IES-VE User Forum

In Apache I was getting a "Surface temperature instability" error in the proposed model, which suggested reducing the timestep to remedy. I did, and the error was fixed. However, when running the Room Load Calculations for the baseline model(s) in the PRM navigator the error reappeared.

If the user was given the option to adjust the settings in the ASHRAE Loads window for the baseline as is the case for the proposed (and from Apache), this error could be corrected. This indicates that the timestep for the baseline is fixed in the PRM while being adjustable for the proposed likely affecting the results.

this error is due to the construction materials being used in proposed/baseline are "light weight" which means there is a thermal transfer happening in a shorter period than your time step, which creates the instability. This is more like a limitation in the software rather than a bug i would say.