Re: [EnergyPlus_Support] Re: COP of AirLoopHVAC:UnitaryHeatPump:AirToAir

[Richard Raustad <RRaustad@xxxxxxxxxxxx>]

What is the range (min/max) on the x (indoor coil entering air temp) and 
y (outdoor coil entering air temp) curve inputs if used? These limits 
can influence the results (the curves output, which also has limits if 
used). Also, 31C is rather high for the indoor coil entering air temp. 
How does this look for other lower temps. You should plot at least 2 
indoor coil entering air temps on the chart to ensure the curves act 
accordingly.

It looks like you divided heating capacity factor by EIR (energy input 
factor). The COP is 1/EIR which would show an increase in COP as outdoor 
temp increased.

I see a downward trend in heating capacity as outdoor air temp increases 
at higher outdoor temps. Find some manufacturers data and verify this is 
correct (or look in the data sets file RooftopPackagedHeatPump.idf). 
This curve appears incorrect to me (i.e., capacity should increase as 
outdoor air temp increases). Heating capacity and power should both 
increase as outdoor temps increase. But capacity increases faster than 
power leading to an increasing EER and COP.

Always question the performance curves since these are what is actually 
simulated.


On 2/13/2013 6:35 AM, FrancescoP wrote:
> I used curves that are used as default in DesignBuilder: DXClgCoilTotalClgCapFuncTemperature and DXClgCoilEnergyInputRatioFuncTemperature
> They are Curve:Biquadratic
> I have plotted them (hopefully correctly)considering the condenser temperature 31°C:
> http://imageshack.us/f/580/dbcurves.jpg/
> It is a "baseline model" therefore it doesn't correspond to a real HVAC system.
> I have seen that in some examples of EnergyPlus as curves for "Total Heating Capacity Function of Temperature Curve" and for "Energy Input Ratio Function of Temperature Curve" objects Curve:Cubic are used (see AirflowNetwork_MultiZone_House.idf  in that case if external temperature increases COP increases). Do you think that neglecting the influence of the condenser temperature on the COP is an acceptable approximation?
> I simulated using those curves. Here the graph with the curves proposed by AirflowNetwork_MultiZone_House.idf :
> http://imageshack.us/f/560/copu.jpg/
> (comparing with the previous graph consider that in the meantime also the peak power of the heat pump was changed)
> Probably I will develop curves using Curve:Biquadratic in order to consider both the condenser temperature and the evaporator temperature. I have found some interesting graphs in H. Ludwig von Cube et al. (1981) "Heat pump technology", Butterworths and in (1979) "Heat pump technology for saving energy", Noyes data corporation.
>
>
>
> --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "FrancescoP"  wrote:
>> I am modeling System 4 - PSZ-HP according to the definition of Annex G of ASHRAE 90.1-2007. In excel I calculated the COP as ratio between "DX Coil Total Heating Rate" and "DX Heating Coil Electric Power" and I plotted the graph (outdoor air temperature ; COP) that you can see here:
>> http://imageshack.us/f/442/copg.jpg/
>> (when the "DX Heating Coil Electric Power" is equal to 0 I imposed the COP equal to 0)
>> In the object AirLoopHVAC:UnitaryHeatPump:AirToAir the field "Maximum Outdoor Dry-Bulb Temperature for Supplemental Heater Operation" is equal to 4°C. I think that is the reason why the COP decreases between 3°C and 5°C: the electric heating coil switches off and the DX coil has to heat the supply air to a greater temperature.
>> The COP decreases also when the outside temperatures are greater than 10°C. I don't understand why.
>> Any comment, please?
>> Best Regards
>> Francesco Passerini
>>
>
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-- 
Richard A. Raustad
Senior Research Engineer
Florida Solar Energy Center
University of Central Florida
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