Purging air from DIY coil solar pool collectors

[skeeter_ca]

I am building a DIY solar pool heater. The system uses 8 coil(irrigation tubing) type collectors.They are being mounted on a stand about 20ft from the pool and about 5 feet higher than the pool. Since it only has a 5 foot rise i wasn't thinking off using in an air break.

I am having two design questions. Should i have the exit on the collectors at the top so air will purge out of the top? I have seen both top and bottom exit with no problems mentioned. And second, how does the return header purge any air out of it?

skeeter

 

[mas985]

By exit, I am assuming you mean the return side of the panel itself? I would always put the return side higher than the supply side. Since the flow rate is split among several panels, the flow through a panel is going to be less so to help the air get purged out of the panels, I would always put the return side of the panel higher than the supply side.

I am having a hard time visualizing what you are planning but as long as air can rise out of the headers and into a return pipe (highest point), then the only piece of plumbing that will be difficult to purge is the return pipe because that goes downwards (I assume). A downward flowing pipe has a critical flow rate that is required to purge the air (i.e. air rising velocity < water downward velocity). That flow rate is somewhere in the 20-40 GPM depending on the drop and pipe size.

There is a slight advantage of a system without a VRV. You can purge the air at high flow rates, and the adjust the flow rate through the panels to be lower if desired. Since the panels remain primed, there is no need to have a priming flow rate again.