Adding on - need advice for long term costs

[MoWheels]

I'm about to add on a 600 sq ft home office and am trying to decide which route to take: mini split system for this room OR upgrading the entire central system. I want to do what makes the most financial sense for the long term.
Background: house and central heat pump system is 10 years old - Payne 3.5 ton SEER 10 system - single unit with air handler in attic. House is in south Georgia (HOT in summer) 2100 sq ft. single floor. Only complaint with current system is the bedroom being used for home office stays too warm in the summers due to lots of computer gear generating heat. All this will be moved to the new construction however.
My question is simply does it make sense to spend probably 2.5 times the cost of the mini split system to upgrade and install a new, bigger system even though it should be more efficient?
Informed opinions appreciated!

[beenthere]

No.
Your office/computer room will heat up quicker then the rest of teh house. So you would need to set the stat lower to keep your computer room cool, causing your A/C to use more elctric then need be.

A ductless mini would be the most economical operating choice.

[MoWheels]

No.
Your office/computer room will heat up quicker then the rest of teh house. So you would need to set the stat lower to keep your computer room cool, causing your A/C to use more elctric then need be.

A ductless mini would be the most economical operating choice.

Thanks for the reply. Hadn't really thought of your point. I was (probably wrongly) assuming a new central system could somehow be "balanced" to handle the extra load generated by the computers. The completely separate mini solves this problem by default.

Is there any "easy" way to compare the operating costs of my 10 yr old SEER 10 system with a new system (which would probably be 13 - 15) and how long it would take to recoup the upgrade expense?

[adrianf]

here's a fpl calculator based on 2800 cooling hours 2 .12

as Beenthere mentioned your office won't be capatable with the rest of the house

zoning would add significant cost mini split is a good option

[MoWheels]

here's a fpl calculator based on 2800 cooling hours 2 .12

as Beenthere mentioned your office won't be capatable with the rest of the house

zoning would add significant cost mini split is a good option

fpl (Florida Power & Light??) 2.12? (I'm a bit thick-headed).

[adrianf]

.12 cents per kwh since I don't know your rate
2 = @ unshifted

[beenthere]

http://www.hvacopcost.com/

[MoWheels]

Ok, now I get it.
Our cost/kwh = 8.9 cents. Per the calculator mentioned, looks like the cost difference between the mini and the whole house redo would take > 10 years to recoup. This doesn't take into account the inevitable energy cost increases though. Thanks for the help, folks!
Seems like the mini systems are more "commodity" items since they are pretty much self-contained. Is any particular brand recognized as better than others or is the local installer's service and reputation more important than brand.

[beenthere]

We all have out prefered brand.
But if parts aren't available in your area, if it would break down. Then it would be the wrong unit for you.

Use what your installer is familar with.