides at least 40-gallons of stored hot water
 Temperature and pressure relief valve 
 Collector feed and return fittings located at front of tank for convenient installation 
 Isolated tank design for better heat retention 
 High efficiency heating element 
 Rheemglas� tank lining resists corrosion and prolongs tank life 
 Patented R-Foam� insulation process 
 Cold water inlet brings cold water to tank bottom to prevent 
� mixing with heated water 
 Anode rod equalizes aggressive water action for prolonged tank life 
 Cold water inlet, hot water outlet, relief valve and anode rod at top 
� of tank for easy access and fast, economical installation 

Product Warranty: 6-Year Limited Tank and Parts Warranty

Energy Information: Approx. R-Factor: R-17.3
 Energy Factor and Average Annual Operating Costs based on D.O.E.
� (Department of Energy) test procedures. D.O.E. national average fuel 
� rate electricity 8.41�/KWH
� Meets all current state requirements for solar storage tanks


Braebyrn

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Posts: 12
Reply with quote  #15 
Oh, as far as the Rheem Solaraide.... it is older.  Maybe I should take it in and have it pressure tested?  I could probably do the pressure testing at a safe location?  Might have to do some research on how to safely test a pressure vessel......

It was built in 8/2008 and has sat empty in my garage for 2 years.  The folks I got it from had used it for about 3 years they said.  It was also pulled and was sitting in their garage.


stmbtwle

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Reply with quote  #16 
My guess it's still good. However you still want to test it before you spend all the time and effort installing it.
__________________
Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
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