[TRNSYS-users] Efficiency of collector

Michaël Kummert kummert at engr.wisc.edu
Mon Oct 18 08:38:39 PDT 2004

> i have a problem with my temperatures of the collector output side.
> I changed my efficency values to (0,55 / 0,007128 / 0,0000324), and the 
> result is ,that the output temperature is rising at some timesteps to 
> endless values.
> The values ,i used before (0,34 / 1,39 / 0,128) ,were worser and the 
> simulation works good.
> The values will sound undersized, but they are right.

If you are referring to the intercept efficiency an the first and second 
order loss coefficients of a solar collector, yes, your values look 
strange to me. I am assuming you use W (although TRNSYS needs those 
parameters in kJ/h) so your first order loss coefficient would be 
0.007128 W/m²-K. This means that your collector efficiency is virtually 
constant. Usual values of the first-order loss coefficient are between 1 
and 2 for evacuated tube collectors, between 3 and 5 for flat-plate 
collectors and "around 15" (wind-dependent) for unglazed collectors.

With your values, the stagnation temperature of your collector is 
something like 4000°C. The other values you mention are also unusual to 
me but they give a more realistic stagnation temperature, which probably 
explains why TRNSYS likes them better.

I hope this helps,

Michaël Kummert


Michaël Kummert

Solar Energy Laboratory - University of Wisconsin-Madison
1303 Engr Res Bldg, 1500 Engineering Drive
Madison, WI 53706

Tel: +1 (608) 263-1589
Fax: +1 (608) 262-8464
E-mail: kummert at engr.wisc.edu

SEL Web Site: http://sel.me.wisc.edu
TRNSYS Web Site: http://sel.me.wisc.edu/trnsys

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