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Re: [TRNSYS-users] Efficiency of collector
- Date: Mon, 18 Oct 2004 10:38:39 -0500
- From: Michaël Kummert <kummert@xxxxxxxxxxxxx>
- Subject: Re: [TRNSYS-users] Efficiency of collector
Florian,
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@xxxxxxxxxxxxx
SEL Web Site: http://sel.me.wisc.edu
TRNSYS Web Site: http://sel.me.wisc.edu/trnsys
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