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Re: [EnergyPlus_Support] DX COP Rating



As explained below, the DX coil performance curves are generic and can be used 
with any weather data.  However, there are some issues to be aware of.

1.  The DX curves in the example files are based on manufacturer's data which 
is published for outdoor dry bulb temperatures ranging from 75 to 115F (23.9 to 
46.1C) and coil entering wet bulb temperatures ranging from 62 to 72F (16.7 to 
22.2C).  When developing such curves, it is important to understand the range 
of input data temperature compared to the range of temperatures to be 
encountered in the simulation.  Interpolation within the range of input data is 
generally very good, extrapolation outside the range of input data can be a 
problem.  

In your case, some extrapolation is needed, because you said the outdoor dry 
bulb temperature can be as high as 50C.  This small amount of extrapolation is 
probably acceptable, but it is a good idea to plot the curves and make sure 
they behave properly over the range of expected conditions.

2.  That said, the curve objects in the example files have been input to limit 
extrapolation using the last four fields in the curve object:

>     12.77778,                !- minimum value of x
>     23.88889,                !- maximum value of x
>     23.88889,                !- minimum value of y
>     46.11111;                !- maximum value of y

These inputs will clip the curves at the stated value.  For example, if the 
outdoor dry bulb exceeds 46.11111, then the curve will be evaluated at 
46.11111.  So, to answer your initial question, you should increase the 
"maximum value of y" in the biquadratic curve objects for CapFT and EIRFT, 
after plotting the curves to confirm that they extrapolate reasonably well.

3.  When autosizing equipment, the DESIGN DAY definitions must change when 
changing locations.  There is no autosizing based on the weather file data.  
The user must put in appropriate design day objects obtained from the ddy file 
which may be found in many of the weather file zip files, or create one based 
on local design data.

Mike


On 19 Jul 2005, at 9:50, Don Shirey wrote:

> Ali:
> 
> The DXSystem:AirLoop object has an input for cooling coil type and name:
> 
> DXSystem:AirLoop
>    A6,  \field Cooling coil type
>         \type choice
>         \required-field
>         \key COIL:DX:CoolingBypassFactorEmpirical
>         \key COIL:DX:CoolingHeatExchangerAssisted
>         \key COIL:DX:MultiSpeed:CoolingEmpirical
>         \key COIL:DX:MultiMode:CoolingEmpirical
>    A7,  \field Cooling coil name
>         \required-field
>         \type object-list
>         \object-list CoolingCoilsDX
> 
> 
> Each of these coil types requests performance curves for that DX Coil.  
> For example, COIL:DX:CoolingBypassFactorEmpirical has the following inputs:
> 
> COIL:DX:CoolingBypassFactorEmpirical,
>   A5 , \field Total Cooling Capacity Modifier Curve (function of 
> temperature)
>        \required-field
>        \type object-list
>        \object-list BiquadraticCurves
>        \note curve = a + b*wb + c*wb**2 + d*edb + e*edb**2 + f*wb*edb
>        \note wb = entering wetbulb temperature (C)
>        \note edb = drybulb temperature seen by the condenser (C)
> .....
>   A7 , \field Energy Input Ratio Modifier Curve (function of temperature)
>        \required-field
>        \type object-list
>        \object-list BiquadraticCurves
>        \note curve = a + b*wb + c*wb**2 + d*edb + e*edb**2 + f*wb*edb
>        \note wb = entering wetbulb temperature (C)
>        \note edb = drybulb temperature seen by the condenser (C)
> 
> 
> This DX cooling coil object requires the names of curve objects that 
> specify total capacity and energy input ratio (1/COP) as a function of 
> the air temperature entering the condenser and the wetbulb temperature 
> of the air entering the cooling coil.  An example curve object for the 
> EIR modifier curve might be:
> 
>   CURVE:BIQUADRATIC,
>     WindACEIRFT,             !- Name
>     0.342414409,             !- Coeff1 Constant
>     0.034885008,             !- Coeff2 x
>     -0.000623700,            !- Coeff3 x**2
>     0.004977216,             !- Coeff4 y
>     0.000437951,             !- Coeff5 y**2
>     -0.000728028,            !- Coeff6 x*y
>     12.77778,                !- minimum value of x
>     23.88889,                !- maximum value of x
>     23.88889,                !- minimum value of y
>     46.11111;                !- maximum value of y
> 
> So the Curve:Biquadratic object above is evaluated every simulation time 
> step that the DX coil is requested to operate to determine the energy 
> input ratio (1/COP) of the DX cooling coil at the entering air 
> temperatures during that simulation time step (i.e., based on the 
> weather conditions specified for the simulation for the condenser 
> entering air temperature and the calculated cooling coil entering air 
> temperature).
> 
> See the IO Reference for DXSystem for more details.  Also, the example 
> input file TermRHDXSystem.idf should be reviewed.
> 
> Don
> 
> 
> 
> Ali_Ajmi wrote:
> 
> > Hi Linda,
> > Do you mean that the COP of the DX system will be calculated based on 
> > the weather condition associated with IDF file. For example if my 
> > weather file is representing a very hot climate where temperature may 
> > reach 50 C, will the performance of the cooling coil adopted to match 
> > that outdoor condition? Because as far as I know the COP curve 
> > coefficients of the DX system are generated at New York, Syracuse 
> > climate condition. Consequently, the energy consumption of the DX will 
> > be performed on that climate condition.
> >
> > Ali
> >
> > Linda Lawrie <linda@xxxxxxxxxx> wrote:
> > At 08:53 AM 7/17/2005, Ali_Ajmi wrote:
> > >Could any one advice of which objects in E+ need to be change if I
> > >use a different than USA weather file. For instance I am using DX
> > >cooling coil so I think the COP rated for the DX system need to be
> > >change, but how? and what else require changing?
> > >
> >
> > It wouldn't be due to the non-USA weather file location -- it would
> > be a change needed due to climate. At least I think that's what
> > you're reasoning for changing the DX cooling coil parameters
> > are? You could, perhaps, autosize your system so that the objects
> > are more in line with your design climatic conditions.
> >
> >
> > Linda
> >
> > EnergyPlus WebSite: http://www.energyplus.gov
> > Owner: EnergyPlus_Support list
> > Member: EnergyPlus Development Team
> >
> 
> 
> 
> 
> The primary EnergyPlus web site is found at:
> http://www.energyplus.gov
> 
> The group web site is:
> http://groups.yahoo.com/group/EnergyPlus_Support/
> 
> Attachments are not allowed -- please post any files to the appropriate folder
> in the Files area of the Support Web Site.
> 
> Yahoo! Groups Links
> 
> 
> 
> 
> 
> 
> 
> 



========================================================
Michael J. Witte, GARD Analytics, Inc.
EnergyPlus Testing and Support      
EnergyPlus-Support@xxxxxxxx




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