It's "Christmas in February" !

[(unknown)]

I'm just about to google and search, but man am I happy!

Some very nice stranger who renovated his roof didnt feel like putting those panels back up, so he gave them to me.

He plans on removing the solar water tank and the circulation pump this summer, I'llmake sure to give him a call.

Those panels use glycol.  Are commercial panels all convertable to "drain-back" systems, or will I have to do some research/use glycol too ?

Cheers

One happy enthusiast!!

[morglum]

I'm quite sure that if I offered to come and remove that  hot water tank  he'd give it to me.

Problem:  I've never even been close to a hot water tank before, let alone one that has glycol going into it.  

What would be a good way to remove such a tank?  How do I drain the water and the glycol out?  I wouldnt want to make a mess in his basement...

cheers

[morglum]

What do you guys think of this guy's way of using a normal electric water heater as a "solar water heater" ?  (http://chuck-wright.com/projects/hotwater.html)

The interest I see in doing this instead of just pre-heating the water like in Gary's project on builditsolar.com  s to allow the water solar heater to offset losses IN the tank too.

[Volvo farmer]

I'm convinced that Gary has the right idea.

I met a guy this winter, really smart guy, who built his own solar hot water system. He had about a 500 gallon tank, drainback, insulated, (4) 4'x10' panels and put all his heating loads into separate coils inside his 500 gallon tank. The idea was really similar to Garys but this guy had differential temperature controllers all over the place, a backup boiler and a bunch of other stuff that I failed to note or appreciate. He heated his floors and his DHW with this system, and had heat left over on a lot of days.

I do not heat any part of my house with solar hot water, but have been thinking about it for years. My current position is that glycol sucks and that drainback rules.

[morglum]

I remember reading a lot of posts where people say drainback>glycol, but I cant remember why.   Cost?  If so, is it still true even he gave me one large bucket?

Assuming I go Gary's way, we could just have the glycol loop heat the 500 Gal storage tank, and have each uses (DHW, eventually floors) use their own heat exchanging coil in the storage thank as well.  

That way, the only way glycol could get into the potable water would be for the system to have 2 leaks: one in the glycol loop and one in the potable water loop.

Is glycol expensive?

Man, this is exciting!

Based on my understanding of Gary's solar DHW, all I need is:

1. plumbing to get the glycol up there and back
   
   
2.  a circulation pump for the glycol
   
   
3.  a heat exchanging coil for the glycol
   
   
4.  a heat exchanging coil for the potable water
   
   
5.  build a large storage tank in the basement to pre-heat DHW before it enters the electric water heater.  

   
   
   

correct?

[morglum]

BTW, here is my "understanding of gary's DHW",

http://vivrenvoyage.com/SIMON/plan_solar_DHW.JPG

I already have the panels, the pump and the sensors.  (and the normal electric tank).

[GaryGary]

Hi,

You must be leading a good clean life to have such good fortune

Not all commercial panels can be used in a drain back system.  Some use a serpentine tube arrangement inside the collector, and won't drain back reliably -- these are not as common as the vertical risers with manifolds, but you should check to make sure.

You may be able to see the tubing through the glazing, or if the manufacturer has a website, check with them.

Assuming the collector uses the vertical riser tubes with horizontal manifolds, you can probably use it for a drain back system.  Chuck Marken's Home Power article on drain backs recommends using riser tubes no less than half an inch in diameter -- so there would be some risk if the collector has small diameter riser tubes.

I like drain backs -- to me, if you get the plumbing right, then they are close to zero maintenance.  You don't have to worry about checking or replacing the antifreeze.

They are also simpler and less expensive to build with fewer parts.

That said, the anti freeze systems work fine as long as you look after them.

If you use the drain back, just be really careful that all the plumbing and the collector itself have slope back towards the tank -- about 1/4 inch per foot is good.

If you go with the antifreeze and heat exchanger, you would effectively have a double wall heat exchanger with the two coils, but I would still use the non-poisonous propylene glycol instead of the car antifreeze.  

You mention a 500 gallon tank -- that's a whole lot of tank for 72 sf of collector.  Beyond a point you really don't gain anything by making it larger -- it just costs more to build and loses heat faster.  I think that a couple hundred gallons would be plenty.

I'd not use the heat exchangers unless there is a clear need for them.  My space heating system has no heat exchangers in the tank.  The collector pump pulls fluid directly from the tank and returns it directly to the tank.  Same for the floor heating system.  The systems that preheat potable water will need a heat exchanger, and (so far) I'm quite happy with the large coil of PEX immersed in the tank.  Its simple, and it gives you 100% efficient heat exchange for the 10 gallons of water that is already sitting in the pipe coil.

Gary

[morglum]

-----------------------------------------------------------------------

Re :Karma

-That's what I was thinking too.

 Karma has been nice lately:  Last summer, I was returned my wallet with the 160$ that were in it.  I gave half to the kind soul.

.  Note to self: Keep offering stuff on Freecycle

-----------------------------------------------------------------------

Re: Solar DWH

Thanks Gary for popping in and giving all these tips!  

-I'll give a look to the solar collectors to figure out if they are serpentine or vertical and if the riser tubes are at least 1/2".  

-Turns out the panels are 4x6 not 4x9 as initially thought.  That means I only have 48 sq ft.    

Q1: Would 200 gallons be too much given this new information?

