Re: [TRNSYS-users] solar collector drainback

[Jeff Thornton <thornton@tess-inc.com>]

We have been modeling solar hot water systems for years and we never model the physical draining of the solar collector and pipes.  We include a drainback tank for the additional losses that it provides and set up controls to mimic the operation of a drainback system.  We allow the pump to run a bit longer after it turns off in order to fill the drainback tank (variable volume tank Type 39) with fluid to it's "drainback volume".  At start-up of the pump, we "throw away" the fluid returning from the collector and return line using a diverting valve until the drainback tank reaches it's "operating volume".  While this isn't perfect, developing pipe and collector models that deal with both air and water filled sections would be difficult.  Besides, the amount of energy that we are talking about is usually very small when compared to the total amount of collected energy over the year.

 

Jeff

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Jeff Thornton

President - TESS LLC

22 N. Carroll Street, Madison WI USA 53703

Office: (608) 274-2577  Fax: (608) 278-1475

www.tess-inc.com

E-Mail: thornton@tess-inc.com

 

On 11/04/2013 9:11 am, Pascual Ortiz, Carol wrote:

Dear all,

 

I would also like to simulate the drain-back of a flat plate collector but I do not know how to do it. So far, I simulated the FPC using the type 1b but now I do not know how can I simulate the drain-back, because if the inlet flow rate of the collector is zero kg/h also the outlet flow rate will be zero. I think that I should change the type 1 for another one, but I do not know which is the type that I should use, could you give me a clue, please?

 

Thank you in advance,

 

 

Carol Pascual

Energía Térmica/Thermal Energy

 

División de Energía y Medio Ambiente/

Energy and Environment Division

 

TECNALIA

Área Anardi,5

Laida Bidea, Edificio 204

E-20730 Azpeitia - Gipuzkoa (Spain)

T 902 760 000*

M 667119581

T +34 946 430 850 (International calls)

carol.pascual@tecnalia.com

www.tecnalia.com

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