RE: [EnergyPlus_Support] Re: Modeling a Packaged Rooftop Heat Pump according to Appendix G

Fabiano,

Here is my perspective on multi-stage thermostats for Baseline systems:

Commercial Heat pumps are available with more than one stage of capacity and generally operate at higher efficiency when operating at less than 100% capacity. This feature is common for anything bigger than a very small (e.g., residential) capacity and could be multiple compressors, a single compressor with multiple capacity stages or even a variable speed compressor.

· With that in mind, an E+ model would use AirLoopHVAC:UnitaryHeatPump:AirToAir:MultiSpeed for system #4.

· There is no multispeed option for the normal System #2 object (ZoneHVAC:PAckagedTerminalHeatPump), but you could use the same object as for System #4 with consideration for the part load curves.

Now about part load curves:

ASHRAE 90.1 does not specify anything about coil or equipment part load curves except for VAV fans. This means, for a Baseline system, that it is up to the judgment of the modeler to select a proper set of curves. No one at GBCI, for example, will have any idea about which curves you used.

My approach is to use curves that are reasonably representative of the Baseline system I am modeling. In the case of multi-speed heat pumps, this is not necessarily simple. You can take the approach of evaluating several models of commercial equipment and deriving your own curves, but not all manufacturers provide enough detailed performance information. The other approach, which is reasonable and a lot less time-consuming for a “fictitious” Baseline system, is to use the curves provided with an E+ example file, like “MultiSpeedHeatPump.idf”. I admit that I normally use example file curves when I am modeling a Baseline system; the E+ team seems to be exceptionally thorough and do not often put something in an example file without some thought. (Keep in mind, though, that example files are not always so realistic, so you must review them and decide if it is reasonable to use their information)

For a Proposed / actual system, of course, you should do your best to derive curves that are appropriate for the specific equipment that is provided for the project. If you are modeling the Proposed system during the design period (before equipment has been purchased), you will probably use a “generic” curve similar to what is used for the Baseline. If you know the actual equipment, including manufacturer and models, then it is much preferred to create a curve based on the manufacturer technical data.

James V Dirkes II, PE, BEMP, LEED AP
www.buildingperformanceteam.com
Energy Analysis, Commissioning & Training Services
1631 Acacia Drive, Grand Rapids, MI 49504 USA
616 450 8653

From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of FrancescoP
Sent: Friday, September 28, 2012 8:48 AM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: RES: [EnergyPlus_Support] Re: Modeling a Packaged Rooftop Heat Pump according to Appendix G

Thank you, Jim!
Have you got any idea about what "multistage space thermostats" mean and about how they can be modeled in EnergyPlus?
Regards
Francesco Passerini