-I'll make sure to use the non-toxic glycol if we don't go drain-back

-I dont think we'll be able to do any space heating with just these two panels, but good comment about circulating the tank's water in the floor instead of heat-exchanging it.

Q2:  Another question if you don't mind:  How did you get those two pipes of glycol (or water) from the basement to the roof?  Right now I see myself having to destroy a few walls..

Cheers,

Simon

[dnix71]

Glycol is just antifreeze. Plain water won't work in a climate where you get freezing weather.

Ethylene glycol is car anti-freeze and very toxic. It's also expensive. Propyl glycol is a food additive and much safer, but you still aren't just supposed to dump it.

If you don't need the solution call a radiator shop. In the US they are required to filter and recycle the stuff. Since it is expensive, they would probably be happy to take it for free.

[morglum]

I thought the point of drainback systems was to remove the water so it doesnt freeze.

If memory serves well, Volvo Farmer is also in Canada and his friend has a drainback  system.

[GaryGary]

Right -- our drain back system with plain water has survived many -20F and worse MT nights.

Gary

[morglum]

Thanks for the confirmation.

Gary, I have a question regarding the following build on your website.

http://www.builditsolar.com/Projects/WaterHeating/DougsSolarWater.htm

He says he has no controller, simply that the pump is plugged to a PV panel, so that "when the sun is out heating the fluid, the pump works".  

Question:  This sounds great, but what about winter?  The PV might be generating electricity, but the collector might still be colder than the hot water tank?

[GaryGary]

Hi,

48 sqft should work well for domestic hot water if your hot water demand is not too large.

I have a collector that is equivalent to about 40 sqft of commercial collector.  I use a 160 gallon EPDM lined tank, and that seems to work fine.  If you get some sunny days followed by some cloudy days, the 160 gallons is big enough to hold up for a couple cloudy days.

Its not that important to get it right on the money -- things don't change very fast as you go larger or smaller.

Gary

[scottsAI]

Morglum,

Exciting.

Drawing shows a closed loop, add an expansion tank, like baseboard heating systems. Closed loop needs to be completely closed keeping out new air. The oxygen burns out the glycol. By keeping out the 02 it will last longer. Just like with a vehicle!

Have fun,

Scott.

[morglum]

i had forgotten about the expansion tank.. thanks!

[GaryGary]

Hi,

This has been the subject of very very long debate threads on the Yahoo "Solar Heat" group.

To me, the direct PV to pump is not an optimal way to go for two reasons:

1. The PV panel does not know anything about the temperature of the water in the storage tank -- so it can't turn the pump on earlier if the storage tank temp is way down, or later if the storage tank temp is way up.  Whereas, a system with a differential controller knows both tank and collector temperature, and can turn the pump on when it makes sense.

   
   

2. The PV panel and the solar thermal collector have opposite dependencies on temperature -- the PV panel gets more efficient with low temps, where the collector has greater losses and lower efficiency with cold temps.  So, if you set up the PV panel to get the pump going at the right sun level when its 70F out, its not going to be right when its 20F out -- it will start the pump too early.

   
   
   

All that said, I think that the direct PV to pump systems work OK (especially in moderate climates), and that differential controller have their own set of little problems.  I would personally lean toward a system with a differential controller, but not by a whole lot -- that's just my personal feel -- no real measurements to back it up.

If you want the best of both worlds, there are some reasonably priced differential controllers for PV powered pumps -- Guy Marsden makes one: http://www.arttec.net

Another unrelated problem with the PV direct for drain back systems is that you often need a pump with a fairly high startup head to get the water up to the top of the collector from the storage tank.  Its hard to find PV direct pumps that have a high startup head capability.

Gary

[morglum]

Thanks Gary, great information again.

Here's a reply I received from a solar water installer in the area regarding converting closed loop--> drain back.  What do you think?  What materials in a closed circulation panel couldnt be safe for potable water?  Isnt it just copper and aluminium?

Cheers

Simon

"  You should not change a closed system to a drain back system.  Manufacturers don't use materials safe for potable water within closed circulation systems."

 

[GaryGary]

Hi,

That does not sound right to me on two fronts.

1. I've never seen anything from a manufacturer that says "my collectors can't be used for potable water".

   
   

2. If you were to do a drain back system, you are still not circulating the potable water through the collector -- the collector loop heats the fluid in the drain back tank.  The heat is then transferred to the potable water via a heat exchanger.  There are "drain down" systems that circulate potable water through the collectors, but a drain back system does not.  

   
   
   

If you went from a closed loop to a drain back then you might possibly be required to change the potable water heat exchanger to double wall one because it might have antifreeze on one side rather than water (depending on the system details), but that issue does not come up in going from closed loop to drain back.

I suppose it would not hurt to email the manufacturer and get a confirmation that there is no problem, but it seems unlikely to me.  

Gary

[hydrosun]

I think you are right about the pv direct to pump is for moderate climates. I've been using that setup for vacuum tube solar heaters with a frost valve to protect from freezing. The vacuum tubes and well insulated pipes lose very little heat so even if the pv and solar heater are not exactly in synch little heat is lost. So for simplicity and low cost it is the way to go in a moderate climate.

Chris

[hydrosun]

I wonder if the Laing ecocirc pump might work for high head startup. It is supposed to start up in lower light conditions at 1 watt output. And can use up to 20 watts. I don't remember  the height limit. I haven't had a chance to experiment with it much yet. I've been using the el cid pumps.

chris