[TRNSYS-users] Solar cooling absorption model

[David BRADLEY]

Raffaele,
   I am afraid that we are no longer actively supporting TRNSYS 16. 
However, I looked at your project quickly. The data file for your 
chiller shows that at low part load ratios, it has some cooling capacity 
but does not require any input energy. The first line of performance 
data in the file is:

0.7237    0.0000

which indicates that at the following conditions:

fraction of design load = 0.
chilled water setpoint = 5.5C
entering cooling water temperature = 24C
inlet hot water temperature = 75C

the device can produce 72.4% of its rated capacity and requires no input 
energy to do so. I would imagine that the reason the chiller is giving 
you a zero COP is that it is operating at low load conditions and the 
model is showing that it needs no input power in order to do so. 
Probably the machine cannot operate at part load less than about 20%, in 
which case the capacity ratio as well as the fraction of design energy 
input ratio should be zero.

As for the auxiliary heater problem, I am less sure as to the cause of 
the problem. However, I did notice that the tank in that loop is 7000L, 
that the pump has a flow rate of 26000L/h and that your time step is 1 
hour. That would mean that the pump (which is always on according to 
your controls) turns over the entire volume of the tank almost 4 times 
per timestep. Actually I am a bit surprised that the simulation runs at 
all! In order for systems to be numerically stable, there must be at 
least enough volume in flow loops to store at least 1 time step of flow. 
Also keep in mind that a system can only make one control decision per 
timestep; a one hour timestep is very long. I would recommend something 
on the order of 1 or 5 minutes.

Best,
  David





On 10/16/2012 16:56, Ralph Lanegan wrote:
> Dear TRNSYS users,
>
> as far as I can see many of you have worked on Solar Cooling models 
> with an absorption chiller.
>
> Attached you can find the one I've tried to build to cool my 900 sqm 
> office (Yazaki SC-30 data file was created by me and cooling tower 
> file was derived from documentation).
>
> Now, the two problems I'm facing here are that absorption machine does 
> not start (COP always zero) and auxiliary heater stops working at 4833 hrs
>
> Is there anyone available to give me support or hints to go ahead?
>
> Thanks in advance
> Raffaele
>
>
>
>
> _______________________________________________
> TRNSYS-users mailing list
> TRNSYS-users at cae.wisc.edu
> https://mailman.cae.wisc.edu/listinfo/trnsys-users

-- 
***************************
David BRADLEY
Principal
Thermal Energy Systems Specialists, LLC
22 North Carroll Street - suite 370
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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