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Net Positive Suction Head - what does the pump "see"?
I've read Dan's post "Understanding primary-secondary pumping", and many others, which have been really helpful. Pertinent take-aways are to pump away from the expansion tank, and to place the air separator/expansion tank on the primary loop - in my case, a heat pump used for cooling. I've got one nagging area of doubt: I'm installing a four-port buffer tank (Heat-Flo HF-22BT44-1.25) to re-pipe my chiller and air handlers in a primary/secondary fashion, as illustrated in the attached diagram. The tank has four connections - two on the left, one on the right, and the fourth at the top. To achieve air extraction, I need to place the spirovent on that top connection - shown with green colored lines. I'm worried about pump cavitation - the tank is 27" tall - if I pipe down 24" and place the pump at floor level, will the pump see the 24" of water column? Is there any difference between this arrangement, versus connecting the pump to one of the side-wall connections, in terms of the pressure of the water column presented to the pump? I would appreciate your comments and suggestions.
Energy Kinetics EK1
SpacePak 3 ton Chiller
Aircell Air Handlers