What do you consider short cycling?

[koldair]

What do you consider “short cycling”? If a system is sized properly and running during the heat of the day and the outside ambient is at the systems design temp. 100F and the cool set point is 75F. What kind of run time would you expect to see?

Assume it’s a 12-13 SEER split system nothing special, with a digital stat, and a PSC motor. All is well… charge, clean filter, clean condenser, etc.

What kind of run/cool times would you expect at 100% load? 10, 15, 20, or more minutes?

[DanW13]

Under those conditions I would expect the AC to run for quite awhile trying to meet a set point of 25 degrees below ambient. Which would be in your favor as far as moisture removal goes. If the system pulled the house down 25 degrees with in a hour or 2 would seriously be a problem and you would feel like a clam inside a house full of moisture.

[Irascible]

100% minutes, so to speak. :)

In these parts design conditions are just a smidge under what you describe. That means a properly sized system around here would run literally nonstop just to maintain the temperature. Design conditions for your area may vary.

The never quite got the whole "X degrees under ambient" thing. AFAIK there is no such standard.

[koldair]

Under those conditions I would expect the AC to run for quite awhile trying to meet a set point of 25 degrees below ambient. Which would be in your favor as far as moisture removal goes. If the system pulled the house down 25 degrees with in a hour or 2 would seriously be a problem and you would feel like a clam inside a house full of moisture.

Here in Texas the outside design temp is 100F and the inside design temp is 75F. So most or all are sized to meet these temperature requirements. Most people complain if the A/C runs for more than an hour at a time. But most systems here are grossly oversized.

I would like to see what others think…:)

[DanW13]

well IMO if your AC is running non stop there are other issues you can address to keep the Ac from having to run non stop, such as insulation in your attic, air sealing, windows, doors sealed, duct work sealed, and maybe get the equipment out of the attic.

[RoBoTeq]

What do you consider “short cycling”? If a system is sized properly and running during the heat of the day and the outside ambient is at the systems design temp. 100F and the cool set point is 75F. What kind of run time would you expect to see? If the system does not operate 100% of the time at set point of 75 degrees while maintaining 75 degrees, it was not sized properly.


Assume it’s a 12-13 SEER split system nothing special, with a digital stat, and a PSC motor. All is well… charge, clean filter, clean condenser, etc.

What kind of run/cool times would you expect at 100% load? 10, 15, 20, or more minutes?
Once again, you should expect it to run 100% of the time when it is at 100% of the design load.

[HVAC9900]

I assume the area of TX you are in has low humidity? If so, can probably get away with short run times.
Here in GA, we like long run times,especially this summer,which has been humid.On a hot day my ac will run a few hours before shutting off,and dumps a bunch of water.

[RoBoTeq]

well IMO if your AC is running non stop there are other issues you can address to keep the Ac from having to run non stop, such as insulation in your attic, air sealing, windows, doors sealed, duct work sealed, and maybe get the equipment out of the attic.
As long as a system is maintaining the designed indoor temperature when the outdoor temperature is at the designed load, running non stop is the best thing for it. Starting a motor is the worst thing we can do to them. The longer they run constantly, the more efficiently they are running.

[koldair]

If the system does not operate 100% of the time at set point of 75 degrees while maintaining 75 degrees, it was not sized properly.


Once again, you should expect it to run 100% of the time when it is at 100% of the design load.

Agreed… So how do you explain this to an upset homeowner?:mad:

[RoBoTeq]

Agreed… So how do you explain this to an upset homeowner?:mad:
Carefully and patiently. If the HO is only upset about the run time, it is just a matter of explaining the energy usage. If the HO is complaining about not being cool enough when the temps go a degree past the design set point, that's a little tougher teaching the HO how to use better window coverage, keep any dampers, such as to fireplaces, closed and maybe not keeping a pot of soup simmering on the stove all day.

[jerrod6]

Any one know the outside and inside cooling and heating design temperatures for Phiadlephia PA? Is there a web site that has this info?

[Juleous]

Home owners think that they are paying more if the unit is always on vs a large unit not always on, educate them a little and they will be happy. Show them the cost over the life of the unit when the repairs are factored in when the unit cycles constantly. Most systems are designed to run between 18 to 22 hrs under normal design, all you have to do is adjust for your local design temp.