Flow through flat plate collector

Kal Row

Big D_2

What flow rate through a flat plate collector

I have some old 3x8 flat plate collectors. They have 3/4" pipe running horizontally top and bottom, and 17 3/8" pipes running vertically between the 3/4" lines. I am wondering what flow-rate I should run through these? I looked at other collectors, and have seen reccommended flow-rates from .22 to 1.5 gal/min. Most new collectors seem to be constructed similar, but have fewer vertical lines. I am thinking I should run a slow flow-rate because they have more vertical lines and hence more water to heat up.

Unknown

slow flow rates = higher exiting temperatures, and less collected BTUs.

Higher flow rates = lower exiting temperatures, and more collected BTUs.

which is correct, I think, depends on your application.

Justin Topel

Flow Rates

We see pretty good results by flowing the capacity of the panel per minute. I roughly figured that you should have close to 1.18 gallons of capacity in these panels if my math is correct. So flows of 1 to 1.5 GPM should work just fine. You could test your flows out a bit by placing a flow setter on the return side and watching your panels for a period of time throughout the day and compare that with the following day by changing the flow setter a bit. If you happen to have the same sunny days in a consecutive row, it should be rather close. Just track the panels temps along with the storage temps. Of course if your tank temps are off from day to day it can make it a little hard to do this. Give it a try. You should be fine at 1.25 GPM per panels. Oh and another thing to do is check the CV if possible on the flow setter. I have seen where guys we trying to use one flow setter for a large array and it would not allow the flow to raise above 4 GPM since their pump was lacking sufficient head. If you are close to the limits of your circulator, watch your flows. Good luck