Adjusting temperature and load convergence based on load scale

asked 2020-05-21 23:44:25 -0500

mehrdad gravatar image

updated 2020-05-24 01:02:28 -0500

I'm getting tons of warnings from a modified DOE prototype model (large office with 12 floors, idf, err). If you don't have time to look at the files, here is a summary:

1- Most of my warnings are caused by Air Loops not converging. To be specific I think the outdoor air heat exchanger is the main reason. There are some oscillations in iterations of air loops. Some of them are almost converged, mostly the zones with a multiplier of 1, and some have relatively big residuals, mostly MID zones with a multiplier of 10 (according to err file).

2- I also received two severe errors caused by reaching maximum days for warm-up (it can be solved as follows).

Warnings can be ignored but they increase the run time (happened 2.4 million times!). As far as I know, one general solution to both of the issue#1 and issue#2 is to increase temperature and load convergence tolerances or I could increase the warmup days and HVAC iterations (which is not favorable for me due to increased run time and uncertainties). Reducing the time step also is not favorable for the same reason. Please let me know if you have anything else in mind. I set the temperature tolerance to maximum but It didn't resolve a considerable amount of warnings.

Here is my question: Is there anything else that I can do for temperature tolerance? Moreover, the load of the MID floor Air Loops is ten times of other Air loops (due to multipliers). The maximum of 0.5 W load convergence tolerance is ridiculous for this load scale. It seems to me that these loops need some sort of large local load convergence tolerance according to this (HOW?):

* Warning ** SimHVAC: Maximum iterations (30) exceeded for all HVAC loops, at RUN PERIOD 1, 09/05 09:10 - 09:15
   **   ~~~   ** The solution for one or more of the Air Loop HVAC systems did not appear to converge
   **   ~~~   ** Air System Named = VAV_MID WITH REHEAT did not converge for mass flow rate
   **   ~~~   ** Check values should be zero. Most Recent values listed first.
   **   ~~~   ** Demand-to-Supply interface mass flow rate check value iteration history trace: 0.477959,0.708581,1.196787,6.106047E-002,0.111426,0.224436,0.542432,0.542429,0.542438,0.542407,
   **   ~~~   ** Supply-to-demand interface deck 1 mass flow rate check value iteration history trace: 0.000000,0.000000,0.000000,0.000000,0.000000,0.000000,0.000000,0.000000,0.000000,0.000000,
   **   ~~~   ** Air System Named = VAV_MID WITH REHEAT did not converge for temperature
   **   ~~~   ** Check values should be zero. Most Recent values listed first.
   **   ~~~   ** Demand-to-Supply interface temperature check value iteration history trace: 0.000000,0.000000,0.000000,0.000000,0.000000,0.000000,0.000000,0.000000,0.000000,0.000000,
   **   ~~~   ** Supply-to-demand interface deck 1 temperature check value iteration history trace: 0.154224,0.227111,0.389214,2.053414E-002,3.727859E-002,7.433808E-002,0.175640,0.175639,0.175642,0.175632,
   **   ~~~   ** Air System Named = VAV_MID WITH REHEAT ...
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Comments

By removing the economizers in the air loop I reached about 200 warnings which is satisfying. Still Supply-to-Demand interface trace shows bad results!

mehrdad gravatar imagemehrdad ( 2020-05-24 01:01:55 -0500 )edit