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Check valves for passive solar hot water system - Page 2

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Posted by Anthony Matonak on October 26, 2007, 12:28 pm
 
mark.fox@gmail.com wrote:
...

Yes. The tank needs to be above the collectors. Even then, if you're
not careful to design the plumbing with the minimum resistance to
the flow of water, it might not work.

Anthony

Posted by DavidMDelaney on October 29, 2007, 2:57 am
 
On Oct 25, 11:21 pm, mark....@gmail.com wrote:

Check valves for thermosyphon systems are famously problematic. The
head available to operate a check valve in a thermosyphon solar water
heater is orders of magnitude less than that assumed by virtually all
available check valves, although, as a previous poster noted, it
should be possible to design a suitably sensitive flap valve.  Shawn
Buckley invented an extremely sensitive fluidic check valve for
thermosyphon solar water heaters in 1981. It is suitable for DIY
fabrication. See my article on it at http://tinyurl.com/2sqe3w . The
article has references to other literature on the Buckley valve and
the system that used it.

David


Posted by Mike Scaife on October 26, 2007, 11:47 pm
 

One pumped system I have running uses a low power 10watt 12 volt DC ELSID
pump and using a spring check value the water flow is very low.
I re-configured both pipes running from the hot water cylinder to the roof
mounted panels to have a thermosiphon loop dropping approx 40cm below the
cylinder before rising up to the roof, the check valve has been removed.
This effectively prevents reverse flow at night when the panels cool down.

Another system uses a higher powered mag DC drive pump and has a brass
flapper type check value sitting horizontally, so little pressure is
required to open or close.

I made an attempt to dismantle the spring check valve, dammed if I can get
it apart, I though if a lighter spring was inserted it would work ok.

One problem I have found with ELSID pumps, they get very noisy and don't
appear to pump well when the water temp approaches 80 degrees C. The higher
powered unit with the 20 watt driver gets very hot, it has a sort of finned
heat dissipater on the driver housing. This makes me think they are not that
efficient.

The best low power pump I have found is designed for automotive auxillary
hot water systems, 12 volt magnetic drive with a life of 50,000 hours. They
are made from some sort of very tough plastic and easilly handle water over
100 degrees C up to 50 psi. - not suitable for mains pressure though.
http://www.daviescraig.com.au/main/display.asp?pid '



Cheers
Mike (NZ)



Posted by Loren Amelang on October 27, 2007, 9:25 pm
 On Sat, 27 Oct 2007 12:47:06 +1300, "Mike Scaife"


The SID driver has no moving parts, it is just electronics plus coils
of wire securely potted in black plastic. Any noise or increase in
noise is entirely a function of the impeller inside the brass and
stainless pump module, and how it fits on the stainless shaft.

I've seen shafts that were scored or damaged make excessive noise, and
become quieter when the shaft was smoothed and polished. I've seen
noise reduced by adjusting the thickness of the little plastic thrust
washer that holds the impeller in position. Sometimes a new impeller,
or swapping impellers with another pump, will fix a noise issue.

I don't mean to make it sound like there is a noise problem. If there
was a conventional mechanical drive motor coupled to the noisiest of
the pump modules I've seen, you'd never notice the sound of the
impeller. You notice it with a SID, because the drive is silent.

As for noise changes with temperature, the impeller is water
lubricated. Especially if you have glycol or additives in your fluid,
the fit issues between impeller and shaft can be hidden or aggravated
by temperature. The factory warns strongly against using pipe joint
compounds anywhere in your system, as they can cause havoc if they
migrate to the impeller bearing.

The SID is power efficient, but its radiative surface is much smaller
than an equivalently powered mechanical motor, plus it is more tightly
coupled to the hot fluid. The oldest SIDs I have were potted directly
into black metal housings. Then for awhile they had a loose-fitting
red plastic case that probably didn't transfer the heat out as well.
Which I assume led to adopting the finned metal case...  

Loren

Posted by Mike Scaife on October 28, 2007, 2:29 am
 
Brand new pump, very clean water, no pipe joint compounds, pump is very
quiet when cold to warm water, makes a loud rattle rumbling sounds when very
hot water in the system, have tried several pumps and they all do the same
thing, all installed as per manufactures spec's, seems sloppy manufacture.
Doesnt exactly inspire confidence as to how long they will last.

Mike



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