Quote:
Originally Posted by Daox
...what would you guys say is short cycling? What should be the minimum run time we should look for? What are other variables that we should be looking at to answer these questions to our best?...
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I can't answer this question for all situations, but I did do some testing on my little homemade heat pump, which was drawing heat from my ground loop. I was set up to measure and calculate quite a large number of variables, and "instantaneous" COP was one of them. By instantaneous, I mean over a period of a minute.
I noticed a repeating pattern of COP ramping up to a 'shoulder' then increasing more gradually to a max, then declining a bit and finally settling into a steady level.
It seemed to me that a Calculus approach would be needed to determine the maximum best time interval. A good approximation could be done by imagining the curve as being composed of a series of thin strips and counting the area in successive strips. This incremental area, divided by time would tell the story.
I did notice that the initial ramp-up and then settling curves were pronounced enough that it was clear that a series of optimum bursts would be more efficient that a single long run.
But the behavior I saw was of my particular setup and I would dis-advise trying to generalize to other systems.
I am quite sure that electric resistance heating would not at all have characteristics similar to my heat pump. In fact the PID controllers count on very short pulses of current to achieve and maintain a temperature.
And, regarding heat pumps in general, in the days of single speed heat pumps, the optimum size of the heat pump was slightly less than the size needed to maintain comfort on the very coldest days, and to plan for axillary heat (electric resistance, wood, gas, etc) to fill the heating gap on those days.
Now with multi-speed compressors, the logic is not so clear, but bigger is not always better.
-AC