The New Pump

One of the things that has been a problem on the $1000 solar water heater design is finding a pump that is in keeping with the project $1000 budget, but at the same time is reliable, and long lived. There are good pumps out there for solar water heating systems, but the prices tend to run in the $250 and up range, and this seems a lot for a $1000 total system budget.

I am trying a SwiftTech MCP350 pump. The pump is actually intended for cooling the processor on over clocked PCs. The pump is very compact, and holds the promise of providing a very long and trouble free life (but this is yet to be confirmed) Price is about $55.

See details below.

SwiftTech MCP350 specifications:

Note that there is also an MCP355 model with greater lift and flow than the MCP350.

This is from the www.swiftnets.com website:

	Nominal voltage	12 V DC
	Operating voltage range	8 to 13.2 VDC
	Minimum startup Voltage	9 VDC
	Nominal power (@ 12 V)	8.3 to 12 W
	Nominal current (@ 12 V)	0.69 to 1 A
	Nominal head (@ 12 V)	10.8 ft (3.3 m)
	Nominal discharge (@ 12 V)	~ 116 GPH (440 LPH)
	Connection size	3/8" barbs (10mm)
	Maximum pressure	22 PSI (1.5 BAR)
	Temperature range	Up to 140°F (60°C)
	Electrical connector	Molex 4 pin
	Weight	7.3 oz (207 gr.)
	Our noise measurement (non lab environment)	24 ~ 26 dBA in a quiet room @ 2'
	Motor type	Electronically commutated, brushless DC, spherical motor
	Pump MTBF (Mean Time Between Failures)	50,000 Hours
	RPM Signal	Single wire on 3 pin connector
	RoHS	Compliant

I believe that this pump is made by Laing, and uses their highly respected electronically commutated, spherical motor design -- the same type of drive uses in their EcoCirc solar pumps.

It is a 12 volt DC pump, so a small power supply is needed -- I use a 2 amp wall wart type supply from Radio Shack.

The maximum fluid temperature for the pump is 140F, which goes well with the design of the $1000 solar water heater, and is another benefit to limiting the maximum storage tank temperature to 140F.

The maximum lift of the pump is 11 ft. So, this limits the distance from the water level in the storage tank to the top of collector to no more than 11 ft. It works find in my system, where the vertical distance is about 8 ft.
Note: that there is a very similar MCP355 model that with a max lift of 15 ft, and somewhat higher flow rates.

The power consumption is only 10 watts! -- the total consumption on mine including the wall wart is 13 watts.

The small, 3/8inch barbed fittings are a bit of a pain to adapt to, but that's life.

The pump is available from a number of internet suppliers who sell water cooling equipment for PCs -- I paid $55 for mine.

So, what is the life likely to be?

I don't know. The Laing D5 pumps which use a similar electrically commutated spherical motor say "The brushless motor has a lifetime in excess of 50,000 hours when operated at nominal voltage...". Maybe the SwiftTech, which seems to be related to the Laing, will do similarly, but hard to say. If it did achieve the 50,000 hour life, at 6 hours a day this would be more than 20 years!

My MCP350 is going on one year, and doing fine.

Note that there is also an MCP 650 which appears to be similar to the 350, but with a higher flow rate -- so, if you have more collector area, this might be an options.

(Thanks to Matt for pointing this out)

A couple links on Laing pumps:

http://www.ober-read.com/laing_ddc.htm (this one looks externally identical to the MCP350)

http://www.ober-read.com/laing_new_d4_page.htm

http://www.lainginc.com/pages/dc_ph.htm (These pumps can be driven from PV panel and have built in MPPT)

Installation

Since my old pump was a submersible, and the SwiftTech is not, I had to redo the pump plumbing. The following pictures show the new arrangement.

The pump is not self priming, and the instructions are quite adamant about not running it dry. So, you need to make sure that the pump always retains its prime. This means mounting the pump below the water level of the tank and making sure that the pump plumbing does not drain or run dry. I used a U-tube arrangement to mount the pump just outside the tank, and well below the tank water level. This arrangement is used on a lot of solar drain back systems, and appears to be working fine.

The U is made from 3/4 and 1/2 inch
CPVC pipe.
The valve at the top allows for
priming the pump and U tube.
The left vertical goes inside the
tank, and the right vertical goes
to the pump outside the tank.

The pump installed.
The pump input is on the left, and
is fed by the U tube with water from
near the bottom of the tank.
The pump outlet is on the right, and
feeds the two orange PEX tubes that
come connect to the bottom of the
two halves of the collector.

The somewhat awkward, but
functional adaptor arrangement to
go from the CPVC pipe to the 3/8
inch tubing that pushes onto
the pump barbed fittings.
The connections to the barbed
fittings should have clamps, which
I will add soon.

The pump is supplied by a U-tube that takes water from near the bottom of the tank to the pump inlet. The U-tube allows the pump to be located below the water line of the tank. The U-tube and pump remain full of water after a drain back of the collector, so the pump always starts with a prime. The valve extending off the top of the U-tube allows the U-tube to be primed for the initial startup or after maintenance.

The fittings on the pump are 3/8 inch barb fittings, so you have to figure out a way to adapt from the 3/4 inch U-tube to tubing that will push over the barb fittings. I used a 3/4 by 1/2 CPVC adaptor to step down to half inch CPVC, and then a SharkBite style connector that Lowes sells to go from the 1/2 inch CPVC to the 3/8 tubing.

On the outlet side, the same kind of adaptor is used to go from the 3/8 tubing to half in CPVC, and then a SharBite T is used to go to branch to the two half inch PEX lines that go to left and right halves of the bottom of the collector.

The connections to the barbed fittings should have clamps, which I will add soon.

Maybe someone has a better way to do this?

The pump is just lightly screwed to a block of wood to keep it in position.

At 13 watts, the pump would pull a bit over 1 amp. I used a 2 amp supply just to account for start up surge.

The supply I used is a regulated, 12 VDC wall wart style supply that Radio Shack carries.

In hooking up the pump, the yellow lead is the +12 volt, and black is the negative.

So Far

The pump has about 8 months of daily operation on it with no problems.

It started up fine the first time. I tried several drain backs and restarts with no drama.

The measured flow rate on my system is 1.7 gpm. This is 0.035 gpm per sqft of collector for my 50 sqft collector, which is (I think) just a touch on the low side, but OK. They do offer a larger model.

The pump and wall wart together use only 13 watts when pumping! -- about 0.5% of the solar energy being collected.

I will report on any problems that come up as time goes on.

While I have high hopes for this pump, it is not really intended for this service, so some caution is in order.

I should also mention that the original March pump I was using is still working just fine -- I just wanted to try this pump because it fits the project budget better.

Gary November 11 & 12, 2008