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Collector Material... - Page 3

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Posted by nicksanspam on May 1, 2004, 11:22 am
 


It seems to me that you are the person who is confused :-)


I'd say "power," vs energy. Collector efficiency is an instantaneous
parameter, hot water output power divided by solar input power, with
a particular flow rate and inlet temperature.


And collector efficiency calculations.


That's a different subject.


 FrUL = 5.247 W/m^2/Degree C?


Ti is the INLET (i for inlet) vs the average fluid temperature,
which would be higher.


Duane didn't ask about Richfield, and the solar intensity on the panel
and water and air temps can vary a lot over 10 hours, which makes this
kind of calculation meaningless:
 

Very mysterious... I can't imagine what was going on in your brain when
your fingers typed that. The units don't even work. Where did the m^2 go?

You might say the average solar power is 6.4kWh/m^2/10hours = 640 W/m^2
(altho it isn't because the sun angle and intensity vary over the day)
and estimate the efficiency as 0.738-5.247*(50-10.6)/640 = 0.41, but
that would be a very gross approximation.


That part looks OK, for a square meter.


Very mysterious.


Duane didn't ask about an input fluid temperature. He asked about an
average fluid temperature. To answer his question, you might do some sort
of calculation involving the fluid flow rate and the collector area to
find the outlet temperature, then average the inlet and outlet temps.


With an undersized heat storage tank.


But your efficiency equation uses an inlet vs average fluid temp.

You've ducked Duane's question a third time, Stephen.
You may have a brilliant career as a politician.

Can you find someone at the factory who actually understands
Duane's question and post a correct answer here?


Say water goes in at temp Ti, which is less than 50C, at the flow rate
specified on your data sheet, and the sun on the panel is 1000 W/m^2...

Nick


Posted by nicksanspam on May 4, 2004, 1:37 pm
 


That's apparently how Europeans spec collector efficiency,
but your Ti is the inlet vs average temp.


Duane didn't ask about Richfield...


Duane asked about an average vs input fluid temperature. To answer his
question, you might do some sort of calculation involving the fluid flow
rate and the collector area to find the outlet temperature, then average
the inlet and outlet temps.


Peter Allen understands Duane's question.


Say water goes in at temp Ti, which is less than 50C, at the flow rate
specified on the data sheet, and the sun on the panel is 1000 W/m^2...

With 0.0687 kg/s of water flow and 2.78 m^2 of solar aperture and
efficiency E = 0.738-5.247(Ti-10)/1000 = 0.6855-0.005247Ti (1) and
(Ti+To)/2 = 50 (2), To = Ti+2.78x1000E/(0.0687kg/sx4.19kJ/kg-c)
= Ti+9.66E (3). Substituting To = 100-Ti (2) on the left side of (3)
and (1) on the right side makes 100-Ti = Ti+9.66(0.6855-0.005247Ti),
so Ti = 47.91 C and E = 0.434, for a 43.4% collection efficiency.

Peter says (2) isn't quite accurate because the water gains more heat
in the first half of the collector than in the second half, since it
is cooler in the first half and loses less heat to the outdoors.

Nick


Posted by Sonideft on May 6, 2004, 12:14 am
 Sounds like Peter and I were very close in our estimates; 43% vs. 41%. Not
bad.

Regards,

Stephen Cumminger
Email: stephen.cumminger@heatwithsolar.com
www.heatwithsolar.com

temperature


Posted by Nick Pine on May 6, 2004, 9:26 am
 

He didn't use goat entrails...

Nick


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