Aw: Re: [EnergyPlus_Support] HVAC System for a Prototyp Supermarket

["'Lara Teutsch ' larateutsch@xxxxxx [EnergyPlus_Support]" <EnergyPlus_Support@xxxxxxxxxxxxxxx>]

Dear Tilek, 

 

thank you very much for your work. I used your sheets to calculate the curves for the compressors I chose. I attached my results.  

I was just wondering now: Why did you also adjust the curve for the subcritical compressors with CoolProp? As Bitzer gives the Q values for subcritical mode I thought it would be fine to just use the results from Bitzer? 

In the files attached you will also find the Compressor for Low Temperature (subcritical).

 

And regarding the HVAC System: It makes sense to have more capacity due to the location, but I am still wondering why the supermarket_Detailed model used 100000 Watt as Gross rated Cooling Capacity although the Model hast around 2000 m² and is located in Miami, where all year AC is also necassary...I am a little confused here. But I guess this problem will be solved a soon as I find out where the exaggerated difference in heat in my buliding is coming from.

And I still don't understand how to do the Part Load Fraction Correlation Curve. I attached my file with my details on the Compressors for HVAC System. Maybe you can help me generating the Part Load Fraction Correlation Curve and tell me if my calculations are ok...

 

Regarding you Mail below: Do you mean I would need theoreticly 16,3 kW less Cooling Capacity for the AC as I have less Heat transfer from the refrigeration cases? 

I will follow your instructions below trying to find the error! 

 

Kind regards

Lara 

 

Gesendet: Montag, 01. Juli 2019 um 16:03 Uhr
Von: "Tilek Aberra tilek.aberra@xxxxxxxxx [EnergyPlus_Support]" <EnergyPlus_Support@xxxxxxxxxxxxxxx>
An: EnergyPlus_Support@xxxxxxxxxxxxxxx
Betreff: Re: [EnergyPlus_Support] HVAC System for a Prototyp Supermarket

 

 

Hi,

The following is the E+ example file for Accra (max goes to 30K W heat gain)

whereas your idf for Accra is 60K.

So definitely there is much heat gain in your idf, and need to look one by one where this comes from.

 

Now analyzing:

For supermarket_detailed.idf (E+ example file)

>Variable Name Refrigeration System Total Cases and Walk Ins Heat Transfer Rate  SELFCONTAINEDSYSTEM

Total Maximum 9,359.61W
Total Minimum 7,210.25W
Total Average 8,356.58W

>Variable Name Refrigeration System Total Cases and Walk Ins Heat Transfer Rate  MEDIUMTEMPSYSTEM

Total Maximum 36,319W
Total Minimum 6,391.47W
Total Average 21,240.2W

>Variable Name Refrigeration System Total Cases and Walk Ins Heat Transfer Rate  LOWTEMPSYSTEM

Total Maximum 16,608.4W
Total Minimum 2,888.07W
Total Average 9,726.39W

 

Roughly total: supermarket_detailed.idf

Total Maximum 9,359.61+ 36,319 +  16,608.4  =62,287W
Total Minimum 7,210.25+ 6,391.47 +  2,888.07  =16,490W
Total Average 8,356.58  + 21,240.2 +  9,726.39 = 39,323W

 

Similarly for Supermarket_Prototyp2.idf
>Variable Name Refrigeration System Total Cases and Walk Ins Heat Transfer Rate  LOWTEMPSYSTEM
Total Maximum 8,479.86W
Total Minimum 1,704.07W
Total Average 6,256.2W
>Variable Name Refrigeration System Total Cases and Walk Ins Heat Transfer Rate  MEDIUMTEMPSYSTEM
Total Maximum 42,083.2W
Total Minimum 3,107.71W
Total Average 16,787.9W
 

Roughly total: Supermarket_Prototyp2.idf

Total Maximum  8,479.86 +  42,083.2 =50,563W

Total Minimum  1,704.07  +  3,107.71    =4,811W
Total Average  6,256.2 +16,787.9  = 23,044W

 

So what does this show, just even seeing the average there is almost 39.3-23.0=16.3kW more refrigeration in supermarket_detailed versus Supermarket_Prototyp2.idf, which means you do not need an AC for the amount of 16.3kW since the fridges inside are doing it for you. The other I will leave for you to analyze is to switch OFF all the fridges in both the above files and see how much is the total AC load difference, that you would found out maybe proportional to the floor area. So I am not sure if you have that much time left to analyze such detailed things, but that is what research is - need to go one by one to see where the exaggerated difference is coming from. The other is that I have advised you in one of my emails that, do incremental changes to the original file to trace where the exaggerated change is coming from. You can still do that. I will leave such type of debugging to you and will get back to you for the HVAC performance curves hopefully tomorrow.

