[TRNSYS-users] SDHW template Tin and Useful energy gain- strange behaviour

[Philip Horn]

I now solved the input temp "misbehavior", it was just a wrong connection...


However, the issue of a rising Quse while increasing the flowrate (in a extreme manner, i.e. that Tout is almost Tin) still confuses me.

How can I determine the optimum flowrate for a maximum of Quse (I try to figure out an optimization for a polymer unglazed flat plate collector, so I am trying to understand the behaviours and parameter sensitivity of the different collector types.)?

Is the solution for that may be linking the pumpcontrol to a designated Tout?
I guess that's the standard way to do it and the standard SDHW uses this control as well.

I tried that and when I used this pumpcontrol strategy I gained:

Quse=2.6 *10'6	with Toutmax in summer around 130 deg C for a flowrate of 200 Kg/h

Quse=3.7 *10'6	with Toutmax in summer around 55 deg C for a flowrate of 20 Kg/h

Quse=2.1 *10'5	with Toutmax in summer around 200 deg C for a flowrate of 2 Kg/h 

(those high temperatures probably occur only for a short timestep whenever the pump starts running...)
 

Here again the question, how can I maximize the Quse of my system?

The dependency of Quse and flowrate seems not to be linear and the resulting Touts are strange as well.

I used the standard efficiency coefficients eta0=0.8 and efflope=13

I try to figure out an optimization for a polymer unglazed flat plate collector, so I am trying to understand the behaviours and parameter sensitivity of the different collector types.



Any thoughts on that?

Best,
Philip


-----Original Message-----
From: Philip Horn 
Sent: Thursday, May 26, 2011 4:15 PM
To: 'trnsys-users at cae.wisc.edu'
Subject: SDHW template Tin and Useful energy gain- strange behaviour

Hi All,

I played around a little bit with different efficiency equations for the collector, and wanted to compare the results.
Therefore I used the SDHW template (with TYPE1 as collector), which uses the outlet of the Tank as inlet temp to the collector.
I erased this connection and set the inlet temp to a fixed 10 deg but in fact is it still varying when I plot it (from 10-13deg).
How come? 

Another thing that I experienced: when I used the system in the normal mode (Tout tank connected to Tin collector), the useful energy gain of the collector is higher than with a fixed (and in average 10 deg K lower) input temperature.

Shouldn't it be the opposite?
As Q=m*cp*(Tout-Tin) , the smaller Tin, the higher Quse (assuming that Tout is not that heavily affected)?

Clarification highly appreciated!!

Best,
Philip