How to pinpoint what causes "Plant Temperature Too Hot During Warmup" Error?

asked 2025-06-05 13:37:03 -0500

I have a vertical ground loop geothermal system, with water to air and water to water heat pumps. I had a successful model a few weeks ago, but when I change any parameter (construction, load), then the model fails with:

* Fatal * CheckForRunawayPlantTemps: Simulation terminated because of run away plant temperatures, too hot

When replacing the geothermal system with a district heating/cooling plant, the model runs successfully. I've tried deleting the DOAS units and Water to Water heat pumps, but it still runs into the same error.

I am wondering if there is a bug within the Water to Air heat pump coils? Is there a way to pinpoint the diagnosis and figure out a solution?

I attached the .osm and .err file here: https://drive.google.com/drive/folder...

answered 2025-06-05 15:12:52 -0500

Greg Estep
939 ●31 ●6

We usually design geothermal system with a geothermal loop and a heat pump loop (primary, secondary pumping scheme). When I get runaway plant temps it is usually on the heat pump loop and usually has to do with low flow issues. Typically the water to water heat pumps request design flow at all times, so ensure that the heat pump loop is accounting for the correct flow rate from that object. Also, do you have the zone WAHP coil water flow mode set to 1-Cycling?
If so, I would recommend the following:

set the minimum flow rate (at the pump) to 10-20% of design).
at the zWAHP, change the coil water flow mode to 3-Constant on demand.
increase your loop min/max range to 0C - 40C

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I appreciate your suggestions! I tried setting the minimum flow rate to 20%, changing the coil water flow to Constant On Demand, and increasing the thresholds of my min/max geo loop. Still running into the same issues. The plant loop demand is absurdly high, and the temperatures are getting well above my threshold. I am not sure what the problem is as of this moment.

Jsorenson77 ( 2025-06-05 20:12:27 -0500 )edit

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