--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Fabiano Domingues Ferreira <fabiano.ferreira@...> wrote:
>
> Ok! Thanks Jim!
>
> Regards,
>
> Fabiano Ferreira
>
> De: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] Em nome de Jim Dirkes
> Enviada em: Thursday, September 27, 2012 4:27 PM
> Para: EnergyPlus_Support@xxxxxxxxxxxxxxx
> Assunto: RE: [EnergyPlus_Support] Re: Modeling a Packaged Rooftop Heat Pump according to Appendix G
>
>
> Perfect!
>
> James V Dirkes II, PE, BEMP, LEED AP
> www.buildingperformanceteam.com<http://www.buildingperformanceteam.com/>
> Energy Analysis, Commissioning & Training Services
> 1631 Acacia Drive, Grand Rapids, MI 49504 USA
> 616 450 8653
>
> From: EnergyPlus_Support@xxxxxxxxxxxxxxx<mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx> [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of Fabiano Domingues Ferreira
> Sent: Thursday, September 27, 2012 2:35 PM
> To: EnergyPlus_Support@xxxxxxxxxxxxxxx<mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx>
> Subject: RES: [EnergyPlus_Support] Re: Modeling a Packaged Rooftop Heat Pump according to Appendix G
>
>
> Hi Jim,
>
> So to comply with the requirement I need to set the supplemental heating coil object type to Coil Heating Eletric and Maximum Outdoor Dry-Bulb Temperature for Supplemental Heater Operation to 4° C?
>
>
>
> [cid:image001.png@...]
> Thanks,
>
> Fabiano Ferreira
>
> De: EnergyPlus_Support@xxxxxxxxxxxxxxx<mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx> [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx]<mailto:[mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx]> Em nome de Jim Dirkes
> Enviada em: Thursday, September 27, 2012 11:40 AM
> Para: EnergyPlus_Support@xxxxxxxxxxxxxxx<mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx>
> Assunto: RE: [EnergyPlus_Support] Re: Modeling a Packaged Rooftop Heat Pump according to Appendix G
>
>
> The AirLoopHVAC:UnitaryHeatPump:AirToAir object has made it easy for you! Notice the "Supplemental Heating Coil Object Type"
>
>
>
> AirLoopHVAC:UnitaryHeatPump:AirToAir
>
> Name
>
> AirLoop_UnitCool1_GymBaseSys4
>
> Availability Schedule Name
>
> SchCpct_FanOpern
>
> Air Inlet Node Name
>
> NodeOut_MA_GymBaseSys4
>
> Air Outlet Node Name
>
> NodeOut_Air_GymBaseSys4
>
> Supply Air Flow Rate During Cooling Operation
>
> Autosize
>
> Supply Air Flow Rate During Heating Operation
>
> Autosize
>
> Supply Air Flow Rate When No Clg or Htg is Needed
>
> Autosize
>
> Controlling Zone or Thermostat Location
>
> Gym
>
> Supply Air Fan Object Type
>
> Fan:ConstantVolume
>
> Supply Air Fan Name
>
> SFan_GymBaseSys4
>
> Heating Coil Object Type
>
> Coil:Heating:DX:SingleSpeed
>
> Heating Coil Name
>
> HtgCoil_GymBaseSys4
>
> Cooling Coil Object Type
>
> Coil:Cooling:DX:SingleSpeed
>
> Cooling Coil Name
>
> ClgCoil1_GymBaseSys4
>
> Supplemental Heating Coil Object Type
>
> Coil:Heating:Electric
>
> Supplemental Heating Coil Name
>
> SupplHtgCoil_GymBaseSys4
>
> Max. Supply Air Temp. from Suppl. Heater
>
> 35
>
> Max. Outdoor DB Temp. for Suppl. Htr Operation
>
> 7.2
>
> Fan Placement
>
> DrawThrough
>
> Supply Air Fan Operating Mode Schedule Name
>
> SchCpct_AlwaysOn
>
>
>
> James V Dirkes II, PE, BEMP, LEED AP
> www.buildingperformanceteam.com<http://www.buildingperformanceteam.com/>
> Energy Analysis, Commissioning & Training Services
> 1631 Acacia Drive, Grand Rapids, MI 49504 USA
> 616 450 8653
>
> From: EnergyPlus_Support@xxxxxxxxxxxxxxx<mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx> [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of direzionecontraria
> Sent: Thursday, September 27, 2012 10:08 AM
> To: EnergyPlus_Support@xxxxxxxxxxxxxxx<mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx>
> Subject: [EnergyPlus_Support] Re: Modeling a Packaged Rooftop Heat Pump according to Appendix G
>
>
>
> I have found a document:
> http://www.google.co.uk/url?sa=t&rct=j&q=ashrae+heat+G3.1.3.1&source=web&cd=1&ved=0CCAQFjAA&url="">
> I think I did confusion between defrost and "electric auxiliary heat"... The electric auxiliary heat shall be a specific electric coil. In EnergyPlus what is the best solution to model the control of electric auxiliary heat system according to G3.1.3.1?
>
> --- In EnergyPlus_Support@xxxxxxxxxxxxxxx<mailto:EnergyPlus_Support%40yahoogroups.com>, "FrancescoP" <direzionecontraria@<mailto:direzionecontraria@>> wrote:
> >
> > Probably I'll impose the condition concerning the temperature for the activation of the auxiliary heat through the field "Maximum Outdoor Dry-Bulb Temperature for Defrost Operation" of the object Coil:Heating:DX:SingleSpeed
> > Do you think that it could be a good solution?
> > The biggest problem in the interpretation of G3.1.3.1 is that I don't understand what "multistage space thermostats" mean.
> > Best Regards
> >
> >
> > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx<mailto:EnergyPlus_Support%40yahoogroups.com>, "Fabiano Domingues Ferreira" <fabiano.ferreira@> wrote:
> > >
> > > Hi,
> > >
> > >
> > >
> > > I'm modeling a project on the DesignBuilder according to the Appendix G of ASHRAE 90.1-2007 Standard.
> > >
> > > According to the Standard the system that I need to model is a Packaged Rooftop Heat Pump. I have a problem to comply with the item G3.1.3.1 Heat Pump, follow bellow.
> > >
> > >
> > >
> > > "G3.1.3.1 Heat Pump. Electric air-source heat pump shall be modeled with electric auxiliary heat. The system shall be controlled with multistage space thermostats and an outdoor air thermostat wired to energize auxiliary heat only on the last thermostat stage and when outdoor air temperature is less than 4°C."
> > >
> > >
> > >
> > > I have already modeled the auxiliary heat, I just don't know how to set the thermostats. Could you tell me how can I set those thermostats on the system?
> > >
> > >
> > >
> > > Regards,
> > >
> > > Fabiano Ferreira
> > >
> > >
> > >
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