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Re: [EnergyPlus_Support] electric power (watts) of PTAC
From the PTAC Eng. Doc:
The PTAC is able to model supply air fan operation in two modes: cycling
fan – cycling coil (i.e., AUTO fan) and continuous fan – cycling coil
(i.e., fan ON). Supply air fan operation is coordinated with the use of
a supply air fan operating mode schedule. Schedule values of 0 denote
cycling fan operation (AUTO fan). Schedule values other than 0 denote
continuous fan operation (fan ON). Fan:OnOff must be used to model AUTO
fan (i.e. if schedule values of 0 occur in the supply air fan operating
mode schedule), while Fan:OnOff or Fan:ConstantVolume can be used to
model fan ON (i.e. if schedule values of 0 do not occur in the supply
air fan operating mode schedule).
YuanLu Li wrote:
>
>
> Hi, Hu Jia
>
> I point out the Schedule Always 4 to you, because in the error file,
> it is in the ophan object warning. The Fan:OnOFF is always one. But
> in your .xls you send earilier seemed to have the zero in the
> schedule. Zero is constant flow, one is on/off auto. Therefore, the
> two schedules are opposing each other.
>
> The ground temperature was also in your error file warning. I tried
> changing it, and it added about one watt to the fan power. I know
> that the efficiency value is included, because when I reduced the
> efficiency from 0.7 to 0.5 the fan power increases.
>
> The other PTAC model in the example file is a 3Zone building in
> Miami. The fan power for the 6m x 6m West Zone was sized to 90
> watts. Those zones without any windows are a lot lower. In this
> model, the template objects were not used. All the sizing objects
> were present and no .expidf was generated. There were only one
> warning on the weather file location data.
>
> I have a feeling that the 5Zone template was not correctly expanded
> for sizing, and therefore generated those warnings. I have not solve
> the problem yet.
>
> I do not have any EPlus project of my own and am doing this as my
> hobby. So long you think my comments are useful, I shall pick up some
> of your questions.
>
>
> Dr. Li
>
>
>
>
> ------------------------------------------------------------------------
> To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> From: hujia06@xxxxxxxxx
> Date: Mon, 23 Nov 2009 15:11:35 -0500
> Subject: Re: [EnergyPlus_Support] electric power (watts) of PTAC
>
>
> I quite appreciate your help. I see the expidf and find the objects
> you mentioned. At first, I did not use the template
> model (PTAC) and used the schedule "Always 4". But when using the
> template model, I did not delete this schedule because I think it will
> not affect my the result.
>
> For the angle of the window blind, I define it deliberately to see the
> effect. I will look at what will happen when changing the ground
> temperate.
>
> From IO manual, the HVACTemplate-Always 4 is the Dual Thermostat of
> HVAC. and HVAC Template-Always 1 is the schedule of fan on/off. For
> my model, the fan is supposed to be on until the HVAC cooling or
> heating coil stops working (it is AUTO FAN because I define 0 in the
> field: Supply Fan Operating Mode Schedule Name).
>
> Jia
>
> On Mon, Nov 23, 2009 at 1:45 PM, YuanLu Li <yli006@xxxxxxxxxxx
> <mailto:yli006@xxxxxxxxxxx>> wrote:
>
>
>
> Hi, Hu Jia
>
> I think you have two items in your IDF which can reduced the
> cooling capacity requirement.
>
> 1) You did not have a Ground temperature below the building in the
> IDF. The program used the default value of 18°C. If you raise
> this value to 22°C, the cooling demand and fan power will
> increase. The best value to use is to run the slab program. The
> estimated value is two degrees below the indoor floor temperature.
> (in IO Manual)
>
> 2) The other component that can reduce the heat load is the window
> blind. You have the angles set to 65, 90, 90 degree. These may
> still block some of the sun light.
>
> Because you are using the template model, the EPlus has added some
> more objects in the .expidf for you. That is also why your Always
> 4 schedule was not used. Another schedule: HVACTemplate-Always
> 4 was generated and used.
