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Re: [EnergyPlus_Support] Re: energy transfer in zone low
System Cooling to the Zone =Â (Volumeflowrate_ zoneair * density_ zoneair * Cp_zoneair * T_zoneair - Volumeflowrate_ supplyair * density_ supplyair * Cp_ supplyair * T_supplyair)
Because Cp and density are very similar this can be rounded for quick checking to
= Volumeflowrate * density * Cp (Tzone - Tsupply) using density = 1.2 and Cp = 1 and Volumeflowrate = supply Volumeflowrate
These equations assume values for moist air, i.e. include both latent and sensible energy.
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For CoP you need to know the energy (usually electrical) input that fuels the machine that will change the temperature of the cooling medium from the return temperature from the coil to the supply temperature. The coil itself can't have a CoP. The energy exiting (or entering) the coil medium goes two places:
1) into the passing air and
2) into the condensate water.
The amount of energy that can be transfered is limited by the physics of the coil. This in turn will effect the coil return medium temperature.
The models in e+ can determine the split and the effectiveness of these physics using the "Bypass Factor" and "NTU" methods (at least by default). Again, there is no energy lost at the coil.
The electrical input required to cool the medium is modelled using the "CoP" or performance curves of the chilling device. For DX machines this includes the coil, but not the fan. However, the standard rating outputs include the fan heat in the calculation as this is the definition of the rating value. E+ still correctly adds fan heat to the supply air stream.
On 5 Jan 2016 6:45 pm, "
alyelhefni@xxxxxxxxx [EnergyPlus_Support]" <
EnergyPlus_Support@xxxxxxxxxxxxxxx> wrote:
Â
the problem arises when calculating COP for the system . It's too low .
So I calculated : (cooling energy of zone / cooling energy of coil ) and the this ratio came = 0.3
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Posted by: Jean Marais <jeannieboef@xxxxxxxxx>
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