I am trying to decide on the exact upgrade path from an existing 2 HP single-speed motor. My two options so far are:
1. 2 HP two-speed motor, single-phase 230 Volt
2. 2 HP single-speed motor, three-phase 230 Volt AND a adjustable speed motor drive (which will accept a single-phase input and output three-phase power)
Option #1 above, the two-speed motor, will output 2 HP at the high speed and only 1/3 HP at the low speed. My dilemma is that I'm not sure whether, after being primed by the high speed, the second-story roof-mounted solar system will run at a system horsepower of only 1/3 HP. The pump curve shows that the 1/3 HP low speed has a max head of only 20 feet (or about 8.6 psi).
In trying to figure this stuff out, I've come to the conclusion that I'm not exactly sure how a roof-mounted solar system affects the system head. Does a solar system, when the solar valve switches to solar mode, add the height of the solar system (i.e. around 18-20 feet) to the system head (which would seemingly max out the available head in low speed mode)? Or does the height (head) of a solar system not matter after priming because the head used in getting the water up to the solar panels is regained by siphon effect of the water coming back down to ground level?
I have read the excellent pool solar heating website at www.powermat.com, but even this leaves me confused because they say in one spot that:And yet the Powermat website SEEMS to show solar heating plumbing that looks like a closed system and use a siphon effect?!?All the pool pump has to do to activate solar is raise the water to the solar panels. From there the water falls back to the pool by gravity. We don't try to make a closed loop where the water falling back down pulls the feed water up creating a syphon effect meaning the pump doesn't have to do any work. No No No. That would create negative pressure in the solar collectors and a negative pressure (a vacuum) can collapse pvc plumbing when it gets hot and hot it will get.
Can anyone help me sort this out?