Power consumption of a heatpump

[Nilpferd]

Hello

My heat pump sends once a day the accumulated power consumption. I want to write the power consumption of the last three days in a bar chart.
So first of all I have to subtract the value from two days ago from the value from yesterday to get the daily consumption and store this fro three days. I don`t need to store all values in node red because I send them to KNX and a TWS also.

Can you help me how to subract the value 2 days ago from the value yesterday?

Best Regards
Erwin

[struland]

Hello,
first I would use the Parser "csv" and the "write file" node to store the data in a csv file.
From there I would write a function to process the data.

PSEUDO CODE
length = getNumberOfRowsInCSVFile()
result = []
for i=0 to length do
   diff = valueOfLine[i]-valueOfLine[i-1]
   result.append({
      day: dateOfLine[i],
      value: diff}
    )

msg.payload = result
return msg

[E1cid]

You can store the last 3 days in context storage with the last accumulated reading, then every day you get a new reading create a chart .

The inject simulates an input of accumulated value for testing, just connect to your daily power consumption input. Will take 3 inputs to fully build chart.

Change 1st rule in change node to increase number of days to display.

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[Nilpferd]

Hello E1cid

thanks a lot. With the random rise it ist working fine and does exactly what I need. Doesnot matter when I cannot understand the expressions.

Still one problem exists: I don`t know where to connect the KNX device node from which the data will be recvd.

[E1cid]

The KNX device should connect where random rise connects, it should feed in the accumulated power consumption once a day and needs to be an integer.

[edit]
The first expression takes the stored array (last3) and adds the new object, containing the time and value., it then removes the first array item if greater than 3 or msg.display.

The second expression creates the payload array for the bar chart.