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Re: [EnergyPlus_Support] Packaged Terminal Air Conditioner
The report variable for *Packaged Terminal Air Conditioner Total Zone
Heating Rate *calculates only the supply air energy rate supplied to the
zone.
*Packaged Terminal Air Conditioner Total Zone Heating Rate* =
AirMassFlow * (Enthalpy_in - Enthalpy_zone)
The report variable *Zone/sys sensible heating rate* also includes this
but has other terms as well.
*Zone/sys sensible heating rate* = SUM(MCpTin) - SUM(MCpTzone) +
NonAirSystemResponse + SysDepZoneLoadsLagged
NonAirSystemResponse includes loads from sources other than the air
system (which may be 0 in your simulation) and SysDepZoneLoadsLagged
includes loads from a window gap from the previous time step (to name
one). Also note that at Row 722 - 731, the Zone/Sys Sensible Load to
Heating Setpoint is negative, the Zone/Sys Sensible Cooling Load is
positive, and the Zone/Sys Sensible Load Predicted is 0 which means the
zone really has no load and the zone temperature is somewhere between
the thermostat's heating and cooling set point temperature. The zone
temperature is "floating". ABOVE 20 C.
Hu Jia wrote:
>
> Hi, all,
>
> I simulate the heating and cooling loads of an office room with a
> window. I use a packaged terminal air conditioner (PTAC) system in
> HVACTemplate:Zone:PTAC, which with a DX cooling coil, a heating coil
> (electric), and an outdoor air mixer. The supply air fan is on/off.
> There is no any other HVAC system. The thermostat is 20 (heating), 24
> (cooling).
>
> From the output file, I got the total HVAC electric power, the fan
> electric power, zone/ sys sensible heating rate, PTAC sensible heating
> rate and so on.
>
> I found that: * Zone/sys sensible heating rate* is equal to *Packaged
> Terminal Air Conditioner Total Zone Heating Rate* for most of time,
> but sometimes, for example, when both of cooling and heating coils
> stop and only fan is on, *Packaged Terminal Air Conditioner Total Zone
> Heating Rate = Fan Electric Power = Total HVAC Electric Demand but is
> not equal to Zone/Sys Sensible Heating Rate.
> *
> All I mentioned above can be found from my uploaded excel file, named
> for "*Heating and cooling loads*" at Problem_Submittals of Yahoo
> Group (URL:
> http://tech.groups.yahoo.com/group/EnergyPlus_Support/files/_Problem_Submittals/
> <http://tech.groups.yahoo.com/group/EnergyPlus_Support/files/_Problem_Submittals/>).
> You can find this from ROW 432 to 443 in the Excel file.
>
> Is someone able to answer any of the following questions?
>
> (1) Could anyone explain why Zone/sys Sensible heating Rate is not
> equal to Packaged Terminal Air Conditioner Total Zone Heating Rate?
>
> (2) What is the difference between Zone/sys Sensible heating Rate and
> Packaged Terminal Air Conditioner Total Zone Heating Rate when only
> PTAC is used?
>
> (3) How to calculate the heating or cooling loads when only PTAC is
> used or when only purchase air is used?
>
> Thank you in advance.
>
> JIA
>
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