[TRNSYS-users] differential controller - Type 2

[David BRADLEY]

Ali,

  Its hard to know what might be going on without looking in detail at 
the project. A couple of pointers; apologies if some of these are very 
basic. Usually the lower input temperature would be set to the tank 
bottom temperature, not to the heat exchanger outlet temperature. If 
your heat exchanger is in-tank (rather than external) then this makes 
less of a difference. Bear in mind that Type2 makes its control decision 
based only on a temperature difference, not on a setpoint. If your 
collector pump is turning on at -25C that means the heat exchanger 
outlet temperature is even lower.

   Types538 and 539 allow you to define thermal capacitance for your 
collector whereas Type1 and Type50 neglect capacitance. In your 
air-based system the capacitance may be less important.

   If -25C is below the ambient temperature and the collector is still 
turning on, have a look at the load side of your tank (or heat 
exchanger). From what you describe, it sounds as though there is 
something driving the tank/HX temperature unrealistically low and that 
you may need to solve that side of the controls rather than focusing on 
the collector side of them.

kind regards,

  David


On 08/08/2021 10:42, Ali Shahrouzian via TRNSYS-users wrote:
>
> Dear TRNSYS users,
>
> Hi,
>
> I’m modelling a solar system to heat a space. It is consisting of two 
> loops: one of them is a water-based solar collector loop as heat 
> source and the other one is an air-based loop included an air-to-water 
> HX, a fan and so forth.
>
> In order to control the solar loop in such a way that it turns off 
> when the incident radiation isn’t sufficient (during night), I’ve used 
> a differential controller (type 2). I connected the collector outlet 
> temperature to Th (parameter 1 for type 2) and the HX outlet 
> temperature to the Tc (parameter 2).
>
> Defining the controller in this same way causes the collector outlet 
> temperature starts from minus temperatures like -25 degrees C over the 
> course of winter days. I face with this issue when I used types 50 
> (PV/T collector), (538 evacuated collector), 539 and … , however using 
> type 1 (flat plate collector) as the solar collector doesn’t cause 
> this issue.
>
> I would appreciate if anyone help me in this case.
>
> And one more thing, as I’ve already explained my system also has a 
> secondary loop included a fan, an air-to-water HX and … . I am 
> wondering whether in order to control the secondary loop when solar 
> loop is off, I should define a new controller (type 2) or I can use 
> the differential controller previous.
>
> Thanks in advance.
>
> Ali
>
>
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-- 
***************************
David BRADLEY
Principal
Thermal Energy Systems Specialists, LLC
3 North Pinckney Street - suite 202
Madison, WI  53703 USA

P:+1.608.274.2577
d.bradley at tess-inc.com

http://www.tess-inc.com
http://www.trnsys.com

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