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Setting Cold Water Temperature

asked 2018-02-07 15:51:12 -0600

updated 2018-05-21 21:48:31 -0600

I'm trying to set Site:WaterMainsTemperature within OpenStudio, but nothing I do is impacting the results (e.g. water heater energy usage is unchanged). I see in DView that Water Heater Use Side Inlet Temperature is wrong (i.e. the temperature spikes over the year), but don't know why. Please see my OpenStudio 2.4.0 screenshots.

Update: I experimented with my model, but still got water temperatures that don't make sense. Here is what I tried (and which is not shown in the screenshots):

  1. Removed the Set Site Water Mains Temperature measure.
  2. Copied the osm file with a new name so as to ignore the associated file folder in hopes of removing unknown issues.
  3. Removed the bypass pipe.
  4. Changed the pump power to something very low (1 W). Plotted Pump Fluid Heat Gain Rate which is low as desired and expected.
  5. Plotted the Water Use Connections Cold Water Temperature, which shows the proper default temperature of 50 F. However, Water Heater Use Side Inlet Temperature is 135 F which doesn't make sense.

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answered 2018-02-16 13:24:12 -0600

Problem solved. The culprit was the adiabatic pipe directly upstream of each water use connection. Once I deleted all of those (or moved them further upstream as shown in the below screenshot), the Set Site Water Mains Temperature measure functioned properly and the Water Heater Use Side Inlet Temperature data was correct.

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answered 2018-02-08 05:04:47 -0600

updated 2018-02-08 05:05:37 -0600

I wrote that measure a long time ago, perhaps something's wrong with it, otherwise it could be your model or an E+ bug.

So let's start assuming the measure is at fault (that's the easiest) before checking the model:

Start by opening your resulting IDF file, and check that you have a Site:WaterMainsTemperature and that it is what you expect, in your case it should be:

Site:WaterMainsTemperature,
  Schedule,  !- Calculation Method {SCHEDULE | CORRELATION}
  Cold Water Temp CZ9;             !- Schedule Name

If so, check that your schedule is also present in the file, and correct.

Second, you can try with the "Correlation" option, you can leave the default values of the measure (these are for JFK airport (NYC) FYI) for now. See if that works better...

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I checked in.idf and Site:WaterMainsTemperature is as you show. Cold Water Temp CZ9 looks correct. Schedule Type Limits Name is "Temperature 1" instead of "Temperature" but I don't think that's an issue. In DView, Water Use Connections Cold Water Temperature matches my Cold Water Temp CZ9 values, but Water Heater Use Side Inlet Temperature is 135 F. Note that my current model does not have bypass pipes, which I believe is what was previously making Water Heater Use Side Inlet Temperature spike over the year. Pump Fluid Heat Gain Rate is very low (1.4 Btu/h).

Bo White gravatar imageBo White ( 2018-02-08 09:45:44 -0600 )edit

I also tried correlation, and those results are similar to my comment above, except that Water Use Connections Cold Water Temperature is sinusoidal as expected.

Bo White gravatar imageBo White ( 2018-02-08 09:55:41 -0600 )edit

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Asked: 2018-02-07 15:51:12 -0600

Seen: 127 times

Last updated: Feb 16