>
> ZoneControl:Thermostat,
> Rinker building office Thermostat, !- Thermostat Name
> Rinker building office, !- Zone Name
> HVACTemplate-Always 4, !- Control Type
> Schedule Name
> ThermostatSetpoint:DualSetpoint, !- Control Type
> Rinker thermostat Dual SP Control; !- Control Type Name
>
> Fan:OnOff,
> Rinker building office PTAC Supply Fan, !- Fan Name
> HVACTemplate-Always 1, !-
> Availability Schedule Name
> 0.7, !- Fan
> Efficiency
> 75, !-
> Delta Pressure {Pa}
> autosize, !- Max
> Flow Rate {m3/s}
> 0.9, !-
> Motor Efficiency
> 1, !-
> Motor in Airstream Fraction
> Rinker building office PTAC Heating Coil Outlet, !- Fan
> Inlet Node
> Rinker building office PTAC Supply Inlet; !- Fan
> Outlet Node Name
>
> I am not sure which one the program is using, when dealing with
> the template model. That was the reason why I always display the
> schedule value to verify in the .csv file.
>
>
>
> Dr. Li
>
>
>
>
> ------------------------------------------------------------------------
> To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> <mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx>
> From: hujia06@xxxxxxxxx <mailto:hujia06@xxxxxxxxx>
> Date: Mon, 23 Nov 2009 11:02:37 -0500
>
> Subject: Re: [EnergyPlus_Support] electric power (watts) of PTAC
>
>
> Hello, Dr. Li, Thank you for your explanation. I understand now.
> Thank you.Jia
>
> On Sun, Nov 22, 2009 at 2:08 PM, YuanLu Li <yli006@xxxxxxxxxxx
> <mailto:yli006@xxxxxxxxxxx>> wrote:
>
>
>
> Hi, Hu Jia
>
>
> RINKER BUILDING OFFICE PTAC SUPPLY FAN:Fan Electric
> Power[W](Hourly:8-17) RINKER BUILDING OFFICE PTAC SUPPLY
> FAN:Fan Delta Temp[C](Hourly:8-17) RINKER BUILDING OFFICE
> PTAC SUPPLY FAN:On/Off Fan Runtime Fraction(Hourly:8-17)
> 7.827441338 8.84E-02 1
> 7.827441338 8.84E-02 1
>
>
>
> When the PLR is 1, the ran electric power is the fan power
> consumption.
>
> This number includes the efficiency values 0.7 and 0.9
> modification, entered in the IDF.
>
> I ran the 5Zone example IDF in the example folder, and it gave
> the fan power ranging from 26 to 44 watts, with the zone area
> from 60 to 140 m2 using Chicago weather file.
>
> I think your number of 7.82 watt for the fan size is reasonable.
>
> You have many DesignDay objects in the IDF. May be you should
> reduce that to two worst case conditions and make sure that
> the equipment is turned on for the required cooling and
> heating temperature, by choosing the day type with the desired
> correct set point schedule.
>
> Using the continuous fan mode, the fan power is displayed,
> when the compressor is off. This can be verified with the
> indicated power divide by the PLR, using the on off mode, or
> at the few transition steps of the continuous mode.
>
> I try the 5Zone example with different DesignDay objects and
> weather file run period, the sized fan size were different.
> For the same zone, the range was from 32 watts to 44 watts.
> The efficiency values are the same as in yours, 0.7 and
> 0.9 for the fan.
>
> When I quoted the half HP window unit, the motor size of
> quarter HP is used for both the condensing and evaporating
> coils. The heat generated by the motor is not normally in the
> cooling air path.
>
> A small table fan consumes about 50 watts, and this include
> the power for turning or oscillating the fan direction. My
> condo fan coil unit fan is 300 watt for 1000 sq.ft. with ducts
> for four rooms. The little fan in the PC power supply is only
> 2W, and its efficiency would be lower than a larger one.
>
> The HVAC power includes the compressor or heater and fan power
> as drawn from the electricity supplier. The heat from the fan
> is normally added into the air path, and a percentage value
> can be set in the fan object. In your IDF I did not see this
> object as a separate item, because this is special PTAC model.
>
> The dual band (type 4) thermostat is also not used (Schedule
> Always 4). I have seen one occasion in the 5Zone example both
> the heating and cooling were on at the same hourly period. I
> need to verify that they are not in the same time step.
