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

[Richard Raustad <RRaustad@xxxxxxxxxxxx>]

You defined COP in your email. How would you define EIR?

Using constant curves for the baseline sounds like cheating to me.


On 2/14/2013 9:35 AM, FrancescoP wrote:
> Thank you, Mr. Raustad.
> You are right: the function proposed by DesignBuilder is valid only for x values (i.e. indoor coil entering air temperature) between 12.77 and 23.88°C. I was wrong because I plotted the graph for indoor coil entering air temperature equal to 31°C. Now I have plotted the graph for indoor coil entering air temperature equal to 23°C:
> http://imageshack.us/f/844/db23.jpg/
> Yes, I divided heating capacity factor by EIR (energy input  factor). I think that the result is the factor that multiplies the COP, isn't it? I don't understand why you wrote the "The COP is 1/EIR" (energy input  factor). COP is defined as "the ratio of the rate of heat delivered to the rate of energy input".
> I have plotted also come curves from RooftopPackagedHeatPump.idf
> http://imageshack.us/f/716/jcip.jpg/
> Yes, there are examples where both heating capacity and power increase as outdoor temps increase but capacity increases faster than power leading to an increasing COP:
> http://www.rheem.co.nz/UserFiles/1/image/commercial-heat-pump-cop-vs-temp.jpg
> Actually, I'm wondering whether for a baseline model for LEED certification I could use constant curves. It would be unrealistic but the baseline model has not to correspond to a real situation.
> With Regards
> Francesco Passerini
>
>
> --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Richard Raustad  wrote:
>> 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
>> 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
>>
>
>
>
> ------------------------------------
>
> Primary EnergyPlus support is found at:
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> Attachments are currently allowed but be mindful that not everyone has a high speed connection.  Limit attachments to small files.
>
> EnergyPlus Documentation is searchable.  Open EPlusMainMenu.pdf under the Documentation link and press the "search" button.
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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
Visit our web site at: http://www.fsec.ucf.edu

UCF - From Promise to Prominence: Celebrating 40 Years



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