[TRNSYS-users] problem with collector type 1b - TRNSYS 18

[Jeff Thornton]

Federico,

Without looking at your project, I’m going to guess that you are running into one of the limitations of the Type 1 model.  Due to its simplifying assumption in the solution, the model can run into issues at very low flow rates and very low loss coefficients.  It was for this reason that we wrote the Type 539 model at TESS.  Our rigorous solution technique does provide continuity all the way to zero flow and no losses.  If you have access to it, I would suggest changing to this model.  If you don’t, and don’t plan on operating near the edges of Type 1’s usability (extremely low losses or very low flow rates), Type 1 does a nice job through standard operating conditions.

Jeff 

Sent from my iPhone

> On Apr 8, 2020, at 1:23 AM, -- Fed -- via TRNSYS-users <trnsys-users at lists.onebuilding.org> wrote:
> 
> 
> Hi everyone,
> 
> I have set up a very simple solar project: just 2 components:
> a weather processor type 15
> a solar collect or type 1b (with 1 m2 area).
> The collector tracks the sun (mode 3) with rotation axis N-S and makes use only of the beam radiation.
> Efficiency as function of mean temperature (mode 2).
> 
> I get weird results that make me doubt that Type 1b works as it should.
> 
> The model is exactly the same every time, but I change the heat loss coefficients (a1 and a2) of the collector.
> 
> When both a1 and a2 are 0.0001, the useful output (as returned by type 1) is 4.43E+06 kJ/m2/year. 
> 
> When a1 is 0.0001, and a2 is 0, the useful output drops unrealistically to to 3.99E+06 kJ/m2/year. 
> 
> The second results is in agreement (just 0.04% off) with the yearly sum of the quantity
> Gb * IAM * eta0
> where
> Gb is the beam radiation on the surface (i only consider beam component)
> IAM is the incidence angle modifier
> eta0 is the peak collector efficiency.
> 
> However, when i set the heat loss coefficients to their actual values,  the yearly energy output from type 1b is not the sum over the year of the quantity:
> 
> Gb * IAM * eta0 - a1*DT - a2*DT^2
> 
> but it is about 11% off...
> 
> If someone has also had problems with type 1 and got to make it work, it would be great to hear 🙂
> 
> Thanks in advance and best regards,
> 
> Federico
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