Usually the term "short cycling" is referring to a system that has a mechanical issue which is causing the cycle to terminate prematurely.

The "normal" cycle rate of an hvac system is not dependent on the tonnage but rather on the heating or cooling load of the structure.

 

Depends on both the indoor and outdoor conditions at the time.

5 minutes on and 5 minutes off is short cycling when its 30 degrees outside.

5 minutes on, and 20 minutes off is not when its 30 degrees outside.

20 minutes on and 5 minutes off when its 30 degrees outside, usually indicates your house needs more insulation or sealed up better.

 

A short recurring period of time in which certain events (Air Conditioning) occur and reach completion or repeat themselves in a regular sequence . In refrigeration/air condition anything less then 30 minutes on and 20 minutes off I consider short cycling, thats assuming, that you have balanced load for the tonnage of the system.

 

The sweet spot would be the least cycles possible that produces a degree of comfort.

A typical cycle is something like this.

Thermostat calls..... compressor comes on. ------------------------ compressor amps ie. 15 amps
Temperature between return and discharge air (delta T) nil.-------compressor amps ie. 15 amps
Time > delta T rises.----------------------------------------------------compressor amps ie. 15 amps
Average 6-11 minutes goes by before maximum delta T.-----------compressor amps ie. 15 amps
Time > Maximum delta T exist for length of cycle ie. 10 min------compressor amps ie. 15 amps

As you can see the time between start-up and delta T stabilizes at maximum the running amps are approximately the same. Therefore the amount of BTUs into the space is less during the ramp-up time as compared to when delta T reaches maximum. Everytime a compressor cycles you pay the same amount of money for KW throughout the cycle. It is obvious that if you have a compressor cycling less than approximately 10 minutes, it is not energy efficient. The longer the cycle on, the higher the efficiency
.

Moral of the rant, ..............get the longest “on” cycle that your comfort will stand for the least amount of your money that is spent on KWH.

 

The jest of the above is to adjust your thermostat for the widest differential your comfort will tolerate to obtain the best efficiency and equipment service length.

 

Use design day to judge

Given you are not supposed too be more than plus 40% oversized in heating, if your unit runs less than 36 minutes per hour on design conditions then it sounds like short cycling
With cooling less than 54 minutes of the hour would be the same.

So with that in mind, remember all those posts in the summer with concerns about the AC not turning off?

 

Short cycling doesnt have to be mechanical. An electrical issue can cause a short cycle, or even extended cycle to occur....faulty / stuck pressure switch, contacts etc.

But I agree with most here with it all depends on load size, equip size, and indoor / outdoor conditions. (and ofcourse a properly operating compressor).

My system for example at home is way oversized. My unit in summer can cool the house from 80 - 70 in about 1/2 hr 45 - min. After that, it will cycle about 4 - 5 times an hour depending if we keep front wooden door closed and blinds shut.

 

looking for this but did not see it yet----

i tink twilli would say dat once your appliance is over 65 YO, j'as 5 min on and even only 55 minutes off requires quite a bit of chemical assistance , eh???

 

my oh my, the entendres: Is there a typical sweet spot to shoot for

oh my, what has dis site become???