[TRNSYS-users] Questions about Types 107 and 680

[David BRADLEY]

Alexandros,


> 1.    Type 107 and Type680 use a normalized catalog data which has 
> limited values for Inlet Hot Water Temperature (from 108.89 (C) to 
> 116.11 (C)), Entering Cooling Water Temperature (from 26.667 (C) to 
> 32.222 (C)), Chilled Water Set point (from 5.556 (C)to 10.000 (C)). Ιf 
> we use values outside this range, do we get wrong results?
possibly. As it mentions in the documentation the components can 
interpolate within the data range given but they cannot extrapolate 
beyond the range. You'll get a notice as to how much of the time the 
components called the data files outside the range. If it happens rarely 
then I would not worry about the consequences. If it is happening all 
the time then the system needs to be better controlled or alternative 
data (with a wider range) is needed.
> 2.    Τhe energy is discharged into the cooling water stream. If we 
> want energy rejection to be done in the air, can we achieve it by 
> changing the value of cp?
I would not recommend doing so. Since the COP of the device is looked up 
from a data file, the effectiveness of the rejection heat exchanger is 
built-in to the performance data file. If the data comes from a machine 
that rejects energy to a water stream then the effectiveness built into 
the COP is that of a brine to water heat exchanger. A brine to air heat 
exchanger would presumably have a different effectiveness and therefore 
a different COP.

In most applications that I have seen the cooling water stream goes to a 
cooling tower where the energy us then rejected to the air. If you have 
a device that rejects directly to air I would try very hard to get its 
performance data and then yes, change the Cp of the rejection stream. If 
you have a device that rejects to a water stream and then to a cooling 
tower I would model it as such.
> 3.    Which working pair ( LiBr-H2O, H2O-NH3 ) is it used in the data 
> file? Ηow can we study the effect of the concentration in the chilled 
> power?
I do not recall what brine was used in the example machine. If I had to 
guess, I would say that it was LiBr-H2O. You cannot examine the effect 
of the brine concentration on performance because performance is read 
from a data file. If you have more than one data file (one for a high 
concentration and one for a lower concentration) then you could examine 
such a modification in the context of the system.
> 4.    The single effect hot water fired absorption chiller is used to 
> solve energy balances between hot water, cooling water, chilled water, 
> auxiliary electrical power. A more detailed analysis is it possible?
No, not really because this is a catalog data lookup table model. You'd 
need to find (or write) a first principals model of the device if you 
want to do a more detailed analysis.

kind regards,
  David


-- 
***************************
David BRADLEY
Principal
Thermal Energy Systems Specialists, LLC
3 North Pinckney Street - suite 202
Madison, WI  53703 USA

P:+1.608.274.2577
F:+1.608.278.1475
d.bradley at tess-inc.com

http://www.tess-inc.com
http://www.trnsys.com

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