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. 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.Jia Hu
On Sat, Nov 21, 2009 at 2:36 PM, YuanLu Li <yli006@xxxxxxxxxxx> wrote:
Hi, Hu Jia
Date: Fri, 20 Nov 2009 17:31:47 -0500
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.
Subject: Re: [EnergyPlus_Support] electric power (watts) of PTAC
Hello, Dr. LiIn 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?JiaOn Fri, Nov 20, 2009 at 4:47 PM, YuanLu Li <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
From: 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> 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>> 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/>
>
> 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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