How critical is sizing AC VFD split systems?

[Vern_in_IL]

I got a mobile home that originally had 2 ton AC central air. The ductwork has gotten leaky over the years, and I end up cooling the crawl space, as well as having a low SEER rating. Now I´m looking to put a split to cool 75 percent of the home. My question with a VFD, does calculating the tonnage really that important? Since it is a VFD it would slow itself down if it was oversized, but if I undersize the unit, it would not keep up.

So it´s better to have a split that is oversized than say one that just gets the job done?

 

[CDX825]

You don't want to over size for cooling because while it will cool the house it won't run long enough to pull the humidity out of the air. Cool with high humidity is not comfortable.

If you are going to use a mini split size it to the space you are going to condition. Don't over size as most of them on the market now are capable of going over the rated capacity in both heat and cool anyway.

 

[Cujet]

I think what he is asking is whether sizing matters as much on a VFD system. Don't know for sure, but I'd guess that an oversized system would perform just fine in this case. My home system does just this.

The variable speed setups simply work very well. I have one in my bedroom, and the main house 5 ton is a 2 speed system, with a 2.5t and 5t compressor. It uses one or the other compressor, as required.

 

[andrew_j]

It’s a very expensive mistake in energy costs, repair or acquisition to wing it and find out it’s incorrectly sized.

I had three wing nuts basically try to size my boiler because of previous size “worked”.

A real engineer downsized boiler and my energy savings were substantial . On coldest days it runs near constant and keeps up. The old would still cycle indicating it was so oversized .