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[EnergyPlus_Support] Re: WindAC output
I can help answer some of your specific questions regarding WindowAC.
See responses inserted below:
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "Alexander Beisteiner"
<alexander.beisteiner@f...> wrote:
> Dear E+ User,
>
> Looking at the WindAC example, I would like to discuss some output
> variables:
>
> RESISTIVE ZONE:Zone/Sys Sensible Cooling Rate[W]
> This version of E+ does not include an output variable for the zone
> total cooling rate. Will future releases provide it?
>
> ZONE1WINDAC:Window AC Sensible Zone Cooling Rate[W]
> ZONE1WINDACDXCOIL:DX Coil Total Cooling Rate[W]
> While the cooling output for a zone represents the zone load for
that
> time step, I assume that the cooling output for a component refers
to
> the component's capacity?
> In comparison, the output total cooling rate for the coil is always
> higher than for the AC unit. Does this come from the fan motor heat
that
> is added to the air stream that has to be compensated by the cooling
> coil- and as a result cooling capacity for the whole AC unit is
lower?
As explained in the IO Reference Manual, the cooling rates and
cooling
energy for the window air conditioner are determined from the outlet
air conditions from the air conditioner and the zone conditions.
These
output variables represent the cooling capacity delivered to the zone
to meet the zone load. The air conditioner cooling coil will
frequently need to remove much more energy than just the capacity
that
is delivered to the zone to meet the zone load (i.e., fan heat plus
the outdoor ventilation air being introduced through the window air
conditioner.
>
> I found that there is hardly any difference in the coil total
cooling
> rate (maximum 0.5%) comparing a blow through and draw through
system.
The total capacity of the dx cooling coil is a function of outdoor
air dry-bulb temperature and inlet air wet-bulb temperature. The
amount of change you see will depend on how much fan heat you are
modeling. See reference manual for object
Coil:DX:CoolingBypassFactorEmpirical.
> Here, I would like to focus on the fan motor heat added the air
stream:
> if the fan is before the coil, its cooling output should be higher
than
> in the case of the fan being behind the coil. Or does the
calculation
> algorithm already account for the motor heat regardless of the
sequence.
The window air conditioner model applies the fan heat to the air
stream where specified (blow through --> fan heat added upstream of
the cooling coil, drawthrough --> fan heat added downstream of the
cooling coil).
> Anyway, this example- WindAC- specifies that 100% of the motor heat
is
> given to the air stream: how can this energy input be checked?
> Looking at the fan input and output temperature, there is hardly any
> increase (maximum 0.2 K) by the fan. In reality fans cause a
temperature
> increase of 1 to 2 K.
Fan heat in windowAC (ductless) systems is usually pretty low (as
opposed to fully ducted air distribution systems). Simply change the
fan and motor efficiencies in the fan object to model whatever
temperature rise you feel is appropriate for your simulation.
>
> Setting the Rated Total Cooling Capacity of the cooling coil 1000 W
(all
> coils in this file) and changing the Rated Air Volume Flow Rate for
all
> components to 0.055 m³/s, output cooling rates for zones, coils
and
AC
> units are beyond the specified 1000 W limit? Is there a certain
limit
> when reducing a coil´s rated total capacity?
For the DX coil object, you specify the rated capacity at certain
conditions. This does not mean that the rated capacity is the
maximum
value that the model will simulate! Air conditioners frequently
operate a conditions where the delivered capacity is higher than the
rated capacity. See the IO reference and Engineering manuals for the
object Coil:DX:CoolingBypassFactorEmpirical for full details on the
model.
>
> Has anybody had similar experience? I would appreciate your
comments
and
> help.
>
> Regards
> Alexander
>
>
> _______________________________________
> DI (FH) Alexander Beisteiner
> Wissenschaftlicher Mitarbeiter
>
> Forschungs- und Technologietransfer Pinkafeld GmbH
> Steinamangerstraße 21
> A - 7423 Pinkafeld
> Tel.: +43-3357-45370 DW 1324
> Fax.: +433357-45370 DW 1010
>
>
>
>
>
> [Non-text portions of this message have been removed]
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