Updated to Main Drain Estimator Tool (Beta v0.2)

Last week, I posted a Main Drain Estimator tool that runs a supply-side hydraulic calculation in loops until it balances. This tool is showing promise as being much more in line with expectations for estimating flow through a main drain.

Based on your feedback from this past week, I've updated the tool to incorporate three different main drain models that insurers have used to estimate main drain flow so that you can compare our results to others.

One important note: all other three models depend on using a 2-inch main drain. If the actual size is different, then the comparison is not applicable (results in N/A in our tool).

I ran an error analysis based on our method; the c-factor is the biggest driver of variability. Using a C-factor that's off by 10 of the real value would result in an error of about 7% of our predicted flow. It's not terrible, but accurate C-factor use without looking inside the pipe would naturally be a source of uncertainty here.

One direction I'd like to take next is to chart the main drain results against a prior flow test and/or against a hydraulic placard. We could add accommodation to account for underground losses when comparing a flow test at the street, and we would be able to represent the main drain test, the flow test, and the hydraulic placard based on riser data on the same chart. 

In theory, should the main drain be clear of obstruction, this could offer a very quick gut-check on whether the main drain results are within expectations from an original water supply (which is the purpose of a main drain test). It could also provide an initial flag if the water supply has degraded below the system design, which would warrant some further evaluation.

There's certainly plenty of nuance and debate here about NFPA 25 inspection and testing scope, but for practical purposes from a building owner or insurer's perspective, a quick-use utility tool that could help find those problematic properties could offer some benefit to the industry.

Check out our updated tool below, and feel free to comment on the updates or your thoughts. Thanks!