need advice on drain down system set up

[ron45]

I posted the in the introduction area of the forum but figured I'd repeat the questions here. hello I have some questions on drain down or back, hot water systems. Been off grid since 83 and need to redesign my radiant floor system as a drain back or down which ever is the current buzz. We built our own passive/ active solar adobe dream house starting in about 85. We have 2 kw pv system on three zomeworks trackers and some on the roof. I have 384 square feet of copper w/aluminum absorber plates. They were put in a radiant floor system during construction of our house. I'm life long musician and knew nothing of building. So mistakes were made along the way. I have a leak in one or more of the zones. When I get that in order I need to convert to drain back and just water or possible with some additives to keep the pump happy. The risers in the collectors are half inch. Headers are 1.5 inches. I can raise or lower one end of each of the three arrays to achieve the proper slope in the sends and returns for proper drainage. I have a quite a bit of old epdm solaroll tubing under or slabs and floors. 3/16ths id. I don't know if all this tubing should be part of the pump head calculations or not. I sorta remember they do matter. Maybe it's just wishful thinking.

I am unsure about the location of the pump in relation to the storage tank. Also the size I might need. I have plenty of grade differential to accommodate proper drainage and tank location. I do not under stand how a closed system could ever drain itself. The little I know suggests the at some part the departing water would develop a vacuum behind as it tried to leave the risers. So I have much to learn.

I look forward to meeting some of you.

Ron

[ron45]

PIC00013.JPG

I thought I load a shot of part of our system here goes……...

[ron45]

Dang, usually there are at least some trollers on the list who'll answer questions in hopes selling something. Is drain down a pariah subject, I just reread my msg. Is it that I didn't put any question marks? See, there's one. This is puzzling, what if I promise to buy something????? There doesn't seem to be a dismal category in the rate this thread pull down. Howbout if I put in some icons…….

Ron

[Naptown]

Ok here you go
You will need a drain down tank with some air space on top when drained
Pump out of the bottom of this tank to the collectors
The return from the collectors at the top runs into the top of the drain down tank.
Key to success is leave an air gap so the return is above the drained back volume in the tank.

[ron45]

Ok here you go
You will need a drain down tank with some air space on top when drained
Pump out of the bottom of this tank to the collectors
The return from the collectors at the top runs into the top of the drain down tank.
Key to success is leave an air gap so the return is above the drained back volume in the tank.

Hello Naptown, and thank you very much for the input. You cleared up something for me and you hit upon another thing I forgot about. From what you say, I gather that it's the air remaining at the top of the tank that allows the tank to be pumped back to the collectors. I wondered how you'd get the water out to the collectors but I wasn't thinking of an air space at the top. Otherwise you be working against a partial vacuum. You mentioned the return at top emptying into the top of the tank what about the line from the bottom of the tank… does it matter where it enters the storage tank?

Ron

[Naptown]

Hello Naptown, and thank you very much for the input. You cleared up something for me and you hit upon another thing I forgot about. From what you say, I gather that it's the air remaining at the top of the tank that allows the tank to be pumped back to the collectors. I wondered how you'd get the water out to the collectors but I wasn't thinking of an air space at the top. Otherwise you be working against a partial vacuum. You mentioned the return at top emptying into the top of the tank what about the line from the bottom of the tank… does it matter where it enters the storage tank?

Ron

The supply line to the collectors needs to be below the lowest water line when the collectors are filled to keep the pump primed.
You can put a vacuum breaker at the highest point in the system but it tends to be another place for a leak to happen. I prefer to maintain a continuous slope on the return line from the collectors (top)

[ron45]

Hi Rich I'm sorry but I don't understand your answer but I very much appreciate your taking the time to help. I'm new to drain down and don't know all the lingo. I think in terms of cold in hot out. When you say water line I don't know if you mean a pipe or a level indication like fill to here… that sort of thing. I build my first and only system in the mid 80s and it wasn't drain down and I don't discuss this stuff all the time.

Ron

[Naptown]

think of the drain down tank as a bucket.
you put a hole in the bottom of the bucket pump the water from the bottom of the bucket.
The water comes back to the bucket and the return pipe drains above the filled water level in the bucket.

[ron45]

think of the drain down tank as a bucket.
you put a hole in the bottom of the bucket pump the water from the bottom of the bucket.
The water comes back to the bucket and the return pipe drains above the filled water level in the bucket.

Thank you Rich. That is as simple as I was imagining the drain down parts of the system. I really appreciate your patience and help.

Ron