>
> The 5Zone model has 146 warnings, because the dry bulb
> temperature was too low. This may be due to the fan power was
> low. If I find any thing later after correcting the error
> warning conditions, I will let you know.
>
>
>
> Dr. Li
>
>
>
>
> ------------------------------------------------------------------------
> To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> <mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx>
> From: hujia06@xxxxxxxxx <mailto:hujia06@xxxxxxxxx>
> Date: Sun, 22 Nov 2009 11:00:41 -0500
>
> Subject: Re: [EnergyPlus_Support] electric power (watts) of PTAC
>
>
> Hello, Dr. Li, Thank you very much. I upload one idf. file and
> weather file to clarify my question. You can see the range of
> HVAC electric power (W) and fan power from the output file.
>
> The URL is
> http://groups.yahoo.com/group/EnergyPlus_Support/files/_Problem_Submittals/input%20and%20weather%20file.zip
> <http://groups.yahoo.com/group/EnergyPlus_Support/files/_Problem_Submittals/input%20and%20weather%20file.zip>
>
>
> Jia Hu
>
>
> On Sat, Nov 21, 2009 at 2:36 PM, YuanLu Li <yli006@xxxxxxxxxxx
> <mailto:yli006@xxxxxxxxxxx>> wrote:
>
>
>
> Hi, Hu Jia
>
> I have not run the model you have quoted.
>
> In general, the PTAC has only one fan, therefore it is
> used all the time for Winter and Summer. The split model
> has two fans, one for the compressor and one for the
> electric heater and coil unit (the fan coil unit) in the
> zone.
>
> The size of the fan is related to the air flow rate. which
> is calculated from the maximum cooling demand and the
> minimum set point temperature. Once it is sized, the fan
> size does not change for the Summer and Winter use. The
> VAV models only varies the damper settings. The extra air
> from the fan is by-passed back to the return air path.
>
> Therefore, the fan power or energy usage listed in the
> simulation run is usually simply calculated form the PLR
> and efficiency of the fan that you have entered.
>
> HVAC,Average,Fan Delta Temp [C]
> HVAC,Sum,Fan Electric Consumption [J]
> HVAC,Average,On/Off Fan Runtime Fraction []
> HVAC,Average,DX Coil Total Cooling Rate [W]
> HVAC,Average,DX Heating Coil Runtime Fraction []
> HVAC,Average,Unitary Heat Pump Fan Part-Load Ratio []
> HVAC,Average,Unitary Heat Pump Compressor Part-Load Ratio []
>
> These are from a heatpump model. I think, similar ones
> should be available from your model as well.
>
> Although the DX bi-quard coefficients are given in the
> object, it is set to unity, so that the efficiency does
> not change with load. There are many fields you can set
> in the model, therefore, it is difficult to tell without
> looking at the IDF.
>
>
>
>
> Dr. Li
>
>
>
>
> ------------------------------------------------------------------------
> To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> <mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx>
> From: hujia06@xxxxxxxxx <mailto:hujia06@xxxxxxxxx>
> Date: Fri, 20 Nov 2009 17:31:47 -0500
>
> Subject: Re: [EnergyPlus_Support] electric power (watts)
> of PTAC
>
>
> Hello, Dr. Li
>
> In my case, *the heating coil type is electric and cooling
> coil type is SingleSpeedDX.*
>
> The power in the xls. is the total power of HVAC
> (including electric consumption of HVAC
> system) and not just the fan electric power. The maxmum
> air flow is autosized by EP.
>
> I got the fan power through this formula: *Maximum of the
> fan power = Max (for a timestep,Variable Fan Electric
> Power / variable Packaged Terminal Air Conditioner Fan
> Part-Load Ratio),* which is suggested by Richard. I think
> the power of the fan may be small because the office is
> small and EP regards the small fan is enough for the HVAC ?
> **
> For the electric consumption (W) of HVAC indicated in slx,
> is it deviated from normal range?
>
> Jia*
> *
>
> On Fri, Nov 20, 2009 at 4:47 PM, YuanLu Li
> <yli006@xxxxxxxxxxx <mailto:yli006@xxxxxxxxxxx>> wrote:
>
>
>
> Hi, Hu Jia
>
> I do not know how you get the fan power of 9W.
