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.
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On Fri, Nov 20, 2009 at 12:50 PM, Richard Raustad <RRaustad@fsec.ucf.edu > 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@fsec.ucf.edu <mailto:RRaustad@fsec.ucf.edu >> 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 Enginee
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