Negative humidity in DOE reference model

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In a nutshell, for this model, the thermostat cooling setpoint for Front_Entry ZN is always 100C, an attempt to communicate no cooling for this zone. This results in the psychrometric routines attempting to find the humidity ratio at a dewpoint of 100C which stretches the boundaries of the function, resulting in the negative humidity ratio. Change those 100s to 99 and the error goes away.

If you want more details . . .

After all of the sizing periods are simulated for sizing, there are some final zone accounting steps to set the zone conditions at the heating and cooling peak. If the zone has no cooling load, the zone temp at cooling peak is set to the minimum value in the thermostat profile . . . blah blah blah . . . and because it's happening after the sizing periods and before the next simulations, that's why the timestamp says <last design="" day="" name=""> at Simulation time=07/21 24:00 - 24:10 (which even in the EnergyPlus world is not a real timestep). A new issue #6787 has been posted to revisit the error check for function PsyWFnTdpPb (return humidity ratio as a function of dry-bulb and pressure) when the saturation pressure comes back greater than the barometric pressure (which is the case here).