Solar Hot Water

Alan1001

Hi
I’ve recently noticed that the solar tubes collector temperature seems to be lower then usual.Its 22degrees outside and the roof collectors are showing a temperature of 78degrees.Is this correct?
I seem to remember seeing the roof temperature above 100 degrees when the outside temp is in around 20degrees.
Do I have a faulty roof stat?
Thanks

championc

Surely if the roof temperature is higher than the water in your tank, the pump should kick in and start transferring that heat into your tank.

So if it previously was 100 and even now at 78, to me, there's something seriously wrong with your setup.

So my tubes are 10 deg higher than the temperature in the tank, and it's constantly around that for transferring the heat into the tank

My pump turn on point is 8k and the turn off point is 4k. Do that turns on the pump 8 deg above the tank temp and turns it off when only 4 deg above tank temp

Alan1001

Sorry meant to say the pump is running and I am getting heat into the solar cylinder..top sensor is at 70 and bottom is at 60 and roof collector sensor is at 150 degrees..would 150 degrees be normal for a day like today 22degrees?

John.G

With a cylinder temp of 70C its more than likely that the solar protection system has shut down the circ pump probably when the cylinder temp reached 70C, when this happens then the collector temperature will very rapidly rise to that 150C or even higher depending on radiation levels, the pump probably will not restart until the collector temp falls to perhaps 90C or so depending on the settings.
I don't think that the pump would be actually running though with those temperatures otherwise the cylinder temperature would be much higher if no protection is enabled.
Also check your system pressure, should be ~ 2.5/3 bar.

championc

I wonder if your pump is running too slowly - it sounds dangerous that the temperature is that high. Like I said, the roof array should only be at most 10 or 11 degrees above the tank sensor.

The only circumstances where your roof array should "boil" should be when the array controller goes into lockout, which in fairness could be when the water in the store hits 70 deg, or thereabouts.

I would suggest that you look at the setting on the controller and see how it is configured to operate.

John.G

Cylinder temp could easily have hit 70c today, mine (flat plates) hit 77C, Tmax is 85C, which F.plates will rarely achieve even with no hot water usage, a TMV controls the cylinder outlet temp to 60C.