[TRNSYS-users] help

Jeff Thornton thornton at tess-inc.com
Fri Apr 28 09:18:25 PDT 2006

> I have been simulating the solar hot water system with a variable flow rate 
> which mainly consists of type 534 solar collector(TESS), type 60 storage 
> tank with one internal heat exchanger and four pipes of type 31. Generally, 
> in type 534, if I set the 'pump control consumption' to 1,it will means 
> that we could keep the collector outlet at the specified condition (eg, the 
> outlet temperature of the collector is 55°C) by varying the flow rate. 
> Unfortunately, I tried running many times but it always indicates these 
> error messages that the UAHx of storage could not converge during one time 
> step and the following time step it will use the value of the last 
> iteration. I have attached fiche tpf .

I think you might have listed the collector type wrong.  Did you mean the Type 538 or 539 collector?  Type 60 is rather notorious for having convergence problems at lower flow rates.  Check to make sure you have enough capacitance in the pipes to hold one timestep worth of fluid and relatively small timesteps.

I honestly prefer the TESS storage tank (Type 534) to Type 60 and have used the combination of Type 539 (collector) and Type 534 (tank) in exactly the way you have described it in quite a few projects without problems.

On another note, we just finieshed a major re-write of the Type 539 collector model.  The model can now accept the collector efficiency test results (FrTAn and FrUL), and derive the collector heat removal factor (Fr).  With Fr known, the transmittance-absorptance product at normal incidence and the collector loss coefficient can be calculated.  With these two quantities known, its very easy to model a noded solar collector (mass effects included) that matches the performance from the collector test.  We'll be making this model available in Library Version 3 but will consider selling it ahead of time if there is interest.


Jeff W. Thornton
President - Thermal Energy System Specialists
2916 Marketplace Drive - Suite 104
Madison WI 53719
(608) 274-2577 

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