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Re: [EnergyPlus_Support] Packaged Terminal Air Conditioner
Yes, it is my guess that these other variables in the Zone/Sys Heating
Rate report that is causing the differences in the two report variables.
That and the fact that the zone temperature is not at the set point.
There are other report variables that can tell you the latent (moisture)
load, but you will have to use a system that can control on relative
humidity for these to be accurate.
Zone/Sys Moisture Load Rate Predicted [kgWater/s]
Zone/Sys Moisture Load Rate Predicted to humidifying setpoint [kgWater/s]
Zone/Sys Moisture Load Rate Predicted to dehumidifying setpoint [kgWater/s]
Multiply these by about 2452000 (21C and 50%RH) to get Watts.
Most load calculations only look at sensible loads required to maintain
zone temperature, but for humidity controlled applications, the latent
load is important as well.
Hu Jia wrote:
>
> Thanks for prompt reply.
>
> At Row 722-731, only the fan is on, and is that right that
> *Zone/system heating rate* is not equal to PTCA sensible heating rate
> because of the SysDepZoneLoadsLagged?
>
> *Another questioin* is that how to calculate the total heating or
> cooling loads of the building under specified thermostat.
> If Zone/sys sensible heating rate just calculate the sensible load,
> what about the latent load?
>
> Thank you.
>
> JIA
>
> 2009/9/28 Richard Raustad <RRaustad@xxxxxxxxxxxx
> <mailto:RRaustad@xxxxxxxxxxxx>>
>
>
>
> 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/>
>
> >
> <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
> >
>
> --
> Richard A. Raustad
> Senior Research Engineer
> Florida Solar Energy Center
> University of Central Florida
> 1679 Clearlake Road
> Cocoa, FL 32922-5703
> Phone: (321) 638-1454
> Fax: (321) 638-1439 or 1010
> Visit our web site at: http://www.fsec.ucf.edu
> <http://www.fsec.ucf.edu/>
>
> UCF - From Promise to Prominence: Celebrating 40 Years
>
>
>
--
Richard A. Raustad
Senior Research Engineer
Florida Solar Energy Center
University of Central Florida
1679 Clearlake Road
Cocoa, FL 32922-5703
Phone: (321) 638-1454
Fax: (321) 638-1439 or 1010
Visit our web site at: http://www.fsec.ucf.edu
UCF - From Promise to Prominence: Celebrating 40 Years
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