Nice description. One missing puzzle piece.
The program also calculates the coil entering air conditions, including outdoor air. This air condition, plus those specified by the user as supply conditions, along with the calculated peak zone air flow rate, are used to size the coil. Additionally, the DX coil uses the CapFT curve to correct the coil size for the off-design entering air condition (adjusts back to 80/67 entering air).
EnergyPlus uses a SummerDesignDay and WinterDesignDay or design period. It applies these outdoor environmental conditions to the building object. All schedules objects for other inputs such as internal loads, infiltration or equipment availability separately define themselves for the designday. The building behaves as it should and the energy required to keep each zone at its required temperature is calculated at each time step. The largest load found over all the time steps is then the peak load that must be satisfied.
Next the program looks at what supply air temperature and humidity was defined by the user. For that design air supply temperature and humidity, the required volume flowrate is calculated to match the peak load.
This flowrate and temperature humidity combination is used in the last step to size all the equipment and includes user over or undersizing factors.
So if you have multiple zones, you may control the central AHU via a master zone or Warmest Zone or, or, or...so many options. The program figures out the total peak volume flowrate required and the required supply temperature humidity.
If you are autosizing the dxcoil, EnergyPlus will figure out what to fill in the fields (such as rated capacity, rated CoP, rated SHR) so that a coil size results such as to meet the supply air conditions required at peak load whilst using a coil model that draws on normalized performance curves. So you end up with a more or less realistic coil that also behaves realistically over a whole range of conditions and not only at peak load times. Similar is true of water coils.
Problems with this procedure tend to occur when the user specifies conditions which cannot be met due to other constraints imposed. Example, a user specifies a design supply temperature that is colder than the design supply water temperature to a water coil.
On 1 Sep 2015 5:09 pm, "a.aelhefni@xxxxxxxxx [EnergyPlus_Support]" <EnergyPlus_Support@xxxxxxxxxxxxxxx> wrote:
hi guys ,
I'm designing a case where I need to size my cooling coil the following way :
Program compares OA peak conditions : 1- peak dry bulb and mean coincident wet bulb temperature
2- peak dew point and mean coincident dry bulb temp
3- peak wet bulb with mean coincident dry bulb temp
and select the case having highest enthalpy .
Therefore by knowing this enthalpy and the enthalpy required after coil , a coil size is selected .
Does energyplus work it that way ? anyone has a hint how the program sizes coils ?
-- Richard Raustad Florida Solar Energy Center 1679 Clearlake Road Cocoa, FL 32922 Ph: (321)638-1454 http://www.fsec.ucf.edu/en/ Program Director Electric Vehicle Transportation Center http://evtc.fsec.ucf.edu/
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