I tried to read the EnergyPlus documentation on page 12. I can't seem to understand what is the purpose of warmup convergence. I can't find any other sources for explanation probably because this is specific to this calculation engine.
The purpose is to establish history in the thermal mass of the building surfaces. All simulation engines use some method to initialize this thermal history, but it's not as visible in some tools.
From the Input Output Reference, Building object, Warmup Convergence: EnergyPlus“runs” the first day of the environment (starting with a set of hard-coded initial conditions: temperatures are initialized to 23C and zone humidity ratios are initialized to the outdoor humidity ratio) until the loads/temperature convergence tolerance values are satisfied (next two fields) or until it reaches “maximum number of warmup days”.
So, in a nutshell, everything starts at 23C, and the first simulation day is repeated until two successive days match within the criteria specified in the Building object.
So for the "history in the thermal mass", the final conditions of the thermal mass in the warm up will be used for the actual simulation instead of arbitrarily declaring its initial temperature etc?
That is correct.
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