Experiment with delta T Forum

Hi All,

Just a quick note on a little experiment I did on our demonstration solar system here in Ecologics.  From some messing with TSol solar modelling software it seemed to show that reducing the delta T ( the difference in temperature between the solar panel and solar cylinder) settings on the controller would increase efficiency a little bit so I tried it here over the last month or so.

The default delta T setting (DTO and DTF on a Resol solar controller) is often 6 degrees K and 4 degrees K.  This means that the solar controller will switch the pump on when the solar panel is 6 degrees hotter than the lower sensor in the hot water cylinder and switch it off when the solar panel temperature has dropped to 4 degrees above the cylinder.

I changed this to 4 degrees and 2 degrees and left it to see the difference.  What I noticed was the heat that was available in the solar panel transferred to the cylinder quite quickly so I was initially encouraged by this however the energy readings I was getting were poorer over the 30 day period than the previous month.  The average solar energy gathered per day was 3 kWh and this dropped to about 2.5 Kwh.  There are a number of things that might have caused this other than the delta T settings but I have switched the settings back and seem to be getting back to a better heat yield from the solar panel.

heinbloed said:

Did the delta-T experiment deliver any results?

Hi Heinbloed,

I didn't bother in the end as I'm trying to come up with a complete set of annual figures that might realistically apply to an average operating system which runs on default settings ( 6 degrees on and 4 degrees off).  This is so we can have a better idea of how these panels really perform in an average Irish situation.  Messing around with the delta T in an attempt to improve performance could distort this figure too much and give misleading results.  Maybe 'll look at it again after March when I have a full set of yearly results.