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RE: [EnergyPlus_Support] How autosizing works

Hi, Murad
I think there is a section (page) 480 of the  IO manual which list the variable that can be autosized.
There are basically two types of autosizing.  One is on the overall size, which is determined by the zone and equipment sizing simulation and used in the simulation.
The other is for convenience in data entry.  Specify the minimum and maximum range, and the simulation program will use a value in the range, and flag a warning when the range is exceeded.
In the Dx coil system, I believe the fan air flow volume is sized to meet the maximum load demand with the stated minimum coil temperature, in the sizing object.  The compressor power, etc. are calculated from the actual energy of cooling supplied by the coil, at the constant fan speed.  (VAV may be different.)
After the simulation, the require air volume and cooling capacity is known.  If you increase the capacity to a higher value, the PLR will change.  If you lower the capacity, the thermostat set point will not be met.
I do not know whether you can enter the cfm/ton value directly.
With a fan on/off system, the zone demand is met by providing the full capacity for a time period and turn off.
The compress is turn off, if the fan is in continuously on mode.
cfm/ton is too general to apply to a working system for simulation, but is sufficient for choosing a finished product.  A low cfm usually has a lower fan noise.

 Dr. Li  


To: EnergyPlus_Support@xxxxxxxxxxxxxxx
From: zabdulmurad@xxxxxxxxx
Date: Sat, 17 Jul 2010 08:18:29 +0000
Subject: [EnergyPlus_Support] How autosizing works

I am trying to do a comparison between user defined parameters and autosized parameters for my HVAC DX system. I am using HVAC template where I set the cooling capacity, heating capacity, and the rated sensible heat factor as autosize. At another simulation run, I manually inserted values to the said parameters. How do I know that my result is incorrect if, for example, the cfm/ton manually put is out of range? The engineering reference does not seem to explain fully the autosizing of the system. Please help.

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