Calculating air conditioning annual run hours

I am trying to create an energy savings spreadsheet calculator for HVAC (specifically condensing unit) replacement. This is not for one specific job, but rather a general calculation sheet that can be used at any of our properties we are look into. One of the key components in determining the savings is the annual run hours and I am looking for some help in determining this value.

I do not need an exact number, but am trying to come up with a good rule of thumb. For example, is there a way to base this on Heating Degree Days or the ASHRAE Climatic Zone?

Does anyone have any information they can provide to help me come up with this value?

Thanks.

submitted by /u/solrose
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