CM TE 047 - Water Flow

Discussion in 'Maintenance and Troubleshooting' started by carpboy, Jan 22, 2013.

  1. carpboy

    carpboy New Member

    Hi all, a couple of months into my new unit here and I am trying to fine tune it. This is an open loop system, 4 tons. This was a replacement to an 9 year old one that had too many refrigerant leaks to repair.

    I am wondering what water flow rates I should have. I am trying to optimize the flow to keep my well pump run time down. Using 3/4 PVC wide open I get 14 GPM. CM gives 1.5 - 3 GPM/ton as a reference. I am curious as to how the water flow is set over the two stages: Is it just a single valve position for the first stage and wide open for the second or is it more intelligent than that, truly infinitely variable? It looks like there is a basic PID loop in the thermostat, I don't know what else it would control but the water flow.

    I would like to find the minimum flow state and then set that to 6-7 GPM.

    As for telling what stage I am in, the only way I can see to do this is to look at the CFM demand on the thermostat. The manual lists a table of airflows for each stage, I presume it is 1 airflow for a stage, different ones for heating vs. cooling.

    I am getting a lot of noise in the pipes when < 10 GPM. The installer claimed this was due to my existing 7/8 CPVC (installation only replaced piping at the unit itself, using 3/4 PVC). His implication was that this was a flow restriction and causing the noise. I argued that the old system had no noise although I did concede that there was a pressure reducer inline (which he did not put in the new system) and that this could have kept it quiet.

    I just got a flowmeter in place and can play with it now. With all valves open I get 14 GPM and it is quiet. So much for the existing piping causing the noise. I turned it down to 10 GPM for now but am trying to figure out what the various flow valve positions are so that I can have it never less than 7 GPM.

    I do have the old pressure reducer but it is suspect. In order to get good flow on my old unit (with an unrelaible flow gauge), I have to adjust it such that water leaked through when the system was off (the pressure managed to open the cheap electric valve). So it may be ok and I could hook it into the line if too noisey, I'd just use some unions to make it easy to pull out.


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