The following remarks were made regarding the article “Due diligence” written by John Siegenthaler, principal, Appropriate Designs, published in the October 2020 issue of Plumbing & Mechanical:
Thank you for the excellent explanation for using two-pipe buffer tanks — I’ve long been a proponent of these tanks for geo applications. In my personal experience, mid-tank temperature sensing is great if holding the tank at temperature 24/7 on multi-zone hydronic applications, but can result in extra operation time and kW use by the geo equipment, and should be managed by a reset control as you suggest with warm weather shutdown to prevent heating the tank during the AC period. I also find that under some circumstances of flow, simply bypassing the tank in which flow through the geo and connected load is equal, that the mid-tank sensor control can keep the geo equipment operating past its thermal high pressure/temperature limit. I choose to also incorporate a return line sensor limit control for the geo to prevent nuisance high-pressure lockouts and unnecessary extra stress on the compressor, which can operate above design conditions when all flow bypasses the buffer tank.
Jeff Persons // Delaware, Ohio
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