[TRNSYS-users] Control strategy heating circuit

[Jeff Thornton]

<I want to heat this mass flow in a heat exchanger to maximum of
60°C and regulate the supply temperature with a tempering valve (In
praxis this would be a mixing loop). The heat on the source side of the
heat exchanger is supplied from the top of a thermal storage (This one
is supplied with heat by a solar thermal system and a seasonal thermal
storage) which will be stratified between 20°C and 97°C. I now want to
determine the mass flow for the source side of the heat exchanger in
dependence of the temperature of the outgoing flow from the thermal
storage and the maximum temperature on the load side of 60°C. I want to
use a variable speed pump and need to control its control signal. It
shouldn't be too hard I guess and a quite normal control strategy which
is comparing the thermal energy of the load and the source side of the
heat exchanger. As the mass flow on the load side and temperature on the
load side differs over the year (load mass flow as mentioned above on a
monthly basis, but constant over the month, source temperature on a time
step basis due to the dynamic structure of the solar thermal and
seasonal storage systems).> 

Simon, 

If you're using a constant
effectiveness heat exchanger, you can calculate the source side flow
rate from a few simple equations in TRNSYS. You can then use the
calculated source side flow rate to find the control signal that you'll
feed to the variable speed pump model to give that flow rate to the heat
exchanger. But there is another option; we've written a heat exchanger
model that does exactly as you suggest for the Drake Landing Solar
Community project (same set-up as you describe). The model also adds a
few controls to avoid running the pump during certain conditions. Let me
know if you're interested and I can forward you the details. 

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 04/12/2013
5:02 am, Simon Janse wrote: 

> Hey together, 
> 
> I need some advice
on a control strategy I want to implement in TrnSys17. 
> 
> Following
problem:
> My heating circuit( A large single building, for simplicity I
neglect losses here) delivers a on a monthly basis changing mass flow
with a return temperature of 40°C and need a supply temperature of 50°C.

> 
> I want to heat this mass flow in a heat exchanger to maximum of
60°C and regulate the supply temperature with a tempering valve (In
praxis this would be a mixing loop). The heat on the source side of the
heat exchanger is supplied from the top of a thermal storage (This one
is supplied with heat by a solar thermal system and a seasonal thermal
storage) which will be stratified between 20°C and 97°C. I now want to
determine the mass flow for the source side of the heat exchanger in
dependence of the temperature of the outgoing flow from the thermal
storage and the maximum temperature on the load side of 60°C. I want to
use a variable speed pump and need to control its control signal. It
shouldn't be too hard I guess and a quite normal control strategy which
is comparing the thermal energy of the load and the source side of the
heat exchanger. As the mass flow on the load side and temperature on the
load side differs over the year (load mass flow as mentioned above on a
monthly basis, but constant over the month, source temperature on a time
step basis due to the dynamic structure of the solar thermal and
seasonal storage systems). 
> 
> I think a PID control would be the
right concept to put into place (and it is existing in TrnSys as well),
but as I'm really not familiar with TrnSys I don't know how to implement
this kind of control strategy. 
> 
> So could anybody give me some
advice what to do here and which control is to be used? It would be much
appreciated. 
> 
> Thank you very much for your help. 
> 
> Best regards

> 
> Simon
 
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