Pretty good work there, Martin.
Although it does not concern most (if not all) pumps that are currently used in the industry, I would like to add that the results (pumps in series being superior than in parallel) are the consequence of two things:
- the actual pump specifications: particularly their relatively high maximum discharge and their head pressure level. Let's imagine for a second that if a DDC could only do 1.5 GPM as maximum discharge, then putting them in parallel would be a much better choice than in series. So keep in mind that these results are not universal but dependent on the pumps specs. Different technology could imply different results
- and we never know what will be coming next!
- the other thing is that no matter how restrictive a loop is, pressure drop always increases with the square of flow rate. In other words, no matter how low restriction a loop is, at 3 GPM and more, we will always face MAJOR pressure drop. This only means that the best thing one should do is to try and enhance pressure in the actual working range of flow rates (1 to 2.5 GPM - see my latest "article" about this) and for that, all the pumps having a max discharge > 3 GPM will be benefit much more from serialization.
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