LM, great question. I regret I don’t have an answer yet. This will certainly be addressed by the time we release 80/20 Triathlon: 2nd Edition, and possibly sooner. Frankly, we’ve not investigated this appropriately to release swim HR zones at this time. I’m confident that they would be different, and likely not compatible with the existing bike and run HR zone calculator.
However, as part of that fact-finding process, I’d be curious to see athletes send me their swim workouts that have Pace + HR. I can then start a database and begin to correlate the samples and refine the swim HR zones.