I’ve a second floor woodshop/photo studio space that’s about 42′ x 25′ x 18′ (cathedral ceiling). It has an open stairwell down to a small foyer + 1/2 bath on ground level. It has an LG heat-pump mini-split system with two wall cassettes in the shop/studio (one in each gable) along with a ceiling cassette in the small office.

I’d like to keep the humidity at about 45-50% to prevent rust on tools and keep wood stabilized.

I assume it’d be best and most cost effective to use the mini-splits to do this, at least during summer, rather than a dedicated dehumidifier?  I assume a dehumidifier would use about as much electricity but would also create heat in the space that would require energy from the mini-splits to cool so best to just use the mini-splits and have the heat pumped outside?  Or am I missing something?

Also, the LG units of a dehumidification mode but I cannot find anything about what its target RH or AH is.  When I’ve tried it the result seems to be about 50% but it also results in a rather cool, ≈68-70°f, space. Nice when working in there but no desire to waste money over cooling when I’m not.  

If I set the units to cooling mode and 77°f I seem to maintain about 50% RH (of course higher actual moisture content due to higher temp).

Any advice welcomed.