Stacy E. Apelt - Bladesmith
Moving to a new shop. Do you suggest that mini split? It’ll be about a 300 sqft insulated ‘shed/barn’
Yes, mini-splits are super. They provide heat and cooling and are very efficient. You want at least a 20-SEER unit, 22 is better. For many people, one costs about $1 a day to run. The difference in cost between a 17SEER and a 22SEER will pay for itself in saved electricity.
Get a good one. The cheap ones that cost $600 or so are not all that great. They are just a window AC unit with the compressor detached. They also are pretty small in capacity 8000-90000BTU. The better units cost a few hundred more and are 12,000-18,000BTU. You may not need it in Corpus Christi, but the Heat/AC units are the best ones for many shops. Condensation every night in the colder months can cause rust on all your tools and equipment.
If you don't need the heat, the AC-only units are fine, but you still want a good BTU capacity.
Just like your mom used to say to you as a kid, "Close the door. We ain't trying to cool/heat the whole neighborhood." Making the shop draft free and having insulation will make an AC unit work better. Pay attention to the overhead space, too. Insulating the ceiling helps a lot. Insulation can pay for itself. While bare stud walls has its own "rustic shop" look, insulation and drywall is neater, cleaner, and will make life in the shop more pleasant. It also makes the building more attractive and useful later on as an art studio, playroom for the kids, or even a spare bedroom for a future owner.
Consider your air in/out requirements for dust extraction and such. If you have a dust extraction system that vents air outside the shop, place the air-in vent near the grinder to allow proper air pressure in a well closed shop as well as not suck out all your cooled air.
The biggest difference in the cheap vs more expensive units is if they can be worked on (fix refrigerant leaks, replace parts, etc.). The cheap ones are basically a disposable unit like a window AC. The better ones are like a small home HVAC unit. The lifespan of the better units is also a lot longer ...especially if you plan on running it continuously. Like any tool, buy what you need. If you just need occasional use, the low price may be worth the eventual replacement. If you want reliable and daily use, get a better unit with a long warranty. Another plus is the better units are whisper quiet, both inside and outside. Many now come voice controlled (Alexa, etc.) and can be programmed that way to raise and lower the temps for day and night. That can save a bunch on your electric bill in some places.
My unit was a knife and sword trade with one of my good customers who runs a big HVAC company. When I asked him about your question, he said, "If you can install it yourself it isn't any good. It takes an AC professional to charge and connect the refrigerant lines." He also said, "You get what you pay for."
Tips:
CHECK and CLEAN the filters regularly in the shop! Nothing makes an AC unit inefficient like a clogged filter!!!
Install the head as far as possible from the grinder and any high dust tools.
Check the outside compressor heat exchanger every year, or more often if you live in a dusty place. Blow it out with compressed air or your leaf blower.
Install the compressor on a sturdy base raised up a foot from the ground and on the shady side of the shop if possible. If it has to be in the direct sun, consider a shed roof over it to provide some shade. (don't restrict air flow from the sides, though)
If it snows in your area, clear snow drifts from the unit in the winter.
Install the head inside so it blows down the length of the shop if possible.
You don't want it blowing directly on you if you can help it.
It is often more efficient to run one at a pre-set temperature range than to turn it off and on. If it is programmable, something like 80° at night and 72° in the day may save money. Same for winter heat, 50° at night and 68° in the day. If it isn't programmable, you can change the setting when you start and end your shop day, or set it to run at a continuous temp, like I do.
water brothers and the kind that don’t have beer in it yet 
