[TRNSYS-users] Solar thermal collectors / absorber temperature

[Jeff Thornton]

Hoofar, 

The mean plate temperature is calculated by several models - but none
that I know of that take the "simple" parameters like Type 1. The reason
for it is simple - the models like Type 1 aren't doing a full energy
balance on the absorber plate. So calculating a mean plate temperature
(factoring in both the changes in the flow direction and across the
tubes) isn't all that easy - or maybe even possible. If the collector
has a linear efficiency equation, you can estimate the mean plate
temperature from: 

Tplate,mean = Tfluid,in + Qu/Area/FrUl * (1-Fr) 

This is courtesy of Duffie and Beckman. But in simple collector models
you only know FrUl - and you don't know Fr separately. 

As for the case with no thermal mass and no flow, the calculated outlet
temperature of these simple models is also equal to the mean fluid
temperature - and with no heat transfer into the fluid - is also then
the mean plate temperature. 

May I ask why you need the mean plate temperature? I do a lot of solar
collector modeling and have never needed it before... 

If it's critical, you could estimate the mean fluid temperature (for a
collector with a small temperature difference) as the average fluid
temperature (in/2 + out/2) and then add a couple of degrees for the
resistance between the plate and the fluid. Typically the mean plate
temperature is slightly higher than the mean fluid temperature - for
cases where the collector is receiving radiation and the inlet
temperature is close to the ambient temperature. 

Jeff 

---
Jeff Thornton
President - TESS LLC
3 N. Pinckney Street, Suite 202, Madison WI USA 53703
Office: (608) 274-2577 Fax: (608) 278-1475
www.tess-inc.com
E-Mail: thornton at tess-inc.com

On 01/14/2021 10:48 am, Hemmatabady, Hoofar via TRNSYS-users wrote: 

> Dear TRNSYS users, 
> 
> For a thermodynamic assessment, I need mean absorber plate temperature of flat plat solar collectors. The temperature is needed even if the collector is idle (e.i, there is no flow rate). Here are my questions: 
> 
> 1) Is there a TRNSYS type, which have plate temperature as an output with simplified required parameters (like those of type 1)? 
> 
> 2) Can TRNSYS components be used for guessing their physical behavior? (e.g., using the average inlet and outlet temperatures of the solar collectors as mean plate temperature even if there is no flow) 
> 
> Best regards, 
> 
> Hoofar 
> 
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