[TRNSYS-users] Temperature control issue

[Jeff Thornton via TRNSYS-users]

<First, I would like the temperature at outlet of the tank (Type 534) to
be greater than or equal to the DHW supply temperature measured every
hour (which I read using Type9a from a data file).> 

I think you'll need to think this through before deciding how to model
it. How are you going to ensure that the tank temperature is above your
desired temperature? What if you have a few cloudy days and/or a high
load? Are you going to have a small boiler to top off the fluid going to
the load? Are you going to employ heating elements or a gas burner
inside of the tank to keep the fluid temperature above your setpoint? Or
do instead mean that you'd like the temperature coming out of the tank
to be at the desired temperature if at all possible (and possibly lower
if the tank isn't hot enough)? In that case you'd use a tempering valve
to mix in cold water to maintain that maximum temperature. 

As for your second question, it's similar to the first one. How are you
going to keep the return temperature above your desired setpoint at
low-solar conditions? Small in-line boiler? Take out less load than the
real system such that the return temperature is fixed at that minimum?
If it's the latter approach then you can use an equation like: 

Tout_Load = MAX((Tin_Load-Qload/Mdot_load/Cp),Tmin_Load) 

I would also caution you about your approach for the HX loop. Make sure
you have small timesteps and pipes leading to/from the load or you are
likely to run into convergence problems. 

Jeff 

---
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 at tess-inc.com

On 01/26/2017 9:37 am, Charles Smith via TRNSYS-users wrote: 

> Dear TRNSYS users, 
> 
> I am trying to model a solar water heating system (SWHS) based on some data that I have, but I am facing two problems related to the temperature control. 
> 
> First, I would like the temperature at outlet of the tank (Type 534) to be greater than or equal to the DHW supply temperature measured every hour (which I read using Type9a from a data file). 
> 
> Second, I know the supply and return temperatures of the radiant floor as well as the flow rate. So I created an equation to model the radiant floor. The equation takes the temperature at HX outlet (Type 534) and subtract what the radiant floor uses in real life to get the return temperature, which is linked to inlet temperature for HX (Type 534). I would like to use a controller so that the return temperature calculated is never below that measured. 
> 
> I tried different controllers, but it does not seem to work out. Does anyone can help me please? 
> 
> Thank you very much. 
> 
> Best regards, 
> 
> Charles 
> 
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