RE: [EnergyPlus_Support] Low solar collector efficiencies?

["Griffith, Brent" <brent_griffith@xxxxxxxx>]

Kristen,

 

Unfortunately our solar collector guru is unavailable for the next month
or so...  

 

But as far as I can tell, the problem is that you are putting too high
flow rates thru the collectors.  The model includes some fairly complex
modifications for when flow rates during the simulation differ from
those during the tested conditions (for details see section 6.20 in
Duffie and Beckman 1991).  Your collectors are running with flow rates
that are 2 to 3 orders of magnitude higher than the flow rates during
the rating testing.  It makes sense to me that efficiencies would be
lower in this situation.  I think it is safer to model actual collector
areas and flow rates more similar to the tested rate, so you should
probably use more collectors or reduce the scale of what you are
modeling. 

 

brent

 

 

________________________________

From: EnergyPlus_Support@xxxxxxxxxxxxxxx
[mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of Kristin Field
Sent: Wednesday, November 28, 2007 12:55 PM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] Low solar collector efficiencies?

 

Has anyone else run a solar collector (thermal) system and output
hourly efficiencies? I did this, and they were extremely low. Based
on manufacturer data (Thermomax AST80 parameters), I would expect
efficiencies in the 50-80% range. But my output shows more like
10-30%. I would think that this would be independent of my loop
configuration.

One thing I wonder about is that my collector surfaces are much larger
than the test surfaces. Each collector surface (there are 6) is about
50m^2, and the test surface is 11m^2. I was hoping not to have to
have 30 collectors in parallel, but if that is what I need to do to
get a normal efficiency, it will be good to know that.

I will upload my .idf and .csv files (.csv has hourly collector
efficiencies for one of the collectors) shortly.

Thanks,
Kristin

P.S. My file names have "CityParkGH" and today's date in them.

 



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