I've been monitoring (WEL0561) my ewt (entering from the loop field) and return water temp. It seems when the GSHP is running, the return water drops below the ewt as expected. But when the unit is not running, the rwt swings higher than the entering water temp. Is this normal?? I moved the sensor thinking it was picking up ambient heat from the cabinet, but the same results are occurring. I'm getting ready to set up my deltaT for the loops and want to get data that is accurate when in operation, not the swing data... Your thoughts....

Hi,
I found the easiest way to ignore this kind of data when the system isn't on is to use some WELserver expressions on the data and use that output for your computations.

Here's what I did. I have an EWT and LWT sensor, and also a System Run (on/off or 1/0) sensor. I used a "Sample and Hold" expression. Sample the EWT and hold it based on "System Run". When the system goes off, the result of the Sample & Hold will lock at the value when the system was on. Do this for both EWT and LWT and compute the delta from those results.

I do this for both EWT and LWT, then find the delta of the 'valid data'. There's still going to be some minor fluctuations, since the WEL checks the devices every 6 seconds (I think) rather than instantaneously.


I would normally recommend you check out my WEL page (0487), but my house is being renovated and most of the sensors are currently disconnected!

I use the sample and hold function function extensively.  For EWT and LWT, like Stuart, I sample & hold these values as a function of when my GSHP units are running.

By using sample and hold, charts like this one (this is my EWT for 13 months, showing the 85° high and 61° low for the 13 month period) are made possible to be clean, without a lot of noisy data:

http://www.welserver.com/cgi-bin/pl...ilyAvg.png

I additionally do a 24 hour rolling average on my EWT and LWT values to further smooth out noise, with a data point sampled every 619 minutes to build the 13 month chart as in the link above.

To keep track of sensors that I do a S&H on, I add the letter 'S' to the variable.  I.e., this chart shows devices EWTS5T_D and EWTS3T_D.  The 'S' reminds me it's a sample and held device, and the _D reminds me it's a 24 hour rolling average filter.

Best regards,

Bill

After rereading what I wrote, it seemed somewhat complicated.  Let me try and rephrase!

I have a number of different WEL devices set up, including a run-sensor (on/off) for whether the system is running or not.  This returns either a 1 if the system in on, or a zero if the system is off.  This device is called SystemOn

I also have a thermo sensor on the EWT and also on the LWT.  This returns a degree F.  I call these EWT_raw and LWT_raw.  Of course, these values change when the system is running, but return to "ambient" basement temp when the system is off.

In order to get a better reading of what the EWT, LWT, and delta are, especially when the system runs for short periods of time, I set up some WEL expressions thus:

I created an expression called EWT_display.  In the Edit expression window, I set input 1 to EWT_raw, for Operator, I put S.  For input 2, I put SystemOn.  I did the same for LWT_display, setting input 1 to LWT_raw, S for the Operator, and SystemOn for input 2.

From then on, anytime I wanted to display or do math with LWT and EWT, I used LWT_display and EWT_display instead of the _raw values.

Why?  Well, the "S" is a Sample & Hold function.  What this means is that as long as Input 2 is "true" (or in this case "1" meaning the system is On), then EWT_display is equal to EWT_raw (the actual temp of the EWT).  But when the system turns off, Input 2 becomes "false" or "0", and EWT_display holds the last previous _raw value.  The sensor itself gradually returns to ambient basement temperature, but the _display expression remains at the last EWT ground loop temperature.

When I calculate delta, I created an expression called DeltaWT.  Input 1 is EWT_display.  Input 2 is LWT_display, and the Operator is "-" (minus).  My DeltaWT is about 8 degrees (or sometimes -8 depending on if the system is heating or cooling).  When the system is off, the DeltaWT stays reading 8, rather than returning to 0 or some 'wrong number' because the 2 expressions used to compute deltaWT (EWT_display and LWT_display) are both locked on the previous values when the system was running.

Come to think of it, I'm not sure I explained it any less complicated.  Feel free to PM me.

Oh, if you want, you can also take the deltaWT and run an "Absolute Value" on it so that it's always a positive value, no matter whether you're heating or cooling.

Thanks Bill for the chart, that is exactly what I'm trying to see - where my temps have been so I can intelligently evaluate my efficiency.

I got the sample and hold and thanks stuart for the line by line building of the expression, that did it for me.

I will be wiring up the module for the tstat's this weekend and will then set up my comparison to sample and hold when it's running. You guys are the WIZARDS !

Thanks for guiding me through this. The manual makes much more sense with the examples you've given me on the specific applications.

Can't tell you enough how much this is appreciated.

Mike