Solar Water Heating "Total System Flow Rate" Parameter

Hi Paul,

My main question regards the definition of total system flow rate in the Solar Water Heating model. Is the total system flow rate parameter the sum of the flow through each collector in parallel, or is it the flow through just one of the collectors? The reason I ask is that we are trying to run a parametric study to find the optimal flow rate, and we are getting very low flows for an 8 collector system (1 gpm or less). 1 gpm divided between 8 collectors is not a lot, but if the total system flow rate parameter is the flow through an individual collector, then it makes a bit more sense.
 
A note in the help page also says that “Collectors are assumed to be flat plate collectors plumbed in parallel, with uniform flow through each collector at the tested flow rate.” Is the saying that the tested flow is the flow through the collectors? If so, what is the total system flow rate parameter determining?

I have read all of the documentation available for this model, and it still is not clear to me.

Hi Chase,

For the default system, the total system flow rate is equal to the collector test flow rate multiplied by the number of collectors. For your parametric study, you may want to change the total system flow rate with the number of collectors.

Thanks,
Paul.

Paul,

Thanks for your response. Just to clarify - you are saying that adjusting the "Total system flow rate" parameter in the "System" section on the "Solar Water Heating" tab does not do anything i.e. the number input for this parameter is ignored because it is actually determined by multiplying the input number of collectors by the chosen collector's test flow rate. Let me know if I am understanding you correctly.

Thanks,
Chase P.

Hi Chase,

Both the total system flow rate and number of collectors are inputs. If you change the number of collectors, you should also change the total system flow rate.

If you want to use the default case as a guideline, for the default case, we set the total system flow rate to the product of the test flow rate and number of collectors. But, you can choose to use a different method to calculate the total system flow rate. For example if you expect there to be some losses in the system that are not reflected in the test flow rate, you could set the total system flow rate to less than the product of the test flow rate and number of collectors.

Best regards,
Paul.

Hi Paul,

Do you have any idea why low system flows (less than 0.5 gpm/collector) consistently result in higher system energy over a year? It seems that as I reduce the total system flow parameter, system energy continues to increase. That such low flows would be ideal seems contrary to what I would expect. Any thoughts?

Thanks,
Chase P.