>
> In your xls, the HVAC power goes to zero, because it
> is a on/off system. The power value has no real
> meaning. PLR is varying and not the equipment power.
>
>
> When the power reading averaged over an hour period,
> it may be very low or zero. That was why I said your
> numbers in the xls were reasonable. The maximum of
> 992 watt is just over one HP, which is the average
> size of a window unit.
>
> A typical window unit has a half horse power
> compressor and a half horse power fan, or two
> quarter HP fans in a split unit. I assume that the
> wattage in the xls is not the fan power alone, and is
> the total power of the HVAC equipment.
>
> A small window unit compressor is the same as the one
> used in your refrigerator.
> A quarter HP fan draws about 200 wats. This amount of
> heat may be added to your cooling load, if the fan
> motor is in the air flow path. The exact amount
> depends on how you define it in the IDF.
>
>
> Dr. Li
>
>
>
>
> ------------------------------------------------------------------------
> To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> <mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx>
> From: hujia06@xxxxxxxxx <mailto:hujia06@xxxxxxxxx>
> Date: Fri, 20 Nov 2009 14:41:42 -0500
> Subject: Re: [EnergyPlus_Support] electric power
> (watts) of PTAC
>
>
> Thank you. And I will check the idf file.
>
> On Fri, Nov 20, 2009 at 12:50 PM, Richard Raustad
> <RRaustad@xxxxxxxxxxxx <mailto:RRaustad@xxxxxxxxxxxx>>
> wrote:
>
> 9 watts is too low.
>
> Hu,Jia wrote:
> >
> >
> >
> > Thank you for your specific explanation.
> >
> > HVAC I used is the templated PTAC provided by
> EnergyPlus, that is, the
> > heating is provided by electric power and
> cooling is supplied by
> > cooling coil.
> >
> > I calculate the fan electric power using the
> first method you
> > provided, and find the maximum of fan electric
> power (W) is about 9W
> > at the design day.
> >
> >
> > On Fri, Nov 20, 2009 at 10:49 AM, Richard Raustad
> > <RRaustad@xxxxxxxxxxxx
> <mailto:RRaustad@xxxxxxxxxxxx>
> <mailto:RRaustad@xxxxxxxxxxxx
> <mailto:RRaustad@xxxxxxxxxxxx>>> wrote:
> >
> >
> >
> > You need to identify the maximum power draw
> of your fan and
> > compare that
> > to your design intent.
> >
> > Report these 2 report variables:
> >
> > Output:Variable,*,Fan Electric Power,timestep;
> > Output:Variable,*,Packaged Terminal Air
> Conditioner Fan Part-Load
> > Ratio,timestep;
> >
> > and, if you are using an On/Off Fan object:
> > Output:Variable,*,On/Off Fan Runtime
> Fraction,timestep;
> >
> > Maximum fan power is then roughly equal to
> Fan Electric Power /
> > Packaged
> > Terminal Air Conditioner Fan Part-Load Ratio
> or is equal to Fan
> > Electric
> > Power / On/Off Fan Runtime Fraction.
> >
> > Another method is to either look for a time
> during the simulation
> > when
> > the PTAC is operating at full load or force
> the PTAC to operate at
> > full
> > load and then look at the reported fan power
> for that time period.
> >
> > You will then need to determine if this
> maximum fan power is
> > representative of your system.
> > Fan power of 900 W sounds high for a PTAC
> (unless it is very
> > large), my
> > AC system at 3 tons (10.5 kW) gives an
> estimated fan power of 0.018 W
> > per W of rated capacity.
> >
> >
> >
> > Hu,Jia wrote:
> > >
> > > Thank you, Richard.
> > >
> > > It is realistic then to have the HVAC
> consumption of 200 W per hour
> > > (let's say on average) or in the range of
> 200-900 W per hour
> > > depending on a day, time, that is,
> external weather conditions.
> > >
> > --
> > 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/>
> > <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
> <http://www.fsec.ucf.edu/>
>
> UCF - From Promise to Prominence: Celebrating 40 Years
>
>
>
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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
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