Hi Jean,Â
Yes, you are right, both models' coils are being autosized. I already checked all inputs in coil:cooling:water, like design water/air flow rate, design inlet/outlet water and air temperature and design inlet/outlet air humidity ratio. All those inputs are being autosized. Â
I would like to check the NTU-effectiveness or bypass factor of the model, but I couldn't find any input or output showing that object. Can you please give me a clue, where do I can find the detail of that object?
I also already tried to set the design water inlet temperature in coil:cooling:water object from autosize to be the same as the chilled water leaving temperature setpoint, in this case 10 C. But, the result is just the same as before. Â
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Another thing, I already show the temperature and mass flow rate output of the model. I take one zone as an example and the results for one time-step are as follows.
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a. model 1 - with leaving chilled water temperature 7 C
  cooling coil inlet temperature = 7 C
  cooling coil outlet temperature = 12.01 C
  chilled water mass flow rate in coil = 0.104 kg/s
  cooling supply air temperature = 13.762 C
  supply air mass flow rate = 0.131 kg/s
b. model 2 - with leaving chilled water temperature 10 C
  cooling coil inlet temperature = 10 C
  cooling coil outlet temperature = 15.05 C
  chilled water mass flow rate in coil = 0.0999 kg/s
  cooling supply air temperature = 13.423 C
  supply air mass flow rate = 0.127 kg/s
I think there is something strange in model 2 output, is it possible to get supply air temperature (13.4 C) which is lower than the cooling coil outlet temperature (15.05 C)? Or do you think there is something wrong with the model or my understanding?Â
Thank you so much for your helpÂ
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This is the juicy stuff of simulation world. See if you can check the supply air coil effectiveness (NTU method) and read up on bypass factor (not that it applies directly to your inputs). If both models' coils are being autosized, it most certainly will give different behaviour.
On 14 Jun 2016 11:42 am, "Julien Marrec
julien.marrec@xxxxxxxxx [EnergyPlus_Support]" <
EnergyPlus_Support@xxxxxxxxxxxxxxx> wrote:
Â
I misunderstood your initial email, I apologize for that. I thought you were getting lower than 10C in the 10C case, an indication that your SPM would have been wrong.
The supply air temperature (or SAT) will be depending on both the chilled water temperature, water flow rate, and air flow rate (this one is determined by the demand of each zone). I would output at the
Detailed timestep the node temperature and mass flow rates for both the chilled water loop and air loop to understand what's going on in detail.
2016-06-14 9:38 GMT+02:00 Annisa Nurul Hidayah
hidayah.annisanurul@xxxxxxxxx [EnergyPlus_Support]
<EnergyPlus_Support@xxxxxxxxxxxxxxx>:
Â
Hi Julien,Â
Thanks for the reply and explanation
Yes, I want the chiller to supply 10 C of water and I already add SetpointManager:Scheduled with a schedule of 10 C.Â
And I also checked the output for chilled water loop supply outlet and it is already 10 C.
I am just a bit confused with the zone supply inlet temperature for the 10 C chilled water temperature.Â
Because, with the same chilled water flow rate for both models (10 C and 7 C) and almost the same dT (delta temperature/ temperature difference), the supply inlet temperature for the 10 C is lower than the 7 C.
For example, the 7 C chilled water temperature with "X" flow rate can produce 13.1 C supply air temperature (the return chilled water temperature around 13.2 C), but the 10 C chilled water temperature with the same flow rate can produce lower temperature, let say 12.9 C (with return chilled water temperature around 16.4 C).Â
NB: Both models are calculated with the same initial condition. Â
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Hi,
The laws of physics are pretty formal about it, energy and mass must be conserved. As Lavoisier said, nothing is created, nothing is lost, everything is transformed.
If you're only using a chilled water coil in an air loop, you cannot produce lower supply air temperature than the inlet chilled water temperature (provided that the entering air temperature at the coil is not even colder...)
I think your slight confusion comes from the term "
Reference leaving chilled water temperature" (see
here). Reference conditions are different than operating conditions.
Basically you specify the chiller characteristics at a reference condition, and then you use a set of curves - that all should have a value of 1.0 at said reference condition - to calculate the characteristics of the chiller at a different operating point, operating point that will be calculated at each timestep given the control you have specified.
In your case, I'd specifically check the setpoint manager you assigned to the chiller plant loop. If you actually want the chiller to supply 10C water, then you should add a SPM:Scheduled with a schedule of 10C on the supply outlet node of the plant loop.
As far as how E+ calculates things, you can always check the Engineering Reference Guide or the source code if you happen to not find what you're looking for (it usually is a last resort situation). Sizing:XXX objects do one thing: they size things. It happens during the sizing runs, at which point these values (airflow and water flow rates for example) are "hardcoded" and then the annual simulation begins.
Hope this helps,
Best,
Julien
2016-06-14 8:22 GMT+02:00
hidayah.annisanurul@xxxxxxxxx [EnergyPlus_Support]
<EnergyPlus_Support@xxxxxxxxxxxxxxx>:
Â
Hi Groups,Â
I just simulated 2 models in energyplus.Â
The first model is aircooled electric chiller with reference leaving chilled water temperature 7 C.Â
And the other model is the same as the first model, but with reference leaving chilled water temperature 10 C.Â
I already updated both models with new EIRFPLR based on their specifications.
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Based on simulation result, cooling/chiller electric energy for the 10 C temperature is lower than the 7 C temperature, which I think it makes sense.Â
But, the problem is in fan electric energy. Both models have the same fan electric energy. I think, based on the theory, The 10 C temperature should have higher fan electric energy than the 7 C temperature.Â
And I already checked the supply inlet temperature from the output:variable,Â
for some zones, the supply inlet temperature in 10 C model is lower than the 7C model. (For example, at the same time and date, in 7 C model, the supply inlet temperature is 13 C, meanwhile, in 10 C model, the supply inlet temperature is only 12 C). I think it is weird because the higher leaving chilled water temperature (10 C) model can produce lower supply air inlet temperature. And of course, It will impact the fan electric energy (in this case, I use the fan:onoff for the supply fan).Â
But, it doesn't happen to all zones. Some zones in 10 C leaving chilled water temperature have higher supply inlet temperature compare to the 7 C model. So, in those zones, the fan electric energy are higher as expected. Â
Does anyone knows how energyplus calculate the supply inlet temperature for each timestep? And Does the cooling supply air temperature setpoint in sizing:zone also impact the supply inlet temperature for the next timestep?Â
And does anyone have the same experience? or any idea? I really need any kind of help
Thanks
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