<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
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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@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