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Grundfos comfort PM 10-16 auto adapt recirc. pump question.

TT_Vert
TT_Vert Member Posts: 57
edited August 2022 in Domestic Hot Water
This hot water recirc. pump has an internal and an external temp sensor for the auto adapt and temperature readings. I have a 1/2" return line from the furthest fixture that sends that hot water back to the tank via this pump.

I plan to use the temperature control option because my usage changes day to day. From reading this it seems to only use the internal temp sensor as it makes no mention of the other. I assume this from reading this in the PDF. It gives little info on how it computes or calculates Ton or Toff but just says the following. t doesn't make mention of utilizing the second sensor like the auto adapt below does as you will see below.


After this I did try the auto adapt option which I feel will not work for me but it also didn't keep that return pipe warm and it probably never would even if it had 14 days of data since hot water usage for us is VERY random

My understanding for using the auto adapt option, is that it uses the external temp sensor (Which they say should be mounted 8-20" from the output of the water heater) to measure the outlet temp and when the pump temp sensor detects a certain difference it turns on the pump. I do not plan to use this as our usage is all over the place so any calendar would be useless for us. I tried this but it did not keep the return pipe warm. For some reason it will stay in standby mode when the sensor is located where they state it and the water obviously gets cool in that return line which allows the hot water at the fixtures to cool down. The first time I power it on it runs and circulates water until it gets up to temp and goes to standby. At this point my understanding is when the temp at the pump gets to this "Ton" threshold it would activate the pump until the temp at the pump was within a certain threshold vs. the sensor at the WH outlet. I get this info from their PDF which leads me to believe that is how this should work.


Any opinions?

Thanks
Dave

Comments

  • Larry Weingarten
    Larry Weingarten Member Posts: 2,785
    Hi, This is only an opinion. What you are describing is sometimes called pulsed pumping. A pulse of hot water is sent through periodically to keep water at a usable temperature essentially all of the time. If you are trying to make things energy efficient, another approach which will use far less energy is called demand pumping. This approach turns on the pump only when you want it, using a button. And, if a motion sensor is installed, the pump is activated when you walk close by whatever fixture. A modification of what you have now is to use a timer to prevent it from operating when you won't be using it. Also, very good, thick, and air sealed insulation on all of the hot water lines will help the current setup to lose less energy. It's sort of a door#1, #2, or #3 decision. ;)

    Yours, Larry
    GGross
  • TT_Vert
    TT_Vert Member Posts: 57
    This pump is designed w/ 2 temperature sensors to detect water temp out of the DWH and at the circ pump itself. I am just clearly not understanding how it is doing it. I thought from the reading in the manual that it looked for a reduction in temp at the circ pump vs. the outlet of DWH and when that temp threshold was met it would again turn on the pump. So far that isn't the case in any mode.
  • GGross
    GGross Member Posts: 404
    Timers, auto-adaptive etc will never work right if your usage changes every day. What @Larry Weingarten said above makes sense to me. I know I have seen a grundfos set up with a sink top button you can push when you go in to the bathroom, and I believe that you can get occupancy sensors so it is automated. The pump you have wants to learn your usage and only recirc in those time frames within that temperature setting. Since you will never have a set schedule of water usage, it will not work as you expect.
  • TT_Vert
    TT_Vert Member Posts: 57
    GGross said:

    Timers, auto-adaptive etc will never work right if your usage changes every day. What @Larry Weingarten said above makes sense to me. I know I have seen a grundfos set up with a sink top button you can push when you go in to the bathroom, and I believe that you can get occupancy sensors so it is automated. The pump you have wants to learn your usage and only recirc in those time frames within that temperature setting. Since you will never have a set schedule of water usage, it will not work as you expect.

    Right which is why I am not using the auto adapt option. I am using an alternative option on this called "Temperature control" It has 100% duty cycle, auto adapt which uses 14 days of usage to determine your schedule and temperature control which is supposed to use sensors to keep the water between a preset temperature from my understanding. And that is where my confusion is as it's going into standby when the DHW outlet temp is hot but the temp at the circ pump is cool. That "should" indicate that is should activate the pump to circulate water to get the pump temp to meet the outlet temp. That would indicate there is hot water at the fixtures.

    Dave
  • hot_rod
    hot_rod Member Posts: 18,254
    make sure the HW and recirc lines are well insulated. That is what drive the cost of DHW recirculation, heat loss to the building.

    A few different opinions on how best to run recirc. If legionella is a concern, that loop should circulate 24/7

    Perhaps the most efficient way to operate is with a switch as Larry mentioned, fire it up as needed.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • TT_Vert
    TT_Vert Member Posts: 57
    hot_rod said:

    make sure the HW and recirc lines are well insulated. That is what drive the cost of DHW recirculation, heat loss to the building.

    A few different opinions on how best to run recirc. If legionella is a concern, that loop should circulate 24/7

    Perhaps the most efficient way to operate is with a switch as Larry mentioned, fire it up as needed.

    I just want the internal temp sensor to work. It's not even trying to retain any water temp. It's always in standby mode when in temperature mode. The instructions are horrible and the fact I can get no support is even worse. if I hadn't already soldered the expensive adapter fittings in for this pump it would be going back.

    Dave