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Do I have a problem with my solar system?

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  • 23-07-2011 5:09pm
    #1
    dfbemt
    Registered Users Posts: 1,398 ✭✭✭


    My system installed 2 years ago - evac tube for hot water, new cylinder, etc.

    All was working fine then stopped this summer. On inspection found that it had been plumbed incorrectly. Was giving me hot water for the 2 years but was working against itself and eventually gave up the ghost.

    Company came out and replumbed, renewed glycol and set up system again. I have been closely monitoring and have 2 questions

    1. Today was the 1st decent day and my panel temp was 140. Can this be correct? No hot water used for the last 4 days and I noticed that the return to the roof from the cylinder was at 70.

    2. With the repair I rarely notice the pump running now. Certainly there is no noise from it. We used to hear it working in the evenings but nothing now. As I said, there was a problem with the initial install so is it the case that the pump is now working properly?

    Thanks for replies.


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    #2
    homer911
    Registered Users Posts: 5,113 ✭✭✭homer911


    Your sensors dont sound correct - theres no way it should be 140C at the panel - whats your system configuration - orientation, number of tubes, size of tank?


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    #3
    ccsolar
    Registered Users Posts: 423 ✭✭ccsolar


    Hi dfbemt

    Your solar system sounds to be working ok going by what you have told us.
    The panels on the roof will reach over 200 degrees if your tank temperature has maxed out.
    The tank temperature is normally set at between 60-80 degrees, when this temperature is reached the solar system will stop working but the solar panels on the roof cannot shut down and the temperature at T1 will continue to rise until it reaches a stagnation temperature of around 215 degrees.
    In order to prevent this you would need to install a heat dump with your solar system.
    The next time your panels are +100 degrees just check the tank temp and and let us know.

    Cc


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    #4
    bob5666
    Registered Users Posts: 202 ✭✭bob5666


    homer911 wrote: »
    Your sensors dont sound correct - theres no way it should be 140C at the panel - whats your system configuration - orientation, number of tubes, size of tank?

    yes can get to that temp on the roof with tubes it happens when the cylinders at temp say 70 c and pump stop running because there is no need to bring it down of the roof and the panel heats up on the roof with the sun and has no way to cool down


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    #5
    championc
    Registered Users Posts: 6,069 ✭✭✭championc


    140 deg C sounds correct if the temperature in the tubes is going nowhere. You have mentioned the temperature of the return from the cylinder to the roof but you have not confirmed the temperature of the water in the cylinder store itself.

    It sounds to me like your pump just is not running at all and that heat is being trapped in the tubes and on the general roof assembley. It sounds like since the water is essentially stagnant in the pipes, then heat is just travelling via gravity down possibly BOTH the flow and return pipes.

    With my system, the pump is running fairly soon once it's hit by direct sunshine. It's in my attic and I can (strain to) hear it whirling away from the landing.

    Can I suggest something. Get a length of electrical cable and stick a plug on it. It should be possible to connect the pump to the mains and hear how it runs.


    C


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    #6
    quentingargan
    Registered Users Posts: 1,627 ✭✭✭quentingargan


    championc wrote: »
    Can I suggest something. Get a length of electrical cable and stick a plug on it. It should be possible to connect the pump to the mains and hear how it runs.
    C

    Agree with everything else in this post, but just if you are doing this, do it at a time when the collector temperature is less than 100C. Don't do it when the panel is at 140....

    I don't know what the installer meant by "working against itself". I assume there was an air lock?

    As per Championc, it woudl be useful to know the cylinder temperatures. If there is no heat dump, then when the cylinder gets to its max temperature, the pump will shut down and the panel will rise to 140C.


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    #7
    dfbemt
    Registered Users Posts: 1,398 ✭✭✭dfbemt


    Thanks to all for replies. An update as of today, a hot sunny day

    - Temp on roof is reading 68° as per digital readout
    - Temp in cylinder is currently 61° as per digital readout

    I think the high temp was caused because the hot water had not been used in 4 days. Thinking about it now and I would start to believe that this was the cause of the 140° reading. However for the experts this may not be the case.

    Not sure what is meant re the electrical cable and the mains. The pump is plugged in and has power. I really don't hear it though, not like I used to hear it but maybe that's because the system was installed incorrectly in the 1st place.

    Re the original installation and the system working againt itself, the pipework got mixed up somewhere along the way !! The flow from the panels was connected to the cylinder outlet and the return to the roof was connected to the cylinder inlet. The coil was being heated in the wrong location.

    Interesting point made by championc re the pump not working and gravity at work. Current dial readings from the flow is 70° and the return is 62°. Are these reasonable based on the roof and cylinder temps above or should they be different if the pump was working?


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    #8
    quentingargan
    Registered Users Posts: 1,627 ✭✭✭quentingargan


    Your system is fine. There is a tiny anomaly in that the flow into the cylinder is hotter than the panel, but that might just be a moment in time.

    If you don't use the hot water (e.g. while on holidays) your panel will regularly go into what is called stagnation. It will heat to 140 degrees or more in that situation. I personally prefer to see some strategy to prevent this, but if it isn't there, I would just be aware that you need to change your glycol more often. Since you have tubes, you can perhaps use the anti-freeze function of your controller as added frost protection.


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    #9
    championc
    Registered Users Posts: 6,069 ✭✭✭championc


    dfbemt wrote: »
    Not sure what is meant re the electrical cable and the mains. The pump is plugged in and has power. I really don't hear it though, not like I used to hear it but maybe that's because the system was installed incorrectly in the 1st place.

    With cylinder temp at 61 deg C then there's nothing wrong - everything seems fine.
    dfbemt wrote: »
    Re the original installation and the system working againt itself, the pipework got mixed up somewhere along the way !! The flow from the panels was connected to the cylinder outlet and the return to the roof was connected to the cylinder inlet. The coil was being heated in the wrong location.

    While I'm no expert, I wouldn't have thought that having the flow and returns of a coil mixed up would have made a huge difference.
    dfbemt wrote: »
    Interesting point made by championc re the pump not working and gravity at work. Current dial readings from the flow is 70° and the return is 62°. Are these reasonable based on the roof and cylinder temps above or should they be different if the pump was working?

    What this seems to imply is that your coil is taking 8 deg C out of the water - transferring this heat into your cylinder so this seems fine too. An expert will know if this is too much or too little. the pump speed would determine the rate of heat transfer (like a radiator into a room)
    dfbemt wrote: »
    I think the high temp was caused because the hot water had not been used in 4 days. Thinking about it now and I would start to believe that this was the cause of the 140° reading. However for the experts this may not be the case.

    Check your system for the cutoff temperature. It may well be set for 65 deg C and so, without a heat dump, if this point is reached, then the pump will stop sending heat to the store and the roof temp will continue to rise and rise until the sunshine stops. I've no dump but my cutoff is set for 90 deg C.


    C


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