Solar heating

Simply Rad_2

HR
I live I a resort community where there are more second homes than we that live here. I am going to install my first drain back system this winter. The reason being is for a second home you need to protect the glycol, I have used the Stecca control with the vacation mode but that is just one more thing for the home owner to forget about. I think a drainback is the way to go for these vacant homes. I think I might even use glycol in the drain back loop to cover my a**. Just my thoughts
Jeffrey

Tim_5

Solar Heat

Can anyone explain the pros and cons of a drain back solar system, as opposed to a system that is charged with Glycol. I am getting quotes on both systems and not sure which way to go.

hot_rod

I've always

installed installed glycol systems. for the most part they have been SDHW systems.

Lately I have been experimenting with DB systems. I think for large array systems, typically heating arrays, they have a lot of value.

As the load lightens, or goes away in the summer months the system drains and doesn't present overheating issues.

Certainly it takes careful installation practices. Plenty of pitch on the piping, some suggest 1/2" per foot.

I predict we will see more DB package systems hitting the market as solar thermal grows. I saw some great packaged systems in Germany this summer.

www.energylabsinc.com shows some good examples of piping and DB components.

I'd determine which is best based on the panels, load, climate, etc.

hr

hot_rod

Everything but the

glycol! That's a chicken s... way to protect a drain back solar system. It's only purpose in a drainback is to cover bad installation practices. In my opinion.

First off glycol has a poorer heat transfer.

It's expensive.

And it can really get cooked when you send cool glycol up to a panel sitting at 350F or more. Once it gets fried a few times it will start attacking system components rather quickly, requiring expensive glycol replacement, possibly piping.

Proper pitch and piping support should be fine to assure drainback operation.

hr

Tim_5

one of my concerns with the drain back system is the shock to the collection panels when a tepid liguid suddenly hits a panel that is very hot

jp_2

good question

but i think the system needs enough intelligence so this does't happen.

hot_rod

Rumors about warranty

when panels are used in a drainback application. Be sure to check with the manufacturers you are considering.

I think Dave from NexGen in Colorado has a special drainback function built into the Resol control he buys. I'm not sure of the logic but he claims it prevents that cold shock, somehow?

I suspect it works like the evacuated tube function (OTC) that many Resol branded controls have. It watches for a predetermined temperature rise between the panel and tank sensor. Then it pulses the pump for 30 seconds at 100%, stores the new reference value and monitors the temperature increase.

hr