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Why isn't logging temp sensor data a common feature of controllers ?

I am new to hydronic controll,
I started investigating on optimizing the curve of an outdoor reset controller (Honeywell T775P)
And I figure that it would be nice to have a log of sensors output data for a long period,
this would give precious indications of problems or suboptimal settings.
I notice that the controller doesn't record data, it seems like such a simple feature to support,
it's a shame that they don't have it.
Can a datalogger be easily added to an existing system ?


  • hot_rod
    hot_rod Member Posts: 22,121
    Plenty of inexpensive data loggers out their these days. Depending on how much data and how often you want to sample it, it gets to be a lot to keep logged. When you start sampling several times a minute or every 5 seconds data piles up quickly it takes huge storage space to keep it all.

    I suspect price is a concern for equipment manufacturers, the really watch pennies when they design and build. They analyze the market to see which features are really needed or customers would pay more for. I think most of the newest mod cons have some data collection included.

    I was looking at buying a used Isuzu truck and took it to a dealer to have it checked. They gave me six pages of reports that pulled from the computer for the past 8 years. It even recored how many revolutions the engine has turned since it was built, 364,765,565.96! How many hours and when the engine ran hot, over 230F, engine run time at various road speeds, braking energy per road mile. The tech explained how to look at the data and crunch through it to see what kind of life it led. The data indicated a lot of engine idle time, and low mph travel turn out it was an Aarons Furniture rental delivery truck.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    HVACNUT Member Posts: 5,829
    Are you using this control in a commercial/ industrial multistage boiler or chiller system, or a simple residential application?
    There are 3 sensors for that control using a boiler. Supply, return and outdoor.
    Once you program the design day temperature, the rest takes care of itself.
    The control that would give you precise indications of a problem is your thermostat.
    What are you trying to achieve by having longterm data from the sensors?
    I'm not familiar with that control. Are there parameter settings other than the design day curve that can be changed to adjust the system temperature, or cycle times. For example, on the Buderus 2107, adjustments can be made according to the type of emmiters, and increase or decrease output temperatures in conjunction with the outdoor sensor.

    Bottom line. Why do you want this data?
  • Gordy
    Gordy Member Posts: 9,546
    Price, and how many would use it to fine tune the ODR.
  • Maxl
    Maxl Member Posts: 6
    I bought a rental property that has central heating and it has a T775P as an outdoor reset controller, the controller was setup by the previous owner, I was wondering what was the best way to set it, and tought that looking at historical data could help. One thing I noticed is that it's return sensor is not connected, i.e. it only has the outdoor sensor and the supply sensor. I wonder if the unit can properly function without the return sensor.
  • Gordy
    Gordy Member Posts: 9,546
    edited September 2017
    A little about your system would help. Cast iron boiler with high temp emitters such as base board, or cast iron radiators sound about right? Is the system zoned?

    Keep in mind with outdoor reset, and a cast iron non condensing boiler only allows you to go so low because return water temps need to be above condensing coming back to the boiler. 135-140 is about as low as you can go.

  • Maxl
    Maxl Member Posts: 6
    The boiler is a Dettson hm200 http://www.dettson.com/products/hm200/ Heat emitters are cast iron radiators, the system is not zoned. The reset curve is
    [(140,-5), (120, 55)] (farenheit).

  • Gordy
    Gordy Member Posts: 9,546
    edited September 2017
    I see that boiler has a integrated bypass for boiler protection.

    Is -5 your areas design day?

    140 sounds about right for ci radiation at that design temp.

    To fine tune your ODR raise the thermostat above desired setpoint. Then if you fall short at design raise the curve. If it gets to warm lower it. This takes time, and adjustments should be made in small increments allowing adjustments to acclimate. This may be hard to accomplish on a rental. Might want to try present settings to see what happens on that design day see if it keeps up which it must.

    In the end with an optimal reset curve the thermostat becomes nothing more than a high limit device. It's purpose then becomes high limit for solar gain, large number of occupants, other heating appliances such as fireplace/wood burner.