# [rrd-users] graphing hvac thermostat?

Simon Hobson linux at thehobsons.co.uk
Sun Apr 1 09:32:25 CEST 2012

```James Russo wrote:

>I have an RRD file with temperature, cooling setpoint, heating
>setpoint, cool flag (are we cooling 1/0) and then heat flag (are we
>heating 1/0).
...
>It would be nice to just throw a vline when calling for cool or
>heat, but I don't think it is possible to capture the "transition"
>of the values and determine the time to put the vline at.

Correct, unless your transition happens to be on a step boundary,
then you won't see a sharp transition between 0 and 1. Once you get
into consolidated data, then it becomes even worse since there may
have been several transitions in (say) a 2 hour period.

What I think you might do is compare the stored cooling flag with
some non-integer number. For example, if you compare against 0.5 then
you've get an indication of whether you were cooling more than you
weren't. Compare against 0.1 and you'll get an indication that you
were doing anything but very little cooling. By the time you
consolidate over a longer period, depending on your choice of
threshold, you could have both cooling and heating showing as active.

You might consider using a range of colours, rather than just 2 or 3.
I think your idea is that you'll plot in (say) blue if you've been
cooling, red if you've been heating, and green if neither. You could
expand that a bit, and use different gradations across the rainbow
between red and blue. You'll need to come up with a formula to
combine the heating and cooling quotients to get a single value - and
this may vary with timescale of graph/consolidation period length.

Just "thinking aloud", this may give a starting point ...
q=1+heating-cooling
If you are heating all the time, then q=2, if you are cooling all the
time then q=0, if you are not using heating or cooling or if you heat
and cool in equal amount (possible over 24 hours or longer) then q=1.
So you might choose to plot in green if 0.9 < q <= 1.1, in 'orangy
green' if 1.1 < q <= 1.25, orange if 1.25 < q <= 1.5, and red of q >
1.5

I think some experimentation may be needed.

--
Simon Hobson

Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
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```