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Hello everyone,
I'm working on a system called geothermal heat pumps assisted by solar energy. I have a problem in the circuit related to the solar energy and production of hot water in which the variation of internal energy of the pipe (represented by type 31) is affecting the temperature of the fluid that will go through the solar collectors. So to solve this problem, l’m trying to remove the pipe from the solar part but when i start the simulation I got an error "Invalid floating point operation" you will find a screen shoot of the error appearing
thanks for your help
kind regards,
You say you're getting an invalid floating point operation error, but the screenshot shows a warning that the simulation did not converge at time = 1 hour.
Convergence problems are commonly caused by using too large a timestep and/or not having enough thermal capacitance (also called thermal mass or thermal storage) in a closed fluid loop. If your timestep is 1 hour, I would recommend reducing it to at least the TRNSYS default of 7.5 minutes or 0.125 hour; in most projects we use either a 5-minute or a 1-minute timestep. Taking the pipe out of your fluid loop will actually make convergence problems worse. If you're concerned about the pipe's influence on the model, you could always try making it a perfectly insulated pipe (set the loss coefficient to 0), placing the pipe after the solar collector, or changing the pipe's initial temperature.
Floating point errors are Fortran errors telling you one of the models in the simulation tried to complete some invalid mathematical operation, such as dividing by 0 or taking the log of a negative number. There was an invalid floating point bug in some solar models in TRNSYS 18.04.0001 that I believe was fixed in TRNSYS 18.05, so I would check your version of TRNSYS (click on the ? in the top menu in Simulation Studio -> About .. -> TRNSYS version is middle bottom of the window) and make sure you're running TRNSYS 18.05.0000 or later. If you're still getting a floating point error, you can either send your project and any files needed to run your project to your distributor for debugging, or you can use a tool like Visual Studio to step through the code and find the error yourself. See this post I wrote on the forum on floating point errors for more information.
ayoub nassa Topic starter
09/06/2023 8:31 am
@a_weiss Thank you for your response. It seems that changing the timestep did not resolve the issue I am facing. I am concerned about the change in internal energy within the pipe, specifically caused by the exchange of energy between the fluid and the pipe. This leads to a rise in the temperature of the fluid in the solar collectors during the night when there is no sunlight. I am now trying to identify the error by steping through the code
A_Weiss 09/06/2023 4:12 pm
@ayoub-nassa Why is there fluid flow in the collectors at night - do you have a pump and a pump controller in your system? If the issue is a temperature rise over the collectors at night, that sounds like an issue with the collector model. What version of TRNSYS are you running? Which solar collector model are you using?
Hello,
Apologies for the delayed response. I'm currently using TRNSYS 18.04.0001 and working with "Solar Collector; Quadratic Efficiency, 2nd Order Incidence Angle Modifiers", specifically "Type 1". In the actual system, the solar circuit pipes are 150 meters long. However, I attempted to reduce the length to 10 meters to observe the impact. Upon visualizing the temperature at the solar collector's outlet, I noticed that the progression is accurate, as depicted in the attached images (please refer to the separate image I will provide in a new response).
The pump is controlled by "Type 165", where the upper input "Th" represents the temperature at the collector's outlet, and the lower input "Tl" represents the temperature at the ground heat exchanger's outlet. The upper dead band is set at 6, and the lower dead band is set at 3. I have examined the control signal at the outlet of "Type 165" and noticed that it is not functioning correctly. For instance, when the controller is off and the difference between Th and Tl is still lower than the upper dead band of 6, the control signal should remain at 0. However, I observed the opposite behavior. This discrepancy might be the reason why the pump is operating during the night. I'm truly puzzled by this issue.
ayoub nassa Topic starter
12/06/2023 9:15 am
The image below is for the case in which the pipe of solar circuit are 150 m long
A_Weiss 12/06/2023 8:24 pm
@ayoub-nassa Would you please send your project and any files needed to run your project to weiss@tess-inc.com? It sounds like you have a good understanding of some fundamentals of setting up a solar hot water heating simulation in TRNSYS. Unfortunately I don't know why the differential controller isn't behaving as expected; it may be related to that convergence warning, but I'd need to see and run the project itself to learn more. In the meantime, I'd recommend installing the latest version of TRNSYS, version 18.05. There was a floating point problem with Type 1 that came up in version 18.04 and was resolved with version 18.05. Minor version updates like this are available to all license holders of the current major version of TRNSYS, all you have to do is follow the download instructions you or your institution got when they purchased TRNSYS. See Tim's reply on the forum post "Updating TRNSYS" for more information.
ayoub nassa Topic starter
16/06/2023 9:17 am
Hello,
If i update TRNSYS to version 18.05. the file that was created on the old version would it be compatible with new version?
Kind regards,
NASSA Ayoub
