Drainback system design
 

Here’s a website I found pretty useful when designing and building my solar hot water system (Solar Water Heater Design). Dr. Ben is a strong proponent for drainback systems due to their simplicity compared to pressurized glycol loops. The site has a focus on larger commercial systems, but the drainback system design is very scalable and there are a lot of useful tid-bits that apply to all systems.

A few of the items I picked up were methods of piping larger systems (importance of reverse-return, and a single high point), piping slope does not have to be quite as steep as commonly thought for drainback, and the limits on the length of a bank of collectors.

Esharp,

I've been all over his website as well as logged in to some of his live webinars.

He is the person who inspired me to do a drainback system at my own house.

One super smart guy there for sure!
Glad you posted his location for all to enjoy.

Take care,

Thanks for sharing. I never realized that the return side of a drain back system is the highest point. Learn something new everyday.

SimpleManLance,

Not sure if we should call it the 'Return side of the collectors actually, even though the water exiting the collector at it's highest point IS in deed the water returning to the storage tank??'

The collectors on the roof are tilted a bit so when water is pumped up thru them the water is pushed from the lowest point of the collector / thru the collectors / and exiting the highest point of the collector piping.

When the pump shuts down the water drains back to the storage tank.

I installed the vacum release valve at the highest point of the piping which I am calling the 'return side' just for a reference point.

I forgot to metion that I had to install insulation over the top of the vacum release valve also because in the winter cold months that valve will be sucking in ice cold air each time a vacum is created in the piping. Don't want ice cold air entering my piping so now it's covered with fiberglass wrap.

I left an air space / air pocket under the insulation so the valve could still breathe/function ok.

ESharp, do you have a thread here that shows/explains your solar hot water setup?

DAOX

not sure if I sent it to you or not previously but I have a pdf file showing my solar hot water system build I can give you/send you via email if anyone would like to see it.

Could it be this one?

http://ecorenovator.org/forum/solar-...r-project.html

Yes, you sent me your pdf solarhotairpanels. Thanks.

Thanks for finding that jeff5may.

Officially, the return of any heat producing system is the pipe going into the heat producer, in this case, the panels. Same with boilers, etc, etc.

It is CRITICAL that the return pipe be thick walled copper (rather than PVC).

Imagine if power shuts off on a sunny day. The collectors heat up to way past 300-400F with no water circulating. This can happen within 10-15 minutes in the middle of the day (brief power outage).

Then power comes on (during the day). Water comes into panels and it flashes into super heated steam. This superheated steam simply turns PVC to a melted mess with water being pumped out.

With copper, the superheated steam must heat up the copper and the heat is dissipated. PVC pipe does not do this.

Don't ask me how I know of this . . . .


Steve