Solar System Upgrade (DHW)...

[WES999]

Back about a year or two I built a DIY solar DHW system based on the build it solar website
http://www.builditsolar.com/Projects/WaterHeating/Metal1K/Metal1K.htm
It worked pretty well but there were a few things that could be improved.

Added another 4'x8' ( now have 2 panels).
Moved the tanks to the other side of the basement to reduce the long horizontal hose run.
Added high temp plastic drum liners, the drums were rusting and leaking.
Added a stainless steel pump, the cast iron one rusted through.
Increased supply hose size from 1/2" to 3/4" for better flow and drain-back.

It has been working really well, with the nice sunny weather we have been having, the system has been making plenty of hot water, today the tank temp is 155. (The digital temp gauge read in )

 

[woodgeek]

Nice. Is this 'preheat' for a conventional heater? If so, are you metering your backup consumption?

Did you follow the plan, i.e. a pex coil for potable DHW? Materials cost? DIY hours?

 

[bmblank]

Can someone explain how a drain-back system works? Is it an unpressurized system? Does the water from the panels go through the pex coils, or doors the water from the tank, leaving the coils for the domestic water?
I'd like something like this to help heat my 1600 gal storage so maybe i wouldn't have to make any fires at all to heat my domestic water. (only method of heating domestic is with a dhw coil in my storage)

 

[GaryGary]

Can someone explain how a drain-back system works? Is it an unpressurized system? Does the water from the panels go through the pex coils, or doors the water from the tank, leaving the coils for the domestic water?
I'd like something like this to help heat my 1600 gal storage so maybe i wouldn't have to make any fires at all to heat my domestic water. (only method of heating domestic is with a dhw coil in my storage)

WES -- looks good!

There are several types of drain backs.

You can get an idea of how the commercial drain back systems work by looking at the Home Power article listed in this section:
http://www.builditsolar.com/Projects/WaterHeating/water_heating.htm#Basics
The article by Marken on drainbacks is good and covers all the common types.
If you don't get Home Power, I believe they still offer the $10 digital subscription with access to back issues.


The drain backs I use are a bit different and may fit your situation better.
They use a large tank that is vented to atmosphere -- the tank just stores heat -- the water in the tank does not change.
The collector loop pump pumps water from the bottom of the tank, through the collector, and then back to the top of the tank. There is no heat exchanger or antifreeze in the collector loop. Freeze protection is provided by the water from the collector drain back into the tank when the pump stops.

For heat domestic water, I use a large pipe coil (300 ft of 1 inch pex) immersed in the large heat storage tank. The cold water flows through the coil on its way to the regular water heater. If the tank is up to temperature, the regular hot water tank does not come on.

If you want to do space heating out of the same heat storage tank, you may be able to just pump water out of the tank, through the radiant floor or hydronic baseboard and back to the tank -- no heat exchanger. This is what I do on my system, and it works fine -- nice and simple.

I like this design because its really simple -- little to fail -- cheap, and eliminating heat exchangers both reduces cost and improves efficiency.

More details: http://www.builditsolar.com/Projects/SpaceHeating/DHWplusSpace/Main.htm

 

[bmblank]

Thanks Gary. I've been reading that last article and i have to say its very interesting.
For me, at 100% wood burning for both heat and domestic, the cost savings is hard to justify. (I get free heat already.) But with simpler and/or cheaper systems the concept of not having to make a fire all summer is getting awfully tempting.

 

[WES999]

Nice. Is this 'preheat' for a conventional heater? If so, are you metering your backup consumption?

Did you follow the plan, i.e. a pex coil for potable DHW? Materials cost? DIY hours?

Yes, water flows through pex coils in the tanks and is heated, it them is fed to a 80gl electric water heater.

I have a hour meter on the water heater to log the on time. Over the last 9 days the water heater has run for
.4 hrs. about .25 cents of electricity.

The collectors were about $175 ea, the pump tanks etc was around $400, the total was somewhere around
$700-$800. Not sure how long it took to build, I worked on it as time permitted.