When you install larger collector arrays or sometimes when you have to deal with limited roof space you end up having more than one bank of collectors. It is important when you have multiple banks to insure that you have relatively equal flow through each bank. If you don’t you may significantly compromise the performance of your overall system. There are a number of ways to accomplish this including; balancing valves, parallel reverse return piping, ball valves/pressure gauge combinations, and flow temperature measurements. Each of these concepts has advantages and disadvantages. For today I will only focus on using flow temperature measurement for two bank arrays. When you use the Steca 0301 differential control (part #: S-DC-12S) you have the ability to use three temperature sensors.
Two of these sensors are used as part of the differential control logic and come with the control. One of these sensors connects to the tank bottom and one to the collector bank exit. If you purchase and install the third sensor (part #: S-S-1KPS) on the outlet of the second collector bank you now have the ability to measure the outgoing fluid temperature from each collector bank. You would also need to install ball valves on the outlet end of each collector bank (before the return lines of each bank meet). With the ability to monitor outlet temperature of each bank you can now restrict the flow (by partially closing the ball valve on the exit of the collector bank) through the bank that has the lowest temperature. You would do this until the outlet temperature of each bank is the same. This system of balancing flows is probably the least expensive when it comes to equipment costs but you need to have a sunny day and a little time to dial in the flows.