Primary-Secondary Loops - Variable Speed Pumping with Minimum Flow
I'm trying to set up autosized primary-secondary heating and chilled water loops, with variable speed primary and secondary flow pumps.
I am modelling as recommended elsewhere in this forum (see here). Only difference is:
I am using headered pumps because it lets me set a minimum pump flow rate as a fraction of maximum (useful when autosizing)
I have bypass on all supply / demand components (if I get it working I will remove the ones that wouldn't normally be in the system)
I have multiple coils on the loop
I need minimum flow rates on both primary and secondary otherwise the energy estimation will be unrealistically low (in the order of 60% flow on primary and 5%-25% flow on secondary). I have tried setting a minimum flow on the pumps (fraction) and on the loop object (flow rate), neither works. I suspect the control hierarchy does not allow these limits to be implemented - but given I've only built a couple of models in energy plus I could be way off.
Has anyone found a way to model this? Preferably in a way that I can include in a measure.
I've tried and abandoned the 'common loop' function - doesn't model variable flow on primary.
Sorry can't upload because I'm new.
Btw, you should have enough reputation to upload a file now.
Thanks for your answer Julien. To clarify what I am after is an intermittent pump which modulates at higher loads, runs at a minimum defined flow rate when there is a small load, and switches off when there is no load. I am having all sorts of problems with my model at the moment which probably contributes my problems with the pumps. I will upload when I have troubleshooted a bit more (probably Monday).
I was recently trying to do the same - constant primary and variable secondary. Or are you doing a variable primary and variable secondary (in which case why not do variable primary only?). Anyway, I found that headered pumps do not work here and went back to regular pumps. Seems to work really well with the Common Pipe simulation. The drawback is, I have to estimate the minimum secondary pump flow in gpm rather than %. No minimum plant loop flow needed.
Also see https://bigladdersoftware.com/epx/doc....
@Matt Koch, note that common pipe for primary/secondary is kinda deprecated and it's recommended to actually use two separate loops with a HeatExchanger:FluidToFluid in between. See Plant Application Guide - Example 3 (2nd paragraph) and Andrew's answer here