 

If what I said above is not clear let me know.

 

Best wishes,

 

Tilek

 

On Mon, Jul 1, 2019 at 1:40 AM Tilek Aberra <tilek.aberra@xxxxxxxxx> wrote:

Hi,

 

I start to look at your question in regards the HVAC, this area is not my expertise (so no quick resp[onse)  - but I am looking into it. What I did in the IDF I sent is to get the simulation to continue, yes if I doubled capacity and I should have done the same to the flow and others that vary hand in hand. Definitely, there is too much heat gain in the model, but it needs to investigate where this is coming from. You need request more output for plotting and inspect.

 

For instance, add these (or more from .rdd files)

 

Output:Variable,*,Zone Air System Sensible Heating Rate,timestep;
Output:Variable,*,Zone Air System Sensible Cooling Rate,timestep;
Output:Variable,*,Zone Air Heat Balance Internal Convective Heat Gain Rate,timestep;
Output:Variable,*,Zone Air Heat Balance Surface Convection Rate,timestep;
Output:Variable,*,Zone Air Heat Balance Interzone Air Transfer Rate,timestep;
Output:Variable,*,Zone Air Heat Balance Outdoor Air Transfer Rate,timestep;
Output:Variable,*,Zone Air Heat Balance System Air Transfer Rate,timestep;
Output:Variable,*,Zone Air Heat Balance System Convective Heat Gain Rate,timestep;
Output:Variable,*,Zone Air Heat Balance Air Energy Storage Rate,timestep;
Output:Variable,*,Zone Exfiltration Heat Transfer Rate,timestep;
Output:Variable,*,Zone Exfiltration Sensible Heat Transfer Rate,timestep;
Output:Variable,*,Zone Exfiltration Latent Heat Transfer Rate,timestep;
Output:Variable,*,Zone Exhaust Air Heat Transfer Rate,timestep;
Output:Variable,*,Zone Exhaust Air Sensible Heat Transfer Rate,timestep;
Output:Variable,*,Zone Exhaust Air Latent Heat Transfer Rate,timestep;

 

And what I see the sales floor has about 60K and backroom 30K Watts convective heat gain? I am not sure why, maybe the local weather has created this - so try it in the original US location and see whether it reduces. So roughly 114W/m^2 - and actually this makes sense since in AUS the assumption is 118W/m^2 (the quick estimate for house air conditioning), not as you said 50W/m2 - maybe this is true in GER or the original IDF file where it is the case.

 

So it needs too much debugging.

 

I will look at the curves question when I get time this week, sorry for the delay.

 

Best wishes,

 

Tilek

 

On Sun, Jun 30, 2019 at 12:15 AM Tilek Aberra <tilek.aberra@xxxxxxxxx> wrote:

I will look at it, but you can take a linear function for part load. Like at 1/4 part load the capacity will also be 1/4 of the max capacity, so forth. Only thing sometimes efficiency varies with load %age and power input can be different. Tomorrow I will respond.

 

Good night!

 

On Sun, 30 Jun 2019 at 12:08 am, larateutsch@xxxxxx [EnergyPlus_Support] <EnergyPlus_Support@xxxxxxxxxxxxxxx> wrote:

 

Thanks a lot! 

 

The File I am using in EnergyPlus does also need the Part Load Fraction Correlation Curve. But the Excel Tool (CurveFitTool) does not calculate this curve. How can I do this? 

 

I attached an Excel File where I put my calculations under the sheet "Prototyp". My Building is a 800 m² Supermarket which is located in Ghana (all year Cooling).

But I cant find a way to calculate the Part Load Fraction Correlation Curve.

 

Thank you for your help. 

Kind regards

 

 

 

 

Attachment not found:
D:\Eudora\Attach\Prototype_transcritical_4KTE

Attachment not found:
D:\Eudora\Attach\CurveFitTool_HVAC Prototyp1.xlsm

Attachment not found:
D:\Eudora\Attach\Energyefficient_transcritical_4MTE -7K_TRANS.xlsx