Debugging an Evacuated Solar Tube Panel

mf16

Hi

I have an Evacuated Solar Tube Panel and am not get a temp on the roof above 50'C?

The pitch of the roof is 52'C and doing some research for Carrigaline,Cork this seems to be ideal - found a site somewhere that calculates the ideal pitch ...

The pipes are well lagged...

There is one AAV at the highest point - the pressure on the system is 2 bar - doesnt seem to be dropping... Maybe trapped air? Whats the best method to purge the system?

Have not tested the sensor probes as yet - need to get an Ohmmeter but cant see anything that really stands out to be the problem..

ANy other things to check...the evacuated tubes themselves seem to be okay - have a velux window in the attic and can check them within 6 feet.

Any other ideas?

Thanks

Mike2006

Sounds like a temp probe problem or else a controller problem.

Get some resistors from maplin and test it. The resistor of a known value will tell you right away if it is the controller or the probes which are at fault.

Do you have PT100 or PT1000 probes on your system?

Mike.

mf16

Probe I have has "NTC 10K B=3950 resistance value"

'C 0 10 20 .... 120
Ohms 33620 20174 12535 ... 407

ccsolar

mf16 wrote: »

Hi

I have an Evacuated Solar Tube Panel and am not get a temp on the roof above 50'C?

The pitch of the roof is 52'C and doing some research for Carrigaline,Cork this seems to be ideal - found a site somewhere that calculates the ideal pitch ...

The pipes are well lagged...

There is one AAV at the highest point - the pressure on the system is 2 bar - doesnt seem to be dropping... Maybe trapped air? Whats the best method to purge the system?

Have not tested the sensor probes as yet - need to get an Ohmmeter but cant see anything that really stands out to be the problem..

ANy other things to check...the evacuated tubes themselves seem to be okay - have a velux window in the attic and can check them within 6 feet.

Any other ideas?

Thanks

Hi
What temperature are you getting at your tank, T2 & T1 ??

mf16

Today

T1 - 27
T2 - 22

mf16

Measured the probes and they seem to be correct...

Controller seems to read a fixed resistance too..

Scratching my head...

mf16

I have PT1000 on T1

and "NTC 10K B=3950 resistance value" on T2

Temp today on T1 is 36'C(res ~1.1k) and T2 26'C

championc

How many tubes do you have and how big is your store ? It may be that your store is too big for the number of tubes.

The second possibility is the setting of the startup and cutoff temp of your pump. The pump should start to transfer heat to your store when the temperature is 8 deg C above the temp at the bottom of the store. The pump should stop when about 4 deg C above the bottom of your store. If the pump continues to run any longer than this, then it's possible that you will end up running cooler glycol through the coil thus cooling down the water in the store.

Watch your system to see that it's gaining heat during very sunny weather to prove that the system can do what it's capable of doing but then also watch to see if the bottom of the store temp ever decreases. It should only after an hour or two of no sunshine (through natural wastage)

I have a data logger on my setup and can see every bit of this happening. Anyone thinking of getting a system, I would strongly suggest getting a solar controller that can log the data - for the sake of another €100 or so.


C

mf16

I have 30 tubes and a 300L tank...
switch-on temperature difference is 10'c and switch off is 5'C (default setting) on workstation.

championc

The first thing to remember is that it gets harder and harder to increase temperature per degree, the higher the temperature is. In addition, you'll possibly (with research) find that you should have about 50 tubes for 300L and then it can be down to the efficiency of the tubes (some perform better that others depending on their type). Not not too well up on the different type types.

So really, have you had any run of maybe three consecutive days of glorious blue skies - while at the same time not using a drop of the hot water ? This would be one way to see if the system can do the job you hope it can do.

The only other thing I wonder about is as to whether the pitch is too great. In Dublin, mine is only between 20 and 25 deg but I'm well chuffed with the results that I get from my system.

I'm only a system owner and picked up all sorts of info in my research before buying.


C

soldsold

championc wrote: »

I have a data logger on my setup and can see every bit of this happening. Anyone thinking of getting a system, I would strongly suggest getting a solar controller that can log the data - for the sake of another €100 or so.
C

Hi championc,

Im interested in using a data logger on my system, can you elaborate on what it is and what the advantages are? A model/ supplier recommendation would be great too, by PM if needed.

Thanks!

Steve

championc

Data logging would have been on option on the Solar Controller. Most manufacturers will have a version of their controller which will allow for data to be written to an SD Card or something similar. I don't believe it's something you can "add" in later - you would need to replace the Controller.

Mine logs the Roof, Bottom of Store and Top of Store Temps and when the pump is runing. So I can look back at any day and see what my system did and so, it's very easy to see what's going on or compare a sunny day this year compared to last, or whatever


C

freddyuk

mf16 wrote: »

Hi

I have an Evacuated Solar Tube Panel and am not get a temp on the roof above 50'C?

The pitch of the roof is 52'C and doing some research for Carrigaline,Cork this seems to be ideal - found a site somewhere that calculates the ideal pitch ...

The pipes are well lagged...

There is one AAV at the highest point - the pressure on the system is 2 bar - doesnt seem to be dropping... Maybe trapped air? Whats the best method to purge the system?

Have not tested the sensor probes as yet - need to get an Ohmmeter but cant see anything that really stands out to be the problem..

ANy other things to check...the evacuated tubes themselves seem to be okay - have a velux window in the attic and can check them within 6 feet.

Any other ideas?

Thanks

The AAV is there to commission the system and it is then turned off (closed) it does not maintain the airfree function. If it is turned off then you can release any trapped air by opening it (not when it is hot).

If it was left to operate as a normal AAV then each time the system stagnated it would release the steam. There should be an isolating valve below the AAV if it was installed correctly.

quentingargan

mf16 wrote: »

Hi

I have an Evacuated Solar Tube Panel and am not get a temp on the roof above 50'C?

The pitch of the roof is 52'C and doing some research for Carrigaline,Cork this seems to be ideal - found a site somewhere that calculates the ideal pitch ...

The pipes are well lagged...

There is one AAV at the highest point - the pressure on the system is 2 bar - doesnt seem to be dropping... Maybe trapped air? Whats the best method to purge the system?

Have not tested the sensor probes as yet - need to get an Ohmmeter but cant see anything that really stands out to be the problem..

ANy other things to check...the evacuated tubes themselves seem to be okay - have a velux window in the attic and can check them within 6 feet.

Any other ideas?

Thanks

If you had trapped air in the system, I would expect the panel temperature to be a lot higher than 50. I have yet to see a temperature probe that reads the wrong temperature - it usually just doesn't read at all, but even if it was wrong, if the controller sees a panel at 50 and a cylinder in the 20s, it will switch on the pump and transfer the heat from one to the other.

I fear that the problem here is within the panel itself.

mf16

I have a workstation like the following on the system(see the attached doc)

there is a valve on the left to remove air from the system - I did that (there was a small bit of air) and will see if that improves things. But probably would have to go up on the roof to open the AAV to remove all the air wouldnt I?