Re: [TRNSYS-users] Chilled Water Cooling System

[a8304506@graduate.hku.hk]

Hi, Nguan Teck.

I think you should be clear of what happens in a simulation as compared with a
real installation.  Most of the chiller models in Trnsys are basically
interpolation of catalogue data.  There is no step-up or step-down of the
chiller compressor to allow for part load performance.  Hence, the chiller
capacity may vary only within a small range according to the different boundary
conditions as compared with the design conditions.  When the building load
varies, the resulting chilled water temperature will change (provided that you
have included a sufficient thermal mass for the chilled water or you may get
non-convergence in the iteration) considerably.  You probaly need to add some
sort of controller to switch the chiller on/off according to the temperature of
the chilled water.

Best Regards
LEE, Chun Kwong
Research assistant
Division of Building Science and Technology
City University of Hong Kong


Quoting #TEO NGUAN TECK# <Z050128@ntu.edu.sg>:

> Hi ALL,
> 
>  
> 
> In simulating my chilled water system (with Fan coil unit using variable
> speed fan and cooling coil; cooling tower using constant pump), I
> connected my equipment to my building model. The system runs and I
> managed to obtain the zone properties (i.e temp and RH). However my
> chiller shows a constant data (i.e. const flow rate, power, heat
> rejection etc) throughout the simulation, even though I used variable
> speed pump for my chilled water.
> 
>  
> 
> I am expecting the chiller data to vary according to the cooling load of
> my building. So my question is, by connecting the cooling equipment to
> my building, will it recognize the different building loads?
> 
>  
> 
> Or can I alternatively use Type682 to obtain the building loads and
> connect it to my chiller system to check its performance? And if I were
> to use this approach, how do I determine the zone properties of my
> building during cooling.
> 
>  
> 
> Or any advice on what may be missing from my original model.
> 
>  
> 
> Note: I am using the sample catalog available in TRNSYS for my chiller.
> 
>  
> 
> Any help is deeply appreciated.
> 
>  
> 
> Nguan Teck
> 
> NTU, Singapore
> 
>