Richard Dif Cont 3/31/10 Test

This was not as conclusive as hoped, mainly due to the poor placement of the collector temperature logger.

Will try again with better placement when the weather cooperates.

But, still, some interesting stuff.

I observed one shutdown in the morning and one in the afternoon (3:47pm) when the controller appeared to shutdown with a difference in sensor voltages well above the expected 22 (or so) mv.  The afternoon one appeared to be a shutdown at 69 mv sensor voltage difference.


On the other hand, I observed one shutdown in the morning (the 10:50am one that I caused by shading the collector) and one the final one in the afternoon (4:10pm) that were right on (23.6 mv and 20 mv respectively).

The two startups I observed were also right on at about 124mv.

I was hoping the plots would clarify this and show whether or not the shutdowns I think I saw with much higher than 22mv differences were real or not, but with the bad sensor placement on the collector temp logger you can't really tell.


One thing you can say is that the controller never kept the pump running to long, and that the return temp was always higher than the supply temp -- all good.


Can you think of anything sort of intermittent "thing" that would cause the controller to shut the pump down once in a while at a higher than expected differential?

But, I guess I'd not spend too much time sweating this until I can get a better plot with good logged collector temps.

But, I would swear I was looking right at the volt meter when the 69 mv afternoon shutdown happened.




The collector logger sensor is very poorly placed -- I'll try to fix that for next test and get it close to the dif cont collector sensor.


The pump motor on logger did not work, but, the supply and return temps both take a very steep dive when then pump turns off, and climb back up steeply when the pump turns on -- so, its easy to see the pump on/off events.


The flow rate through the 95 sf of collector is 5.4 gpm (0.057 gpm/sf) -- a bit on the high side, but well within the Heliodyne recommendations.



The Full Day:


Blue -- water returning from collector (sensor on outside of copper pipe with insulation over it) F

Red  -- water returning from collector ("

Light purple -- top of tank temp F

Dark purple -- bottom of tank temp F

Black -- Collector temp F


So, if the collector is only collecting heat if the Red line is above the Blue line (return is hotter than supply)



There are showers at about 9am and 2pm -- these account for the tank temp drops at these times.


Some blow ups of startup and shutdown events below.







The shutoff at 10:50 am was one I was measuring the sensor differential voltage.  It was 23.6 mv at shutoff, which seems perfect.

On restart at 10:59 am it was 124 mv, which again seems perfect.


The return water was only about 0.4F hotter than supply water at shutdown.

This is lower than some of the other shutdowns, but may have to do with the collector being shaded by the panels I put in front of it.

You can see the dramatic rise in collector temp right after the shutdown when I removed the shading panels. 






this looks like a shutdown due to a cloud:

Pump turned off at about 3:06pm.

Looks like a cloud came over.

With the collector sensor so poorly located, its hard to tell if the dif cont turned off at just the right point, but it looks OK to me.  The return temp was 0.94 F above the supply temp at turn off -- that seems good.


Pump turned back on when collector temp came back up.

After turnon, return temp is about 1.5 F above supply temp.



Shutdown for the Day





The shutdown at 3:47pm was the one where I thought I measured a differential voltage between the two dif controller sensors for 69 mv at shutdown.


At shutdown, the return is 1.3F hotter than supply, so based on the one just above, there is a bit more difference, but not a lot.

With the bad collector sensor position, its hard to get much from the plot to either confirm or not the early shutdown.


Its kind of odd how the collector temp trends down after the 3:47pm shutdown, but the pump starts up again.

At the 3:58 pm startup, the sensor voltage difference was 122.7 mv, which seems just right.

The Caleffi temps were:  145.5F collector, and 132.2 F tank -- again, just about right for the 12 F dif I had set.


At turn off at 4:15pm, the final supply to return temp diff is about 0.8F, which seems fine, and agrees pretty well with plot just above.


Guess I'm inclined to discount the collector temp logger curve altogether -- its does not seem to agree with anything -- will try to fix.








A Shower:


The roughly 1:50pm event is a shower.





Gary March 31, 2010