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[EnergyPlus_Support] Re: Unitary DX for cooling - not sizing well



1 minute pulldown time is unrealistic, i aggree. As I understand it, this influences only the Air Volume Flow Calculation, right. Meaning the air volume flow rate capacities of the equipment will be too large.

What is a realistic pull down rate? 10 min? 1hr? As stated before, ASHRAE requires less than 300 hrs per year, for hours SP not met. I could run a parametric simulation testing different averaging intervals to get best results and set the Averaging Window this way. But no one else is doing this, so how do they size?

Also, I would have to decide on a fixed tolerance for the SP not met reporting, before the parametric study. James uses 0.5ºC from what I remember. The default is 0.2ºC (0.5ºF from DOE). Allowed by ASHRAE 55 is 1.1ºC (2ºF) peak to peak variation over a 0.25hr period. Minimum throttling range for low-temperature radiant systems is 0.5ºC. 

ASHRAE 90.1 2010 defines 
temperature control throttling range: 
as the number of degrees that the room temperature must change to go from no-heating to full heating or from no-cooling to full cooling.
unmet load hour: 
an hour in which one or more zones is outside of the thermostat setpoint plus or minus one half of the temperature control throttling range. Any hour with one or more zones with an unmet cooling load or unmet heating load is defined as an unmet load hour.




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