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Plant loop temperatures are getting far too hot

asked Mar 3

jferamo89's avatar

updated Mar 3

Hi everyone,

I'm Julio, and I'm running an energy simulation for a production plant with high cooling loads throughout most of the year. The system includes air-to-water heat pumps for both heating and cooling connected to cooling and heating coils in the AHU for space heating and cooling. The design temperatures for the cooling coils are 7/12C and 40/45C for the heating coils.

When I run the heating and cooling design week simulations, everything works fine. However, when I run the full-year simulation, I encounter a severe error that prevents the simulation from completing "Plant temperatures are getting far too hot". I've been stuck on this issue for a few days now and haven’t been able to figure out the cause or how to resolve it.

I’m not very experienced with advanced energy modeling, so troubleshooting this error has been quite challenging. I’d really appreciate any insights or suggestions from those familiar with similar issues.

Thanks in advance for any help.C:\fakepath\Severe error.JPG C:\fakepath\Heating and cooling heat pumps.JPG C:\fakepath\Plant loop temperatures.JPG C:\fakepath\Fluid to fluid hx.JPG C:\fakepath\Set point manager outdoor control.JPG

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Hello, According to your error message, the problem is in your "HW secondary loop". looking at your HVAC schematic, I see you are using design builder, but I can't quite tell which loop this is. Please specify which loop is getting the error and provide the schematic and input dialogs for that loop.

Also, I don't see any air-to-water heat pumps. I see W2W HPs and air cooled chillers and a fluid cooler.

Greg Estep's avatar Greg Estep  ( Mar 3 )

Hi Greg, Yes, the secondary loop is the one from the HX to the AHU heating Coils. Design Builder Version 6 cannot model ASHP, this is the closest I could think of. I share the screenshot of the settings for the secondary loop in Google drive. https://drive.google.com/file/d/1TiMk...https://drive.google.com/file/d/1G6at...

Regards, Julio

jferamo89's avatar jferamo89  ( Mar 3 )

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answered Mar 5

Greg Estep's avatar

updated Mar 5

Hi Julio, why don't you download the latest version of design builder? This way you can model ASHPs. https://designbuilder.co.uk/download/...

regarding your error message: It would be helpful to see the HW secondary loop schematic. Your HVAC system is sharing energy on the condenser loop between the chilled water and hot water loops. Each of these loops serve chilled water and hot water coils in AHUs, correct? Why are you connecting the HW and CHW loops to heat exchangers? They should be able to connect directly to the AHU HW and CHW coils. I would remove the HW secondary loop and make direct connections. If that doesn't work, provide some more images of the HW secondary loop and I can help further.

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Hi Greg, I have two loops in the actual design:

-Primary: Supply to the equipment (chillers)

-Secondary: Pumping to supply the consumers (AHUs)

I found this was the most accurate way to represent this system. Do you know if this can be defined differently?

jferamo89's avatar jferamo89  ( Mar 5 )
1

DB allows for primary/secondary chilled water, but not hot water. So, you are correct in using a Fluid HX. The fluid HX should be set to type = ideal, and control type = uncontrolled on. the error message suggests that pump heat is building up and that there is a cooling demand on the loop. I have had success by setting the pump minimum flow rate to about 10% of design.

Greg Estep's avatar Greg Estep  ( Mar 5 )

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Asked: Mar 3

Seen: 112 times

Last updated: Mar 04