Simplifed(?) drainback Solar Thermal (for small) Hot tub heating

NIMAN

solar thermal (simplified) hot tub drainback.GIF

Based on this comment on closed thread:

https://forum.heatinghelp.com/discussion/comment/1061692/#Comment_1061692

But you also need a way for the supply to the collectors to drain. A small tube run between supply and return will allow the supply to the collectors to drain back, once the pump is off.

I prefer not to use air vents or vacuum breakers as neither holds up well to the harsh conditions found on collectors.

I was wondering if my attached image configuration is something similar to what Larry Weingarten might (/ does) have had in mind - i'd like to forget about Glycol and a heat exchanger in my, planned. modest hot tub.

Could that work? how small could/should the "small" tube between supply/return be?

hot_rod

I've never piped that air break in any of the drainbacks I have done. I have two pressurized DB systems on my shop and home now, one with a 27' long collector, they drain fine.

The red pipe above the tub, in your drawing will allow air into the piping

NIMAN

Hi Bob.

I see you were involved in that 2007 thread - perserverance & congratulations 🤗

I now guess an "easy" Drainback type setup for open hot tub scenario could be unreasonable.

Good to hear that long collector system works fine … the little i've read about Solar Thermal makes me think DB is, relatively, under-appreciated.

Anyway, thanks for your comment.

Larry Weingarten

Hi, If the red pipe ends underwater, I'm not sure how air could get back into the system, allowing the collectors to drain. Drilling a small hole in the pipe above water level, can fix this and not have any of the longevity problems vents and vacuum breakers have. 👍️

Yours, Larry