Variable Speed Pump

Hi all,

I want to install a pump for pumping water through 3/4 Copper pipe (much like your home heating system boiler pump) but with speed control.

GPM from about zero to 15 GPM 18' of head (we beleive this to be true).

Any items come to mind? If not, I'll use a small VFD (automationdirect) and couple it to a 3phase motor.

Jim

I guess I'm a little uncertain of your question. There are also some gaps in your info.

Assuming a centrifugal pump you could just use a motor operated ball valve to throttle the pump discharge. This isn't as energy efficient as a VFD but might be easier and cheaper to implement. If you are using a positive displacement pump then a VFD is a good choice, but some chemical feed pumps (like LMO) have their own variable displacement mechanism internal to the pump and no other control is needed.

You had better make sure on head, as power is directly proportional to it and if you are wrong you might overload the motor.

If you want precise control you may need a peristaltic or other kind of chemical feed pump.

You probably won't get 0-15 gpm range. Almost any pump, including centrifugals, have a limit on turndown. Check your supplier. Also, motor heating may become a problem at low speeds.

http://www.pumped101.com/

here is a good site that has some of the calculations Tom just mentioned on head pressure etc.

Similar to TomJ's comments: Is more of a process/system design question than a PLC/control question.

Although is directly related to a Controls Engineer's typical challenge: Trying to control a system when that system is not capabible of doing what somebody else expects it to do.

Thanks!



The project is pumping glycol for solar panels. I am doing a massive up grade on an array. 600,000 BTU's per day total generation and with that much energy it would be nice to optimize as much as possible. Automatically adjust the flow based on the amount of sun captured. IE clouds roll in the output drops, slow the pump. Different parts of the day produce different amounts of energy.



Adjustable valves to divert flow is a option, but if there is a pump solution out there, I rather go that route.



Then I have the mission of moving the water long distances, so head is high. Moving water to slow will cause an over heating condition (no movement will result on 350+F deg. Dangerous)

Considering the size of the system, (15 GPM & 3/4" line). I would tend to go with 4 small pumps like the ones used in the under-floor heating systems. 4 pumps = 16 different rates of flow. If each bank of pumps were sized at 1, 2, 4, & 8 gpm; this would give you a flow rate 0-15 gpm in 1 gpm increments controlled by 4 PLC outputs. These pumps are small, reliable, inexpensive, readily available (Home Depot & the like) & easily replaceable. Also a single pump failure would not shut down the colletor.

JTE said:

Adjustable valves to divert flow is a option, but if there is a pump solution out there, I rather go that route.

Click to expand...

Just to clarify, you are describing a bypass or blow-off system, which is certainly feasible and will provide flow control to the process but won't provide any energy savings.

What I was intending to describe, assuming you have a centrifugal pump, is actually throttling the pump discharge. This causes the pump to shift left on its curve, with the net result higher pressure at lower flow rate. The net result is reduced energy consumption.

Do a google on hydronic system pumps. These will probably be much more suitable to what you are wanting to do.

Oh yeah.

Taco makes a "VV" line. 0-10 volts or 4-20ma.

Just what the doctor ordered.

http://www.taco-hvac.com/uploads/FileLibrary/102-142.pdf

Jim