How to find best heating/cooling time

Hi all,

i’m using a reversible heat pump as heat source in the winter. As summer’s really hot this year, I’ve tried the reversible feature and noticed (as to be expected) it’s most efficient during cold conditions outside.

Therefore I’d like to optimize the times the heat pump will cool. Heating is also affected, as a rule would be simply applicable to the heating season. Reaching a target temperature is not as important as efficient operation.

My setup has this item T_Outside, which shows the current outside temperature. Persisted by RRD a chart like this is available showing temperature and time:

Here are my first thoughts on this:

  • Approximately time based will narrow the time window when the heat pump may start
  • Clear falling temperatures in this time window indicate preferable times
  • When deciding, my rule evaluates the rightmost data (current time)

Now my question: How to detect using persistence and rule engine?

Any thoughts on this would be really appreciated.


Sorry, how to detect what?

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So you don’t care about the absolute temperature. You only care to find whether the temperature is falling over a certain time period, correct?

Hi Sascha,

I’m not entirely sure what your question is. but I’ve been wondering about something similar:
what time should openhab turn on the heat so that the room is ready at a given time.

like you mention, with heat pumps there are a few factors

  1. the outside temp
  2. the inside temp
  3. the target temp
  4. the heating performance of the room. ie how long does it take to heat

If this is your question, and you want to implement this in opebhab rules, you’d need to come up with a formula that perhaps runs in a rule every 5 minutes and turns on the heat pump. Otherwise I think that it might be beyond the basics of openhab rules and would most satisfactorily involve some machine learning.

I crunched all the data I have and came to this conclusion for heating (at least for my house):

  1. outside temperature makes no difference (it only varies by ±5C)
  2. inside humidity makes no difference (it only varies by ±5%)
  3. there is a linear relationship between the temperature difference and the time it take to reach the target.
  4. the variations are influenced by internal factors - cooking, doors open etc.

For me, all I need to do is measure the time it takes on average to change the room by one degree. Then use that choose when to turn on the heat pump.