Sizing a heat dump for a solar system Forum

Hi All,

Just a few notes below on how to size a heat dump.

Assuming the worst case scenario for a heat dump as such:

1. The householder is going away for two weeks in summer and typically the sun begins to shine the minute they put their foot outside the front door to leave.  A hot summer' day in Ireland can produce insolation levels of 1000W/m2 so we must measure the heat output of the array under these solar conditions.

2. Assume the solar panel heats the cylinder to a maximum temperature of 70 degrees (this is determined by the max temp programmed into the controller) so the mean temperature of the fluid in the solar panel is about 70 – 80 degrees and the ambient temperature is in the high 20s to 30 degrees Celsius (it's a hot summer's day..).  Subtract the ambient temperature from the mean temp of the panel and you get about 50 degrees of a differential.

3. Check the solar panel 's power out put under these conditions,  these are available on the EN 12975 test reports.  For the Ecologics 20 tube panel the figure is 823 Watts, for the 30 tube panel the figure is 1.5 times this, for the 40 tube panel this is double this and so on..

4. So the maximum amount of power that can be produced by a 20 tube solar panel under these conditions is 823 watts, so if you have a 20 tube panel installed this is the energy that needs to be dissipated by the Heat Dump.

5.  Source a radiator that can safely dissipate the required amount of energy and install it in a place where it won't get covered and where there is reasonable air flow to allow the heat escape.  Sometimes the hotpress is used but you must ensure that the radiator doesn't get covered with last week's washing!

6. Install a three port motorised divert valve on the flow of the solar circuit which will divert to the radiator on command from the pre-programmed controller.

Hope this helps!

Simon.