High efficiency pump 1

[Muleman]

I need to pump 3-6 gpm of 50/50 glycol and water at 15-20 psig for heat tracing production lines. There is no electrical power, so I'm trying to do it with a 24 V solar system and as such efficiency is a primary concern. I inherited a pilot test with solar pannels, batteries, inverter, AC motor and centrifugal pump but it is woefully inefficient--batteries to hydraulic hp runs about 3.2%. I plan to eliminate the inverter, go with a brushless DC motor/controller and a gear pump. By my calcs this raises the efficiency to about 30% with most of the gain due to the pump. Is there another type pump I should be considering? I've heard from one vender that claim they make a pump with around 85% efficiency but they wanted $8k for it and for that cost, I'd rather buy more panels and batteries.

 

[BigInch]

What's wrong with a centrifugal pump? Its only water, not toothpaste. You can get low or high efficiency centrifugal pumps and I don't think you'll need to spend 8000, unless you've got a very high flow or high pressure application. I'll bet your maintenance expenses will be lower too.

 

[Muleman]

I'm no pump guru so I assumed for low flow rates, cent pmps are usually less efficient. I've spent quite a bit of time surfing the web and I see very few mfg of small cent pmps that give much performance data--other than end points. Those that did give data showed performance similar to the pilot test described above. But, you've encouraged me so I'll look some more. Thanks.

 

[BigInch]

Gear pumps are usually beat centrifugals when pumping hi viscosity fluids or Bingham fluids with high variable shear rates. The problem you may have with your centrifugal search may be that, if the capacity is too very low, there may not be much of a market for super hi eff centrifugal units, because the payback would take years and years at such low flowrates. It would be much cheaper for the user to use a lower eff pump rather than pay for a super hi eff speciality pump. The efficiency for centrifugals is optimized for flowrate and pump speed. They usually top out at 86% efficiency, but some can be as low as 60%. How much flow do you want and what elevation do you have? Maybe I can tell you where to look.

 

[Muleman]

Average flow rate is 6 gpm with a discharge pressure of 15 psig. I was thinking along the same lines as you describe about the smaller cent pmps, that's why I quit looking. I've looked at companies like Gould and they show pump curves with efficiencies much better than I've measured, but the capacities are orders of magnitudes larger than I need.

 

[BigInch]

Thought you might run into that. Try looking for gardening pumps, fountain pumps, etc.

http://www.plumbingsupply.com/pondstff.html

Has a couple that have shut-off (no flow) heads that scratch your water head range (30 ft), running them at > 0 flow will give you somewhat lower head/pressure output. Eff's not given. You might even have to change the motor and speed if you're using DC, but you should be able to find something and make it work for US$200-300, even with a motor changeout. Not thousands.

 

[Artisi]

Do a search in google - where are plenty of sites to look at for solar pumps.

Naresuan University
Phitsanulok
Thailand

 

[trashcanman]

Why go to the trouble of a pump & piping system? Why not use electric heat tracing cable? It probably uses no more power than a pump & is much simpler. Use self-regulating type by Thermon or Raychem, and save a lot of hassel.