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Solar collector - Temperature out of range

Hello everyone, I am modelling a DHW system in which water is pre warmed in a tank thanks to a solar collector and then reaches the nominal temperature within an air-to-water heat pump. When the simulation ends I get this warning:

* Warning * GetSpecificHeatGlycol: Temperature is out of range (too high) for fluid [CIRCUITO SOLARE GLYCOL CONCENTRATION] specific heat * * ~~~ ** ..Called From:UpdateSolarCollector,Temperature=[126.21], supplied data range=[-20.00,125.00]

which is a recurring error. I have gone through all the questions I have found on this topic but never could find a solution to fix this issue. I am working with Design Builder v4.7, using EnergyPlus 8.4. Any suggestion using either of the software would be good. Even a solution from Open Studio could help.

Edit: if I analyse the outlet temperature from the solar collectors, I never even reach 80°C.

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In DesignBuilder v4.7, you can edit the fluid type while editing the plant loop. It looks like you have selected a glycol option instead of water, based on your plant loop's name CIRCUITO SOLARE GLYCOL CONCENTRATION. While editing the plant loop, you can also define a glycol concentration. This sets the range of temperatures that EnergyPlus should use to calculate various properties for your glycol loop each timestep. One of those is specific heat, as indicated at the beginning of your warning (GetSpecificHeatGlycol is the part of the EnergyPlus source code performing this property calculation each timestep). From your fluid type and glycol concentration settings in DesignBuilder, the range of temperatures that EnergyPlus expects is -20 $^\circ$C to 125 $^\circ$C, and this warning indicates that there was a timestep where the glycol temperature exceeded 125 $^\circ$C and reached 126.21 $^\circ$C.

This warning message is from the first timestep where this issue occurred. Near the bottom of the error file is a recurring errors list that will tell you:

• how many other timesteps had this issue
• what environments (warmup, sizing, weather file simulation) had this issue
• what range of values occurred for this issue

If the range of values is only a little above 125 $^\circ$C, then you may be able to ignore these warnings as that is not far past the expected glycol maximum temperature. If the range does exceed something drastic (say, 150 $^\circ$C) then you will likely need to address this issue of overheating in the glycol loop. This can be done in lots of ways (reduce collector area, adjust availability and other plant loop controls, etc.).

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Hello Aaron, thank you for your answer. I already have given a look to the two previous posts you linked, but I couldn't find a solution. The warning happens around 19000 times, all during the simulation and the temperature goes up to 187°C. Among the solutions I tried without success there are:

• Changing the DHW flow
• Changing the glycol flow and concentration
• Decreasing the collector surface
• Running the pump continuously
• Deleting the bypass
• Trying to use a template for the collector performance
• Changing the collector availability

Do you have any additional suggestions?

( 2021-01-12 02:55:42 -0600 )edit

I found out there was a problem with the efficiency equation and the incidence angle modifiers. For the former, apparently the collectors perform too well, while for the latter I had made a mistake. Thank you for your help.

( 2021-01-12 09:35:14 -0600 )edit

@DavideLiviero if it's a problem with the efficiency equation and incidence angle modifiers in the EnergyPlus source code, you should see if this has already been reported as an issue for the development team to fix. If not, you should make a new issue.

( 2021-01-12 12:01:41 -0600 )edit