I installed a DX drainback system with 10-gallon drainback tank. I filled the small DX tank to within 1/2" of the top of the sight glass as the instructions called for. When I energize the Taco pump, it does its job and pumps the water up to the panels (located on the roof), but the 10-gallon tank runs just about dry before I can hear the returning water drop into the tank (the sight glass remains completely empty while the pump is running). Consequently, the Taco pump can be heard to be sucking air quit loudly (at least that is what I am assuming it is doing). I've shut the system down since then, until I can get an idea of what to do about this.
I actually have two questions about this:
1. Common sense tells me that I should just add some more water to the 10-gallon drainback tank, but how much will be too much?
2. With the tank running nearly dry while the Taco pump is pumping water to the panels, I don't see how there is anyway the heat exchanger coil within the tank is able to receive the heat from the collector water, since there doesn't seem to be any water surrounding the coil at that point. While again, the solution seems to be to add more water, I am afraid that the amount of water needed to submerge the coil while the circulator is running will be more than the capacity of the tank when the circulator is not running and the water has drained back to the tank.
The solar water panels (three panels total) are located with a supply run of about 31 feet and a return run of about 45 feet, using 3/4" copper pipe. I calculate that I use almost 2 gallons of water for both the supply and return lines. Does it seem reasonable that the panels themselves would hold the other (nearly) 7 gallons of water (assuming that there is a gallons worth of reserve left in the tank when the sight glass is filled to within a 1/2" of the top)?
Anyway, some insight from others who have installed this system before would be helpful. I am used to Taco pumps operating quietly, so this brand new pump, making this noise has me concerned.
Sean
