"Downsizing" an oversized A/C

[NiHaoMike]

Let's suppose you have a building with a way oversized (central or large package) A/C (or heat pump), either due to recent energy efficiency renovations or as a result of a bad HVAC engineer. The A/C is otherwise in good condition and has many more years of service left.

Solution 1 - Replace the compressor and TXV with smaller ones. Expensive in parts even if you buy surplus, also very labor intensive.

Solution 2 - Replace the whole unit. Even more expensive and selling the old unit is unlikely to offset much cost.

Solution 3 - Change the refrigerant to a lower pressure refrigerant (e.g R22 to R134a) to lower the capacity. Labor intensive, especially if the oil has to be changed to POE.

Solution 4 - Add a VFD. Not cheap if you have to buy the VFD new, but very economical if you can get a surplus VFD. Relatively low labor cost and doesn't even need an EPA certification. Also get the benefits of a variable speed system. The high tech naysayers don't like this solution, but why listen to them?