[TRNSYS-users] 2 independet + 1 dependent variables in look-up files

[David BRADLEY]

Leen,
   Unless I am misunderstanding what you want to do, the solution is 
quite easy as long as you are able and willing to write a new Type; 
TRNSYS has a built-in kernel subroutine called InterpolateData (formerly 
called DynamicData) that performs exactly the function that you are 
looking for. The subroutine is called from a Type with the values of as 
many as 6 independent variables. The subroutine looks through an 
external file, finds and returns the values of as many as 10 dependent 
variables that correspond to the input values. The subroutine 
interpolates linearly between values but cannot extrapolate beyond the 
range of values that is given in the data file.

   Before you go too far down the path of writing a new heat pump model, 
I would recommend that you look through the TESS HVAC Library 
documentation on existing heat pump models and also take a look at the 
code of some of those models. Most of them stay away from energy rate 
control (in which a precalculated load is imposed on the heat pump) and 
stick with temperature level control (in which case heat pump capacity 
and fraction of full load power are computed based on inlet and ambient 
conditions.) Those models may be what you are looking for or could be 
modified with little effort to better suit your needs.
Best,
  David



On 1/8/2013 06:35, leen peeters wrote:
> Hi all,
> We are trying to model more accurately a heat pump for which the 
> performance should ideally be read out from a text or excel file.
> The data depend on 3 parameters (outdoor and indoor air temperature, 
> requested output).
> Part load ratios are hard to define, as the actual capacity depends on 
> the model type and the outdoor conditions. So it seems logic to use 
> excell. However, values are not a function, but should be looked up in 
> the excell table, potentially interpolated, ... and to make it more 
> challenging, the final SPF does depend on PLR, outdoor and indoor 
> temperature. So it is not just using the external temperature and 
> required capacity to calculate PLR and consequently use that PLR plus 
> indoor temperature to calculate SPF.
> Calling 6 different excell files in a simulation of 8760*4 steps will 
> take considerable time. The current standard TRNSYS look up model 
> allows two independent parameters defining the output ... so 
> insufficiently accurate.
> any suggestions on how to solve that?
> thanks,
> leen
>
>
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> TRNSYS-users at cae.wisc.edu
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-- 
***************************
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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