[TRNSYS-users] TRNSYS-users Digest, Vol 144, Issue 24

Tue Dec 13 13:15:52 PST 2016

Jeff,

First of all, thanks for your time. Also, sorry for the unclean project I
sent, I'm a mess.

I'm attaching now a new image of my project, hopefully a little more decent
one. Now I explain in detail the connections:

There are two independent systems with two solar collectors loop. The
control system and configuration logic is the same. The outlet temperature
and flow of Type 543's heat exchanger is connected to the Type 538 inlets.
The solar collectors on their side are connected to the Type 695 variable
pump. Nonetheless, I know Type 695 ignores the inlet flow. What I do
instead is that I connect the the "Fraction of maximum flow" of Type 538 to
the "Control Function" input on Type 695, wich has the same rated flow.
Also, to soften the control, I use Type 93 between Type 538 and 695.
Finally, Type 695 is connected to the heat exchanger's inlet temperature
and flow.

I will test the massles control collector idea tomorrow morning, and then
report if it solved the problem.

I hope you have a good day, thanks again
Javier Vega
Mechanical Engineering Student, Universidad de Concepción, Chile

2016-12-13 17:39 GMT-03:00 via TRNSYS-users <
trnsys-users at lists.onebuilding.org>:

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>    1. Re: Energy losses on solar collector's heat exchanger before
>       the loop starts (Jeff Thornton via TRNSYS-users)
>
>
> ---------- Mensaje reenviado ----------
> From: Jeff Thornton via TRNSYS-users <trnsys-users at lists.onebuilding.org>
> To: trnsys-users at lists.onebuilding.org
> Cc:
> Date: Tue, 13 Dec 2016 14:39:46 -0600
> Subject: Re: [TRNSYS-users] Energy losses on solar collector's heat
> exchanger before the loop starts
>
> Javier,
>
> It might help to send the printers, integrators and output devices to a
> hidden layer so we can see your project a bit more clearly, but I do have
> one question.  Are you using the outputs of the solar collectors to set the
> flow rates in their respective loops?  Both 538 and 539 will calculate the
> required flow rate to meet the desired outlet temperature.  This flow rate
> will need to be identical throughout that loop (pumps, tanks etc.).  Double
> check that first.  Otherwise I may suggest that you remove the capacitance
> from the collector and add a few pipes in each loop.  There are times that
> the control algorithms will deliver strange-looking results with collectors
> with mass.
>
> The ideal way to handle this situation is to have a control collector (a
> collector that sees the same inlet temperature, ambient temperature and
> solar radiation but has no mass).  This control collector is then used to
> set the flow rate for the real loop which contains the collectors with
> mass.  We use that approach routinely and with good results.
>
>
>
> Jeff
>
>
>
> ---
> Jeff Thornton
> President - TESS LLC
> 22 N. Carroll Street, Madison WI USA 53703
> Office: (608) 274-2577  Fax: (608) 278-1475www.tess-inc.com
> E-Mail: thornton at tess-inc.com
>
> On 12/13/2016 2:21 pm, Javier Vega via TRNSYS-users wrote:
>
> Hello TRNSYS community,
>
> I'm using Type 538 and 539 to model ETC and Flat Plate collectors. I have
> them connected to Type 695 (variable speed pump) and a HX in a solar water
> tank modeled through Type 543 (Coiled). In the tank, there is also another
> HX connected to a Heat Pump water loop.
>
> I'm using Type 538 and Type 539 in Control Mode 4, meaning the solar
> collector loop works only if the fluid can win energy. But, nevertheless,
> everytime the solar collectors activate and start to supply energy, I get
> negative power peaks. I've noticed the same occurs sometimes with the heat
> pump's heat exchanger, but just a few times.
>
> I haven't calculated the impact of this phenomenon in my whole simulation.
> Anyway, should I really expect this results in my calculations? Maybe it's
> the effect of the capacitance of the collectors array.
>
> I will attach some images that may help. The units are in kW and the info
> shown in the plot correspond to the energy transfer rate in the Heat
> Exchangers.
>
> [image: Imágenes integradas 1]
>
> [image: Imágenes integradas 2]
>
> Thanks in advance, greets from
> Javier Vega Benavente
> Mechanical Engineering Student, Universidad de Concepción, Chile
>
>
>
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