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Re: [EnergyPlus_Support] Outputs
The zone heat balance includes the impact of VENTILATION before computing the
"Zone/sys sensible load to cooling setpoint predicted". The HVAC system (the
PURCHASED AIR) sees the net load including any increase or decrease in load due
to the VENTILATION air. So, in answer to the specific questions:
1. For PURCHASED AIR (with zero outside air flow in the PURCHASED AIR object),
zone/sys cooling
energy will be reported only when the coils are on.
2. Zone/sys sensible load to cooling setpoint predicted is the load to be
delivered by the HVAC system. VENTILATION objects are not considered to be
part of the HVAC system in EnergyPlus. So, for PURCHASED AIR this is the
cooling coil sensible load.
3. Correct. The mechanical ventilation report variables only report outside
air delivered from an HVAC system, and it only supports systems which are
modeled with an AIR PRIMARY LOOP, not zone equipment.
4. To achieve your goal of detemining the load due to ventilaiton air, three
options come to mind:
a) Do 2 runs, one with VENTILATION and one without.
b) Report the zone/sys sensible cooling load, Zone Ventilation Sensible Heat
Loss, and Zone Ventilation Sensible Heat Gain on an hourly basis. Then you can
analyze the hourly results to determine the benefits and penalties of the
ventilation air.
c) Use COMPACT HVAC and model a unitary system with outside air provided by
the HVAC system. Then the mechanical ventilation report variables will sort
out the load impact of the outside air (cooling load increase, cooling load
decrease, etc.)
Mike
On 18 Aug 2006 at 12:26, Clarice Bleil de Souza wrote:
> Hi everybody,
>
> I am having a look at some of the EPlus outputs and would like to check
> couple of things about them.
>
> 1) Report variable: Zone/sys sensible cooling energy
>
> According to the Input/output reference guide this refers to the sensible
> energy supplied by the system to the zone reporting the cooling delivered by
> the HVAC to the zone. It does not always indicate the operation of the cooling
> coil. It says that if supply air is cooled by outside air it will be reported
> as a cooling load even if the coils are off.
>
> On that note my question is: if I am using Purchased Air with no outside air,
> just recirculation, BUT I am defining a ventilation object the zone/sys
> cooling energy will be reported only when the coils are ON ? I ask that
> because I do have air from the outside that might be cooling the zone - as I
> specified a ventilation object - but this air is not influencing the supply
> air as it is not being mixed with the return air of the Purcahsed Air - it is
> being delivered to the zone directly. Would the zone/sys cooling energy be
> reporting a cooling load with the coils off, even if there is a ventilation
> object assigned to the zone, if the Outside air is set to "NO" in the
> purchased air object?
>
> 2) Report variable: Zone/sys sensible load to cooling setpoint predicted
>
> According to the documentation this variable reports the predicted sensible
> load required to meet the setpoint. Again will this variable refers to the
> loads due to the coils ON or all the cooling loads being delivered when I
> simulate using a Purchased Air object?
>
> 3) Report variable: Ventilation loads reports
>
> I noticed that there are new report variables in version 1.3 refering to
> ventilation loads. I tried to use them with the same settings, Purchased air
> objects, no outside air specified for it BUT ventilation objects being used
> instead. I got null values fro all the variables refering to the ventilation
> reports. Do these reports only refer to ventilation loads when specified
> through oustide air objects? If I use the ventilation object only - even with
> mechanical ventilation sets - this variables will report me null values - is
> that correct?
>
> I wanted to check that because I would like to isolate cooling loads due to
> coils on from cooling loads due to ventilation only - but setting this
> ventilation separately from my ideal machine. Would this be possible in any
> way?
>
> Thanks a lot for the help
>
> Best regards,
>
> Clarice
>
>
>
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>
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>
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========================================================
Michael J. Witte, GARD Analytics, Inc.
EnergyPlus Testing and Support
EnergyPlus-Support@xxxxxxxx
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