I'm due for a new home a/c. Compressor is now obsolete r22 refrigerant from 2004 and evaporator is likely mid 80's.
Now low on gas, so not much cooling performance.
The feds have a design excel worksheet with a ream of macros that help you figure the performance of the a/c, or in my case a new heat pump.
I have done the insulated walls, windows, roof and basement coldest winter heat loss and hottest summer heat gain for my house, along with air change ventilation factors .
Now to do the performance characteristics. I will likely keep the high efficiency natural gas furnace for coldest heating days or shoulder heating when weekday electrical prices are high, and let the heat pump do the shoulder season overnight and weekend home heating.
Now to figure if go with a two speed, with all but hottest summer on low speed, and winter on high speed on the coldest of the shoulder seasons.
Or if capital costs of two speed are too much, go with a bit bigger fixed single speed heat pump and run the furnace a bit more often in the winter.
I will likely put out bids for the specified size heat pump with option for one or two speed, with units specified from two or three OEM vendors, as not all a.c guys are dealers for all the OEM's.
Then disclose info on the existing furnace and they are to furnish smart thermostat and any air handler interface board to work with the existing furnace fan.
And when I say smart thermostat I really mean it. You program its clock, date calendar, cost of electricity schedule, cost of natural gas, and efficiency factors for electric and gas and allowable temp deltas from aim point.
Taking this approach I hope to eliminate a lot of song and dance a/c outfits, that specialize in bait and switch.